National Instruments Network Card SCXI 1125 User Manual

TM  
SCXI  
SCXI-1125 User Manual  
SCXI-1125 User Manual  
April 2008  
372425B-01  
 
 
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Conventions  
The following conventions are used in this manual:  
<>  
Angle brackets that contain numbers separated by an ellipsis represent a  
range of values associated with a bit or signal name—for example,  
P0.<3..0>.  
»
The » symbol leads you through nested menu items and dialog box options  
to a final action. The sequence File»Page Setup»Options directs you to  
pull down the File menu, select the Page Setup item, and select Options  
from the last dialog box.  
This icon denotes a note, which alerts you to important information.  
This icon denotes a caution, which advises you of precautions to take to  
avoid injury, data loss, or a system crash. When this symbol is marked on a  
product, refer to the Read Me First: Safety and Radio-Frequency  
Interference for information about precautions to take.  
When symbol is marked on a product, it denotes a warning advising you to  
take precautions to avoid electrical shock.  
When symbol is marked on a product it, denotes a component that may be  
hot. Touching this component may result in bodily injury.  
bold  
Bold text denotes items that you must select or click in the software, such  
as menu items and dialog box options. Bold text also denotes parameter  
names.  
italic  
Italic text denotes variables, emphasis, a cross-reference, or an introduction  
to a key concept. Italic text also denotes text that is a placeholder for a word  
or value that you must supply.  
monospace  
Text in this font denotes text or characters that you should enter from the  
keyboard, sections of code, programming examples, and syntax examples.  
This font is also used for the proper names of disk drives, paths, directories,  
programs, subprograms, subroutines, device names, functions, operations,  
variables, filenames, and extensions.  
monospace bold  
Bold text in this font denotes the messages and responses that the computer  
automatically prints to the screen. This font also emphasizes lines of code  
that are different from the other examples.  
monospace italic  
Italic text in this font denotes text that is a placeholder for a word or value  
that you must supply.  
 
 
Chapter 1  
What You Need to Get Started ......................................................................................1-1  
National Instruments Documentation ............................................................................1-2  
Installing Application Software, NI-DAQ, and the DAQ Device .................................1-4  
Installing the SCXI-1125 Module into the SCXI Chassis...............................1-4  
Manually Adding Modules in NI-DAQmx .....................................................1-6  
Installing SCXI Using Traditional NI-DAQ (Legacy) in Software ................1-6  
Verifying and Self-Testing the Installation .....................................................1-6  
Chapter 2  
Ground-Referenced Signal..............................................................................2-2  
Floating Signal.................................................................................................2-3  
AC-Coupling ...................................................................................................2-4  
Pin Assignments ............................................................................................................2-5  
Temperature Sensor Connection .....................................................................2-7  
Rear Signal Connector.....................................................................................2-7  
© National Instruments Corporation  
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Contents  
Chapter 3  
SCXI-1125 Software-Configurable Settings................................................................. 3-1  
Common Software-Configurable Settings...................................................... 3-1  
Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis  
to an E/M Series DAQ Device for Multiplexed Scanning........................... 3-2  
Creating a Virtual Channel............................................................... 3-6  
Verifying the Signal ...................................................................................................... 3-6  
Verifying the Signal in Traditional NI-DAQ (Legacy) .................................. 3-7  
Chapter 4  
Gain ............................................................................................................................... 4-1  
Filter Bandwidth and Cutoff Frequency........................................................................ 4-2  
Multiplexed Hardware Operation Theory....................................................... 4-3  
Chapter 5  
Making High-Voltage Measurements ........................................................................... 5-4  
Developing Your Application in NI-DAQmx............................................................... 5-5  
Typical Program Flowchart ............................................................................ 5-5  
General Discussion of Typical Flowchart....................................................... 5-7  
Creating a Task Using DAQ Assistant or Programmatically........... 5-7  
Adjusting Timing and Triggering..................................................... 5-7  
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Text Based ADEs..............................................................................5-14  
Measurement Studio (Visual Basic, .NET, and C#)........................................5-14  
Programmable NI-DAQmx Properties..............................................5-14  
Developing Your Application in Traditional NI-DAQ (Legacy) ..................................5-15  
NI-DAQ (Legacy) in LabVIEW...................................................................5-19  
Convert Scaling Using Traditional NI-DAQ (Legacy) in LabVIEW .............5-20  
Traditional NI-DAQ (Legacy) CVI Examples................................................5-29  
Traditional NI-DAQ (Legacy) Measurement Studio Examples......................5-29  
Calibration .....................................................................................................................5-30  
Calibration Procedures ....................................................................................5-30  
One-Point Offset Calibration ............................................................5-31  
Two-Point Gain and Offset Calibration............................................5-32  
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Contents  
Appendix A  
Specifications  
Using SCXI Channel Strings with Traditional NI-DAQ (Legacy) 7.0  
or Later  
Appendix C  
Common Questions  
Glossary  
Index  
Figures  
Figure 2-1.  
Figure 2-2.  
Figure 2-3.  
Figure 2-4.  
Connecting a Ground-Referenced Signal ............................................. 2-2  
Connecting a Floating Signal................................................................ 2-3  
Connecting a Floating AC-Coupled Signal .......................................... 2-4  
Connecting a Ground-Referenced AC-Coupled Signal........................ 2-4  
Figure 4-1.  
SCXI-1125 Block Diagram................................................................... 4-1  
Figure 5-1.  
Figure 5-2.  
Typical Program Flowchart .................................................................. 5-6  
LabVIEW Channel Property Node with Lowpass Frequency  
Set at 10 kHz on Channel SC1Mod1/ai0 .............................................. 5-12  
Typical SCXI-1125 Program Flow  
with Traditional NI-DAQ (Legacy)...................................................... 5-17  
Using the AI Parameter VI to Set Up the SCXI-1125.......................... 5-19  
Figure 5-3.  
Figure 5-4.  
Figure A-1. SCXI-1125 Dimensions........................................................................ A-7  
Figure C-1.  
Removing the SCXI-1125..................................................................... C-2  
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Contents  
Tables  
Table 2-1.  
Front Signal Pin Assignments ..............................................................2-6  
Table 2-2.  
Rear Signal Pin Assignments ................................................................2-8  
Table 5-1.  
Table 5-2.  
Table 5-3.  
Table 5-4.  
Table 5-5.  
Table 5-6.  
Extended Gain and Range Using the SCXI-1327 or SCXI-1313A.......5-4  
Extended Gain and Range Using the TBX-1316 ..................................5-5  
NI-DAQmx Properties ..........................................................................5-8  
Programming a Task in LabVIEW........................................................5-10  
NI-DAQmx Properties ..........................................................................5-15  
Settings for Configuring the SCXI-1125  
Through the AI Parameter.....................................................................5-18  
Configuration Functions........................................................................5-22  
NI-DAQ Functions Used to Configure SCXI-1125..............................5-23  
Gain Values and Input Limits ..............................................................5-31  
Table 5-7.  
Table 5-8.  
Table 5-9.  
Table A-1.  
Table A-2.  
Input Signal Range Versus Gain ...........................................................A-1  
Terminal Block Maximum Voltages.....................................................A-8  
Table D-1.  
Table D-2.  
Comparison of the SCXI-1125 with the SCXI-1120 ............................D-1  
Digital Signals on the SCXI-1125.........................................................D-3  
© National Instruments Corporation  
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1
About the SCXI-1125  
This chapter introduces the SCXI-1125 module and explains how to install  
the software and hardware.  
The SCXI-1125 is an eight-channel isolated analog input conditioning  
module with programmable gain and filter settings on each channel and  
is jumperless. Each channel has 12 programmable gain settings from  
1 to 2000 and two programmable filter settings of either 4 Hz or 10 kHz.  
Each channel has an external circuit for grounding the inputs that you can  
use for offset calibration. An onboard EEPROM provides nonvolatile  
storage of software correction constants for both gain and offset.  
The SCXI-1125 provides up to 300 Vrms working isolation per channel and  
has an input range of up to 1000 VDC when using an appropriate attenuator  
terminal block. The SCXI-1125 supports both multiplexed and parallel  
output modes and includes a cold-junction compensation (CJC) channel  
that you can scan in multiplexed mode.  
What You Need to Get Started  
To set up and use the SCXI-1125 module, you need the following:  
Hardware  
SCXI-1125 module  
One of the following terminal blocks:  
SCXI-1305  
SCXI-1313A  
SCXI-1320  
SCXI-1327  
SCXI-1328  
SCXI-1338  
TBX-1316  
TBX-1328  
TBX-1329  
© National Instruments Corporation  
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About the SCXI-1125  
Note For maximum allowable voltage for a particular terminal block refer to Table A-2,  
Terminal Block Maximum Voltages.  
SCXI or PXI/SCXI combination chassis  
One of the following:  
E/M Series DAQ device  
SCXI-1600 module  
A computer if using an SCXI chassis  
Cabling, cable adapter, and sensors as required for your  
application  
Software  
NI-DAQ 7.0 or later  
One of the following software packages:  
LabVIEW  
LabWindows/CVI™  
Measurement Studio  
Documentation  
Read Me First: Safety and Radio-Frequency Interference  
DAQ Getting Started Guide  
SCXI Quick Start Guide  
SCXI-1125 User Manual  
Documentation for your hardware  
Documentation for your software  
National Instruments Documentation  
The SCXI-1125 User Manual is one piece of the documentation set for data  
acquisition (DAQ) systems. You could have any of several types of  
manuals depending on the hardware and software in the system. Use the  
manuals you have as follows:  
SCXI or PXI chassis manual—Read this manual for maintenance  
information on the chassis and for installation instructions.  
The DAQ Getting Started Guide—This document has information on  
installing NI-DAQ and the E/M Series DAQ device. Install these  
before you install the SCXI module.  
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Chapter 1  
About the SCXI-1125  
The SCXI Quick Start Guide—This document contains a quick  
overview for setting up an SCXI chassis, installing SCXI modules and  
terminal blocks, and attaching sensors. It also describes setting up the  
SCXI system in MAX.  
The SCXI hardware user manuals—Read these manuals next  
for detailed information about signal connections and module  
configuration. They also explain, in greater detail, how the module  
works and contain application hints.  
Accessory installation guides or manuals—If you are using accessory  
products, read the terminal block and cable assembly installation  
guides. They explain how to physically connect the relevant pieces  
of the system. Consult these guides when you are making the  
connections.  
The E/M Series DAQ device documentation—This documentation has  
detailed information about the E/M Series DAQ device that plugs into  
or is connected to the computer. Use this documentation for hardware  
installation and configuration instructions, specification information  
about the E/M Series DAQ device, and application hints.  
Software documentation—You may have both application software  
and NI-DAQ software documentation. National Instruments (NI)  
application software includes LabVIEW, LabWindows/CVI, and  
Measurement Studio. After you set up the hardware system, use either  
your application software documentation or the NI-DAQ  
documentation to help you write your application. If you have a large,  
complex system, it is worthwhile to look through the software  
documentation before you configure the hardware.  
One or more of the following help files for software information:  
Start»Programs»National Instruments»NI-DAQ»  
NI-DAQmx Help  
Start»Programs»National Instruments»NI-DAQ»  
Traditional NI-DAQ User Manual  
Start»Programs»National Instruments»NI-DAQ»  
Traditional NI-DAQ Function Reference Help  
NI application notes or tutorials—NI has additional material on  
measurements available at ni.com/support.  
You can download NI documents from ni.com/manuals. To download  
the latest version of NI-DAQ, click Drivers and Updates at ni.com.  
© National Instruments Corporation  
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Chapter 1  
About the SCXI-1125  
Installing Application Software, NI-DAQ, and the  
DAQ Device  
Refer to the DAQ Getting Started Guide packaged with the NI-DAQ  
software to install your application software, NI-DAQ driver software, and  
the DAQ device to which you will connect the SCXI-1125. NI-DAQ 7.0 or  
later is required to configure and program the SCXI-1125 module. If you  
do not have NI-DAQ 7.0 or later, you can either contact a NI sales  
representative to request it on a CD or download the latest NI-DAQ version  
from ni.com.  
Note Refer to the Read Me First: Safety and Radio-Frequency Interference document  
before removing equipment covers or connecting or disconnecting any signal wires.  
Installing the SCXI-1125 Module into the SCXI Chassis  
Refer to the SCXI Quick Start Guide to install your SCXI-1125 module.  
Refer to the SCXI Quick Start Guide to install the cable adapter and connect  
the SCXI modules to the DAQ device.  
If you have already installed the appropriate software, refer to Chapter 3,  
Configuring and Testing, to configure the SCXI-1125 module(s).  
Refer to the SCXI Quick Start Guide to connect the SCXI modules to the  
DAQ device.  
If you have already installed the appropriate software, refer to Chapter 3,  
Configuring and Testing, to configure the SCXI-1125 module(s).  
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Chapter 1  
About the SCXI-1125  
Connecting the SCXI-1125 to a n E/M Series DAQ Device for  
Parallel Scanning  
This configuration allows you to route all eight channels of the SCXI-1125  
it is connected. In this mode, you cannot directly access the CJC channel.  
Use this mode if you require a higher scanning rate than an SCXI system in  
multiplexed mode allows.  
If you have not already installed all the modules, refer to the Installing the  
SCXI-1125 Module into the SCXI Chassis section, then complete the  
following steps:  
1. Power off the SCXI chassis and the computer that contains the  
E/M Series DAQ device.  
2. Insert the cable adapter into the rear of the SCXI-1125 module that is  
to be accessed in parallel mode by the E/M Series DAQ device. Refer  
to the installation guide for the cable assembly for more information.  
3. Connect the cable to the back of the cable adapter ensuring that the  
cable fits securely.  
4. Connect the other end of the cable to the E/M Series DAQ device that  
you want to use to access the SCXI-1125 in parallel mode.  
5. Connect additional SCXI-1125 modules intended for parallel mode  
operation by repeating steps 2 through 4.  
6. Check the installation, making sure the cable is securely fastened at  
both ends.  
7. Power on the SCXI chassis.  
8. Power on the computer.  
If you have already installed the appropriate software, you are ready to  
configure the SCXI-1125 module(s) you installed for parallel mode  
operation.  
Verifying the SCXI-1125 Installation in Software  
Refer to the SCXI Quick Start Guide for information on verifying the SCXI  
installation.  
Installing SCXI Using NI-DAQmx in Software  
Refer to the SCXI Quick Start Guide for information on installing modules  
using NI-DAQmx in software.  
© National Instruments Corporation  
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Chapter 1  
About the SCXI-1125  
Manually Adding Modules in NI-DAQmx  
If you did not auto-detect the SCXI modules, you must manually add each  
of the modules. Refer to the SCXI Quick Start Guide to manually add  
modules.  
Note NI recommends auto-detecting modules for the first time configuration of the  
chassis.  
Installing SCXI Using Traditional NI-DAQ (Legacy) in Software  
Refer to the SCXI Quick Start Guide for information on installing modules  
using Traditional NI-DAQ (Legacy) in software.  
Manually Adding Modules in Traditional NI-DAQ (Legacy)  
If you did not auto-detect the SCXI modules, you must manually add each  
of the modules. Refer to the SCXI Quick Start Guide to manually add  
modules.  
Note NI recommends auto-detecting modules for the first time configuration of the  
chassis.  
Verifying and Self-Testing the Installation  
The verification procedure for the SCXI chassis is the same for both  
NI-DAQmx and Traditional NI-DAQ (Legacy). To test the successful  
installation for the SCXI chassis, refer to the SCXI Quick Start Guide.  
Verify that the chassis is powered on and correctly connected to an  
E/M Series DAQ device.  
After verifying and self-testing the installation, the SCXI system should  
operate properly with your ADE software. If the test did not complete  
successfully, refer to Chapter 3, Configuring and Testing, for  
troubleshooting steps.  
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Chapter 1  
About the SCXI-1125  
Troubleshooting the Self-Test Verification  
If the Self-Test Verification did not verify the chassis configuration,  
complete the steps in this section to troubleshoot the SCXI configuration.  
Troubleshooting in NI-DAQmx  
If you get a Verify SCXI Chassis message box showing the SCXI  
chassis model number, Chassis ID: x, and one or more messages  
stating Slot Number: x Configuration has module: SCXI-XXXX  
or 1125, hardware in chassis is: Empty, take the following  
troubleshooting actions:  
Make sure the SCXI chassis is powered on.  
Make sure all SCXI modules are properly installed in the chassis.  
Refer to the SCXI Quick Start Guide for proper installation  
instructions.  
Make sure the cable between the SCXI chassis and E/M Series  
DAQ device is properly connected.  
Inspect the cable connectors for bent pins.  
Make sure you are using the correct NI cable assembly.  
Test the E/M Series DAQ device to verify it is working properly.  
Refer to the E/M Series DAQ device help file for more  
information.  
If you get a Verify SCXI Chassis message box showing the SCXI  
chassis model number, Chassis ID: x, and the message Slot  
Number: x Configuration has module: SCXI-XXXX or 1125,  
hardware in chassis is: SCXI-YYYY, 1125, or Empty, complete the  
following troubleshooting steps to correct the error.  
1. Expand the list of NI-DAQmx devices by clicking the + next to  
NI-DAQmx Devices.  
2. Right-click the SCXI chassis and click Properties to load the  
chassis configurator.  
3. Under the Modules tab, ensure that the cabled module is listed in  
the correct slot.  
4. If the cabled module is not listed in the correct slot, complete the  
following troubleshooting steps:  
a. If the cabled module is not listed in the correct slot and the  
slot is empty, click the drop-down listbox next to the correct  
slot and select the cabled module. Configure the cabled  
© National Instruments Corporation  
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About the SCXI-1125  
module following the steps listed in the SCXI Quick Start  
Guide. Click OK.  
b. If another module appears where the cabled module should  
be, click the drop-down listbox next to the correct slot and  
select the cabled module. A message box appears asking you  
to confirm the module replacement. Click OK. Configure the  
cabled module following the steps listed in the SCXI Quick  
Start Guide. Click OK.  
Ensure that you have the highest priority SCXI module cabled to the  
E/M Series DAQ device. Refer to the SCXI Quick Start Guide to find  
out which SCXI module in the chassis should be cabled to the  
E/M Series DAQ device.  
After checking the preceding items, return to the Troubleshooting the  
Self-Test Verification section and retest the SCXI chassis.  
If these measures do not successfully configure the SCXI system, contact  
NI. Refer to the Signal Conditioning Technical Support Information  
document for contact information.  
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2
Connecting Signals  
This chapter describes the input and output signals connections to the  
SCXI-1125 module with the module front connector and the rear signal  
connector. This chapter also includes specifications and connection  
instructions for the signals on the SCXI-1125 module connectors.  
Notes Refer to the Read Me First: Safety and Radio-Frequency Interference document  
before removing equipment covers or connecting or disconnecting any signal wires.  
For EMC compliance, operate this device with shielded cabling.  
The isolated channels of the SCXI-1125 allow you to make precision  
high-voltage measurements or low-voltage measurement of signals riding  
on high common-mode voltages while protecting sensitive computer parts  
and equipment connected to the module. The isolated amplifiers fulfill  
two purposes on the SCXI-1125 module. First, they can convert a small  
signal riding on a high common-mode voltage into a single-ended signal  
with respect to the SCXI-1125 chassis ground. With this conversion, you  
can extract the analog input signal from a high common-mode voltage  
before sampling by the E/M Series DAQ device. Second, the isolation  
amplifier amplifies and filters an input signal resulting in increased  
measurement resolution and accuracy. The following sections explain how  
to make signal connections to maximize the effectiveness of the  
SCXI-1125 for conditioning analog signals.  
AC and DC Voltage Connections  
You can make input signal connections to the SCXI-1125 through the front  
signal connector or through accessory terminal blocks. Chapter 1, About  
the SCXI-1125, contains a list of SCXI-1125-compatible terminal blocks.  
Terminal blocks have features such as screw-terminal connectivity, BNC  
connectivity, cold-junction temperature measurement, and attenuation.  
The pin assignment for the SCXI-1125 front signal connector is shown in  
Table 2-1. The positive input terminal for each channel is in Column A and  
the negative input terminal for each channel is in Column C. Input  
connections to each channel are fully floating with respect to ground and  
© National Instruments Corporation  
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Chapter 2  
Connecting Signals  
completely isolated from other channels. You can operate with  
common-mode voltage levels up to 300 Vrms  
.
Figures 2-1 through 2-4 show signal connection methods that give the  
highest noise immunity.  
Ground-Referenced Signal  
When the negative input signal line is connected either directly or  
indirectly to earth ground (usually at the transducer end), connect this line  
to the negative input terminal, as shown in Figure 2-1. No ground  
connection is made at the SCXI-1125. This situation includes cases where  
a floating source can be riding on a high common-mode voltage that is  
ground referenced.  
+
+
+
Vout  
Vs  
+
High  
CMV  
I
Vcm  
Module  
Figure 2-1. Connecting a Ground-Referenced Signal  
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Chapter 2  
Connecting Signals  
Floating Signal  
In cases where both signal lines at the transducer end are floating and no  
common-mode voltage exists, establish an earth connection at the  
SCXI-1125 by connecting the negative input line to chassis ground in the  
terminal block, as shown in Figure 2-2. This eliminates noise that can ride  
on the floating signal. If the floating signal is not configured like  
Figure 2-2, the noise can couple to the chassis ground through the amplifier  
and exhibit a differential mode signal that can be amplified by the  
amplifier. Connecting the signal to chassis ground breaks the isolation  
barrier.  
+
+
+
Vout  
Vs  
I
Module  
Figure 2-2. Connecting a Floating Signal  
© National Instruments Corporation  
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Chapter 2  
Connecting Signals  
AC-Coupling  
You can have an application where you wish to measure only AC voltages  
and remove the DC component of a signal before amplification and  
sampling. In such cases, you can connect a capacitor in series with one or  
both input terminals of the SCXI-1125, as shown in Figures 2-3 and 2-4.  
A resistor is connected across the input terminals of the channel to DC  
reference the input stage of the SCXI-1125. You do not need to use a bias  
resistor with any high-voltage terminal blocks, since the terminal blocks  
already have a resistor between the input terminals, or with the SCXI-1305  
BNC connectivity terminal block, since this terminal block already has an  
AC-coupling option built in.  
+
+
+
Vout  
Rbias  
Vs  
I
Module  
Figure 2-3. Connecting a Floating AC-Coupled Signal  
Caution Connecting a signal source to chassis ground in Figures 2-2 and 2-3, breaks the  
isolation barrier.  
+
+
+
Rbias  
Vout  
Vs  
I
+
High  
CMV  
Vcm  
Module  
Figure 2-4. Connecting a Ground-Referenced AC-Coupled Signal  
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Chapter 2  
Connecting Signals  
The value of the bias resistor should be between 100 kΩ and 1 MΩ. An  
added DC offset voltage results, due to input bias current flowing through  
the bias resistor. For example, with a 1 MΩ bias resistor and the specified  
maximum input bias current of 1 nA, you have a maximum added input  
offset voltage of 1 mV in addition to the initial offset voltage.  
Since only the AC signal is of interest when AC-coupling, you can choose  
to remove the DC offset in software by using a simple highpass filter.  
Caution Pins A2, A4, A8, C2, C4, C6, and C8 on the front signal connector are not isolated  
and do not have the same protection circuitry as the positive and negative analog input pairs  
discussed in the Floating Signal section. Hooking up external signals to these pins can  
damage the SCXI-1125 module.  
Pin Assignments  
The front signal connector is a special 32-pin DIN C male front connector  
used for connecting analog input signals, including the CJC, to the analog  
circuitry of the SCXI-1125. This connection allows access to the eight  
differential analog input signals. The positive terminal is AIx + and the  
negative terminal AIx –. A missing pin exists between two consecutive  
input channels to meet the UL spacing requirements for high voltage  
signals. CJ TEMP is the signal connection used by the cold-junction  
channel on the SCXI-1125. The signals on pins A6, A8, C6, and C8 are  
reserved for serial communication. The +5 V signal and CHS GND signals  
are used as the power supply and ground signals for the CJC sensor and  
other circuitry on the terminal block. The pin assignments for the  
SCXI-1125 front signal connection are shown in Table 2-1.  
Caution Do not make signal connections to pins A2, A4, A6, A8, C2, C4, C6, or C8 on the  
front signal connector. Connecting external signals to these pins can damage the  
SCXI-1125 Module.  
© National Instruments Corporation  
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SCXI-1125 User Manual  
 
