National Instruments SCXI-1125 User Manual

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SCXI

SCXI-1125 User Manual

April 2008 372425B-01

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The SCXI-1125 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.

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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 a product, refer to the Read Me First: Safety and Radio-Frequency Interference for information about 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, 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.

monospace bold Bold text in this font denotes the messages and responses that the computer

automatically prints to the screen. This font also emphasizes lines of code that are different from the other examples.

monospace italic

Italic text in this font denotes text that is a placeholder for a word or value that you must supply.

Chapter 1 About the SCXI-1125

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

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

Installing Application Software, NI-DAQ, and the DAQ Device .................................1-4

Installing the SCXI-1125 Module into the SCXI Chassis...............................1-4

Connecting the SCXI-1125 in an SCXI Chassis

to an E/M Series DAQ Device for Multiplexed Scanning ...........................1-4

Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis

to an E/M Series DAQ Device for Multiplexed Scanning ...........................1-4

Connecting the SCXI-1125 to a n E/M Series DAQ Device

for Parallel Scanning ....................................................................................1-5

Verifying the SCXI-1125 Installation in Software ........................................................1-5

Installing SCXI Using NI-DAQmx in Software .............................................1-5

Manually Adding Modules in NI-DAQmx .....................................................1-6

Installing SCXI Using Traditional NI-DAQ (Legacy) in Software ................1-6

Manually Adding Modules in Traditional NI-DAQ (Legacy) ........................1-6

Verifying and Self-Testing the Installation .....................................................1-6

Troubleshooting the Self-Test Verification ...................................................................1-7

Troubleshooting in NI-DAQmx ......................................................................1-7

Chapter 2 Connecting Signals

AC and DC Voltage Connections..................................................................................2-1

Ground-Referenced Signal ..............................................................................2-2

Floating Signal.................................................................................................2-3

AC-Coupling ...................................................................................................2-4

Pin Assignments ............................................................................................................2-5

Temperature Sensor Connection .....................................................................2-7

Rear Signal Connector.....................................................................................2-7

Contents

Chapter 3 Configuring and Testing

SCXI-1125 Software-Configurable Settings .................................................................3-1

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

Filter Bandwidth ............................................................................... 3-1

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

Connecting the SCXI-1125 in an SCXI Chassis

to an E/M Series DAQ Device for Multiplexed Scanning........................... 3-2

Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis

to an E/M Series DAQ Device for Multiplexed Scanning........................... 3-2

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

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

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

Traditional NI-DAQ (Legacy) ........................................................................ 3-4

Configuring Module Property Pages

in Traditional NI-DAQ (Legacy)................................................... 3-5

Creating a Virtual Channel ............................................................... 3-6

Verifying the Signal ...................................................................................................... 3-6

Verifying the Signal in NI-DAQmx Using a Task or Global Channel........... 3-6

Verifying the Signal in Traditional NI-DAQ (Legacy) .................................. 3-7

Verifying the Signal Using Channel Strings .................................... 3-7

Verifying the Signal Using Virtual Channel .................................... 3-8

Chapter 4 Theory of Operation

Gain ............................................................................................................................... 4-1

Filter Bandwidth and Cutoff Frequency ........................................................................ 4-2

Operating in Multiplexed Mode .................................................................................... 4-2

Multiplexed Hardware Operation Theory....................................................... 4-3

Operating in Parallel Mode ........................................................................................... 4-3

Theory of Parallel Hardware Operation.......................................................... 4-4

Chapter 5 Using the SCXI-1125

Temperature Measurements Using Thermocouples...................................................... 5-1

Making High-Voltage Measurements ........................................................................... 5-4

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

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

General Discussion of Typical Flowchart....................................................... 5-7

Creating a Task Using DAQ Assistant or Programmatically ........... 5-7

Adjusting Timing and Triggering..................................................... 5-7

SCXI-1125 User Manual vi ni.com

Contents

Configuring Channel Properties........................................................5-8

Acquiring, Analyzing, and Presenting ..............................................5-9

Completing the Application ..............................................................5-9

Developing an Application Using LabVIEW..................................................5-9

Using a DAQmx Channel Property Node in LabVIEW ...................5-11

Specifying Channel Strings in NI-DAQmx.....................................................5-12

Text Based ADEs..............................................................................5-14

Measurement Studio (Visual Basic, .NET, and C#)........................................5-14

Programmable NI-DAQmx Properties..............................................5-14

Developing Your Application in Traditional NI-DAQ (Legacy) ..................................5-15

Traditional NI-DAQ (Legacy) in LabVIEW...................................................5-16

Typical Program Flow ......................................................................5-17

Configure the SCXI-1125 Settings Using Traditional NI-DAQ

(Legacy) in LabVIEW ..................................................................................5-18

Configure, Start Acquisition, and Take Readings Using Traditional

NI-DAQ (Legacy) in LabVIEW...................................................................5-19

Convert Scaling Using Traditional NI-DAQ (Legacy) in LabVIEW .............5-20

Analyze and Display Using Traditional NI-DAQ (Legacy) in LabVIEW ...... 5-20

Traditional NI-DAQ (Legacy) in Text-Based ADEs ......................................5-21

Configuring System Settings Using Traditional NI-DAQ (Legacy) C API....5-21

Configure Module Settings Using Traditional NI-DAQ (Legacy) C API ...... 5-22

Perform Offset Null Compensation

Using Traditional NI-DAQ (Legacy) C API ................................................5-23

Perform Acquisition Using Traditional NI-DAQ (Legacy) C API .................5-23

Perform Scaling, Analysis, and Display..........................................................5-24

Using Software for Multiplexed Scanning ......................................................5-24

LabVIEW and the SCXI Channel String ..........................................5-25

LabVIEW and the Virtual Channel String ........................................5-26

Performing a Multiplexed Scan.......................................................................5-27

C and Low-Level DAQ Functions .................................................... 5-28

Using Software for Parallel Scanning .............................................................5-28

LabVIEW and Parallel Mode............................................................5-28

C and Parallel Mode..........................................................................5-29

Other Application Documentation and Material ...........................................................5-29

Traditional NI-DAQ (Legacy) CVI Examples ................................................5-29

Traditional NI-DAQ (Legacy) Measurement Studio Examples......................5-29

Calibration .....................................................................................................................5-30

Calibration Procedures ....................................................................................5-30

One-Point Offset Calibration ............................................................5-31

Two-Point Gain and Offset Calibration ............................................5-32

Contents

Appendix A Specifications

Appendix B Using SCXI Channel Strings with Traditional NI-DAQ (Legacy) 7.0 or Later

Appendix C Removing the SCXI-1125

Appendix D Common Questions

Glossary

Index

Figures

Figure 2-1. Connecting a Ground-Referenced Signal ............................................. 2-2

Figure 2-2. Connecting a Floating Signal................................................................ 2-3

Figure 2-3. Connecting a Floating AC-Coupled Signal ..........................................2-4

Figure 2-4. Connecting a Ground-Referenced AC-Coupled Signal ........................ 2-4

Figure 4-1. SCXI-1125 Block Diagram................................................................... 4-1

Figure 5-1. Typical Program Flowchart .................................................................. 5-6

Figure 5-2. LabVIEW Channel Property Node with Lowpass Frequency

Set at 10 kHz on Channel SC1Mod1/ai0 .............................................. 5-12

Figure 5-3. Typical SCXI-1125 Program Flow

with Traditional NI-DAQ (Legacy) ...................................................... 5-17

Figure 5-4. Using the AI Parameter VI to Set Up the SCXI-1125 .......................... 5-19

Figure A-1. SCXI-1125 Dimensions ........................................................................ A-7

Figure C-1. Removing the SCXI-1125.....................................................................C-2

SCXI-1125 User Manual viii ni.com

Tables

Contents

Table 2-1. Front Signal Pin Assignments ..............................................................2-6

Table 2-2. Rear Signal Pin Assignments ................................................................2-8

Table 5-1. Extended Gain and Range Using the SCXI-1327 or SCXI-1313A....... 5-4

Table 5-2. Extended Gain and Range Using the TBX-1316 ..................................5-5

Table 5-3. NI-DAQmx Properties ..........................................................................5-8

Table 5-4. Programming a Task in LabVIEW........................................................5-10

Table 5-5. NI-DAQmx Properties ..........................................................................5-15

Table 5-6. Settings for Configuring the SCXI-1125

Through the AI Parameter.....................................................................5-18

Table 5-7. Configuration Functions........................................................................5-22

Table 5-8. NI-DAQ Functions Used to Configure SCXI-1125 ..............................5-23

Table 5-9. Gain Values and Input Limits ..............................................................5-31

Table A-1. Input Signal Range Versus Gain ...........................................................A-1

Table A-2. Terminal Block Maximum Voltages.....................................................A-8

Table D-1. Comparison of the SCXI-1125 with the SCXI-1120 ............................D-1

Table D-2. Digital Signals on the SCXI-1125.........................................................D-3

About the SCXI-1125

This chapter introduces the SCXI-1125 module and explains how to install the software and hardware.

The SCXI-1125 is an eight-channel isolated analog input conditioning module with programmable gain and filter settings on each channel and is jumperless. Each channel has 12 programmable gain settings from 1 to 2000 and two programmable filter settings of either 4 Hz or 10 kHz. Each channel has an external circuit for grounding the inputs that you can use for offset calibration. An onboard EEPROM provides nonvolatile storage of software correction constants for both gain and offset.

The SCXI-1125 provides up to 300 V has an input range of up to 1000 VDC when using an appropriate attenuator terminal block. The SCXI-1125 supports both multiplexed and parallel output modes and includes a cold-junction compensation (CJC) channel that you can scan in multiplexed mode.

What You Need to Get Started

To set up and use the SCXI-1125 module, you need the following:

❑ Hardware

– SCXI-1125 module

– One of the following terminal blocks:

• SCXI-1305

• SCXI-1313A

• SCXI-1320

• SCXI-1327

• SCXI-1328

• SCXI-1338

• TBX-1316

• TBX-1328

• TBX-1329

working isolation per channel and

rms

Chapter 1 About the SCXI-1125

Note For maximum allowable voltage for a particular terminal block refer to Table A-2,

Terminal Block Maximum Voltages.

– SCXI or PXI/SCXI combination chassis

– One of the following:

• E/M Series DAQ device

• SCXI-1600 module

– A computer if using an SCXI chassis

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

application

❑ Software

– NI-DAQ 7.0 or later

– One of the following software packages:

•LabVIEW

™

• LabWindows

• Measurement Studio

/CVI

™

❑ Documentation

– Read Me First: Safety and Radio-Frequency Interference

– DAQ Getting Started Guide

– SCXI Quick Start Guide

– SCXI-1125 User Manual

– Documentation for your hardware

– Documentation for your software

National Instruments Documentation

The SCXI-1125 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:

• SCXI or PXI 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.

SCXI-1125 User Manual 1-2 ni.com

Chapter 1 About the SCXI-1125

• 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.

• The SCXI hardware user manuals—Read these manuals next 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—If you are using accessory products, 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 E/M Series DAQ device that plugs into or is connected to the computer. Use this documentation for hardware installation and configuration instructions, specification information about the E/M Series 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

• NI application notes or tutorials—NI has additional material on measurements available at

ni.com/support.

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-1125

Installing Application Software, NI-DAQ, and the 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-1125. NI-DAQ 7.0 or later is required to configure and program the SCXI-1125 module. If you do not have NI-DAQ 7.0 or later, you can either contact a 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: Safety and Radio-Frequency Interference document

before removing equipment covers or connecting or disconnecting any signal wires.

Installing the SCXI-1125 Module into the SCXI Chassis

Refer to the SCXI Quick Start Guide to install your SCXI-1125 module.

Connecting the SCXI-1125 in an SCXI Chassis to an E/M Series DAQ Device for Multiplexed Scanning

Refer to the SCXI Quick Start Guide to install the cable adapter and connect the SCXI modules to the DAQ device.

If you have already installed the appropriate software, refer to Chapter 3,

Configuring and Testing, to configure the SCXI-1125 module(s).

Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis to an E/M Series DAQ Device for Multiplexed Scanning

Refer to the SCXI Quick Start Guide to connect the SCXI modules to the DAQ device.

If you have already installed the appropriate software, refer to Chapter 3,

Configuring and Testing, to configure the SCXI-1125 module(s).

SCXI-1125 User Manual 1-4 ni.com

Chapter 1 About the SCXI-1125

Connecting the SCXI-1125 to a n E/M Series DAQ Device for Parallel Scanning

This configuration allows you to route all eight channels of the SCXI-1125 in parallel to eight input channels of the E/M Series DAQ device to which it is connected. In this mode, you cannot directly access the CJC channel. Use this mode if you require a higher scanning rate than an SCXI system in multiplexed mode allows.

If you have not already installed all the modules, refer to the Installing the

SCXI-1125 Module into the SCXI Chassis section, then complete the

following steps:

1. Power off the SCXI chassis and the computer that contains the E/M Series DAQ device.

2. Insert the cable adapter into the rear of the SCXI-1125 module that is to be accessed in parallel mode by the E/M Series DAQ device. Refer to the installation guide for the cable assembly for more information.

3. Connect the cable to the back of the cable adapter ensuring that the cable fits securely.

4. Connect the other end of the cable to the E/M Series DAQ device that you want to use to access the SCXI-1125 in parallel mode.

5. Connect additional SCXI-1125 modules intended for parallel mode operation by repeating steps 2 through 4.

6. Check the installation, making sure the cable is securely fastened at both ends.

7. Power on the SCXI chassis.

8. Power on the computer.

If you have already installed the appropriate software, you are ready to configure the SCXI-1125 module(s) you installed for parallel mode operation.

Verifying the SCXI-1125 Installation in Software

Refer to the SCXI Quick Start Guide for information on verifying the SCXI installation.

Installing SCXI Using NI-DAQmx in Software

Refer to the SCXI Quick Start Guide for information on installing modules using NI-DAQmx in software.

Chapter 1 About the SCXI-1125

Manually Adding Modules in NI-DAQmx

If you did not auto-detect the SCXI modules, you must manually add each of the modules. Refer to the SCXI Quick Start Guide to manually add modules.

Note NI recommends auto-detecting modules for the first time configuration of the

chassis.

Installing SCXI Using Traditional NI-DAQ (Legacy) in Software

Refer to the SCXI Quick Start Guide for information on installing modules using Traditional NI-DAQ (Legacy) in software.

Manually Adding Modules in Traditional NI-DAQ (Legacy)

If you did not auto-detect the SCXI modules, you must manually add each of the modules. Refer to the SCXI Quick Start Guide to manually add modules.

Note NI recommends auto-detecting modules for the first time configuration of the

chassis.

Verifying and Self-Testing the Installation

The verification procedure for the SCXI chassis is the same for both NI-DAQmx and Traditional NI-DAQ (Legacy). To test the successful installation for the SCXI chassis, refer to the SCXI Quick Start Guide. Verify that the chassis is powered on and correctly connected to an E/M Series DAQ device.

