National Instruments Switch NI 7831R User Manual

Reconfigurable I/O  
NI 7831R User Manual  
Reconfigurable I/O Devices for  
PCI/PXI/CompactPCI Bus Computers  
NI 7831R User Manual  
April 2004 Edition  
Part Number 370489B-01  
 
   
Important Information  
Warranty  
The NI 7831R is warranted against defects in materials and workmanship for a period of one year from the date of shipment, as evidenced by  
receipts or other documentation. National Instruments will, at its option, repair or replace equipment that proves to be defective during the  
warranty period. This warranty includes parts and labor.  
The media on which you receive National Instruments software are warranted not to fail to execute programming instructions, due to defects  
in materials and workmanship, for a period of 90 days from date of shipment, as evidenced by receipts or other documentation. National  
Instruments will, at its option, repair or replace software media that do not execute programming instructions if National Instruments receives  
notice of such defects during the warranty period. National Instruments does not warrant that the operation of the software shall be  
uninterrupted or error free.  
A Return Material Authorization (RMA) number must be obtained from the factory and clearly marked on the outside of the package before  
any equipment will be accepted for warranty work. National Instruments will pay the shipping costs of returning to the owner parts which are  
covered by warranty.  
National Instruments believes that the information in this document is accurate. The document has been carefully reviewed for technical  
accuracy. In the event that technical or typographical errors exist, National Instruments reserves the right to make changes to subsequent  
editions of this document without prior notice to holders of this edition. The reader should consult National Instruments if errors are suspected.  
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Under the copyright laws, this publication may not be reproduced or transmitted in any form, electronic or mechanical, including photocopying,  
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Instruments Corporation.  
Trademarks  
CompactRIO, LabVIEW, National Instruments, NI, ni.com, NI Developer Zone, and RTSIare trademarks of National Instruments  
Corporation.  
Product and company names mentioned herein are trademarks or trade names of their respective companies.  
Patents  
For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txtfile  
on your CD, or ni.com/patents.  
WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS  
(1) NATIONAL INSTRUMENTS PRODUCTS ARE NOT DESIGNED WITH COMPONENTS AND TESTING FOR A LEVEL OF  
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PROCESS AND SAFETY LEVEL OF SUCH SYSTEM OR APPLICATION.  
 
Compliance  
Compliance with FCC/Canada Radio Frequency Interference  
Regulations  
Determining FCC Class  
The Federal Communications Commission (FCC) has rules to protect wireless communications from interference. The FCC  
places digital electronics into two classes. These classes are known as Class A (for use in industrial-commercial locations only)  
or Class B (for use in residential or commercial locations). All National Instruments (NI) products are FCC Class A products.  
Depending on where it is operated, this Class A product could be subject to restrictions in the FCC rules. (In Canada, the  
Department of Communications (DOC), of Industry Canada, regulates wireless interference in much the same way.) Digital  
electronics emit weak signals during normal operation that can affect radio, television, or other wireless products.  
All Class A products display a simple warning statement of one paragraph in length regarding interference and undesired  
operation. The FCC rules have restrictions regarding the locations where FCC Class A products can be operated.  
Consult the FCC Web site at www.fcc.govfor more information.  
FCC/DOC Warnings  
This equipment generates and uses radio frequency energy and, if not installed and used in strict accordance with the instructions  
in this manual and the CE marking Declaration of Conformity*, may cause interference to radio and television reception.  
Classification requirements are the same for the Federal Communications Commission (FCC) and the Canadian Department  
of Communications (DOC).  
Changes or modifications not expressly approved by NI could void the user’s authority to operate the equipment under the  
FCC Rules.  
Class A  
Federal Communications Commission  
This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to part 15 of the FCC  
Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated  
in a commercial environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and  
used in accordance with the instruction manual, may cause harmful interference to radio communications. Operation of this  
equipment in a residential area is likely to cause harmful interference in which case the user is required to correct the interference  
at their own expense.  
Canadian Department of Communications  
This Class A digital apparatus meets all requirements of the Canadian Interference-Causing Equipment Regulations.  
Cet appareil numérique de la classe A respecte toutes les exigences du Règlement sur le matériel brouilleur du Canada.  
Compliance with EU Directives  
Users in the European Union (EU) should refer to the Declaration of Conformity (DoC) for information* pertaining to the  
CE marking. 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/hardref.nsf, search by model number or product line,  
and click the appropriate link in the Certification column.  
*
The CE marking Declaration of Conformity contains important supplementary information and instructions for the user or  
installer.  
 