 
Chapter 2  
Connecting Signals  
Table 2-1. Front Signal Pin Assignments  
Front Connector Diagram  
Pin Number  
Column A  
AI 0 +  
Column B  
Column C  
AI 0 –  
32  
31  
30  
29  
28  
27  
26  
25  
24  
23  
22  
21  
20  
19  
18  
17  
16  
15  
14  
13  
12  
11  
10  
9
Column  
A
B
C
AI 1 +  
AI 1 –  
32  
31  
30  
29  
28  
27  
26  
25  
24  
23  
22  
21  
20  
19  
18  
17  
16  
15  
14  
13  
12  
11  
10  
9
NC  
NC  
AI 2 +  
AI 2 –  
AI 3 +  
AI 3 –  
NC  
NC  
AI 4 +  
AI 4 –  
AI 5 +  
AI 5 –  
NC  
NC  
AI 6 +  
AI 6 –  
AI 7 +  
AI 7 –  
NC  
NC  
8
7
6
8
RSVD  
RSVD  
5
7
4
6
RSVD  
RSVD  
3
5
2
1
4
+5 V  
CJ TEMP  
3
NC means no connection  
— means no pin  
2
CHS GND  
RSVD  
1
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Chapter 2  
Connecting Signals  
Temperature Sensor Connection  
Pin C4 on the front signal connector is used to connect to a terminal block  
temperature sensor. The temperature sensor channel is not isolated and is  
referenced to the chassis ground. The connection is overvoltage protected  
to 25 VDC with power on and 15 VDC with power off.  
Rear Signal Connector  
The rear signal connector is a 50-pin male ribbon cable connector used for  
analog signal connectivity and communication between the  
SCXI-1125 and the connected DAQ device. The rear signal connector  
allows the DAQ device to access all eight differential analog output signals  
from the SCXI-1125. The positive terminal of each analog output is  
CH x + and the negative terminal CH x –. Grounding signals, AI GND  
and OUT REF, provide reference signals needed in the various analog  
referencing modes on the E/M Series DAQ device. In multiplexed mode,  
the CH 0 signal pair is used for sending all eight channels of the  
SCXI-1125, and other analog signals from other modules, to the connected  
E/M Series DAQ device. If the module is directly connected to the E/M  
Series DAQ device, the other analog channels of the E/M Series DAQ  
device are still unavailable for general-purpose analog input because they  
are still connected to the amplifier outputs of the SCXI-1125 in multiplexed  
mode.  
The communication signals between the DAQ device and the SCXI system  
are SER DAT IN, SER DAT OUT, DAQ D*/A, SLOT 0 SEL*, SER CLK,  
and AI HOLD COMP, AI HOLD. The digital ground, D GND on pins 24  
and 33, provides a separate ground reference for the communication  
signals. SER DAT IN, SER DAT OUT, DAQ D*/A, SLOT 0 SEL*, and  
SER CLK are the communication lines for programming the SCXI-1125.  
The AI HOLD COMP, AI HOLD and SYNC signals are the signals  
necessary for multiplexed mode scanning. If the E/M Series DAQ device is  
connected to the SCXI-1125, these digital lines are unavailable for  
general-purpose digital I/O. The rear signal pin assignments are shown in  
Table 2-2.  
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Chapter 2  
Connecting Signals  
Table 2-2. Rear Signal Pin Assignments  
Rear Connector  
Diagram  
Signal Name  
Pin Number  
Pin Number  
Signal Name  
AI GND  
CH 0 +  
CH 1 +  
CH 2 +  
CH 3 +  
CH 4 +  
CH 5 +  
CH 6 +  
CH 7 +  
OUT REF  
NC  
1
2
AI GND  
3
4
CH 0 –  
1
3
5
7
9
2
4
5
6
CH 1–  
6
7
8
CH 2 –  
8
9
10  
12  
14  
16  
18  
20  
22  
24  
26  
28  
30  
32  
34  
36  
38  
40  
42  
44  
46  
48  
50  
CH 3 –  
10  
11 12  
13 14  
15 16  
17 18  
19 20  
21 22  
23 24  
25 26  
27 28  
29 30  
31 32  
33 34  
35 36  
37 38  
39 40  
41 42  
43 44  
45 46  
47 48  
49 50  
11  
13  
15  
17  
19  
21  
23  
25  
27  
29  
31  
33  
35  
37  
39  
41  
43  
45  
47  
49  
CH 4 –  
CH 5 –  
CH 6 –  
CH 7 –  
NC  
NC  
NC  
D GND  
SER DAT IN  
DAQ D*/A  
SLOT 0 SEL*  
NC  
SER DAT OUT  
NC  
NC  
NC  
D GND  
NC  
NC  
AI HOLD COMP, AI HOLD  
SER CLK  
NC  
NC  
NC  
NC means no  
connection  
NC  
NC  
NC  
NC  
NC  
SYNC  
NC  
NC  
NC  
NC  
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3
Configuring and Testing  
This chapter discusses configuring the SCXI-1125 in MAX for use with  
either NI-DAQmx or Traditional NI-DAQ (Legacy), creating and testing a  
virtual channel, global channel or task. For more information on the  
relationship between the settings and the measurements and how to  
configure settings in your application, refer to Chapter 4, Theory of  
Operation.  
SCXI-1125 Software-Configurable Settings  
This section describes the common software configurable settings and how  
to verify the signal using both NI-DAQmx and Traditional NI-DAQ  
(Legacy).  
Common Software-Configurable Settings  
This section describes the most frequently used software-configurable  
settings for the SCXI-1125. Refer to Chapter 4, Theory of Operation, for a  
complete list of software-configurable settings.  
Filter Bandwidth  
Filter bandwidth is a software-configurable setting that allows you to select  
a lowpass filter cutoff frequency. You can choose 4.0 Hz or 10 kHz.  
Gain/Input Range  
Gain/input range is a software-configurable setting that allows you to  
choose the appropriate amplification to fully utilize the range of the  
E/M Series DAQ device. In most applications NI-DAQ chooses and sets  
the gain for you determined by the input range.  
© National Instruments Corporation  
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SCXI-1125 User Manual  
 
                   
Chapter 3  
Configuring and Testing  
Refer to the SCXI Quick Start Guide to install the cable adapter and connect  
the SCXI modules to the DAQ device.  
If you have already installed the appropriate software, refer to Chapter 3,  
Configuring and Testing, to configure the SCXI-1125 module(s).  
Refer to the SCXI Quick Start Guide to connect the SCXI modules to the  
DAQ device.  
If you have already installed the appropriate software, refer to Chapter 3,  
Configuring and Testing, to configure the SCXI-1125 module(s).  
Configurable Settings in MAX  
Note If you are not using an NI ADE, using an NI ADE prior to version 7.0, or are using  
an unlicensed copy of an NI ADE, additional dialog boxes from the NI License Manager  
continue to appear until you install version 7.0 or later of an NI ADE.  
This section describes where users can access each software-configurable  
setting for modification in MAX. The location of the settings varies  
depending on the version of NI-DAQ you use. Refer to either the  
NI-DAQmx section or the Traditional NI-DAQ (Legacy) section. You also  
can refer to the DAQ Getting Started Guide and the SCXI Quick Start Guide  
for more information on installing and configuring your hardware. You also  
can use the DAQ Assistant to graphically configure common measurement  
tasks, channels, or scales.  
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Chapter 3  
Configuring and Testing  
NI-DAQmx  
In NI-DAQmx, you can configure software settings such as filter  
bandwidth and gain/input signal range in the following ways:  
Task or global channel in MAX  
Functions in your application  
Note All software-configurable settings are not configurable both ways. This section only  
discusses settings in MAX. Refer to Chapter 4, Theory of Operation, for information on  
using functions in your application.  
These sections describe settings that you can change in MAX and where  
they are located.  
Filter bandwidth—configure the Device tab using either NI-DAQmx  
Task or NI-DAQmx Global Channel. You also can set the value  
through your application.  
Input signal range—configure the input signal range using either  
NI-DAQmx Task or NI-DAQmx Global Channel. When you set the  
minimum and maximum range of NI-DAQmx Task or NI-DAQmx  
Global Channel, the driver selects the best gain for the measurement.  
You also can set it through your application.  
Modes of operation—configure only using chassis installation in  
software. Refer to Chapter 1, About the SCXI-1125, for more  
information on chassis installation. The default setting in NI-DAQmx  
is multiplexed.  
Terminal block attenuation—for terminal blocks with manually  
adjustable attenuation such as the SCXI-1327, you must configure the  
attenuator in the chassis configurator. Refer to the SCXI Quick Start  
Guide for more information.  
Note Refer to Chapter 4, Theory of Operation, for information on configuring the settings  
for your application using Traditional NI-DAQ (Legacy).  
Creating a Voltage Global Channel or Task  
To create a new NI-DAQmx global task or channel, complete the following  
steps:  
1. Double-click Measurement & Automation on the desktop.  
2. Right-click Data Neighborhood and select Create New.  
3. Select NI-DAQmx Task or NI-DAQmx Global Channel, and click  
Next.  
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Chapter 3  
Configuring and Testing  
4. Select Analog Input.  
5. Select Voltage.  
6. If you are creating a task, you can select a range of channels by holding  
down the <Shift> key while selecting the channels. You can select  
multiple individual channels by holding down the <Ctrl> key while  
selecting channels. If you are creating a channel, you can only select  
one channel. Click Next.  
7. Name the task or channel and click Finish.  
8. In the box labelled Channel List, select the channel(s) you want to  
configure. You can select a range of channels by holding down the  
<Shift> key while selecting the channels. You can select multiple  
individual channels by holding down the <Ctrl> key while selecting  
channels.  
9. Enter the specific values for your application in the Settings tab.  
Context help information for each setting is provided on the right side  
of the screen. Refer to Chapter 3, Configuring and Testing, for more  
information.  
10. Click the Device tab and select the autozero mode and lowpass filter  
cutoff frequency.  
11. If you are creating a task and want to set timing or triggering controls,  
enter the values in the Task Timing and Task Triggering tabs.  
Traditional NI-DAQ (Legacy)  
In Traditional NI-DAQ (Legacy), you can configure software settings, such  
as configuration, voltage excitation level, filter bandwidth, gain/input  
signal range, and calibration settings in the following three ways:  
module property pages in MAX  
virtual channels properties in MAX  
functions in your ADE  
Note All software-configurable settings are not configurable in all three ways. This  
section only discusses settings in MAX. Refer to Chapter 4, Theory of Operation, for  
information on using functions in your application.  
Most of these settings are available in module properties and/or using  
virtual channels:  
Filter bandwidth—configure only using module properties. You also  
can set bandwidth through your application. The default filter  
bandwidth level for Traditional NI-DAQ (Legacy) is 4 Hz.  
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Configuring and Testing  
Gain/input signal range—configure gain using module properties.  
When you set the minimum and maximum range of the virtual  
channel, the driver selects the best gain. The default gain setting  
for Traditional NI-DAQ (Legacy) is 1000.  
Terminal block gain—this setting is only configurable if you selected  
a terminal block that supports adjustable attenuation.  
Modes of operation—configure only using module properties. The  
default setting in Traditional NI-DAQ (Legacy) is multiplexed mode.  
Note Refer to Chapter 4, Theory of Operation, for information on configuring the settings  
for your application using Traditional NI-DAQ (Legacy).  
Configuring Module Property Pages in Traditional  
NI-DAQ (Legacy)  
1. Right-click the SCXI-1125 module you want to configure and select  
Properties. Click General.  
2. If the module you are configuring is connected to an E Series DAQ  
device, select that device by using Connected to. If you want this  
E Series DAQ device to control the chassis, confirm there is a check in  
the This device will control the chassis checkbox. If the module you  
are configuring is not connected to an E Series DAQ device, select  
None.  
3. Click the Channel tab. Select the appropriate gain and filter for each  
channel. If you want to configure all the channels at the same time,  
select the Channel drop-down menu, scroll to the bottom, and select  
All Channels. Refer to the SCXI-1125 Software-Configurable Settings  
section for a detailed description of each setting. Click Apply.  
4. Click Accessory. Select the accessory you connected to the module. If  
the accessory has a configurable gain, select the desired gain. When  
configuration is complete, click OK.  
The Traditional NI-DAQ (Legacy) chassis and SCXI-1125 should now be  
configured properly. If you need to change the module configuration,  
right-click the module and repeat steps 1 through 4. Test the system  
following the steps in the Troubleshooting the Self-Test Verification  
section of Chapter 1, About the SCXI-1125.  
© National Instruments Corporation  
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SCXI-1125 User Manual  
 
