National Instruments SCXI-1503 User Manual

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SCXI-1503 User Manual

March 2007 374271A-01

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The SCXI-1503 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.

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Conventions

The following conventions are used in this manual:

<> Angle brackets that contain numbers separated by an ellipsis represent a

range of values associated with a bit or signal name—for example, P0.<3..0>.

» The » symbol leads you through nested menu items and dialog box options

to a final action. The sequence File»Page Setup»Options directs you to pull down the File menu, select the Page Setup item, and select Options from the last dialog box.

This icon denotes a note, which alerts you to important information.

This icon denotes a caution, which advises you of precautions to take to avoid injury, data loss, or a system crash. When this symbol is marked on the product, refer to the Read Me First: Safety and Radio-Frequency Interference document, shipped with the product, for precautions to take.

When symbol is marked on a product it denotes a warning advising you to take precautions to avoid electrical shock.

When symbol is marked on a product it denotes a component that may be hot. Touching this component may result in bodily injury.

bold Bold text denotes items that you must select or click in the software, such

as menu items and dialog box options. Bold text also denotes parameter names.

italic Italic text denotes variables, emphasis, a cross-reference, hardware labels,

or an introduction to a key concept. Italic text also denotes text that is a placeholder for a word or value that you must supply.

monospace Text in this font denotes text or characters that you should enter from the

keyboard, sections of code, programming examples, and syntax examples. This font is also used for the proper names of disk drives, paths, directories, programs, subprograms, subroutines, device names, functions, operations, variables, filenames, and extensions.

Chapter 1 About the SCXI-1503

What You Need to Get Started ......................................................................................1-1

National Instruments Documentation ............................................................................1-2

Installing Application Software, NI-DAQ, and the E/M Series DAQ Device ..............1-4

Installing the SCXI-1503 Module into the SCXI Chassis...............................1-4

Installing the Terminal Block..........................................................................1-4

Configuring the SCXI System Software .........................................................1-4

Verifying the SCXI-1503 Installation............................................................................1-5

Chapter 2 Connecting Signals

Analog Input Signal Connections ..................................................................................2-1

Ground-Referencing the Signals .....................................................................2-2

Connecting Resistive Devices to the SCXI-1503 ..........................................................2-2

4-Wire Configuration ......................................................................................2-3

2-Wire Configuration ......................................................................................2-4

3-Wire Resistive Sensor Configuration...........................................................2-5

Lead-Resistance Compensation Using a 3-Wire Resistive Sensor

and Two Matched Current Sources ..............................................................2-6

Front Connector .............................................................................................................2-7

Rear Signal Connector ...................................................................................................2-10

Rear Signal Connector Descriptions ...............................................................2-11

Chapter 3 Configuring and Testing

SCXI-1503 Software-Configurable Settings .................................................................3-1

Common Software-Configurable Settings ......................................................3-1

Gain/Input Range ..............................................................................3-1

Input Coupling ..................................................................................3-2

CJC Source/Value .............................................................................3-2

Auto-Zero..........................................................................................3-2

Configurable Settings in MAX ......................................................................................3-2

NI-DAQmx......................................................................................................3-3

Creating a Global Channel or Task...................................................3-3

Verifying the Signal.......................................................................................................3-4

Verifying the Signal in NI-DAQmx Using a Task or Global Channel ...........3-4

Contents

Chapter 4 Theory of Operation

Rear Signal Connector, SCXIbus Connector, and SCXIbus Interface.......................... 4-3

Digital Control Circuitry ............................................................................................... 4-3

Analog Circuitry............................................................................................................ 4-3

Analog Input Channels.................................................................................... 4-3

Operation of the Current Sources .................................................................................. 4-4

Theory of Multiplexed Operation.................................................................................. 4-4

Measuring Temperature with Resistive Transducers .................................................... 4-5

RTDs ............................................................................................................... 4-5

RTD Measurement Errors ................................................................ 4-6

The Relationship Between Resistance and Temperature in RTDs... 4-6

Thermistors ..................................................................................................... 4-10

Thermistor Measurement Circuits .................................................... 4-11

Resistance/Temperature Characteristic of Thermistors.................... 4-12

Chapter 5 Using the SCXI-1503

Developing Your Application in NI-DAQmx............................................................... 5-1

Typical Program Flowchart ............................................................................ 5-1

General Discussion of Typical Flowchart....................................................... 5-3

Creating a Task Using DAQ Assistant or Programmatically ........... 5-3

Adjusting Timing and Triggering..................................................... 5-3

Configuring Channel Properties ....................................................... 5-4

Acquiring, Analyzing, and Presenting.............................................. 5-7

Completing the Application.............................................................. 5-8

Developing an Application Using LabVIEW ................................................. 5-8

Using a NI-DAQmx Channel Property Node in LabVIEW ............. 5-10

Specifying Channel Strings in NI-DAQmx .................................................... 5-11

Text Based ADEs ............................................................................. 5-11

Programmable NI-DAQmx Properties ............................................. 5-13

Calibration .....................................................................................................................5-13

Internal/Self-Calibration ................................................................................. 5-13

External Calibration ........................................................................................ 5-13

SCXI-1503 User Manual vi ni.com

Appendix A Specifications

Appendix B Removing the SCXI-1503

Appendix C Common Questions

Glossary

Index

Figures

Figure 2-1. 4-Wire Resistive Sensor Connected in a 4-Wire Configuration ...........2-3

Figure 2-2. 2-Wire Resistive Sensor Connected in a 2-Wire Configuration ...........2-4

Figure 2-3. 3-Wire Resistive Sensor Configuration.................................................2-5

Figure 2-4. 3-Wire Configuration Using Matched Current Sources........................2-6

Contents

Figure 4-1. Block Diagram of SCXI-1503...............................................................4-2

Figure 4-2. 2-Wire RTD Measurement....................................................................4-6

Figure 4-3. Resistance-Temperature Curve for a 100 Ω Platinum RTD,

α = 0.00385 ...........................................................................................4-7

Figure 4-4. Resistance-Temperature Curve for a 2,252 Ω Thermistor ....................4-11

Figure 4-5. Thermistor Measurement with Constant Current Excitation ................4-11

Figure 5-1. Typical Program Flowchart for Voltage Measurement Channels......... 5-2

Figure A-1. SCXI-1503 Dimensions ........................................................................A-5

Figure B-1. Removing the SCXI-1503 .....................................................................B-2

Contents

Tables

Table 1-1. Supported SCXI-1503 Terminal Blocks ............................................... 1-4

Table 2-1. Front Signal Pin Assignments .............................................................. 2-8

Table 2-2. Signal Descriptions ............................................................................... 2-9

Table 2-3. Rear Signal Pin Assignments................................................................ 2-10

Table 2-4. SCXI-1503 50-Pin Rear Connector Signals ........................................ 2-11

Table 4-1. Platinum RTD Types ............................................................................ 4-8

Table 5-1. NI-DAQmx Voltage Measurement Properties ..................................... 5-4

Table 5-2. NI-DAQmx RTD Measurement Properties ......................................... 5-5

Table 5-3. NI-DAQmx Thermistor Measurement Properties ............................... 5-6

Table 5-4. NI-DAQmx Thermocouple Measurement Properties .......................... 5-7

Table 5-5. Programming a Task in LabVIEW ...................................................... 5-8

Table A-1. RTD Measurement Accuracy ............................................................... A-2

SCXI-1503 User Manual viii ni.com

About the SCXI-1503

This manual describes the electrical and mechanical aspects of the SCXI-1503 module and contains information concerning its installation and operation. The SCXI-1503 module provides 16 differential input channels and 16 channels of 100 μA current excitation and one cold junction sensor channel. The SCXI-1503 is ideally suited for measuring resistive transducers, such as RTDs or thermistors.

Each channel has an amplifier with a selectable gain of 1 or 100 and a lowpass filter with a 5 Hz cutoff frequency to reject 50/60 Hz noise.

The SCXI-1503 can programmatically connect each input to ground, which greatly improves its accuracy by enabling a self-calibration of each input to reduce offset drift errors.

You can multiplex several SCXI-1503 modules and other SCXI modules into a single channel on the DAQ device, greatly increasing the number of analog input signals that you can digitize.

Detailed specifications of the SCXI-1503 modules are listed in Appendix A, Specifications.

What You Need to Get Started

To set up and use the SCXI-1503, you need the following items:

❑ Hardware

– SCXI-1503 module

– One of the following terminal blocks:

• SCXI-1306—front-mount terminal block with screw terminal connectivity.

• SCXI-1310—custom kit for custom connectivity.

• TBX-96—DIN EN mount terminal block with screw terminal connectivity.

– SCXI or PXI/SCXI combo chassis

Chapter 1 About the SCXI-1503

– One of the following:

• SCXI-1600

• E/M Series DAQ device

– Computer

– Cabling, cable adapter, and sensors as required for your

application

❑ Software

– NI-DAQ 8.1 or later

– Application software, such as LabVIEW, LabWindows

Measurement Studio, or other programming environments

❑ Documentation

– Read Me First: Safety and Radio-Frequency Interference

– DAQ Getting Started Guide

– SCXI Quick Start Guide

– SCXI-1503 User Manual

– Terminal block installation guide

– Documentation for your software

™

/CVI™,

❑ Tools

– Wire cutter

– Wire stripper

– Flathead screwdriver

– Phillips screwdriver

National Instruments Documentation

The SCXI-1503 User Manual is one piece of the documentation set for data acquisition (DAQ) systems. You could have any of several types of manuals depending on the hardware and software in the system. Use the manuals you have as follows:

• The SCXI Quick Start Guide—This document contains a quick overview for setting up an SCXI chassis, installing SCXI modules and terminal blocks, and attaching sensors. It also describes setting up the SCXI system in MAX.

SCXI-1503 User Manual 1-2 ni.com

Chapter 1 About the SCXI-1503

• SCXI or PXI/SCXI chassis manual—Read this manual for maintenance information on the chassis and for installation instructions.

• The DAQ Getting Started Guide—This document has information on installing NI-DAQ and the E/M Series DAQ device. Install these before you install the SCXI module.

• The SCXI hardware user manuals—Read these manuals for detailed information about signal connections and module configuration. They also explain, in greater detail, how the module works and contain application hints.

• Accessory installation guides or manuals—Read the terminal block and cable assembly installation guides. They explain how to physically connect the relevant pieces of the system. Consult these guides when you are making the connections.

• The E/M Series DAQ device documentation—This documentation has detailed information about the DAQ device that plugs into or is connected to the computer. Use this documentation for hardware installation and configuration instructions, specification information about the DAQ device, and application hints.

• Software documentation—You may have both application software and NI-DAQ software documentation. National Instruments (NI) application software includes LabVIEW, LabWindows/CVI, and Measurement Studio. After you set up the hardware system, use either your application software documentation or the NI-DAQ documentation to help you write your application. If you have a large, complex system, it is worthwhile to look through the software documentation before you configure the hardware.

• One or more of the following help files for software information:

– Start»Programs»National Instruments»NI-DAQ»

NI-DAQmx Help

– Start»Programs»National Instruments»NI-DAQ»

Traditional NI-DAQ User Manual

– Start»Programs»National Instruments»NI-DAQ»

Traditional NI-DAQ Function Reference Help

You can download NI documents from the latest version of NI-DAQ, click Drivers and Updates at

ni.com/manuals. To download

ni.com.

Chapter 1 About the SCXI-1503

Installing Application Software, NI-DAQ, and the E/M Series DAQ Device

Refer to the DAQ Getting Started Guide packaged with the NI-DAQ software to install your application software, NI-DAQ driver software, and the DAQ device to which you will connect the SCXI-1503. NI-DAQ 8.1 or later is required to configure and program the SCXI-1503 module. If you do not have NI-DAQ 8.1 or later, you can either contact an NI sales representative to request it on a CD or download the latest NI-DAQ version from

ni.com.

