National Instruments NI 6238, NI 6239 User Manual

DAQ M Series

NI 6238/6239 User Manual

Isolated Current Input/Current Output Devices

NI 6238/6239 User Manual

July 2006 371913A-01

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The NI 6238/6239 is warranted against defects in materials and workmanship for a period of three years from the date of shipment, as evidenced by receipts or other documentation. National Instruments will, at its option, repair or replace equipment that proves to be defective during the warranty period. This warranty includes parts and labor.

The media on which you receive National Instruments software are warranted not to fail to execute programming instructions, due to defects in materials and workmanship, for a period of 90 days from date of shipment, as evidenced by receipts or other documentation. National Instruments will, at its option, repair or replace software media that do not execute programming instruc tions if National Instruments receives notice of such defects during the warranty period. National Instruments does not warrant that the operation of the software shall be uninterrupted or error free.

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About This Manual

Conventions ...................................................................................................................xiii

Related Documentation.................................................................................................. xiv

NI-DAQ........................................................................................................... xiv

NI-DAQmx for Linux...................................................................................... xiv

NI-DAQmx Base.............................................................................................xv

LabVIEW ........................................................................................................xv

LabWindows™/CVI™....................................................................................xvi

Measurement Studio........................................................................................xvi

ANSI C without NI Application Software ......................................................xvi

.NET Languages without NI Application Software ........................................xvii

Device Documentation and Specifications......................................................xvii

Training Courses .............................................................................................xvii

Technical Support on the Web ........................................................................xvii

Chapter 1 Getting Started

Installing NI-DAQmx ....................................................................................................1-1

Installing Other Software...............................................................................................1-1

Installing the Hardware..................................................................................................1-1

Device Pinouts ...............................................................................................................1-1

Device Specifications ....................................................................................................1-2

Device Accessories and Cables .....................................................................................1-2

Chapter 2 DAQ System Overview

DAQ Hardware ..............................................................................................................2-1

DAQ-STC2......................................................................................................2-2

Calibration Circuitry........................................................................................2-3

Sensors and Transducers................................................................................................ 2-3

Cables and Accessories.................................................................................................. 2-4

Custom Cabling...............................................................................................2-4

Programming Devices in Software................................................................................2-5

Chapter 3 Connector Information

I/O Connector Signal Descriptions................................................................................3-1

RTSI Connector Pinout.................................................................................................. 3-3

Contents

Chapter 4 Analog Input

Analog Input Circuitry .................................................................................................. 4-1

Analog Input Range....................................................................................................... 4-2

Connecting Analog Current Input Signals .................................................................... 4-3

Analog Input Ground-Reference Settings ..................................................................... 4-5

Multichannel Scanning Considerations......................................................................... 4-8

Analog Input Data Acquisition Methods....................................................................... 4-10

Analog Input Triggering................................................................................................ 4-11

Field Wiring Considerations.......................................................................................... 4-11

Analog Input Timing Signals ........................................................................................ 4-12

Method 1 ......................................................................................................... 4-3

Method 2 ......................................................................................................... 4-4

Configuring AI Ground-Reference Settings in Software ................. 4-7

Use Short High-Quality Cabling..................................................................... 4-8

Minimize Current Step between Adjacent Channels ...................................... 4-8

Avoid Scanning Faster Than Necessary ......................................................... 4-9

Example 1 ......................................................................................... 4-9

Example 2 ......................................................................................... 4-9

Software-Timed Acquisitions ......................................................................... 4-10

Hardware-Timed Acquisitions........................................................................ 4-10

Buffered ............................................................................................ 4-10

Non-Buffered.................................................................................... 4-11

AI Sample Clock Signal.................................................................................. 4-15

Using an Internal Source .................................................................. 4-16

Using an External Source ................................................................. 4-16

Routing AI Sample Clock Signal to an Output Terminal................. 4-16

Other Timing Requirements ............................................................. 4-17

AI Sample Clock Timebase Signal ................................................................. 4-17