     
Chapter 3  
Configuring and Testing  
Creating a Virtual Channel  
To create a virtual channel, complete the following steps:  
1. Right-click Data Neighborhood and select Create New.  
2. Select Traditional NI-DAQ Virtual Channel and click Finish.  
3. Click Add Channel.  
4. Select Analog Input from the drop-down list and click Next.  
5. Enter the Channel Name and Channel Description, and click Next.  
6. Select Voltage from the drop-down list and click Next.  
7. Enter the units and input range, and click Next.  
8. Select the appropriate scaling option and click Next.  
9. Enter the following information:  
10. What DAQ hardware will be used? from the drop-down list.  
a. What channel on your DAQ hardware? from the drop-down list.  
b. Which analog input mode will be used? from the drop-down list.  
11. Click Finish.  
Verifying the Signal  
This section describes how to take measurements using test panels in order  
to verify signal, and configuring and installing a system in NI-DAQmx and  
Traditional NI-DAQ (Legacy).  
Verifying the Signal in NI-DAQmx Using a Task or Global Channel  
You can verify the signals on the SCXI-1125 using NI-DAQmx by  
completing the following steps:  
1. Expand Data Neighborhood.  
2. Expand NI-DAQmx Tasks.  
3. Click the task.  
4. Click the Add Channels or Remove Channels button to add/remove  
channels.  
5. In the window that appears, click the + next to the module of interest.  
6. Select the channel(s) you want to verify. You can select a block of  
channels by holding down the <Shift> key or multiple channels by  
holding down the <Ctrl> key. Click OK.  
7. Enter the appropriate information on the Settings tab.  
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Chapter 3  
Configuring and Testing  
8. Click the Device tab.  
9. Enter the appropriate information on the Device tab.  
10. Click the Test button.  
11. Click the Start button.  
12. After you have completed verifying the channels, click the Stop  
button.  
You have now verified the SCXI-1125 configuration and signal connection.  
Note For more information on how to further configure the SCXI-1125, or how to use  
LabVIEW to configure the module and take measurements, refer to Chapter 4, Theory of  
Operation.  
Verifying the Signal in Traditional NI-DAQ (Legacy)  
This section discusses how to verify the signal in Traditional NI-DAQ  
(Legacy) using channel strings and virtual channels.  
Verifying the Signal Using Channel Strings  
The format of the channel string is as follows:  
obx ! scy ! mdz ! channel  
where  
obx is the onboard E Series DAQ device channel, with x representing  
a particular channel where the multiplexed channels are sent. This  
value is 0 for E Series DAQ device channel 0 in a single-chassis  
system. In a multichassis or remote chassis system, the E Series DAQ  
device channel x corresponds to chassis number n – 1, where E Series  
DAQ device channel x is used for scanning the nth chassis in the  
system.  
scy is the SCXI chassis ID, where y is the number you chose when  
configuring the chassis.  
mdz is the slot position where the module is located, with z being the  
particular slot number. The slots in a chassis are numbered from left to  
right, starting with 1.  
channel is the channel that is sampled from module z.  
Use the format obx ! scy ! mdz !n to verify the signal, where n is a  
single input channel.  
© National Instruments Corporation  
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SCXI-1125 User Manual  
 
   
Chapter 3  
Configuring and Testing  
Complete the following steps to use channel strings in verifying the signal:  
1. Expand Devices and Interfaces.  
2. Expand Traditional NI-DAQ Devices.  
3. Right-click the appropriate E Series DAQ device.  
4. Click Test Panels.  
5. Enter the channel string.  
6. Enter the input limits.  
7. Select the Data Mode.  
8. Select the Y Scale Mode.  
Refer to the LabVIEW Measurements Manual for more information and for  
proper formatting of channel strings for different uses.  
Verifying the Signal Using Virtual Channel  
If you have already created a virtual channel, complete the following steps  
to verify the signal:  
1. Right-click the virtual channel you want to verify and select Test.  
2. In Channel Names, select the channel you want to verify.  
3. When you have completed verifying the channel, click Close.  
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4
Theory of Operation  
The section includes a brief overview and a detailed discussion of the  
circuit features of the module. The two major modes of operation,  
multiplexed and parallel mode, are discussed. Refer to Figure 4-1 while  
reading this section.  
Gain Select  
Lowpass  
Filter  
Lowpass  
Filter  
AI 0  
AI 7  
AI 0+  
AI 0–  
+
+
Buffer  
AI 0  
Analog  
Multiplexer  
AI 7+  
AI 7–  
Scan  
Clock  
To  
Analog  
Bus  
Analog  
Bus  
Switch  
Multiplexer  
Control  
Gain Select  
Lowpass  
Filter  
Lowpass  
Filter  
+
+
AI 7  
Digital Interface  
and Control  
MTEMP  
Figure 4-1. SCXI-1125 Block Diagram  
Gain  
The SCXI-1125 has 12 different gain settings, from 1 to 2000, enabling  
signal ranges 5 V to 2.5 mV. When the SCXI-1125 is used with a  
terminal block that provides attenuation, the input range expands up to  
1000 V. Refer to Appendix A, Specifications for a full list of input ranges.  
© National Instruments Corporation  
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SCXI-1125 User Manual  
 