Note Refer to the Read Me First: Radio-Frequency Interference document before

removing equipment covers or connecting or disconnecting any signal wires.

Installing the SCXI-1503 Module into the SCXI Chassis

Refer to the SCXI Quick Start Guide to install your SCXI-1503 module.

Installing the Terminal Block

Table 1-1 shows the supported SCXI-1503 terminal blocks. Refer to the SCXI Quick Start Guide and the terminal block installation guide for more information about the terminal block.

Table 1-1. Supported SCXI-1503 Terminal Blocks

Terminal Block CJC Sensor Measurement Type

SCXI-1306 Ye s Resistive temperature

measurements

TBX-96 No Custom signals

SCXI-1310 No

Configuring the SCXI System Software

Refer to the SCXI Quick Start Guide and the user manuals of the modules in your application to configure and verify them in software.

SCXI-1503 User Manual 1-4 ni.com

Verifying the SCXI-1503 Installation

Refer to the SCXI Quick Start Guide, for details about testing the SCXI chassis and module installation in software. Refer to Chapter 3,

Configuring and Testing, for details about setting up a task and verifying

the input signal.

Chapter 1 About the SCXI-1503

Connecting Signals

This chapter describes the input and output signal connections to the SCXI-1503 module with the module front connector and rear signal connector. This chapter also includes connection instructions for the signals on the SCXI-1503 module when using the SCXI-1306 terminal block.

In addition to this section, refer to the installation guide of the terminal block for detailed information regarding connecting the signals. If you are using a custom cable or connector block, refer to the Front Connector section.

Analog Input Signal Connections

Each differential input (AI+ and AI–) goes to a separate filter and amplifier that is multiplexed to the module output buffer. If the terminal block has a temperature sensor, the sensor output—connected to pins A3 and/or A4 (CJ SENSOR)—is also filtered and multiplexed to the module output buffer.

The differential input signal range of an SCXI-1503 module input channel is ±10 V when using a gain of 1 or ±0.1 V when using a gain of 100. This differential input range is the maximum measurable voltage difference between the positive and negative channel inputs. The common-mode input signal range of an SCXI-1503 module input channel is ±10 V. This common-mode input range for either positive or negative channel input is the maximum input voltage that results in a valid measurement. Each channel includes input protection circuitry to withstand the accidental application of voltages up to ±42 VDC powered on or ±25 VDC powered off.

Caution Exceeding the input damage level (±42 VDC powered on or ±25 VDC powered

off between input channels and chassis ground) can damage the SCXI-1503 module, the SCXIbus, and the DAQ device. NI is not liable for any injuries resulting from such signal connections.

Chapter 2 Connecting Signals

Note Exceeding the differential or common-mode input channel ranges results in a

distorted signal measurement, and can also increase the settling time requirement of the connected E/M Series DAQ device.

Ground-Referencing the Signals

Do not ground signals that are already ground-referenced; doing so results in a ground loop, which can adversely affect the measurement accuracy. Directly grounding floating signals to the chassis ground without using a bias resistor is not recommended as this can result in noisy readings

Connecting Resistive Devices to the SCXI-1503

You can connect resistive devices to the SCXI signal conditioning system in a 4-, 2-, or 3-wire configuration. Figures 2-1 through 2-4 illustrate various ways to connect sensors for current excitation and voltage measurements using the SCXI-1503 with the SCXI-1306 terminal block.

Refer to the appropriate ADE and SCXI documentation for information concerning setting appropriate voltage gains for the analog inputs.

You can use the SCXI-1306 terminal block to make signal connections to the SCXI-1503. When using the SCXI-1306 terminal block, refer to the SCXI-1306 Terminal Block Installation Guide.

SCXI-1503 User Manual 2-2 ni.com

4-Wire Configuration

The 4-wire configuration, also referred to as a Kelvin connection, is shown in Figure 2-1. The 4-wire configuration uses one pair of wires to deliver the excitation current to the resistive sensor and uses a separate pair of wires to sense the voltage across the resistive sensor. Because of the high input impedance of the differential amplifier, negligible current flows through the sense wires. This results in a very small lead-resistance voltage drop error. The main disadvantage of the 4-wire connection is the greater number of field wires required.

Chapter 2 Connecting Signals

+ –

SCXI-1503

Channel X

I = 100 µA

External Sensor SCXI-1306

IEX+

AI+

AI–

IEX–

CH X

Figure 2-1. 4-Wire Resistive Sensor Connected in a 4-Wire Configuration

Chapter 2 Connecting Signals

2-Wire Configuration

The basic 2-wire configuration is shown in Figure 2-2. In this configuration an error voltage (V excitation current (I

the error voltage is:

This is the most commonly used configuration for connecting thermistors to a signal conditioning system because the large sensitivity of thermistors usually results in the introduction of a negligible error by the lead resistances.

RTDs typically have a much smaller sensitivity and nominal resistance than thermistors, therefore a 2-wire configuration usually results in the introduction of larger errors by the lead resistance.

) is introduced into the measurement equal to the

) times the sum of the two lead resistances, RL1 and

. If we assume equal lead resistances, RL1= RL2= RL, the magnitude of

2RLI

SCXI-1306External Sensor SCXI-1503

IEX+

AI+

AI–

IEX–

Channel X

+ –

I = 100 µA

CH X

Figure 2-2. 2-Wire Resistive Sensor Connected in a 2-Wire Configuration

SCXI-1503 User Manual 2-4 ni.com

3-Wire Resistive Sensor Configuration

If you are using a 3-wire resistive sensor, you can reduce the error voltage by one-half over the 2-wire measurement by connecting the device as shown in Figure 2-3. In this configuration, very little current flows through

and therefore RL2 is the only lead resistance that introduces an error into

the measurement. The resulting measurement error is:

VE RL2I

Chapter 2 Connecting Signals

SCXI-1306External Sensor

IEX+

AI+

AI–

IEX–

CH X

+ –

SCXI-1503

Channel X

I = 100 µA

Figure 2-3. 3-Wire Resistive Sensor Configuration

Chapter 2 Connecting Signals

Lead-Resistance Compensation Using a 3-Wire Resistive Sensor and Two Matched Current Sources

You can compensate for the errors introduced by lead-resistance voltage drops by using a 3-wire resistive sensor and two matched current sources connected as shown in Figure 2-4.

SCXI-1306External Sensor

EX0+

AI0+

AI0–

EX0–

EX1+

AI1+

AI1–

EX1–

+ –

SCXI-1503

I = 100 µA

Figure 2-4. 3-Wire Configuration Using Matched Current Sources

SCXI-1503 User Manual 2-6 ni.com

Chapter 2 Connecting Signals

In this configuration, the lead-resistance voltage drop across RL3 is converted into a common-mode voltage that is rejected by the differential amplifier. Also, the polarity of the lead-resistance voltage drops across R and R

are series opposing, relative to the inputs of the differential

amplifier, eliminating their effect on the voltage measured across R

Note R

and RL2 are assumed to be equal.

The effectiveness of this method depends on the matching of the current sources. Each current source on the SCXI-1503 has an accuracy of ±0.05%. This accuracy results in a worst-case matching of ±0.1%. Refer to the Chapter 4, Theory of Operation, for accuracy considerations of RTDs and thermistors.

Front Connector

The pin assignments for the SCXI-1503 front signal connector are shown in Table 2-1.

Note Do not make any connections to RSVD pins.

Chapter 2 Connecting Signals

Table 2-1. Front Signal Pin Assignments

Front Connector Diagram Pin Number Column A Column B Column C

32 GND AI0– AI0+

Column

A B C

NC—no connection

RSVD—reserved

31 GND AI1– AI1+

30 GND AI2– AI2+

29 GND AI3– AI3+

28 RSVD AI4– AI4+

27 RSVD AI5– AI5+

26 RSVD AI6– AI6+

25 RSVD AI7– AI7+

24 NC IEX0– IEX0+

23 NC IEX1– IEX1+

22 NC IEX2– IEX2+

21 NC IEX3– IEX3+

20 RSVD IEX4– IEX4+

19 RSVD IEX5 IEX5+

18 NC IEX6– IEX6+

17 NC IEX7– IEX7+

16 GND AI8– AI8+

15 GND AI9– AI9+

14 GND AI10– AI10+

13 GND AI11– AI11+

12 NC AI12– AI12+

11 NC AI13– AI13+

10 NC AI14– AI14+

9 NC AI15– AI15+

8 NC IEX8– IEX8+

7 NC IEX9– IEX9+

6 NC IEX10– IEX10+

5 NC IEX11– IEX11+

4 CJ SENSOR IEX12– IEX12+

3 CJ SENSOR IEX13– IEX13+

2 CGND IEX14– IEX14+

1 +5 V IEX15– IEX15+

SCXI-1503 User Manual 2-8 ni.com

Chapter 2 Connecting Signals

Table 2-2. Signal Descriptions

Pin Signal Name Description

A1 +5 V +5 VDC Source—Used to power circuitry on the

terminal block. 0.1 mA of source not protected.

A13 – A16,

GND Ground—Tied to the SCXI module ground.

A29 – A32

A1, A19, A20, A25 – A28

RSVD Reserved—This pin is reserved. Do not connect

any signal to this pin.

A2 C GND Chassis Ground—Connects to the SCXI chassis.

B24 – B17, B8 – B1

IEX<0..7> –, IEX<8..15> –

Negative Excitation—Connects to the channel ground reference. This is the return path for the corresponding IEX+ channel.

C24 – C17, C8 – C1

IEX<0..7> +, IEX<8..15> +

Positive Excitation—Connects to the positive current output of the channel.

A3, A4 CJ SENSOR Cold-Junction Temperature Sensor

Input—Connects to the temperature sensor of the terminal block.

B30 – B 25, B16 – B9

C32 – C25, C16 – C9

AI <0..7> –, AI <8..15> –

AI <0..7> +, AI <8..15> +

Negative Input Channels—Negative side of differential input channels.

Positive Input Channels—Positive side of differential input channels.

Chapter 2 Connecting Signals

Rear Signal Connector

Table 2-3 shows the SCXI-1503 module rear signal connector pin assignments.

Table 2-3. Rear Signal Pin Assignments

Rear Connector Diagram Signal Name Pin Number Pin Number Signal Name

AI GND 1 2 AI GND

AI 0 + 3 4 AI 0 –

NC 5 6 NC

910

11 12

13 14

15 16

17 18

19 20

21 22

23 24

25 26

27 28

29 30

31 32

33 34

35 36

37 38

39 40

41 42

43 44

45 46

47 48

49 50

NC 7 8 NC

NC 9 10 NC

NC 11 12 NC

NC 13 14 NC

NC 15 16 NC

NC 17 18 NC

NC 19 20 NC

NC 21 22 NC

NC 23 24 DIG GND

SER DAT IN 25 26 SER DAT OUT

DAQ D*/A 27 28 NC

SLOT 0 SEL* 29 30 NC

NC 31 32 NC

DIG GND 33 34 NC

NC 35 36 SCAN CLK

SER CLK 37 38 NC

NC 39 40 NC

NC 41 42 NC

RSVD 43 44 NC

NC 45 46 RSVD

NC means no connection.

RSVD means reserved.

SCXI-1503 User Manual 2-10 ni.com

NC 47 48 NC

NC 49 50 NC

Chapter 2 Connecting Signals

Rear Signal Connector Descriptions

The rear signal connector on the cabled module is the interface between the DAQ device and all modules in the SCXI chassis. AI 0 is used to differentially multiplex all 16 channels, the CJ sensor, and analog signals from the modules to the connected DAQ device.

The communication signals between the DAQ device and the SCXI system are listed in Table 2-4. If the DAQ device is connected to the SCXI-1503, these digital lines are unavailable for general-purpose digital I/O.