About This Manual  
Conventions ...................................................................................................................vii  
Chapter 1  
Software Development ..................................................................................................1-5  
LabVIEW FPGA Module................................................................................1-5  
Cables and Optional Equipment ....................................................................................1-7  
Chapter 2  
Types of Signal Sources ................................................................................................2-7  
Floating Signal Sources...................................................................................2-7  
Ground-Referenced Signal Sources ................................................................2-7  
Input Modes ...................................................................................................................2-7  
Differential Connection Considerations (DIFF Input Mode)..........................2-9  
Differential Connections for Ground-Referenced Signal Sources....2-9  
Differential Connections for Nonreferenced  
or Floating Signal Sources .............................................................2-10  
© National Instruments Corporation  
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Contents  
Connecting Digital I/O Signals ..................................................................................... 2-16  
RTSI Trigger Bus .......................................................................................................... 2-19  
Switch Settings.............................................................................................................. 2-21  
Chapter 3  
Loading Calibration Constants...................................................................................... 3-1  
Internal Calibration........................................................................................................ 3-1  
External Calibration....................................................................................................... 3-2  
Appendix A  
Specifications  
Appendix B  
Connecting I/O Signals  
Appendix C  
Appendix D  
Technical Support and Professional Services  
Glossary  
NI 7831R User Manual  
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About This Manual  
This manual describes the electrical and mechanical aspects of the  
National Instruments 7831R device and contains information concerning  
its operation and programming.  
The NI 7831R device is a Reconfigurable I/O (RIO) device. The NI 7831R  
has eight independent, 16-bit analog input (AI) channels, eight  
independent, 16-bit analog output (AO) channels, and 96 digital I/O (DIO)  
lines.  
Conventions  
The following conventions appear 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,  
DIO<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  
the device, refer to the Safety Information section of Chapter 1,  
Introduction, for precautions to take.  
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 and hardware labels.  
italic  
Italic text denotes variables, emphasis, a cross reference, or an introduction  
to a key concept. This font 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,  
© National Instruments Corporation  
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About This Manual  
programs, subprograms, subroutines, device names, functions, operations,  
variables, filenames, and extensions.  
Reconfigurable I/O Documentation  
The NI 7831R User Manual is one piece of the documentation set for your  
RIO system and application. Depending on the hardware and software you  
use for your application, you could have any of several types of  
documentation. The documentation includes the following documents:  
Getting Started with the NI 7831R—This document lists what you  
need to get started, describes how to unpack and install the hardware  
and software, and contains information about connecting I/O signals to  
the NI 7831R.  
LabVIEW FPGA Module Release Notes—This document contains  
information about installing and getting started with the  
LabVIEW FPGA Module. Select Start»Program Files»National  
Instruments»<LabVIEW>»Module Documents»LabVIEW  
FPGA»Release Notes to view this document.  
LabVIEW FPGA Module User Manual—This manual describes how  
to use the LabVIEW FPGA Module to create virtual instruments (VIs)  
that run on the NI 7831R. Select Start»Program Files»National  
Instruments»<LabVIEW>»Module Documents»FPGA User  
Interface to view this document.  
FPGA Interface User Guide—This manual describes how to control  
and communicate with FPGA VIs running on R Series devices. Select  
Start»Program Files»National Instruments»<LabVIEW>»  
Module Documents»LabVIEW FPGA»LabVIEW FPGA Module  
User Manual to view this document.  
LabVIEW Help—This help file contains information about using the  
LabVIEW FPGA Module, LabVIEW, and the LabVIEW Real-Time  
Module with the NI 7831R. Select Help»VI, Function, & How-To  
Help in LabVIEW to view the LabVIEW Help.  
LabVIEW Real-Time Module User Manual—This manual contains  
information about how to build deterministic applications using the  
LabVIEW Real-Time Module.  
NI 7831R User Manual  
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About This Manual  
Related Documentation  
The following documents contain information you might find helpful:  
NI Developer Zone tutorial, Field Wiring and Noise Considerations  
for Analog Signals, at ni.com/zone  
PICMG CompactPCI 2.0 R3.0  
PXI Hardware Specification Revision 2.1  
PXI Software Specification Revision 2.1  
© National Instruments Corporation  
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1
Introduction  
This chapter describes the NI 7831R, describes the concept of the  
Reconfigurable I/O device, describes the optional software and equipment,  
and contains information about the NI 7831R.  
About the NI 7831R  
The NI 7831R is an R Series device with 96 digital I/O (DIO) lines, eight  
independent, 16-bit analog output (AO) channels, and eight independent,  
16-bit analog input (AI) channels.  
A user-reconfigurable FPGA (Field-Programmable Gate Array) controls  
the digital and analog I/O lines on the NI 7831R. The FPGA on the R Series  
device allows you to define the functionality and timing of the device. You  
can change the functionality of the FPGA on the R Series device in  
LabVIEW using the LabVIEW FPGA Module to create and download a  
custom virtual instrument (VI) to the FPGA. Using the FPGA Module, you  
can graphically design the timing and functionality of the R Series device.  
If you only have LabVIEW but not the FPGA Module, you cannot create  
new FPGA VIs, but you can create VIs that run on Windows or an RT target  
to control existing FPGA VIs.  
Some applications require tasks such as real-time, floating-point  
processing or datalogging while performing I/O and logic on the R Series  
device. You can use the LabVIEW Real-Time Module to perform these  
additional applications while communicating with and controlling the  
R Series device.  
The R Series device contains flash memory to store VIs for automatic  
loading of the FPGA when the system is powered on.  
The NI 7831R device uses the Real-Time System Integration (RTSI) bus to  
easily synchronize several measurement functions to a common trigger or  
timing event. The PXI chassis can accommodate multiple devices. The  
NI PCI-7831R accesses the RTSI bus through a RTSI cable connected  
© National Instruments Corporation  
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Chapter 1  
Introduction  
between devices. The NI PXI-7831R accesses the RTSI bus through the  
PXI trigger lines implemented on the PXI backplane.  
Refer to Appendix A, Specifications, for detailed NI 7831R specifications.  
Using PXI with CompactPCI  
Using PXI-compatible products with standard CompactPCI products is an  
important feature provided by PXI Hardware Specification Revision 2.1  
and PXI Software Specification Revision 2.1. If you use a PXI-compatible  
plug-in card in a standard CompactPCI chassis, you cannot use  
PXI-specific functions, but you still can use the basic plug-in card  
functions. For example, the RTSI bus on the R Series device is available in  
a PXI chassis but not in a CompactPCI chassis.  
The CompactPCI specification permits vendors to develop sub-buses that  
coexist with the basic PCI interface on the CompactPCI bus. Compatible  
operation is not guaranteed between CompactPCI devices with different  
sub-buses nor between CompactPCI devices with sub-buses and PXI.  
The standard implementation for CompactPCI does not include these  
sub-buses. The R Series device works in any standard CompactPCI chassis  
adhering to the PICMG CompactPCI 2.0 R3.0 core specification.  
PXI-specific features are implemented on the J2 connector of the  
CompactPCI bus. Table 1-1 lists the J2 pins used by the NI 7831R. The  
NI 7831R is compatible with any CompactPCI chassis with a sub-bus that  
does not drive these lines. Even if the sub-bus is capable of driving these  
lines, the R Series device is still compatible as long as those pins on the  
sub-bus are disabled by default and are never enabled.  
Caution Damage can result if the J2 lines are driven by the sub-bus.  
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Table 1-1. Pins Used by the NI PXI-7831R  
NI PXI-7831R Signal  
PXI Pin Name  
PXI J2 Pin Number  
PXI Trigger<0..7>  
PXI Trigger<0..7>  
A16, A17, A18, B15, B18, C18,  
E16, E18  
PXI Clock 10 MHz  
PXI Star Trigger  
LBLSTAR<0..12>  
PXI Clock 10 MHz  
PXI Star Trigger  
LBL<0..12>  
E17  
D17  
A1, A19, C1, C19, C20, D1, D2,  
D15, D19, E1, E2, E19, E20  
LBR<0..12>  
LBR<0..12>  
A2, A3, A20, A21, B2, B20, C3,  
C21, D3, D21, E3, E15, E21  
Overview of Reconfigurable I/O  
This section explains reconfigurable I/O and describes how to use the  
FPGA Module to build high-level functions in hardware.  
Refer to Chapter 2, Hardware Overview of the NI 7831R, for descriptions  
of the I/O resources on the NI 7831R.  
Reconfigurable I/O Concept  
The NI 7831R is based on a reconfigurable FPGA core surrounded by fixed  
I/O resources for analog and digital input and output. You can configure  
the behavior of the reconfigurable core to match the requirements of the  
measurement and control system. You can implement this user-defined  
behavior as an FPGA VI to create an application-specific I/O device.  
Flexible Functionality  
Flexible functionality allows the NI 7831R to match individual application  
requirements and to mimic the functionality of fixed I/O devices. For  
example, you can configure a R Series device in one application for three  
32-bit quadrature encoders and then reconfigure the R Series device in  
another application for eight 16-bit event counters.  
You also can use the R Series device in timing and triggering applications  
with the LabVIEW Real-Time Module, such as control and  
hardware-in-the-loop (HIL) simulations. For example, you can configure  
the R Series device for a single-timed loop in one application and then  
reconfigure the device in another application for four independent timed  
loops with separate I/O resources.  
© National Instruments Corporation  
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Introduction  
User-Defined I/O Resources  
You can create your own custom measurements using the fixed I/O  
resources. For example, one application might require an event counter that  
increments when a rising edge appears on any of three digital input lines.  
Another application might require a digital line to be asserted after an  
analog input exceeds a programmable threshold.  
Device-Embedded Logic and Processing  
You can implement LabVIEW logic and processing in the FPGA of the  
R Series device. Typical logic functions include Boolean operations,  
comparisons, and basic mathematical operations. You can implement  
multiple functions efficiently in the same design, operating sequentially or  
in parallel. You can implement more complex algorithms such as control  
loops. You are limited only by the size of the FPGA.  
Reconfigurable I/O Architecture  
Figure 1-1 shows an FPGA connected to fixed I/O resources and a bus  
interface. The fixed I/O resources include A/D converters (ADCs), D/A  
converters (DACs), and digital I/O lines.  
Fixed I/O Resource  
Fixed I/O Resource  
FPGA  
Fixed I/O Resource  
Fixed I/O Resource  
Bus Interface  
Figure 1-1. High-Level FPGA Functional Overview  
Software accesses the R Series device through the bus interface, and the  
FPGA connects the bus interface and the fixed I/O to make possible timing,  
triggering, processing, and custom I/O functions using the LabVIEW  
FPGA Module.  
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The FPGA logic provides timing, triggering, processing, and custom I/O  
measurements. Each fixed I/O resource used by the application uses a small  
portion of the FPGA logic that controls the fixed I/O resource. The bus  
interface also uses a small portion of the FPGA logic to provide software  
access to the device.  
The remaining FPGA logic is available for higher level functions such as  
timing, triggering, and counting. The functions use varied amounts of logic.  
You can place useful applications in the FPGA. How much FPGA space  
your application requires depends on your need for I/O recovery, I/O, and  
logic algorithms.  
The FPGA does not retain the VI when it is powered off, so you must reload  
the VI each time you power on. You can load the VI from onboard flash  
memory or from software over the bus interface. One advantage to using  
flash memory is that the VI can start executing almost immediately after  
power up, instead of waiting for the computer to completely boot and load  
the FPGA. Refer to the LabVIEW FPGA Module User Manual for more  
information about how to store your VI in flash memory.  
Reconfigurable I/O Applications  
You can use the LabVIEW FPGA Module to create or acquire new VIs for  
your application. The FPGA Module allows you to define custom  
functionality for the R Series device using a subset of LabVIEW  
functionality. Refer to the FPGA Module examples located in the  
<LabVIEW>\examples\FPGAdirectory for examples of FPGA VIs.  
Software Development  
You can use LabVIEW with the LabVIEW FPGA Module to program the  
NI 7831R. To develop real-time applications that control the NI 7831R,  
you can use LabVIEW with the LabVIEW Real-Time Module.  
LabVIEW FPGA Module  
The FPGA Module enables you to use LabVIEW to create VIs that run on  
the FPGA of the R Series device. Use the FPGA Module VIs and functions  
to control the I/O, timing, and logic of the R Series device and to generate  
interrupts for synchronization. Refer to the LabVIEW FPGA Interface User  
Guide, available by selecting Start»Program Files»National  
Instruments»<LabVIEW>»Module Documents»FPGA Interface User  
Guide, for information about the FPGA Interface functions.  
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You can use Interactive Front Panel Communication to communicate  
directly with the VI running on the FPGA. You can use Programmatic  
FPGA Interface Communication to programmatically control and  
communicate with FPGA VIs from host VIs.  
Use the FPGA Interface functions when you target LabVIEW for Windows  
or an RT target to create host VIs that wait for interrupts and control the  
FPGA by reading and writing the FPGA VI running on the R Series device.  
Note If you use the R Series device without the FPGA Module, you can use the Download  
VI or Attributes to Flash Memory utility available by selecting Start»Program Files»  
National Instruments»NI-RIO to download precomplied FPGA VIs to the flash memory  
of the R Series device. This utility is installed by the NI-RIO CD. You also can use the  
utility to configure the analog input mode, to synchronize the clock R Series device to the  
PXI clock (for NI PXI-7831R only), and to configure when the VI loads from flash  
memory.  
LabVIEW Real-Time Module  
The LabVIEW Real-Time Module extends the LabVIEW development  
environment to deliver deterministic, real-time performance.  
You can write host VIs that run in Windows or on RT targets to  
communicate with FPGA VIs that run on the NI 7831R. You can develop  
Real-Time VIs with LabVIEW and the LabVIEW Real-Time Module, and  
then download the VIs to run on a hardware target with a real-time  
operating system. The LabVIEW Real-Time Module allows you to use the  
NI 7831R in RT Series PXI systems being controlled in real time by a VI.  
The NI 7831R plug-in device is designed as a single-point AI, AO, and DIO  
complement to the LabVIEW Real-Time Module. Refer to the LabVIEW  
Real-Time Module User Manual and the LabVIEW Help, available by  
selecting Help»VI, Function, & How-To Help, for more information  
about the LabVIEW Real-Time Module.  
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Introduction  
Cables and Optional Equipment  
National Instruments offers a variety of products you can use with R Series  
devices, including cables, connector blocks, and other accessories, as  
shown in Table 1-2.  
Table 1-2. Cables and Accessories  
NI 7831R  
Cable  
Cable Description  
Connector  
Accessories  
SH68-C68-S  
Shielded 68-pin VHDCI  
male connector to female  
0.050 series D-type  
MIO or DIO Connects to the following  
standard 68-pin screw  
terminal blocks:  
connector. The cable is  
constructed with 34 twisted  
wire pairs and an overall  
shield.  
• SCB-68  
• CB-68LP  
• CB-68LPR  
• TBX-68  
SMC68-68-RMIO  
Shielded 68-pin VHDCI  
male connector to female  
0.050 series D-type  
MIO only  
Connects to the following  
standard 68-pin screw  
terminal blocks:  
connector. The cable is  
constructed with individually  
shielded twisted-pairs for the  
analog input channels plus an  
additional shield around all  
the analog signals. This cable  
provides superior noise  
immunity on the MIO  
connector.  
• SCB-68  
• CB-68LP  
• CB-68LPR  
• TBX-68  
© National Instruments Corporation  
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Introduction  
Table 1-2. Cables and Accessories (Continued)  
NI 7831R  
Cable  
NSC68-262650  
Cable Description  
Connector  
Accessories  
Non-shielded cable connects MIO only  
from 68-pin VHDCI male  
connector to two 26-pin  
26-pin headers can connect  
to the following 5B  
backplanes for analog signal  
conditioning:  
female headers plus one  
50-pin female header. The  
pinout of these headers  
• 5B08 (8-channel)  
• 5B01 (16-channel)  
allows for direct connection  
to 5B backplanes for analog  
signal conditioning and SSR  
backplanes for digital signal  
conditioning.  
50-pin header can connect to  
the following SSR  
backplanes for digital signal  
conditioning:  
• 8-channel backplane  
• 16-channel backplane  
• 32-channel backplane  
NSC68-5050  
Non-shielded cable connects DIO only  
from 68-pin VHDCI male  
connector to two 50-pin  
female headers. The pinout  
of these headers allows for  
direct connection to SSR  
backplanes for digital signal  
conditioning.  
50-pin headers can connect  
to the following SSR  
backplanes for digital signal  
• 8-channel backplane  
• 16-channel backplane  
• 32-channel backplane  
Refer to Appendix B, Connecting I/O Signals, for more information about  
using these cables and accessories to connect I/O signals to the NI 7831R.  
Refer to ni.com/catalogfor the most current cabling options.  
Custom Cabling  
NI offers a variety of cables for connecting signals to the NI 7831R. If you  
need to develop a custom cable, a nonterminated shielded cable is available  
from NI. The SHC68-NT-S connects to the NI 7831R VHDCI connectors  
on one end of the cable. The other end of the cable is not terminated. This  
cable ships with a wire list identifying the wires that correspond to each  
NI 7831R pin. Using this cable, you can quickly connect the NI 7831R  
signals that you need to the connector of your choice. Refer to Appendix B,  
Connecting I/O Signals, for the NI 7831R connector pinouts.  
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Chapter 1  
Introduction  
Safety Information  
The following section contains important safety information that you must  
follow when installing and using the NI 7831R.  
Do not operate the NI 7831R in a manner not specified in this document.  
Misuse of the NI 7831R can result in a hazard. You can compromise the  
safety protection built into the NI 7831R if the NI 7831R is damaged in any  
way. If the NI 7831R is damaged, return it to NI for repair.  
Do not substitute parts or modify the NI 7831R except as described in this  
document. Use the NI 7831R only with the chassis, modules, accessories,  
and cables specified in the installation instructions. You must have all  
covers and filler panels installed during operation of the NI 7831R.  
Do not operate the NI 7831R in an explosive atmosphere or where there  
might be flammable gases or fumes. If you must operate the NI 7831R in  
such an environment, it must be in a suitably rated enclosure.  
If you need to clean the NI 7831R, use a soft, nonmetallic brush. Make sure  
that the NI 7831R is completely dry and free from contaminants before  
returning it to service.  
Operate the NI 7831R only at or below Pollution Degree 2. Pollution is  
foreign matter in a solid, liquid, or gaseous state that can reduce dielectric  
strength or surface resistivity. The following is a description of pollution  
degrees:  
Pollution Degree 1—No pollution or only dry, nonconductive  
pollution occurs. The pollution has no influence.  
Pollution Degree 2—Only nonconductive pollution occurs in most  
cases. Occasionally, however, a temporary conductivity caused by  
condensation can be expected.  
Pollution Degree 3—Conductive pollution occurs, or dry,  
nonconductive pollution occurs that becomes conductive due to  
condensation.  
You must insulate signal connections for the maximum voltage for which  
the NI 7831R is rated. Do not exceed the maximum ratings for the  
NI 7831R. Do not install wiring while the NI 7831R is live with electrical  
signals. Do not remove or add connector blocks when power is connected  
to the system. Remove power from signal lines before connecting them to  
or disconnecting them from the NI 7831R.  
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Introduction  
Operate the NI 7831R at or below the installation category1 listed in the  
section Maximum working voltage, in Appendix A, Specifications.  
Measurement circuits are subjected to working voltages2 and transient  
stresses (overvoltage) from the circuit to which they are connected during  
measurement or test. Installation categories establish standard impulse  
withstand voltage levels that commonly occur in electrical distribution  
systems. The following list describes installation categories:  
Installation Category I—Measurements performed on circuits not  
directly connected to the electrical distribution system referred to as  
MAINS3 voltage. This category is for measurements of voltages from  
specially protected secondary circuits. Such voltage measurements  
include signal levels, special equipment, limited-energy parts of  
equipment, circuits powered by regulated low-voltage sources, and  
electronics.  
Installation Category II—Measurements performed on circuits  
directly connected to the electrical distribution system. This category  
refers to local-level electrical distribution, such as that provided by a  
standard wall outlet (for example, 115 V for U.S. or 230 V for Europe).  
Examples of Installation Category II are measurements performed on  
household appliances, portable tools, and similar products.  
Installation Category III—Measurements performed in the building  
installation at the distribution level. This category refers to  
measurements on hard-wired equipment such as equipment in fixed  
installations, distribution boards, and circuit breakers. Other examples  
are wiring, including cables, bus-bars, junction boxes, switches,  
socket-outlets in the fixed installation, and stationary motors with  
permanent connections to fixed installations.  
Installation Category IV—Measurements performed at the primary  
electrical supply installation (<1,000 V). Examples include electricity  
meters and measurements on primary overcurrent protection devices  
and on ripple control units.  
1
Installation categories, also referred to as measurement categories, are defined in electrical safety standard IEC 61010-1.  
2
3
Working voltage is the highest rms value of an AC or DC voltage that can occur across any particular insulation.  
MAINS is defined as a hazardous live electrical supply system that powers equipment. Suitably rated measuring circuits can  
be connected to the MAINS for measuring purposes.  
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2
Hardware Overview  
of the NI 7831R  
This chapter presents an overview of the hardware functions and  
I/O connectors on the NI 7831R.  
Figure 2-1 shows a block diagram for the NI 7831R. Figure 2-2 shows the  
parts locator diagram for the NI PXI-7831R. Figure 2-3 shows the parts  
locator diagram for the NI PCI-7831R.  
Calibration  
DACs  
Configuration  
Control  
Flash  
Memory  
Input Mux  
AI+  
AI–  
+
16-Bit  
ADC  
Instrumentation  
Amplifier  
x8 Channels  
Input Mode Mux  
AISENSE  
AIGND  
User-  
Voltage  
Temperature  
Sensor  
Control  
Reference  
Bus  
Interface  
Configurable  
FPGA on RIO  
Devices  
Data/Address/  
Control  
Calibration  
Mux  
Address/Data  
2
Calibration  
DACs  
16-Bit  
DAC  
x8 Channels  
Digital I/O (16)  
Digital I/O (40)  
PXI Local Bus (NI PXI-7831R only)  
RTSI Bus  
Digital I/O (40)  
Figure 2-1. NI 7831R Block Diagram  
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SW1  
Figure 2-2. Parts Locator Diagram for the NI PXI-7831R  
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SW1  
Figure 2-3. Parts Locator Diagram for the NI PCI-7831R  
Analog Input  
The NI 7831R has eight independent, 16-bit AI channels that you  
can sample simultaneously or at different rates. The input mode is  
software-configurable, and the input range is fixed at 10 V. The  
converters return data in two’s complement format. Table 2-1 shows the  
ideal output code returned for a given AI voltage.  
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Hardware Overview of the NI 7831R  
Table 2-1. Ideal Output Code and AI Voltage Mapping  
Output Code (Hex)  
(Two’s Complement)  
Input Description  
AI Voltage  
9.999695  
Full-scale range –1 LSB  
Full-scale range –2 LSB  
Midscale  
7FFF  
7FFE  
0000  
8001  
8000  
9.999390  
0.000000  
Negative full-scale range +1 LSB  
Negative full-scale range  
Any input voltage  
–9.999695  
–10.000000  
Output Code  
---------------------------------  
× 10.0 V  
32,768  
Input Modes  
The NI 7831R input mode is software configurable. The input channels  
support three input modes—differential (DIFF), referenced single-ended  
(RSE), and nonreferenced single-ended (NRSE). The selected input mode  
applies to all the input channels. Table 2-2 describes the three input modes.  
Table 2-2. Available Input Modes for the NI 7831R  
Input Mode  
Description  
DIFF  
When the NI 7831R is configured in DIFF input mode, each channel uses two  
AI lines. The positive input pin connects to the positive terminal of the onboard  
instrumentation amplifier. The negative input pin connects to the negative input  
of the instrumentation amplifier.  
RSE  
When the NI 7831R is configured in RSE input mode, each channel uses only its  
positive AI pin. This pin connects to the positive terminal of the onboard  
instrumentation amplifier. The negative input of the instrumentation amplifier  
connects internally to the AI ground (AIGND).  
NRSE  
When the NI 7831R is configured in NRSE input mode, each channel uses only  
its positive AI pin. This pin connects to the positive terminal of the onboard  
instrumentation amplifier. The negative input of the instrumentation amplifier on  
each AI channel connects internally to the AISENSE input pin.  
The NI 7831R AI range is fixed at 10 V.  
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Connecting Analog Input Signals  
The AI signals for the NI 7831R are AI<0..7>+, AI<0..7>–, AIGND, and  
AISENSE. The AI<0..7>+ and AI<0..7>– signals are connected to the  
eight AI channels of the NI 7831R. For all input modes, the AI<0..7>+  
signals are connected to the positive input of the instrumentation amplifier  
on each channel. The signal connected to the negative input of the  
instrumentation amplifier depends on how you configure the input mode of  
the device.  
In differential input mode, signals connected to AI<0..7>– are routed to the  
negative input of the instrumentation amplifier for each channel. In RSE  
input mode, the negative input of the instrumentation amplifier for each  
channel is internally connected to AIGND. In NRSE input mode, the  
AISENSE signal is connected internally to the negative input of the  
instrumentation amplifier for each channel. In DIFF and RSE input modes,  
AISENSE is not used.  
Caution Exceeding the differential and common-mode input ranges distorts the input  
signals. Exceeding the maximum input voltage rating can damage the NI 7831R and the  
computer. NI is not liable for any damage resulting from such signal connections. The  
maximum input voltage ratings are listed in Table B-2, NI 7831R I/O Signal Summary.  
AIGND is a common AI signal that is routed directly to the ground tie point  
on the NI 7831R. You can use this signal for a general analog ground tie  
point to the NI 7831R if necessary.  
Connection of AI signals to the NI 7831R depends on the input mode of the  
AI channels you are using and the type of input signal source. With  
different input modes, you can use the instrumentation amplifier in  
different ways. Figure 2-4 shows a diagram of the NI 7831R  
instrumentation amplifier.  
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Hardware Overview of the NI 7831R  
Vin+  
+
Instrumentation  
Amplifier  
+
Measured  
Voltage  
Vm  
Vin–  
Vm = [Vin+ – Vin–]  
Figure 2-4. NI 7831R Instrumentation Amplifier  
The instrumentation amplifier applies common-mode voltage rejection  
and presents high input impedance to the AI signals connected to the  
NI 7831R. Input multiplexers on the device route signals to the positive and  
negative inputs of the instrumentation amplifier. The instrumentation  
amplifier converts two input signals to a signal that is the difference  
between the two input signals. The amplifier output voltage is referenced to  
it performs A/D conversions.  
You must reference all signals to ground either at the source device or at the  
NI 7831R. If you have a floating source, reference the signal to ground by  
using RSE input mode or the DIFF input mode with bias resistors. Refer to  
the Differential Connections for Nonreferenced or Floating Signal Sources  
section of this chapter for more information about these input modes. If you  
have a grounded source, do not reference the signal to AIGND. You can  
avoid this reference by using DIFF or NRSE input modes.  
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Types of Signal Sources  
When configuring the input channels and making signal connections,  
you must first determine whether the signal sources are floating or ground  
referenced. The following sections describe these two signal types.  
Floating Signal Sources  
A floating signal source is not connected to the building ground system but  
instead has an isolated ground-reference point. Some examples of floating  
signal sources are outputs of transformers, thermocouples, battery-powered  
devices, optical isolator outputs, and isolation amplifiers. An instrument or  
device that has an isolated output is a floating signal source. You must  
connect the ground reference of a floating signal to the NI 7831R AIGND  
through a bias resistor to establish a local or onboard reference for the  
signal. Otherwise, the measured input signal varies as the source floats out  
of the common-mode input range.  
Ground-Referenced Signal Sources  
A ground-referenced signal source is connected to the building system  
ground, so it is already connected to a common ground point with respect  
to the NI 7831R, assuming that the computer is plugged into the same  
power system. Instruments or devices with nonisolated outputs that plug  
into the building power system are ground referenced signal sources.  
The difference in ground potential between two instruments connected to  
the same building power system is typically between 1 and 100 mV. This  
difference can be much higher if power distribution circuits are improperly  
connected. If a grounded signal source is improperly measured, this  
difference might appear as a measurement error. The connection  
instructions for grounded signal sources are designed to eliminate this  
ground potential difference from the measured signal.  
Input Modes  
The following sections discuss single-ended and differential measurements  
and considerations for measuring both floating and ground-referenced  
signal sources.  
Figure 2-5 summarizes the recommended input mode for both types of  
signal sources.  
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Hardware Overview of the NI 7831R  
Signal Source Type  
Floating Signal Source  
Grounded Signal Source  
(Not Connected to Building Ground)  
Examples  
Examples  
• Ungrounded Thermocouples  
• Signal Conditioning with  
Isolated Outputs  
• Plug-in Instruments with  
Nonisolated Outputs  
Input  
• Battery Devices  
AI<i>(+)  
AI<i>(+)  
+
+
+
+
V1  
V1  
AI<i>(–)  
AI<i>(–)  
Differential  
(DIFF)  
AIGND<i>  
AIGND<i>  
See text for information on bias resistors.  
NOT RECOMMENDED  
AI<i>  
AI  
+
+
+
+
V1  
V1  
AIGND<i>  
Single-Ended —  
Ground  
+
V
g
Referenced  
(RSE)  
AIGND  
Ground-loop losses, Vg, are added to  
measured signal.  
AI<i>  
AI<i>  
+
+
+
+
V1  
V1  
AISENSE  
AISENSE  
Single-Ended —  
Nonreferenced  
(NRSE)  
AIGND<i>  
AIGND<i>  
See text for information on bias resistors.  
Figure 2-5. Summary of Analog Input Connections  
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Differential Connection Considerations (DIFF Input Mode)  
In DIFF input mode, the NI 7831R measures the difference between the  
positive and negative inputs. DIFF input mode is ideal for measuring  
ground-referenced signals from other devices. When using DIFF input  
mode, the input signal connects to the positive input of the instrumentation  
amplifier and its reference signal, or return, connects to the negative input  
of the instrumentation amplifier.  
Use differential input connections for any channel that meets any of the  
following conditions:  
The input signal is low-level (less than 1 V).  
The leads connecting the signal to the NI 7831R are greater than  
3 m (10 ft).  
The input signal requires a separate ground-reference point or return  
signal.  
The signal leads travel through noisy environments.  
Differential signal connections reduce noise pickup and increase  
common-mode noise rejection. Differential signal connections also allow  
input signals to float within the common-mode limits of the  
instrumentation amplifier.  
Differential Connections for Ground-Referenced  
Signal Sources  
Figure 2-6 shows how to connect a ground-referenced signal source to a  
channel on the NI 7831R configured in DIFF input mode.  
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Hardware Overview of the NI 7831R  
AI+  
+
Ground-  
Referenced  
Signal  
+
AI–  
Instrumentation  
Amplifier  
Vs  
+
Source  
Measured  
Voltage  
Vm  
Common-  
Mode  
Noise and  
Ground  
+
Vcm  
x8 Channels  
AISENSE  
AIGND  
Potential  
I/O Connector  
DIFF Input Mode Selected  
Figure 2-6. Differential Input Connections for Ground-Referenced Signals  
With this connection type, the instrumentation amplifier rejects both the  
common-mode noise in the signal and the ground potential difference  
between the signal source and the NI 7831R ground, shown as Vcm  
in Figure 2-6. In addition, the instrumentation amplifier can reject  
common-mode noise pickup in the leads connecting the signal sources to  
the device. The instrumentation amplifier can reject common-mode signals  
when V+in and V–in (input signals) are both within their specified input  
ranges. Refer to Appendix A, Specifications, for more information about  
input ranges.  
Differential Connections for Nonreferenced or  
Floating Signal Sources  
Figure 2-7 shows how to connect a floating signal source to a channel on  
the NI 7831R configured in DIFF input mode.  
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AI+  
AI–  
+
Bias  
Resistors  
(see text)  
+
Floating  
Signal  
Source  
Instrumentation  
Amplifier  
Vs  
+
Measured  
Voltage  
Vm  
Bias  
Current  
Return  
Paths  
x8 Channels  
AISENSE  
AIGND  
I/O Connector  
DIFF Input Mode Selected  
Figure 2-7. Differential Input Connections for Nonreferenced Signals  
Figure 2-7 shows two bias resistors connected in parallel with the signal  
leads of a floating signal source. If you do not use the resistors and the  
source is truly floating, the source might not remain within the  
common-mode signal range of the instrumentation amplifier, causing  
erroneous readings. You must reference the source to AIGND by  
connecting the positive side of the signal to the positive input of the  
instrumentation amplifier and connecting the negative side of the signal to  
AIGND and to the negative input of the instrumentation amplifier without  
resistors. This connection works well for DC-coupled sources with low  
source impedance, less than 100 .  
For larger source impedances, this connection leaves the differential signal  
path significantly out of balance. Noise that couples electrostatically onto  
the positive line does not couple onto the negative line because it is  
connected to ground. Hence, this noise appears as a differential-mode  
signal instead of a common-mode signal, and the instrumentation amplifier  
does not reject it. In this case, instead of directly connecting the negative  
line to AIGND, connect it to AIGND through a resistor that is about 100  
times the equivalent source impedance. The resistor puts the signal path  
nearly in balance. About the same amount of noise couples onto both  
connections, which yields better rejection of electrostatically coupled  
noise. Also, this input mode does not load down the source, other than the  
very high-input impedance of the instrumentation amplifier.  
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Hardware Overview of the NI 7831R  
You can fully balance the signal path by connecting another resistor of the  
same value between the positive input and AIGND, as shown in Figure 2-7.  
This fully balanced input mode offers slightly better noise rejection but has  
the disadvantage of loading down the source with the series combination  
(sum) of the two resistors. If, for example, the source impedance is 2 kΩ  
and each of the two resistors is 100 k, the resistors load down the source  
with 200 kand produce a –1% gain error.  
Both inputs of the instrumentation amplifier require a DC path to ground  
for the instrumentation amplifier to work. If the source is AC coupled  
(capacitively coupled), the instrumentation amplifier needs a resistor  
between the positive input and AIGND. If the source has low-impedance,  
choose a resistor that is large enough not to significantly load the source but  
small enough not to produce significant input offset voltage as a result of  
input bias current, typically 100 kto 1 M. In this case, connect the  
negative input directly to AIGND. If the source has high output impedance,  
balance the signal path as previously described using the same value  
resistor on both the positive and negative inputs. Loading down the source  
causes some gain error.  
Single-Ended Connection Considerations  
When the NI 7831R AI signal is referenced to a ground that can be shared  
with other input signals, it forms a single-ended connection. The input  
signal connects to the positive input of the instrumentation amplifier and  
the ground connects to the negative input of the instrumentation amplifier.  
You can use single-ended input connections for any input signal that meets  
the following conditions:  
The input signal is high-level (>1 V).  
The leads connecting the signal to the NI 7831R are less than  
3 m (10 ft).  
The input signal can share a common reference point with other  
signals.  
Use DIFF input connections for greater signal integrity for any input signal  
that does not meet the preceding conditions.  
You can configure in software the NI 7831R channels for RSE or NRSE  
input modes. Use the RSE input mode for floating signal sources. In this  
case, the NI 7831R provides the reference ground point for the external  
signal. Use the NRSE input mode for ground-referenced signal sources. In  
this case, the external signal supplies its own reference ground point and the  
NI 7831R should not supply one.  
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In single-ended input modes, electrostatic and magnetic noise couples into  
the signal connections more than in differential input modes. The coupling  
is the result of differences in the signal path. Magnetic coupling  
is proportional to the area between the two signal conductors. Electrical  
coupling is a function of how much the electric field differs between the  
two conductors.  
Single-Ended Connections for Floating Signal  
Sources (RSE Input Mode)  
Figure 2-8 shows how to connect a floating signal source to a channel on  
the NI 7831R configured for RSE input mode.  
AI+  
AI–  
+
Instrumentation  
Amplifier  
+
Measured  
Voltage  
Vm  
+
Floating  
Signal  
Source  
Vs  
x8 Channels  
AISENSE  
AIGND  
I/O Connector  
RSE Input Mode Selected  
Figure 2-8. Single-Ended Input Connections for Nonreferenced or Floating Signals  
Single-Ended Connections for Grounded Signal  
Sources (NRSE Input Mode)  
To measure a grounded signal source with a single-ended input mode, you  
must configure the NI 7831R in the NRSE input mode. Then connect the  
signal to the positive input of the NI 7831R instrumentation amplifier and  
connect the signal local ground reference to the negative input of the  
instrumentation amplifier. The ground point of the signal should be  
connected to AISENSE. Any potential difference between the NI 7831R  
ground and the signal ground appears as a common-mode signal at both the  
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Chapter 2  
Hardware Overview of the NI 7831R  
positive and negative inputs of the instrumentation amplifier. The  
instrumentation amplifier rejects this difference. If the input circuitry of a  
NI 7831R is referenced to ground in RSE input mode, this difference in  
ground potentials appears as an error in the measured voltage.  
Figure 2-9 shows how to connect a grounded signal source to a channel on  
the NI 7831R configured for NRSE input mode.  
AI+  
AI–  
+
Ground-  
Referenced  
Signal  
+
Instrumentation  
Amplifier  
Vs  
+
Source  
Measured  
Voltage  
Vm  
Common-  
Mode  
Noise and  
Ground  
+
x8 Channels  
Vcm  
AISENSE  
AIGND  
Potential  
I/O Connector  
Figure 2-9. Single-Ended Input Connections for Ground-Referenced Signals  
Common-Mode Signal Rejection Considerations  
Figures 2-6 and 2-9 show connections for signal sources that are already  
referenced to some ground point with respect to the NI 7831R. In these  
cases, the instrumentation amplifier can reject any voltage caused by  
ground potential differences between the signal source and the device.  
With differential input connections, the instrumentation amplifier can  
reject common-mode noise pickup in the leads connecting the signal  
sources to the device. The instrumentation amplifier can reject  
common-mode signals when V+in and V–in (input signals) are both within  
their specified input ranges. Refer to Appendix A, Specifications, for more  
information about input ranges.  
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Analog Output  
The NI 7831R has eight 16-bit AO channels. The bipolar output range is  
fixed at 10 V. Some applications require that the AO channels power on  
to known voltage levels. To set the power-on levels, you can configure the  
NI 7831R to load and run your VI when the system powers on. This VI can  
set the AO channels to the desired voltage levels. The VI interprets data  
written to the DAC in two’s complement format. Table 2-3 shows the ideal  
AO voltage generated for a given input code.  
Table 2-3. Ideal Output Voltage and Input Code Mapping  
Input Code (Hex)  
Output Description  
Full-scale range –1 LSB  
Full-scale range –2 LSB  
Midscale  
AO Voltage  
9.999695  
9.999390  
0.000000  
–9.999695  
(Two’s Complement)  
7FFF  
7FFE  
0000  
8001  
Negative full-scale range,  
+1 LSB  
Negative full-scale range  
Any output voltage  
–10.000000  
8000  
AO Voltage  
------------------------------  
× 32,768  
10.0 V  
Note If your VI does not set the output value for an AO channel, then the AO channel  
voltage output will be undefined.  
Connecting Analog Output Signals  
The AO signals are AO <0..7> and AOGND.  
AO <0..7> are the eight available AO channels. AOGND is the ground  
reference signal for the AO channels.  
Figure 2-10 shows how to make AO connections to the NI 7831R.  
© National Instruments Corporation  
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Chapter 2  
Hardware Overview of the NI 7831R  
AO0  
Channel 0  
+
Load  
VOUT 0  
AOGND0  
x8 Channels  
NI 7831R  
Figure 2-10. Analog Output Connections  
Digital I/O  
The NI 7831R has 96 bidirectional DIO lines that you can individually  
configure for either input or output. When the system powers on, the DIO  
lines are high-impedance. To set another power-on state, you can configure  
the NI 7831R to load a VI when the system powers on. This VI can then set  
the DIO lines to any power-on state.  
Connecting Digital I/O Signals  
The DIO signals on the NI 7831R MIO connector are DGND and  
and DIO<0..39>. The DIO<0..n> signals make up the DIO port and DGND  
is the ground reference signal for the DIO port. The NI 7831R has one MIO  
and two DIO connectors for a total of 96 DIO lines.  
Refer to Figure B-1, NI 7831R Connector Locations, and Figure B-2,  
NI 7831R I/O Connector Pin Assignments, for the connector locations and  
the I/O connector pin assignments on the NI 7831R.  
The DIO lines on the NI 7831R are TTL-compatible. When configured as  
inputs, they can receive signals from 5 V TTL, 3.3 V LVTTL, 5 V CMOS,  
and 3.3 V LVCMOS devices. When configured as outputs, they can send  
signals to 5 V TTL, 3.3 V LVTTL, and 3.3 V LVCMOS devices. Because  
the digital outputs provide a nominal output swing of 0 to 3.3 V  
(3.3 V TTL), the DIO lines cannot drive 5 V CMOS logic levels.  
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Hardware Overview of the NI 7831R  
To interface to 5 V CMOS devices, you must provide an external pull-up  
resistor to 5 V. This resistor pulls up the 3.3 V digital output from the  
NI 7831R to 5 V CMOS logic levels. Refer to Appendix A, Specifications,  
for detailed DIO specifications.  
Caution Exceeding the maximum input voltage ratings, listed in Table B-2, NI 7831R I/O  
Signal Summary, can damage the NI 7831R and the computer. NI is not liable for any  
damage resulting from such signal connections.  
Caution Do not short the DIO lines of the NI 7831R directly to power or to ground. Doing  
so can damage the NI 7831R by causing excessive current to flow through the DIO lines.  
You can connect multiple NI 7831R digital output lines in parallel to  
provide higher current sourcing or sinking capability. If you connect  
multiple digital output lines in parallel, your application must drive all of  
these lines simultaneously to the same value. If you connect digital lines  
together and drive them to different values, excessive current can flow  
through the DIO lines and damage the NI 7831R. Refer to Appendix A,  
Specifications, for more information about DIO specifications.  
© National Instruments Corporation  
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NI 7831R User Manual  
 
