NI 2501 User manual

Computer-Based
Instruments
NI 2501/2503 User Manual
24-Channel Two-Wire Multiplexer
NI 2501/2503 User Manual
June 1998 Edition
Part Number 321906A-01

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©Copyright 1998 National Instruments Corporation. All rights reserved.

Important Information
Warranty
The NI 2501 and NI 2503 are 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 manual 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 MERCHANTABILITY OR FITNESS FOR APARTICULAR PURPOSE. CUSTOMER’SRIGHT TO RECOVER DAMAGES CAUSED
BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE
CUSTOMER. NATIONAL INSTRUMENTS WILL NOT BE LIABLE FOR DAMAGES RESULTING FROM LOSS OF DATA, PROFITS, USE OF PRODUCTS,
OR INCIDENTAL OR CONSEQUENTIAL DAMAGES, EVEN IF ADVISED OF THE POSSIBILITY THEREOF. This limitation of the liability of
National Instruments will apply regardless of the form of action, whether in contract or tort, including 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
CVI™, LabVIEW™, NI-SWITCH™, and PXI™are trademarks of National Instruments Corporation.
Product and company names listed are trademarks or trade names of their respective companies.
WARNING REGARDING MEDICAL AND CLINICAL USE OF NATIONAL INSTRUMENTS PRODUCTS
National Instruments products are not designed with components and testing intended to ensure a level of reliability
suitable for use in treatment and diagnosis of humans. Applications of National Instruments products involving medical
or clinical treatment can create a potential for accidental injury caused by product failure, or by errors on the part of the
user or application designer. Any use or application of National Instruments products for or involving medical or clinical
treatment must be performed by properly trained and qualified medical personnel, and all traditional medical safeguards,
equipment, and procedures thatare appropriate in the particular situation to prevent serious injury ordeath should always
continue to be used when National Instruments products are being used. National Instruments products are NOT intended
to be a substitute for any form of established process, procedure, or equipment used to monitor or safeguard human health
and safety in medical or clinical treatment.

Compliance
FCC/DOC Radio Frequency Interference
Class A Compliance
This equipment generates and uses radio frequency energy and, if not installed and used in strict accordance
with the instructions in this manual, 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). This equipment has been tested and found to comply with the
following two regulatory agencies:
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 will be required to correct the
interference at his own expense.
Notices to User: Changes or modifications not expressly approved by National Instruments could void
the user’s authority to operate the equipment under the FCC Rules.
This device complies with the FCC rules only if used with shielded interface cables
of suitable quality and construction. National Instruments used such cables to test
this device and provides them for sale to the user. The use of inferior or nonshielded
interface cables could void the user’s authority to operate the equipment under the
FCC rules.
If necessary, consult National Instruments or an experienced radio/television technician for additional
suggestions. The following booklet prepared by the FCC may also be helpful: Interference to Home
Electronic Entertainment Equipment Handbook. This booklet is available from the U.S. Government
Printing Office, Washington, DC 20402.
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.

Conventions
The following conventions are used in this manual.
< > Angle brackets containing numbers separated by an ellipsis represent a
range of values associated with a port, bit, or signal name (for example,
ACH<0..7> stands for the signals ACH0 through ACH7).
This icon to the left of bold italicized text denotes a note, which alerts
you to important information.
This icon to the left of bold italicized text denotes a caution, which
advises you of precautions to take to avoid injury, data loss, or a
system crash.
This icon to the left of bold italicized text denotes a warning, which advises
you of precautions to take to avoid being electrically shocked.
bold italic Bold italic text denotes a note, caution, or warning.
italic Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. This font also denotes text from which you supply the
appropriate word or value, as in CHx.
!