Table 2-4. SCXI-1503 50-Pin Rear Connector Signals

NI-DAQmx

SCXI

Signal Name

1, 2 AI GND AI GND — Analog input ground—connects to

3 AI 0 + AI 0 + Input Channel 0 positive—used to

Device Signal

Name

Direction Description

the analog input ground of the DAQ device.

differentially multiplex all 16 channels, the CJ sensor, and analog signals from the modules to the connected DAQ device.

4 AI 0 – AI 0 – Input Channel 0 negative—used to

differentially multiplex all 16 channels, the CJ sensor, and analog signals from the modules to the connected DAQ device.

24, 33 DIG GND D GND — Digital ground—these pins supply

the reference for E/M Series DAQ device digital signals and are connected to the module digital ground.

25 SER DAT IN P0.0 Input Serial data in—this signal taps into

the SCXIbus MOSI line to send serial input data to a module or Slot 0.

Chapter 2 Connecting Signals

Table 2-4. SCXI-1503 50-Pin Rear Connector Signals (Continued)

SCXI

Signal Name

NI-DAQmx

Device Signal

Name

Direction Description

26 SER DAT OU

P0.4 Output Serial data out—this signal taps

into the SCXIbus MISO line to accept serial output data from a module.

27 DAQ D*/A P0.1 Input Board data/address line—this

signal taps into the SCXIbus D*/A line to indicate to the module whether the incoming serial stream is data or address information.

29 SLOT 0 SEL* P0.2 Input Slot 0 select—this signal taps into

the SCXIbus INTR* line to indicate whether the information on MOSI is being sent to a module or Slot 0.

36 SCAN CLK AI HOLD COMP,

AI HOLD

Input Scan clock—a rising edge indicates

to the scanned SCXI module that the E/M Series DAQ device has taken a sample and causes the module to advance channels.

37 SER CLK EXTSTROBE* Input Serial clock—this signal taps into

the SCXIbus SPICLK line to clock the data on the MOSI and MISO lines.

43, 46 RSVD RSVD Input Reserved.

Note: All other pins are not connected.

SCXI-1503 User Manual 2-12 ni.com

Configuring and Testing

This chapter discusses configuring the SCXI-1503 in MAX using NI-DAQmx, creating and testing a virtual channel, global channel, and/or task.

Notes You must have NI-DAQmx 8.1 or later installed.

Refer to the SCXI Quick Start Guide if you have not already configured the chassis.

SCXI-1503 Software-Configurable Settings

This section describes how to set the gain/input signal range and how to configure your software for compatible sensor types. It also describes how to perform configuration of these settings for the SCXI-1503 in NI-DAQmx. For more information on the relationship between the settings and the measurements and how to configure settings in your application, refer to Chapter 4, Theory of Operation.

Common Software-Configurable Settings

This section describes the most frequently used software-configurable settings for the SCXI-1503. Refer to Chapter 5, Using the SCXI-1503, for a complete list of software-configurable settings.

Gain/Input Range

Gain/input range is a software-configurable setting that allows you to choose the appropriate amplification to fully utilize the range of the E/M Series DAQ device. In most applications NI-DAQ chooses and sets the gain for you determined by the input range. This feature is described in Chapter 5, Using the SCXI-1503. Otherwise, you should determine the appropriate gain using the input signal voltage range and the full-scale limits of the SCXI-1503 output. You can select a gain of 1 or 100 on a per channel basis.

Chapter 3 Configuring and Testing

Input Coupling

The front end of the SCXI-1503 includes a software configurable switch that allows you to programmatically connect the input channels of the SCXI-1503 to either the front connector or internal ground. When using autozero, the coupling mode is set automatically. Refer to Table 5-1,

NI-DAQmx Voltage Measurement Properties, for details about the

available input coupling modes supported by the SCXI-1503.

CJC Source/Value

When using a terminal block that has a CJ sensor for thermocouple measurements, you can set the CJC source as internal, which scans the sensor at the beginning of each measurement and scales the readings accordingly.

Auto-Zero

Setting the Auto-zero mode to Once improves the accuracy of the measurement. With auto-zero enabled, the inputs of the SCXI-1503 are internally grounded. The driver makes a measurement when the task begins and then subtracts the measured offset from all future measurements.

Configurable Settings in MAX

Note If you are not using an NI ADE or are using an unlicensed copy of an NI ADE,

additional dialog boxes from the NI License Manager appear allowing you to create a task or global channel in unlicensed mode. These messages continue to appear until you install version 8.1 or later of an NI ADE.

This section describes where you can access each software-configurable setting in MAX. The location of the settings varies depending on the version of NI-DAQmx you use. Refer to the DAQ Getting Started Guide and the SCXI Quick Start Guide for more information on installing and configuring the hardware. You can use DAQ Assistant to graphically configure common measurement tasks, channels, or scales.

SCXI-1503 User Manual 3-2 ni.com

NI-DAQmx

Note All software-configurable settings are not configurable both ways. This section only

discusses settings in MAX. Refer to Chapter 5, Using the SCXI-1503, for information on using functions in your application.

Chapter 3 Configuring and Testing

Using NI-DAQmx, you can configure software settings such as sensor type and gain/input signal range in the following ways:

• Task or global channel in MAX

• Functions in your application

Dependent upon the terminal block configuration use, you can use the SCXI-1503 module to make the following types of measurements:

• Voltage input

• Thermocouple

•RTD

• Thermistors

Creating a Global Channel or Task

To create a new voltage, temperature, or current input NI-DAQmx global task or channel, complete the following steps:

1. Double-click Measurement & Automation on the desktop.

2. Right-click Data Neighborhood and select Create New.

3. Select NI-DAQmx Task or NI-DAQmx Global Channel, and click Next.

4. Select Analog Input.

5. Select one of the following:

• Voltage

• Temperature and then select one of the following:

– Iex Thermistor

– RTD

– Thermocouple

– Vex Thermistor

6. If you are creating a task, you can select a range of channels by holding down the <Shift> key while selecting the channels. You can select multiple individual channels by holding down the <Ctrl> key while

Chapter 3 Configuring and Testing

7. Name the task or channel and click Finish.

8. Select the channel(s) you want to configure. You can select a range of

Note If you want to add channels of various measurement types to the same task, click

the Add Channels button to select the measurement type for the additional channels.

9. Enter the specific values for your application in the Settings tab.

10. If you are creating a task and want to set timing or triggering controls,

11. Click Device and select Auto Zero mode if desired.

selecting channels. If you are creating a channel, you can only select one channel. Click Next.

channels by holding down the <Shift> key while selecting the channels. You can select multiple individual channels by holding down the <Ctrl> key while selecting channels.

Context help information for each setting is provided on the right side of the screen. Configure the input signal range using either NI-DAQmx Task or NI-DAQmx Global Channel. When you set the minimum and maximum range of NI-DAQmx Task or NI-DAQmx Global Channel, the driver selects the best gain for the measurement. You also can set it through your application.

enter the values in the Task Timing and Task Triggering tabs.

Verifying the Signal

This section describes how to take measurements using test panels in order to verify signal, and configuring and installing a system in NI-DAQmx.

Verifying the Signal in NI-DAQmx Using a Task or Global Channel

You can verify the signals on the SCXI-1503 using NI-DAQmx by completing the following steps:

1. Expand Data Neighborhood.

2. Expand NI-DAQmx Tasks.

3. Click the task you created in the Creating a Global Channel or Task section.

4. Select the channel(s) you want to verify. You can select a block of channels by holding down the <Shift> key or multiple channels by holding down the <Ctrl> key. Click OK.

5. Enter the appropriate information on the Settings and Device tab.

SCXI-1503 User Manual 3-4 ni.com

Chapter 3 Configuring and Testing

6. Click the Test button.

7. Click the Start button.

8. After you have completed verifying the channels, click the Stop

button.

You have now verified the SCXI-1503 configuration and signal connection.

Note For more information on how to further configure the SCXI-1503, or how to use

LabVIEW to configure the module and take measurements, refer to Chapter 5, Using the

SCXI-1503.

Theory of Operation

This chapter provides a brief overview and a detailed discussion of the circuit features of the SCXI-1503 module. Refer to Figure 4-1 while reading this section.

Chapter 4 Theory of Operation

Rear Signal Connector

AI 0 +

AI 0 –

Source

Calibration

Mux

Buffer Buffer

AI GND

Switch Mux

OUT REF

Switch

32-to-1 Mux

Switch

Buffer

SCXIbus Connector

AB 0 +

AB 0 –

Interface

SCXIbus

and Control

Digital Interface

Input Select

Calibration EEPROM

Gain Select

Buffer

AI 0 +

Filter

Lowpass

Inst.

Amp

AI 0 –

Gain 0

–

AI 15 +

Filter

Lowpass

Inst.

Amp

AI 15 –

–

Gain 31

IEX 0 +

Input Protection

and Lowpass Filter

IEX 15 +

100 µA

IEX 15 –

CJSENSOR

100 µA

IEX 0 –

Front Signal Connector

Figure 4-1. Block Diagram of SCXI-1503

SCXI-1503 User Manual 4-2 ni.com

Chapter 4 Theory of Operation

The major components of the SCXI-1503 modules are as follows:

• Rear signal connector

• SCXIbus connector

• SCXIbus interface

• Digital control circuitry

• Analog circuitry

The SCXI-1503 modules consist of 16 multiplexed input channels, each with a software-programmable gain of 1 or 100. Each input channel has its own lowpass filter. Each channel has a fixed 100 μA current excitation. The SCXI-1503 modules also have a digital section for automatic control of channel scanning, temperature sensor selection, gain selection, and auto-zero mode.

Rear Signal Connector, SCXIbus Connector, and SCXIbus Interface

The SCXIbus controls the SCXI-1503 module. The SCXIbus interface connects the rear signal connector to the SCXIbus, allowing a DAQ device to control the SCXI-1503 module and the rest of the chassis.

Digital Control Circuitry

The digital control circuitry consists of the Address Handler and registers that are necessary for identifying the module, reading/setting calibration information, setting the gain, and selecting the appropriate channel.

Analog Circuitry

The analog circuitry per channel consists of a fixed lowpass filter and an amplifier with a software selectable gain of 1 or 100. The CJ SENSOR channel has a lowpass filter buffered by a unity gain amplifier. The channels and CJ SENSOR are multiplexed to a single output buffer.

Analog Input Channels

Each of the 16 differential analog input channels feeds to a separate instrumentation amplifier with a programmable gain of 1 or 100. Each channel has a fixed 100 μA current excitation. Then the signal passes through a fixed 2-pole, 5 Hz lowpass filter.

Chapter 4 Theory of Operation

The CJ SENSOR input channel is used to read the sensor temperature from the terminal block. The temperature sensor is for cold-junction compensation of thermocouple measurements. The CJ SENSOR channel also passes through a 5 Hz lowpass filter to reject unwanted noise on the SCXI-1503. Along with the other 16 input channels, the CJ SENSOR is multiplexed to the output buffer, where it can be read by the DAQ device.

Operation of the Current Sources

The current sources on the SCXI-1503 continuously provide 16 channels of 100 μA current excitation. These current sources are on whenever the SCXI chassis is powered-on. The current sources on the SCXI-1503 are designed to be accurate to within ±0.05% of the specified value with a temperature drift of no more than ±5 ppm/°C. The high accuracy and stability of these current sources makes them especially well suited to measuring resistance to a high degree of accuracy.

Theory of Multiplexed Operation

In multiplexed mode, all input channels of an SCXI module are multiplexed into a single analog input channel of the DAQ device. Multiplexed mode operation is ideal for high channel count systems. Multiplexed mode is typically used for performing scanning operations with the SCXI-1503. The power of SCXI multiplexed mode scanning is its ability to route many input channels to a single channel of the DAQ device.

The multiplexing operation of the analog input signals is performed entirely by multiplexers in the SCXI modules, not inside the DAQ device or SCXI chassis. In multiplexed mode the SCXI-1503 scanned channels are kept by the NI-DAQ driver in a scan list. Immediately prior to a multiplexed scanning operation, the SCXI chassis is programmed with a module scan list that controls which module sends its output to the SCXIbus during a scan through the cabled SCXI module.