After verifying and self-testing the installation, the SCXI system should operate properly with your ADE software. If the test did not complete successfully, refer to Chapter 3, Configuring and Testing, for troubleshooting steps.

SCXI-1125 User Manual 1-6 ni.com

Chapter 1 About the SCXI-1125

Troubleshooting the Self-Test Verification

If the Self-Test Verification did not verify the chassis configuration, complete the steps in this section to troubleshoot the SCXI configuration.

Troubleshooting in NI-DAQmx

• If you get a Verify SCXI Chassis message box showing the SCXI chassis model number, Chassis ID: x, and one or more messages stating Slot Number: x Configuration has module: SCXI-XXXX or 1125, hardware in chassis is: Empty, take the following troubleshooting actions:

– Make sure the SCXI chassis is powered on.

– Make sure all SCXI modules are properly installed in the chassis.

Refer to the SCXI Quick Start Guide for proper installation instructions.

– Make sure the cable between the SCXI chassis and E/M Series

DAQ device is properly connected.

– Inspect the cable connectors for bent pins.

– Make sure you are using the correct NI cable assembly.

– Test the E/M Series DAQ device to verify it is working properly.

Refer to the E/M Series DAQ device help file for more information.

• If you get a Verify SCXI Chassis message box showing the SCXI chassis model number, Chassis ID: x, and the message Slot

Number: x Configuration has module: SCXI-XXXX or 1125, hardware in chassis is: SCXI-YYYY, 1125, or Empty, complete the

following troubleshooting steps to correct the error.

1. Expand the list of NI-DAQmx devices by clicking the + next to

NI-DAQmx Devices.

2. Right-click the SCXI chassis and click Properties to load the

chassis configurator.

3. Under the Modules tab, ensure that the cabled module is listed in

the correct slot.

4. If the cabled module is not listed in the correct slot, complete the

following troubleshooting steps:

a. If the cabled module is not listed in the correct slot and the

slot is empty, click the drop-down listbox next to the correct slot and select the cabled module. Configure the cabled

Chapter 1 About the SCXI-1125

module following the steps listed in the SCXI Quick Start Guide. Click OK.

b. If another module appears where the cabled module should

be, click the drop-down listbox next to the correct slot and select the cabled module. A message box appears asking you to confirm the module replacement. Click OK. Configure the cabled module following the steps listed in the SCXI Quick Start Guide. Click OK.

• Ensure that you have the highest priority SCXI module cabled to the E/M Series DAQ device. Refer to the SCXI Quick Start Guide to find out which SCXI module in the chassis should be cabled to the E/M Series DAQ device.

• After checking the preceding items, return to the Troubleshooting the

Self-Test Verification section and retest the SCXI chassis.

If these measures do not successfully configure the SCXI system, contact NI. Refer to the Signal Conditioning Technical Support Information document for contact information.

SCXI-1125 User Manual 1-8 ni.com

Connecting Signals

This chapter describes the input and output signals connections to the SCXI-1125 module with the module front connector and the rear signal connector. This chapter also includes specifications and connection instructions for the signals on the SCXI-1125 module connectors.

Notes Refer to the Read Me First: Safety and Radio-Frequency Interference document

before removing equipment covers or connecting or disconnecting any signal wires.

For EMC compliance, operate this device with shielded cabling.

The isolated channels of the SCXI-1125 allow you to make precision high-voltage measurements or low-voltage measurement of signals riding on high common-mode voltages while protecting sensitive computer parts and equipment connected to the module. The isolated amplifiers fulfill two purposes on the SCXI-1125 module. First, they can convert a small signal riding on a high common-mode voltage into a single-ended signal with respect to the SCXI-1125 chassis ground. With this conversion, you can extract the analog input signal from a high common-mode voltage before sampling by the E/M Series DAQ device. Second, the isolation amplifier amplifies and filters an input signal resulting in increased measurement resolution and accuracy. The following sections explain how to make signal connections to maximize the effectiveness of the SCXI-1125 for conditioning analog signals.

AC and DC Voltage Connections

You can make input signal connections to the SCXI-1125 through the front signal connector or through accessory terminal blocks. Chapter 1, About

the SCXI-1125, contains a list of SCXI-1125-compatible terminal blocks.

Terminal blocks have features such as screw-terminal connectivity, BNC connectivity, cold-junction temperature measurement, and attenuation.

The pin assignment for the SCXI-1125 front signal connector is shown in Table 2-1. The positive input terminal for each channel is in Column A and the negative input terminal for each channel is in Column C. Input connections to each channel are fully floating with respect to ground and

Chapter 2 Connecting Signals

completely isolated from other channels. You can operate with common-mode voltage levels up to 300 V

Figures 2-1 through 2-4 show signal connection methods that give the highest noise immunity.

Ground-Referenced Signal

When the negative input signal line is connected either directly or indirectly to earth ground (usually at the transducer end), connect this line to the negative input terminal, as shown in Figure 2-1. No ground connection is made at the SCXI-1125. This situation includes cases where a floating source can be riding on a high common-mode voltage that is ground referenced.

rms

–

High

CMV

–

Module

out

–

Figure 2-1. Connecting a Ground-Referenced Signal

SCXI-1125 User Manual 2-2 ni.com

Floating Signal

Chapter 2 Connecting Signals

In cases where both signal lines at the transducer end are floating and no common-mode voltage exists, establish an earth connection at the SCXI-1125 by connecting the negative input line to chassis ground in the terminal block, as shown in Figure 2-2. This eliminates noise that can ride on the floating signal. If the floating signal is not configured like Figure 2-2, the noise can couple to the chassis ground through the amplifier and exhibit a differential mode signal that can be amplified by the amplifier. Connecting the signal to chassis ground breaks the isolation barrier.

–

Module

Figure 2-2. Connecting a Floating Signal

out

–

Chapter 2 Connecting Signals

AC-Coupling

You can have an application where you wish to measure only AC voltages and remove the DC component of a signal before amplification and sampling. In such cases, you can connect a capacitor in series with one or both input terminals of the SCXI-1125, as shown in Figures 2-3 and 2-4. A resistor is connected across the input terminals of the channel to DC reference the input stage of the SCXI-1125. You do not need to use a bias resistor with any high-voltage terminal blocks, since the terminal blocks already have a resistor between the input terminals, or with the SCXI-1305 BNC connectivity terminal block, since this terminal block already has an AC-coupling option built in.

Caution

Connecting a signal source to chassis ground in Figures 2-2 and 2-3, breaks the

isolation barrier.

–

bias

Module

–

Figure 2-3. Connecting a Floating AC-Coupled Signal

–

bias

High CMV

Module

–

out

Figure 2-4. Connecting a Ground-Referenced AC-Coupled Signal

SCXI-1125 User Manual 2-4 ni.com

The value of the bias resistor should be between 100 kΩ and 1 MΩ . An added DC offset voltage results, due to input bias current flowing through the bias resistor. For example, with a 1 MΩ bias resistor and the specified maximum input bias current of 1 nA, you have a maximum added input offset voltage of ±1 mV in addition to the initial offset voltage.

Since only the AC signal is of interest when AC-coupling, you can choose to remove the DC offset in software by using a simple highpass filter.

Caution Pins A2, A4, A8, C2, C4, C6, and C8 on the front signal connector are not isolated

and do not have the same protection circuitry as the positive and negative analog input pairs discussed in the Floating Signal section. Hooking up external signals to these pins can damage the SCXI-1125 module.

Pin Assignments

The front signal connector is a special 32-pin DIN C male front connector used for connecting analog input signals, including the CJC, to the analog circuitry of the SCXI-1125. This connection allows access to the eight differential analog input signals. The positive terminal is AIx + and the negative terminal AIx –. A missing pin exists between two consecutive input channels to meet the UL spacing requirements for high voltage signals. CJ TEMP is the signal connection used by the cold-junction channel on the SCXI-1125. The signals on pins A6, A8, C6, and C8 are reserved for serial communication. The +5 V signal and CHS GND signals are used as the power supply and ground signals for the CJC sensor and other circuitry on the terminal block. The pin assignments for the SCXI-1125 front signal connection are shown in Table 2-1.

Chapter 2 Connecting Signals

Caution Do not make signal connections to pins A2, A4, A6, A8, C2, C4, C6, or C8 on the

front signal connector. Connecting external signals to these pins can damage the SCXI-1125 Module.

Chapter 2 Connecting Signals

Table 2-1. Front Signal Pin Assignments

Front Connector Diagram Pin Number Column A Column B Column C

32 AI 0 + — AI 0 –

Column

A B C

NC means no connection

— means no pin

31 — — —

30 AI 1 + — AI 1 –

29 — — —

28 NC — NC

27 — — —

26 AI 2 + — AI 2 –

25 — — —

24 AI 3 + — AI 3 –

23 — — —

22 NC — NC

21 — — —

20 AI 4 + — AI 4 –

19 — — —

18 AI 5 + — AI 5 –

17 — — —

16 NC — NC

15 — — —

14 AI 6 + — AI 6 –

13 — — —

12 AI 7 + — AI 7 –

11 — — —

10 NC — NC

9 — — —

8 RSVD — RSVD

7 — — —

6 RSVD — RSVD

5 — — —

4 +5 V — CJ TEMP

3 — — —

2 CHS GND — RSVD

1 — — —

SCXI-1125 User Manual 2-6 ni.com

Temperature Sensor Connection

Pin C4 on the front signal connector is used to connect to a terminal block temperature sensor. The temperature sensor channel is not isolated and is referenced to the chassis ground. The connection is overvoltage protected to ±25 VDC with power on and ±15 VDC with power off.

Rear Signal Connector

The rear signal connector is a 50-pin male ribbon cable connector used for analog signal connectivity and communication between the SCXI-1125 and the connected DAQ device. The rear signal connector allows the DAQ device to access all eight differential analog output signals from the SCXI-1125. The positive terminal of each analog output is CH x + and the negative terminal CH x –. Grounding signals, AI GND and OUT REF, provide reference signals needed in the various analog referencing modes on the E/M Series DAQ device. In multiplexed mode, the CH 0 signal pair is used for sending all eight channels of the SCXI-1125, and other analog signals from other modules, to the connected E/M Series DAQ device. If the module is directly connected to the E/M Series DAQ device, the other analog channels of the E/M Series DAQ device are still unavailable for general-purpose analog input because they are still connected to the amplifier outputs of the SCXI-1125 in multiplexed mode.

Chapter 2 Connecting Signals

The communication signals between the DAQ device and the SCXI system are SER DAT IN, SER DAT OUT, DAQ D*/A, SLOT 0 SEL*, SER CLK, and AI HOLD COMP, AI HOLD. The digital ground, D GND on pins 24 and 33, provides a separate ground reference for the communication signals. SER DAT IN, SER DAT OUT, DAQ D*/A, SLOT 0 SEL*, and SER CLK are the communication lines for programming the SCXI-1125. The AI HOLD COMP, AI HOLD and SYNC signals are the signals necessary for multiplexed mode scanning. If the E/M Series DAQ device is connected to the SCXI-1125, these digital lines are unavailable for general-purpose digital I/O. The rear signal pin assignments are shown in Table 2-2.

Chapter 2 Connecting Signals

Rear Connector

Diagram

Table 2-2. Rear Signal Pin Assignments

Signal Name Pin Number Pin Number Signal Name

AI GND 1 2 AI GND

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 means no

connection

CH 0 + 3 4 CH 0 –

CH 1 + 5 6 CH 1–

CH 2 + 7 8 CH 2 –

CH 3 + 9 10 CH 3 –

CH 4 + 11 12 CH 4 –

CH 5 + 13 14 CH 5 –

CH 6 + 15 16 CH 6 –

CH 7 + 17 18 CH 7 –

OUT REF 19 20 NC

NC 21 22 NC

NC 23 24 D 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

D GND 33 34 NC

NC 35 36 AI HOLD COMP, AI HOLD

SER CLK 37 38 NC

NC 39 40 NC

NC 41 42 NC

NC 43 44 NC

NC 45 46 SYNC

NC 47 48 NC

NC 49 50 NC

SCXI-1125 User Manual 2-8 ni.com

Configuring and Testing

This chapter discusses configuring the SCXI-1125 in MAX for use with either NI-DAQmx or Traditional NI-DAQ (Legacy), creating and testing a virtual channel, global channel or task. 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.

SCXI-1125 Software-Configurable Settings

This section describes the common software configurable settings and how to verify the signal using both NI-DAQmx and Traditional NI-DAQ (Legacy).

Common Software-Configurable Settings

This section describes the most frequently used software-configurable settings for the SCXI-1125. Refer to Chapter 4, Theory of Operation, for a complete list of software-configurable settings.

Filter Bandwidth

Filter bandwidth is a software-configurable setting that allows you to select a lowpass filter cutoff frequency. You can choose 4.0 Hz or 10 kHz.

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.

Chapter 3 Configuring and Testing

Connecting the SCXI-1125 in an SCXI Chassis to an E/M Series DAQ Device for Multiplexed Scanning

Refer to the SCXI Quick Start Guide to install the cable adapter and connect the SCXI modules to the DAQ device.

If you have already installed the appropriate software, refer to Chapter 3,

Configuring and Testing, to configure the SCXI-1125 module(s).

Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis to an E/M Series DAQ Device for Multiplexed Scanning

Refer to the SCXI Quick Start Guide to connect the SCXI modules to the DAQ device.

If you have already installed the appropriate software, refer to Chapter 3,

Configuring and Testing, to configure the SCXI-1125 module(s).

Configurable Settings in MAX

Note If you are not using an NI ADE, using an NI ADE prior to version 7.0, 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 7.0 or later of an NI ADE.

This section describes where users can access each software-configurable setting for modification in MAX. The location of the settings varies depending on the version of NI-DAQ you use. Refer to either the

NI-DAQmx section or the Traditional NI-DAQ (Legacy) section. You also

can refer to the DAQ Getting Started Guide and the SCXI Quick Start Guide for more information on installing and configuring your hardware. You also can use the DAQ Assistant to graphically configure common measurement tasks, channels, or scales.

SCXI-1125 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 4, Theory of Operation, for information on using functions in your application.

Chapter 3 Configuring and Testing

In NI-DAQmx, you can configure software settings such as filter bandwidth and gain/input signal range in the following ways:

• Task or global channel in MAX

• Functions in your application

These sections describe settings that you can change in MAX and where they are located.

• Filter bandwidth—configure the Device tab using either NI-DAQmx Task or NI-DAQmx Global Channel. You also can set the value through your application.

• Input signal range—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.

• Modes of operation—configure only using chassis installation in software. Refer to Chapter 1, About the SCXI-1125, for more information on chassis installation. The default setting in NI-DAQmx is multiplexed.

• Terminal block attenuation—for terminal blocks with manually adjustable attenuation such as the SCXI-1327, you must configure the attenuator in the chassis configurator. Refer to the SCXI Quick Start Guide for more information.

Note Refer to Chapter 4, Theory of Operation, for information on configuring the settings

for your application using Traditional NI-DAQ (Legacy).