© National Instruments Corporation vii NI 2501/2503 User Manual
Contents
Chapter 1
Routing Signals with Your NI 2501/2503
About the NI 2501/2503 ................................................................................................1-1
Analog Bus......................................................................................................1-2
Triggers............................................................................................................1-2
Cold-Junction Sensor Channel........................................................................1-3
NI 2501 Amplifier...........................................................................................1-3
Connecting Signals ........................................................................................................1-4
Front Connector...............................................................................................1-4
Contact Protection..........................................................................................................1-8
Terminal Blocks.............................................................................................................1-9
Software Choices...........................................................................................................1-9
NI-SWITCH Driver Software .........................................................................1-9
National Instruments Application Software....................................................1-9
Third Party Software .......................................................................................1-10
Chapter 2
NI 2501/2503 Operation
Functional Overview......................................................................................................2-1
Multiplexer.....................................................................................................................2-4
Two-wire .........................................................................................................2-4
One-Wire.........................................................................................................2-4
Four-wire.........................................................................................................2-5
Switch Control Circuitry................................................................................................2-5
Random Scanning..........................................................................................................2-5
PXI Interface..................................................................................................................2-6
Triggers............................................................................................................2-6
External Trigger Input.......................................................................2-6
Scanner Advanced.............................................................................2-7
Modes................................................................................................2-7
Initiating Scanning...........................................................................................2-7
Multicard Triggering.......................................................................................2-8
Appendix A
Specifications

Contents
NI 2501/2503 User Manual viii
© National Instruments Corporation
Appendix B
Accessories
Appendix C
Customizing Your Card
Appendix D
Architecture Drawings
Appendix E
Common Questions
Appendix F
Customer Communication
Glossary
Index
Figures
Figure 1-1. Front Connector Pinout Assignments for Two-Wire Mode .................1-5
Figure 1-2. Front Connector Pinout Assignments for One-Wire Mode..................1-6
Figure 1-3. Front Connector Pinout Assignments for Four-Wire Mode.................1-7
Figure 2-1. NI 2501 Module Block Diagram ..........................................................2-2
Figure 2-2. NI 2503 Module Block Diagram ..........................................................2-3
Figure C-1. Bent and Trimmed Resistor ..................................................................C-2
Figure D-1. NI 2501 Switch Architecture ................................................................ D-2
Figure D-2. NI 2503 Switch Architecture ................................................................ D-3
Tables
Table 1-1. Front Connector Signal Description ....................................................1-8

© National Instruments Corporation 1-1 NI 2501/2503 User Manual
1
Routing Signals with Your
NI 2501/2503
This manual describes the electrical and mechanical aspects of the
NI 2501 FET multiplexer and the NI 2503 mechanical relay multiplexer
and contains information concerning their installation and operation.
This manual uses the term NI 2501/2503 whenever information applies
to both instruments.
About the NI 2501/2503
This section summarizes the features and operation of the NI 2501/2503
switch card. Refer to Chapter 2, NI 2501/2503 Operation, for more
complete details. In addition, refer to Appendix A, Specifications, for
detailed specifications of the two switch cards.
The NI 2501 is a FET switch card, and the NI 2503 is an armature
relay switch card. Each consists of a 24 x 1 two-wire multiplexer in
PXI/Compact PCI format. You can take advantage of the switch card’s
flexibility to handle a wide variety of test systems through the use of
various accessories and software configurations. You can use the National
Instruments NI-SWITCH software included with your kit to configure and
operate the NI 2501/2503 switch card.
The NI 2501/2503 can also operate as two 12 x 1 or four 6 x 1 two-wire
multiplexers. You can use software-configurable switches to configure the
switch card as a 48 x 1 one-wire multiplexer for making large numbers of
common referenced measurements. In addition, the NI 2501/2503 can
operate as a 12 x 1 four-wire multiplexer to handle resistive measurements,
such as thermistors or RTDs. By adding a TB-2606 terminal block, you can
further configure the NI 2501/2503 as a 6 x 4 two-wire matrix. Refer to
Appendix B, Accessories, for more information on terminal blocks you can
order from National Instruments.
You can also use multiple NI 2501/2503 cards together to expand the size
of the multiplexer or matrix. For example, you can connect two cards to
create a 48 x 1 two-wire multiplexer or a 12 x 4 two-wire matrix.