The list can contain channels in any physical order and the multiplexer can sequence the channel selection from the scan list in any order. The ordering of scanned channels need not be sequential. Channels can occur multiple times in a single scan list. The scan list can contain an arbitrary number of channels for each module entry in the scan list, limited to a total of 512 channels per DAQ device. This is referred to as flexible scanning (random scanning). Not all SCXI modules provide flexible scanning.

SCXI-1503 User Manual 4-4 ni.com

Chapter 4 Theory of Operation

The module includes first-in first-out (FIFO) memory for storing the channel scan list defined in your application code. NI-DAQ drivers load the FIFO based on the channel assignments you make in your application. You need not explicitly program the module FIFO as this is done automatically for you by the NI-DAQ driver.

When you configure a module for multiplexed mode operation, the routing of multiplexed signals to the DAQ device depends on which module in the SCXI system is cabled to the DAQ device. There are several possible scenarios for routing signals from the multiplexed modules to the DAQ device.

If the scanned SCXI-1503 module is not directly cabled to the DAQ device, the module sends its signals through the SCXIbus to the cabled module. The cabled module, whose routing is controlled by the SCXI chassis, routes the SCXIbus signals to the DAQ device through the AI 0 pin on its rear signal connector.

If the DAQ device scans the cabled module, the module routes its input signals through the AI 0 pin on its rear signal connector to a single channel on the DAQ device.

Measuring Temperature with Resistive Transducers

This section discusses RTDs and thermistors, and describes accuracy considerations when connecting resistive transducers to the signal conditioning system.

RTDs

A resistive-temperature detector (RTD) is a temperature-sensing device whose resistance increases with temperature. An RTD consists of a wire coil or deposited film of pure metal. RTDs are made of different metals and have different resistances, but the most popular RTD is made of platinum and has a nominal resistance of 100 Ω at 0 °C.

RTDs are known for their excellent accuracy over a wide temperature range. Some RTDs have accuracies as high as 0.01 Ω (0.026 °C) at 0 °C. RTDs are also extremely stable devices. Common industrial RTDs drift less than 0.1 °C/year, and some models are stable to within 0.0025 °C/year.

RTDs are sometimes difficult to measure because they have relatively low nominal resistance (commonly 100 Ω) that changes only slightly with temperature (less than 0.4 Ω/°C). To accurately measure these small

Chapter 4 Theory of Operation

changes in resistance, you must use special configurations that minimize measured errors caused by lead-wire resistance.

RTD Measurement Errors

Because the RTD is a resistive device, you must pass a current through the device and monitor the resulting voltage. However, any resistance in the lead wires that connect the measurement system to the RTD adds error to the readings. For example, consider a 2-wire RTD element connected to a measurement system that also supplies a constant current, I RTD. As shown in Figure 4-2, the voltage drop across the lead resistances (labeled R

) adds an error voltage to the measured voltage.

–

, to excite the

Figure 4-2. 2-Wire RTD Measurement

For example, a lead resistance of 0.3 Ω in each wire adds a 0.6 Ω error to the resistance measurement. For a platinum RTD at 0 °C with α = 0.00385, the lead resistance equates to an error of approximately

0.6 Ω

----------------------------- 1.6 °C=

0.385 Ω / °C

Chapter 2, Connecting Signals, describes different ways of connecting resistive devices to the SCXI system.

The Relationship Between Resistance and Temperature in RTDs

Compared to other temperature-measurement devices, the output of an RTD is relatively linear with respect to temperature. The temperature coefficient, called alpha (α), differs between RTD curves. Although various manufacturers specify alpha differently, alpha is most commonly

SCXI-1503 User Manual 4-6 ni.com

Chapter 4 Theory of Operation

defined as the change in RTD resistance from 0 to 100 °C, divided by the resistance at 0 °C, divided by 100 °C:

–

α( Ω /Ω/°C)

-----------------------------=

100R0

100 ° C×

where

is the resistance of the RTD at 100 °C.

100

is the resistance of the RTD at 0 °C.

For example, a 100 Ω platinum RTD with α = 0.003911 has a resistance of

139.11 Ω at 100 °C.

Figure 4-3 displays a typical resistance-temperature curve for a 100 Ω platinum RTD.

480

400

320

240

160

320 400 480 560 640 720 800 8800 80 160 240 960

Figure 4-3. Resistance-Temperature Curve for a 100 Ω Platinum RTD, α = 0.00385

Chapter 4 Theory of Operation

Although the resistance-temperature curve is relatively linear, accurately converting measured resistance to temperature requires curve fitting. The following Callendar-Van Dusen equation is commonly used to approximate the RTD curve:

RTR01 AT BT2CT 100–()

++ +[]=

where

is the resistance of the RTD at temperature T.

is the resistance of the RTD at 0 °C.

A, B, and C are the Callendar-Van Dusen coefficients shown in

Tabl e 4-1.

T is the temperature in °C.

Table 4-1 lists the RTD types and their corresponding coefficients.

Table 4-1. Platinum RTD Types

Temperature

Coefficient of

Standard

IEC-751 DIN 43760 BS 1904 ASTM-E1137

Resistance

(TCR, PPM)

3851 100 Ω

Typical

1000 Ω

Callendar-Van

Dusen Coefficient

A = 3.9083 × 10

B = –5.775 × 10

C = –4.183 × 10

EN-60751

Low cost vendor compliant

3750 1000 Ω A = 3.81 × 10

B = –6.02 × 10

C = –6.0 × 10

JISC 1604 3916 100 Ω A = 3.9739 × 10

B = –5.870 × 10

C = –4.4 × 10

US Industrial Standard D-100 American

3920 100 Ω A = 3.9787 × 10

B = –5.8686 × 10

C = –4.167 × 10

–3

–7

–12

–3

–7

–12

–3

–7

–12

–3

–7

–12

SCXI-1503 User Manual 4-8 ni.com

Chapter 4 Theory of Operation

Table 4-1. Platinum RTD Types (Continued)

Temperature

Coefficient of

Resistance

Standard

US Industrial

(TCR, PPM)

3911 100 Ω A = 3.9692 × 10 Standard American

ITS-90 3928 100 Ω A = 3.9888 × 10

No standard. Check TCR.

Typical

Callendar-Van

Dusen Coefficient

B = –5.8495 × 10

C = –4.233 × 10

B = –5.915 × 10

C = –3.85 × 10

–12

–3

–7

–12

–3

–7

For temperatures above 0 °C, coefficient C equals 0, reducing this equation to a quadratic. If you pass a known current, I measure the output voltage developed across the RTD, V

, through the RTD and

, you can solve

for T as follows:

-------

–

------------------------------------------------------------------------------------------------=

⎛⎞

–0.5 R

⎜⎟

⎝⎠

–+

A24R0BR

⎛⎞ ⎝⎠

-------–

where

is the measured RTD voltage.

is the excitation current.

Chapter 4 Theory of Operation

Thermistors

A thermistor is a piece of semiconductor made from metal oxides, pressed into a small bead, disk, wafer, or other shape, sintered at high temperatures, and finally coated with epoxy or glass. The resulting device exhibits an electrical resistance that varies with temperature.

There are two types of thermistors: negative temperature coefficient (NTC) thermistors, whose resistance decreases with increasing temperature, and positive temperature coefficient (PTC) thermistors, whose resistance increases with increasing temperature. NTC thermistors are more commonly used than PTC thermistors, especially for temperature measurement applications.

A main advantage of thermistors for temperature measurement is their extremely high sensitivity. For example, a 2,252 Ω thermistor has a sensitivity of –100 Ω/°C at room temperature. Higher resistance thermistors can exhibit temperature coefficients of –10 kΩ/°C or more. In comparison, a 100 Ω platinum RTD has a sensitivity of only 0.4 Ω/°C.

Also, the physically small size and low thermal mass of a thermistor bead allows a very fast response to temperature changes.

Another advantage of the thermistor is its relatively high resistance. Thermistors are available with base resistances (at 25 °C) ranging from hundreds to millions of ohms. This high resistance diminishes the effect of inherent resistances in the lead wires, which can cause significant errors with low resistance devices such as RTDs. For example, while RTD measurements typically require 3- or 4-wire connections to reduce errors caused by lead-wire resistances, 2-wire connections to thermistors are usually adequate.

The major trade-off for the high resistance and sensitivity of the thermistor is its highly nonlinear output and relatively limited operating range. Depending on the type of thermistor, the upper range is typically limited to around 300 °C. Figure 4-4 shows the resistance-temperature curve for a 2,252 Ω thermistor. The curve of a 100 Ω RTD is also shown for comparison.

SCXI-1503 User Manual 4-10 ni.com

Chapter 4 Theory of Operation

Figure 4-4. Resistance-Temperature Curve for a 2,252 Ω Thermistor

The thermistor has been used primarily for high-resolution measurements over limited temperature ranges. However, continuing improvements in thermistor stability, accuracy, and interchangeability have prompted increased use of thermistors in a variety of applications.

Thermistor Measurement Circuits

This section details information about thermistor measurement circuits. The most common technique is to use a current-source, and measure the voltage developed across the thermistor. Figure shows the measured voltage V

equals RT × IEX.

–

V0 = I

x R

Thermisto

Figure 4-5. Thermistor Measurement with Constant Current Excitation

Chapter 4 Theory of Operation

The maximum resistance of the thermistor is determined from the current excitation value and the maximum voltage range of the input device. When using the SCXI-1503, the maximum measurable resistance is 100 kΩ.

The level of the voltage output signal depends directly on the thermistor resistance and magnitude of the current excitation. Do not use a higher level of current excitation in order to produce a higher level output signal because the current causes the thermistor to heat internally, leading to temperature-measurement errors. This phenomena is called self-heating. When current passes through the thermistor, power dissipated by the thermistor equaling (I

RT), heats the thermistor.

Thermistors, with their small size and high resistance, are particularly prone to these self-heating errors. Manufacturers typically specify this self-heating as a dissipation constant, which is the power required to heat the thermistor 1 °C from ambient temperature (mW/°C). The dissipation constant depends heavily on how easily heat is transferred away from the thermistor, so the dissipation constant can be specified for different media—in still air, water, or oil bath. Typical dissipation constants range anywhere from less than 0.5 mW/°C for still air to 10 mW/°C or higher for a thermistor immersed in water. A 2,252 Ω thermistor powered by a 100 μA excitation current dissipates:

R 100 μA22,252 Ω× 0.0225 mW==

If this thermistor has a dissipation constant of 10 mW/°C, the thermistor self-heats 0.00225 °C so the self-heating from the 100 μA source of the SCXI-1503 is negligible for most applications. It is still important to carefully read self-heating specifications of the thermistors.

Resistance/Temperature Characteristic of Thermistors

The resistance-temperature behavior of thermistors is highly dependent upon the manufacturing process. Therefore, thermistor curves are not standardized to the extent that thermocouple or RTD curves are standardized. Typically, thermistor manufacturers supply the resistance-versus-temperature curves or tables for their particular devices. You can, however, approximate the thermistor curve relatively accurately with the Steinhart-Hart equation:

T(° K )

SCXI-1503 User Manual 4-12 ni.com

------------------------------------------------------------------= ++

abln R

()[]c ln RT()[]

Chapter 4 Theory of Operation

where

T(°K) is the temperature in degrees Kelvin, equal to T(°C) + 273.15.

is the resistance of the thermistor.

a, b, and c are coefficients obtained from the thermistor manufacturer or calculated from the resistance-versus-temperature curve.

Using the SCXI-1503

This chapter makes suggestions for developing your application and provides basic information regarding calibration.