Creating a Voltage Global Channel or Task

To create a new 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.

Chapter 3 Configuring and Testing

4. Select Analog Input.

5. Select Voltage.

6. If you are creating a task, you can select a range of channels by holding

7. Name the task or channel and click Finish.

8. In the box labelled Channel List, select the channel(s) you want to

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

10. Click the Device tab and select the autozero mode and lowpass filter

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

down the <Shift> key while selecting the channels. You can select multiple individual channels by holding down the <Ctrl> key while selecting channels. If you are creating a channel, you can only select one channel. Click Next.

configure. 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 selecting channels.

Context help information for each setting is provided on the right side of the screen. Refer to Chapter 3, Configuring and Testing, for more information.

cutoff frequency.

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

Traditional NI-DAQ (Legacy)

In Traditional NI-DAQ (Legacy), you can configure software settings, such as configuration, voltage excitation level, filter bandwidth, gain/input signal range, and calibration settings in the following three ways:

• module property pages in MAX

• virtual channels properties in MAX

• functions in your ADE

Note All software-configurable settings are not configurable in all three ways. This

section only discusses settings in MAX. Refer to Chapter 4, Theory of Operation, for information on using functions in your application.

Most of these settings are available in module properties and/or using virtual channels:

• Filter bandwidth—configure only using module properties. You also can set bandwidth through your application. The default filter bandwidth level for Traditional NI-DAQ (Legacy) is 4 Hz.

SCXI-1125 User Manual 3-4 ni.com

Chapter 3 Configuring and Testing

• Gain/input signal range—configure gain using module properties. When you set the minimum and maximum range of the virtual channel, the driver selects the best gain. The default gain setting for Traditional NI-DAQ (Legacy) is 1000.

• Terminal block gain—this setting is only configurable if you selected a terminal block that supports adjustable attenuation.

• Modes of operation—configure only using module properties. The default setting in Traditional NI-DAQ (Legacy) is multiplexed mode.

Note Refer to Chapter 4, Theory of Operation, for information on configuring the settings

for your application using Traditional NI-DAQ (Legacy).

Configuring Module Property Pages in Traditional NI-DAQ (Legacy)

1. Right-click the SCXI-1125 module you want to configure and select Properties. Click General.

2. If the module you are configuring is connected to an E Series DAQ device, select that device by using Connected to. If you want this E Series DAQ device to control the chassis, confirm there is a check in the This device will control the chassis checkbox. If the module you are configuring is not connected to an E Series DAQ device, select None.

3. Click the Channel tab. Select the appropriate gain and filter for each channel. If you want to configure all the channels at the same time, select the Channel drop-down menu, scroll to the bottom, and select All Channels. Refer to the SCXI-1125 Software-Configurable Settings section for a detailed description of each setting. Click Apply.

4. Click Accessory. Select the accessory you connected to the module. If the accessory has a configurable gain, select the desired gain. When configuration is complete, click OK.

The Traditional NI-DAQ (Legacy) chassis and SCXI-1125 should now be configured properly. If you need to change the module configuration, right-click the module and repeat steps 1 through 4. Test the system following the steps in the Troubleshooting the Self-Test Verification section of Chapter 1, About the SCXI-1125.

Chapter 3 Configuring and Testing

Creating a Virtual Channel

To create a virtual channel, complete the following steps:

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

2. Select Traditional NI-DAQ Virtual Channel and click Finish.

3. Click Add Channel.

4. Select Analog Input from the drop-down list and click Next.

5. Enter the Channel Name and Channel Description, and click Next.

6. Select Voltage from the drop-down list and click Next.

7. Enter the units and input range, and click Next.

8. Select the appropriate scaling option and click Next.

9. Enter the following information:

10. What DAQ hardware will be used? from the drop-down list.

11. Click Finish.

a. What channel on your DAQ hardware? from the drop-down list.

b. Which analog input mode will be used? from the drop-down list.

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 and Traditional NI-DAQ (Legacy).

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

You can verify the signals on the SCXI-1125 using NI-DAQmx by completing the following steps:

1. Expand Data Neighborhood.

2. Expand NI-DAQmx Tasks.

3. Click the task.

4. Click the Add Channels or Remove Channels button to add/remove

channels.

5. In the window that appears, click the + next to the module of interest.

6. 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.

7. Enter the appropriate information on the Settings tab.

SCXI-1125 User Manual 3-6 ni.com

8. Click the Device tab.

9. Enter the appropriate information on the Device tab.

10. Click the Test button.

11. Click the Start button.

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

button.

You have now verified the SCXI-1125 configuration and signal connection.

Note For more information on how to further configure the SCXI-1125, or how to use

LabVIEW to configure the module and take measurements, refer to Chapter 4, Theory of

Operation.

Verifying the Signal in Traditional NI-DAQ (Legacy)

This section discusses how to verify the signal in Traditional NI-DAQ (Legacy) using channel strings and virtual channels.

Verifying the Signal Using Channel Strings

The format of the channel string is as follows:

obx

! scy ! mdz ! channel

Chapter 3 Configuring and Testing

where

•obx is the onboard E Series DAQ device channel, with x representing

a particular channel where the multiplexed channels are sent. This value is 0 for E Series DAQ device channel 0 in a single-chassis system. In a multichassis or remote chassis system, the E Series DAQ device channel x corresponds to chassis number n – 1, where E Series DAQ device channel x is used for scanning the nth chassis in the system.

•scy is the SCXI chassis ID, where y is the number you chose when

configuring the chassis.

•mdz is the slot position where the module is located, with z being the

particular slot number. The slots in a chassis are numbered from left to right, starting with 1.

• channel is the channel that is sampled from module z.

Use the format single input channel.

obx ! scy ! mdz ! n to verify the signal, where n is a

Chapter 3 Configuring and Testing

Complete the following steps to use channel strings in verifying the signal:

1. Expand Devices and Interfaces.

2. Expand Traditional NI-DAQ Devices.

3. Right-click the appropriate E Series DAQ device.

4. Click Test Panels.

5. Enter the channel string.

6. Enter the input limits.

7. Select the Data Mode.

8. Select the Y Scale Mode.

Refer to the LabVIEW Measurements Manual for more information and for proper formatting of channel strings for different uses.

Verifying the Signal Using Virtual Channel

If you have already created a virtual channel, complete the following steps to verify the signal:

1. Right-click the virtual channel you want to verify and select Test.

2. In Channel Names, select the channel you want to verify.

3. When you have completed verifying the channel, click Close.

SCXI-1125 User Manual 3-8 ni.com

Theory of Operation

The section includes a brief overview and a detailed discussion of the circuit features of the module. The two major modes of operation, multiplexed and parallel mode, are discussed. Refer to Figure 4-1 while reading this section.

Gain Select

AI 0

AI 7

Gain

Lowpass

Filter

–

Gain Select

Front Signal Connector

Lowpass

Filter

–

MTEMP

Lowpass

Filter

Lowpass

Filter

AI 0

Analog

Multiplexer

AI 7

Multiplexer

Control

Figure 4-1. SCXI-1125 Block Diagram

Buffer

Analog

Switch

Bus

Digital Interface

and Control

Scan

Clock

AI 0+

AI 0–

AI 7+

AI 7–

Rear Signal Connector

SCXIbus Connector

The SCXI-1125 has 12 different gain settings, from 1 to 2000, enabling signal ranges ±5 V to ±2.5 mV. When the SCXI-1125 is used with a terminal block that provides attenuation, the input range expands up to 1000 V. Refer to Appendix A, Specifications for a full list of input ranges.

Chapter 4 Theory of Operation

Refer to the Configurable Settings in MAX section of Chapter 3,

Configuring and Testing, for more information about programmatically

setting gain using range settings in MAX. For more information about programmatically setting gain using range settings in NI-DAQmx and Traditional NI-DAQ (Legacy), refer to the Developing Your Application in

NI-DAQmx section or the Developing Your Application in Traditional NI-DAQ (Legacy) section, respectively, of Chapter 5, Using the SCXI-1125.

Filter Bandwidth and Cutoff Frequency

The SCXI-1125 provides two filtering stages with an overall response of a four-pole Butterworth filter. You can control the cutoff frequency of the filter through software. You can choose 4 Hz or 10 kHz. For additional flexibility in cutoff frequency settings and for greater suppression, NI recommends combining the hardware filtering provided by the SCXI-1125 with digital filtering. NI recommends using the Advanced Analysis functions of LabVIEW, LabWindows/CVI, or Measurement Studio. By combining hardware anti-aliasing with digital filtering, you can choose any cutoff frequency.

The Advanced Analysis functions are only available in LabVIEW Full or Professional Development Systems, and LabWindows/CVI Base or Full Development Systems.

Refer to the Configurable Settings in MAX section of Chapter 3,

Configuring and Testing, for more information about programmatically

setting the cutoff frequency of the filter in MAX. For more information about programmatically setting the cutoff frequency of the filter in NI-DAQmx and Traditional NI-DAQ (Legacy), refer to the Developing

Your Application in NI-DAQmx section or the Developing Your Application in Traditional NI-DAQ (Legacy) section, respectively, of

Chapter 5, Using the SCXI-1125.

Operating in Multiplexed Mode

You can configure the SCXI-1125 to operate in multiplexed mode as described in Chapter 1, About the SCXI-1125. Using this mode of operation, you can scan all input channels of the SCXI-1125 into one output channel that is read by the National Instruments DAQ device. You can also multiplex the CJC channel that connects to a sensor on the SCXI terminal block for making temperature measurements.

SCXI-1125 User Manual 4-2 ni.com

Multiplexed Hardware Operation Theory

When you configure a module for multiplexed mode operation, the routing of multiplexed signals to the E/M Series DAQ device depends on which module in the SCXI system is cabled to the E/M Series DAQ device. There are several possible scenarios for routing signals from the multiplexed modules to the E/M Series DAQ device. If the module being scanned is not directly cabled to the E/M Series 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 E/M Series DAQ device through the CH0 signal on the rear signal connector. If the E/M Series DAQ device scans the cabled module, the module routes its input signals through the CH0 signal on the rear signal connector. The power of SCXI multiplexed scanning is its ability to route many input channels to a single channel on the E/M Series DAQ device.

Note The SCXI-1125 parallel outputs continuously drive the rear signal connector output

pins even when you configure the module in multiplexed mode. If the module is cabled to an E/M Series DAQ device in multiplexed mode, the differential inputs 1 through 7 on the E/M Series DAQ device cannot be used for general-purpose analog input. Refer to Appendix D, Common Questions, for more information on available pins on the rear signal connector.

Chapter 4 Theory of Operation

Multiplexed mode is typically used for performing scanning operations with the SCXI-1125. 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. You can specify this list to scan the modules in the chassis in any order, with an arbitrary number of channels for each module entry in the list. You can randomly scan the channels on the SCXI-1125, meaning channels can be in any order and occur multiple times in a single scan. When performing multiple scans, the list pointer of the module automatically wraps around and starts scanning with the first channel in the scan list.

Operating in Parallel Mode

You can configure the SCXI-1125 to operate in parallel mode as described in Chapter 1, About the SCXI-1125. In parallel mode, all eight analog output channels on the SCXI-1125 are connected to eight analog input channels on the E/M Series DAQ device. The CJC channel is not accessible. Every SCXI-1125 configured for parallel mode must have a E/M Series DAQ device directly cabled to it.

Chapter 4 Theory of Operation

Theory of Parallel Hardware Operation

In parallel mode, the CH0 signal on the rear signal connector is configured as the output of the SCXI-1125 analog input channel 0. The rear signal connector carries each of the analog outputs of the SCXI-1125 to the connected DAQ device. You can use an SCXI-1180 feedthrough connector to make each of the outputs available at the front of the chassis; which is useful for cascading these signals to other modules for additional signal conditioning purposes. Parallel mode allows you to bypass scanning and you are not limited by the settling time required by the multiplexer of SCXI-1125. You can scan the channels more accurately at a faster rate, depending on which E/M Series DAQ device you connect to the module.

SCXI-1125 User Manual 4-4 ni.com

Using the SCXI-1125

This chapter discusses typical applications for the SCXI-1125. While this list is not comprehensive, it provides some guidance on how to improve measurement accuracy for some of the most popular applications of the SCXI-1125. Advanced operations such as calibration and using the CJC channel are discussed as well.

Temperature Measurements Using Thermocouples

Making isolated temperature measurements from thermocouples is a common use of the SCXI-1125. This section discusses how to use thermocouples, CJC, and how to calculate the temperature accuracy of the SCXI-1125.

NI recommends using the SCXI-1328 terminal block to make thermocouple measurements with the SCXI-1125. Although you can use many of the SCXI terminal blocks for thermocouple measurements, the SCXI-1328 has an isothermal design that reduces temperature gradients within the terminal block housing. This design reduces the CJC errors which might reduce the accuracy of your temperature measurement. Most SCXI terminal blocks available for the SCXI-1125 contain a cold-junction temperature sensor, which is used for measuring ambient temperature. This sensor connects to a special channel on the SCXI-1125 inside the terminal block close to where the thermocouple connects to the screw terminals.

Note Place the SCXI chassis away from extreme temperature gradients to minimize the

temperature gradient inside the terminal block and maintain its isothermal nature for accurate CJC.

A thermocouple relies on the principle that a small voltage that varies with temperature is produced at the junction of two dissimilar metals. CJC is necessary because the junction between the end of the thermocouple lead wires and the screw terminals produces a small potential difference, adding error to the thermocouple voltage. Knowing the temperature at the point where the thermocouple is connected to the measurement instrument allows you to determine the correct temperature reading at the thermocouple junction. Due to the nonlinear relationship between

Chapter 5 Using the SCXI-1125

thermocouple junction voltage and temperature, this voltage conversion (linearization) is best done through software.

NI-DAQ has built-in scaling for most thermocouple types. In NI-DAQmx, you can create a thermocouple task or global channel. In Traditional NI-DAQ (Legacy), you can create a thermocouple virtual channel.

If you choose to not let the driver scale the voltage readings for you in software, you must do several conversions by using conversion coefficients that reflect the voltage-temperature relationship for the type of thermocouple and CJC being used. Complete the following steps to accurately determine thermocouple temperature:

1. Read the voltage from the CJC sensor and convert this voltage to a temperature.

2. Convert this temperature to the corresponding voltage for the thermocouple type in use.

3. Read the input voltage from the thermocouple.

4. Add the two voltages.

5. Translate the resultant voltage into the thermocouple temperature reading.

You have completed the steps to get the true temperature reading from the thermocouple junction.

National Instruments software ADEs have useful conversion functions for CJC. In LabVIEW, virtual channels with the CJC channel invoked or the Convert Thermocouple Reading VI are used. In C, use the NI-DAQ function, function

Thermocouple_Convert. In C, you might also need to use the

Thermistor_Convert, if your terminal block uses a thermistor

to perform CJC. For more information about CJC, refer to your software ADE user documentation.