Chapter 1 Routing Signals with Your NI 2501/2503
NI 2501/2503 User Manual 1-2
© National Instruments Corporation
Caution The maximum voltage is different for the NI 2501 and NI 2503 switch cards.
If you intend to use more than one type of card, be sure you do not exceed the
maximum voltage of any card in your system. Refer to Appendix A, Specifications,
for information.
Analog Bus
The NI 2501/2503 works with a four-wire analog bus. You connect the
analog bus to the switch card through its main front-panel connector.
You can use the analog bus to simplify connecting multiple cards to an
instrument such as a digital multimeter (DMM). This bus makes it possible
to create large systems using multiple switch cards.
For example, if you have two NI 2501/2503 cards—or one of each—in two
adjacent slots, you can connect them through the analog bus and create a
48 x 1 two-wire multiplexer. With this flexibility, you keep the wiring of
the modules to a minimum while you create large switching solutions. In
such cases, the scanning architecture uses some of the PXI trigger lines for
synchronization and delivers full access to all of the scanning features for
the cards. The National Instruments software you receive with the
NI 2501/2503 handles the complexity of programming the cards.
Triggers
Two triggers are used to handshake the NI 2501/2503 switch with PXI
instruments or other external instruments. The Scanner Advanced trigger
indicates when the card has closed all the necessary switches for the next
scan and the switches have settled, or debounced. This trigger is typically
wired to a measurement device, such as a DMM, which is configured to
take a reading when it receives the trigger.
The External Trigger Input trigger is sourced by another instrument, such
as the DMM, and causes the NI 2501/2503 to advance to the next entry
in the scan list. The triggers can be routed to the front connector of the
NI 2501/2503, to any of the PXI TTL triggers, or to the PXI star trigger. If
no external trigger input is available, you can have the software trigger the
NI 2501/2503 to advance to the next entry in the scan list.
Refer to Chapter 2, NI 2501/2503 Operation, for more information on
triggers.
!

Chapter 1 Routing Signals with Your NI 2501/2503
© National Instruments Corporation 1-3 NI 2501/2503 User Manual
Cold-Junction Sensor Channel
For low-voltage measurements, such as those provided by thermocouples,
the NI 2503 has very low thermal offset—less than 2 µV—to ensure
accurate measurements. For cold-junction compensation when switching
thermocouples, the NI 2501/2503 has a dedicated channel for a
temperature sensor. The National Instruments TB-2605 and TBX-68S
terminal blocks both have onboard temperature sensors that connect to the
dedicated cold-junction sensor channel.
NI 2501 Amplifier
The NI 2501 has an amplifier with a gain of 1. This amplifier can be
switched in-line before the COM0 signal and theAB0 signal. The amplifier
helps to decrease the settling time of the FET switch. The amplifier’s
high impedance isolates the FET from the resistance, capacitance,
and inductance in the external wiring. This isolation decreases the
resistance/capacitance time constant seen by the FET, which improves
settling time.
The amplifier has an offset that should be calibrated for more accurate
measurements. The calibration data can be stored into and retrieved from
the EEPROM on the board. The software you received with your switch
card includes API function calls to retrieve and store calibration data.
When the amplifier is used, the switch card becomes directional, where
CHxis for signal inputs and COM0 or AB0 are for signal outputs.
The NI 2501 also has an amplifier in the CJS0+ to COM0+ signal path.
This amplifier in the cold-junction sensor signal path is used to improve
settling time performance. It prevents the impedance of the cold-junction
sensor from increasing the settling time when switching the CJS channel.
As a result, when scanning thermocouples, the settling time for the
cold-junction sensor channel should be about the same as for the channels
with the thermocouples.