Developing Your Application in NI-DAQmx

Note If you are not using an NI ADE, using an NI ADE prior to version 8.1, or are using

an unlicensed copy of an NI ADE, additional dialog boxes from the NI License Manager appear allowing you to create a task or global channel in unlicensed mode. These messages continue to appear until you install version 8.1 or later of an NI ADE.

This section describes how to configure and use NI-DAQmx to control the SCXI-1503 in LabVIEW, LabWindows/CVI, and Measurement Studio. These ADEs provide greater flexibility and access to more settings than MAX, but you can use ADEs in conjunction with MAX to quickly create a customized application.

Typical Program Flowchart

Figure 5-1 shows a typical program voltage measurement flowchart for creating a task to configure channels, take a measurement, analyze the data, present the data, stop the measurement, and clear the task.

Chapter 5 Using the SCXI-1503

Create Task in

DAQ Assistant

or MAX

Further Configure

Channels?

Ye s

Configure Channels

Start Measurement

Ye s

Create Task Using

DAQ Assistant?

Ye s

Create Another

Channel?

Ye s

Process

Data

Ye s

Create a Task

Programmatically

Create Channel

Hardware

Timing/Triggering?

Ye s

Adjust Timing Settings

Analyze Data?

Display Data?

Read Measurement

Clear Task

Graphical

Display Tools

Ye s

Continue Sampling?

Stop Measurement

Figure 5-1. Typical Program Flowchart for Voltage Measurement Channels

SCXI-1503 User Manual 5-2 ni.com

General Discussion of Typical Flowchart

The following sections briefly discuss some considerations for a few of the steps in Figure 5-1. These sections are meant to give an overview of some of the options and features available when programming with NI-DAQmx.

Creating a Task Using DAQ Assistant or Programmatically

When creating an application, you must first decide whether to create the appropriate task using the DAQ Assistant or programmatically in the ADE.

Developing your application using DAQ Assistant gives you the ability to configure most settings such as measurement type, selection of channels, excitation voltage, signal input limits, task timing, and task triggering. You can access the DAQ Assistant through MAX or your NI ADE. Choosing to use the DAQ Assistant can simplify the development of your application. NI recommends creating tasks using the DAQ Assistant for ease of use, when using a sensor that requires complex scaling, or when many properties differ between channels in the same task.

If you are using an ADE other than an NI ADE, or if you want to explicitly create and configure a task for a certain type of acquisition, you can programmatically create the task from your ADE using functions or VIs. If you create a task using the DAQ Assistant, you can still further configure the individual properties of the task programmatically with functions or property nodes in your ADE. NI recommends creating a task programmatically if you need explicit control of programmatically adjustable properties of the DAQ system.

Chapter 5 Using the SCXI-1503

Programmatically adjusting properties for a task created in the DAQ Assistant overrides the original, or default, settings only for that session. The changes are not saved to the task configuration. The next time you load the task, the task uses the settings originally configured in the DAQ Assistant.

Adjusting Timing and Triggering

There are several timing properties that you can configure through the DAQ Assistant or programmatically using function calls or property nodes. If you create a task in the DAQ Assistant, you can still modify the timing properties of the task programmatically in your application.

When programmatically adjusting timing settings, you can set the task to acquire continuously, acquire a buffer of samples, or acquire one point at a

Chapter 5 Using the SCXI-1503

Note You cannot adjust some properties while a task is running. For these properties, you

must stop the task, make the adjustment, and re-start the application. Tables 5-1 through 5-3 assume all properties are configured before the task is started.

time. For continuous acquisition, you must use a while loop around the acquisition components even if you configured the task for continuous acquisition using MAX or the DAQ Assistant. For continuous and buffered acquisitions, you can set the acquisition rate and the number of samples to read in the DAQ Assistant or programmatically in your application. By default, the clock settings are automatically set by an internal clock based on the requested sample rate. You also can select advanced features such as clock settings that specify an external clock source, internal routing of the clock source, or select the active edge of the clock signal.

Configuring Channel Properties

All ADEs used to configure the SCXI-1503 access an underlying set of NI-DAQmx properties. Table 5-1 shows some of these properties. You can use Table 5-1 to determine what kind of properties you need to set to configure the module for your application. For a complete list of NI-DAQmx properties, refer to your ADE help file.

Table 5-1. NI-DAQmx Voltage Measurement Properties

DAQ

Assistant

Property Short Name Description

Analog Input»Maximum Value

AI.Max Specifies the maximum value

you expect to measure. The

Accessible

Ye s

SCXI-1503 gain and E/M Series DAQ device range are computed automatically from this value.

Analog Input»Minimum Value

AI.Min Specifies the minimum value

you expect to measure. The

Ye s

SCXI-1503 gain and E/M Series DAQ device range are computed automatically from this value.

SCXI-1503 User Manual 5-4 ni.com

Chapter 5 Using the SCXI-1503

Table 5-1. NI-DAQmx Voltage Measurement Properties (Continued)

Property Short Name Description

DAQ

Assistant

Accessible

Analog Input»General Properties»Advanced» Gain and Offset»Gain Value

Analog Input»General Properties»Advanced» High Accuracy Settings» Auto Zero Mode

Analog Input»General Properties»Advanced» Input Configuration» Coupling

Table 5-2. NI-DAQmx RTD Measurement Properties

Property Short Name Description

Analog Input»Temperature» RTD»Type

AI.Gain Specifies a gain factor to apply

to the signal conditioning portion of the channel. The SCXI-1503 supports 1 or 100.

AI.AutoZeroMode Specifies when to measure

ground. NI-DAQmx subtracts the measured ground voltage from every sample. The SCXI-1503 supports None or Once.

AI.Coupling Specifies the input coupling of

the channel. The SCXI-1503 supports DC and GND coupling.

AI.RTD.Type Specifies the type of

RTD connected to the channel.

Ye s

DAQ

Assistant

Accessible

Ye s

Analog Input»Temperature» RTD»R0

AI.RTD.R0 Specifies the

resistance in ohms of

Ye s

the sensor at 0 °C.

Chapter 5 Using the SCXI-1503

Table 5-2. NI-DAQmx RTD Measurement Properties (Continued)

Property Short Name Description

DAQ

Assistant

Accessible

Analog Input»Temperature» RTD»Custom»A, B, C

Analog Input»General Properties»Signal Conditioning»Resistance Configuration

Table 5-3. NI-DAQmx Thermistor Measurement Properties

Property Short Name Description

Analog Input»Temperature» Thermistor»R1

Analog Input»Temperature» Thermistor»Custom»A, B, C

AI.RTD.A AI.RTD.B AI.RTD.C

Specifies the A, B, or C constant of the Callendar-Van Dusen equation when using a custom RTD type.

AI.Resistance.Cfg Specifies the

resistance configuration for the channel, such as 2-wire, 3-wire, or 4-wire.

AI.Thrmistr.R1 Specifies the resistance in

ohms of the sensor at 0 °C.

AI.Thrmistr.A AI.Thrmistr.B AI.Thrmistr.C

Specifies the A, B, or C constant of the Steinhart-Hart thermistor equation, which NI-DAQmx uses to scale thermistors.

Ye s

DAQ

Assistant

Accessible

Ye s

SCXI-1503 User Manual 5-6 ni.com

Chapter 5 Using the SCXI-1503

Table 5-4. NI-DAQmx Thermocouple Measurement Properties

Property Short Name Description

DAQ

Assistant

Accessible

Analog Input»Temperature» Thermocouple»Type

Analog Input»Temperature» Thermocouple»CJC Source

Analog Input»Temperature» Thermocouple»CJC Value

Analog Input»Temperature» Thermocouple»CJC Channel

Note This is not a complete list of NI-DAQmx properties and does not include every

property you may need to configure your application. It is a representative sample of important properties to configure for voltage measurements. For a complete list of NI-DAQmx properties and more information about NI-DAQmx properties, refer to your ADE help file.

AI.Thermcpl.Type Specifies the type of

thermocouple connected to the channel.

AI.Thermcpl.CJCSrc Indicates the source of

cold-junction compensation.

AI.Thermcpl.CJCVal Specifies the

temperature of the cold-junction if the CJC source is constant value.

AI.Thermcpl.CJCChan Indicates the channel

that acquires the temperature of the cold junction if CJC is channel.

Ye s

Acquiring, Analyzing, and Presenting

After configuring the task and channels, you can start the acquisition, read measurements, analyze the data returned, and display it according to the needs of your application. Typical methods of analysis include digital filtering, averaging data, performing harmonic analysis, applying a custom scale, or adjusting measurements mathematically.

NI provides powerful analysis toolsets for each NI ADE to help you perform advanced analysis on the data without requiring you to have a programming background. After you acquire the data and perform any required analysis, it is useful to display the data in a graphical form or log it to a file. NI ADEs provide easy-to-use tools for graphical display, such as

Chapter 5 Using the SCXI-1503

charts, graphs, slide controls, and gauge indicators. NI ADEs have tools that allow you to easily save the data to files such as spread sheets for easy viewing, ASCII files for universality, or binary files for smaller file sizes.

Completing the Application

After you have completed the measurement, analysis, and presentation of the data, it is important to stop and clear the task. This releases any memory used by the task and frees up the DAQ hardware for use in another task.

Note In LabVIEW, tasks are automatically cleared.

Developing an Application Using LabVIEW

This section describes in more detail the steps shown in the typical program flowchart in Figure 5-1, such as how to create a task in LabVIEW and configure the channels of the SCXI-1503. If you need more information or for further instructions, select Help»VI, Function, & How-To Help from the LabVIEW menu bar.

Note Except where otherwise stated, the VIs in Table 5-5 are located on the Functions»

All Functions»NI Measurements»DAQmx - Data Acquisition subpalette and

accompanying subpalettes in LabVIEW.

Table 5-5. Programming a Task in LabVIEW

Flowchart Step VI or Program Step

Create Task in DAQ Assistant Create a DAQmx Task Name Control located on the

Controls»All Controls»I/O»DAQmx Name Controls

Create a Task Programmatically (optional)

subpalette, right-click it, and select

Assistant)

DAQmx Create Task.vi located on the Functions»All

Functions»NI Measurements»DAQmx - Data Acquisition» DAQmx Advanced Task Options subpalette—This VI is

New Task (DAQ

optional if you created and configured the task using the DAQ Assistant. However, if you use it in LabVIEW, any changes you make to the task are not saved to a task in MAX.

SCXI-1503 User Manual 5-8 ni.com

Chapter 5 Using the SCXI-1503

Table 5-5. Programming a Task in LabVIEW (Continued)

Flowchart Step VI or Program Step

Create Virtual Channel(s) DAQMX Create Virtual Channel.vi located on the

Functions»All Functions»NI Measurements»DAQmx - Data Acquisition subpalette—Use this VI to add virtual channels to

the task. Select the type of virtual channel based on the measurement you plan to perform.

Adjust Timing Settings (optional)

DAQmx Timing.vi (Sample Clock by default)—This VI is

optional if you created and configured the task using the DAQ Assistant. Any timing settings modified with this VI are not saved in the DAQ Assistant. They are only available for the present session.

Configure Channels (optional)

NI-DAQmx Channel Property Node, refer to the Using a

NI-DAQmx Channel Property Node in LabVIEW section for

more information. This step is optional if you created and fully configured the channels using the DAQ Assistant. Any channel modifications made with a channel property node are not saved in the task in the DAQ Assistant. They are only available for the present session.

Start Measurement DAQmx Start Task.vi

Read Measurement DAQmx Read.vi

Analyze Data Some examples of data analysis include filtering, scaling,

harmonic analysis, or level checking. Some data analysis tools are located on the Functions»Signal Analysis subpalette and on the Functions»All Functions»Analyze subpalette.

Display Data You can use graphical tools such as charts, gauges, and graphs

to display the data. Some display tools are located on the Controls»All Controls»Numeric»Numeric Indicator subpalette and Controls»All Controls»Graph subpalette.