           
Chapter 4  
Theory of Operation  
Configuring and Testing, for more information about programmatically  
setting gain using range settings in MAX. For more information about  
programmatically setting gain using range settings in NI-DAQmx and  
Traditional NI-DAQ (Legacy), refer to the Developing Your Application in  
NI-DAQmx section or the Developing Your Application in Traditional  
NI-DAQ (Legacy) section, respectively, of Chapter 5, Using the  
SCXI-1125.  
Filter Bandwidth and Cutoff Frequency  
The SCXI-1125 provides two filtering stages with an overall response of a  
four-pole Butterworth filter. You can control the cutoff frequency of the  
filter through software. You can choose 4 Hz or 10 kHz. For additional  
flexibility in cutoff frequency settings and for greater suppression, NI  
recommends combining the hardware filtering provided by the SCXI-1125  
with digital filtering. NI recommends using the Advanced Analysis  
functions of LabVIEW, LabWindows/CVI, or Measurement Studio. By  
combining hardware anti-aliasing with digital filtering, you can choose any  
cutoff frequency.  
The Advanced Analysis functions are only available in LabVIEW Full or  
Professional Development Systems, and LabWindows/CVI Base or Full  
Development Systems.  
Configuring and Testing, for more information about programmatically  
setting the cutoff frequency of the filter in MAX. For more information  
about programmatically setting the cutoff frequency of the filter in  
NI-DAQmx and Traditional NI-DAQ (Legacy), refer to the Developing  
Your Application in NI-DAQmx section or the Developing Your  
Application in Traditional NI-DAQ (Legacy) section, respectively, of  
Chapter 5, Using the SCXI-1125.  
Operating in Multiplexed Mode  
You can configure the SCXI-1125 to operate in multiplexed mode as  
described in Chapter 1, About the SCXI-1125. Using this mode of  
operation, you can scan all input channels of the SCXI-1125 into one  
output channel that is read by the National Instruments DAQ device. You  
can also multiplex the CJC channel that connects to a sensor on the SCXI  
terminal block for making temperature measurements.  
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Chapter 4  
Theory of Operation  
Multiplexed Hardware Operation Theory  
When you configure a module for multiplexed mode operation, the routing  
of multiplexed signals to the E/M Series DAQ device depends on which  
module in the SCXI system is cabled to the E/M Series DAQ device. There  
are several possible scenarios for routing signals from the multiplexed  
modules to the E/M Series DAQ device. If the module being scanned is not  
directly cabled to the E/M Series DAQ device, the module sends its signals  
through the SCXIbus to the cabled module. The cabled module, whose  
routing is controlled by the SCXI chassis, routes the SCXIbus signals to the  
E/M Series DAQ device through the CH0 signal on the rear signal  
connector. If the E/M Series DAQ device scans the cabled module, the  
module routes its input signals through the CH0 signal on the rear signal  
connector. The power of SCXI multiplexed scanning is its ability to route  
many input channels to a single channel on the E/M Series DAQ device.  
Note The SCXI-1125 parallel outputs continuously drive the rear signal connector output  
pins even when you configure the module in multiplexed mode. If the module is cabled to  
an E/M Series DAQ device in multiplexed mode, the differential inputs 1 through 7 on the  
E/M Series DAQ device cannot be used for general-purpose analog input. Refer to  
Appendix D, Common Questions, for more information on available pins on the rear signal  
connector.  
Multiplexed mode is typically used for performing scanning operations  
with the SCXI-1125. Immediately prior to a multiplexed scanning  
operation, the SCXI chassis is programmed with a module scan list that  
controls which module sends its output to the SCXIbus during a scan. You  
can specify this list to scan the modules in the chassis in any order, with an  
arbitrary number of channels for each module entry in the list. You can  
randomly scan the channels on the SCXI-1125, meaning channels can be in  
any order and occur multiple times in a single scan. When performing  
multiple scans, the list pointer of the module automatically wraps around  
Operating in Parallel Mode  
You can configure the SCXI-1125 to operate in parallel mode as described  
in Chapter 1, About the SCXI-1125. In parallel mode, all eight analog  
output channels on the SCXI-1125 are connected to eight analog input  
channels on the E/M Series DAQ device. The CJC channel is not  
accessible. Every SCXI-1125 configured for parallel mode must have a  
E/M Series DAQ device directly cabled to it.  
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Theory of Operation  
Theory of Parallel Hardware Operation  
In parallel mode, the CH0 signal on the rear signal connector is configured  
as the output of the SCXI-1125 analog input channel 0. The rear signal  
connector carries each of the analog outputs of the SCXI-1125 to the  
connected DAQ device. You can use an SCXI-1180 feedthrough connector  
to make each of the outputs available at the front of the chassis; which is  
useful for cascading these signals to other modules for additional signal  
conditioning purposes. Parallel mode allows you to bypass scanning and  
you are not limited by the settling time required by the multiplexer of  
SCXI-1125. You can scan the channels more accurately at a faster rate,  
depending on which E/M Series DAQ device you connect to the module.  
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Using the SCXI-1125  
This chapter discusses typical applications for the SCXI-1125. While this  
list is not comprehensive, it provides some guidance on how to improve  
measurement accuracy for some of the most popular applications of the  
SCXI-1125. Advanced operations such as calibration and using the CJC  
channel are discussed as well.  
Temperature Measurements Using Thermocouples  
Making isolated temperature measurements from thermocouples is a  
common use of the SCXI-1125. This section discusses how to use  
thermocouples, CJC, and how to calculate the temperature accuracy of the  
SCXI-1125.  
NI recommends using the SCXI-1328 terminal block to make  
thermocouple measurements with the SCXI-1125. Although you can use  
many of the SCXI terminal blocks for thermocouple measurements, the  
SCXI-1328 has an isothermal design that reduces temperature gradients  
within the terminal block housing. This design reduces the CJC errors  
which might reduce the accuracy of your temperature measurement. Most  
SCXI terminal blocks available for the SCXI-1125 contain a cold-junction  
temperature sensor, which is used for measuring ambient temperature. This  
sensor connects to a special channel on the SCXI-1125 inside the terminal  
block close to where the thermocouple connects to the screw terminals.  
Note Place the SCXI chassis away from extreme temperature gradients to minimize the  
temperature gradient inside the terminal block and maintain its isothermal nature for  
accurate CJC.  
A thermocouple relies on the principle that a small voltage that varies with  
temperature is produced at the junction of two dissimilar metals. CJC is  
necessary because the junction between the end of the thermocouple lead  
wires and the screw terminals produces a small potential difference, adding  
error to the thermocouple voltage. Knowing the temperature at the point  
where the thermocouple is connected to the measurement instrument  
allows you to determine the correct temperature reading at the  
thermocouple junction. Due to the nonlinear relationship between  
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thermocouple junction voltage and temperature, this voltage conversion  
(linearization) is best done through software.  
NI-DAQ has built-in scaling for most thermocouple types. In NI-DAQmx,  
you can create a thermocouple task or global channel. In Traditional  
NI-DAQ (Legacy), you can create a thermocouple virtual channel.  
If you choose to not let the driver scale the voltage readings for you in  
software, you must do several conversions by using conversion coefficients  
that reflect the voltage-temperature relationship for the type of  
thermocouple and CJC being used. Complete the following steps to  
accurately determine thermocouple temperature:  
1. Read the voltage from the CJC sensor and convert this voltage to a  
temperature.  
2. Convert this temperature to the corresponding voltage for the  
thermocouple type in use.  
3. Read the input voltage from the thermocouple.  
4. Add the two voltages.  
5. Translate the resultant voltage into the thermocouple temperature  
reading.  
You have completed the steps to get the true temperature reading from the  
thermocouple junction.  
National Instruments software ADEs have useful conversion functions for  
CJC. In LabVIEW, virtual channels with the CJC channel invoked or the  
Convert Thermocouple Reading VI are used. In C, use the NI-DAQ  
function, Thermocouple_Convert. In C, you might also need to use the  
function Thermistor_Convert, if your terminal block uses a thermistor  
to perform CJC. For more information about CJC, refer to your software  
ADE user documentation.  
To calculate the temperature accuracy of your SCXI-1125, you must  
consider several factors. First, the type of sensor and the temperature range  
you expect directly affects which gain your SCXI-1125 module uses for  
voltage readings, thereby directly affecting the resolution with which you  
can read temperature. After determining the range necessary for your  
application, you can apply the measurement accuracy specifications of the  
SCXI-1125; such as offset error, gain error, and noise to determine how  
these will affect your temperature measurement. Next, you must consider  
the accuracy of your cold-junction sensor and incorporate this into the total  
temperature error of your reading. Finally, the accuracy of the DAQ device  
you use must be factored in to determine your overall system error.  
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Complete the following steps to calculate the overall temperature error  
using the SCXI-1125 with an E Series MIO DAQ device:  
1. Based on the required temperature range and the type of sensor,  
determine the gain to use. For example, using a K-type thermocouple  
with a required temperature range of 0 to 100 °C, the corresponding  
voltage range is –1.002 mV to 4.0962 mV (averaging 41.0 µV/°C in  
this range). For this example, use a gain of 1000 for this temperature  
range to get maximum temperature resolution.  
2. Next, look up the analog accuracy specifications from Appendix A,  
Specifications, for the gain and filter settings you have chosen. You  
must consider how offset, gain, and system noise affect your  
measurement. You might also consider common-mode rejection,  
temperature drift, and other specifications based on the operating  
environment. For example, using a gain of 1000, the offset error is  
0.2 µV, the gain error is 0.03% which corresponds to 1.43 µV at  
full-scale temperature, and the system noise is 100 Vrms (use peak  
noise which is about 3 times this, or 300 nVpk) because of the 4 Hz  
filter. In this example you might or might not be able to average out the  
noise. The total error is 1.73 µV at the full-scale temperature range,  
which gives a preliminary accuracy of 0.04 °C (1.73 µV divided by  
41.0 µV/°C).  
3. Next, consider the accuracy of the cold-junction sensor you are using.  
For example, using the SCXI-1328, which, at about room temperature  
with little temperature gradient, has an accuracy of 0.5 °C. You must  
convert this temperature accuracy back to a voltage corresponding to a  
K-type thermocouple accuracy at 25 °C. This conversion produces  
about 20 µV of error.  
4. Add the two voltages and determine the overall temperature error. For  
example, the total error due to the SCXI portion of the system in this  
example now becomes 21.73 µV. This total error corresponds to  
about 0.53 °C (21.73 µV divided by 41.0 µV/°C) temperature error  
using the K-type thermocouple at this range.  
5. Determine the contribution of DAQ device error. For example, if using  
a 12-bit DAQ device, the DAQ device contributes a gain of 2, and  
therefore the code width becomes 2.44 µV. As a result, the total system  
error now becomes (21.73 µV + 2.44 µV), which corresponds to  
about 0.59 °C. If you were to choose a 16-bit board, you can achieve a  
code width of 0.153 µV, producing a total system error of 0.53 °C.  
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Making High-Voltage Measurements  
Another common use of the SCXI-1125 is to make measurements up to  
1000 VDC. Making measurements beyond 5 V requires use of the an  
attenuator terminal block. The SCXI-1327 and SCXI-1313A terminal  
blocks have a selectable attenuator for choosing between no attenuation or  
100:1 attenuation, which allows you to use the SCXI-1125 with up to  
300 Vrms when using the SCXI-1327 and up to 150 Vrms when using the  
SCXI-1313A.  
The TBX-1316 has a fixed 200:1 attenuation, which allows you to use the  
SCXI-1125 with up to 1000 VDC, Measurement Category I.  
The SCXI-1327 and SCXI-1313A also include a cold-junction sensor so  
you can combine thermocouple measurements with high-voltage  
measurements. When making signal connections, or when working with  
high-voltage signals, refer to the terminal block installation guide. If you  
are using the SCXI-1125 to measure signals with attenuation on the  
terminal block, an external bias resistor is not needed, because a bias  
resistor is already used for achieving the attenuation.  
Table 5-1 lists the extended ranges of gain possible with the SCXI-1327  
and SCXI-1313A. Table 5-2 lists the extended gain possible with the  
TBX-1316.  
Table 5-1. Extended Gain and Range Using the SCXI-1327 or SCXI-1313A  
Overall  
Gain  
Input  
Range  
SCXI-1125  
Gain  
SCXI-1327  
Attenuation  
SCXI-1313A  
Attenuation  
0.01  
0.02  
0.002  
0.05  
0.1  
300 V  
250 V  
150 V  
100 V  
50 V  
25 V  
10 V  
2 V  
1
2
100  
100  
100  
100  
100  
100  
100  
100  
2
100  
100  
100  
100  
100  
100  
5
10  
20  
50  
250  
0.2  
0.5  
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Table 5-2. Extended Gain and Range Using the TBX-1316  
Overall  
Gain  
Input  
Range  
SCXI-1125  
Gain  
TBX-1316  
Attenuation  
0.005  
0.01  
0.025  
0.05  
0.1  
1000 V  
500 V  
200 V  
100 V  
50 V  
1
2
200  
200  
200  
200  
200  
200  
5
10  
20  
50  
250  
0.25  
1.25  
20 V  
4 V  
The overall input impedance is reduced when attenuating the input, but this  
is acceptable in most applications. Refer to terminal block installation  
guides for more information. Appendix A, Specifications, shows how the  
analog input specifications are affected with the addition of the SCXI-1327  
terminal block.  
Developing Your Application in NI-DAQmx  
Note If you are not using an NI ADE, using an NI ADE prior to version 7.0, or are using  
an unlicensed copy of an NI ADE, NI License Manager displays additional dialog boxes  
so you can create a task or global channel in unlicensed mode. These dialog boxes continue  
to appear until you install version 7.0 or later of an NI ADE.  
This section describes how to configure and use NI-DAQmx to control the  
SCXI-1125 in LabVIEW, LabWindows/CVI, and Measurement Studio.  
These ADEs provide greater flexibility and access to more settings than  
MAX, but you can use ADEs in conjunction with MAX to quickly create a  
customized application.  
Typical Program Flowchart  
Figure 5-1 shows a typical program flowchart for creating a task to  
configure channels, take a measurement, analyze and present the data, stop  
the measurement, and clear the task.  
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eYs  
No  
Create Task Using  
DAQ Assistant?  
Create a Task  
Programmatically  
Yes  
Create Task in  
DAQ Assistant  
or MAX  
Create Channel  
(Application Specific)  
Create Another  
Channel?  
No  
Hardware  
Timing/Triggering?  
No  
No  
Further Configure  
Channels?  
Yes  
Yes  
Adjust Timing Settings  
Configure Channels  
Yes  
Analyze Data?  
No  
Process  
Data  
Start Measurement  
Read Measurement  
Yes  
Display Data?  
No  
Graphical  
Display Tools  
Yes  
Continue Sampling?  
No  
Stop Measurement  
Clear Task  
Figure 5-1. Typical Program Flowchart  
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General Discussion of Typical Flowchart  
The following sections discuss briefly considerations for a few of the steps  
in Figure 5-1. These sections give an overview of some of the options and  
features available when programming with NI-DAQmx.  
Creating a Task Using DAQ Assistant or  
Programmatically  
When creating an application, first you must decide whether to create the  
appropriate task using the DAQ Assistant or programmatically in the ADE.  
Developing your application using DAQ Assistant gives you the ability to  
configure most settings such as measurement type, selection of channels,  
excitation voltage, signal input limits, task timing, and task triggering. You  
can access the DAQ Assistant through MAX or your NI ADE. Choosing to  
use the DAQ Assistant can simplify the development of your application.  
NI recommends creating tasks using the DAQ Assistant for ease of use,  
when using a sensor that requires complex scaling, or when many  
properties differ between channels in the same task.  
If you are using an ADE other than an NI ADE, or if you want to explicitly  
create and configure a task for a certain type of acquisition, you can  
programmatically create the task from your ADE using functions or VIs.  
If you create a task using the DAQ Assistant, you can still further configure  
the individual properties of the task programmatically with functions  
or property nodes in your ADE. NI recommends creating a task  
programmatically if you need explicit control of programmatically  
adjustable properties of the DAQ system.  
Programmatically adjusting properties for a task created in the DAQ  
Assistant overrides the original, or default, settings only for that session.  
The changes are not saved to the task configuration. The next time you load  
the task, the task uses the settings originally configured in the DAQ  
Assistant.  
Adjusting Timing and Triggering  
There are several timing properties that you can configure through the  
DAQ Assistant or programmatically using function calls or property nodes.  
If you create a task in the DAQ Assistant, you can still modify the timing  
properties of the task programmatically in your application.  
When programmatically adjusting timing settings, you can set the task to  
acquire continuously, acquire a buffer of samples, or acquire one point at a  
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time. For continuous acquisition, you must use a while loop around the  
acquisition components even if you configured the task for continuous  
acquisition using MAX or the DAQ Assistant. For continuous and buffered  
acquisitions, you can set the acquisition rate and the number of samples to  
read in the DAQ Assistant or programmatically in your application. By  
default, the clock settings are automatically set by an internal clock based  
on the requested sample rate. You also can select advanced features such as  
clock settings that specify an external clock source, internal routing of the  
clock source, or select the active edge of the clock signal.  
Configuring Channel Properties  
All ADEs used to configure the SCXI-1125 access an underlying set of  
NI-DAQmx properties. Table 5-3 shows some of these properties. You can  
use Table 5-3 to determine what kind of properties you need to set to  
configure the module for your application. For a complete list of  
NI-DAQmx properties, refer to your ADE help file.  
Note You cannot adjust some properties while a task is running. For these properties, you  
must stop the task, make the adjustment, and re-start the application. Figure 5-1 assumes  
all properties are configured before the task is started.  
Table 5-3. NI-DAQmx Properties  
Property  
Short Name  
AI.Max  
Description  
Analog Input»General Properties»  
Advanced»Range»High  
Specifies the upper limit of the  
input range.  
Analog Input»General Properties»  
Advanced»Range»Low  
AI.Min  
Specifies the lower limit of the  
input range.  
Analog Input»General Properties»  
Filter»Analog Lowpass»Cutoff  
Frequency  
AI.Lowpass.CutoffFreq Specifies in hertz the  
frequency corresponding to the  
–3 dB cutoff of the filter. You  
can specify 4.0 or 10000.  
Note This is not a complete list of NI-DAQmx properties and does not include every  
property you may need to configure your application. It is a representative sample of  
important properties to configure for measurements. For a complete list of NI-DAQmx  
properties and more information about NI-DAQmx properties, refer to your ADE help file.  
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Acquiring, Analyzing, and Presenting  
After configuring the task and channels, you can start the acquisition, read  
measurements, analyze the data returned, and display it according to the  
needs of your application. Typical methods of analysis include digital  
filtering, averaging data, performing harmonic analysis, applying a custom  
scale, or adjusting measurements mathematically.  
NI provides powerful analysis toolsets for each NI ADE to help you  
perform advanced analysis on the data without requiring you to have a  
programming background. After you acquire the data and perform any  
required analysis, it is useful to display the data in a graphical form or log  
it to a file. NI ADEs provide easy-to-use tools for graphical display, such as  
charts, graphs, slide controls, and gauge indicators. NI ADEs have tools  
that allow you to easily save the data to files such as spread sheets for easy  
viewing, ASCII files for universality, or binary files for smaller file sizes.  
Completing the Application  
After you have completed the measurement, analysis, and presentation of  
the data, it is important to stop and clear the task. This releases any memory  
used by the task and frees up the DAQ hardware for use in another task.  
Note In LabVIEW, tasks are automatically cleared.  
Developing an Application Using LabVIEW  
This section describes in more detail the steps shown in the typical program  
flowchart in Figure 5-1, such as how to create a task in LabVIEW and  
configure the channels of the SCXI-1125. If you need more information or  
for further instructions, select Help»VI, Function, & How-To Help from  
the LabVIEW menu bar.  
Note Except where otherwise stated, the VIs in Table 5-4 are located on the Functions»  
All Functions»NI Measurements»DAQmx - Data Acquisition subpalette and  
accompanying subpalettes in LabVIEW.  
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Table 5-4. Programming a Task in LabVIEW  
VI or Program Step  
Flowchart Step  
Create Task in DAQ Assistant  
Create a DAQmx Task Name Constantlocated on the  
Controls»Modern»I/O»DAQmx Name Controls subpalette,  
right-click it, and select New NI-DAQmxTask (MAX...).  
Create a Task  
Programmatically (optional)  
DAQmx Create Task.vi—This VI is optional if you created  
and configured your task using the DAQ Assistant. However, if  
you use it in LabVIEW, any changes you make to the task will not  
be saved to a task in MAX.  
Create AI Channel (optional)  
DAQmx Create Virtual Channel.vi(AI Voltage by default,  
to change to a channel, click AI Voltage and select the type of  
analog input you want.—This VI is optional if you created and  
configured your task and channels using the DAQ Assistant. Any  
channels created with this VI are not saved in the DAQ Assistant.  
They are only available for the present session of the task in  
LabVIEW.  
Adjust Timing Settings  
(optional)  
DAQmx Timing.vi(Sample Clock by default)—This VI is  
Assistant. Any timing settings modified with this VI are not  
saved in the DAQ Assistant. They are only available for the  
present session.  
Configure Channels (optional) DAQmx Channel Property Node, refer to the Using a DAQmx  
Channel Property Node in LabVIEW section for more  
information. This step is optional if you created and fully  
configured the channels using the DAQ Assistant. Any channel  
modifications made with a channel property node are not saved  
in the task in the DAQ Assistant. They are only available for the  
present session.  
DAQmx Start Task.vi  
DAQmx Read.vi  
Start Measurement  
Read Measurement  
Analyze Data  
Some examples of data analysis include filtering, scaling,  
harmonic analysis, or level checking. Some data analysis tools  
are located on the Functions»Signal Analysis subpalette and on  
the Functions»All Functions»Analyze subpalette.  
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Table 5-4. Programming a Task in LabVIEW (Continued)  
VI or Program Step  
Flowchart Step  
Display Data  
You can use graphical tools such as charts, gauges, and graphs  
to display your data. Some display tools are located on the  
Controls»All Controls»Numeric»Numeric Indicators  
subpalette and Controls»All Controls»Graph subpalette.  
Continue Sampling  
For continuous sampling, use a While Loop. If you are using  
hardware timing, you also need to set the DAQmx Timing.vi  
sample mode to Continuous Samples. To do this, right-click the  
terminal of the DAQmx Timing.vilabeled sample mode and  
click Create»Constant. Click the box that appears and select  
Continuous Samples.  
Stop Measurement  
Clear Task  
DAQmx Stop Task.vi(This VI is optional, clearing the task  
automatically stops the task.)  
DAQmx Clear Task.vi  
Using a DAQmx Channel Property Node in LabVIEW  
You can use property nodes in LabVIEW to manually configure the  
channels. To create a LabVIEW property node, complete the following  
steps:  
1. Launch LabVIEW.  
2. Create the property node in a new VI or in an existing VI.  
3. Open the block diagram view.  
4. From the Functions toolbox, select Measurement I/O»  
DAQmx - Data Acquisition, and select DAQmx Channel Property  
Node.  
5. Use the ActiveChans box to specify exactly what channel(s) you want  
to configure. If you want to configure several channels with different  
properties, separate the lists of properties with another ActiveChans  
box and assign the appropriate channel to each list of properties.  
Note If you do not use Active Channels, the properties are set on all of the channels in  
the task.  
6. Right-click ActiveChans, and select Add Element. Left-click the new  
ActiveChans box. Navigate through the menus, and select the  
property you wish to define.  
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7. Change the property to read or write to either get the property or write  
a new value. Right-click the property, go to Change To, and select  
Write, Read, or Default Value.  
8. After you have added the property to the property node, right-click the  
terminal to change the attributes of the property, add a control,  
constant, or indicator.  
Figure 5-2. LabVIEW Channel Property Node with Lowpass Frequency Set at 10 kHz  
on Channel SC1Mod1/ai0  
9. To add another property to the property node, right-click an existing  
property and left-click Add Element. To change the new property,  
left-click it and select the property you wish to define.  
Note Refer to the LabVIEW Help for information about property nodes and specific  
NI-DAQmx properties.  
Specifying Channel Strings in NI-DAQmx  
Use the channel input of DAQmx Create Channel to specify the  
SCXI-1125 channels. The input control/constant has a pull-down menu  
showing all available external channels. The strings take one of the  
following forms:  
single device identifier/channel number—for example SC1Mod1/ch0  
multiple, noncontinuous channels—for example SC1Mod1/ch0,  
SC1Mod1/ch4  
multiple continuous channels—for example SC1Mod1/ch0:4  
(channels 0 through 4)  
cold junction channel—SC1Mod1/_cjtemp  
When you have a task containing SCXI-1125 channels, you can set the  
properties of the channels programmatically using the DAQmx Channel  
Property Node.  
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Follow the general programming flowchart or open an example to build a  
basic virtual channel. You can use property nodes in LabVIEW to control,  
configure, and customize the NI-DAQmx task and SCXI-1125. To create a  
LabVIEW property node, complete the following steps:  
1. Launch LabVIEW.  
2. Create the property node in a new Virtual Instrument (VI) or in an  
existing VI.  
3. Open the block diagram view.  
4. From the Functions tool bar, select NI Measurements,  
DAQmx - Data Acquisition, and select the type of property node you  
wish to configure.  
5. Use the ActiveChans box to specify what channel(s) you want to  
configure. If you want to configure several channels with different  
properties, separate the lists of properties with another ActiveChans  
box, and assign the appropriate channel to each list of properties.  
6. Right-click ActiveChan and select Add Element. Left-click the new  
ActiveChan box. Navigate through the menus and select the property  
you wish to define.  
7. You must change the property to read or write to either get the property  
or write a new value. Right-click the property, go to Change To, and  
select Write, Read, or Default Value.  
8. After you have added the property to the property node, right-click  
the terminal to change the attributes of the property, add a control,  
constant, or indicator.  
9. To add another property to the property node, right-click an existing  
property and left-click Add Element. To change the new property,  
left-click it and select the property you wish to define.  
Note Refer to the LabVIEW Help for information about property nodes and specific  
NI-DAQmx properties.  
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Text Based ADEs  
You can use text based ADEs such as LabWindows/CVI, Measurement  
Studio, Visual Basic, .NET, and C# to create code for using the  
SCXI-1125.  
LabWindows/CVI  
LabWindows/CVI works with the DAQ Assistant in MAX to generate  
code for a task. You can then use the appropriate function call to modify  
the task. To create a configurable channel or task in LabWindows/CVI,  
complete the following steps:  
1. Launch LabWindows/CVI.  
3. From the menu bar, select Tools»Create/Edit DAQmx Tasks.  
4. Choose Create New Task In MAX or Create New Task In Project  
to load the DAQ Assistant.  
5. Configure the NI-DAQmx task following the instructions in the  
Creating a Voltage Global Channel or Task section.  
6. The DAQ Assistant creates the code for the task based on the  
parameters you define in MAX and the device defaults. To change  
a property of the channel programmatically, use the  
DAQmxSetChanAttributefunction.  
Note Refer to the NI LabWindows/CVI Help for more information on creating NI-DAQmx  
tasks in LabWindows/CVI and NI-DAQmx property information.  
Measurement Studio (Visual Basic, .NET, and C#)  
When creating a task in Visual Basic .NET and C#, follow the general  
programming flow in Figure 5-1. You can then use the appropriate function  
calls to modify the task. This example creates a new task and configures an  
NI-DAQmx channel on the SCXI-112511251125. You can use the same  
functions for Visual Basic .NET and C#.  
Programmable NI-DAQmx Properties  
All of the different ADEs that configure the SCXI-1125 access an  
underlying set of NI-DAQmx properties. Table 5-5 provides a list of some  
of the properties that configure the SCXI-1125. You can use this list to  
determine what kind of properties you need to set to configure the device  
for your application. For a complete list of NI-DAQmx properties, refer to  
your ADE help file.  
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Table 5-5. NI-DAQmx Properties  
Property  
Short Name  
Description  
Analog Input»General Properties»  
Advanced»Range»High  
AI.Max  
AI.Min  
AI.Gain  
Specifies the upper limit of the  
input range.  
Analog Input»General Properties»  
Advanced»Range»Low  
Specifies the lower limit of the  
input range.  
Analog Input»General Properties»  
Advanced»Gain and Offset»  
Gain Value  
Specifies a gain factor to apply to  
the signal conditioning portion  
of the channel.  
Analog Input»Measurement Type  
AI.MeasType  
Indicates the measurement to take  
with the analog input channel.  
Note This is not a complete list of NI-DAQmx properties and does not include every  
property you may need to configure your application. For a complete list of NI-DAQmx  
properties and more information on NI-DAQmx properties, refer to your ADE help file.  
Developing Your Application in Traditional NI-DAQ  
(Legacy)  
Note If you are not using an NI ADE, using an NI ADE prior to version 7.0, or are using  
an unlicensed copy of an NI ADE, additional dialog boxes from the NI License Manager  
appear allowing you to create a task or global channel in unlicensed mode. These messages  
continue to appear until you install version 7.0 or later of an NI ADE.  
This section describes how to configure and use Traditional NI-DAQ  
(Legacy) to control the SCXI-1125 in LabVIEW, LabWindows/CVI,  
Measurement Studio, and other text-based ADEs. These NI ADEs provide  
greater flexibility and access to more settings than MAX, but you can use  
ADEs in conjunction with MAX to quickly create a customized  
application.  
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Traditional NI-DAQ (Legacy) in LabVIEW  
LabVIEW is a graphical programming environment for test and  
measurement application development with built-in easy to use tools for  
data acquisition, analysis, and display. You can use functional graphical  
blocks called subVIs to easily create a custom application that fully utilizes  
the SCXI-1125 programmable functionality. Traditional NI-DAQ  
(Legacy) provides several standard data acquisition subVIs as well as  
subVIs specifically for use with the SCXI-1125.  
For applications using Traditional NI-DAQ (Legacy) in LabVIEW, there  
are two typical methods of addressing SCXI-1125 channels—virtual  
channels (specifically virtual channels) and SCXI channel strings.  
channel addressing methods to use in your LabVIEW application.  
When you use virtual channels, the maximum number of channels per  
E Series DAQ device is 512 in multichassis systems. NI recommends using  
the virtual channel for ease of use. Refer to Appendix B, Using SCXI  
Channel Strings with Traditional NI-DAQ (Legacy) 7.0 or Later, for more  
information on how to create a virtual channel.  
The SCXI channel string allows you to combine large numbers of channels  
into fewer scan list entries, to measure the signal voltage level directly for  
custom scaling, and to dynamically perform an offset null compensation in  
your application. NI recommends using SCXI channel strings for more  
advanced applications. In LabVIEW, an array of these channel strings  
configures multiple modules for scanning. When using SCXI channel  
strings, you can scan up to 3,072 channels in a multichassis system using a  
single E Series DAQ device.  
Note You cannot mix virtual channels with the SCXI channel strings within the same  
channel string array.  
To use virtual channels, enter the name of a virtual channel into the analog  
input channel string. If using multiple virtual channels, enter them in a  
different index in the channel string array, or separate them using a comma.  
Since you can randomly scan analog input virtual channels, you can enter  
the virtual channels you want to scan in any order or repeatedly in a channel  
string array.  
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Typical Program Flow  
After you have determined how you want to address the channels and  
whether you want to configure the SCXI-1125 in MAX or LabVIEW, you  
can design your application using a typical program flow such as the one  
shown in Figure 5-3.  
Use  
Virtual Channel  
SCXI Channel String  
Configure  
Virtual Channel  
or SCXI Channel  
String  
Acquisition Settings  
Create Virtual  
Channel in MAX  
Configure  
Mode Properties  
Start Acquisition  
Take Measurements  
Yes  
Continue  
Sampling?  
No  
Scale, Analyze,  
and Display  
Clear Acquisition  
Error Handling  
Figure 5-3. Typical SCXI-1125 Program Flow with Traditional NI-DAQ (Legacy)  
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Configure the SCXI-1125 Settings Using Traditional NI-DAQ (Legacy) in  
LabVIEW  
You can configure SCXI-1125 settings in MAX using the virtual channel.  
To configure and control the SCXI-1125 from LabVIEW, use the  
AI Parameter VI. You can find AI Parameter VI in the function subpalette  
Data Acquisition»Analog Input»Advanced Analog Input.  
A parameter changed by the AI Parameter VI takes effect in hardware when  
AI Start VI is called, not when AI Parameter VI is called. The AI parameter  
VI merely changes the configuration in the driver memory. When called,  
the AI Start VI reads the configuration settings in the driver memory and  
then sends the actual control information to the SCXI-1125 module. A  
setting established through AI Parameter VI is only valid for the LabVIEW  
session and does not change the setting in MAX.  
You can use the AI Parameter VI to configure the SCXI-1125 settings  
shown in Table 5-6.  
Table 5-6. Settings for Configuring the SCXI-1125 Through the AI Parameter  
Allowable Settings  
AI Parameter VI  
Parameter  
(Float In, Boolean In, or Value In)  
Software-  
Configurable  
Setting  
Name  
Value  
Data Type  
Float In (dbl)  
Values  
4.0, 10000.0  
Filter  
Filter Setting  
14  
Bandwidth  
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An example of using the AI Parameter VI to control an SCXI-1125 is  
shown in Figure 5-4.  
Figure 5-4. Using the AI Parameter VI to Set Up the SCXI-1125  
Configure, Start Acquisition, and Take Readings Using Traditional  
NI-DAQ (Legacy) in LabVIEW  
After you have performed an offset null compensation and configured the  
SCXI-1125 settings for your application, you can use the intermediate  
analog input functions AI Config VI, AI Start VI, AI Read VI, and AI Clear  
VI to create your data acquisition application. You can find the  
intermediate data acquisition Traditional NI-DAQ (Legacy) functions in  
the function subpalettes Data Acquisition»Analog Input. NI recommends  
using the intermediate analog input functions for most SCXI-1125  
applications. For more information about using the intermediate data  
acquisition Traditional NI-DAQ (Legacy) functions, refer to the LabVIEW  
Measurements Manual. You also can use the LabVIEW Help for more  
detailed information about the various inputs and outputs of these  
functions.  
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Convert Scaling Using Traditional NI-DAQ (Legacy) in LabVIEW  
If you need scaling, you can either use an analog input voltage virtual  
channel with a custom scale configured in MAX or SCXI channel strings,  
and provide scaling in your LabVIEW application.  
If you are using SCXI channel strings, you can easily convert the  
SCXI-1125 voltage signal measurements in your application into scaled  
units of interest such as pounds or newtons. LabVIEW has some common  
conversion scaling functions such as the Scaling Constant Tuner VI in the  
function subpalette Data Acquisition»Signal Conditioning.  
You also can use an Expression Node or Formula Node to convert voltage  
signal measurements into whatever units your application requires. You can  
find an Expression Node in the function subpalette Numeric. You can find  
Formula Nodes in the Function subpalettes Analyze»Mathematics»  
Formula. For more information about using the Expression Node or  
Formula Node, refer to the LabVIEW User Manual. You also can use the  
LabVIEW Help for more detailed information about how to use these nodes  
to perform mathematical calculations such as scaling conversions.  
Analyze and Display Using Traditional NI-DAQ (Legacy) in LabVIEW  
In LabVIEW, you can easily analyze SCXI-1125 measurements with a  
variety of powerful analysis functions that you can find in the function  
subpalettes Analyze»Waveform Conditioning and Analyze»Signal  
Processing. You can perform post acquisition processing such as  
waveform comparisons, harmonic analysis, and digital filtering. For more  
information about these VIs, refer to the LabVIEW Analysis Concepts  
manual. You also can use the LabVIEW Help for more detailed information  
about how to use the analysis VIs.  
In LabVIEW, you also can easily display SCXI-1125 measurements with a  
variety of graphical waveform graphs, numeric slides, gauges, and other  
indicators. You can find useful graphical controls and indicators for user  
interaction with your application in the controls subpalettes. For more  
information about these VIs, refer to the LabVIEW User Manual. You also  
can use the LabVIEW Help for more detailed information about how to use  
graphical controls and indicators in your application.  
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Traditional NI-DAQ (Legacy) in Text-Based ADEs  
NI text-based ADEs, such as LabWindows/CVI, Measurement Studio  
for Microsoft Visual Basic, and Measurement Studio for Microsoft  
Visual C++, offer help in the development of test and measurement  
applications. These ADEs provide easy data acquisition, data analysis,  
graphical display, and data logging tools. Refer to the ADE user manual for  
more information about how to use these features.  
The high-level data acquisition tools provided in LabWindows/CVI and  
Measurement Studio allow you to easily use virtual channels configured in  
MAX providing easy configuration and programming of the data  
acquisition systems. However, some of the more advanced features of the  
SCXI-1125 are not accessible through this easy-to-use API. For more  
advanced features or for more explicit control of the programmatic  
attributes, use the low-level DAQ functions provided in the Traditional  
NI-DAQ (Legacy) C API. Refer to the ADE user documentation for more  
information about how to use the high-level data acquisition tools that are  
provided in your NI ADE.  
For more advanced SCXI-1125 applications, or if you are using an ADE  
other than an NI ADE, you can use the Traditional NI-DAQ (Legacy) C API  
to call functions from the DAQ driver dynamically linked library (dll).  
Configuring System Settings Using Traditional NI-DAQ (Legacy) C API  
Start the configuration of the acquisition by ensuring that the SCXI-1125  
module and SCXI chassis are in their default states, and that the driver  
software configuration matches the states the actual physical hardware  
configuration. After setting the hardware and software to the defaults of the  
module(s), you can configure any module settings that vary from the  
default configuration settings. You also should configure the acquisition  
parameters using the functions in Table 5-7. For additional information  
such as the function prototypes, parameters, and usage instructions for each  
function, refer to the Traditional NI-DAQ (Legacy) Function Reference  
Help installed by default in Start»Programs»National Instruments»  
NI-DAQ.  
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Table 5-7. Configuration Functions  
Description  
Function  
SCXI_Reset  
Resets the hardware such as the specified module to its default state.  
You also can use SCXI_Resetto reset the SCXI chassis Slot 0 scanning  
circuitry or reset the entire chassis.  
The SCXI-1125 default conditions are:  
Gain set at 1000.0  
4 Hz lowpass filter  
SCXI_Load_Config  
Loads the SCXI chassis configuration information you established in  
MAX. Sets the software states of the chassis and the modules present to  
their default states. This function makes no changes to the hardware  
state of the SCXI chassis or modules. It is possible to programmatically  
change the configuration you established in MAX using the  
SCXI_Set_Configfunction.  
SCXI_SCAN_Setup  
Initializes multiplexing circuitry for a scanned data acquisition  
operation. Initialization includes storing a table of the channel sequence  
and gain setting for each channel to be digitized (MIO and AI devices  
only). You cannot repeat channels or use nonsequential channels when  
using the SCXI_SCAN_Setupfunction.  
SCXI_MuxCtr_Setup  
Programs the E Series DAQ device with the correct number of channels  
multiplexed per scan. This number must match the total number of  
channels programmed in SCXI_SCAN_Setup.  
Note NI strongly recommends monitoring the built-in error status of each NI-DAQ  
function. The NI-DAQ C API provides the NIDAQErrorHandlerfunction, which ensures  
that a specified NI-DAQ function executed properly, and assists in handling error messages  
and reporting.  
Configure Module Settings Using Traditional NI-DAQ (Legacy) C API  
After configuring the hardware for acquisition, you must load the various  
channel attributes such as filter, gain, and excitation appropriate for your  
application explicitly using the NI-DAQ function calls shown in Table 5-8.  
For more information regarding each setting, refer to the Traditional  
NI-DAQ (Legacy) Function Reference Help installed by default in  
Start»Programs»National Instruments»NI-DAQ.  
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Table 5-8. NI-DAQ Functions Used to Configure SCXI-1125  
Channel  
Setting  
Significant  
Parameters  
Possible Parameters  
Values  
NI-DAQ Function to Use  
SCXI_Set_Gain  
Gain  
f64 gain  
(gain setting)  
1, 2, 5, 10, 20, 50, 100,  
200, 250, 500, 1000,  
2000  
SCXI_Configure_Filter  
Bandwidth  
f64 freq  
4.0, 10,000.0 Hz  
(filter cutoff  
frequency if  
filterMode = 1)  
Perform Offset Null Compensation Using Traditional NI-DAQ (Legacy)  
C API  
After configuring the system settings and module properties, you  
can perform an offset null compensation programmatically using  
SCXI_Calibrate. SCXI_Calibratetakes measurements and adjusts the  
coarse and fine offset null potentiometers to minimize or eliminate any  
electrical offset for a channel. Repeat this process for each channel by  
calling the SCXI_Calibratefunction in a loop. Use the resulting  
imbalance in your application as a software correction factor by  
determining the residual voltage from the imbalance, and subtracting this  
residual offset from each future measurement. For more information  
regarding the operation of SCXI_Calibrate, refer to the Traditional  
NI-DAQ (Legacy) Function Reference Help installed by default in Start»  
Programs»National Instruments»NI-DAQ.  
Perform Acquisition Using Traditional NI-DAQ (Legacy) C API  
There are several NI-DAQ functions you can use to take measurements.  
Usually in SCXI the preference is to take multiple samples from multiple  
channels using the SCAN_Opfunction. SCAN_Opperforms a synchronous,  
multiple-channel scanned data acquisition operation. SCAN_Opdoes not  
return until Traditional NI-DAQ (Legacy) acquires all the data or an  
acquisition error occurs (MIO, AI, and DSA devices only). For this reason,  
it is sometimes useful to use SCAN_Opin conjunction with the function  
Timeout_Config, which establishes a timeout limit synchronous  
functions to ensure that these functions eventually return control to your  
application. After acquiring data using SCAN_Op, the resultant data is not  
organized by channel, so you should demultiplex the data using  
SCAN_Demux. SCAN_Demuxrearranges, or demultiplexes, data acquired by  
a SCAN_Opinto row-major order, meaning each row of the array holding  
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the data corresponds to a scanned channel for easier access by  
C applications. BASIC applications need not call SCAN_Demuxto  
rearrange two-dimensional arrays since these arrays are accessed in  
column-major order. For more information regarding each acquisition  
function, refer to the Traditional NI-DAQ (Legacy) Function Reference  
Help installed by default in Start»Programs»National Instruments»  
NI-DAQ.  
Perform Scaling, Analysis, and Display  
After acquiring raw voltage data from the acquisition functions, most  
applications require adjustment by device calibration constants for  
accuracy, scaling measured voltage, analysis, and graphical display.  
The SCXI-1125 has stored software calibration constants loaded on the  
module EEPROM that are used to achieve the absolute accuracy  
specifications. SCXI_Scalescales an array of binary data acquired from  
an SCXI channel to voltage using the stored software calibration constants  
when it scales the data. You must call SCAN_Demuxbefore SCXI_Scaleif  
you have multiple channels in the scan. For more information regarding  
SCXI_Scale, refer to the Traditional NI-DAQ (Legacy) Function  
Reference Help installed by default in Start»Programs»National  
Instruments»NI-DAQ.  
After you have adjusted the measurement by the appropriate calibration  
constants using SCXI_Scale, you can use a function from the NI  
conversion library convert.hto convert a voltage or voltage buffer from  
a voltage to units of temperature or strain. NI-ADEs also provide many  
powerful analysis functions to perform digital filtering, harmonic analysis,  
averaging, and complex mathematics on measurements.  
After performing scaling and analysis on the acquired data, you can display  
the measurements in several ways. You can use any built in GUI tools in  
your ADE. NI ADEs provide many graphical controls and indicators such  
as charts, graphs, gauges, slides, and plots that you can use to display  
the data. There is also a built in function, found in nidaqex.h, called  
NIDAQPlotWaveformthat you can use to generate a simple plot of the  
data.  
Using Software for Multiplexed Scanning  
Performing scanning operations in software depends on the ADE you are  
using. While using LabVIEW, or Visual Basic, all scanning operations are  
prepared in software by using an SCXI channel string as the input to the  
channel parameter in the analog input VI or function. These ADEs also  
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support virtual channels using Data Neighborhood (DAQ Channel Wizard)  
in MAX. In LabWindows/CVI, C, or C++ development environments,  
several NI-DAQ function calls need to be made to set up each module  
involved in the scan, the chassis, and the E Series DAQ device controlling  
the scan. In Measurement Studio, SCXI channels must be configured as  
virtual channels (tags) in MAX.  
A discussion describing how to implement multiplexed scanning in the  
different ADEs follows. Refer to your ADE manual and the DAQ analog  
input examples that come with your application software for more detailed  
information on programming the SCXI modules for scanning in  
multiplexed mode.  
LabVIEW and the SCXI Channel String  
For LabVIEW, and Visual Basic, the channel string determines the  
sequence in which SCXI channels are scanned. In LabVIEW, an array of  
these channel strings configures multiple modules in the scan list. When the  
application program runs, the channel string is used for programming the  
channel information into the SCXI system. The format of the channel string  
is as follows:  
obx ! scy ! mdz ! channels  
where  
obx is the onboard E Series DAQ device channel, with x representing  
a particular channel where the multiplexed channels are sent. This  
value is 0 for DAQ channel 0 in a single-chassis system. In a  
multichassis or remote chassis system, however, the E Series DAQ  
device channel x corresponds to chassis number n–1, where DAQ  
device channel x is used for scanning the nth chassis in the system.  
scy is the SCXI chassis ID, where y is the number you chose when  
configuring your chassis.  
mdz is the slot position where the module is located, with z being the  
particular slot number. The slots in a chassis are numbered from left to  
right, starting with 1.  
Note The obx ! specifier is optional and causes the gains on the module and E Series  
DAQ device to be automatically set to fit the input limits parameter. When this specifier is  
omitted, the default gain on the E Series DAQ device, usually the lowest gain, is used, but  
the SCXI-1125 gain is adjusted to fit the input limits.  
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The last parameter, channels, is the list of channels that are scanned for  
module z. It can have several formats:  
obx ! scy ! mdz ! n, where n is a single input channel.  
obx ! scy ! mdz ! n1:n2, where n1 and n2 represent a sequential  
list of input channels, inclusive.  
obx ! scy ! mdz ! cjtemp, where cjtempis the CJC channel.  
You can scan this channel with other analog input channels. For  
compatibility reasons, you can use mtempin place of cjtemp.  
obx ! scy ! mdz ! (n1, n2, n3:n4, n1, n5, n2), where n1, n2, and  
n5 represent single channels, not necessarily sequential, and n3 and n4  
represent the endpoints of a sequential list of channels, inclusive. In  
this case, channels n1 and n2 have explicitly been repeated in the  
channel list. This random scanning format is not supported on all SCXI  
modules.  
obx!scy !mdz !calgndn1:n2 where n1 and n2 represent a list of  
autozeroed channels, inclusive. In this case autozero channels cannot  
be scanned with input channels or the cold-junction channel, but must  
be scanned separately. This feature is useful for measuring offsets that  
appear due to temperature drifts in the analog circuitry. You can  
subtract these offsets from subsequent input readings to correct for  
temperature drift. Refer to Appendix A, Specifications, for  
determining how temperature drift can affect your measurement  
accuracy.  
Note Repeating channels or having channels out of sequence in a scan list is not supported  
on all SCXI modules. Please refer to the manual of each module for information on this  
feature.  
LabVIEW and the Virtual Channel String  
For LabVIEW, Measurement Studio, and Visual Basic, the channel string  
can also contain virtual channels. For the SCXI-1125, these virtual  
channels are analog input channels you create that have custom names  
(called tags in Measurement Studio), that perform scaling, linearization,  
autozeroing, and CJC transparently without additional code. Virtual  
channels are useful when sensors requiring different scaling factors are  
used on the same SCXI-1125 channel. Using virtual channels, sensors  
needing special scaling can be used in a generic analog input application  
without performing hard-coded scaling or linearization. If the scaling  
changes or you want to connect a different sensor to the SCXI-1125, no  
changes are needed in the application. All that is required is creating a  
different virtual channel and using its name in the channel string.  
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Note You cannot mix virtual channels with the SCXI channel strings shown in the  
previous section.  
To create a virtual channel for the SCXI-1125, insert a new analog input  
channel in the Data Neighborhood path in MAX, name it, and then follow  
the software prompts to create virtual temperature channels, voltage  
channels, or customized analog input channels. For more information on  
virtual channels, consult the MAX online help file.  
To use the virtual channels, enter the name of the virtual channel into the  
analog input channel string. If using multiple virtual channels, separate  
them using a comma or enter them in a different index in the channel string  
array. The application does all scaling, linearization, autozeroing, and CJC  
automatically.  
Note Virtual analog input channels can be randomly scanned; therefore, virtual channels  
can be entered in any order or repeated in the channel string.  
Performing a Multiplexed Scan  
To perform a multiplexed scan in your application, perform the following  
steps:  
1. Open an analog input example in your ADE.  
2. Enter the appropriate SCXI channel string or virtual channel string into  
the channels parameter.  
3. Either enter the input limits for signals connected to the module to  
adjust the gain settings in your system, or use the default gain settings  
from the configuration utility, and then run the application. When  
using virtual channels, the default input limits configured in the virtual  
channel configurator are used.  
You have completed a multiplexed scan using your SCXI-1125.  
This is not a comprehensive discussion of SCXI scanning using LabVIEW  
or Measurement Studio, but it should give you enough information to help  
you get started with the examples that are shipped with these software  
packages.  
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C and Low-Level DAQ Functions  
When using a C-based environment, several steps are needed to configure  
the SCXI-1125 for multiplexed scanning. The following procedure outlines  
the steps for programming with the low-level DAQ function calls:  
1. Prepare the SCXI-1125 settings by either loading the original SCXI  
configuration settings using SCXI_Load_Config, or by specifying  
the gain and filter settings using SCXI_Set_Gainand  
SCXI_Configure_Filter.  
2. Use SCXI_SCAN_Setupto specify the module scan list, the start  
channel of each module, and the number of channels to scan on each  
module. SCXI_SCAN_Setupaccepts an array of start channels and an  
array of the number of channels to scan in each module. It is not  
possible to repeat channels or use nonsequential channels using  
SCXI_SCAN_Setup.  
3. Next, use SCXI_MuxCtr_Setupto program the E Series DAQ device  
with the correct number of channels multiplexed per scan. This  
number must match the total number of channels programmed in  
step 2.  
You are now ready to acquire the channel data with the E Series DAQ  
device. If you are using a multifunction E Series DAQ device, you can use  
SCAN_OPto perform the scanning operation. After scanning, convert the  
binary data to voltage data using SCXI_Scale. Refer to the NI-DAQ User  
Manual for additional information on scanning with DAQ devices.  
Using Software for Parallel Scanning  
channel strings or function calls for setting up channel sequencing as is  
required in multiplexed mode. Scanning the SCXI-1125 channels on a  
differentially configured DAQ device is done as if there were no  
SCXI-1125 module connected. The only requirement is that you must  
configure the module for parallel mode in MAX as described in Chapter 1,  
About the SCXI-1125.  
In LabVIEW, the SCXI-1125 configuration settings are automatically  
passed from MAX. LabVIEW can also set the SCXI-1125 configuration  
parameter, operating mode, to parallel or multiplexed programmatically  
by using the Set SCXI Information VI. In Measurement Studio, set the  
operating mode using MAX as described in Chapter 1, About the  
SCXI-1125.  
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After parallel mode has been configured in software, you can scan the  
SCXI-1125 channels by entering the corresponding E Series DAQ device  
channels or a sequential SCXI channel string in the channel parameter in  
the analog input application. You can also enter virtual channels; however,  
in parallel mode, virtual channels containing CJC are disabled in MAX.  
C and Parallel Mode  
When using a C-based ADE, you need no special steps for configuring the  
chassis, the SCXI-1125, or the E Series DAQ device for parallel scanning.  
You still have to configure the gain and filter settings by using  
SCXI_Set_Gainand SCXI_Configure_Filter. You can use any of the  
E Series DAQ device analog input functions to get the data from the eight  
channels of the SCXI module. After scanning, convert the binary data to  
voltage data by using SCXI_Scale.Refer to the NI-DAQ User Manual for  
additional information on parallel scanning of SCXI modules.  
Other Application Documentation and Material  
Refer to the ADE manual and the DAQ analog input examples that  
come with your application software for more detailed information on  
programming the SCXI modules for scanning in multiplexed mode.  
Traditional NI-DAQ (Legacy) CVI Examples  
Many example programs ship with NI-DAQ. For more example  
information on how to create tasks and channels, refer to the example  
programs. By default, the example programs are installed in C:\Program  
Files\National Instruments\CVI x.x\Samples. More examples  
are installed by default in C:\Program Files\National  
Instruments\NI-DAQ\Examples.  
Traditional NI-DAQ (Legacy) Measurement Studio Examples  
Many example programs ship with NI-DAQ. For more example  
information on how to create tasks and channels, refer to the example  
programs. By default, the example programs are installed in C:\Program  
Files\National Instruments\Measurement Studio 7.0. More  
examples are installed by default in C:\Program Files\National  
Instruments\NI-DAQ\Examples.  
© National Instruments Corporation  
5-29  
SCXI-1125 User Manual  
 
