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.
In no event shall National Instruments be liable for any damages arising out of or related to this document or the information contained in it.
EXCEPT AS SPECIFIED HEREIN, NATIONAL INSTRUMENTS MAKES NO WARRANTIES, EXPRESS OR IMPLIED, AND SPECIFICALLY DISCLAIMS ANY WARRANTY OF
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negligence. Any action against National Instruments must be brought within one year after the cause of action accrues. National Instruments
shall not be liable for any delay in performance due to causes beyond its reasonable control. The warranty provided herein does not cover
damages, defects, malfunctions, or service failures caused by owner’s failure to follow the National Instruments installation, operation, or
maintenance instructions; owner’s modification of the product; owner’s abuse, misuse, or negligent acts; and power failure or surges, fire,
flood, accident, actions of third parties, or other events outside reasonable control.
Copyright
Under the copyright laws, this publication may not be reproduced or transmitted in any form, electronic or mechanical, including photocopying,
recording, storing in an information retrieval system, or translating, in whole or in part, without the prior written consent of National
Instruments Corporation.
Trademarks
CompactRIO™, LabVIEW™, National Instruments™, NI™, ni.com™, NI Developer Zone™, and RTSI™ are 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
RELIABILITY SUITABLE FOR USE IN OR IN CONNECTION WITH SURGICAL IMPLANTS OR AS CRITICAL COMPONENTS IN
ANY LIFE SUPPORT SYSTEMS WHOSE FAILURE TO PERFORM CAN REASONABLY BE EXPECTED TO CAUSE SIGNIFICANT
INJURY TO A HUMAN.
(2) IN ANY APPLICATION, INCLUDING THE ABOVE, RELIABILITY OF OPERATION OF THE SOFTWARE PRODUCTS CAN BE
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COMPUTER HARDWARE MALFUNCTIONS, COMPUTER OPERATING SYSTEM SOFTWARE FITNESS, FITNESS OF COMPILERS
AND DEVELOPMENT SOFTWARE USED TO DEVELOP AN APPLICATION, INSTALLATION ERRORS, SOFTWARE AND
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DEVICES, TRANSIENT FAILURES OF ELECTRONIC SYSTEMS (HARDWARE AND/OR SOFTWARE), UNANTICIPATED USES OR
MISUSES, OR ERRORS ON THE PART OF THE USER OR APPLICATIONS DESIGNER (ADVERSE FACTORS SUCH AS THESE ARE
HEREAFTER COLLECTIVELY TERMED “SYSTEM FAILURES”). ANY APPLICATION WHERE A SYSTEM FAILURE WOULD
CREATE A RISK OF HARM TO PROPERTY OR PERSONS (INCLUDING THE RISK OF BODILY INJURY AND DEATH) SHOULD
NOT BE RELIANT SOLELY UPON ONE FORM OF ELECTRONIC SYSTEM DUE TO THE RISK OF SYSTEM FAILURE. TO AVOID
DAMAGE, INJURY, OR DEATH, THE USER OR APPLICATION DESIGNER MUST TAKE REASONABLY PRUDENT STEPS TO
PROTECT AGAINST SYSTEM FAILURES, INCLUDING BUT NOT LIMITED TO BACK-UP OR SHUT DOWN MECHANISMS.
BECAUSE EACH END-USER SYSTEM IS CUSTOMIZED AND DIFFERS FROM NATIONAL INSTRUMENTS' TESTING
PLATFORMS AND BECAUSE A USER OR APPLICATION DESIGNER MAY USE NATIONAL INSTRUMENTS PRODUCTS IN
COMBINATION WITH OTHER PRODUCTS IN A MANNER NOT EVALUATED OR CONTEMPLATED BY NATIONAL
INSTRUMENTS, THE USER OR APPLICATION DESIGNER IS ULTIMATELY RESPONSIBLE FOR VERIFYING AND VALIDATING
THE SUITABILITY OF NATIONAL INSTRUMENTS PRODUCTS WHENEVER NATIONAL INSTRUMENTS PRODUCTS ARE
INCORPORATED IN A SYSTEM OR APPLICATION, INCLUDING, WITHOUT LIMITATION, THE APPROPRIATE DESIGN,
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.
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
Reconfigurable I/O Architecture.....................................................................1-4
Software Development ..................................................................................................1-5
LabVIEW FPGA Module................................................................................1-5
LabVIEW Real-Time Module.........................................................................1-6
Cables and Optional Equipment ....................................................................................1-7
Chapter 2
Connecting Analog Input Signals..................................................................................2-5
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
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Contents
Connecting Analog Output Signals............................................................................... 2-15
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
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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.
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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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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
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.
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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
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
Guide, available by selecting Start»Program Files»National
Instruments»<LabVIEW>»Module Documents»FPGA Interface User
Guide, for information about the FPGA Interface functions.
© National Instruments Corporation
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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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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
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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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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 2-3. 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
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
the device ground. The NI 7831R ADC measures this output voltage when
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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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
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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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
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
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 Ω.
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 kΩ, the resistors load down the source
with 200 kΩ and 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 kΩ to 1 MΩ. 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
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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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
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.
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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,
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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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.
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.
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Hardware Overview of the NI 7831R
Figure 2-11 shows signal connections for three typical DIO applications.
LED
TTL or
LVCMOS
Compatible |