To calculate the temperature accuracy of your SCXI-1125, you must consider several factors. First, the type of sensor and the temperature range you expect directly affects which gain your SCXI-1125 module uses for voltage readings, thereby directly affecting the resolution with which you can read temperature. After determining the range necessary for your application, you can apply the measurement accuracy specifications of the SCXI-1125; such as offset error, gain error, and noise to determine how these will affect your temperature measurement. Next, you must consider the accuracy of your cold-junction sensor and incorporate this into the total temperature error of your reading. Finally, the accuracy of the DAQ device you use must be factored in to determine your overall system error.

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Chapter 5 Using the SCXI-1125

Complete the following steps to calculate the overall temperature error using the SCXI-1125 with an E Series MIO DAQ device:

1. Based on the required temperature range and the type of sensor, determine the gain to use. For example, using a K-type thermocouple with a required temperature range of 0 to 100 °C, the corresponding voltage range is –1.002 mV to 4.0962 mV (averaging 41.0 µV/°C in this range). For this example, use a gain of 1000 for this temperature range to get maximum temperature resolution.

2. Next, look up the analog accuracy specifications from Appendix A,

Specifications, for the gain and filter settings you have chosen. You

must consider how offset, gain, and system noise affect your measurement. You might also consider common-mode rejection, temperature drift, and other specifications based on the operating environment. For example, using a gain of 1000, the offset error is ± 0.2 µV, the gain error is ± 0.03% which corresponds to ± 1.43 µV at full-scale temperature, and the system noise is 100 V noise which is about 3 times this, or 300 nV

) because of the 4 Hz

(use peak

rms

filter. In this example you might or might not be able to average out the noise. The total error is ± 1.73 µV at the full-scale temperature range, which gives a preliminary accuracy of ± 0.04 °C (1.73 µV divided by

41.0 µV/°C).

3. Next, consider the accuracy of the cold-junction sensor you are using. For example, using the SCXI-1328, which, at about room temperature with little temperature gradient, has an accuracy of ± 0.5 °C. You must convert this temperature accuracy back to a voltage corresponding to a K-type thermocouple accuracy at 25 °C. This conversion produces about ± 20 µV of error.

4. Add the two voltages and determine the overall temperature error. For example, the total error due to the SCXI portion of the system in this example now becomes ± 21.73 µV. This total error corresponds to about ± 0.53 °C (21.73 µV divided by 41.0 µV/°C) temperature error using the K-type thermocouple at this range.

5. Determine the contribution of DAQ device error. For example, if using a 12-bit DAQ device, the DAQ device contributes a gain of 2, and therefore the code width becomes 2.44 µV. As a result, the total system error now becomes ± (21.73 µV + 2.44 µV), which corresponds to about 0.59 °C. If you were to choose a 16-bit board, you can achieve a code width of 0.153 µV, producing a total system error of 0.53 °C.

Chapter 5 Using the SCXI-1125

Making High-Voltage Measurements

Another common use of the SCXI-1125 is to make measurements up to 1000 VDC. Making measurements beyond ± 5 V requires use of the an attenuator terminal block. The SCXI-1327 and SCXI-1313A terminal blocks have a selectable attenuator for choosing between no attenuation or 100:1 attenuation, which allows you to use the SCXI-1125 with up to 300 V SCXI-1313A.

The TBX-1316 has a fixed 200:1 attenuation, which allows you to use the SCXI-1125 with up to 1000 VDC, Measurement Category I.

The SCXI-1327 and SCXI-1313A also include a cold-junction sensor so you can combine thermocouple measurements with high-voltage measurements. When making signal connections, or when working with high-voltage signals, refer to the terminal block installation guide. If you are using the SCXI-1125 to measure signals with attenuation on the terminal block, an external bias resistor is not needed, because a bias resistor is already used for achieving the attenuation.

Table 5-1 lists the extended ranges of gain possible with the SCXI-1327 and SCXI-1313A. Table 5-2 lists the extended gain possible with the TBX-1316.

when using the SCXI-1327 and up to 150 V

rms

when using the

rms

Table 5-1. Extended Gain and Range Using the SCXI-1327 or SCXI-1313A

Overall

Gain

Input

Range

SCXI-1125

Gain

SCXI-1327

Attenuation

SCXI-1313A

Attenuation

0.01 ± 300 V 1 100 —

0.02 ± 250 V 2 100 —

0.002 ± 150 V 2 100 100

0.05 ± 100 V 5 100 100

0.1 ± 50 V 10 100 100

0.2 ± 25 V 20 100 100

0.5 ± 10 V 50 100 100

2.5 ± 2 V 250 100 100

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Chapter 5 Using the SCXI-1125

Table 5-2. Extended Gain and Range Using the TBX-1316

Overall

Gain

0.005 ± 1000 V 1 200

0.01 ± 500 V 2 200

0.025 ± 200 V 5 200

0.05 ± 100 V 10 200

0.1 ± 50 V 20 200

0.25 ± 20 V 50 200

1.25 ± 4 V 250 200

The overall input impedance is reduced when attenuating the input, but this is acceptable in most applications. Refer to terminal block installation guides for more information. Appendix A, Specifications, shows how the analog input specifications are affected with the addition of the SCXI-1327 terminal block.

Input

Range

SCXI-1125

Gain

Developing Your Application in NI-DAQmx

Note If you are not using an NI ADE, using an NI ADE prior to version 7.0, or are using

an unlicensed copy of an NI ADE, NI License Manager displays additional dialog boxes so you can create a task or global channel in unlicensed mode. These dialog boxes continue to appear until you install version 7.0 or later of an NI ADE.

TBX-1316

Attenuation

This section describes how to configure and use NI-DAQmx to control the SCXI-1125 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 flowchart for creating a task to configure channels, take a measurement, analyze and present the data, stop the measurement, and clear the task.

Chapter 5 Using the SCXI-1125

Create Task in

DAQ Assistant

or MAX

Further Configure

Channels?

Ye s

Configure Channels

Start Measurement

Create Task Using

DAQ Assistant?

Ye s

Create Another

Channel?

NoYes

Process

Data

Create a Task

Programmatically

Create Channel

(Application Specific)

Ye s

Hardware

Timing/Triggering?

Ye s

Adjust Timing Settings

Analyze Data?

Read Measurement

Ye s

Graphical

Display Tools

Ye s

Clear Task

Display Data?

Continue Sampling?

Stop Measurement

Figure 5-1. Typical Program Flowchart

SCXI-1125 User Manual 5-6 ni.com

General Discussion of Typical Flowchart

The following sections discuss briefly considerations for a few of the steps in Figure 5-1. These sections 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, first you must 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-1125

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-1125

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. Figure 5-1 assumes 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-1125 access an underlying set of NI-DAQmx properties. Table 5-3 shows some of these properties. You can use Table 5-3 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 5-3. NI-DAQmx Properties

Property Short Name Description

Analog Input»General Properties» Advanced»Range»High

Analog Input»General Properties» Advanced»Range»Low

Analog Input»General Properties» Filter»Analog Lowpass»Cutoff Frequency

AI.Max Specifies the upper limit of the

input range.

AI.Min Specifies the lower limit of the

input range.

AI.Lowpass.CutoffFreq Specifies in hertz the

frequency corresponding to the –3 dB cutoff of the filter. You can specify 4.0 or 10000.

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 measurements. For a complete list of NI-DAQmx properties and more information about NI-DAQmx properties, refer to your ADE help file.

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Chapter 5 Using the SCXI-1125

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 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-1125. 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 5-4 are located on the Functions»

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

accompanying subpalettes in LabVIEW.

Chapter 5 Using the SCXI-1125

Table 5-4. Programming a Task in LabVIEW

Flowchart Step VI or Program Step

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

Controls»Modern»I/O»DAQmx Name Controls subpalette, right-click it, and select New NI-DAQmxTask (MAX...).

Create a Task Programmatically (optional)

DAQmx Create Task.vi—This VI is optional if you created

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

Create AI Channel (optional) DAQmx Create Virtual Channel.vi (AI Voltage by default,

to change to a channel, click AI Voltage and select the type of analog input you want.—This VI is optional if you created and configured your task and channels using the DAQ Assistant. Any channels created with this VI are not saved in the DAQ Assistant. They are only available for the present session of the task in LabVIEW.

Adjust Timing Settings (optional)

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

optional if you created and configured your 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) DAQmx Channel Property Node, refer to the Using a 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

Read Measurement

DAQmx Start Task.vi

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.

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Chapter 5 Using the SCXI-1125

Table 5-4. Programming a Task in LabVIEW (Continued)

Flowchart Step VI or Program Step

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

to display your data. Some display tools are located on the Controls»All Controls»Numeric»Numeric Indicators 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.

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 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 Measurement I/O»

DAQmx - Data Acquisition, and select DAQmx Channel Property Node.

5. Use the ActiveChans box 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 ActiveChans box and assign the appropriate channel to each list of properties.

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.

Chapter 5 Using the SCXI-1125

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

NI-DAQmx properties.

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.

Figure 5-2. LabVIEW Channel Property Node with Lowpass Frequency Set at 10 kHz

on Channel SC1Mod1/ai0

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.

Specifying Channel Strings in NI-DAQmx

Use the channel input of DAQmx Create Channel to specify the SCXI-1125 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/ch0,

SC1Mod1/ch4

• multiple continuous channels—for example SC1Mod1/ch0:4 (channels 0 through 4)

• cold junction channel—

SC1Mod1/_cjtemp

When you have a task containing SCXI-1125 channels, you can set the properties of the channels programmatically using the DAQmx Channel Property Node.

SCXI-1125 User Manual 5-12 ni.com

SC1Mod1/ch0

Chapter 5 Using the SCXI-1125

Follow the general programming flowchart or open an example to build a basic virtual channel. You can use property nodes in LabVIEW to control, configure, and customize the NI-DAQmx task and SCXI-1125. To create a LabVIEW property node, complete the following steps:

1. Launch LabVIEW.

2. Create the property node in a new Virtual Instrument (VI) or in an existing VI.

3. Open the block diagram view.

4. From the Functions tool bar, select NI Measurements, DAQmx - Data Acquisition, and select the type of property node you wish to configure.

5. Use the ActiveChans box to specify what channel(s) you want to configure. If you want to configure several channels with different properties, separate the lists of properties with another ActiveChans box, and assign the appropriate channel to each list of properties.

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

7. You must 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.

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

NI-DAQmx properties.

Chapter 5 Using the SCXI-1125

Text Based ADEs

You can use text based ADEs such as LabWindows/CVI, Measurement Studio, Visual Basic, .NET, and C# to create code for using the SCXI-1125.

LabWindows/CVI

LabWindows/CVI works with the DAQ Assistant in MAX to generate code for a 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. Configure the NI-DAQmx task following the instructions in the

Creating a Voltage Global Channel or Task section.

6. 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.

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, .NET, and C#)

When creating a task in Visual Basic .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 channel on the SCXI-112511251125. You can use the same functions for Visual Basic .NET and C#.

Programmable NI-DAQmx Properties

All of the different ADEs that configure the SCXI-1125 access an underlying set of NI-DAQmx properties. Table 5-5 provides a list of some of the properties that configure the SCXI-1125. 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.

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Chapter 5 Using the SCXI-1125

Table 5-5. NI-DAQmx Properties

Property Short Name Description

Analog Input»General Properties» Advanced»Range»High

Analog Input»General Properties» Advanced»Range»Low

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

Analog Input»Measurement Type AI.MeasType Indicates the measurement to take

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

property you may need to configure your application. For a complete list of NI-DAQmx properties and more information on NI-DAQmx properties, refer to your ADE help file.

AI.Max Specifies the upper limit of the

input range.

AI.Min Specifies the lower limit of the

input range.

AI.Gain Specifies a gain factor to apply to

the signal conditioning portion of the channel.

with the analog input channel.

Developing Your Application in Traditional NI-DAQ (Legacy)

Note If you are not using an NI ADE, using an NI ADE prior to version 7.0, or are using

This section describes how to configure and use Traditional NI-DAQ (Legacy) to control the SCXI-1125 in LabVIEW, LabWindows/CVI, Measurement Studio, and other text-based ADEs. These NI 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.

Chapter 5 Using the SCXI-1125

Traditional NI-DAQ (Legacy) in LabVIEW

LabVIEW is a graphical programming environment for test and measurement application development with built-in easy to use tools for data acquisition, analysis, and display. You can use functional graphical blocks called subVIs to easily create a custom application that fully utilizes the SCXI-1125 programmable functionality. Traditional NI-DAQ (Legacy) provides several standard data acquisition subVIs as well as subVIs specifically for use with the SCXI-1125.

For applications using Traditional NI-DAQ (Legacy) in LabVIEW, there are two typical methods of addressing SCXI-1125 channels—virtual channels (specifically virtual channels) and SCXI channel strings. Depending on the needs of your application, you choose one of these channel addressing methods to use in your LabVIEW application.

When you use virtual channels, the maximum number of channels per E Series DAQ device is 512 in multichassis systems. NI recommends using the virtual channel for ease of use. Refer to Appendix B, Using SCXI

Channel Strings with Traditional NI-DAQ (Legacy) 7.0 or Later, for more

information on how to create a virtual channel.

The SCXI channel string allows you to combine large numbers of channels into fewer scan list entries, to measure the signal voltage level directly for custom scaling, and to dynamically perform an offset null compensation in your application. NI recommends using SCXI channel strings for more advanced applications. In LabVIEW, an array of these channel strings configures multiple modules for scanning. When using SCXI channel strings, you can scan up to 3,072 channels in a multichassis system using a single E Series DAQ device.

Note You cannot mix virtual channels with the SCXI channel strings within the same

channel string array.

To use virtual channels, enter the name of a virtual channel into the analog input channel string. If using multiple virtual channels, enter them in a different index in the channel string array, or separate them using a comma.

Since you can randomly scan analog input virtual channels, you can enter the virtual channels you want to scan in any order or repeatedly in a channel string array.

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Chapter 5 Using the SCXI-1125

Typical Program Flow

After you have determined how you want to address the channels and whether you want to configure the SCXI-1125 in MAX or LabVIEW, you can design your application using a typical program flow such as the one shown in Figure 5-3.

Virtual Channel

Create Virtual

Channel in MAX

Use

Virtual Channel

or SCXI Channel

String

Start Acquisition

Take Measurements

Continue

Sampling?

Scale, Analyze,

and Display

Clear Acquisition

SCXI Channel String

Configure

Acquisition Settings

Configure

Mode Properties

Ye s

Error Handling

Figure 5-3. Typical SCXI-1125 Program Flow with Traditional NI-DAQ (Legacy)

Chapter 5 Using the SCXI-1125

Configure the SCXI-1125 Settings Using Traditional NI-DAQ (Legacy) in LabVIEW

You can configure SCXI-1125 settings in MAX using the virtual channel. To configure and control the SCXI-1125 from LabVIEW, use the AI Parameter VI. You can find AI Parameter VI in the function subpalette Data Acquisition»Analog Input»Advanced Analog Input.