Chapter 2  
Hardware Overview of the NI 7831R  
Figure 2-11 shows signal connections for three typical DIO applications.  
LED  
TTL or  
LVCMOS  
Compatible  
Devices  
+5 V  
DGND  
*
DIO<4..7>  
DIO<0..3>  
5 V CMOS  
TTL, LVTTL, CMOS, or LVCMOS Signal  
+5 V  
Switch  
DGND  
I/O Connector  
NI 7831R  
*
3.3 V CMOS  
Use a pull-up resistor when driving 5 V CMOS devices.  
Figure 2-11. Example Digital I/O Connections  
Figure 2-11 shows DIO<0..3> configured for digital input and DIO<4..7>  
configured for digital output. Digital input applications include receiving  
TTL, LVTTL, CMOS, or LVCMOS signals and sensing external device  
states, such as the state of the switch shown in the figure. Digital output  
applications include sending TTL or LVCMOS signals and driving external  
devices, such as the LED shown in Figure 2-11.  
The NI 7831R SH68-C68-S shielded cable contains 34 twisted pairs of  
conductors. To maximize the digital I/O available on the NI 7831R, some  
of the DIO lines are twisted with power or ground and some DIO lines are  
twisted with other DIO lines. To obtain maximum signal integrity, place  
edge-sensitive or high-frequency digital signals on the DIO lines that are  
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Hardware Overview of the NI 7831R  
paired with power or ground. Because the DIO lines that are twisted with  
other DIO lines can couple noise onto each other, use these lines for static  
signals or non-edge-sensitive, low-frequency digital signals. Examples of  
high-frequency or edge-sensitive signals include clock, trigger, pulse-width  
modulation (PWM), encoder, and counter signals. Examples of static  
signals or non-edge-sensitive, low-frequency signals include LEDs,  
switches, and relays. Table 2-4 summarizes these guidelines.  
Table 2-4. DIO Signal Guidelines for the NI 7831R  
SH68-C68-S Shielded Cable  
Signal Pairing  
Recommended Types  
of Digital Signals  
Digital Lines  
Connector 0, DIO<0..7>;  
Connector 1, DIO<0..27>;  
Connector 2, DIO<0..27>  
DIO line paired with power  
or ground  
All types—high-frequency or  
low-frequency signals,  
edge-sensitive or  
non-edge-sensitive signals  
Connector 0, DIO<8..15>;  
Connector 1, DIO<28..39>;  
Connector 2, DIO<28..39>  
DIO line paired with another  
DIO line  
Static signals or  
non-edge-sensitive,  
low-frequency signals  
RTSI Trigger Bus  
The NI 7831R can send and receive triggers through the RTSI trigger bus.  
The RTSI bus provides eight shared triggers lines that connect to all the  
devices on the bus. In PXI, the trigger lines are shared between all the PXI  
slots in a bus segment. In PCI, the RTSI bus is implemented through a  
ribbon cable connected to the RTSI connector on each device that needs to  
access the RTSI bus.  
You can use the RTSI trigger lines to synchronize the NI 7831R to any  
other device that supports RTSI triggers. On the NI PCI-7831R, the RTSI  
trigger lines are labeled RTSI/TRIG<0..6> and RTSI/OSC. On the  
NI PXI-7831R, the RTSI trigger lines are labeled PXI/TRIG<0..7>. In  
addition, the NI PXI-7831R can use the PXI star trigger line to send or  
receive triggers from a device plugged into Slot 2 of the PXI chassis. The  
PXI star trigger line on the NI PXI-7831R is PXI/STAR.  
The NI 7831R can configure each RTSI trigger line either as an input or an  
output signal. Because each trigger line on the RTSI bus is connected in  
parallel to all the other RTSI devices on the bus, only one device should  
drive a particular RTSI trigger line at a time. For example, if one  
NI PXI-7831R is configured to send out a trigger pulse on PXI/TRIG0,  
© National Instruments Corporation  
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NI 7831R User Manual  
 