Chapter 1 Routing Signals with Your NI 2501/2503
NI 2501/2503 User Manual 1-4
© National Instruments Corporation
Connecting Signals
This section describes the signal connections to the NI 2501/2503 module
via the module front connector. This section also includes specifications
and connection instructions for the signals on the NI 2501/2503 module
connectors.
Caution Static electricity is a major cause of component failure. To prevent damage to the
electrical components in the module, observe antistatic precautions whenever
removing a module from the chassis or whenever working on a module.
Front Connector
The pinout assignments for the NI 2501/2503 front connector vary
depending on the wiring mode you use. The following three diagrams show
the pin assignments for two-wire mode, one-wire mode, and four-wire
mode, respectively. Two-wire mode is shown first because it is the most
common configuration. Table 1-1, following the diagrams, describes the
connector signals. For more information on the wiring modes, refer to the
Multiplexer section in Chapter 2, NI 2501/2503 Operation.
!

Chapter 1 Routing Signals with Your NI 2501/2503
© National Instruments Corporation 1-5 NI 2501/2503 User Manual
Figure 1-1. Front Connector Pinout Assignments for Two-Wire Mode
CH23-
CH22-
CH21-
CH20-
CH19-
CH18-
GND
+5 V
COM3-
COM2-
CH17-
CH16-
CH15-
CH14-
CH13-
CH12-
AB2-
AB0-
CH11-
CH10-
CH9-
1_WIRE_LO_REF
CH8-
CH7-
CH6-
COM1-
COM0-
CH5-
CH4-
CH3-
CH2-
CH1-
CH0-
CJS0-
135
236
337
438
539
640
741
842
943
10 44
11 45
12 46
13 47
14 48
15 49
16 50
17 51
18 52
19 53
20 54
21 55
22 56
23 57
24 58
25 59
26 60
27 61
28 62
29 63
30 64
31 65
32 66
33 67
34 68
CH23+
CH22+
CH21+
CH20+
CH19+
CH18+
EXT_TRIG_IN
SCAN_ADV
COM3+
COM2+
CH17+
CH16+
CH15+
CH14+
CH13+
CH12+
AB2+
AB0+
CH11+
CH10+
CH9+
GND
CH8+
CH7+
CH6+
COM1+
COM0+
CH5+
CH4+
CH3+
CH2+
CH1+
CH0+
CJS0+

Chapter 1 Routing Signals with Your NI 2501/2503
NI 2501/2503 User Manual 1-6
© National Instruments Corporation
Figure 1-2. Front Connector Pinout Assignments for One-Wire Mode
CH47
CH46
CH45
CH44
CH43
CH42
GND
+5 V
COM3- (CH42-CH48)
COM2- (CH36-CH41)
CH41
CH40
CH39
CH38
CH37
AB1-
AB0-
CH36
CH35
CH34
CH33
1_WIRE_LO_REF
CH32
CH31
CH30
COM1- (CH30-CH35)
COM0-
CH29
CH28
CH27
CH26
CH25
CH24
CJS-
135
236
337
438
539
640
741
842
943
10 44
11 45
12 46
13 47
14 48
15 49
16 50
17 51
18 52
19 53
20 54
21 55
22 56
23 57
24 58
25 59
26 60
27 61
28 62
29 63
30 64
31 65
32 66
33 67
34 68
CH23
CH22
CH21
CH20
CH19
CH18
EXT_TRIG_IN
SCAN_ADV
COM3+ (CH18-CH23)
COM2+ (CH12-CH17)
CH17
CH16
CH15
CH14
CH13
AB1+
AB0+
CH12
CH11
CH10
CH9
GND
CH8
CH7
CH6
COM1+ (CH6-CH11)
COM0+
CH5
CH4
CH3
CH2
CH1
CH0
CJS+