AI Convert Clock Signal................................................................................. 4-18

Using an Internal Source .................................................................. 4-18

Using an External Source ................................................................. 4-19

Routing AI Convert Clock Signal to an Output Terminal ................ 4-19

Using a Delay from Sample Clock to Convert Clock ...................... 4-19

Other Timing Requirements ............................................................. 4-20

AI Convert Clock Timebase Signal ................................................................ 4-21

AI Hold Complete Event Signal ..................................................................... 4-21

AI Start Trigger Signal.................................................................................... 4-22

Using a Digital Source...................................................................... 4-22

Routing AI Start Trigger to an Output Terminal.............................. 4-22

AI Reference Trigger Signal........................................................................... 4-23

Using a Digital Source...................................................................... 4-24

Routing AI Reference Trigger Signal to an Output Terminal .......... 4-24

NI 6238/6239 User Manual vi ni.com

AI Pause Trigger Signal ..................................................................................4-24

Getting Started with AI Applications in Software......................................................... 4-25

Chapter 5 Analog Output

Analog Output Circuitry ................................................................................................5-1

Analog Output Data Generation Methods .....................................................................5-2

Software-Timed Generations...........................................................................5-2

Hardware-Timed Generations .........................................................................5-2

Analog Output Triggering .............................................................................................5-4

Connecting Analog Current Output Signals..................................................................5-4

Analog Output Timing Signals ......................................................................................5-5

AO Start Trigger Signal...................................................................................5-5

AO Pause Trigger Signal.................................................................................5-6

AO Sample Clock Signal................................................................................. 5-8

AO Sample Clock Timebase Signal................................................................5-9

Getting Started with AO Applications in Software .......................................................5-10

Contents

Using a Digital Source ......................................................................4-24

Routing AI Pause Trigger Signal to an Output Terminal .................4-25

Non-Buffered ....................................................................................5-3

Buffered ............................................................................................5-3

Using a Digital Source ......................................................................5-6

Routing AO Start Trigger Signal to an Output Terminal..................5-6

Using a Digital Source ......................................................................5-7

Routing AO Pause Trigger Signal to an Output Terminal................5-8

Using an Internal Source...................................................................5-8

Using an External Source..................................................................5-8

Routing AO Sample Clock Signal to an Output Terminal................ 5-8

Other Timing Requirements..............................................................5-9

Chapter 6 Digital Input and Output

I/O Protection................................................................................................................. 6-1

Programmable Power-Up States....................................................................................6-1

Connecting Digital I/O Signals......................................................................................6-2

Logic Conventions.........................................................................................................6-3

Getting Started with DIO Applications in Software......................................................6-4

Contents

Chapter 7 Counters

Counter Input Applications ........................................................................................... 7-3

Counter Output Applications......................................................................................... 7-21

Counting Edges............................................................................................... 7-3

Single Point (On-Demand) Edge Counting...................................... 7-3

Buffered (Sample Clock) Edge Counting......................................... 7-4

Non-Cumulative Buffered Edge Counting....................................... 7-5

Controlling the Direction of Counting.............................................. 7-5

Pulse-Width Measurement.............................................................................. 7-6

Single Pulse-Width Measurement .................................................... 7-6

Buffered Pulse-Width Measurement ................................................ 7-6

Period Measurement ....................................................................................... 7-7

Single Period Measurement.............................................................. 7-8

Buffered Period Measurement.......................................................... 7-8

Semi-Period Measurement.............................................................................. 7-9

Single Semi-Period Measurement .................................................... 7-9

Buffered Semi-Period Measurement ................................................ 7-10

Frequency Measurement................................................................................. 7-10

Method 1—Measure Low Frequency with One Counter................. 7-10

Method 1b—Measure Low Frequency with One Counter

(Averaged) ..................................................................................... 7-11

Method 2—Measure High Frequency with Two Counters .............. 7-12

Method 3—Measure Large Range of Frequencies Using Two

Counters......................................................................................... 7-13