A parameter changed by the AI Parameter VI takes effect in hardware when AI Start VI is called, not when AI Parameter VI is called. The AI parameter VI merely changes the configuration in the driver memory. When called, the AI Start VI reads the configuration settings in the driver memory and then sends the actual control information to the SCXI-1125 module. A setting established through AI Parameter VI is only valid for the LabVIEW session and does not change the setting in MAX.

You can use the AI Parameter VI to configure the SCXI-1125 settings shown in Table 5-6.

Table 5-6. Settings for Configuring the SCXI-1125 Through the AI Parameter

Allowable Settings

Software-

Configurable

Setting

AI Parameter VI

Parameter

Name

Val ue Data Type Va lue s

(Float In, Boolean In, or Value In)

Filter Bandwidth

SCXI-1125 User Manual 5-18 ni.com

Filter Setting 14 Float In (dbl) 4.0, 10000.0

Chapter 5 Using the SCXI-1125

An example of using the AI Parameter VI to control an SCXI-1125 is shown in Figure 5-4.

Figure 5-4. Using the AI Parameter VI to Set Up the SCXI-1125

Configure, Start Acquisition, and Take Readings Using Traditional NI-DAQ (Legacy) in LabVIEW

After you have performed an offset null compensation and configured the SCXI-1125 settings for your application, you can use the intermediate analog input functions AI Config VI, AI Start VI, AI Read VI, and AI Clear VI to create your data acquisition application. You can find the intermediate data acquisition Traditional NI-DAQ (Legacy) functions in the function subpalettes Data Acquisition»Analog Input. NI recommends using the intermediate analog input functions for most SCXI-1125 applications. For more information about using the intermediate data acquisition Traditional NI-DAQ (Legacy) functions, refer to the LabVIEW Measurements Manual. You also can use the LabVIEW Help for more detailed information about the various inputs and outputs of these functions.

Chapter 5 Using the SCXI-1125

Convert Scaling Using Traditional NI-DAQ (Legacy) in LabVIEW

If you need scaling, you can either use an analog input voltage virtual channel with a custom scale configured in MAX or SCXI channel strings, and provide scaling in your LabVIEW application.

If you are using SCXI channel strings, you can easily convert the SCXI-1125 voltage signal measurements in your application into scaled units of interest such as pounds or newtons. LabVIEW has some common conversion scaling functions such as the Scaling Constant Tuner VI in the function subpalette Data Acquisition»Signal Conditioning.

You also can use an Expression Node or Formula Node to convert voltage signal measurements into whatever units your application requires. You can find an Expression Node in the function subpalette Numeric. You can find Formula Nodes in the Function subpalettes Analyze»Mathematics» Formula. For more information about using the Expression Node or Formula Node, refer to the LabVIEW User Manual. You also can use the LabVIEW Help for more detailed information about how to use these nodes to perform mathematical calculations such as scaling conversions.

Analyze and Display Using Traditional NI-DAQ (Legacy) in LabVIEW

In LabVIEW, you can easily analyze SCXI-1125 measurements with a variety of powerful analysis functions that you can find in the function subpalettes Analyze»Waveform Conditioning and Analyze»Signal Processing. You can perform post acquisition processing such as waveform comparisons, harmonic analysis, and digital filtering. For more information about these VIs, refer to the LabVIEW Analysis Concepts manual. You also can use the LabVIEW Help for more detailed information about how to use the analysis VIs.

In LabVIEW, you also can easily display SCXI-1125 measurements with a variety of graphical waveform graphs, numeric slides, gauges, and other indicators. You can find useful graphical controls and indicators for user interaction with your application in the controls subpalettes. For more information about these VIs, refer to the LabVIEW User Manual. You also can use the LabVIEW Help for more detailed information about how to use graphical controls and indicators in your application.

SCXI-1125 User Manual 5-20 ni.com

Traditional NI-DAQ (Legacy) in Text-Based ADEs

NI text-based ADEs, such as LabWindows/CVI, Measurement Studio for Microsoft Visual Basic, and Measurement Studio for Microsoft Visual C++, offer help in the development of test and measurement applications. These ADEs provide easy data acquisition, data analysis, graphical display, and data logging tools. Refer to the ADE user manual for more information about how to use these features.

The high-level data acquisition tools provided in LabWindows/CVI and Measurement Studio allow you to easily use virtual channels configured in MAX providing easy configuration and programming of the data acquisition systems. However, some of the more advanced features of the SCXI-1125 are not accessible through this easy-to-use API. For more advanced features or for more explicit control of the programmatic attributes, use the low-level DAQ functions provided in the Traditional NI-DAQ (Legacy) C API. Refer to the ADE user documentation for more information about how to use the high-level data acquisition tools that are provided in your NI ADE.

For more advanced SCXI-1125 applications, or if you are using an ADE other than an NI ADE, you can use the Traditional NI-DAQ (Legacy) C API to call functions from the DAQ driver dynamically linked library (dll).

Chapter 5 Using the SCXI-1125

Configuring System Settings Using Traditional NI-DAQ (Legacy) C API

Start the configuration of the acquisition by ensuring that the SCXI-1125 module and SCXI chassis are in their default states, and that the driver software configuration matches the states the actual physical hardware configuration. After setting the hardware and software to the defaults of the module(s), you can configure any module settings that vary from the default configuration settings. You also should configure the acquisition parameters using the functions in Table 5-7. For additional information such as the function prototypes, parameters, and usage instructions for each function, refer to the Traditional NI-DAQ (Legacy) Function Reference

Help installed by default in Start»Programs»National Instruments» NI-DAQ.

Chapter 5 Using the SCXI-1125

Function Description

Table 5-7. Configuration Functions

SCXI_Reset

SCXI_Load_Config

SCXI_SCAN_Setup

SCXI_MuxCtr_Setup

Resets the hardware such as the specified module to its default state. You also can use

SCXI_Reset to reset the SCXI chassis Slot 0 scanning

circuitry or reset the entire chassis.

The SCXI-1125 default conditions are:

• Gain set at 1000.0

• 4 Hz lowpass filter

Loads the SCXI chassis configuration information you established in MAX. Sets the software states of the chassis and the modules present to their default states. This function makes no changes to the hardware state of the SCXI chassis or modules. It is possible to programmatically change the configuration you established in MAX using the

SCXI_Set_Config function.

Initializes multiplexing circuitry for a scanned data acquisition operation. Initialization includes storing a table of the channel sequence and gain setting for each channel to be digitized (MIO and AI devices only). You cannot repeat channels or use nonsequential channels when using the

SCXI_SCAN_Setup function.

Programs the E Series DAQ device with the correct number of channels multiplexed per scan. This number must match the total number of channels programmed in

SCXI_SCAN_Setup.

Note NI strongly recommends monitoring the built-in error status of each NI-DAQ

function. The NI-DAQ C API provides the

NIDAQErrorHandler function, which ensures

that a specified NI-DAQ function executed properly, and assists in handling error messages and reporting.

Configure Module Settings Using Traditional NI-DAQ (Legacy) C API

After configuring the hardware for acquisition, you must load the various channel attributes such as filter, gain, and excitation appropriate for your application explicitly using the NI-DAQ function calls shown in Table 5-8. For more information regarding each setting, refer to the Traditional NI-DAQ (Legacy) Function Reference Help installed by default in Start»Programs»National Instruments»NI-DAQ.

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Chapter 5 Using the SCXI-1125

Table 5-8. NI-DAQ Functions Used to Configure SCXI-1125

Channel

Setting

Gain

NI-DAQ Function to Use

SCXI_Set_Gain

Significant

Parameters

f64 gain (gain setting)

Possible Parameters

Val ue s

1, 2, 5, 10, 20, 50, 100, 200, 250, 500, 1000, 2000

Bandwidth

SCXI_Configure_Filter

f64 freq

4.0, 10,000.0 Hz (filter cutoff frequency if filterMode = 1)

Perform Offset Null Compensation Using Traditional NI-DAQ (Legacy) C API

After configuring the system settings and module properties, you can perform an offset null compensation programmatically using

SCXI_Calibrate. SCXI_Calibrate takes measurements and adjusts the

coarse and fine offset null potentiometers to minimize or eliminate any electrical offset for a channel. Repeat this process for each channel by calling the imbalance in your application as a software correction factor by determining the residual voltage from the imbalance, and subtracting this residual offset from each future measurement. For more information regarding the operation of

NI-DAQ (Legacy) Function Reference Help installed by default in Start» Programs»National Instruments»NI-DAQ.

SCXI_Calibrate function in a loop. Use the resulting

SCXI_Calibrate, refer to the Traditional

Perform Acquisition Using Traditional NI-DAQ (Legacy) C API

There are several NI-DAQ functions you can use to take measurements. Usually in SCXI the preference is to take multiple samples from multiple channels using the multiple-channel scanned data acquisition operation. return until Traditional NI-DAQ (Legacy) acquires all the data or an acquisition error occurs (MIO, AI, and DSA devices only). For this reason, it is sometimes useful to use

Timeout_Config, which establishes a timeout limit synchronous

functions to ensure that these functions eventually return control to your application. After acquiring data using organized by channel, so you should demultiplex the data using

SCAN_Demux. SCAN_Demux rearranges, or demultiplexes, data acquired by

SCAN_Op into row-major order, meaning each row of the array holding

SCAN_Op function. SCAN_Op performs a synchronous,

SCAN_Op does not

SCAN_Op in conjunction with the function

SCAN_Op, the resultant data is not

Chapter 5 Using the SCXI-1125

the data corresponds to a scanned channel for easier access by C applications. BASIC applications need not call rearrange two-dimensional arrays since these arrays are accessed in column-major order. For more information regarding each acquisition function, refer to the Traditional NI-DAQ (Legacy) Function Reference

Help installed by default in Start»Programs»National Instruments» NI-DAQ.

Perform Scaling, Analysis, and Display

After acquiring raw voltage data from the acquisition functions, most applications require adjustment by device calibration constants for accuracy, scaling measured voltage, analysis, and graphical display.

The SCXI-1125 has stored software calibration constants loaded on the module EEPROM that are used to achieve the absolute accuracy specifications. an SCXI channel to voltage using the stored software calibration constants when it scales the data. You must call you have multiple channels in the scan. For more information regarding

SCXI_Scale, refer to the Traditional NI-DAQ (Legacy) Function

Reference Help installed by default in Start»Programs»National

Instruments»NI-DAQ.

SCXI_Scale scales an array of binary data acquired from

SCAN_Demux to

SCAN_Demux before SCXI_Scale if

After you have adjusted the measurement by the appropriate calibration constants using conversion library

SCXI_Scale, you can use a function from the NI

convert.h to convert a voltage or voltage buffer from

a voltage to units of temperature or strain. NI-ADEs also provide many powerful analysis functions to perform digital filtering, harmonic analysis, averaging, and complex mathematics on measurements.

After performing scaling and analysis on the acquired data, you can display the measurements in several ways. You can use any built in GUI tools in your ADE. NI ADEs provide many graphical controls and indicators such as charts, graphs, gauges, slides, and plots that you can use to display the data. There is also a built in function, found in

NIDAQPlotWaveform that you can use to generate a simple plot of the

nidaqex.h, called

data.

Using Software for Multiplexed Scanning

Performing scanning operations in software depends on the ADE you are using. While using LabVIEW, or Visual Basic, all scanning operations are prepared in software by using an SCXI channel string as the input to the channel parameter in the analog input VI or function. These ADEs also

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Chapter 5 Using the SCXI-1125

support virtual channels using Data Neighborhood (DAQ Channel Wizard) in MAX. In LabWindows/CVI, C, or C++ development environments, several NI-DAQ function calls need to be made to set up each module involved in the scan, the chassis, and the E Series DAQ device controlling the scan. In Measurement Studio, SCXI channels must be configured as virtual channels (tags) in MAX.

A discussion describing how to implement multiplexed scanning in the different ADEs follows. Refer to your ADE manual and the DAQ analog input examples that come with your application software for more detailed information on programming the SCXI modules for scanning in multiplexed mode.

LabVIEW and the SCXI Channel String

For LabVIEW, and Visual Basic, the channel string determines the sequence in which SCXI channels are scanned. In LabVIEW, an array of these channel strings configures multiple modules in the scan list. When the application program runs, the channel string is used for programming the channel information into the SCXI system. The format of the channel string is as follows:

obx ! scy ! mdz ! channels

where

•obx is the onboard E Series DAQ device channel, with x representing

a particular channel where the multiplexed channels are sent. This value is 0 for DAQ channel 0 in a single-chassis system. In a multichassis or remote chassis system, however, the E Series DAQ device channel x corresponds to chassis number n–1, where DAQ device channel x is used for scanning the nth chassis in the system.

•scy is the SCXI chassis ID, where y is the number you chose when

configuring your chassis.

•mdz is the slot position where the module is located, with z being the

particular slot number. The slots in a chassis are numbered from left to right, starting with 1.

Note The

obx !

specifier is optional and causes the gains on the module and E Series DAQ device to be automatically set to fit the input limits parameter. When this specifier is omitted, the default gain on the E Series DAQ device, usually the lowest gain, is used, but the SCXI-1125 gain is adjusted to fit the input limits.

Chapter 5 Using the SCXI-1125

The last parameter, channels, is the list of channels that are scanned for module z. It can have several formats:

•

obx ! scy ! mdz ! n, where n is a single input channel.

•

obx ! scy ! mdz ! n1:n2, where n1 and n2 represent a sequential

list of input channels, inclusive.

•

obx ! scy ! mdz ! cjtemp, where cjtemp is the CJC channel.

You can scan this channel with other analog input channels. For compatibility reasons, you can use

•

obx ! scy ! mdz ! (n1, n2, n3:n4, n1, n5, n2), where n1, n2, and

mtemp in place of cjtemp.

n5 represent single channels, not necessarily sequential, and n3 and n4 represent the endpoints of a sequential list of channels, inclusive. In this case, channels n1 and n2 have explicitly been repeated in the channel list. This random scanning format is not supported on all SCXI modules.

•

! scy ! mdz ! calgnd n1:n2 where n1 and n2 represent a list of

autozeroed channels, inclusive. In this case autozero channels cannot be scanned with input channels or the cold-junction channel, but must be scanned separately. This feature is useful for measuring offsets that appear due to temperature drifts in the analog circuitry. You can subtract these offsets from subsequent input readings to correct for temperature drift. Refer to Appendix A, Specifications, for determining how temperature drift can affect your measurement accuracy.

Note Repeating channels or having channels out of sequence in a scan list is not supported

on all SCXI modules. Please refer to the manual of each module for information on this feature.

LabVIEW and the Virtual Channel String

For LabVIEW, Measurement Studio, and Visual Basic, the channel string can also contain virtual channels. For the SCXI-1125, these virtual channels are analog input channels you create that have custom names (called tags in Measurement Studio), that perform scaling, linearization, autozeroing, and CJC transparently without additional code. Virtual channels are useful when sensors requiring different scaling factors are used on the same SCXI-1125 channel. Using virtual channels, sensors needing special scaling can be used in a generic analog input application without performing hard-coded scaling or linearization. If the scaling changes or you want to connect a different sensor to the SCXI-1125, no changes are needed in the application. All that is required is creating a different virtual channel and using its name in the channel string.