Chapter 1 Routing Signals with Your NI 2501/2503
© National Instruments Corporation 1-7 NI 2501/2503 User Manual
Figure 1-3. Front Connector Pinout Assignments for Four-Wire Mode
Warning Any connections that exceed the maximum settings for the NI 2501/2503 can
result in an electrical shock hazard and damage to the NI 2501/2503 module and
any or all of the boards connected to the PXI backplane. National Instruments is
NOT liable for any damages or injuriesresulting from exceeding maximum voltage
ratings. Refer to Appendix A, Specifications, for information.
CH11_SENSE-
CH10_SENSE-
CH9_SENSE-
CH8_SENSE-
CH7_SENSE-
CH6_SENSE-
GND
+5 V
COM1_SENSE-
COM0_SENSE-
CH5_SENSE-
CH4_SENSE-
CH3_SENSE-
CH2_SENSE-
CH1_SENSE-
AB1_SENSE-
AB0_SENSE+
CH0_SENSE-
CH11_SENSE+
CH10_SENSE+
CH9_SENSE+
1_WIRE_LO_REF
CH8_SENSE+
CH7_SENSE+
CH6_SENSE+
COM1_SENSE+
COM0_SENSE+
CH5_SENSE+
CH4_SENSE+
CH3_SENSE+
CH2_SENSE+
CH1_SENSE+
CH0_SENSE+
CJS-
135
236
337
438
539
640
741
842
943
10 44
11 45
12 46
13 47
14 48
15 49
16 50
17 51
18 52
19 53
20 54
21 55
22 56
23 57
24 58
25 59
26 60
27 61
28 62
29 63
30 64
31 65
32 66
33 67
34 68
CH11-
CH10-
CH9-
CH8-
CH7-
CH6-
EXT_TRIG_IN
SCAN_ADV
COM1-
COM0-
CH5-
CH4-
CH3-
CH2-
CH1-
AB1-
AB0-
CH0-
CH11+
CH10+
CH9+
GND
CH8+
CH7+
CH6+
COM1+
COM0+
CH5+
CH4+
CH3+
CH2+
CH1+
CH0+
CJS+

Chapter 1 Routing Signals with Your NI 2501/2503
NI 2501/2503 User Manual 1-8
© National Instruments Corporation
Contact Protection
Caution When inductive loads are connected to the relays, a large counter electromotive
force may occur at relay switching time due to the energy stored in the inductive
load. These flyback voltages can severely damage the relay contacts and greatly
shorten the life of the relay.
It is best to limit flyback voltages at your inductive load by installing a flyback
diode for DC loads or a movistor for AC loads.
Table 1-1. Front Connector Signal Description
Signal Name Type Description
+5 V Output +5 VDC Source—Powers the temperature sensor
ontheterminalblock.0.2mAof sourceprotected
by a resettable poly fuse.
GND Output Ground
CJS±Input Cold-junction Temperature Sensor Input—
Connects to the temperature sensor of the
terminal block.
1_WIRE_LO_REF Input The common reference signal used in one-wire
mode.
EXT_TRIG_IN Input External Trigger Input—Trigger from an
instrument to advance the switch card to the next
scan entry.
SCAN_ADV Output Scanner Advanced—Trigger to an instrument
that indicated the switch card has advanced to the
next scan and relays are debounced.
CH<0..23>±
CH<0..47> one-wire
CHA<0..11>±
CHB<0..11>±
Input/Output Channels—Where signals are connected to the
switch card. CHx+ and CHx– are switched
together.
COMA<0..3>±
COMB<0..1>±Input/Output Common—The common for each of the four
banks.
AB<0..1>±
AB<0..1>_SENSE±Input/Output Analog Bus—Used to wire multiple switch cards
to an instrument such as a DMM.
!