Choosing a Method for Measuring Frequency................................. 7-14

Position Measurement..................................................................................... 7-16

Measurements Using Quadrature Encoders...................................... 7-16

Measurements Using Two Pulse Encoders ...................................... 7-18

Two-Signal Edge-Separation Measurement ................................................... 7-19

Single Two-Signal Edge-Separation Measurement.......................... 7-19

Buffered Two-Signal Edge-Separation Measurement...................... 7-20

Simple Pulse Generation................................................................................. 7-21

Single Pulse Generation.................................................................... 7-21

Single Pulse Generation with Start Trigger...................................... 7-21

Retriggerable Single Pulse Generation............................................. 7-22

Pulse Train Generation.................................................................................... 7-23

Continuous Pulse Train Generation.................................................. 7-23

Frequency Generation..................................................................................... 7-24

Using the Frequency Generator........................................................ 7-24

Frequency Division......................................................................................... 7-25

Pulse Generation for ETS ............................................................................... 7-25

NI 6238/6239 User Manual viii ni.com

Contents

Counter Timing Signals .................................................................................................7-26

Counter n Source Signal..................................................................................7-26

Routing a Signal to Counter n Source...............................................7-27

Routing Counter n Source to an Output Terminal ............................7-27

Counter n Gate Signal .....................................................................................7-28

Routing a Signal to Counter n Gate ..................................................7-28

Routing Counter n Gate to an Output Terminal................................7-28

Counter n Aux Signal ......................................................................................7-28

Routing a Signal to Counter n Aux...................................................7-28

Counter n A, Counter n B, and Counter n Z Signals .......................................7-29

Routing Signals to A, B, and Z Counter Inputs ................................7-29

Routing Counter n Z Signal to an Output Terminal..........................7-29

Counter n Up_Down Signal ............................................................................7-29

Counter n HW Arm Signal..............................................................................7-29

Routing Signals to Counter n HW Arm Input...................................7-30

Counter n Internal Output and Counter n TC Signals .....................................7-30

Routing Counter n Internal Output to an Output Terminal...............7-30

Frequency Output Signal.................................................................................7-30

Routing Frequency Output to a Terminal .........................................7-31

Default Counter Terminals ............................................................................................7-31

Counter Triggering ........................................................................................................7-32

Arm Start Trigger ............................................................................................7-32

Start Trigger.....................................................................................................7-32

Pause Trigger...................................................................................................7-32

Other Counter Features.................................................................................................. 7-33

Cascading Counters.........................................................................................7-33

Counter Filters.................................................................................................7-33

Prescaling ........................................................................................................7-34

Duplicate Count Prevention ............................................................................ 7-35

Example Application That Works Correctly

(No Duplicate Counting)................................................................ 7-35

Example Application That Works Incorrectly

(Duplicate Counting)......................................................................7-36

Example Application That Prevents Duplicate Count......................7-37

When To Use Duplicate Count Prevention.......................................7-38

Enabling Duplicate Count Prevention in NI-DAQmx......................7-38

Synchronization Modes...................................................................................7-38

80 MHz Source Mode.......................................................................7-39

Other Internal Source Mode..............................................................7-39

External Source Mode.......................................................................7-40

Contents

Chapter 8 PFI

Using PFI Terminals as Timing Input Signals .............................................................. 8-2

Exporting Timing Output Signals Using PFI Terminals............................................... 8-3

Using PFI Terminals as Static Digital Inputs and Outputs............................................ 8-3

Connecting PFI Input Signals........................................................................................ 8-3

PFI Filters ...................................................................................................................... 8-4

I/O Protection ................................................................................................................ 8-5

Programmable Power-Up States.................................................................................... 8-6

Connecting Digital I/O Signals ..................................................................................... 8-6

Chapter 9 Isolation and Digital Isolators

Digital Isolation............................................................................................................. 9-2

Benefits of an Isolated DAQ Device............................................................................. 9-2

Reducing Common-Mode Noise................................................................................... 9-3