SCXI-1125 User Manual 5-26 ni.com

Note You cannot mix virtual channels with the SCXI channel strings shown in the

previous section.

To create a virtual channel for the SCXI-1125, insert a new analog input channel in the Data Neighborhood path in MAX, name it, and then follow the software prompts to create virtual temperature channels, voltage channels, or customized analog input channels. For more information on virtual channels, consult the MAX online help file.

To use the virtual channels, enter the name of the virtual channel into the analog input channel string. If using multiple virtual channels, separate them using a comma or enter them in a different index in the channel string array. The application does all scaling, linearization, autozeroing, and CJC automatically.

Note Virtual analog input channels can be randomly scanned; therefore, virtual channels

can be entered in any order or repeated in the channel string.

Performing a Multiplexed Scan

To perform a multiplexed scan in your application, perform the following steps:

1. Open an analog input example in your ADE.

2. Enter the appropriate SCXI channel string or virtual channel string into

the channels parameter.

3. Either enter the input limits for signals connected to the module to

adjust the gain settings in your system, or use the default gain settings from the configuration utility, and then run the application. When using virtual channels, the default input limits configured in the virtual channel configurator are used.

Chapter 5 Using the SCXI-1125

You have completed a multiplexed scan using your SCXI-1125.

This is not a comprehensive discussion of SCXI scanning using LabVIEW or Measurement Studio, but it should give you enough information to help you get started with the examples that are shipped with these software packages.

Chapter 5 Using the SCXI-1125

C and Low-Level DAQ Functions

When using a C-based environment, several steps are needed to configure the SCXI-1125 for multiplexed scanning. The following procedure outlines the steps for programming with the low-level DAQ function calls:

1. Prepare the SCXI-1125 settings by either loading the original SCXI configuration settings using the gain and filter settings using

SCXI_Configure_Filter.

2. Use

SCXI_SCAN_Setup to specify the module scan list, the start

channel of each module, and the number of channels to scan on each module.

SCXI_SCAN_Setup accepts an array of start channels and an

array of the number of channels to scan in each module. It is not possible to repeat channels or use nonsequential channels using

SCXI_SCAN_Setup.

3. Next, use

SCXI_MuxCtr_Setup to program the E Series DAQ device

with the correct number of channels multiplexed per scan. This number must match the total number of channels programmed in step 2.

You are now ready to acquire the channel data with the E Series DAQ device. If you are using a multifunction E Series DAQ device, you can use

SCAN_OP to perform the scanning operation. After scanning, convert the

binary data to voltage data using Manual for additional information on scanning with DAQ devices.

SCXI_Load_Config, or by specifying

SCXI_Set_Gain and

SCXI_Scale. Refer to the NI-DAQ User

Using Software for Parallel Scanning

Performing scanning operations in parallel mode requires no special channel strings or function calls for setting up channel sequencing as is required in multiplexed mode. Scanning the SCXI-1125 channels on a differentially configured DAQ device is done as if there were no SCXI-1125 module connected. The only requirement is that you must configure the module for parallel mode in MAX as described in Chapter 1,

About the SCXI-1125.

LabVIEW and Parallel Mode

In LabVIEW, the SCXI-1125 configuration settings are automatically passed from MAX. LabVIEW can also set the SCXI-1125 configuration parameter, operating mode, to parallel or multiplexed programmatically by using the Set SCXI Information VI. In Measurement Studio, set the operating mode using MAX as described in Chapter 1, About the

SCXI-1125.

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Chapter 5 Using the SCXI-1125

After parallel mode has been configured in software, you can scan the SCXI-1125 channels by entering the corresponding E Series DAQ device channels or a sequential SCXI channel string in the channel parameter in the analog input application. You can also enter virtual channels; however, in parallel mode, virtual channels containing CJC are disabled in MAX.

C and Parallel Mode

When using a C-based ADE, you need no special steps for configuring the chassis, the SCXI-1125, or the E Series DAQ device for parallel scanning. You still have to configure the gain and filter settings by using

SCXI_Set_Gain and SCXI_Configure_Filter. You can use any of the

E Series DAQ device analog input functions to get the data from the eight channels of the SCXI module. After scanning, convert the binary data to voltage data by using additional information on parallel scanning of SCXI modules.

SCXI_Scale. Refer to the NI-DAQ User Manual for

Calibration

The SCXI-1125 is shipped with a calibration certificate and is calibrated by the factory to the specifications described in Appendix A, Specifications. Calibration constants are stored inside the calibration EEPROM and provide software correction values that are used by your application development software to correct your measurements for both offset and gain errors in the module.

Due to the nature of the analog circuitry in your SCXI-1125 module, gain errors tend to be more stable over time, therefore requiring less frequent calibration. Offset errors, however, are more susceptible to drift due to time, temperature, and other environmental changes, and can affect the measurement accuracy of your module. You may wish to periodically calibrate the module for offset drift using the following procedure to ensure that the measurements on the SCXI-1125 are as accurate as possible. Refer to Appendix A, Specifications, for more details about the analog stability of your SCXI-1125 module.

Calibration Procedures

You can calibrate the offset on the SCXI-1125 using National Instruments software. When calibrating the offset on the SCXI-1125, make sure the DAQ device you are using has been calibrated recently or you will invalidate the offset calibration on the SCXI-1125. The SCXI-1125 provides input switching that allows you to programmatically shunt the differential input channels of the SCXI-1125. Once the channels are shunted, the channel can be read by a calibrated DAQ device or calibrated DMM. These offsets voltages, read by the calibrated device, can be saved in the calibration EEPROM in the SCXI-1125 for software correction of offset.

Caution Ensure that the calibration on the DAQ device or DMM you are using is up to date

and traceable. If you adjust the gain or offset values using an uncalibrated device, you will invalidate the calibration on the SCXI-1125 and any measurements taken with the module may not be accurate.

Remember that the calibration you perform on the SCXI-1125 is only as accurate as the calibration device you are using. Refer to Appendix A,

Specifications, for accuracy specifications for the SCXI-1125.

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Chapter 5 Using the SCXI-1125

One-Point Offset Calibration

To perform offset calibration on your module, follow this procedure if you are using LabVIEW:

1. Make sure the DAQ device or DMM you are using has a valid calibration and meets the accuracy specifications for your application.

2. In LabVIEW, use the SCXI Calibrate VI to calibrate your module.

a. Enter the DAQ device and the SCXI channel string for the

channels you want to calibrate.You can calibrate only one channel at a time.

b. Select internal calibration as the calibration operation you are

going to perform.

c. Select the Default EEPROM load area as the area you want to

update.

d. The offset varies with the selected gain value. Therefore, enter the

high and low limits that correspond to the gain value for which you are calibrating offset. Refer to Table 5-9 for a list of the gain values and the corresponding input limits you must enter.

e. Enter 0.0 as the input reference voltage.

3. Run the application.

4. Repeat steps 2 through 3 for calibrating the offset for additional channels or gain combinations.

Table 5-9. Gain Values and Input Limits

Gain Range (±)

1 5 V

2 2.5 V

5 1 V

10 0.5 V

20 0.25 V

50 0.125 V

100 0.05 V

200 0.025 V

250 0.020 V

500 0.010 V

Chapter 5 Using the SCXI-1125

Table 5-9. Gain Values and Input Limits (Continued)

Gain Range (±)

1000 0.005 V

2000 0.0025 V

If you are using a C-based ADE, use the following procedure to do an offset calibration on the SCXI-1125:

1. Make sure the DAQ device or DMM you are using has a valid calibration and meets the accuracy specifications for your application.

2. Use the NI-DAQ function

SCXI_Calibrate to calibrate one channel

of the SCXI-1125.

a. Enter the DAQ device, DAQ channel, module slot, and module

channel for the channel you want to calibrate.

b. Select internal calibration (0) as the operation you are going to

perform.

c. Select the load area (1) as the EEPROM area you want to update.

d. Since offset varies with gain, enter the gain setting for which you

are calibrating offset.

e. Enter

f. Enter

1 for the terminal block gain since it is not used.

0.0 as the input reference voltage.

3. Repeat step 2 for calibrating additional channels.

The SCXI-1125 may take a few seconds to perform the calibration. After completion, your module will have new calibration constants stored for the channels and gains you calibrated.

Two-Point Gain and Offset Calibration

If you also need to calibrate the gain constants on the SCXI-1125, you must use an external reference to perform a two-point calibration. Please refer to the SCXI-1125 Calibration Procedures document for more information on doing an external two-point gain and offset calibration.

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Specifications

This appendix lists the specifications for the SCXI-1125 modules. These specifications are typical at 25 °C unless otherwise noted.

Input Characteristics

Overall Gain Overall Voltage Range

Table A-1. Input Signal Range Versus Gain

SCXI-1125

Gain

1 ±5 V

2 ±2.5 V

5 ±1 V

10 ±500 mV

20 ±250 mV

50 ±100 mV

100 ±50 mV

200 ±25 mV

250 ±20 mV

500 ±10 mV

1000 ±5 mV

2000 ±2.5 mV

Note Refer to Tables 5-1 and 5-2 for extended range using the SCXI-1313A, SCXI-1327,

and TBX-1316.

or VDC 1

peak

or VDC 2

peak

or VDC 5

peak

or VDC 10

peak

or VDC 20

peak

or VDC 50

peak

or VDC 100

peak

or VDC 200

peak

or VDC 250

peak

or VDC 500

peak

or VDC 1000

peak

or VDC 2000

peak

Appendix A Specifications

Overvoltage protection

Isolated connector pins:

Powered on and off..........................±300 V

Inputs protected ...............................CH0..CH7

Non-isolated connector pins:

Powered on and off..........................+5.5V/– 0.5 V

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Appendix A Specifications

Absolute

System Noise (peak, 3 sigma)

Accuracy at

Temperature Drift

Single Point Average

(mV)

Full Scale

Offset

(uV/°C)

% of

Reading/°C

Offset

% of Reading

Typ ic al Max 4 Hz 10 kHz 4 Hz 10 kHz

Gain

0.005 0.3996 1.25 854 mV 115 mV 1.62 V 25 mV 401 mV 0.0034 132 mV 14.0V

0.02 0.2548 0.65 250 mV 309 mV 478 mV 7 mV 100 mV 0.0029 44 mV 2.0V

0.05 0.2548 0.65 100 mV 12 mV 183 mV 2.6 mV 41 mV 0.0029 22 mV 790mV

0.1 0.2548 0.65 50 mV 6 mV 111 mV 1.3 mV 21 mV 0.0029 11 mV 400mV

0.2 0.2548 0.65 25 mV 3 mV 48 mV 641 μV 11 mV 0.0029 4.4 mV 200mV

±25 V

0.5 0.2548 0.65 10 mV 1 mV 19.1 mV 238 μV 4.1 mV 0.0029 2.2 mV 80.0mV

±10 V

±5 V 1 0.07 0.52 5.0 mV 530 μV 8.6 mV 122 μV 2.1 mV 0.0027 251 μV 33.0mV

±2.5 V 2 0.07 0.52 2.5 mV 254 μV 4.3 mV 60 μV 1.1 mV 0.0027 126 μV 16.5mV

±1 V 5 0.07 0.52 1.0 mV 110 μV 1.7 mV 24 μV 403 μV 0.0027 51 μV 6.6mV

±500 mV 10 0.07 0.52 500 μV 69 μV 882 μV 13 μV 202 μV 0.0027 26 μV 3.31mV

±250 mV 20 0.07 0.52 250 μV 32.0 μV 474 μV 6.3 μV 101 μV 0.0027 13 μV 1.65mV

±100 mV 50 0.07 0.52 110 μV 11 μV 180 μV 2.4 μV 41 μV 0.0027 5.5 μV 670μV

±50 mV 100 0.07 0.52 60 μV 6.2 μV 88.2 μV 1.3 μV 21 μV 0.0027 3.0 μV 340μV

±25 mV 200 0.08 0.52 30 μV 2.6 μV 47.9 μV 0.60 μV 11 μV 0.0027 1.7 μV 170μV

±20 mV 250 0.08 0.53 25 μV 2.3 μV 37.1 μV 0.50 μV 7 μV 0.0027 1.5 μV 140μV

Overall

1, 2, 3

Nominal Range

Absolute Accuracy

±1000 VDC

±250 V

±100 V

±50 V

Appendix A Specifications

Absolute

System Noise (peak, 3 sigma)

Full Scale

Accuracy at

Offset

% of

Temperature Drift

Single Point Average

(mV)

(uV/°C)

Reading/°C

Offset

% of Reading

Typ ic al Max 4 Hz 10 kHz 4 Hz 10 kHz

Gain

Overall

refers to sinusoidal waveform; V refers to DC or AC peak.

rms

Absolute accuracy (15 to 35 ºC). To calculate the absolute accuracy for the SCXI-1125 visit ni.com/accuracy.2 V

With TBX-1316 high-voltage terminal block.

Nominal Range

±10 mV 500 0.08 0.53 20 μV 1.3 μV 21.8 μV 0.27 μV 4.70 μV 0.0027 1.0 μV 80μV

±5 mV 1000 0.08 0.53 15 μV 0.72 μV 14.9 μV 0.17 μV 3.2 μV 0.0027 0.7 μV 45μV

±2.5 mV 2000 0.09 0.54 15 μV 0.42 μV 11.2 μV 0.10 μV 2.5 μV 0.0027 0.6 μV 31μV

With SCXI-1327 high-voltage terminal block.