Chapter 1 Routing Signals with Your NI 2501/2503
© National Instruments Corporation 1-9 NI 2501/2503 User Manual
Terminal Blocks
Several terminal blocks with screw terminals are available for easy signal
connection to the NI 2501/2503 inputs. Refer to Appendix B, Accessories.
Software Choices
Youhave several optionstochoose from when programming your National
Instruments switch card. You can use the NI-SWITCH driver software, or
National Instruments application software.
NI-SWITCH Driver Software
The NI-SWITCH instrument driver is an Intelligent Virtual Instrument
(IVI) compliant instrument driver that is bundled with NI-SWITCH cards
at no cost.
NI-SWITCH features a set of operations and attributes that exercise all
the functionality of the switching hardware, including configuration,
opening/closing, and scanning. In addition, NI-SWITCH comes with an
interactive soft front panel and online documentation.
NI-SWITCH eliminates the need to understand complex register
programming and interrupt handling in the Microsoft operating systems,
and frees you to focus on creating your test system.
National Instruments Application Software
LabVIEW and LabWindows/CVI are innovative program development
software packages for data acquisition and control applications. LabVIEW
uses graphical programming, whereas LabWindows/CVI enhances
traditional programming languages. Both packages include extensive
libraries for data acquisition, instrument control, data analysis, and
graphical data presentation. Using LabVIEW or LabWindows/CVI can
significantly reduce the development time for your data acquisition and
control application.
LabVIEW features interactive graphics, a state-of-the-art user interface,
and a powerful graphical programming language. The LabVIEW
NI-SWITCH VI Library, a series of virtual instruments (VIs) for using
LabVIEW with National Instruments switch hardware, is included with
the NI-SWITCH driver.

Chapter 1 Routing Signals with Your NI 2501/2503
NI 2501/2503 User Manual 1-10
© National Instruments Corporation
LabWindows/CVI features interactive graphics, a state-of-the-art user
interface, and uses the ANSI standard C programming language. The
LabWindows/CVI NI-SWITCH Library, a series of functions for using
LabWindows/CVI with National Instruments switch hardware, is included
with the NI-SWITCH driver.
Third Party Software
The NI-SWITCH instrument driver also includes support files for
Microsoft Visual C++ and Microsoft Visual Basic. Please see the
NI-SWITCH readme file for version support information.

© National Instruments Corporation 2-1 NI 2501/2503 User Manual
2
NI 2501/2503 Operation
This chapter contains a functional overview of the NI 2501/2503
module and explains the operationof each functional unit making up the
NI 2501/2503 module.
Functional Overview
The block diagrams on the following pages illustrate the key functional
components of the switch card modules. Figure 2-1 shows the NI 2501 and
Figure 2-2 shows the NI 2503.
The major components of the NI 2501/2503 modules are as follows:
• Multiplexer
• Relay/FET switch control circuitry
• Random scanning
• PXIbus interface
• Triggers

Chapter 2 NI 2501/2503 Operation
NI 2501/2503 User Manual 2-2
© National Instruments Corporation
Figure 2-1. NI 2501 Module Block Diagram
Front Connector
PXIbus Connector
CH0
CH5
Com0
CH6
CH11
CH12
CH17
CH18
CH23
Com1
Com2
Com3
AISENSE
Cold Junction Sensor
FET Mux
FET Mux
FET Mux
FET Mux
FET Mux
One Wire /
Unity Gain
Amplifier
Select
Two Wire
Select
FET Switch Control
Triggers PXI Interface
Scan Memory
Analog Bus0
Analog Bus1

Chapter 2 NI 2501/2503 Operation
© National Instruments Corporation 2-3 NI 2501/2503 User Manual
Figure 2-2. NI 2503 Module Block Diagram
Front Connector
PXIbus Connector
CH0
CH5
Com0
CH6
CH11
CH12
CH17
CH18
CH23
Com1
Com2
Com3
AISENSE
Cold Junction Sensor
Relay Mux
Relay Mux
Relay Mux
Relay Mux
Relay Mux
One Wire /
Two Wire
Select
Relay Control
Triggers PXI Interface
Scan Memory
Analog Bus0
Analog Bus1