Chapter 10 Digital Routing and Clock Generation

Clock Routing................................................................................................................ 10-1

80 MHz Timebase........................................................................................... 10-2

20 MHz Timebase........................................................................................... 10-2

100 kHz Timebase .......................................................................................... 10-2

External Reference Clock ............................................................................... 10-2

10 MHz Reference Clock................................................................................ 10-3

Synchronizing Multiple Devices ................................................................................... 10-3

Real-Time System Integration Bus (RTSI)................................................................... 10-3

RTSI Connector Pinout................................................................................... 10-4

Using RTSI as Outputs ................................................................................... 10-5

Using RTSI Terminals as Timing Input Signals............................................. 10-6

RTSI Filters..................................................................................................... 10-6

PXI Clock and Trigger Signals...................................................................................... 10-7

PXI_CLK10 .................................................................................................... 10-8

PXI Triggers.................................................................................................... 10-8

PXI_STAR Trigger ......................................................................................... 10-8

PXI_STAR Filters........................................................................................... 10-8

NI 6238/6239 User Manual x ni.com

Chapter 11 Bus Interface

DMA Controllers ...........................................................................................................11-1

PXI Considerations ........................................................................................................11-2

PXI Clock and Trigger Signals........................................................................ 11-2

PXI and PXI Express.......................................................................................11-2

Using PXI with CompactPCI ..........................................................................11-3

Data Transfer Methods ..................................................................................................11-3

Direct Memory Access (DMA).......................................................................11-3

Interrupt Request (IRQ)...................................................................................11-4

Programmed I/O ..............................................................................................11-4

Changing Data Transfer Methods between DMA and IRQ ............................11-4

Chapter 12 Triggering

Triggering with a Digital Source ...................................................................................12-1

Appendix A Device-Specific Information

NI 6238 ..........................................................................................................................A-1

NI 6239 ..........................................................................................................................A-4

Contents

Appendix B Troubleshooting

Analog Input ..................................................................................................................B-1

Analog Output................................................................................................................B-2

Counters ......................................................................................................................... B-3

Appendix C Technical Support and Professional Services

Glossary

Index

Figures

Figure A-1. NI 6238 Pinout ......................................................................................A-2

Figure A-2. NI 6239 Pinout ......................................................................................A-5

About This Manual

The NI 6238/6239 User Manual contains information about using the NI 6238 and NI 6239 M Series data acquisition (DAQ) devices with NI-DAQmx 8.1 and later. National Instruments 6238/6239 devices feature up to eight differential analog input (AI) channels, two analog output (AO) channels, two counters, six lines of digital input (DI), and four lines of digital output (DO).

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, AO <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 tip, which alerts you to advisory information.

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 NI 6238/6239 Specifcations 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.

About This Manual

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.

Installing NI-DAQmx

The DAQ Getting Started Guide, which you can download at

ni.com/manuals, offers NI-DAQmx users step-by-step instructions for

installing software and hardware, configuring channels and tasks, and getting started developing an application.

ni.com/manuals.

Installing Other Software

If you are using other software, refer to the installation instructions that accompany your software.

Installing the Hardware

The DAQ Getting Started Guide contains non-software-specific information on how to install PCI and PXI devices, as well as accessories and cables.

Device Pinouts

Refer to Appendix A, Device-Specific Information, for NI 6238/6239 device pinouts.

Chapter 1 Getting Started

Device Specifications

Refer to the NI 6238/6239 Specifications, available on the NI-DAQ Device Document Browser or on NI 6238/6239 devices.

ni.com/manuals, for more detailed information

Device Accessories and Cables

NI offers a variety of accessories and cables to use with your DAQ device. Refer to Appendix A, Device-Specific Information, or information.

ni.com for more

NI 6238/6239 User Manual 1-2 ni.com

DAQ System Overview

Figure 2-1 shows a typical DAQ system, which includes sensors, transducers, cables that connect the various devices to the accessories, the M Series device, programming software, and PC. The following sections cover the components of a typical DAQ system.