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Analog Inputs

Appendix A Specifications

Number of input channels ...................... 8 differential

Input range .............................................± 2.5 mVDC to ±5 VDC

Input coupling ........................................ DC (or AC with SCXI-1305 or

TBX-1329)

Input impedance

Normal powered on ........................>1 G || 100 pF in parallel

Powered off/overload...................... 4.5 M

With SCXI-1327 .............................1 M

With TBX-1316 .............................. 40 M

Input bias current ................................... ±100 pA typical, ±1 nA max

Filter type ...............................................3-pole Butterworth filter response

Bandwidth (–3dB cut-off frequency)

4 Hz filter ........................................ 4 Hz ±5%

10 kHz filter .................................... 10 kHz ±5%

Full power bandwidth.............. 7 kHz ±5%

With SCXI-1327 or SCXI-1313A high-voltage

terminal blocks ........................ 2.6 kHz ±5%

With TBX-1316 high-voltage

terminal block .......................... 500 Hz ±5%

Slew rate

Typical.............................................0.15 V/μs

Minimum.........................................0.1 V/μs

Scan interval accuracy

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

±0.006%.........................................10 μs

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

Common Mode Rejection Ratio, 50/60 Hz (CMRR)

4 Hz filter enabled........................... 160 dB

10kHz filter enabled........................ 98 dB

Appendix A Specifications

Normal Mode Rejection, 50/60 Hz (NMRR)

Crosstalk at 1kHz

Input coupling

Power Consumption

+18.5 V ...................................................140 mA max

– 18.5 V ..................................................140 mA max

+5 V ........................................................10 mA max

Output Characteristics

Output range ...........................................±5.0 V

4 Hz filter enabled ...........................60 dB

Adjacent channels............................–75 dB

All other channels............................– 90 dB

Default .............................................DC

Using SCXI-1305 or TBX-1329 .....AC or DC

Output impedance

Multiplexed output mode ................100 Ω

Parallel output mode........................330 Ω

Transfer Characteristics

Nonlinearity

All ranges.........................................0.02% of full scale range

Stability

Recommended warm-up time.................15 minutes

Offset drift ..............................................± (0.42 + 250/gain) μV/ °C

Gain drift.................................................± 20 ppm/ °C typical

Calibration

External calibration interval ...................1 year

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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-1125 Dimensions

Weight.................................................... 641 g (22.6 oz)

Appendix A Specifications

Maximum Working Voltage

Maximum voltage rating refers to the signal voltage plus the common mode voltage (Signal + common mode). Voltage of each input shall remain within 300 V of ground.

Channel-to-earth .....................................300 V, Measurement Category II

Channel-to-channel.................................300 V, Measurement Category II

Table A-2. Terminal Block Maximum Voltages

Module Signal Range Maximum Voltage and Category [Insulation]

SCXI-1313A 150 V 150 V, Measurement Category II

[channel-to-channel, channel-to-earth]

SCXI-1327 300 V 300 V, Measurement Category II

[bank-to-bank, bank-to-earth]

TBX-1316 600 V 600 V, Measurement Category II

[Basic; channel-to-channel]

1000 V 1000 V, Measurement Category I

[Basic; channel-to-channel]

Cautions The SCXI-1125 is rated for Measurement Category II and is intended to carry

signal voltages no greater than 300 V. Do not use the SCXI-1125 for connection to signals or for measurements within Categories III or IV.

When hazardous voltages (>42.4 V

/60 VDC) are present on any channel, all channels are

considered hazardous. Ensure that external wiring or any circuits connected to the device are properly insulated from human contact.

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

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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

in the Certification column.

, search by model number or product line, and click the appropriate link

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

Appendix A Specifications

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

For EMC compliance, operate this device with shielded cabling.

CE Compliance

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

• 2006/95/EC; Low-Voltage Directive (safety)

• 2004/108/EC; 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

certification

in the Certification column.

, search by model number or product line, and click the appropriate link

ni.com/

Appendix A Specifications

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Environmental Management

National Instruments is committed to designing and manufacturing products in an environmentally responsible manner. NI recognizes that eliminating certain hazardous substances from our products is beneficial not only to the environment but also to NI customers.

For additional environmental information, refer to the NI and the Environment Web page at environmental regulations and directives with which NI complies, as well as any other environmental information not included in this document.

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

National Instruments

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National InstrumentsЁ೑RoHS

(For information about China RoHS compliance, go to

ni.com/environment/weee.htm.

ni.com/environment. This page contains the

RoHS

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(RoHS)

SCXI-1125 User Manual A-10 ni.com

Using SCXI Channel Strings with Traditional NI-DAQ (Legacy) 7.0 or Later

Note This appendix is not applicable if you use the virtual channels to configure and

measure the SCXI channels. Virtual channels are configured using MAX. If you use virtual channels, you address the SCXI channels by specifying the channel name(s) in the channel string input.

When using LabVIEW, and Visual Basic, the SCXI channel string determines which SCXI channels are scanned and the scanning sequence. The SCXI channel string allows you to take measurements from several channels on one module with only one channel string entry. An array of these channel string entries configures multiple modules for scanning. When the application program runs, the channel string is used for programming the channel information into the SCXI system.

The format of the channel string is as follows:

obx ! scy ! mdz !

where

•

is the onboard E/M Series DAQ device channel, with x

representing a particular channel where the multiplexed channels are sent. This value is 0 for E/M Series DAQ device channel 0 in a single-chassis system. In a multichassis or remote chassis system, the E/M Series DAQ device channel

– 1, where E/M Series DAQ device channel x is used for scanning

the nth chassis in the system.

•

is the SCXI chassis ID, where y is the number you chose when

configuring the chassis.

•

is the slot position where the module is located, with z being the

particular slot number. The slots in a chassis are numbered from left to right starting with 1.

channels

corresponds to chassis number

Appendix B Using SCXI Channel Strings with Traditional NI-DAQ (Legacy) 7.0 or Later

channels

is the list of channels that are scanned for module z. It can have

several formats:

•

obx ! scy ! mdz !

•

obx ! scy ! mdz ! (n0, n2), where n0,

, where nx is a single input channel.

are individual input

channel that are not necessarily sequential.

•

obx ! scy ! mdz ! n0:

, where n0 and n3 represent an ascending

sequential list of input channels, inclusive.

•

obx ! scy ! mdz ! (n0, n2, n3:n4, n1, n5, n2), where

n0, n2

, and n5 represent single channels, not necessarily sequential,

and

and n4 represent the endpoints of an ascending sequential list

of channels, inclusive. In this case, channels

and n2 are explicitly

repeated in the channel list.

Notes Using parenthesis surrounding multiple channels in a channel string is important

for correct scanning operation of the SCXI channels.

In a single-chassis system, the

obx ! specifier is optional and causes the gains on the

module and E/M Series DAQ device to be automatically set to fit the input limits parameter. When this specifier is omitted, the default gain on the E/M Series DAQ device, usually the lowest gain, is used, but the SCXI-1125 gain is adjusted to fit the input limits. NI recommends using the

obx ! specifier.

Repeating channels or having channels out of sequence in a scan list is not supported on all SCXI modules. Refer to the manual of each module for information on this feature, which is referred to as flexible scanning or random scanning.

For more information about using SCXI channel string, refer to the LabVIEW Measurements Manual and SCXI-1125 shipping examples.

SCXI-1125 User Manual B-2 ni.com

Removing the SCXI-1125

This appendix explains how to remove the SCXI-1125 from MAX and an SCXI chassis.

Note Figure C-1 shows an SCXI chassis, but the same steps are applicable to a PXI/SCXI

combination chassis.

Removing the SCXI-1125 from MAX

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

1. Expand Devices and Interfaces to display the list of installed devices

and interfaces.

2. Expand NI-DAQmx Devices and/or Traditional NI-DAQ Devices to

display the chassis.

3. Expand the appropriate chassis to display the installed modules.

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

5. You are presented with a confirmation window. 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 deleted.

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

Removing the SCXI-1125 from a Chassis

Consult the documentation for the chassis and accessories for additional instructions and precautions. To remove the SCXI-1125 module from an chassis, complete the following steps while referring to Figure C-1:

1. Power off the chassis. Do not remove the SCXI-1125 module from a chassis that is powered on.

Appendix C Removing the SCXI-1125

2. If the SCXI-1125 is the module cabled to the E Series DAQ device,

3. Remove any terminal block that connects to the SCXI-1125.

4. Rotate the thumbscrews that secure the SCXI-1125 to the chassis

5. Remove the SCXI-1125 by pulling steadily on both thumbscrews until

disconnect the cable.

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

the module slides completely out.

S C

1 0

1Cable 2 SCXI Module Thumbscrews 3SCXI-1125 4 Sensor

5 4 3 2 1

ADDRESS

SCXI

M A

I N F

R A

M E

5Terminal Block 6 SCXI Chassis Power Switch 7 SCXI Chassis

Figure C-1. Removing the SCXI-1125

SCXI-1125 User Manual C-2 ni.com

Common Questions

This appendix lists common questions related to the use of the SCXI-1125.

The SCXI-1125 is backward compatible with the SCXI-1120, but what are the major differences between the SCXI-1120 and the SCXI-1125?

Table D-1 compares the major specifications and features of the two modules. Other specifications and features of the SCXI-1125 are the same or very similar to the SCXI-1120.

Table D-1. Comparison of the SCXI-1125 with the SCXI-1120

Feature SCXI-1120 SCXI-1125

Analog input 8 8

Input range ±5 V, ±250 V with SCXI-1327 ±5 V, ±300 V with SCXI-1327,

±1000 VDC with TBX-1316

Isolation 250 V

Gains 1, 2, 5, 10, 20, 50, 100, 200, 250, 500,

1000, and 2000 jumper selectable

Filters 4 Hz or 10 kHz jumper selectable 4 Hz or 10 kHz software selectable

Autozero Not supported Software configurable and scannable

Calibration Manually rotateable potentiometers

for one-point offset calibration

Scanning 333 kS/s with consecutive channels 333 kS/s with nonconsecutive and

CJC scanning M TEMP (non-scannable) or

D TEMP (direct channel)

Offset error ±6 µV ± 3 mV/gain 0.2 mV/gain typical

Gain error ±0.2% typ, ±0.6% max ±0.03% typ, ±0.08% max

rms

1, 2, 5, 10, 20, 50, 100, 200, 250, 500, 1000, and 2000 software selectable

Software internal one-point offset calibration, software external two-point offset and gain calibration, and onboard calibration constant storage in EEPROM

repeating channels (random scanning)

M TEMP, CJ TEMP (scannable)

300 V

rms

Appendix D Common Questions

Which version of NI-DAQ is needed to work with the SCXI-1125 and how do I get the most current version of NI-DAQ?

You must have NI-DAQ 7.0 or later. Visit

ni.com and follow the link,

Download Software»Drivers and Updates»Search Drivers and Updates, and type in the keyword

NI-DAQ to find the latest version of

NI-DAQ for your operating system.

I have gone over the Verifying the SCXI-1125 Installation in Software in Chapter 1, About the SCXI-1125, yet I still cannot correctly test and verify that my SCXI-1125 is working. What should I do now?

Unfortunately, there always exists the chance that something is not operating correctly in your system, or the combination of the components in your system is not operating correctly together. You may now have to call or e-mail a technical support representative.

The technical support representative will often suggest additional troubleshooting measures to try in order to isolate the problem. If requesting technical support by phone, have your system near at hand so that you can try these measures immediately.

Can I use the unused analog input channels of the E/M Series DAQ device if I am directly cabled to the SCXI-1125?

It depends. The SCXI-1125 always outputs channels 1 through 7 to the rear signal connector to permit parallel mode scanning. If you are using a 16-channel (8 differential inputs) E/M Series DAQ device, all E/M Series DAQ channels are unusable for general-purpose analog input. If you have a module in the chassis that does not have parallel mode, connect the E/M Series DAQ device to it and use a breakout connector to connect to the unused channels on the E/M Series DAQ device. If you are directly connected to a higher input channel device, such as a 64-channel (32 differential inputs) E/M Series DAQ device, only the lower eight differential inputs are unusable.

Which digital lines are unavailable on the E/M Series DAQ device if I am cabled to an SCXI-1125 module?

Table D-2 shows the digital lines that are used by the SCXI-1125 for communication and scanning. These lines are unavailable for general-purpose digital I/O if the SCXI-1125 is connected to the E/M Series DAQ device.

SCXI-1125 User Manual D-2 ni.com

Appendix D Common Questions

Table D-2. Digital Signals on the SCXI-1125

Traditional

DAQ Signal

Name

DAQmx

Signal Name

SCXI Signal

Name

50-Pin

Connector

68-Pin

Connector

Direction

DIO0 P0.0 SER DAT IN 25 52 Output

DIO4 P0.4 SER DAT OUT 26 19 Input

DIO1 P0.1 DAQ D*/A 27 17 Output

DIO2 P0.2 SLOT 0 SEL* 29 49 Output

SCANCLK AI HOLD

SCAN CLK 36 46 Output COMP, AI HOLD

EXTSROBE* EXTSROBE SER CLK 37 45 Output

STARTSCAN AI SAMP

SYNC* 46 38 Output CLK, AI SAMP

In LabVIEW, can I use different input limits for the same SCXI-1125 channel if I repeat the channel in the SCXI channel string array?

No, the SCXI-1125 cannot dynamically change the gain settings during scanning. Therefore, channels with similar input ranges should be grouped together in the channel string array. Make sure that repeated channels in different indices of the channel string array have the same input limits in the corresponding input limits array.

In LabVIEW, can I use virtual channels with parallel mode channels on the SCXI-1125?

Yes, virtual channels work with parallel mode operation on the SCXI-1125. The E/M Series DAQ device must be directly connected to the module in parallel mode operation. Also, virtual channels that use built-in CJC are disabled and cannot be used in parallel mode.

In LabVIEW, can I use the calgnd channel string when the SCXI-1125 is in parallel mode?

Yes, you can autozero the SCXI-1125 in LabVIEW when using the module in parallel mode.

Appendix D Common Questions

In LabVIEW, can I use a VI to change my filter setting?

In NI-DAQmx, you can change the filter settings using a DAQmx Channel property node. In Traditional NI-DAQ (Legacy), there is no VI available to do this. You must use the configuration utility in MAX to configure the filter setting of each channel.

In C, can I randomly scan the SCXI-1125 using low level Traditional NI-DAQ (Legacy) function calls?

No, using C, you can scan only consecutive channels using traditional SCXI channel programming. Refer to the NI-DAQ function reference manual for more details on SCXI scanning.

SCXI-1125 User Manual D-4 ni.com

Glossary

Symbol Prefix Value

ppico10

nnano10

μ micro 10

m milli 10

k kilo 10

Mmega10

Ggiga10

Ttera10

Numbers/Symbol

° Degrees.

≥ Greater than or equal to.

– 12

– 9

– 6

– 3

≤ Less than or equal to.

Ω Ohms.

/Per.

% Percent.

± Plus or minus.

+5 V (signal) +5 VDC source signal.

Glossary

A/D analog-to-digital

absolute accuracy The maximum difference between the measured value from a data

acquisition device and the true voltage applied to the input, typically specified as ± voltage.

AC alternating current

ADC analog-to-digital converter—An electronic device, often an integrated

circuit, that converts an analog voltage to a digital number.

ADE

AI GND analog input ground

AI HOLD COMP, AI HOLD

amplification A type of signal conditioning that improves accuracy in the resulting

autozero

application development environment—A software environment incorporating the development, debug, and analysis tools for software development.

clock that triggers scanning

digitized signal by increasing signal amplitude relative to noise.

A procedure for eliminating offsets generated by an amplifier stage.

bandwidth The range of frequencies present in a signal, or the range of frequencies to

which a measuring device can respond.

bias current The small input current flowing into or out of the input terminals of an

amplifier.

bit one binary digit, either 0 or 1

BNC

Bayonet-Neill-Concelman—A type of coaxial connector used in situations requiring shielded cable for signal connections and/or controlled impedance applications.

SCXI-1125 User Manual G-2 ni.com

CCelsius

Glossary

CH channel

channel

chassis The enclosure that houses, powers, and controls SCXI modules.

