National Instruments 321906B-01 User manual

Brand: National Instruments

Model: 321906B-01

Type: User manual

Computer-Based

Instruments

NI 2501/2503 User Manual

24-Channel Two-Wire Multiplexer

NI 2501/2503 User Manual

July 1998 Edition

Part Number 321906B-01

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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.

XCEPT

SPECIFIED

HEREIN

, N

ATIONAL

NSTRUMENTS

MAKES

WARRANTIES

EXPRESS

IMPLIED

AND

SPECIFICALLY

DISCLAIMS

ANY

WARRANTY

MERCHANTABILITY

FITNESS

FOR

PARTICULAR

PURPOSE

. C

USTOMER

’

RIGHT

RECOVER

DAMAGES

CAUSED

FAULT

NEGLIGENCE

THE

PART

ATIONAL

NSTRUMENTS

SHALL

LIMITED

THE

AMOUNT

THERETOFORE

PAID

THE

CUSTOMER

. N

ATIONAL

NSTRUMENTS

WILL

NOT

LIABLE

FOR

DAMAGES

RESULTING

FROM

LOSS

DATA

PROFITS

USE

PRODUCTS

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CONSEQUENTIAL

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. 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.

Under the copyright laws, this publication may not be reproduced or transmitted in any form, electronic or mechanical,

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the prior written consent of National Instruments Corporation.

Trademarks

CVI

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, 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 that are appropriate in the particular situation to prevent serious injury or death 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,

CH<0..7> stands for the signals CH0 through CH7).

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..........................................................................................................1-10

Terminal Blocks.............................................................................................................1-10

Software Choices...........................................................................................................1-10

NI-SWITCH Driver Software .........................................................................1-10

National Instruments Application Software....................................................1-11

Third Party Software .......................................................................................1-11

Chapter 2

NI 2501/2503 Operation

Functional Overview......................................................................................................2-1

Multiplexer.....................................................................................................................2-4

Two-Wire Mode..............................................................................................2-4

One-Wire Mode...............................................................................................2-4

Four-Wire Mode..............................................................................................2-5

Matrix Mode....................................................................................................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...........................................................................................2-8

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 1-4. Front Connector Pinout Assignments to Create a 6 x 4 Matrix............ 1-8

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 ....................................................1-9

National Instruments Corporation 1-1 NI 2501/2503 User Manual

Routing Signals with Your

NI2501/2503

This manual describes the electrical and mechanical aspects of the

NI2501 FET multiplexer and the NI2503 mechanical relay multiplexer

and contains information concerning their installation andoperation.

This manual uses the term NI2501/2503 whenever information applies

to both instruments.

About the NI2501/2503

This section summarizes the features and operation of the NI2501/2503

switch card. Refer to Chapter2, NI2501/2503 Operation, for more

complete details. In addition, refer to AppendixA, Specifications,

fordetailed specifications of the two switch cards.

The NI2501 is a FET switch card, and the NI2503 is an armature

relayswitch 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 NI2501/2503 switch card.

The NI2501/2503 can also operate as two 12 x 1 or four 6 x 1 two-wire

multiplexers. You can use software-configurable switches to configure

theswitch card as a 48 x 1 one-wire multiplexer for making large numbers

of common referenced measurements. In addition, the NI2501/2503 can

operate as a 12 x 1 four-wire multiplexer to handle resistive measurements,

such as thermistors or RTDs. Finally, you can use a National Instruments

TB-2606 terminal block to further configure the NI2501/2503 as a 6 x 4

two-wire matrix.

The Connecting Signals section of this chapter contains more information

on one-wire, two-wire, four-wire, and matrix configurations, and includes

diagrams of the pinout connections to make.

Chapter 1 Routing Signals with Your NI 2501/2503

NI 2501/2503 User Manual 1-2

National Instruments Corporation

Refer to AppendixB, Accessories, for more information on terminal blocks

you can order from National Instruments.

You can also use multiple NI2501/2503 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.

Caution The maximum voltage is different for the NI2501 and NI2503 switch cards.

Ifyou 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 AppendixA, Specifications,

for information.

Analog Bus

The NI2501/2503 works with a four-wire analog bus. You connect the

analog bus to the switch card through its main front-panel connector.

Youcan 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 NI2501/2503 cards—or one of each—in two

adjacent slots, you can connect them through the analog bus and create a

48x1 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

NI2501/2503 handles the complexity of programming the cards.

Triggers

Two triggers are used to handshake the NI2501/2503 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 NI2501/2503 to advance to the next entry

inthe scan list. The triggers can be routed to the front connector of the

NI2501/2503, 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

NI2501/2503 to advance to the next entry in the scan list.

Chapter 1 Routing Signals with Your NI 2501/2503

National Instruments Corporation 1-3 NI 2501/2503 User Manual

Refer to Chapter 2, NI 2501/2503 Operation, for more information on

triggers.

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 the AB0 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

CHx is 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 four diagrams show

the pin assignments for two-wire mode, one-wire mode, four-wire mode,

and matrix 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.

