National Instruments NI 6221, NI 6225, NI 6220, NI 6224, NI 6250 User Manual

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Page 1

DAQ M Series

M Series User Manual

NI 622x, NI 625x, and NI 628x Devices

M Series User Manual

June 2007 371022H-01

Page 2

Support

Worldwide Technical Support and Product Information

ni.com

National Instruments Corporate Headquarters

11500 North Mopac Expressway Austin, Texas 78759-3504 USA Tel: 512 683 0100

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For further support information, refer to the Technical Support and Professional Services appendix. To comment on National Instruments documentation, refer to the National Instruments Web site at the info code

feedback.

ni.com/info and enter

Page 3

Important Information

Warranty

M Series devices are warranted against defects in materials and workmanship for a period of one year from the date of shipment, as evidenced by receipts or other documentation. National Instruments will, at its option, repair or replace equipment that proves to be defective during the warranty period. This warranty includes parts and labor.

The media on which you receive National Instruments software are warranted not to fail to execute programming instructions, due to defects in materials and workmanship, for a period of 90 days from date of shipment, as evidenced by receipts or other documentation. National Instruments will, at its option, repair or replace software media that do not execute programming 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.

A Return Material Authorization (RMA) number must be obtained from the factory and clearly marked on the outside of the package before any equipment will be accepted for warranty work. National Instruments will pay the shipping costs of returning to the owner parts which are covered by warranty.

National Instruments believes that the information in this document is accurate. The document has been carefully reviewed for technical accuracy. In the event that technical or typographical errors exist, National Instruments reserves the right to make changes to subsequent editions of this document without prior notice to holders of this edition. The reader should consult National Instruments if errors are suspected. In no event shall National Instruments be liable for any damages arising out of or related to this document or the information contained in it.

XCEPT AS SPECIFIED HEREIN, NATIONAL INSTRUMENTS MAKES NO WARRANTIES, EXPRESS OR IMPLIED, AND SPECIFICALLY DISCLAIMS ANY WARRANTY OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. CUSTOMER’S RIGHT TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL

NSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER. NATIONAL INSTRUMENTS WILL NOT BE LIABLE FOR DAMAGES RESULTING

FROM LOSS OF DATA, PROFITS, USE OF PRODUCTS, OR INCIDENTAL OR CONSEQUENTIAL DAMAGES, EVEN IF ADVISED OF THE POSSIBILITY THEREOF. This limitation of

the liability of National Instruments will apply regardless of the form of action, whether in contract or tort, including negligence. Any action against National Instruments must be brought within one year after the cause of action accrues. National Instruments shall not be liable for any delay in performance due to causes beyond its reasonable control. The warranty provided herein does not cover damages, defects, malfunctions, or service failures caused by owner’s failure to follow the National Instruments installation, operation, or maintenance instructions; owner’s modification of the product; owner’s abuse, misuse, or negligent acts; and power failure or surges, fire, flood, accident, actions of third parties, or other events outside reasonable control.

Copyright

Under the copyright laws, this publication may not be reproduced or transmitted in any form, electronic or mechanical, including photocopying, recording, storing in an information retrieval system, or translating, in whole or in part, without the prior written consent of National Instruments Corporation.

National Instruments respects the intellectual property of others, and we ask our users to do the same. NI software is protected by copyright and other intellectual property laws. Where NI software may be used to reproduce software or other materials belonging to others, you may use NI software only to reproduce materials that you may reproduce in accordance with the terms of any applicable license or other legal restriction.

Trademarks

National Instruments, NI, ni.com, and LabVIEW are trademarks of National Instruments Corporation. Refer to the Terms of Use section on

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is the registered trademark of Apple Computer, Inc. Other product and company names mentioned herein are trademarks or trade names

FireWire of their respective companies.

Members of the National Instruments Alliance Partner Program are business entities independent from National Instruments and have no agency, partnership, or joint-venture relationship with National Instruments.

Patents

For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txt file on your CD, or ni.com/patents.

WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS

(1) NATIONAL INSTRUMENTS PRODUCTS ARE NOT DESIGNED WITH COMPONENTS AND TESTING FOR A LEVEL OF RELIABILITY SUITABLE FOR USE IN OR IN CONNECTION WITH SURGICAL IMPLANTS OR AS CRITICAL COMPONENTS IN ANY LIFE SUPPORT SYSTEMS WHOSE FAILURE TO PERFORM CAN REASONABLY BE EXPECTED TO CAUSE SIGNIFICANT INJURY TO A HUMAN.