Continue Sampling For continuous sampling, use a While Loop. If you are using

hardware timing, you also need to set the

DAQmx Timing.vi

sample mode to Continuous Samples. To do this, right-click the terminal of the

DAQmx Timing.vi labeled sample mode and

click Create»Constant. Click the box that appears and select Continuous Samples.

Chapter 5 Using the SCXI-1503

Table 5-5. Programming a Task in LabVIEW (Continued)

Flowchart Step VI or Program Step

Stop Measurement DAQmx Stop Task.vi (This VI is optional, clearing the task

automatically stops the task.)

Clear Task DAQmx Clear Task.vi

Using a NI-DAQmx Channel Property Node in LabVIEW

You can use property nodes in LabVIEW to manually configure the channels. To create a LabVIEW property node, complete the following steps:

1. Launch LabVIEW.

2. Create the property node in a new VI or in an existing VI.

3. Open the block diagram view.

4. From the Functions toolbox, select All Functions»NI Measurements»DAQmx - Data Acquisition, and select

Channel Property Node

5. The ActiveChans property is displayed by default. This allows you to specify exactly what channel(s) you want to configure. If you want to configure several channels with different properties, separate the lists of properties with another Active Channels box and assign the appropriate channel to each list of properties.

DAQmx

Note If you do not use Active Channels, the properties are set on all of the channels in

the task.

6. Right-click ActiveChans, and select Add Element. Left-click the new ActiveChans box. Navigate through the menus, and select the property you wish to define.

7. Change the property to read or write to either get the property or write a new value. Right-click the property, go to Change To, and select Write, Read, or Default Value.

8. After you have added the property to the property node, right-click the terminal to change the attributes of the property, add a control, constant, or indicator.

9. To add another property to the property node, right-click an existing property and left-click Add Element. To change the new property, left-click it and select the property you wish to define.

SCXI-1503 User Manual 5-10 ni.com

Note Refer to the LabVIEW Help for information about property nodes and specific

NI-DAQmx properties.

Specifying Channel Strings in NI-DAQmx

Use the channel input of DAQmx Create Channel to specify the SCXI-1503 channels. The input control/constant has a pull-down menu showing all available external channels. The strings take one of the following forms:

• single device identifier/channel number—for example

• multiple, noncontinuous channels—for example SC1Mod1/ai0,

SC1Mod1/ai4

• multiple continuous channels—for example (channels 0 through 4)

When you have a task containing SCXI-1503 channels, you can set the properties of the channels programmatically using the DAQmx Channel Property Node.

Text Based ADEs

You can use text based ADEs such as LabWindows/CVI, Measurement Studio, Visual Basic 6, .NET, and C# to create code for using the SCXI-1503.

Chapter 5 Using the SCXI-1503

SC1Mod1/ai0

SC1Mod1/ai0:4

LabWindows/CVI

LabWindows/CVI works with the DAQ Assistant in MAX to generate code for an voltage measurement task. You can then use the appropriate function call to modify the task. To create a configurable channel or task in LabWindows/CVI, complete the following steps:

1. Launch LabWindows/CVI.

2. Open a new or existing project.

3. From the menu bar, select Tools»Create/Edit DAQmx Tasks.

4. Choose Create New Task In MAX or Create New Task In Project to load the DAQ Assistant.

5. The DAQ Assistant creates the code for the task based on the parameters you define in MAX and the device defaults. To change a property of the channel programmatically, use the

DAQmxSetChanAttribute function.

Chapter 5 Using the SCXI-1503

Note Refer to the NI LabWindows/CVI Help for more information on creating NI-DAQmx

tasks in LabWindows/CVI and NI-DAQmx property information.

Measurement Studio (Visual Basic 6, .NET, and C#)

When creating an voltage measurement task in Visual Basic 6, .NET and C#, follow the general programming flow in Figure 5-1. You can then use the appropriate function calls to modify the task. This example creates a new task and configures an NI-DAQmx voltage measurement channel on the SCXI-1503. You can use the same functions for Visual Basic 6, .NET and C#.

The following text is a function prototype example:

void AIChannelCollection.CreateVoltageChannel(

System.String physicalChannelName,

System.String nameToAssignChannel,

System.Double minVal,

System.Double maxVal);

To actually create and configure the channel, you would enter something resembling the following example code:

Task myTask = new

NationalInstruments.DAQmx.Task(“myTaskName”);

MyTask.DAQmxCreateAIVoltageChan (

“SC1Mod1/ai0”, // System.String physicalChannelName

“Voltage0”, // System.String nameToAssignChannel

-10.0, // System.Double minVal

10.0); // System.Double maxVal

// setting attributes after the channel is created

AIChannel myChannel = myTask.AIChannels[“Voltage0”];

myChannel.AutoZeroMode = kAutoZeroTypeOnce;

Modify the example code above or the code from one of the shipping examples as needed to suit your application.

Note You can create and configure the voltage measurement task in MAX and

load it into your application with the function call

NationalInstruments.DAQmx.DaqSystem.Local.LoadTask.

Refer to the NI Measurement Studio Help for more information on creating NI-DAQmx tasks in LabWindows/CVI and NI-DAQmx property information.

SCXI-1503 User Manual 5-12 ni.com

Note Tables 5-1 through 5-4 are not complete lists of NI-DAQmx properties and do not

include every property you may need to configure voltage measurements. It is a representative sample of important properties to configure voltage measurements. For a complete list of NI-DAQmx properties and more information on NI-DAQmx properties, refer to your ADE help file.

Calibration

Chapter 5 Using the SCXI-1503

Programmable NI-DAQmx Properties

All of the different ADEs that configure the SCXI-1503 access an underlying set of NI-DAQmx properties. Tables 5-1 through 5-4 provide a list of some of the properties that configure the SCXI-1503. You can use this list to determine what kind of properties you need to set to configure the device for your application. For a complete list of NI-DAQmx properties, refer to your ADE help file.

The SCXI-1503 is shipped with a calibration certificate and is calibrated at the factory to the specifications described in Appendix A, Specifications. Calibration constants are stored inside the calibration EEPROM and provide software correction values your application development software uses to correct the measurements for both offset and gain errors in the module.

Internal/Self-Calibration

You can self-calibrate the SCXI-1503 in MAX by right-clicking the module and selecting Self Calibrate. The NI-DAQmx Self Calibrate Device function does the same. A self-calibration of the SCXI-1503 grounds all the input channels and stores the resulting measurement as an offset correction constant on the module. You should perform a self-calibration every time you install the SCXI-1503 to a new system.

Note You should self-calibrate the connected DAQ device before self-calibrating the

SCXI-1503.

External Calibration

If you have an accurate calibrator and DMM, you can externally calibrate the SCXI-1503 gain and offset constants using NI-DAQmx functions. You can also calibrate the 100 μA current excitation.

Chapter 5 Using the SCXI-1503

Note Performing an external calibration of the SCXI-1503 permanently overwrites the

factory calibration settings, which impacts the accuracy of the inputs.

The functions that are required for externally calibrating the SCXI-1503 are available in NI-DAQmx 8.1 or later. Refer to the NI-DAQmx Help for details about these functions.

Most external calibration documents for SCXI modules are available to download from

ni.com/calibration by clicking Manual Calibration

Procedures. For external calibration of modules not listed there, Basic

Calibration Service or Detailed Calibration Service is recommended. You can get information about both of these calibration services from

ni.com/calibration. NI recommends performing an external

calibration once a year.

SCXI-1503 User Manual 5-14 ni.com

Specifications

This appendix lists the specifications for the SCXI-1503 modules. These specifications are typical at 25 °C unless otherwise noted.

Analog Input

Input Characteristics

Number of channels ............................... 16 differential

Input coupling ........................................DC

Input signal ranges ................................. ±100 mV (gain = 100) or

Input overvoltage protection

Powered on ..................................... ±42 VDC

Powered off..................................... ±25 V

Inputs protected............................... AI<0..15>

CJ sensor input protection............... ±15 VDC powered on or off

±10 V (gain = 1)

Transfer Characteristics

Nonlinearity ........................................... 0.005% FSR

Input offset error (RTI)

Gain = 1

Calibrated

With autozero enabled

Assumes 1,000 point average, 25 °C ±10 °C over one year.

Assumes 1,000 point average, ±1 °C of autozero temperature.

..............................±650 μV max

±250 μV typ

........... ±300 μV max

±150 μV typ

Appendix A Specifications

Gain = 100

Calibrated

................................±25 μV max

±10 μV typ

With autozero enabled

............±10 μV max

±5 μV typ

Gain error (relative to calibration reference)

Gain = 1 or 100

Calibrated

................................0.074% of reading max

0.02% of reading typ

RTD Measurement Accuracy

Table A-1. RTD Measurement Accuracy

Measured

Temperature °C

–100 to 0 0.60 0.23 1.09 0.46

0 to 25 0.62 0.23 1.11 0.47

100 Ω Max °C 100 Ω Typ °C 1000 Ω Max °C 1000 Ω Ty p °C

25 to 100 0.69 0.25 1.20 0.49

100 to 500 1.11 0.37 1.68 0.65

500 to 1200 2.06 0.65 2.81 1.04

Notes: The accuracies in this table reflect using the module in4-wire mode. They do not include errors from the RTD including lead-wire errors when using 2- or 3-wire connection.

The accuracies assume auto-zero is enabled and the environmental conditions are 25 °C ±10 °C over a one year period.

These accuracies were computed using a standard RTD with a TCR of 3851.

Amplifier Characteristics

Input coupling.........................................DC

Input impedance

Normal powered on .........................>1 GΩ

Input bias current ....................................±2.8 nA

Assumes 1,000 point average, 25 °C ±10 °C over one year.

Assumes 1,000 point average, ±1 °C of autozero temperature.

SCXI-1503 User Manual A-2 ni.com

CMRR characteristics (DC to 60 Hz)

Gain 1.............................................. –75 dB min

–90 dB typ

Gain 100.......................................... –106 dB min

–110 dB typ

Output range........................................... ±10 V

Output impedance .................................. 91 Ω

Dynamic Characteristics

Minimum scan interval (per channel, any gain)

±0.012% accuracy........................... 3 μs

±0.0061% accuracy......................... 10 μs

±0.0015% accuracy......................... 20 μs

Noise characteristics (RTI)

Gain = 1

10 Hz to 1 MHz .............................. 100 μV

Gain = 100

10 Hz to 1 MHz .............................. 1 μV

0.1 to 10 Hz..................................... 0.5 μV

Appendix A Specifications

rms

p-p

Filter

Cutoff frequency (–3 dB)....................... 5 Hz

NMR (60 Hz) .........................................–40 dB min

Step response characteristics (gain 1 or 100)

To 0.0015%..................................... 0.6 s

Stability

Recommended warm-up time ................ 20 min

Offset temperature coefficient

Gain = 1 .......................................... ±35 μV/°C max

±10 μV/°C typ

Gain = 100 ...................................... ±1.5 μV/°C max

±0.5 μV/°C typ

Appendix A Specifications

Gain temperature coefficient

(gain 1 or 100) ........................................±15 ppm/°C max

Excitation

Channels .................................................16 single-ended outputs

Current output.........................................100 μA

Accuracy.................................................±0.05%

Temperature drift....................................±5 ppm/°C

Output voltage compliance .....................10 V

Maximum resistive load .........................100 kΩ

Overvoltage protection ...........................±40 VDC

Measurement Category...........................CAT I

Power Requirements From SCXI Backplane

V+ ...........................................................18.5 to 25 VDC, 170 mA

±5 ppm/°C typ

V– ...........................................................–18.5 to –25 VDC, –170 mA

+5 V ........................................................+4.75 to 5.25 VDC, 50 mA

Environmental

Operating temperature ............................0 to 50 °C

Storage temperature ................................–20 to 70 °C

Humidity.................................................10 to 90% RH, noncondensing

Maximum altitude...................................2,000 meters

Pollution Degree (indoor use only) ........2

SCXI-1503 User Manual A-4 ni.com

Physical

Appendix A Specifications

3.0 cm

(1.2 in.)