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 injuries resulting from exceeding maximum

voltage ratings. Refer to Appendix A, Specifications, for information.

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–

AB1–

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+

AB1+

AB0+

CH11+

CH10+

CH9+

GND

CH8+

CH7+

CH6+

COM1+

COM0+

CH5+

CH4+

CH3+

CH2+

CH1+

CH0+

CJS0+

not used in two-wire mode

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

CH36

AB1–

AB0–

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

CH12

AB1+

AB0+

CH11

CH10

CH9

GND

CH8

CH7

CH6

COM1+ (CH6–CH11)

COM0+

CH5

CH4

CH3

CH2

CH1

CH0

CJS+

not used in one-wire mode

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

CH11B–

CH10B–

CH9B–

CH8B–

CH7B–

CH6B–

GND

+5 V

COM1B–

COM0B–

CH5B–

CH4B–

CH3B–

CH2B–

CH1B–

CH0B–

AB0B–

AB0A–

CH11A–

CH10A–

CH9A–

1_WIRE_LO_REF

CH8A–

CH7A–

CH6A–

COM1A–

COM0A–

CH5A–

CH4A–

CH3A–

CH2A–

CH1A–

CH0A–

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

CH11B+

CH10B+

CH9B+

CH8B+

CH7B+

CH6B+

EXT_TRIG_IN

SCAN_ADV

COM1B+

COM0B+

CH5B+

CH4B+

CH3B+

CH2B+

CH1B+

CH0B+

AB0B+

AB0A+

CH11A+

CH10A+

CH9A+

GND

CH8A+

CH7A+

CH6A+

COM1A+

COM0A+

CH5A+

CH4A+

CH3A+

CH2A+

CH1A+

CH0A+

CJS+

not used in four-wire mode

Chapter 1 Routing Signals with Your NI 2501/2503

NI 2501/2503 User Manual 1-8

National Instruments Corporation

Figure 1-4. Front Connector Pinout Assignments to Create a 6 x 4 Matrix

For matrix mode, connect all pins with the same name together external to

the switch card. The National Instruments TB-2606 terminal block

connects the necessary pins to create the 6 x 4 matrix.

COL5–

COL4–

COL3–

COL2–

COL1–

COL0–

GND

+5 V

ROW3–

ROW2–

COL5–

COL4–

COL3–

COL2–

COL1–

COL0–

AB1– (ROW2–)

AB0– (ROW0–)

COL5–

COL4–

COL3–

COL2–

COL1–

COL0–

ROW1–

ROW0–

COL5–

COL4–

COL3–

COL2–

COL1–

COL0–

CJS–

135

236

337

438

539

640

741

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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

COL5+

COL4+

COL3+

COL2+

COL1+

COL0+

EXT_TRIG_IN

SCAN_ADV

ROW3+

ROW2+

COL5+

COL4+

COL3+

COL2+

COL1+

COL0+

AB1+ (ROW2+)

AB0+ (ROW0+)

COL5+

COL4+

COL3+

GND

COL2+

COL1+

COL0+

ROW1+

ROW0+

COL5+

COL4+

COL3+

COL2+

COL1+

COL0+

CJS+

1_WIRE_LO_REF

not used in matrix mode

Chapter 1 Routing Signals with Your NI 2501/2503

National Instruments Corporation 1-9 NI 2501/2503 User Manual

Table 1-1. Front Connector Signal Description

Signal Name Type Description

+5 V Output +5 VDC Source—Powers the temperature sensor

on the terminal block. 0.2 mA of source protected

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..47> (one wire)

CH<0..23>± (two wire)

CH<0..11>A± (four wire)

CH<0..11>B± (four wire)

Input/Output Channels—Where signals are connected to the

switch card. CHx+ and CHx– are switched

together.

COM0± (one wire)

COM<0..3>± (two wire)

COM<0..1>A± (four wire)

COM<0..1>B± (four wire)

Input/Output Common—The common for each bank.

AB0± (one wire)

AB<0..1>± (two wire)

AB0A± (four wire)

AB0B± (four wire)

Input/Output Analog Bus—Used to wire multiple switch cards

to an instrument such as a DMM.

COL<0..5>± Input/Output Columns—Where signals are connected to the

switch card. The card behaves as a matrix when

proper external wiring is added.

ROW<0..3>± Input/Output Rows—Where signals are connected to the

switch card. In matrix configuration any row

can be connected to any column.

Chapter 1 Routing Signals with Your NI 2501/2503

NI 2501/2503 User Manual 1-10

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.

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

You have several options to choose 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.

Chapter 1 Routing Signals with Your NI 2501/2503

National Instruments Corporation 1-11 NI 2501/2503 User Manual

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.

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

NI 2501/2503 Operation

This chapter contains a functional overview of the NI 2501/2503

module and explains the operation of 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

One Wire /

Unity Gain

Amplifier

Select

Two Wire

Select

FET Switch Control

Triggers

PXI Interface

Scan Memory

Analog Bus0

Analog Bus1

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