CJ TEMP cold-junction temperature sensor signal

CJC cold-junction compensation

CLK clock input signal

CMRR

code width The smallest detectable change in an input voltage of a DAQ device.

cold-junction compensation

Conformité Européenne—The European emissions control standard. The CE mark certifies that a product complies to relevant CE regulations. CE is a common standard for all countries in the EU (European Union).

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 group to form ports. Ports usually consist of either four or eight digital channels.

common-mode rejection ratio—A measure of the capability of an instrument to reject a signal that is common to both input leads.

A method of compensating for inaccuracies in thermocouple circuits.

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

cutoff frequency

The frequency at which the filter attenuates the input 3 dB, or half of its original power.

D/A digital-to-analog

D*/A data/Address

D GND digital ground signal

Glossary

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

sensors, transducers, and test probes or fixtures and inputting them to a computer for processing; (2) collecting and measuring the same kinds of electrical signals with A/D and/or DIO boards plugged into a computer, and possibly generating control signals with D/A and/or DIO boards in the same computer.

DAQ device A device that collects signals for data acquisition devices. Examples are

MIO and 1200 boards.

dB decibel—The unit for expressing a logarithmic measure of the ratio of

two signal levels: dB = 20 log

(V1/V2), for signals in volts.

DC direct current

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

multiple channels and conversion devices.

differential input

An input circuit that actively responds to the difference between two terminals, rather than the difference between one terminal and ground.

DIN deutsche Industrie Norme

DIO digital I/O

DMM

digital multimeter—A digital instrument capable of measuring several different fundamental electrical characteristics, most often voltage, resistance, and current.

EEPROM electrically erasable programmable read-only memory—ROM that can be

erased with an electrical signal and reprogrammed.

EMC electromechanical compliance

EMI electromagnetic interference

SCXI-1125 User Manual G-4 ni.com

Glossary

filtering A type of signal conditioning that allows you to remove unwanted signal

components from the signal you are trying to measure.

FSR full-scale range

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

gain accuracy A measure of deviation of the gain of an amplifier from the ideal gain.

gain error See gain accuracy.

GND ground

Hz hertz

I/O input/output—The transfer of data to/from a computer system involving

communications channels, operator interface devices, and/or data acquisition and control interfaces.

in. inch

input bias current The current that flows into the inputs of a circuit.

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

circuit.

Glossary

isolation A type of signal conditioning in which you isolate the transducer signals

from the computer for safety purposes. Isolating the signals protects you and your computer from large voltage spikes and makes sure the measurements from the DAQ device are not affected by differences in ground potentials.

isothermal

Maintenance of constant temperature across an area. Isothermal construction of terminal blocks increases thermocouple measurement accuracy.

K kelvin

linearization A type of signal conditioning in which software linearizes the voltage levels

from transducers, so the voltages can be scaled to measure physical phenomena.

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.

, when used with

M TEMP multiplexed temperature sensor signal. See also CJ TEMP.

max Minimum.

min (1) minutes

(2) minimum

MIO multifunction I/O

multiplex

SCXI-1125 User Manual G-6 ni.com

To assign more than one signal to a channel.

Glossary

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

into one module output so that your cabled DAQ device has access to the module’s multiplexed output as well as the outputs on all other multiplexed modules in the chassis through the SCXIbus.

mux multiplexer—A switching device with multiple inputs that sequentially

connects each of its inputs to its single output, typically at high speeds, in order to measure several signals with a single analog-to-digital converter.

NC not connected

NI-DAQ

noise

The driver software needed to use National Instruments DAQ devices and SCXI components.

Analog. Unwanted signals. Noise comes from both external sources, such as the AC power line, motors, generators, transformers, fluorescent lights, soldering irons, CRT displays, computers, electrical storms, welders, and radio transmitters, and internal sources, such as digital clocks, microprocessors, and switched mode power supplies. Video system noise can take various forms, including snow, which is a random video noise. It corrupts signals you are trying to send or receive.

offset error

offset null compensation

A constant error added to a measurement along the whole transfer curve. For example, in mx+b, the offset error is b.

The provision in strain-gauge signal conditioning hardware to remove the unwanted offset voltage present at the output of a strain-gauge bridge when no strain is applied.

parallel mode A type of SCXI operating mode in which the module sends each of its

output channels directly to a separate analog input channel of the DAQ device connected to the module.

passband The range of input frequencies that are passed to the filter output without

attenuation.

Glossary

ppm parts per million

PXI

A rugged, open system for modular instrumentation based on CompactPCI, with special mechanical, electrical, and software features. The PXIbus standard was originally developed by National Instruments in 1997, and is now managed by the PXIbus Systems Alliance.

resolution The smallest signal increment that can be detected by a measurement

system. Resolution can be expressed in bits, in proportions, or in percent of full scale. For example, a system has 12-bit resolution, one part in 4,096 resolution, and 0.0244% of full scale.

RMA return Material Authorization

rms root mean square

RSVD reserved bit/signal

RTI referred to input—Calculates a specification relative to the input range.

s seconds

sample An instantaneous measurement of a signal, normally using an

analog-to-digital converter in an E Series DAQ device.

sample rate The number of samples a system takes over a given time period, usually

expressed in samples per second.

scan One or more analog or digital input samples. Typically, the number of input

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

SCANCLK Scan clock signal used to increment the next channel after each E Series

DAQ device analog-to-digital conversion.

SCXI-1125 User Manual G-8 ni.com

Glossary

SCXI Signal Conditioning eXtensions for Instrumentation—the National

Instruments product line for conditioning low-level signals within an external chassis near sensors so only high-level signals are sent to DAQ boards in the noisy PC environment.

SCXIbus The analog bus where SCXI analog signals are routed.

SER CLK A 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 out to cabled DAQ device

sensor

A device that responds to a physical stimulus (heat, light, sound, pressure, motion, flow, and so on), and produces a corresponding electrical signal. Primary characteristics of sensors are sensitivity, frequency range, and linearity.

settling time

The time required for an amplifier, relays, or other circuits to reach a stable mode of operation.

shunt See autozero.

shunt calibration The method of calibrating the gain of strain-gauge data acquisition channel

by placing a resistor of known value in parallel with a bridge element.

signal conditioning The manipulation of signals to prepare them for digitizing.

Slot 0

strain

The first slot in a VXI or SCXI system.

The relative deformation of an object subjected to stress. Hence, strain is dimensionless.

SYNC synchronization pulse for scanning

system noise A measure of the amount of noise seen by an analog circuit or an ADC

when the analog inputs are grounded.

Glossary

thermocouple A temperature sensor created by joining two dissimilar metals. The

junction produces a small voltage as a function of the temperature.

typ typical

UL Underwriters Laboratory

Vvolts

VDC volts direct current

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

voltage excitation A source that supplies the voltage needed by a sensor for its proper

rms

Channel names that can be defined outside of the application and used without having to perform scaling operations. Virtual channels are called custom channels in MAX 3.0 and later.

operation.

volts, root mean square

working isolation A level of protection pertaining to a working voltage.

working voltage The highest voltage that should be applied to a product in normal use,

normally well under the breakdown voltage for safety margin.

SCXI-1125 User Manual G-10 ni.com

Index

AC and DC voltage connections, 2-1

AC-coupling, 2-4 floating AC-coupled signal connection

(figure), 2-4 floating signal, 2-3 floating signal connection (figure), 2-3 front signal connector

figure, 2-6 table, 2-6

ground-referenced AC-coupled signal

connection (figure), 2-4 ground-referenced signal, 2-2 ground-referenced signal connection

(figure), 2-2

analog input channels on DAQ device, D-2

C language

multiplexed scanning operations, 5-27 parallel scanning operations, 5-28 scanning channels, D-4

calibration

gain values and input limits (table), 5-31 one-point offset calibration, 5-31 overview, 5-30 two-point gain and offset calibration, 5-32

channel string

calgnd channel string, D-3 SCXI, 5-25 virtual, 5-26

channels

C language scanning, D-4 questions about, D-3 unused analog input channels on DAQ

device, D-2

common questions, D-1 configuration

troubleshooting self-test verification, 1-7

configuration settings

filter bandwidth, 3-1, 4-2 gain, 3-1, 4-1

connecting SCXI-1125 to DAQ device

See also DAQ devices for parallel scanning, 1-5

connectors

front signal connector

pin assignments

figure, 2-6 table, 2-6

rear signal connector

description, 2-7 pin assignments

figure, 2-8 table, 2-8

conventions used in the manual, iv

DAQ device

connecting with SCXI-1125

for parallel scanning, 1-5 unavailable digital lines, D-2 unused analog input channels, D-2

DAQ devices

connecting to SCXI-1125 for multiplexed

scanning

in PXI combination chassis, 1-4, 3-2

in SCXI chassis, 1-4, 3-2

DC voltage connections. See AC and DC voltage

connections

Index

digital lines, unavailability on DAQ device,

D-2 digital signals on SCXI-1125 (table), D-3 documentation

conventions used in the manual, iv

electromagnetic compatibility

specifications, A-9 environmental specifications, A-8

filter setting, changing, D-4 filters

bandwidth configuration, 3-1, 4-2

floating signal connections

AC-coupled signal connection

(figure), 2-4

description, 2-3

front signal connector

pin assignments

figure, 2-6 table, 2-6

input characteristics, A-1 installation

connecting SCXI-1125 to DAQ device for

parallel scanning, 1-5

connecting to DAQ device for

multiplexed scanning

in PXI combination chassis, 1-4, 3-2

in SCXI chassis, 1-4, 3-2 into SCXI chassis, 1-4 removing SCXI-1125

from Measurement & Automation

Explorer, C-1

from SCXI chassis, C-1

LabVIEW

multiplexed scanning operations

SCXI channel string, 5-25

virtual channel string, 5-26 parallel scanning operations, 5-28

low-level DAQ functions, in multiplexed

scanning, 5-28

gain

configuration, 3-1, 4-1

ground-referenced signal connections

AC-coupled signal connection

(figure), 2-4

description, 2-2

high-voltage measurements, 5-4

SCXI-1125 User Manual I-2 ni.com

maximum working voltage, A-8 Measurement & Automation Explorer

removing SCXI-1125, C-1 self-test verification

troubleshooting, 1-7

multiplexed mode

operating in, 4-2 performing scans, 5-27

C and low-level DAQ functions, 5-28 rear signal connector pin assignments

figure, 2-8

table, 2-8

Index

theory of multiplexed hardware

operation, 4-3

using software for scanning operations

LabVIEW and SCXI channel

string, 5-25

LabVIEW and virtual channel

string, 5-26

multiplexed mode operation

connecting to SCXI-1125 for DAQ device

in PXI combination, 1-4, 3-2 in SCXI chassis, 1-4, 3-2

NI-DAQ version required, D-2

parallel mode

connecting SCXI-1125 to DAQ

device, 1-5 theory of parallel hardware operation, 4-4 using software for scanning

C and parallel mode, 5-29

LabVIEW and parallel mode, 5-28 physical specifications, A-7 pin assignments

front connector (table), 2-6

PXI combination chassis, 1-4, 3-2

rear signal connector

description, 2-7 pin assignments

figure, 2-8

table, 2-8 regulatory compliance specifications, A-9

removing SCXI-1125

from Measurement & Automation

Explorer, C-1

from SCXI chassis, C-1

safety specifications, A-9 SCXI channel string, 5-25 SCXI chassis

connecting SCXI-1125 to DAQ device,

1-4, 3-2

SCXI-1125

calibration, 5-30 common questions, D-1 digital signals (table), D-3 multiplexed mode, 4-2 parallel mode, 4-3 signal connections, 2-1 specifications, A-1

self-test verification

troubleshooting, 1-7, D-2

signal connections

See also connectors AC and DC voltage connections, 2-1

AC-coupling, 2-4 floating AC-coupled signal

connection (figure), 2-4 floating signal, 2-3 floating signal connection

(figure), 2-3 front signal connector (figure), 2-6 ground-referenced AC-coupled

signal connection (figure), 2-4 ground-referenced signal, 2-2 ground-referenced signal connection

(figure), 2-2

digital signals (table), D-3

National Instruments SCXI-1125 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

SCXI-1125 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 DAQ Device

Installing the SCXI-1125 Module into the SCXI Chassis

Connecting the SCXI-1125 in an SCXI Chassis to an E/M Series DAQ Device for Multiplexed Scanning

Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis to an E/M Series DAQ Device for Multiplexed Scanning

Connecting the SCXI-1125 to a n E/M Series DAQ Device for Parallel Scanning

Verifying the SCXI-1125 Installation in Software

Installing SCXI Using NI-DAQmx in Software

Manually Adding Modules in NI-DAQmx

Installing SCXI Using Traditional NI-DAQ (Legacy) in Software

Manually Adding Modules in Traditional NI-DAQ (Legacy)

Verifying and Self-Testing the Installation

Troubleshooting the Self-Test Verification

Troubleshooting in NI-DAQmx

AC and DC Voltage Connections

Ground-Referenced Signal

Figure 2-1. Connecting a Ground-Referenced Signal

Floating Signal

Figure 2-2. Connecting a Floating Signal

AC-Coupling

Figure 2-3. Connecting a Floating AC-Coupled Signal

Figure 2-4. Connecting a Ground-Referenced AC-Coupled Signal

Pin Assignments

Table 2-1. Front Signal Pin Assignments

Temperature Sensor Connection

Rear Signal Connector

Table 2-2. Rear Signal Pin Assignments

SCXI-1125 Software-Configurable Settings

Common Software-Configurable Settings

Filter Bandwidth

Gain/Input Range

Connecting the SCXI-1125 in an SCXI Chassis to an E/M Series DAQ Device for Multiplexed Scanning

Connecting the SCXI-1125 in a PXI/SCXI Combination Chassis to an E/M Series DAQ Device for Multiplexed Scanning

Configurable Settings in MAX

NI-DAQmx

Creating a Voltage Global Channel or Task

Traditional NI-DAQ (Legacy)

Configuring Module Property Pages in Traditional NI-DAQ (Legacy)

Creating a Virtual Channel

Verifying the Signal

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

Verifying the Signal in Traditional NI-DAQ (Legacy)

Verifying the Signal Using Channel Strings

Verifying the Signal Using Virtual Channel

Gain

Figure 4-1. SCXI-1125 Block Diagram

Filter Bandwidth and Cutoff Frequency

Operating in Multiplexed Mode

Multiplexed Hardware Operation Theory

Operating in Parallel Mode

Theory of Parallel Hardware Operation

Temperature Measurements Using Thermocouples

Making High-Voltage Measurements

Table 5-1. Extended Gain and Range Using the SCXI-1327 or SCXI-1313A

Table 5-2. Extended Gain and Range Using the TBX-1316

Developing Your Application in NI-DAQmx

Typical Program Flowchart

Figure 5-1. Typical Program Flowchart

General Discussion of Typical Flowchart

Creating a Task Using DAQ Assistant or Programmatically

Adjusting Timing and Triggering

Configuring Channel Properties