17.2 cm (6.8 in.)

18.8 cm (7.4 in.)

Figure A-1. SCXI-1503 Dimensions

Weight.................................................... 745 g (26.3 oz)

Maximum Working Voltage

Maximum working voltage refers to the signal voltage plus the common-mode voltage.

Signal + common mode ......................... Each input should remain

within ±10 V of AI GND

Appendix A Specifications

Safety

This product is designed to meet the requirements of the following standards of safety for electrical equipment for measurement, control, and laboratory use:

• IEC 61010-1, EN-61010-1

• UL 61010-1, CSA 61010-1

Note For UL and other safety certifications, refer to the product label or visit

ni.com/certification, search by model number or product line, and click the

appropriate link in the Certification column.

Electromagnetic Compatibility

This product is designed to meet the requirements of the following standards of EMC for electrical equipment for measurement, control, and laboratory use:

• EN 61326 EMC requirements; Minimum Immunity

• EN 55011 Emissions; Group 1, Class A

• CE, C-Tick, ICES, and FCC Part 15 Emissions; Class A

Note For EMC compliance, operate this device according to product documentation.

CE Compliance

This product meets the essential requirements of applicable European Directives, as amended for CE marking, as follows:

• 73/23/EEC; Low-Voltage Directive (safety)

• 89/336/EEC; Electromagnetic Compatibility Directive (EMC)

Note Refer to the Declaration of Conformity (DoC) for this product for any additional

regulatory compliance information. To obtain the DoC for this product, visit

ni.com/certification, search by model number or product line, and click the

appropriate link in the Certification column.

Waste Electrical and Electronic Equipment (WEEE)

EU Customers At the end of their life cycle, all products must be sent to a WEEE recycling

center. For more information about WEEE recycling centers and National Instruments WEEE initiatives, visit

SCXI-1503 User Manual A-6 ni.com

ni.com/environment/weee.htm.

Removing the SCXI-1503

This appendix explains how to remove the SCXI-1503 from MAX and an SCXI chassis or PXI/SCXI combination chassis.

Removing the SCXI-1503 from MAX

To remove a module from MAX, complete the following steps after launching MAX:

1. Expand Devices and Interfaces.

2. Click the + next to NI-DAQmx to expand the list of installed chassis.

3. Click the + next to the appropriate chassis to expand the list of installed

modules.

4. Right-click the module or chassis you want to delete and click Delete.

5. A confirmation window opens. Click Yes to continue deleting the module or chassis or No to cancel this action.

Note Deleting the SCXI chassis deletes all modules in the chassis. All configuration

information for these modules is also lost.

The SCXI chassis and/or SCXI module(s) should now be removed from the list of installed devices in MAX.

Removing the SCXI-1503 from a Chassis

Consult the documentation for the chassis and accessories for additional instructions and precautions. To remove the SCXI-1503 module from a chassis, complete the following steps while referring to Figure B-1:

1. Power off the chassis. Do not remove the SCXI-1503 module from a chassis that is powered on.

2. If the SCXI-1503 is the module cabled to the E/M Series DAQ device, disconnect the cable.

3. Remove any terminal block that connects to the SCXI-1503.

Appendix B Removing the SCXI-1503

4. Rotate the thumbscrews that secure the SCXI-1503 to the chassis

Remove the SCXI-1503 by pulling steadily on both thumbscrews until the module slides completely out.

counterclockwise until they are loose, but do not completely remove the thumbscrews.

S C

X I

1 1 0

1Cable 2 SCXI Module Thumbscrews

3SCXI-1503 4Terminal Block

5 4 3 2 1

ADDRESS

SCXI

M A

I N

F R

M E

Figure B-1. Removing the SCXI-1503

5 SCXI Chassis Power S witch 6 SCXI Chassis

SCXI-1503 User Manual B-2 ni.com

Common Questions

This appendix lists common questions related to the use of the SCXI-1503.

Which version of NI-DAQ works with the SCXI-1503, and how do I get the most current version of NI-DAQ?

You must have NI-DAQ 8.1 or later. Visit the NI Web site at select Download Software»Drivers and Updates»Search Drivers and Updates. Enter the keyword for your operating system.

I cannot correctly test and verify that my SCXI-1503 is working. What should I do?

Unfortunately, there is always the chance that one or more components in the system are not operating correctly. You may have to call or email a technical support representative. The technical support representative often suggests troubleshooting measures. If requesting technical support by phone, have the system nearby so you can try these measures immediately. NI contact information is listed in the Technical Support Information document.

Can the SCXI-1503 current outputs be interactively controlled in MAX or programmatically controlled using NI-DAQ function calls, LabVIEW, or Measurement Studio?

No. The current-output level is 100 μA as long as the chassis is powered on. You cannot power off or adjust the current output using MAX, NI-DAQ function calls, or an ADE such as LabVIEW or Measurement Studio. If you require this functionality, consider using an SCXI-1124 module or NI 670X device instead.

NI-DAQ to find the latest version of NI-DAQ

ni.com and

How can I ground a floating voltage measurement?

You can use the IEX– terminal of each channel as a ground reference. Refer to the SCXI-1306 Terminal Block Installation Guide for details about using the SCXI-1306 DIP switches to control ground referencing.

Appendix C Common Questions

Can I connect N current-output channels in parallel to create a precision current source that provides N × 100 μA?

Yes, you can connect the current output in parallel. When connecting the output in parallel, connect the appropriate IEX+ terminals together and the corresponding IEX– terminals together.

Can I connect N current-output channels in series to achieve a higher terminal-voltage compliance limit?

No. Each current source is ground referenced. Therefore, you cannot place multiple current-outputs in series.

Are the SCXI-1503 channels isolated with respect to each other, the E/M Series DAQ device, or ground?

No. The SCXI-1503 does not contain any isolation circuitry. If you require isolation, consider the SCXI-1124 or SCXI-1125 module instead.

Can I modify the SCXI-1503 circuitry to generate current at a level different than 100 μA?

No. Do not attempt to modify any circuitry in the SCXI-1503.

Are there any user-serviceable parts inside the SCXI-1503?

No. There are no fuses, potentiometers, switches, socketed resistors, or jumpers inside the module. Disassembly of the module for any reason can void its warranty and nullify its accuracy specification.

Can I access the unused analog-input channels of the E/M Series DAQ device if it is directly cabled to the SCXI-1503 in a single-chassis system?

Yes. E/M Series DAQ device channels 1 through 7 are available to measure unconditioned signals. Use an SCXI-1180 or the 50-pin breakout connector on the SCXI-1346 or SCXI-1349 cable adapter to route signals to these channels.

Which digital lines are unavailable on the E/M Series DAQ device if I am cabled to an SCXI-1503 module?

Table 2-4 shows the digital lines that are used by the SCXI-1503 for communication and scanning. These lines are unavailable for general-purpose digital I/O if the SCXI-1503 is connected to the E/M Series DAQ device.

SCXI-1503 User Manual C-2 ni.com

Appendix C Common Questions

Does short-circuiting a current-output channel do any damage to the SCXI-1503?

No. The SCXI-1503 delivers 100 μA into any load from 0 Ω to 100 kΩ.

Does open-circuiting a current-output channel damage the SCXI-1503? What is the open-circuit voltage level?

No. An SCXI-1503 current-output channel is not damaged if no load is connected. The open-circuit voltage is 12.4 VDC.

Glossary

Symbol Prefix Value

µ micro 10

m milli 10

k kilo 10

Mmega10

Numbers/Symbols

% percent

+ positive of, or plus

– negative of, or minus

± plus or minus

< less than

–6

–3

/per

°degree

Ω ohms

+5 V (signal) +5 VDC source signal

A amperes

ADE application development environment such as LabVIEW,

LabWindows/CVI, Visual Basic, C, and C++

AI analog input

AI GND analog input ground signal

Glossary

bit one binary digit, either 0 or 1

CE European emissions control standard

C GND chassis ground signal

channel pin or wire lead to which you apply, or from which you read, an analog or

digital signal. Analog signals can be single-ended or differential. For digital signals, channels (also known as lines) are grouped to form ports.

chassis the enclosure that houses, powers, and controls SCXI modules

CLK clock input signal

common-mode voltage voltage that appears on both inputs of a differential amplifier

current excitation a source that supplies the current needed by a sensor for its proper operation

D/A digital-to-analog

D*/A Data/Address

DAQ data acquisition—(1) collecting and measuring electrical signals from

sensors, transducers, and test probes or fixtures and processing the measurement data using a computer; (2) collecting and measuring the same kinds of electrical signals with A/D and/or DIO devices plugged into a computer, and possibly generating control signals with D/A and/or DIO devices in the same computer

DAQ device a data acquisition device. Examples are E/M Series data acquisition devices

DAQ D*/A the data acquisition device data/address line signal used to indicate whether

the SER DAT IN pulse train transmitted to the SCXI chassis contains data or address information

device a plug-in data acquisition device, module, card, or pad that can contain

multiple channels and conversion devices. SCXI modules are distinct from devices, with the exception of the SCXI-1200, which is a hybrid.

SCXI-1503 User Manual G-2 ni.com

Glossary

D GND digital ground signal

differential amplifier an amplifier with two input terminals, neither of which are tied to a ground

reference, whose voltage difference is amplified

DIN Deutsche Industrie Norme (German Industrial Standard)

DIO digital input/output

DoC Declaration of Conformity

drivers/driver software

software that controls a specific hardware device such as an E/M Series DAQ device

EMC electromagnetic compliance

EMI electromagnetic interference

excitation a voltage or current source used to energize a sensor or circuit

EXT CLK external clock signal

gain the factor by which a signal is amplified, sometimes expressed in decibels

ID identifier

IEX+ positive excitation channel

IEX– negative excitation channel

in. inch or inches

input impedance the measured resistance and capacitance between the input terminals of a

circuit

Glossary

jumper a small rectangular device used to connect two adjacent posts on a circuit

board. Jumpers are used on some SCXI modules and terminal blocks to either select certain parameters or enable/disable circuit functionality.

lead resistance the small resistance of a lead wire. The resistance varies with the lead

length and ambient temperature. If the lead wire carries excitation current, this varying resistance can cause measurement error.

m meters

M (1) Mega, the standard metric prefix for 1 million or 10

units of measure such as volts and hertz; (2) mega, the prefix for 1,048,576,

or 2

, when used with B to quantify data or computer memory

MISO master-in-slave-out signal

, when used with

MOSI master-out-slave-in signal

multiplex to route one of many input signals to a single output

multiplexed mode an SCXI operating mode in which analog input channels are multiplexed

into one module output so that the cabled E/M Series DAQ device has access to the multiplexed output of the module as well as the outputs of all other multiplexed modules in the chassis

NC not connected (signal)

NI-DAQ the driver software needed in order to use National Instruments E/M Series

DAQ devices and SCXI components

NI-DAQmx

SCXI-1503 User Manual G-4 ni.com

The latest NI-DAQ driver with new VIs, functions, and development tools for controlling measurement devices.

Glossary

output voltage compliance

OUT REF output reference signal

the largest voltage that can be generated across the output of a current source without the current going out of specification

ppm parts per million

PXI PCI eXtensions for Instrumentation—an open specification that builds on

the CompactPCI specification by adding instrumentation-specific features

RMA Return Material Authorization

RSVD reserved bit, pin, or signal

RTD resistance-temperature detector

lead resistance

s seconds

S samples

scan one or more analog samples taken at the same time, or nearly the same time.

Typically, the number of input samples in a scan is equal to the number of channels in the input group. For example, one scan, acquires one new sample from every analog input channel in the group.