Sensors and

Transducers

DAQ Hardware

Cables and

Accessories

DAQ hardware digitizes input signals, performs D/A conversions to generate analog output signals, and measures and controls digital I/O signals. Figure 2-2 features the components of the NI 6238/6239 devices.

DAQ

Hardware

Figure 2-1. Components of a Typical DAQ System

DAQ

Software

Personal

Computer

Chapter 2 DAQ System Overview

Analog Input

Analog Output

I/O Connector

Counters

PFI/Static DI

AI GND

AO GND

P0.GND

Isolation

Barrier

Digital

Isolators

Routing

and Clock

Generation

RTSI

Bus

Interface

Bus

DAQ-STC2

PFI/Static DO

P1.GND

Figure 2-2. General NI 6238/6239 Block Diagram

The DAQ-STC2 implements a high-performance digital engine for NI 6238/6239 data acquisition hardware. Some key features of this engine include the following:

• Flexible AI and AO sample and convert timing

• Many triggering modes

• Independent AI and AO FIFOs

• Generation and routing of RTSI signals for multi-device synchronization

• Generation and routing of internal and external timing signals

• Two flexible 32-bit counter/timer modules with hardware gating

• Static DIO signals

• PLL for clock synchronization

• PCI/PXI interface

• Independent scatter-gather DMA controllers for all acquisition and generation functions

NI 6238/6239 User Manual 2-2 ni.com

Calibration Circuitry

The M Series analog inputs and outputs can self calibrate to correct gain and offset errors. You can calibrate the device to minimize AI and AO errors caused by time and temperature drift at run time. No external circuitry is necessary; an internal reference ensures high accuracy and stability over time and temperature changes.

Factory-calibration constants are permanently stored in an onboard EEPROM and cannot be modified. When you self-calibrate the device, software stores new constants in a user-modifiable section of the EEPROM. To return a device to its initial factory calibration settings, software can copy the factory-calibration constants to the user-modifiable section of the EEPROM. Refer to the NI-DAQmx Help or the LabVIEW 8.x Help for more information on using calibration constants.

Sensors and Transducers

Sensors can generate electrical signals to measure physical phenomena, such as temperature, force, sound, or light. Some commonly used sensors are strain gauges, thermocouples, thermistors, angular encoders, linear encoders, and resistance temperature detectors (RTDs).

Chapter 2 DAQ System Overview

Note Current input measurement devices can only interface with sensors that output a current.

To measure signals from these various transducers, you must convert them into a form that a DAQ device can accept. For example, the output voltage of most thermocouples is very small and susceptible to noise. Therefore, you may need to amplify or filter the thermocouple output before digitizing it, or use the smallest measurement range available within the DAQ device.

For more information about sensors, refer to the following:

• For general information about sensors, visit

• If you are using LabVIEW, refer to the LabVIEW Help by selecting

Help»Search the LabVIEW Help in LabVIEW, and then navigate to the Taking Measurements book on the Contents tab.

• If you are using other application software, refer to Common Sensors in the NI-DAQmx Help, which can be accessed from Start»All Programs»National Instruments»NI-DAQ»NI-DAQmx Help.

ni.com/sensors.

Chapter 2 DAQ System Overview

Cables and Accessories

NI offers a variety of products to use with NI 6238/6239 devices, including cables, connector blocks, and other accessories, as follows:

• Cables and cable assemblies

– Shielded

– Unshielded ribbon

• Screw terminal connector blocks, shielded and unshielded

• RTSI bus cables

Custom Cabling

For more specific information about these products, refer to

Refer to the Custom Cabling section of this chapter, the Field Wiring

Considerations section of Chapter 4, Analog Input, and Appendix A, Device-Specific Information, for information on how to select accessories

for your M Series device.