   
Chapter 2  
Hardware Overview of the NI 7831R  
the remaining devices on that PXI bus segment must have PXI/TRIG0  
configured as an input.  
Caution Do not drive the same RTSI trigger bus line with the NI 7831R and another device  
simultaneously. Such signal driving can damage both devices. NI is not liable for any  
damage resulting from such signal driving.  
For more information on using and configuring triggers, select Help»VI,  
Function, & How-To Help in LabVIEW to view the LabVIEW Help.  
Refer to the PXI Hardware Specification Revision 2.1 and PXI Software  
Specification Revision 2.1 at pxisa.orgfor more information about PXI  
triggers.  
PXI Local Bus (for NI PXI-7831R only)  
The NI PXI-7831R can communicate with other PXI devices using the PXI  
local bus. The PXI local bus is a daisy-chained bus that connects each PXI  
peripheral slot with its adjacent peripheral slot on either side. For example,  
the right local bus lines from a PXI peripheral slot connect to the left local  
bus lines of the adjacent slot on the right. Each local bus is 13 lines wide.  
All of these lines connect to the FPGA on the NI PXI-7831R. The PXI local  
bus right lines on the NI PXI-7831R are PXI/LBR<0..12>. The PXI local  
bus left lines on the NI PXI-7831R are PXI/LBLSTAR<0..12>.  
The NI PXI-7831R can configure each PXI local bus line either as an input  
or an output signal. Only one device can drive the same physical local bus  
line at a time. For example, if the NI PXI-7831R is configured to drive a  
signal on PXI/LBR 0, the device in the slot immediately to the right must  
have its PXI/LBLSTAR 0 line configured as an input.  
Caution Do not drive the same PXI local bus line with the NI PXI-7831R and another  
device simultaneously. Such signal driving can damage both devices. NI is not liable for  
any damage resulting from such signal driving.  
The NI PXI-7831R local bus lines are only compatible with 3.3 V signaling  
LVTTL and LVCMOS levels.  
Caution Do not enable the local bus lines on an adjacent device if the device drives  
anything other than 0–3.3V LVTTL signal levels on the NI PXI-7831R. Enabling the lines  
in this way can damage the NI PXI-7831R. NI is not liable for any damage resulting from  
enabling such lines.  
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Chapter 2  
Hardware Overview of the NI 7831R  
The left local bus lines from the left peripheral slot of a PXI backplane  
(Slot 2) are routed to the star trigger lines of up to 13 other peripheral slots  
in a two-segment PXI system. This configuration provides a dedicated,  
delay-matched trigger signal between the first peripheral slot and the  
other peripheral slots for precise trigger timing signals. For example, an  
NI PXI-7831R in Slot 2 can send an independent trigger signal to each  
device plugged into Slots <3..15> using the PXI/LBLSTAR<0..12>. Each  
device receives its trigger signal on its own dedicated star trigger line.  
Caution Do not configure the NI 7831R and another device to drive the same physical star  
trigger line simultaneously. Such signal driving can damage the NI 7831R and the other  
device. NI is not liable for any damage resulting from such signal driving.  
Refer to the PXI Hardware Specification Revision 2.1 and PXI Software  
Specification Revision 2.1 at www.pxisa.orgfor more information about  
PXI triggers.  
Switch Settings  
Refer to Figure 2-2 for the location of switch SW1 on the NI PXI-7831R  
and Figure 2-3 for the location of switch SW1 on the NI PCI-7831R. For  
normal operation, switch 1 is in the OFF position. To prevent a VI stored  
in flash memory from loading to the FPGA at power up, move switch 1 to  
the ON position, as shown in Figure 2-12.  
ON  
ON  
1 2 3  
1 2 3  
a. Normal Operation (Default)  
b. Prevent VI From Loading  
Figure 2-12. Switch Settings on Switch SW1  
Complete the following steps to prevent a VI stored in flash memory from  
loading to the FPGA:  
1. Power off and unplug the PXI/CompactPCI chassis or PCI computer.  
2. Remove the NI 7831R from the PXI/CompactPCI chassis or PCI  
computer.  
3. Move switch 1 to the ON position, as shown in Figure 2-12b.  
© National Instruments Corporation  
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NI 7831R User Manual  
 