           
Chapter 5  
Using the SCXI-1125  
Calibration  
The SCXI-1125 is shipped with a calibration certificate and is calibrated by  
the factory to the specifications described in Appendix A, Specifications.  
Calibration constants are stored inside the calibration EEPROM and  
provide software correction values that are used by your application  
development software to correct your measurements for both offset and  
gain errors in the module.  
Due to the nature of the analog circuitry in your SCXI-1125 module, gain  
errors tend to be more stable over time, therefore requiring less frequent  
calibration. Offset errors, however, are more susceptible to drift due to time,  
temperature, and other environmental changes, and can affect the  
measurement accuracy of your module. You may wish to periodically  
calibrate the module for offset drift using the following procedure to ensure  
that the measurements on the SCXI-1125 are as accurate as possible. Refer  
to Appendix A, Specifications, for more details about the analog stability  
of your SCXI-1125 module.  
Calibration Procedures  
You can calibrate the offset on the SCXI-1125 using National Instruments  
software. When calibrating the offset on the SCXI-1125, make sure the  
DAQ device you are using has been calibrated recently or you will  
invalidate the offset calibration on the SCXI-1125. The SCXI-1125  
provides input switching that allows you to programmatically shunt the  
differential input channels of the SCXI-1125. Once the channels are  
shunted, the channel can be read by a calibrated DAQ device or calibrated  
DMM. These offsets voltages, read by the calibrated device, can be saved  
in the calibration EEPROM in the SCXI-1125 for software correction of  
offset.  
Caution Ensure that the calibration on the DAQ device or DMM you are using is up to date  
and traceable. If you adjust the gain or offset values using an uncalibrated device, you will  
invalidate the calibration on the SCXI-1125 and any measurements taken with the module  
may not be accurate.  
Remember that the calibration you perform on the SCXI-1125 is only as  
accurate as the calibration device you are using. Refer to Appendix A,  
Specifications, for accuracy specifications for the SCXI-1125.  
SCXI-1125 User Manual  
5-30  
ni.com  
 