SCAN CLK scan clock signal used to increment to the next channel after each

E/M Series DAQ device analog-to-digital conversion

SCXI Signal Conditioning eXtensions for Instrumentation

SCXIbus located in the rear of an SCXI chassis, the SCXIbus is the backplane that

connects modules in the same chassis to each other

Glossary

sensor a type of transducer that converts a physical phenomenon into an electrical

signal

SER CLK serial clock signal used to synchronize digital data transfers over the

SER DAT IN and SER DAT OUT lines

SER DAT IN serial data input signal

SER DAT OUT serial data output signal

signal conditioning the manipulation of signals to prepare them for digitizing

Slot 0 refers to the power supply and control circuitry in the SCXI chassis

SLOT 0 SEL slot 0 select signal

SPI CLK serial peripheral interface clock signal

thermistor a thermally sensitive resistor

Traditional NI-DAQ (Legacy)

transducer a device capable of converting energy from one form to another

An upgrade to the earlier version of NI-DAQ. Traditional NI-DAQ (Legacy) has the same VIs and functions and works the same way as NI-DAQ 6.9.x. You can use both Traditional NI-DAQ (Legacy) and NI-DAQmx on the same computer, which is not possible with NI-DAQ

6.9.x.

UL Underwriters Laboratory

Vvolts

VAC volts, alternating current

VDC volts, direct current

SCXI-1503 User Manual G-6 ni.com

Glossary

VI virtual instrument—(1) a combination of hardware and/or software

elements, typically used with a PC, that has the functionality of a classic stand-alone instrument; (2) a LabVIEW software module (VI), which consists of a front panel user interface and a block diagram program

virtual channels channel names that can be defined outside the application and used without

having to perform scaling operations

Wwatts

Index

Numerics

2-wire configuration of resistive devices, 2-4 3-wire resistive sensor

connected in 2-wire configuration, 2-5 lead-resistance compensation

with two matched current sources, 2-6

4-wire configuration of resistive devices, 2-3

adjusting timing and triggering, 5-3 AI 0 signal, multiplexing, 2-11 amplifier characteristics specifications, A-2 analog circuitry

analog input channels, 4-3

CJ SENSOR, 4-3 analog input channels, 4-3 analog input signal connections, 2-1

ground-referencing of signals, 2-2 analog input signals, multiplexed, 4-4 analog input specifications, A-1

amplifier characteristics, A-2

dynamic characteristics, A-3

input characteristics, A-1

transfer characteristics, A-1 applications

developing in NI-DAQmx, 5-1

acquiring, analyzing, and

presenting, 5-7 completing, 5-8 LabVIEW, 5-8 program flowchart (figure), 5-2 programmable properties, 5-13 specifying channel strings, 5-11

cables, custom, 2-1 calibration, SCXI-1503, 5-13 CE compliance specifications, A-6 channel properties, configuring, 5-4 channels, voltage measurement flowchart

(figure), 5-2

circuitry

analog, 4-3

digital control, 4-3 CJC source/value, 3-2 common questions, C-1 common software-configurable settings

CJC source/value, 3-2

gain/input range, 3-1 configuration, 3-1

channel properties, 5-4

SCXI-1503

common software settings, 3-1

settings in MAX

NI-DAQmx, 3-3

creating a global channel or

task, 3-3

verifying signal, 3-4

NI-DAQmx, 3-4 configuration and testing, 3-1 configuration settings, gain/input range, 3-1 configuring channel properties, 5-4 connecting resistive devices to SCXI-1503, 2-2

2-wire configuration, 2-4 3-wire resistive sensor connected in 2-wire

configuration, 2-5 4-wire configuration, 2-3 lead-resistance compensation

using 3-wire resistive sensor

and two matched current

sources, 2-6

Index

conventions used in the manual, iv creating a task

DAQ Assistant, 5-3 programmatically, 5-3

current output channels, questions

about, C-1, C-3 current sources, operating, 4-4 custom cables, 2-1

DAQ Assistant, creating a task, 5-3 DAQ device

accessing unused analog input

channels, C-2

DAQ devices

unavailable digital lines, C-2 digital control circuitry, 4-3 dynamic characteristics specifications, A-3

E/M Series DAQ devices, 4-4 electromagnetic compatibility

specifications, A-6 environment specifications, A-4 excitation specifications, A-4

filters specifications, A-3 front connector

pin assignments (table), 2-8

gain/input range, configuration, 3-1

input characteristics specifications, A-1 installation into SCXI chassis, 1-4

LabVIEW

developing an application, 5-8 programming a task (table), 5-8 using a NI-DAQmx channel property

node, 5-10

LabWindows/CVI

creating code for using SCXI-1503, 5-11

maximum working voltage specifications, A-5 Measurement & Automation Explorer

configurable settings, 3-2 removing the SCXI-1503, B-1

measurement properties, NI-DAQmx

RTD (table), 5-5 thermistor (table), 5-6 thermocouple (table), 5-7 voltage (table), 5-4

Measurement Studio

creating code for using SCXI-1503, 5-12

multiplexed mode operation

theory, 4-4

multiplexing

analog input signals, 4-4 SCXI-1503, 4-4 with AI 0 signal, 2-11

NI-DAQ version required, C-1 NI-DAQmx

configurable settings, 3-3 developing applications, 5-1

acquiring, analyzing, and

presenting, 5-7 adjusting timing and triggering, 5-3 completing, 5-8 configuring channel properties, 5-4 LabVIEW, 5-8

SCXI-1503 User Manual I-2 ni.com

Index

NI-DAQmx channel property

node, 5-10 program flowchart (figure), 5-2 programmable properties, 5-13 specifying channel strings, 5-11

RTD measurement properties (table), 5-5 thermistor measurement properties

(table), 5-6

thermocouple measurement properties

(table), 5-7

voltage measurement properties

(table), 5-4

operation of current sources, 4-4

physical specifications, A-5 pin assignments

front connector (table), 2-8

power requirements from SCXI

backplane, A-4

questions and answers, C-1

rear signal connector, 4-3

descriptions, 2-11

removing the SCXI-1503

from Measurement & Automation

Explorer, B-1

resistive devices, connecting to SCXI-1503

2-wire configuration, 2-4 3-wire resistive sensor connected to

2-wire configuration, 2-5

4-wire configuration, 2-3

lead-resistance compensation

using 3-wire resistive sensor and

two matched current sources, 2-6

RTD

measurement properties (table), 5-5

RTDs (resistive-temperature detectors)

measurement errors, 4-6 overview, 4-5 relationship between resistance and

temperature, 4-6

resistance-temperature curve (figure), 4-7

safety specifications, A-6 SCXI-1503

calibration, 5-13 common questions, C-1 common software settings, 3-1 communication signals (table), 2-11 configuration settings, 3-1 major components, 4-3 measurements, 3-3 multiplexing, 4-4 removing (figure), B-2 removing from SCXI chassis, B-1 taking measurements. See measurements using

LabWindows/CVI to create

code, 5-11

Measurement Studio to create

code, 5-12

SCXIbus

connector, 4-3

interface, 4-3 self-test verification, troubleshooting, C-1 signal connections

analog input, 2-1

front connector

pin assignments (table), 2-8

Index

signals

verifying, 3-4

NI-DAQmx, 3-4 software, NI-DAQ version required, C-1 specifications

analog input, A-1 CE compliance, A-6 electromagnetic compatibility, A-6 environment, A-4 excitation, A-4 filters, A-3 maximum working voltage, A-5 physical, A-5 power requirements from SCXI

backplane, A-4 safety, A-6 stability, A-3

specifying channel strings in

NI-DAQmx, 5-11

stability specifications, A-3

taking measurements. See measurements temperature measurement with resistive

transducers, 4-5

connecting resistive devices to

SCXI-1503, 2-2

2-wire configuration, 2-4 3-wire resistive sensor connected in

2-wire configuration, 2-5

4-wire configuration, 2-3

lead resistance compensation

using 3-wire resistive sensor and two

matched current sources, 2-6

RTDs

measurement errors, 4-6 overview, 4-5 relationship between resistance and

temperature, 4-6

resistance temperature curve

(figure), 4-7

thermistors

measurement circuits, 4-11 overview, 4-10 resistance/temperature

characteristics, 4-12

resistance-temperature curve

(figure), 4-11 theory of multiplexed operation, 4-4 theory of operation

analog circuitry, 4-3 digital circuitry, 4-3 rear signal connector, 4-3 SCXIbus connector, 4-3 SCXIbus interface, 4-3 theory of multiplexed operation, 4-4

thermistor, measurement properties

(table), 5-6

thermistors

measurement circuits, 4-11 overview, 4-10 resistance/temperature

characteristics, 4-12

resistance-temperature curve

(figure), 4-11

thermocouple, measurement properties

(table), 5-7 timing and triggering, adjusting, 5-3 transfer characteristics specifications, A-1 troubleshooting

incorrect test and verification, C-1

verifying

signal, 3-4

NI-DAQmx, 3-4

troubleshooting, C-1

Visual Basic

creating code for the SCXI-1503, 5-11

SCXI-1503 User Manual I-4 ni.com

National Instruments SCXI-1503 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

SCXI-1503 User Manual

Support

Worldwide Technical Support and Product Information

National Instruments Corporate Headquarters

Worldwide Offices

Important Information

Warranty

Copyright

Trademarks

Patents

WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS

Conventions

Contents

What You Need to Get Started

National Instruments Documentation

Installing Application Software, NI-DAQ, and the E/M Series DAQ Device

Installing the SCXI-1503 Module into the SCXI Chassis

Installing the Terminal Block

Table 1-1. Supported SCXI-1503 Terminal Blocks

Configuring the SCXI System Software

Verifying the SCXI-1503 Installation

Analog Input Signal Connections

Ground-Referencing the Signals

Connecting Resistive Devices to the SCXI-1503

4-Wire Configuration

Figure 2-1. 4-Wire Resistive Sensor Connected in a 4-Wire Configuration

2-Wire Configuration

Figure 2-2. 2-Wire Resistive Sensor Connected in a 2-Wire Configuration

3-Wire Resistive Sensor Configuration

Figure 2-3. 3-Wire Resistive Sensor Configuration

Lead-Resistance Compensation Using a 3-Wire Resistive Sensor and Two Matched Current Sources

Figure 2-4. 3-Wire Configuration Using Matched Current Sources

Front Connector

Table 2-1. Front Signal Pin Assignments

Table 2-2. Signal Descriptions

Rear Signal Connector

Table 2-3. Rear Signal Pin Assignments

Rear Signal Connector Descriptions

Table 2-4. SCXI-1503 50-Pin Rear Connector Signals

SCXI-1503 Software-Configurable Settings

Common Software-Configurable Settings

Gain/Input Range

Input Coupling

CJC Source/Value

Auto-Zero

Configurable Settings in MAX

NI-DAQmx

Creating a Global Channel or Task

Verifying the Signal

Verifying the Signal in NI-DAQmx Using a Task or Global Channel

Figure 4-1. Block Diagram of SCXI-1503

Rear Signal Connector, SCXIbus Connector, and SCXIbus Interface

Digital Control Circuitry

Analog Circuitry

Analog Input Channels

Operation of the Current Sources

Theory of Multiplexed Operation

Measuring Temperature with Resistive Transducers

RTDs

RTD Measurement Errors

Figure 4-2. 2-Wire RTD Measurement

The Relationship Between Resistance and Temperature in RTDs

Figure 4-3. Resistance-Temperature Curve for a 100 Ω Platinum RTD, α = 0.00385

Table 4-1. Platinum RTD Types

Thermistors

Figure 4-4. Resistance-Temperature Curve for a 2,252 Ω Thermistor

Thermistor Measurement Circuits

Figure 4-5. Thermistor Measurement with Constant Current Excitation

Resistance/Temperature Characteristic of Thermistors

Developing Your Application in NI-DAQmx

Typical Program Flowchart

Figure 5-1. Typical Program Flowchart for Voltage Measurement Channels

General Discussion of Typical Flowchart

Creating a Task Using DAQ Assistant or Programmatically

Adjusting Timing and Triggering

Configuring Channel Properties