NI offers cables and accessories for many applications. However, if you want to develop your own cable, the following kits can assist you:

• TB-37F-37SC—37-pin solder cup terminals, shell with strain relief

• TB-37F-37CP—37-pin crimp & poke terminals, shell with strain

relief

Also, adhere to the following guidelines for best results:

• For AI signals, use shielded, twisted-pair wires for each AI pair of differential inputs. Connect the shield for each signal pair to the ground reference at the source.

• Route the analog lines separately from the digital lines.

• When using a cable shield, use separate shields for the analog and digital sections of the cable. Failure to do so results in noise coupling into the analog signals from transient digital signals.

ni.com.

For more information on the connectors used for DAQ devices, refer to the KnowledgeBase document, Specifications and Manufacturers for Board Mating Connectors, by going to

rdspmb.

NI 6238/6239 User Manual 2-4 ni.com

ni.com/info and entering the info code

Programming Devices in Software

National Instruments measurement devices are packaged with NI-DAQ driver software, an extensive library of functions and VIs you can call from your application software, such as LabVIEW or LabWindows/CVI, to program all the features of your NI measurement devices. Driver software has an application programming interface (API), which is a library of VIs, functions, classes, attributes, and properties for creating applications for your device.

NI-DAQ includes two NI-DAQ drivers, Traditional NI-DAQ (Legacy) and NI-DAQmx. M Series devices use the NI-DAQmx driver. Each driver has its own API, hardware configuration, and software configuration. Refer to the DAQ Getting Started Guide for more information about the two drivers.

NI-DAQmx includes a collection of programming examples to help you get started developing an application. You can modify example code and save it in an application. You can use examples to develop a new application or add example code to an existing application.

To locate LabVIEW and LabWindows/CVI examples, open the National Instruments Example Finder.

• In LabVIEW, select Help»Find Examples.

• In LabWindows/CVI, select Help»NI Example Finder.

Chapter 2 DAQ System Overview

Measurement Studio, Visual Basic, and ANSI C examples are located in the following directories:

• NI-DAQmx examples for Measurement Studio-supported languages are in the following directories:

–

MeasurementStudio\VCNET\Examples\NIDaq

– MeasurementStudio\DotNET\Examples\NIDaq

• NI-DAQmx examples for ANSI C are in the

NI-DAQ\Examples\DAQmx ANSI C Dev directory

For additional examples, refer to

zone.ni.com.

Connector Information

The I/O Connector Signal Descriptions and RTSI Connector Pinout sections contain information on M Series connectors. Refer to Appendix A, Device-Specific Information, for device I/O connector pinouts.

I/O Connector Signal Descriptions

Table 3-1 describes the signals found on the I/O connectors. Not all signals are available on all devices.

Table 3-1. I/O Connector Signals

Signal Name Reference Direction Description

AI GND — — Analog Input Ground—These terminals are the input bias

current return point. AI GND and AO GND are connected on the device.

Note: AI GND and AO GND are isolated from earth ground, chassis ground, P0.GND, and P1.GND.

AI <0..7>± AI GND Input Analog Input Channels 0 to 7±—AI 0+ and AI 0– are the

positive and negative inputs of differential analog input channel 0. Similarly, the following signal pairs also form differential input channels:

Also refer to the Analog Input Ground-Reference Settings section of Chapter 4, Analog Input.

Note: AI <0..7>± are isolated from earth ground and chassis ground.

AO <0..1> AO GND Output Analog Output Channels 0 to 1—These terminals supply the

current output of AO channels 0 to 1.

Note: AO <0..1> are isolated from earth ground and chassis ground.

Chapter 3 Connector Information

Table 3-1. I/O Connector Signals (Continued)

Signal Name Reference Direction Description

AO GND — — Analog Output Ground—AO GND is the reference for

AO <0..1>. AI GND and AO GND are connected on the device.

Note: AI GND and AO GND are isolated from earth ground, chassis ground, P0.GND, and P1.GND.

PFI <0..5>/P0.<0..5> P0.GND Input Programmable Function Interface or Static Digital Input

Channels 0 to 5—Each of these terminals can be individually configured as an input directional PFI terminal or a digital input terminal.