(2) IN ANY APPLICATION, INCLUDING THE ABOVE, RELIABILITY OF OPERATION OF THE SOFTWARE PRODUCTS CAN BE IMPAIRED BY ADVERSE FACTORS, INCLUDING BUT NOT LIMITED TO FLUCTUATIONS IN ELECTRICAL POWER SUPPLY, COMPUTER HARDWARE MALFUNCTIONS, COMPUTER OPERATING SYSTEM SOFTWARE FITNESS, FITNESS OF COMPILERS AND DEVELOPMENT SOFTWARE USED TO DEVELOP AN APPLICATION, INSTALLATION ERRORS, SOFTWARE AND HARDWARE COMPATIBILITY PROBLEMS, MALFUNCTIONS OR FAILURES OF ELECTRONIC MONITORING OR CONTROL DEVICES, TRANSIENT FAILURES OF ELECTRONIC SYSTEMS (HARDWARE AND/OR SOFTWARE), UNANTICIPATED USES OR MISUSES, OR ERRORS ON THE PART OF THE USER OR APPLICATIONS DESIGNER (ADVERSE FACTORS SUCH AS THESE ARE HEREAFTER COLLECTIVELY TERMED “SYSTEM FAILURES”). ANY APPLICATION WHERE A SYSTEM FAILURE WOULD CREATE A RISK OF HARM TO PROPERTY OR PERSONS (INCLUDING THE RISK OF BODILY INJURY AND DEATH) SHOULD NOT BE RELIANT SOLELY UPON ONE FORM OF ELECTRONIC SYSTEM DUE TO THE RISK OF SYSTEM FAILURE. TO AVOID DAMAGE, INJURY, OR DEATH, THE USER OR APPLICATION DESIGNER MUST TAKE REASONABLY PRUDENT STEPS TO PROTECT AGAINST SYSTEM FAILURES, INCLUDING BUT NOT LIMITED TO BACK-UP OR SHUT DOWN MECHANISMS. BECAUSE EACH END-USER SYSTEM IS CUSTOMIZED AND DIFFERS FROM NATIONAL INSTRUMENTS’ TESTING PLATFORMS AND BECAUSE A USER OR APPLICATION DESIGNER MAY USE NATIONAL INSTRUMENTS PRODUCTS IN COMBINATION WITH OTHER PRODUCTS IN A MANNER NOT EVALUATED OR CONTEMPLATED BY NATIONAL INSTRUMENTS, THE USER OR APPLICATION DESIGNER IS ULTIMATELY RESPONSIBLE FOR VERIFYING AND VALIDATING THE SUITABILITY OF NATIONAL INSTRUMENTS PRODUCTS WHENEVER NATIONAL INSTRUMENTS PRODUCTS ARE INCORPORATED IN A SYSTEM OR APPLICATION, INCLUDING, WITHOUT LIMITATION, THE APPROPRIATE DESIGN, PROCESS AND SAFETY LEVEL OF SUCH SYSTEM OR APPLICATION.

Page 4

Compliance

Compliance with FCC/Canada Radio Frequency Interference Regulations

Determining FCC Class

The Federal Communications Commission (FCC) has rules to protect wireless communications from interference. The FCC places digital electronics into two classes. These classes are known as Class A (for use in industrial-commercial locations only) or Class B (for use in residential or commercial locations). All National Instruments (NI) products are FCC Class A products.

Depending on where it is operated, this Class A product could be subject to restrictions in the FCC rules. (In Canada, the Department of Communications (DOC), of Industry Canada, regulates wireless interference in much the same way.) Digital electronics emit weak signals during normal operation that can affect radio, television, or other wireless products.

All Class A products display a simple warning statement of one paragraph in length regarding interference and undesired operation. The FCC rules have restrictions regarding the locations where FCC Class A products can be operated.

Consult the FCC Web site at

FCC/DOC Warnings

This equipment generates and uses radio frequency energy and, if not installed and used in strict accordance with the instructions in this manual and the CE marking Declaration of Conformity*, may cause interference to radio and television reception. Classification requirements are the same for the Federal Communications Commission (FCC) and the Canadian Department of Communications (DOC).

Changes or modifications not expressly approved by NI could void the user’s authority to operate the equipment under the FCC Rules.

Class A

Federal Communications Commission

This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the instruction manual, may cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful interference in which case the user is required to correct the interference at their own expense.

www.fcc.gov for more information.

Canadian Department of Communications

This Class A digital apparatus meets all requirements of the Canadian Interference-Causing Equipment Regulations. Cet appareil numérique de la classe A respecte toutes les exigences du Règlement sur le matériel brouilleur du Canada.

Compliance with EU Directives

Users in the European Union (EU) should refer to the Declaration of Conformity (DoC) for information* pertaining to the CE marking. Refer to the Declaration of Conformity (DoC) for this product for any additional regulatory compliance information. To obtain the DoC for this product, visit and click the appropriate link in the Certification column.

* The CE marking Declaration of Conformity contains important supplementary information and instructions for the user or

installer.