   
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Hardware Overview of the NI 7831R  
4. Reinsert the NI 7831R into the PXI/CompactPCI chassis or PCI  
computer. Refer to the Installing the Hardware section of the Getting  
Started with the NI 7831R document for installation instructions.  
5. Plug in and power on the PXI/CompactPCI chassis or PCI computer.  
After completing this procedure, a VI stored in flash memory does not load  
to the FPGA at power-on. You can use software to configure the NI 7831R  
if necessary. To return to the defaults of loading from flash memory, repeat  
the previous procedure but return switch 1 to the OFF position in step 3.  
You can use this switch to enable/disable the ability to load from flash. In  
addition to this switch, you must configure the device with the software to  
autoload.  
Note When the NI 7831R is powered on with switch 1 in the ON position, the analog  
circuitry does not return properly calibrated data. Move the switch to the ON position only  
while you are using software to reconfigure the NI 7831R for the desired power-up  
behavior. Afterward, return switch 1 to the OFF position.  
Power Connections  
Two pins on each I/O connector supply 5 V from the computer power  
supply using a self-resetting fuse. The fuse resets automatically within a  
few seconds after the overcurrent condition is removed. The +5V pins are  
referenced to DGND and can power external digital circuitry. The  
NI 7831R has the following power rating:  
+4.50 to +5.25 VDC at 1 A (250 mA max per +5V pin, 1 A max total for  
all +5V lines on the device)  
Caution Do not connect the +5V power pins directly to analog or digital ground or to any  
other voltage source on the NI 7831R or any other device under any circumstance. Doing  
so can damage the NI 7831R and the computer. NI is not liable for damage resulting from  
such a connection.  
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Chapter 2  
Hardware Overview of the NI 7831R  
Field Wiring Considerations  
Environmental noise can seriously affect the measurement accuracy of the  
device if you do not take proper care when running signal wires between  
signal sources and the device. The following recommendations mainly  
apply to AI signal routing to the device. They also apply to signal routing  
in general.  
Take the following precautions to minimize noise pickup and maximize  
measurement accuracy:  
Use differential AI connections to reject common-mode noise.  
Use individually shielded, twisted-pair wires to connect AI signals to  
the device. With this type of wire, the signals attached to the positive  
and negative inputs are twisted together and then covered with a shield.  
You then connect this shield only at one point to the signal source  
ground. This kind of connection is required for signals traveling  
through areas with large magnetic fields or high electromagnetic  
interference.  
Route signals to the device carefully. Keep cabling away from noise  
sources. The most common noise source in a PXI DAQ system is the  
video monitor. Keep the monitor and the analog signals as far apart as  
possible.  
Use the following recommendations for all signal connections to the  
NI 7831R:  
Separate NI 7831R signal lines from high-current or high-voltage  
lines. These lines can induce currents in or voltages on the NI 7831R  
signal lines if they run in parallel paths at a close distance. To reduce  
the magnetic coupling between lines, separate them by a reasonable  
distance if they run in parallel or run the lines at right angles to each  
other.  
Do not run signal lines through conduits that also contain power lines.  
Protect signal lines from magnetic fields caused by electric motors,  
welding equipment, breakers, or transformers by running them through  
special metal conduits.  
Refer to the NI Developer Zone tutorial, Field Wiring and Noise  
Considerations for Analog Signals, at ni.com/zonefor more information.  
© National Instruments Corporation  
2-23  
NI 7831R User Manual  
 
 
3
Calibration  
Calibration is the process of determining and/or adjusting the accuracy of  
an instrument to minimize measurement and output voltage errors. On the  
NI 7831R, onboard calibration DACs (CalDACs) correct these errors.  
Because the analog circuitry handles calibration, the data read from the  
AI channels or written to the AO channels in the FPGA VI is already  
calibrated.  
Three levels of calibration are available for the NI 7831R to ensure the  
accuracy of its analog circuitry. The first level, loading calibration  
constants, is the fastest, easiest, and least accurate. The intermediate level,  
internal calibration, is the preferred method of assuring accuracy in your  
application. The last level, external calibration, is the slowest, most  
difficult, and most accurate.  
Loading Calibration Constants  
The NI 7831R is factory calibrated before shipment at approximately 25 °C  
to the levels indicated in Appendix A, Specifications. The onboard  
nonvolatile flash memory stores the calibration constants for the device.  
Calibration constants are the values that were written to the CalDACs to  
achieve calibration in the factory. The NI 7831R hardware reads these  
constants from the flash memory and loads them into the CalDACs at  
power-on. This occurs before you load a VI into the FPGA.  
Internal Calibration  
With internal calibration, the NI 7831R can measure and correct almost all  
of its calibration-related errors without any external signal connections.  
NI provides software to perform an internal calibration. This internal  
calibration process, which generally takes less than two minutes, is the  
preferred method of assuring accuracy in your application. Internal  
calibration minimizes the effects of any offset and gain drifts, particularly  
those due to changes in temperature. During the internal calibration  
process, the AI and AO channels are compared to the NI 7831R onboard  
voltage reference. The offset and gain errors in the analog circuitry are  
calibrated out by adjusting the CalDACs to minimize these errors.  
© National Instruments Corporation  
3-1  
NI 7831R User Manual  
 