As an input, each input PFI terminal can be used to supply an external source for AI or AO timing signals or counter/timer inputs.

Note: PFI <0..5>/P0.<0..5> are isolated from earth ground, chassis ground, AI GND, AO GND, and P1.GND.

PFI <6..9>/P1.<0..3> P1.GND Output Programmable Function Interface or Static Digital

Output Channels 6 to 9—Each of these terminals can be individually configured as an output directional PFI terminal or a digital output terminal.

As a PFI output, you can route many different internal AI or AO timing signals to each PFI terminal. You also can route the counter/timer outputs to each PFI terminal.

Note: PFI <6..9>/P1.<0..3> are isolated from earth ground, chassis ground, AI GND, AO GND, and P0.GND.

NC — — No connect—Do not connect signals to these terminals.

P0.GND — — Digital Ground—P0.GND supplies the reference for input

PFI <0..5>/P0.<0..5>.

Note: P0.GND is isolated from earth ground, chassis ground, AI GND, AO GND, and P1.GND.

P1.GND — — Digital Ground—P1.GND supplies the reference for output

P1.VCC — — Digital Output Power—P1.VCC supplies the power for

AO POWER SUPPLY — — Analog Output Power Supply—AO POWER SUPPLY

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PFI <6..9>/P1.<0..3>.

Note: P1.GND is isolated from earth ground, chassis ground, AI GND, AO GND, and P0.GND.

digital output lines. The actual power consumed depends on the load connected between the digital output and P1.GND.

supplies power to the analog current output terminals.

Chapter 3 Connector Information

Table 3-1. I/O Connector Signals (Continued)

Signal Name Reference Direction Description

CAL+ — — External Calibration Positive Reference—CAL+ supplies

the positive reference during external calibration of the NI 6238/6239.

CAL– — — External Calibration Negative Reference—CAL– supplies

the negative reference during external calibration of the NI 6238/6239.

RTSI Connector Pinout

Refer to the RTSI Connector Pinout section of Chapter 10, Digital Routing

and Clock Generation, for information on the RTSI connector.

Analog Input

Figure 4-1 shows the analog input circuitry of NI 6238 and NI 6239 devices.

AI <0..7>+

Mux

AI Terminal

AI <0..7>–

I/O Connector

AI GND

Analog Input Circuitry

Configuration

Selection

Isolation

Barrier

NI-PGIA

Input Range

Selection

Figure 4-1. NI 6238/6239 Analog Input Circuitry

ADC

Digital

Isolators

AI FIFO

AI Data

I/O Connector

You can connect analog input signals to the M Series device through the I/O connector. The proper way to connect analog input signals is outlined in the

Connecting Analog Current Input Signals section. Also refer to

Appendix A, Device-Specific Information, for device I/O connector pinouts.

MUX

Each M Series device has one analog-to-digital converter (ADC). The multiplexers (MUX) route one AI channel at a time to the ADC through the NI-PGIA.

Instrumentation Amplifier (NI-PGIA)

The NI programmable gain instrumentation amplifier (PGIA) is a measurement and instrument class amplifier that minimizes settling times

Chapter 4 Analog Input

for all input ranges. The NI-PGIA can amplify or attenuate an AI signal to ensure that you use the maximum resolution of the ADC.

M Series devices use the NI-PGIA to deliver high accuracy even when sampling multiple channels with small input ranges at fast rates. M Series devices can sample channels in any order at the maximum conversion rate, and you can individually program each channel in a sample with a different input range.

A/D Converter

The analog-to-digital converter (ADC) digitizes the AI signal by converting the analog voltage into a digital number.

Isolation Barrier and Digital Isolators

The digital isolators across the isolation barrier provide a ground break between the isolated analog front end and the earth/chassis/building ground.

AI FIFO

M Series devices can perform both single and multiple A/D conversions of a fixed or infinite number of samples. A large first-in-first-out (FIFO) buffer holds data during AI acquisitions to ensure that no data is lost. M Series devices can handle multiple A/D conversion operations with DMA, interrupts, or programmed I/O.