     
Chapter 5  
Using the SCXI-1125  
One-Point Offset Calibration  
To perform offset calibration on your module, follow this procedure if you  
are using LabVIEW:  
1. Make sure the DAQ device or DMM you are using has a valid  
calibration and meets the accuracy specifications for your application.  
2. In LabVIEW, use the SCXI Calibrate VI to calibrate your module.  
a. Enter the DAQ device and the SCXI channel string for the  
channels you want to calibrate.You can calibrate only one channel  
at a time.  
b. Select internal calibration as the calibration operation you are  
going to perform.  
c. Select the Default EEPROM load area as the area you want to  
update.  
d. The offset varies with the selected gain value. Therefore, enter the  
high and low limits that correspond to the gain value for which  
you are calibrating offset. Refer to Table 5-9 for a list of the gain  
values and the corresponding input limits you must enter.  
e. Enter 0.0 as the input reference voltage.  
3. Run the application.  
4. Repeat steps 2 through 3 for calibrating the offset for additional  
channels or gain combinations.  
Table 5-9. Gain Values and Input Limits  
Gain  
1
Range ( )  
5 V  
2
2.5 V  
5
1 V  
10  
0.5 V  
20  
0.25 V  
0.125 V  
0.05 V  
0.025 V  
0.020 V  
0.010 V  
50  
100  
200  
250  
500  
© National Instruments Corporation  
5-31  
SCXI-1125 User Manual  
 
       
Chapter 5  
Using the SCXI-1125  
Table 5-9. Gain Values and Input Limits (Continued)  
Gain  
1000  
2000  
Range ( )  
0.005 V  
0.0025 V  
If you are using a C-based ADE, use the following procedure to do an offset  
calibration on the SCXI-1125:  
1. Make sure the DAQ device or DMM you are using has a valid  
calibration and meets the accuracy specifications for your application.  
2. Use the NI-DAQ function SCXI_Calibrateto calibrate one channel  
of the SCXI-1125.  
a. Enter the DAQ device, DAQ channel, module slot, and module  
channel for the channel you want to calibrate.  
b. Select internal calibration (0) as the operation you are going to  
perform.  
c. Select the load area (1) as the EEPROM area you want to update.  
d. Since offset varies with gain, enter the gain setting for which you  
are calibrating offset.  
e. Enter 1for the terminal block gain since it is not used.  
f. Enter 0.0as the input reference voltage.  
3. Repeat step 2 for calibrating additional channels.  
The SCXI-1125 may take a few seconds to perform the calibration. After  
completion, your module will have new calibration constants stored for the  
channels and gains you calibrated.  
Two-Point Gain and Offset Calibration  
If you also need to calibrate the gain constants on the SCXI-1125, you must  
use an external reference to perform a two-point calibration. Please refer to  
the SCXI-1125 Calibration Procedures document for more information on  
doing an external two-point gain and offset calibration.  
SCXI-1125 User Manual  
5-32  
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A
Specifications  
This appendix lists the specifications for the SCXI-1125 modules. These  
specifications are typical at 25 °C unless otherwise noted.  
Input Characteristics  
Table A-1. Input Signal Range Versus Gain  
SCXI-1125  
Gain  
Overall Gain  
Overall Voltage Range  
5 Vpeak or VDC  
1
2
1
2
2.5 Vpeak or VDC  
1 Vpeak or VDC  
5
5
10  
500 mVpeak or VDC  
250 mVpeak or VDC  
100 mVpeak or VDC  
50 mVpeak or VDC  
25 mVpeak or VDC  
20 mVpeak or VDC  
10 mVpeak or VDC  
5 mVpeak or VDC  
2.5 mVpeak or VDC  
10  
20  
20  
50  
50  
100  
200  
250  
500  
1000  
2000  
100  
200  
250  
500  
1000  
2000  
Note Refer to Tables 5-1 and 5-2 for extended range using the SCXI-1313A, SCXI-1327,  
and TBX-1316.  
© National Instruments Corporation  
A-1  
SCXI-1125 User Manual  
 
         
Appendix A  
Specifications  
Overvoltage protection  
Isolated connector pins:  
Powered on and off.......................... 300 V  
Inputs protected ...............................CH0..CH7  
Non-isolated connector pins:  
Powered on and off..........................+5.5V/–0.5 V  
SCXI-1125 User Manual  
A-2  
ni.com  
 
Appendix A  
Specifications  
© National Instruments Corporation  
A-3  
SCXI-1125 User Manual  
 
Appendix A  
Specifications  
SCXI-1125 User Manual  
A-4  
ni.com  
 
Appendix A  
Specifications  
Analog Inputs  
Number of input channels...................... 8 differential  
Input range ............................................. 2.5 mVDC to 5 VDC  
Input coupling ........................................ DC (or AC with SCXI-1305 or  
TBX-1329)  
Input impedance  
Normal powered on ........................ >1 G || 100 pF in parallel  
Powered off/overload...................... 4.5 M  
With SCXI-1327............................. 1 M  
With TBX-1316 .............................. 40 M  
Input bias current ................................... 100 pA typical, 1 nA max  
Filter type ............................................... 3-pole Butterworth filter response  
Bandwidth (–3dB cut-off frequency)  
4 Hz filter........................................ 4 Hz 5%  
10 kHz filter.................................... 10 kHz 5%  
Full power bandwidth.............. 7 kHz 5%  
With SCXI-1327 or  
SCXI-1313A high-voltage  
terminal blocks ........................ 2.6 kHz 5%  
With TBX-1316 high-voltage  
terminal block.......................... 500 Hz 5%  
Slew rate  
Typical.............................................0.15 V/μs  
Minimum.........................................0.1 V/μs  
Scan interval accuracy  
0.012%..........................................3 μs  
0.006%.........................................10 μs  
0.0015%........................................20 μs  
Common Mode Rejection Ratio, 50/60 Hz (CMRR)  
4 Hz filter enabled........................... 160 dB  
10kHz filter enabled........................ 98 dB  
© National Instruments Corporation  
A-5  
SCXI-1125 User Manual  
 