     
Chapter 3  
Calibration  
If you have NI-RIO installed, you can find the internal calibration utility at  
Start»All Programs»National Instruments»NI-RIO»device»Calibrate  
7831R Device. Device is the NI PXI-7831R or NI PCI-7831R device.  
Immediately after internal calibration, the only significant residual  
calibration error is gain error due to time and temperature drift of the  
onboard voltage reference. You can minimize gain errors by performing an  
external calibration. If you are primarily taking relative measurements, then  
you can ignore a small amount of gain error and self-calibration is  
sufficient.  
The flash memory on the NI 7831R stores the results of an internal  
calibration so the CalDACs automatically load with the newly calculated  
calibration constants the next time the NI 7831R is powered on.  
External Calibration  
An external calibration refers to calibrating your device with a known  
external reference rather than relying on the onboard reference. The  
NI 7831R has an onboard calibration reference to ensure the accuracy of  
self-calibration. The reference voltage is measured at the factory and stored  
in the flash memory for subsequent internal calibrations. Externally  
calibrate the device annually or more often if you use it at extreme  
temperatures.  
During the external calibration process, the onboard reference value is  
re-calculated. This compensates for any time or temperature drift-related  
errors in the onboard reference that might have occurred since the last  
calibration. You can save the results of the external calibration process to  
flash memory so that the NI 7831R loads the new calibration constants the  
next time it is powered on. The device uses the newly measured onboard  
reference level for subsequent internal calibrations.  
To externally calibrate your device, use an external reference several times  
more accurate than the device itself.  
Refer to the NI 7831R Calibration Procedure for a detailed calibration  
procedure for the NI 7831R, available by clicking Manual Calibration  
Procedures at ni.com/calibration.  
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A
Specifications  
This appendix lists the specifications of the NI 7831R. These specifications  
are typical at 25 °C unless otherwise noted.  
Analog Input  
Input Characteristics  
Number of channels ............................... 8  
Input modes............................................ DIFF, RSE, NRSE  
(software-selectable; selection  
applies to all 8 channels)  
Type of ADC.......................................... Successive approximation  
Resolution .............................................. 16 bits, 1 in 65,536  
Conversion time ..................................... 4 µs  
Maximum sampling rate ........................ 200 kS/s (per channel)  
Input impedance  
Powered on ..................................... 10 Gin parallel with 100 pF  
Powered off..................................... 4 kmin  
Overload.......................................... 4 kmin  
Input signal range................................... 10 V  
Input bias current ................................... 2 nA  
Input offset current................................. 1 nA  
Input coupling ........................................ DC  
Maximum working voltage  
(signal + common mode) ....................... Inputs should remain  
within 12 V of ground  
© National Instruments Corporation  
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NI 7831R User Manual  
 
       
Appendix A  
Specifications  
Overvoltage protection ........................... 42 V  
Data transfers..........................................Interrupts, programmed I/O  
Accuracy Information  
Relative  
Absolute Accuracy  
Accuracy  
Noise +  
Quantization  
(µV)  
Absolute  
Accuracy  
at Full  
Scale  
( mV)  
Nominal Range (V)  
Positive Negative  
% of Reading  
24  
Resolution (µV)  
Temp  
Drift  
(%/°C)  
Full  
Full  
Offset Single  
Single  
Point Averaged  
Scale  
Scale  
Hours  
1 Year  
(µV)  
Point Averaged  
10.0  
–10.0  
0.0496 0.0507  
2542  
1779 165  
0.0005  
7.78  
2170 217  
Note: Accuracies are valid for measurements following an internal calibration. Measurement accuracies are listed for  
operational temperatures within 1 °C of internal calibration temperature and 10 °C of external or factory-calibration  
temperature. Temp drift applies only if ambient is greater than 10 °C of previous external calibration.  
DC Transfer Characteristics  
INL.......................................................... 3 LSB typ, 6 LSB max  
DNL........................................................–1.0 to +2.0 LSB max  
No missing codes resolution...................16 bits typ, 15 bits min  
CMRR, DC to 60 Hz ..............................86 dB  
Dynamic Characteristics  
Bandwidth  
Small signal (–3 dB)........................650 kHz  
Large signal (1% THD)...................55 kHz  
System noise...........................................1.8 LSBrms  
(including quantization)  
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Appendix A  
Specifications  
Settling Time  
Accuracy  
Step Size  
20.0 V  
2.0 V  
16 LSB  
7.5 µs  
2.7 µs  
1.7 µs  
4 LSB  
10.3 µs  
4.1 µs  
2.9 µs  
2 LSB  
40 µs  
5.1 µs  
3.6 µs  
0.2 V  
Crosstalk................................................. –80 dB, DC to 100 kHz  
Analog Output  
Output Characteristics  
Number of channels ............................... 8 single-ended, voltage output  
Resolution .............................................. 16 bits, 1 in 65,536  
Update time............................................ 1.0 µs  
Max update rate...................................... 1 MS/s  
Type of DAC.......................................... Enhanced R-2R  
Data transfers ......................................... Interrupts, programmed I/O  
Accuracy Information  
Absolute Accuracy  
Absolute  
Accuracy at  
Nominal Range (V)  
% of Reading  
Positive Full  
Scale  
Negative Full  
Scale  
Temp Drift  
(%/°C)  
Full Scale  
(mV)  
24 Hours  
1 Year  
Offset (µV)  
10.0  
–10.0  
0.0335  
0.0351  
2366  
0.0005  
5.88  
Note: Accuracies are valid for analog output following an internal calibration. Analog output accuracies are listed for  
operation temperatures within 1 °C of internal calibration temperature and 10 °C of external or factory calibration  
temperature. Temp Drift applies only if ambient is greater than 10 °C of previous external calibration.  
© National Instruments Corporation  
A-3  
NI 7831R User Manual  
 
Appendix A  
Specifications  
DC Transfer Characteristics  
INL.......................................................... 0.5 LSB typ, 4.0 LSB max  
DNL........................................................ 0.5 LSB typ, 1 LSB max  
Monotonicity ..........................................16 bits, guaranteed  
Voltage Output  
Range...................................................... 10 V  
Output coupling ......................................DC  
Output impedance...................................1.25 Ω  
Current drive........................................... 2.5 mA  
Protection................................................Short-circuit to ground  
Power-on state ........................................User configurable  
Dynamic Characteristics  
Settling time  
Accuracy  
Step Size  
20.0 V  
2.0 V  
16 LSB  
6.0 µs  
2.2 µs  
1.5 µs  
4 LSB  
6.2 µs  
2.9 µs  
2.6 µs  
2 LSB  
7.2 µs  
3.8 µs  
3.6 µs  
0.2 V  
Slew rate .................................................10 V/µs  
Noise.......................................................150 µVrms, DC to 1 MHz  
Glitch energy  
at midscale transition.............................. 200 mV for 3 µs  
Digital I/O  
Number of channels................................96 input/output  
Compatibility..........................................TTL  
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Appendix A  
Specifications  
Digital logic levels  
Level  
Min  
0.0 V  
2.0 V  
Max  
0.8 V  
5.5 V  
0.4 V  
Input low voltage (VIL)  
Input high voltage (VIH)  
Output low voltage (VOL),  
where IOUT = –Imax (sink)  
Output high voltage (VOH),  
where IOUT = Imax (source)  
2.4 V  
Maximum output current  
I
max (source)..................................... 5.0 mA  
max (sink)........................................ 5.0 mA  
I
Input leakage current.............................. 10 µA  
Power-on state........................................ Programmable, by line  
Data transfers ......................................... Interrupts, programmed I/O  
Protection  
Input................................................ –0.5 to 7.0 V  
Output ............................................. Short-circuit (up to eight lines  
may be shorted at a time)  
Reconfigurable FPGA  
Number of logic slices ........................... 5,120  
Equivalent number of logic cells .... 11,520  
Available embedded RAM..................... 81,920 bytes  
Timebase ................................................ 40, 80, 120, 160, or 200 MHz  
Timebase reference sources  
NI PCI-7831R................................. Onboard clock only  
NI PXI-7831R................................. Onboard clock, phase-locked to  
PXI 10 MHz clock  
Timebase accuracy  
Onboard clock................................. 100 ppm, 250 ps jitter  
© National Instruments Corporation  
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NI 7831R User Manual  
 
Appendix A  
Specifications  
Phase locked to PXI 10 MHz  
Clock(NI PXI-7831R only) ....................Adds 350 ps jitter, 300 ps skew  
Additional frequency dependent jitter  
40 MHz............................................None  
80 MHz............................................400 ps  
120 MHz..........................................720 ps  
160 MHz..........................................710 ps  
200 MHz..........................................700 ps  
Calibration  
Recommended warm-up time.................15 minutes  
Calibration interval.................................1 year  
Onboard calibration reference  
DC level...........................................5.000 V ( 3.5 mV)  
(actual value stored  
in Flash memory)  
Temperature coefficient................... 5 ppm/°C max  
Long-term stability.......................... 20 ppm/  
1,000 h  
Note Refer to Calibration Certificates at ni.com/calibrationto generate a  
calibration certificate for the NI 7831R.  
Bus Interface  
PXI (NI PXI-7831R only) ......................Master, slave  
PCI (NI PCI-7831R only).......................Master, slave  
Power Requirement  
+5 VDC ( 5%) .......................................450 mA (typ), 700 mA (max)  
(does not include current drawn  
from the +5 V line on the  
I/O connectors)  
+3.3 VDC ( 5%) ....................................335 mA (typ), 730 mA (max)  
(does not include current sourced  
by the digital outputs. To  
calculate the total current sourced  
NI 7831R User Manual  
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Appendix A  
Specifications  
by the digital outputs use the  
following equation:  
j
current sourced on channel i  
i = 1  
Where j is the number of digital outputs being used to source current.  
Power available at I/O connectors ......... +4.50 to +5.25 VDC at 1 A total,  
250 mA per I/O connector pin  
Physical  
Dimensions (not including connectors)  
NI PXI-7831R................................. 16 cm by 10 cm (6.3 in. by 3.9 in.)  
NI PCI-7831R................................. 17 cm by 11 cm (6.7 in. by 4.3 in.)  
I/O connectors........................................ Three 68-pin female high-density  
VHDCI type  
Maximum Working Voltage  
Maximum working voltage refers to the signal voltage plus the  
common-mode voltage.  
Channel-to-earth..................................... 12 V, Installation Category I  
Channel-to-channel ................................ 24 V, Installation Category I  
Environmental  
The NI 7831R is intended for indoor use only.  
Operating Environment  
Using 40 MHz timebase......................... 0 to 55 °C, tested in accordance  
with IEC-60068-2-1 and  
IEC-60068-2-2  
Using 80 MHz timebase......................... 0 to 55 °C in all NI PXI chassis  
except the following:  
0 to 40 °C when installed in an  
NI PXI-1000/B or NI PXI-101X  
© National Instruments Corporation  
A-7  
NI 7831R User Manual  
 
Appendix A  
Specifications  
chassis, tested in accordance with  
IEC-60068-2-1 and  
IEC-60068-2-2  
Relative humidity range..........................10 to 90%, noncondensing, tested  
in accordance with  
IEC-60068-2-56  
Altitude ...................................................2,000 m at 25 °C ambient  
temperature  
Storage Environment  
Ambient temperature range ....................–20 to 70 °C tested in accordance  
with IEC-60068-2-1 and  
IEC-60068-2-2  
Relative humidity range..........................5 to 95%, noncondensing, tested  
in accordance with  
IEC-60068-2-56  
Note Clean the device with a soft, non-metallic brush. Make sure that the device is  
completely dry and free from contaminants before returning it to service.  
Shock and Vibration (for NI PXI-7831R Only)  
Operational Shock ..................................30 g peak, half-sine, 11 ms pulse  
Tested in accordance with  
IEC-60068-2-27. Test profile  
developed in accordance with  
MIL-PRF-28800F.  
Random Vibration  
Operating.........................................5 to 500 Hz, 0.3 grms  
Nonoperating...................................5 to 500 Hz, 2.4 grms  
Tested in accordance with  
IEC-60068-2-64. Nonoperating  
test profile exceeds the  
requirements of  
MIL-PRF-28800F, Class 3.  
NI 7831R 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 3111-1, UL 61010B-1  
CAN/CSA C22.2 No. 1010.1  
Note Refer to the product label, or visit ni.com/hardref.nsf, search by model number  
or product line, and click the appropriate link in the Certification column for UL and other  
safety certifications.  
Electromagnetic Compatibility  
Emissions ............................................... EN 55011 Class A at 10 m  
FCC Part 15A above 1 GHz  
Immunity................................................ EN 61326:1997 + A2: 2001,  
Table 1  
EMC/EMI............................................... CE, C-Tick, and FCC Part 15  
(Class A) compliant  
Note For full 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:  
Low-Voltage Directive (safety) ............. 73/23/EEC  
Electromagnetic Compatibility  
Directive (EMC) .................................... 89/336/EEC  
Note Refer to the Declaration of Conformity (DoC) for this product for any additional  
regulatory compliance information. Visit ni.com/hardref.nsf, search by model  
number or product line, and click the appropriate link in the Certification column to obtain  
the DoC for this product.  
© National Instruments Corporation  
A-9  
NI 7831R User Manual  
 