Analog Input Range

Input range refers to the set of input voltages or currents that an analog input channel can digitize with the specified accuracy. The NI-PGIA amplifies or attenuates the AI signal depending on the input range. You can individually program the input range of each AI channel on your M Series device.

The input range affects the resolution of the M Series device for an AI channel. Resolution refers to the voltage or current of one ADC code.

For example, a 16-bit ADC converts analog current inputs into one of 65,536 (= 2 values are spread fairly evenly across the input range. So, for an input range of ±20 mA, the current of each code of a 16-bit ADC is:

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) codes—that is, one of 65,536 possible digital values. These

Chapter 4 Analog Input

(20 mA – (–20 mA))

M Series devices use a calibration method that requires some codes (typically about 5% of the codes) to lie outside of the specified range. This calibration method improves absolute accuracy, but it increases the nominal resolution of input ranges by about 5% over what the formulas shown above would indicate.

Choose an input range that matches the expected input range of your signal. A large input range can accommodate a large signal variation, but reduces the measurement resolution. Choosing a smaller input range improves the measurement resolution, but may result in the input signal going out of range.

For more information on programming these settings, refer to the NI-DAQmx Help or the LabVIEW 8.x Help.

Table 4-1 shows the input ranges and resolutions supported by the NI 6238 and NI 6239 devices.

Table 4-1. Input Ranges for NI 6238/6239

Input Range

= 610 nA

Nominal Resolution Assuming

5% Over Range

20 mA 640 nA

Connecting Analog Current Input Signals

When making signal connections, caution must be taken with the voltage level of the signal going into the device. There are two types of connections that can be made.

Method 1

Method 1, shown in Figure 4-2, connects AI + and AI – inputs at a voltage level with respect to AI GND. Verify that the voltage levels on the AI + and AI – side do not exceed the common-mode input range of ±10 V. Common-mode input range is the voltage input range with respect to AI GND (AI + versus AI GND, AI – versus AI GND, or AI + versus AI –).

Chapter 4 Analog Input

AI +

Isolation

Barrier

Method 2

AI –

–

AI GND

–

AI GND

Figure 4-2. Analog Current Input Connection Method 1

Method 2, shown in Figure 4-3, ties the AI – input to AI GND. When measuring current up to 20 mA, this type of connection ensures that the voltage level on both the positive and negative side are within the common-mode input range for NI 6238/6239 devices.

Isolation

Barrier

AI +

AI –

AI GND

–

Figure 4-3. Analog Current Input Connection Method 2

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National Instruments NI 6238, NI 6239 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

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Worldwide Technical Support and Product Information

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Worldwide Offices

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WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS

Contents

About This Manual

Conventions

Related Documentation

NI-DAQ

NI-DAQmx for Linux

NI-DAQmx Base

LabVIEW

Measurement Studio

ANSI C without NI Application Software

.NET Languages without NI Application Software

Device Documentation and Specifications

Training Courses

Technical Support on the Web

Installing NI-DAQmx

Installing Other Software

Installing the Hardware

Device Pinouts

Device Specifications

Device Accessories and Cables

DAQ Hardware

Figure 2-1. Components of a Typical DAQ System

DAQ-STC2

Figure 2-2. General NI 6238/6239 Block Diagram

Calibration Circuitry

Sensors and Transducers

Cables and Accessories

Custom Cabling

Programming Devices in Software

I/O Connector Signal Descriptions

Table 3-1. I/O Connector Signals

RTSI Connector Pinout

Analog Input Circuitry

Figure 4-1. NI 6238/6239 Analog Input Circuitry

Analog Input Range

Table 4-1. Input Ranges for NI 6238/6239

Connecting Analog Current Input Signals

Method 1

Method 2

Figure 4-2. Analog Current Input Connection Method 1

Figure 4-3. Analog Current Input Connection Method 2