Appendix A  
Specifications  
Normal Mode Rejection, 50/60 Hz (NMRR)  
4 Hz filter enabled ...........................60 dB  
Crosstalk at 1kHz  
Adjacent channels............................–75 dB  
All other channels............................–90 dB  
Input coupling  
Default.............................................DC  
Using SCXI-1305 or TBX-1329 .....AC or DC  
Power Consumption  
+18.5 V ...................................................140 mA max  
– 18.5 V ..................................................140 mA max  
+5 V ........................................................10 mA max  
Output Characteristics  
Output range ........................................... 5.0 V  
Output impedance  
Multiplexed output mode ................100 Ω  
Parallel output mode........................330 Ω  
Transfer Characteristics  
Nonlinearity  
All ranges.........................................0.02% of full scale range  
Stability  
Recommended warm-up time.................15 minutes  
Offset drift .............................................. (0.42 + 250/gain) μV/°C  
Gain drift................................................. 20 ppm/°C typical  
External calibration interval ...................1 year  
SCXI-1125 User Manual  
A-6  
ni.com  
 
     
Appendix A  
Specifications  
Physical  
3.0 cm  
(1.2 in.)  
17.2 cm  
(6.8 in.)  
18.8 cm  
(7.4 in.)  
Figure A-1. SCXI-1125 Dimensions  
Weight.................................................... 641 g (22.6 oz)  
© National Instruments Corporation  
A-7  
SCXI-1125 User Manual  
 
 
Appendix A  
Specifications  
Maximum Working Voltage  
Maximum voltage rating refers to the signal voltage plus the common  
mode voltage (Signal + common mode). Voltage of each input shall remain  
within 300 V of ground.  
Channel-to-earth .....................................300 V, Measurement Category II  
Channel-to-channel.................................300 V, Measurement Category II  
Table A-2. Terminal Block Maximum Voltages  
Module  
Signal Range  
Maximum Voltage and Category [Insulation]  
SCXI-1313A  
150 V  
300 V  
600 V  
1000 V  
150 V, Measurement Category II  
[channel-to-channel, channel-to-earth]  
SCXI-1327  
TBX-1316  
300 V, Measurement Category II  
[bank-to-bank, bank-to-earth]  
600 V, Measurement Category II  
[Basic; channel-to-channel]  
1000 V, Measurement Category I  
[Basic; channel-to-channel]  
Cautions The SCXI-1125 is rated for Measurement Category II and is intended to carry  
signal voltages no greater than 300 V. Do not use the SCXI-1125 for connection to signals  
or for measurements within Categories III or IV.  
When hazardous voltages (>42.4 Vpk/60 VDC) are present on any channel, all channels are  
considered hazardous. Ensure that external wiring or any circuits connected to the device  
are properly insulated from human contact.  
Environmental  
Operating temperature ............................0 to 50 °C  
Storage temperature................................–20 to 70 °C  
Humidity.................................................10 to 90% RH, noncondensing  
Maximum altitude...................................2,000 meters  
Pollution Degree (indoor use only) ........2  
SCXI-1125 User Manual  
A-8  
ni.com  
 
     
Appendix A  
Specifications  
Safety  
This product is designed to meet the requirements of the following  
standards of safety for electrical equipment for measurement, control,  
and laboratory use:  
IEC 61010-1, EN-61010-1  
UL 61010-1, CSA 61010-1  
Note For UL and other safety certifications, refer to the product label or visit ni.com/  
certification, search by model number or product line, and click the appropriate link  
in the Certification column.  
Electromagnetic Compatibility  
This product is designed to meet the requirements of the following  
standards of EMC for electrical equipment for measurement, control,  
and laboratory use:  
EN 61326 EMC requirements; Minimum Immunity  
EN 55011 Emissions; Group 1, Class A  
CE, C-Tick, ICES, and FCC Part 15 Emissions; Class A  
Notes For EMC compliance, operate this device according to product documentation.  
For EMC compliance, operate this device with shielded cabling.  
CE Compliance  
This product meets the essential requirements of applicable European  
Directives, as amended for CE marking, as follows:  
2006/95/EC; Low-Voltage Directive (safety)  
2004/108/EC; Electromagnetic Compatibility Directive (EMC)  
Note Refer to the Declaration of Conformity (DoC) for this product for any additional  
regulatory compliance information. To obtain the DoC for this product, visit ni.com/  
certification, search by model number or product line, and click the appropriate link  
in the Certification column.  
© National Instruments Corporation  
A-9  
SCXI-1125 User Manual  
 
     
Appendix A  
Specifications  
Environmental Management  
National Instruments is committed to designing and manufacturing  
products in an environmentally responsible manner. NI recognizes that  
eliminating certain hazardous substances from our products is beneficial  
not only to the environment but also to NI customers.  
For additional environmental information, refer to the NI and the  
Environment Web page at ni.com/environment. This page contains the  
environmental regulations and directives with which NI complies, as well  
as any other environmental information not included in this document.  
Waste Electrical and Electronic Equipment (WEEE)  
EU Customers At the end of their life cycle, all products must be sent to a WEEE recycling  
center. For more information about WEEE recycling centers and National Instruments  
WEEE initiatives, visit ni.com/environment/weee.htm.  
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(For information about China RoHS compliance, go to  
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SCXI-1125 User Manual  
A-10  
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B
Using SCXI Channel Strings with  
Traditional NI-DAQ (Legacy) 7.0  
or Later  
Note This appendix is not applicable if you use the virtual channels to configure and  
measure the SCXI channels. Virtual channels are configured using MAX. If you use virtual  
channels, you address the SCXI channels by specifying the channel name(s) in the channel  
string input.  
When using LabVIEW, and Visual Basic, the SCXI channel string  
determines which SCXI channels are scanned and the scanning sequence.  
The SCXI channel string allows you to take measurements from several  
channels on one module with only one channel string entry. An array of  
these channel string entries configures multiple modules for scanning.  
When the application program runs, the channel string is used  
for programming the channel information into the SCXI system.  
The format of the channel string is as follows:  
obx ! scy ! mdz ! channels  
where  
obxis the onboard E/M Series DAQ device channel, with x  
representing a particular channel where the multiplexed channels are  
sent. This value is 0 for E/M Series DAQ device channel 0 in a  
single-chassis system. In a multichassis or remote chassis system, the  
E/M Series DAQ device channel xcorresponds to chassis number  
n – 1, where E/M Series DAQ device channel xis used for scanning  
the nth chassis in the system.  
scyis the SCXI chassis ID, where yis the number you chose when  
configuring the chassis.  
mdzis the slot position where the module is located, with zbeing the  
particular slot number. The slots in a chassis are numbered from left to  
right starting with 1.  
© National Instruments Corporation  
B-1  
SCXI-1125 User Manual  
 
     
Appendix B  
Using SCXI Channel Strings with Traditional NI-DAQ (Legacy) 7.0 or Later  
channelsis the list of channels that are scanned for module z. It can have  
several formats:  
obx ! scy ! mdz ! nx, where nxis a single input channel.  
obx ! scy ! mdz ! (n0, n2), where n0, n2are individual input  
channel that are not necessarily sequential.  
obx ! scy ! mdz ! n0:n3, where n0and n3represent an ascending  
sequential list of input channels, inclusive.  
obx ! scy ! mdz ! (n0, n2, n3:n4, n1, n5, n2), where  
n0, n2, and n5represent single channels, not necessarily sequential,  
and n3and n4represent the endpoints of an ascending sequential list  
of channels, inclusive. In this case, channels n1and n2are explicitly  
repeated in the channel list.  
Notes Using parenthesis surrounding multiple channels in a channel string is important  
for correct scanning operation of the SCXI channels.  
In a single-chassis system, the obx !specifier is optional and causes the gains on the  
module and E/M Series DAQ device to be automatically set to fit the input limits  
parameter. When this specifier is omitted, the default gain on the E/M Series DAQ device,  
usually the lowest gain, is used, but the SCXI-1125 gain is adjusted to fit the input limits.  
NI recommends using the obx !specifier.  
Repeating channels or having channels out of sequence in a scan list is not supported on  
all SCXI modules. Refer to the manual of each module for information on this feature,  
which is referred to as flexible scanning or random scanning.  
For more information about using SCXI channel string, refer to the  
LabVIEW Measurements Manual and SCXI-1125 shipping examples.  
SCXI-1125 User Manual  
B-2  
ni.com  
 
C
Removing the SCXI-1125  
This appendix explains how to remove the SCXI-1125 from MAX and an  
SCXI chassis.  
Note Figure C-1 shows an SCXI chassis, but the same steps are applicable to a PXI/SCXI  
combination chassis.  
Removing the SCXI-1125 from MAX  
To remove a module from MAX, complete the following steps after  
launching MAX:  
1. Expand Devices and Interfaces to display the list of installed devices  
and interfaces.  
2. Expand NI-DAQmx Devices and/or Traditional NI-DAQ Devices to  
display the chassis.  
3. Expand the appropriate chassis to display the installed modules.  
4. Right-click the module or chassis you want to delete and click Delete.  
5. You are presented with a confirmation window. Click Yes to continue  
deleting the module or chassis or No to cancel this action.  
Note Deleting the SCXI chassis deletes all modules in the chassis. All configuration  
information for these modules is also deleted.  
The SCXI chassis and/or SCXI module(s) should now be removed from the  
list of installed devices in MAX.  
Removing the SCXI-1125 from a Chassis  
Consult the documentation for the chassis and accessories for additional  
instructions and precautions. To remove the SCXI-1125 module from an  
chassis, complete the following steps while referring to Figure C-1:  
1. Power off the chassis. Do not remove the SCXI-1125 module from a  
chassis that is powered on.  
© National Instruments Corporation  
C-1  
SCXI-1125 User Manual  
 
     
Appendix C  
Removing the SCXI-1125  
2. If the SCXI-1125 is the module cabled to the E Series DAQ device,  
disconnect the cable.  
3. Remove any terminal block that connects to the SCXI-1125.  
4. Rotate the thumbscrews that secure the SCXI-1125 to the chassis  
counterclockwise until they are loose, but do not completely remove  
the thumbscrews.  
5. Remove the SCXI-1125 by pulling steadily on both thumbscrews until  
the module slides completely out.  
7
1
6
5
4
3
2
1
ARDES  
SCXI  
N  
F
R
A
M
E
5
S
C
X
I
1
1
0
0
2
4
3
1
2
3
4
Cable  
5
6
7
Terminal Block  
SCXI Chassis Power Switch  
SCXI Chassis  
SCXI Module Thumbscrews  
SCXI-1125  
Sensor  
Figure C-1. Removing the SCXI-1125  
SCXI-1125 User Manual  
C-2  
ni.com  
 
 
D
Common Questions  
This appendix lists common questions related to the use of the SCXI-1125.  
The SCXI-1125 is backward compatible with the SCXI-1120, but what  
are the major differences between the SCXI-1120 and the SCXI-1125?  
Table D-1 compares the major specifications and features of the two  
modules. Other specifications and features of the SCXI-1125 are the same  
or very similar to the SCXI-1120.  
Table D-1. Comparison of the SCXI-1125 with the SCXI-1120  
Feature  
Analog input  
Input range  
SCXI-1120  
SCXI-1125  
8
8
5 V, 250 V with SCXI-1327  
5 V, 300 V with SCXI-1327,  
1000 VDC with TBX-1316  
Isolation  
Gains  
250 Vrms  
300 Vrms  
1, 2, 5, 10, 20, 50, 100, 200, 250, 500, 1, 2, 5, 10, 20, 50, 100, 200, 250, 500,  
1000, and 2000 jumper selectable  
4 Hz or 10 kHz jumper selectable  
Not supported  
1000, and 2000 software selectable  
4 Hz or 10 kHz software selectable  
Software configurable and scannable  
Filters  
Autozero  
Calibration  
Manually rotateable potentiometers  
for one-point offset calibration  
Software internal one-point offset  
calibration, software external  
two-point offset and gain calibration,  
and onboard calibration constant  
storage in EEPROM  
Scanning  
333 kS/s with consecutive channels  
333 kS/s with nonconsecutive and  
repeating channels (random scanning)  
CJC scanning  
M TEMP (non-scannable) or  
D TEMP (direct channel)  
M TEMP, CJ TEMP (scannable)  
Offset error  
Gain error  
6 µV 3 mV/gain  
0.2 mV/gain typical  
0.2% typ, 0.6% max  
0.03% typ, 0.08% max  
© National Instruments Corporation  
D-1  
SCXI-1125 User Manual  
 
         
Appendix D  
Common Questions  
Which version of NI-DAQ is needed to work with the SCXI-1125 and  
how do I get the most current version of NI-DAQ?  
You must have NI-DAQ 7.0 or later. Visit ni.comand follow the link,  
Download Software»Drivers and Updates»Search Drivers and  
Updates, and type in the keyword NI-DAQto find the latest version of  
NI-DAQ for your operating system.  
I have gone over the Verifying the SCXI-1125 Installation in Software in  
Chapter 1, About the SCXI-1125, yet I still cannot correctly test and  
verify that my SCXI-1125 is working. What should I do now?  
Unfortunately, there always exists the chance that something is not  
operating correctly in your system, or the combination of the components  
in your system is not operating correctly together. You may now have to call  
or e-mail a technical support representative.  
The technical support representative will often suggest additional  
troubleshooting measures to try in order to isolate the problem. If  
requesting technical support by phone, have your system near at hand so  
that you can try these measures immediately.  
Can I use the unused analog input channels of the E/M Series DAQ  
device if I am directly cabled to the SCXI-1125?  
It depends. The SCXI-1125 always outputs channels 1 through 7 to the rear  
signal connector to permit parallel mode scanning. If you are using a  
16-channel (8 differential inputs) E/M Series DAQ device, all E/M Series  
DAQ channels are unusable for general-purpose analog input. If you have  
a module in the chassis that does not have parallel mode, connect the  
E/M Series DAQ device to it and use a breakout connector to connect to the  
unused channels on the E/M Series DAQ device. If you are directly  
connected to a higher input channel device, such as a 64-channel  
(32 differential inputs) E/M Series DAQ device, only the lower  
eight differential inputs are unusable.  
Which digital lines are unavailable on the E/M Series DAQ device if I  
am cabled to an SCXI-1125 module?  
Table D-2 shows the digital lines that are used by the SCXI-1125 for  
communication and scanning. These lines are unavailable for  
general-purpose digital I/O if the SCXI-1125 is connected to the  
E/M Series DAQ device.  
SCXI-1125 User Manual  
D-2  
ni.com  
 
             
Appendix D  
Common Questions  
Table D-2. Digital Signals on the SCXI-1125  
Traditional  
DAQ Signal  
Name  
DAQmx  
Signal Name  
SCXI Signal  
Name  
50-Pin  
Connector  
68-Pin  
Connector  
Direction  
Output  
Input  
DIO0  
P0.0  
P0.4  
P0.1  
P0.2  
SER DAT IN  
SER DAT OUT  
DAQ D*/A  
25  
26  
27  
29  
36  
52  
19  
17  
49  
46  
DIO4  
DIO1  
Output  
Output  
Output  
DIO2  
SLOT 0 SEL*  
SCAN CLK  
SCANCLK  
AI HOLD  
COMP,  
AI HOLD  
EXTSROBE*  
STARTSCAN  
EXTSROBE  
SER CLK  
SYNC*  
37  
46  
45  
38  
Output  
Output  
AI SAMP  
CLK,  
AI SAMP  
In LabVIEW, can I use different input limits for the same SCXI-1125  
channel if I repeat the channel in the SCXI channel string array?  
No, the SCXI-1125 cannot dynamically change the gain settings during  
scanning. Therefore, channels with similar input ranges should be grouped  
together in the channel string array. Make sure that repeated channels in  
different indices of the channel string array have the same input limits in  
the corresponding input limits array.  
In LabVIEW, can I use virtual channels with parallel mode channels  
on the SCXI-1125?  
Yes, virtual channels work with parallel mode operation on the SCXI-1125.  
The E/M Series DAQ device must be directly connected to the module in  
parallel mode operation. Also, virtual channels that use built-in CJC are  
disabled and cannot be used in parallel mode.  
In LabVIEW, can I use the calgnd channel string when the SCXI-1125  
is in parallel mode?  
Yes, you can autozero the SCXI-1125 in LabVIEW when using the module  
in parallel mode.  
© National Instruments Corporation  
D-3  
SCXI-1125 User Manual  
 