B
Connecting I/O Signals  
This appendix describes how to make input and output signal connections  
to the NI 7831R I/O connectors.  
The NI 7831R has two DIO connectors with 40 DIO lines per connector,  
and one MIO connector with eight AI lines, eight AO lines, and 16 DIO  
lines.  
Figure B-1 shows the I/O connector locations for the NI PXI-7831R and  
the NI PCI-7831R.  
NI PXI-7831R  
Reconfigurable I/O  
Figure B-1. NI 7831R Connector Locations  
© National Instruments Corporation  
B-1  
NI 7831R User Manual  
 
         
Appendix B  
Connecting I/O Signals  
Figure B-2 shows the I/O connector pin assignments for the I/O connectors  
on the NI 7831R. The DIO connector pin assignment applies to  
connectors <1..2> on the NI 7831R. The MIO connector pin assignment  
applies to connector 0 on the NI 7831R.  
34 68  
34 68  
DIO38  
AI0–  
DIO39  
DIO37  
DIO35  
DIO33  
DIO31  
DIO29  
DIO27  
DIO26  
DIO25  
DIO24  
DIO23  
DIO22  
DIO21  
DIO20  
DIO19  
DIO18  
DIO17  
AI0+  
DIO36 33 67  
DIO34 32 66  
AIGND1 33 67  
AI132 66  
AIGND0  
AI1+  
31 65  
30 64  
31 65  
30 64  
DIO32  
DIO30  
AI2–  
AI2+  
AIGND3  
AIGND2  
AI3+  
DIO28 29 63  
+5V 28 62  
+5V 27 61  
DGND 26 60  
AI329 63  
AI428 62  
AI4+  
AIGND5 27 61  
AI526 60  
AIGND4  
AI5+  
DGND  
DGND 24 58  
AI6–  
AIGND7 24 58  
25 59  
25 59  
AI6+  
AIGND6  
AI7+  
23 57  
22 56  
21 55  
23 57  
22 56  
21 55  
DGND  
DGND  
DGND  
AI7–  
No Connect  
AOGND0  
AISENSE  
AO0  
DGND 20 54  
19 53  
AOGND1 20 54  
19 53  
AO1  
DGND  
AOGND2  
AO2  
DGND 18 52  
DGND 17 51  
AOGND3 18 52  
AOGND4 17 51  
AO3  
DIO16  
AO4  
16 50  
15 49  
16 50  
15 49  
DGND  
DGND  
AOGND5  
AOGND6  
DIO15  
DIO14  
AO5  
AO6  
DGND 14 48  
DGND 13 47  
DGND 12 46  
DGND 11 45  
DGND 10 44  
AOGND7 14 48  
DIO14 13 47  
DIO12 12 46  
DIO10 11 45  
DIO8 10 44  
DIO13  
DIO12  
DIO11  
DIO10  
DIO9  
DIO8  
DIO7  
DIO6  
DIO5  
DIO4  
DIO3  
DIO2  
DIO1  
DIO0  
AO7  
DIO15  
DIO13  
DIO11  
DIO9  
DIO7  
DIO6  
DIO5  
DIO4  
DIO3  
DIO2  
DIO1  
DIO0  
+5V  
DGND  
DGND  
9
8
7
6
5
4
3
2
1
43  
42  
41  
40  
39  
38  
37  
36  
35  
DGND  
DGND  
9
8
7
6
5
4
3
2
1
43  
42  
41  
40  
39  
38  
37  
36  
35  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
+5V  
DIO Connector Pin Assignment  
MIO Connector Pin Assignment  
Figure B-2. NI 7831R I/O Connector Pin Assignments  
To access the signals on the I/O connectors, you must connect a cable from  
the I/O connector to a signal accessory. Plug the small VHDCI connector  
end of the cable into the appropriate I/O connector and connect the other  
end of the cable to the appropriate signal accessory.  
NI 7831R User Manual  
B-2  
ni.com  
 
   
Appendix B  
Connecting I/O Signals  
.
Table B-1. I/O Connector Signal Descriptions  
Signal Name  
Reference  
Direction  
Description  
+5V  
DGND  
Output  
+5 VDC Source—These pins supply 5 V from the computer  
power supply using a self-resetting 1 A fuse. No more than  
250 mA should be pulled from a single pin.  
AI<0..7>+  
AI<0..7>–  
AIGND  
AIGND  
AIGND  
Input  
Input  
Positive input for Analog Input channels 0 through 7.  
Negative input for Analog Input channels 0 through 7.  
Analog Input Ground—These pins are the reference point for  
single-ended measurements in RSE configuration and the  
bias current return point for differential measurements.  
All three ground references—AIGND, AOGND, and  
DGND—are connected to each other on the NI 7831R.  
AISENSE  
AO<0..7>  
AOGND  
AIGND  
AOGND  
Input  
Output  
Analog Input Sense—This pin serves as the reference node  
for AI <0..7> when the device is configured for NRSE mode.  
Analog Output channels 0 through 7. Each channel can  
source or sink up to 2.5 mA.  
Analog Output Ground—The analog output voltages  
are referenced to this node. All three ground  
references—AIGND, AOGND, and DGND—are  
connected to each other on the NI 7831R.  
DGND  
Digital Ground—These pins supply the reference for the  
digital signals at the I/O connector and the 5 V supply.  
All three ground references—AIGND, AOGND, and  
DGND—are connected to each other on the NI 7831R.  
DIO<0..15>  
Connector 0  
DGND  
Input or  
Output  
Digital I/O signals.  
DIO<0..39>  
Connector <1..2>  
Caution Connections that exceed any of the maximum ratings of input or output signals  
on the NI 7831R can damage the NI 7831R and the computer. Maximum input ratings for  
each signal are in the Protection column of Table B-2. NI is not liable for any damage  
resulting from such signal connections  
© National Instruments Corporation  
B-3  
NI 7831R User Manual  
 
Appendix B  
Connecting I/O Signals  
Table B-2. NI 7831R I/O Signal Summary  
Signal  
Type and  
Direction  
Impedance  
Input/  
Output  
Protection  
(Volts)  
On/Off  
Source  
Sink  
Signal Name  
(mA at V)  
(mA at V)  
Rise Time  
Bias  
+5V  
DO  
AI  
AI<0..7>+  
10 Gin  
parallelwith  
100 pF  
42/35  
2 nA  
AI<0..7>–  
AI  
10 Gin  
parallelwith  
100 pF  
42/35  
2 nA  
AIGND  
AO  
AI  
AISENSE  
10 Gin  
parallelwith  
100 pF  
42/35  
2 nA  
AO<0..7>  
AO  
1.25 Ω  
Short-  
circuit to  
ground  
2.5 at 10  
2.5 at –10  
10 V/µs  
AOGND  
DGND  
AO  
DO  
DIO<0..15>  
Connector 0  
DIO  
–0.5  
to +7.0  
5.0 at 2.4  
5.0 at 0.4  
12 ns  
DIO<0..39>  
Connector <1..2>  
AI = Analog Input  
AO = Analog Output  
DIO = Digital Input/Output  
DO = Digital Output  
Connecting to CompactRIO Extension I/O Chassis  
You can use the CompactRIO R Series Expansion chassis and CompactRIO  
I/O modules with the NI 7831R. Refer to the CompactRIO R Series  
Expansion System Installation Instructions for information about  
connecting the chassis to the NI 7831R.  
NI 7831R User Manual  
B-4  
ni.com  
 
   
Appendix B  
Connecting I/O Signals  
Connecting to 5B and SSR Signal Conditioning  
NI provides cables that allow you to connect signals from the NI 7831R  
directly to 5B backplanes for analog signal conditioning and SSR  
backplanes for digital signal conditioning.  
The NSC68-262650 cable connects the signals on the NI 7831R MIO  
connector directly to 5B and SSR backplanes. This cable has a 68-pin male  
VHDCI connector on one end that plugs into the NI 7831R MIO connector.  
The other end of this cable provides two 26-pin female headers plus one  
50-pin female header.  
One of the 26-pin headers contains all the NI 7831R analog input signals.  
You can plug this connector directly into a 5B backplane for analog input  
signal conditioning. The NI 7831R AI<0..7> correspond to the 5B  
backplane channels <0..7> in sequential order. Configure the AI channels  
to use the NRSE input mode when using 5B signal conditioning.  
The other 26-pin header contains all the NI 7831R analog output signals.  
You can plug this connector directly into a 5B backplane for AO signal  
conditioning. The NI 7831R AO<0..7> correspond to the 5B backplane  
channels <0..7> in sequential order.  
The 50-pin header contains the 16 DIO lines available on the NI 7831R  
MIO connector. You can plug this header directly into an SSR backplane  
for digital signal conditioning. DIO lines <0..15> correspond to the 5B  
backplane Slots <0..15> in sequential order.  
The 5B connector pinouts are compatible with eight-channel 5B08  
backplanes and 16-channel 5B01 backplanes. Because the NI 7831R has  
eight AI channels, you have access to the first eight channels in a  
16-channel backplane. The SSR connector pinout is compatible with  
eight-, 16-, 24-, and 32-channel SSR backplanes. You can connect to an  
SSR backplane containing a number of channels unequal to the 16 DIO  
lines available on the 50-pin header. In this case, you have access to only  
the channels that exist on both the SSR backplane and the NSC68-262650  
cable 50-pin header.  
Figure B-3 shows the connector pinouts when using the NSC68-262650  
cable.  
© National Instruments Corporation  
B-5  
NI 7831R User Manual  
 
Appendix B  
Connecting I/O Signals  
NC  
NC  
NC  
NC  
NC  
1
3
5
7
9
2
4
6
8
10  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
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  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DIO15  
DIO14  
DIO13  
DIO12  
DIO11  
DIO10  
DIO9  
DIO8  
DIO7  
DIO6  
DIO5  
DIO4  
DIO3  
DIO2  
DIO1  
DIO0  
+5V  
AO0  
AOGND0  
AO1  
AO2  
AOGND2  
AO3  
AO4  
AOGND4  
AO5  
AO6  
AOGND6  
AO7  
1
3
5
7
9
2
4
6
8
10  
NC  
NC  
AOGND1  
NC  
NC  
AOGND3  
NC  
NC  
AOGND5  
NC  
NC  
AI0+  
AIGND0  
AI1+  
AI2+  
AIGND2  
AI3+  
AI4+  
AIGND4  
AI5+  
AI6+  
AIGND6  
AI7+  
1
3
5
7
9
2
4
6
8
10  
AI0–  
AI1–  
AIGND1  
AI2–  
AI3–  
AIGND3  
AI4–  
AI5–  
AIGND5  
AI6–  
AI7–  
11 12  
13 14  
15 16  
17 18  
19 20  
21 22  
23 24  
25 26  
11 12  
13 14  
15 16  
17 18  
19 20  
21 22  
23 24  
25 26  
AOGND7  
NC  
AIGND7  
NC  
NC  
AISENSE  
AO 0–7 Connector  
Pin Assignment  
AI 0–7 Connector  
Pin Assignment  
DIO 0–15 Connector  
Pin Assignment  
Figure B-3. Connector Pinouts when Using NSC68-262650 Cable  
The NSC68-5050 cable connects the signals on the NI 7831R DIO  
connectors directly to SSR backplanes for digital signal conditioning. This  
cable has a 68-pin male VHDCI connector on one end that plugs into the  
NI 7831R DIO connectors. The other end of this cable provides two 50-pin  
female headers.  
You can plug each of these 50-pin headers directly into an 8-, 16-, 24-, or  
32-channel SSR backplane for digital signal conditioning. One of the  
50-pin headers contains DIO<0..23> from the NI 7831R DIO connector.  
These lines correspond to Slots <0..23> on an SSR backplane in sequential  
order. The other 50-pin header contains DIO<24..39> from the NI 7831R  
DIO connector. These lines correspond to Slots <0..15> on an SSR  
backplane in sequential order. You can connect to an SSR backplane  
containing a number of channels unequal to the number of lines on the  
NI 7831R User Manual  
B-6  
 
ni.com  
Appendix B  
Connecting I/O Signals  
NSC68-5050 cable header. In this case, you have access only to the  
channels that exist on both the SSR backplane and the NSC68-5050 cable  
header you are using.  
Figure B-4 shows the connector pinouts when using the NSC68-5050  
cable.  
DIO23  
DIO22  
DIO21  
DIO20  
DIO19  
DIO18  
DIO17  
DIO16  
DIO15  
DIO14  
DIO13  
DIO12  
DIO11  
DIO10  
DIO9  
DIO8  
DIO7  
DIO6  
DIO5  
DIO4  
DIO3  
DIO2  
DIO1  
1
3
5
7
9
2
4
6
8
10  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
1
3
5
7
9
2
4
6
8
10  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
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 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  
NC  
DIO39  
DIO38  
DIO37  
DIO36  
DIO35  
DIO34  
DIO33  
DIO32  
DIO31  
DIO30  
DIO29  
DIO28  
DIO27  
DIO26  
DIO25  
DIO24  
+5V  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DGND  
DIO0  
+5V  
DIO 0–23 Connector  
Pin Assignment  
DIO 24–39 Connector  
Pin Assignment  
Figure B-4. Connector Pinouts when Using the NSC68-5050 Cable  
© National Instruments Corporation  
B-7  
NI 7831R User Manual  
 