         
Appendix D  
Common Questions  
In LabVIEW, can I use a VI to change my filter setting?  
In NI-DAQmx, you can change the filter settings using a DAQmx Channel  
property node. In Traditional NI-DAQ (Legacy), there is no VI available to  
do this. You must use the configuration utility in MAX to configure the  
filter setting of each channel.  
In C, can I randomly scan the SCXI-1125 using low level Traditional  
NI-DAQ (Legacy) function calls?  
No, using C, you can scan only consecutive channels using traditional  
SCXI channel programming. Refer to the NI-DAQ function reference  
manual for more details on SCXI scanning.  
SCXI-1125 User Manual  
D-4  
ni.com  
 
     
Glossary  
Symbol  
Prefix  
pico  
Value  
10–12  
10–9  
10– 6  
10–3  
103  
p
n
nano  
micro  
milli  
kilo  
μ
m
k
M
G
T
mega  
giga  
106  
109  
tera  
1012  
Numbers/Symbol  
°
Degrees.  
Ω
/
Greater than or equal to.  
Less than or equal to.  
Ohms.  
Per.  
%
Percent.  
Plus or minus.  
+5 VDC source signal.  
+5 V (signal)  
© National Instruments Corporation  
G-1  
SCXI-1125 User Manual  
 
 
Glossary  
A
A/D  
analog-to-digital  
absolute accuracy  
The maximum difference between the measured value from a data  
acquisition device and the true voltage applied to the input, typically  
specified as voltage.  
AC  
alternating current  
ADC  
analog-to-digital converter—An electronic device, often an integrated  
circuit, that converts an analog voltage to a digital number.  
ADE  
application development environment—A software environment  
incorporating the development, debug, and analysis tools for software  
development.  
AI GND  
analog input ground  
AI HOLD COMP,  
AI HOLD  
clock that triggers scanning  
amplification  
A type of signal conditioning that improves accuracy in the resulting  
digitized signal by increasing signal amplitude relative to noise.  
autozero  
A procedure for eliminating offsets generated by an amplifier stage.  
B
bandwidth  
The range of frequencies present in a signal, or the range of frequencies to  
which a measuring device can respond.  
bias current  
The small input current flowing into or out of the input terminals of an  
amplifier.  
bit  
one binary digit, either 0 or 1  
BNC  
Bayonet-Neill-Concelman—A type of coaxial connector used in situations  
requiring shielded cable for signal connections and/or controlled  
impedance applications.  
SCXI-1125 User Manual  
G-2  
ni.com  
 
 
Glossary  
C
C
Celsius  
CE  
Conformité Européenne—The European emissions control standard. The  
CE mark certifies that a product complies to relevant CE regulations. CE is  
a common standard for all countries in the EU (European Union).  
CH  
channel  
channel  
Pin or wire lead to which you apply or from which you read an analog or  
digital signal. Analog signals can be single-ended or differential. For digital  
signals, channels group to form ports. Ports usually consist of either four or  
eight digital channels.  
chassis  
CJ TEMP  
CJC  
The enclosure that houses, powers, and controls SCXI modules.  
cold-junction temperature sensor signal  
cold-junction compensation  
CLK  
clock input signal  
CMRR  
common-mode rejection ratio—A measure of the capability of an  
instrument to reject a signal that is common to both input leads.  
code width  
The smallest detectable change in an input voltage of a DAQ device.  
A method of compensating for inaccuracies in thermocouple circuits.  
cold-junction  
compensation  
common-mode voltage  
cutoff frequency  
Voltage that appears on both inputs of a differential amplifier.  
The frequency at which the filter attenuates the input 3 dB, or half of its  
original power.  
D
D/A  
digital-to-analog  
data/Address  
D*/A  
D GND  
digital ground signal  
© National Instruments Corporation  
G-3  
SCXI-1125 User Manual  
 
 
Glossary  
DAQ  
Data acquisition—(1) collecting and measuring electrical signals from  
sensors, transducers, and test probes or fixtures and inputting them to a  
computer for processing; (2) collecting and measuring the same kinds of  
electrical signals with A/D and/or DIO boards plugged into a computer, and  
possibly generating control signals with D/A and/or DIO boards in the  
same computer.  
DAQ device  
dB  
A device that collects signals for data acquisition devices. Examples are  
MIO and 1200 boards.  
decibel—The unit for expressing a logarithmic measure of the ratio of  
two signal levels: dB = 20 log10 (V1/V2), for signals in volts.  
DC  
direct current  
device  
A plug-in data acquisition board, module, card, or pad that can contain  
multiple channels and conversion devices.  
differential input  
An input circuit that actively responds to the difference between two  
terminals, rather than the difference between one terminal and ground.  
DIN  
deutsche Industrie Norme  
digital I/O  
DIO  
DMM  
digital multimeter—A digital instrument capable of measuring several  
different fundamental electrical characteristics, most often voltage,  
resistance, and current.  
E
EEPROM  
electrically erasable programmable read-only memory—ROM that can be  
erased with an electrical signal and reprogrammed.  
EMC  
EMI  
electromechanical compliance  
electromagnetic interference  
SCXI-1125 User Manual  
G-4  
ni.com  
 
Glossary  
F
filtering  
A type of signal conditioning that allows you to remove unwanted signal  
components from the signal you are trying to measure.  
FSR  
full-scale range  
G
gain  
The factor by which a signal is amplified, sometimes expressed in decibels.  
gain accuracy  
gain error  
GND  
A measure of deviation of the gain of an amplifier from the ideal gain.  
See gain accuracy.  
ground  
H
Hz  
hertz  
I
I/O  
input/output—The transfer of data to/from a computer system involving  
communications channels, operator interface devices, and/or data  
acquisition and control interfaces.  
in.  
inch  
input bias current  
input impedance  
The current that flows into the inputs of a circuit.  
The measured resistance and capacitance between the input terminals of a  
circuit.  
© National Instruments Corporation  
G-5  
SCXI-1125 User Manual  
 
Glossary  
isolation  
A type of signal conditioning in which you isolate the transducer signals  
from the computer for safety purposes. Isolating the signals protects you  
and your computer from large voltage spikes and makes sure the  
measurements from the DAQ device are not affected by differences in  
ground potentials.  
isothermal  
Maintenance of constant temperature across an area. Isothermal  
construction of terminal blocks increases thermocouple measurement  
accuracy.  
K
K
kelvin  
L
linearization  
A type of signal conditioning in which software linearizes the voltage levels  
from transducers, so the voltages can be scaled to measure physical  
phenomena.  
M
m
meters  
M
(1) Mega, the standard metric prefix for 1 million or 106, when used with  
units of measure such as volts and hertz; (2) mega, the prefix for 1,048,576,  
or 220, when used with B to quantify data or computer memory.  
M TEMP  
max  
multiplexed temperature sensor signal. See also CJ TEMP.  
Minimum.  
min  
(1) minutes  
(2) minimum  
MIO  
multifunction I/O  
multiplex  
To assign more than one signal to a channel.  
SCXI-1125 User Manual  
G-6  
ni.com  
 
Glossary  
multiplexed mode  
An SCXI operating mode in which analog input channels are multiplexed  
into one module output so that your cabled DAQ device has access to the  
module’s multiplexed output as well as the outputs on all other multiplexed  
modules in the chassis through the SCXIbus.  
mux  
multiplexer—A switching device with multiple inputs that sequentially  
connects each of its inputs to its single output, typically at high speeds, in  
order to measure several signals with a single analog-to-digital converter.  
N
NC  
not connected  
NI-DAQ  
The driver software needed to use National Instruments DAQ devices and  
SCXI components.  
noise  
Analog. Unwanted signals. Noise comes from both external sources, such  
as the AC power line, motors, generators, transformers, fluorescent lights,  
soldering irons, CRT displays, computers, electrical storms, welders, and  
radio transmitters, and internal sources, such as digital clocks,  
microprocessors, and switched mode power supplies. Video system noise  
can take various forms, including snow, which is a random video noise. It  
corrupts signals you are trying to send or receive.  
O
offset error  
A constant error added to a measurement along the whole transfer curve.  
For example, in mx+b, the offset error is b.  
offset null  
compensation  
The provision in strain-gauge signal conditioning hardware to remove the  
unwanted offset voltage present at the output of a strain-gauge bridge when  
no strain is applied.  
P
parallel mode  
A type of SCXI operating mode in which the module sends each of its  
output channels directly to a separate analog input channel of the DAQ  
device connected to the module.  
passband  
The range of input frequencies that are passed to the filter output without  
attenuation.  
© National Instruments Corporation  
G-7  
SCXI-1125 User Manual  
 
Glossary  
ppm  
PXI  
parts per million  
A rugged, open system for modular instrumentation based on CompactPCI,  
with special mechanical, electrical, and software features. The PXIbus  
standard was originally developed by National Instruments in 1997, and is  
now managed by the PXIbus Systems Alliance.  
R
resolution  
The smallest signal increment that can be detected by a measurement  
system. Resolution can be expressed in bits, in proportions, or in percent of  
full scale. For example, a system has 12-bit resolution, one part in 4,096  
resolution, and 0.0244% of full scale.  
RMA  
rms  
return Material Authorization  
root mean square  
RSVD  
RTI  
reserved bit/signal  
referred to input—Calculates a specification relative to the input range.  
S
s
seconds  
sample  
An instantaneous measurement of a signal, normally using an  
analog-to-digital converter in an E Series DAQ device.  
sample rate  
scan  
The number of samples a system takes over a given time period, usually  
expressed in samples per second.  
One or more analog or digital input samples. Typically, the number of input  
samples in a scan is equal to the number of channels in the input group. For  
example, one pulse from the scan clock produces one scan which acquires  
one new sample from every analog input channel in the group.  
SCANCLK  
Scan clock signal used to increment the next channel after each E Series  
DAQ device analog-to-digital conversion.  
SCXI-1125 User Manual  
G-8  
ni.com  
 
Glossary  
SCXI  
Signal Conditioning eXtensions for Instrumentation—the National  
Instruments product line for conditioning low-level signals within an  
external chassis near sensors so only high-level signals are sent to DAQ  
boards in the noisy PC environment.  
SCXIbus  
The analog bus where SCXI analog signals are routed.  
SER CLK  
A serial clock signal used to synchronize digital data transfers over the SER  
DAT IN and SER DAT OUT lines.  
SER DAT IN  
SER DAT OUT  
sensor  
serial data input signal  
serial data out to cabled DAQ device  
A device that responds to a physical stimulus (heat, light, sound, pressure,  
motion, flow, and so on), and produces a corresponding electrical signal.  
Primary characteristics of sensors are sensitivity, frequency range, and  
linearity.  
settling time  
The time required for an amplifier, relays, or other circuits to reach a stable  
mode of operation.  
shunt  
See autozero.  
shunt calibration  
The method of calibrating the gain of strain-gauge data acquisition channel  
by placing a resistor of known value in parallel with a bridge element.  
signal conditioning  
Slot 0  
The manipulation of signals to prepare them for digitizing.  
The first slot in a VXI or SCXI system.  
strain  
The relative deformation of an object subjected to stress. Hence, strain is  
dimensionless.  
SYNC  
synchronization pulse for scanning  
system noise  
A measure of the amount of noise seen by an analog circuit or an ADC  
when the analog inputs are grounded.  
© National Instruments Corporation  
G-9  
SCXI-1125 User Manual  
 
Glossary  
T
thermocouple  
A temperature sensor created by joining two dissimilar metals. The  
junction produces a small voltage as a function of the temperature.  
typ  
typical  
U
UL  
Underwriters Laboratory  
V
V
volts  
VDC  
VI  
volts direct current  
virtual instrument—(1) a combination of hardware and/or software  
elements, typically used with a PC, that has the functionality of a classic  
stand-alone instrument (2) a LabVIEW software module (VI), which  
consists of a front panel user interface and a block diagram program.  
virtual channels  
Channel names that can be defined outside of the application and used  
without having to perform scaling operations. Virtual channels are called  
custom channels in MAX 3.0 and later.  
voltage excitation  
Vrms  
A source that supplies the voltage needed by a sensor for its proper  
operation.  
volts, root mean square  
W
working isolation  
A level of protection pertaining to a working voltage.  
working voltage  
The highest voltage that should be applied to a product in normal use,  
normally well under the breakdown voltage for safety margin.  
SCXI-1125 User Manual  
G-10  
ni.com  
 
Index  
common questions, D-1  
troubleshooting self-test verification, 1-7  
configuration settings  
filter bandwidth, 3-1, 4-2  
gain, 3-1, 4-1  
A
AC and DC voltage connections, 2-1  
(figure), 2-4  
connecting SCXI-1125 to DAQ device  
See also DAQ devices  
connectors  
front signal connector  
front signal connector  
pin assignments  
figure, 2-6  
table, 2-6  
rear signal connector  
description, 2-7  
ground-referenced AC-coupled signal  
connection (figure), 2-4  
ground-referenced signal, 2-2  
ground-referenced signal connection  
pin assignments  
figure, 2-8  
table, 2-8  
C
C language  
multiplexed scanning operations, 5-27  
parallel scanning operations, 5-28  
scanning channels, D-4  
calibration  
DAQ device  
connecting with SCXI-1125  
unavailable digital lines, D-2  
gain values and input limits (table), 5-31  
one-point offset calibration, 5-31  
overview, 5-30  
two-point gain and offset calibration, 5-32  
channel string  
connecting to SCXI-1125 for multiplexed  
scanning  
calgnd channel string, D-3  
in PXI combination chassis, 1-4, 3-2  
in SCXI chassis, 1-4, 3-2  
DC voltage connections. See AC and DC voltage  
connections  
virtual, 5-26  
channels  
C language scanning, D-4  
questions about, D-3  
unused analog input channels on DAQ  
device, D-2  
© National Instruments Corporation  
I-1  
SCXI-1125 User Manual  
 
 
Index  
digital lines, unavailability on DAQ device,  
D-2  
digital signals on SCXI-1125 (table), D-3  
documentation  
I
input characteristics, A-1  
parallel scanning, 1-5  
connecting to DAQ device for  
in SCXI chassis, 1-4, 3-2  
into SCXI chassis, 1-4  
E
specifications, A-9  
removing SCXI-1125  
from Measurement & Automation  
Explorer, C-1  
F
filter setting, changing, D-4  
filters  
bandwidth configuration, 3-1, 4-2  
(figure), 2-4  
description, 2-3  
front signal connector  
pin assignments  
L
multiplexed scanning operations  
SCXI channel string, 5-25  
virtual channel string, 5-26  
low-level DAQ functions, in multiplexed  
table, 2-6  
G
gain  
maximum working voltage, A-8  
Measurement & Automation Explorer  
removing SCXI-1125, C-1  
self-test verification  
troubleshooting, 1-7  
multiplexed mode  
configuration, 3-1, 4-1  
ground-referenced signal connections  
(figure), 2-4  
description, 2-2  
operating in, 4-2  
performing scans, 5-27  
C and low-level DAQ functions, 5-28  
rear signal connector pin assignments  
figure, 2-8  
H
high-voltage measurements, 5-4  
table, 2-8  
SCXI-1125 User Manual  
I-2  
 
ni.com  
operation, 4-3  
using software for scanning operations  
string, 5-25  
removing SCXI-1125  
from SCXI chassis, C-1  
LabVIEW and virtual channel  
string, 5-26  
S
multiplexed mode operation  
in PXI combination, 1-4, 3-2  
in SCXI chassis, 1-4, 3-2  
safety specifications, A-9  
SCXI chassis  
1-4, 3-2  
SCXI-1125  
N
calibration, 5-30  
common questions, D-1  
digital signals (table), D-3  
multiplexed mode, 4-2  
parallel mode, 4-3  
signal connections, 2-1  
specifications, A-1  
P
parallel mode  
device, 1-5  
self-test verification  
theory of parallel hardware operation, 4-4  
using software for scanning  
C and parallel mode, 5-29  
LabVIEW and parallel mode, 5-28  
physical specifications, A-7  
pin assignments  
See also connectors  
floating AC-coupled signal  
PXI combination chassis, 1-4, 3-2  
floating signal connection  
R
ground-referenced AC-coupled  
signal connection (figure), 2-4  
ground-referenced signal, 2-2  
ground-referenced signal connection  
(figure), 2-2  
rear signal connector  
description, 2-7  
pin assignments  
figure, 2-8  
table, 2-8  
regulatory compliance specifications, A-9  
digital signals (table), D-3  
© National Instruments Corporation  
I-3  
SCXI-1125 User Manual  
 
Index  
front connector  
overview, 2-1  
accurate method for temperature  
determination, 5-2  
guide for calculating overall temperature  
error, 5-3  
software  
string, 5-25  
overview, 5-1  
string, 5-26  
parallel scanning operations  
C and parallel mode, 5-29  
LabVIEW and parallel mode, 5-28  
See temperature measurements using  
thermocouples  
troubleshooting  
specifications  
electromagnetic compatibility, A-9  
environmental, A-8  
input characteristics, A-1  
maximum working voltage, A-8  
physical, A-7  
regulatory compliance, A-9  
safety, A-9  
verifying and self-testing the configuration  
troubleshooting, 1-7  
stability, A-6  
virtual channel string, 5-26  
transfer characteristics, A-6  
stability specifications, A-6  
SCXI-1125 User Manual  
I-4  
 
ni.com  

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