C
Using the SCB-68  
Shielded Connector Block  
This appendix describes how to connect input and output signals to the  
NI 7831R with the SCB-68 shielded connector block.  
The SCB-68 has 68 screw terminals for I/O signal connections. To use the  
SCB-68 with the NI 7831R, you must configure the SCB-68 as a  
general-purpose connector block. Refer to Figure C-1 for the  
general-purpose switch configuration.  
S5 S4 S3  
S1  
S2  
Figure C-1. General-Purpose Switch Configuration for the SCB-68 Terminal Block  
After configuring the SCB-68 switches, you can connect the I/O signals to  
the SCB-68 screw terminals. Refer to Appendix B, Connecting I/O Signals,  
for the connector pin assignments for the NI 7831R. After connecting  
I/O signals to the SCB-68 screw terminals, you can connect the SCB-68 to  
the NI 7831R with the SH68-C68-S shielded cable.  
© National Instruments Corporation  
C-1  
NI 7831R User Manual  
 
   
D
Technical Support and  
Professional Services  
Visit the following sections of the National Instruments Web site at  
ni.comfor technical support and professional services:  
Support—Online technical support resources at ni.com/support  
include the following:  
Self-Help Resources—For immediate answers and solutions,  
visit the award-winning National Instruments Web site for  
software drivers and updates, a searchable KnowledgeBase,  
product manuals, step-by-step troubleshooting wizards, thousands  
of example programs, tutorials, application notes, instrument  
drivers, and so on.  
Free Technical Support—All registered users receive free Basic  
Service, which includes access to hundreds of Application  
Engineers worldwide in the NI Developer Exchange at  
ni.com/exchange. National Instruments Application Engineers  
make sure every question receives an answer.  
Training and Certification—Visit ni.com/trainingfor  
self-paced training, eLearning virtual classrooms, interactive CDs,  
and Certification program information. You also can register for  
instructor-led, hands-on courses at locations around the world.  
System Integration—If you have time constraints, limited in-house  
technical resources, or other project challenges, NI Alliance Program  
members can help. To learn more, call your local NI office or visit  
ni.com/alliance.  
Declaration of Conformity (DoC)—A DoC is our claim of  
compliance with the Council of the European Communities using  
the manufacturer’s declaration of conformity. This system affords  
the user protection for electronic compatibility (EMC) and product  
safety. You can obtain the DoC for your product by visiting  
ni.com/hardref.nsf.  
Calibration Certificate—If your product supports calibration,  
you can obtain the calibration certificate for your product at  
ni.com/calibration.  
© National Instruments Corporation  
D-1  
NI 7831R User Manual  
 
   
Appendix D  
Technical Support and Professional Services  
If you searched ni.comand could not find the answers you need, contact  
your local office or NI corporate headquarters. Phone numbers for our  
worldwide offices are listed at the front of this manual. You also can visit  
the Worldwide Offices section of ni.com/niglobalto access the branch  
office Web sites, which provide up-to-date contact information, support  
phone numbers, email addresses, and current events.  
NI 7831R User Manual  
D-2  
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
mega  
giga  
106  
109  
Numbers/Symbols  
°
Degrees.  
>
<
Greater than.  
Greater than or equal to.  
Less than.  
Less than or equal to.  
Negative of, or minus.  
Ohms.  
/
Per.  
%
Percent.  
Plus or minus.  
Positive of, or plus.  
+
© National Instruments Corporation  
G-1  
NI 7831R User Manual  
 
 
Glossary  
Square root of.  
+5V  
+5 VDC source signal.  
A
A
Amperes.  
A/D  
AC  
ADC  
Analog-to-digital.  
Alternating current.  
Analog-to-digital converter—An electronic device, often an integrated  
circuit, that converts an analog voltage to a digital number.  
AI  
Analog input.  
AI<i>  
AIGND  
AISENSE  
AO  
Analog input channel signal.  
Analog input ground signal.  
Analog input sense signal.  
Analog output.  
AO<i>  
AOGND  
ASIC  
Analog output channel signal.  
Analog output ground signal.  
Application-Specific Integrated Circuit—A proprietary semiconductor  
component designed and manufactured to perform a set of specific  
functions.  
B
bipolar  
A signal range that includes both positive and negative values (for example,  
–5 to +5 V).  
NI 7831R User Manual  
G-2  
© National Instruments Corporation  
 
Glossary  
C
C
Celsius.  
CalDAC  
CH  
Calibration DAC.  
Channel—Pin or wire lead to which you apply or from which you read the  
analog or digital signal. Analog signals can be single-ended or differential.  
For digital signals, you group channels to form ports. Ports usually consist  
of either four or eight digital channels.  
cm  
Centimeter.  
CMOS  
CMRR  
Complementary metal-oxide semiconductor.  
Common-mode rejection ratio—A measure of an instrument’s ability to  
reject interference from a common-mode signal, usually expressed in  
decibels (dB).  
common-mode voltage  
CompactPCI  
Any voltage present at the instrumentation amplifier inputs with respect to  
amplifier ground.  
Refers to the core specification defined by the PCI Industrial Computer  
Manufacturer’s Group (PICMG).  
D
D/A  
Digital-to-analog.  
DAC  
Digital-to-analog converter—An electronic device, often an integrated  
circuit, that converts a digital number into a corresponding analog voltage  
or current.  
DAQ  
dB  
Data acquisition—A system that uses the computer to collect, receive, and  
generate electrical signals.  
Decibel—The unit for expressing a logarithmic measure of the ratio of  
two signal levels: dB = 20log10 V1/V2, for signals in volts.  
DC  
Direct current.  
DGND  
DIFF  
Digital ground signal.  
Differential mode.  
© National Instruments Corporation  
G-3  
NI 7831R User Manual  
 
Glossary  
DIO  
Digital input/output.  
DIO<i>  
DMA  
Digital input/output channel signal.  
Direct memory access—A method by which data can be transferred  
to/from computer memory from/to a device or memory on the bus while the  
processor does something else. DMA is the fastest method of transferring  
data to/from computer memory.  
DNL  
DO  
Differential nonlinearity—A measure in LSB of the worst-case deviation of  
code widths from their ideal value of 1 LSB.  
Digital output.  
E
EEPROM  
Electrically erasable programmable read-only memory—ROM that can be  
erased with an electrical signal and reprogrammed.  
F
FPGA  
Field-Programmable Gate Array.  
FPGA VI  
A configuration that is downloaded to the FPGA and that determines the  
functionality of the hardware.  
G
glitch  
An unwanted signal excursion of short duration that is usually unavoidable.  
H
h
Hour.  
HIL  
Hz  
Hardware-in-the-loop.  
Hertz.  
NI 7831R User Manual  
G-4  
© National Instruments Corporation  
 
Glossary  
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.  
INL  
Relative accuracy.  
L
LabVIEW  
Laboratory Virtual Instrument Engineering Workbench. LabVIEW is a  
graphical programming language that uses icons instead of lines of text to  
create programs.  
LSB  
Least significant bit.  
M
m
Meter.  
max  
Maximum.  
MIMO  
min  
Multiple input, multiple output.  
Minimum.  
MIO  
Multifunction I/O.  
monotonicity  
A characteristic of a DAC in which the analog output always increases as  
the values of the digital code input to it increase.  
mux  
Multiplexer—A switching device with multiple inputs that sequentially  
connects each of its inputs to its output, typically at high speeds, in order to  
measure several signals with a single analog input channel.  
© National Instruments Corporation  
G-5  
NI 7831R User Manual  
 
Glossary  
N
noise  
An undesirable electrical signal—Noise comes from external sources such  
as the AC power line, motors, generators, transformers, fluorescent lights,  
CRT displays, computers, electrical storms, welders, radio transmitters,  
and internal sources such as semiconductors, resistors, and capacitors.  
Noise corrupts signals you are trying to send or receive.  
NRSE  
Nonreferenced single-ended mode—All measurements are made with  
respect to a common (NRSE) measurement system reference, but the  
voltage at this reference can vary with respect to the measurement system  
ground.  
O
OUT  
Output pin—A counter output pin where the counter can generate various  
TTL pulse waveforms.  
P
PCI  
Peripheral Component Interconnect—A high-performance expansion bus  
architecture originally developed by Intel to replace ISA and EISA. It is  
achieving widespread acceptance as a standard for PCs and work-stations.  
PCI offers a theoretical maximum transfer rate of 132 MB/s.  
port  
(1) A communications connection on a computer or a remote controller.  
(2) A digital port, consisting of four or eight lines of digital input and/or  
output.  
ppm  
pu  
Parts per million.  
Pull-up.  
PWM  
PXI  
Pulse-width modulation.  
PCI eXtensions for Instrumentation—An open specification that builds off  
the CompactPCI specification by adding instrumentation-specific features.  
NI 7831R User Manual  
G-6  
© National Instruments Corporation  
 
Glossary  
R
RAM  
Random-access memory—The generic term for the read/write memory that  
is used in computers. RAM allows bits and bytes to be written to it as well  
as read from. Various types of RAM are DRAM, EDO RAM, SRAM, and  
VRAM.  
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.  
RIO  
rms  
Reconfigurable I/O.  
Root mean square.  
RSE  
Referenced single-ended mode—All measurements are made with respect  
to a common reference measurement system or a ground. Also called a  
grounded measurement system.  
RTSI  
Real-time system integration bus—The timing and triggering bus that  
connects multiple devices directly. This allows for hardware  
synchronization across devices.  
S
s
Seconds.  
Samples.  
S
S/s  
Samples per second—Used to express the rate at which a DAQ board  
samples an analog signal.  
signal conditioning  
slew rate  
The manipulation of signals to prepare them for digitizing.  
The voltage rate of change as a function of time. The maximum slew rate  
of an amplifier is often a key specification to its performance. Slew rate  
limitations are first seen as distortion at higher signal frequencies.  
© National Instruments Corporation  
G-7  
NI 7831R User Manual  
 
Glossary  
T
THD  
Total harmonic distortion—The ratio of the total rms signal due to  
harmonic distortion to the overall rms signal, in decibel or a percentage.  
thermocouple  
A temperature sensor created by joining two dissimilar metals. The  
junction produces a small voltage as a function of the temperature.  
TTL  
Transistor-transistor logic.  
two’s complement  
Given a number x expressed in base 2 with n digits to the left of the radix  
point, the (base 2) number 2n x.  
V
V
Volts.  
VDC  
VHDCI  
VI  
Volts direct current.  
Very high density cabled interconnect.  
Virtual instrument—Program in LabVIEW that models the appearance and  
function of a physical instrument.  
VIH  
VIL  
Volts, input high.  
Volts, input low.  
VOH  
VOL  
Vrms  
Volts, output high.  
Volts, output low.  
Volts, root mean square.  
W
waveform  
Multiple voltage readings taken at a specific sampling rate.  
NI 7831R User Manual  
G-8  
© National Instruments Corporation  
 

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