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

Page 5

About This Manual

Conventions ...................................................................................................................xv

Related Documentation..................................................................................................xvi

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

Applying the Signal Label to USB-622x/625x Screw Terminal Devices......................1-2

USB Cable Strain Relief ................................................................................................1-3

Chapter 2 DAQ System Overview

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

DAQ-STC2 and DAQ-6202 ............................................................................2-2

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

Signal Conditioning .......................................................................................................2-3

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

Signal Conditioning Options ...........................................................................2-4

SCXI..................................................................................................2-4

SCC ...................................................................................................2-5

5B Series ...........................................................................................2-5

Cables and Accessories..................................................................................................2-6

Custom Cabling ...............................................................................................2-6

Programming Devices in Software ................................................................................2-7

Chapter 3 Connector and LED Information

I/O Connector Signal Descriptions ................................................................................3-2

M Series and E Series Pinout Comparison ....................................................................3-5

+5 V Power Source ........................................................................................................3-7

USB Chassis Ground .....................................................................................................3-7

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Contents

Disk Drive Power Connector......................................................................................... 3-8

USB Device Fuse Replacement..................................................................................... 3-9

RTSI Connector Pinout ................................................................................................. 3-12

LED Patterns ................................................................................................................. 3-13

Chapter 4 Analog Input

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

Analog Input Lowpass Filter......................................................................................... 4-4

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

Multichannel Scanning Considerations ......................................................................... 4-7

Analog Input Data Acquisition Methods....................................................................... 4-11

Analog Input Triggering................................................................................................ 4-12

Connecting Analog Input Signals.................................................................................. 4-13

Connecting Floating Signal Sources ............................................................................. 4-15

When to Use the Disk Drive Power Connector ..............................................3-8

Disk Drive Power Connector Installation ....................................................... 3-8

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

Use Low Impedance Sources.......................................................................... 4-8

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

Carefully Choose the Channel Scanning Order ..............................................4-9

Avoid Switching from a Large to a Small Input Range ................... 4-9

Insert Grounded Channel between Signal Channels ........................ 4-9

Minimize Voltage Step between Adjacent Channels ....................... 4-10

Avoid Scanning Faster Than Necessary ......................................................... 4-10

Example 1 ......................................................................................... 4-10

Example 2 ......................................................................................... 4-10

Software-Timed Acquisitions ......................................................................... 4-11

Hardware-Timed Acquisitions........................................................................ 4-11

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

Non-Buffered.................................................................................... 4-12

What Are Floating Signal Sources? ................................................................ 4-15

When to Use Differential Connections with Floating Signal Sources............ 4-15

When to Use Non-Referenced Single-Ended (NRSE) Connections

with Floating Signal Sources ....................................................................... 4-15

When to Use Referenced Single-Ended (RSE) Connections

with Floating Signal Sources ....................................................................... 4-16

Using Differential Connections for Floating Signal Sources.......................... 4-16

Using Non-Referenced Single-Ended (NRSE) Connections

for Floating Signal Sources.......................................................................... 4-19

Using Referenced Single-Ended (RSE) Connections for Floating

Signal Sources.............................................................................................. 4-20

M Series User Manual vi ni.com

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Contents

Connecting Ground-Referenced Signal Sources ...........................................................4-21

What Are Ground-Referenced Signal Sources? ..............................................4-21

When to Use Differential Connections with Ground-Referenced

Signal Sources ..............................................................................................4-21

When to Use Non-Referenced Single-Ended (NRSE) Connections

with Ground-Referenced Signal Sources .....................................................4-22

When to Use Referenced Single-Ended (RSE) Connections with

Ground-Referenced Signal Sources..............................................................4-22

Using Differential Connections for Ground-Referenced Signal Sources........4-23

Using Non-Referenced Single-Ended (NRSE) Connections

for Ground-Referenced Signal Sources ........................................................4-24

Field Wiring Considerations..........................................................................................4-25

Analog Input Timing Signals.........................................................................................4-25

AI Sample Clock Signal ..................................................................................4-28

Using an Internal Source...................................................................4-29

Using an External Source..................................................................4-29

Routing AI Sample Clock Signal to an Output Terminal.................4-29

Other Timing Requirements..............................................................4-29

AI Sample Clock Timebase Signal..................................................................4-30

AI Convert Clock Signal .................................................................................4-31

Using an Internal Source...................................................................4-32

Using an External Source..................................................................4-32

Routing AI Convert Clock Signal to an Output Terminal ................4-32

Using a Delay from Sample Clock to Convert Clock.......................4-32

Other Timing Requirements..............................................................4-33

AI Convert Clock Timebase Signal.................................................................4-35

AI Hold Complete Event Signal......................................................................4-36

AI Start Trigger Signal ....................................................................................4-36

Using a Digital Source ......................................................................4-36

Using an Analog Source ...................................................................4-37

Routing AI Start Trigger to an Output Terminal ..............................4-37

AI Reference Trigger Signal ...........................................................................4-37

Using a Digital Source ......................................................................4-38

Using an Analog Source ...................................................................4-38

Routing AI Reference Trigger Signal to an Output Terminal ..........4-38

AI Pause Trigger Signal ..................................................................................4-39

Using a Digital Source ......................................................................4-39

Using an Analog Source ...................................................................4-39

Routing AI Pause Trigger Signal to an Output Terminal .................4-39

Getting Started with AI Applications in Software.........................................................4-40

Page 8

Contents

Chapter 5 Analog Output

AO Offset and AO Reference Selection........................................................................ 5-2

Minimizing Glitches on the Output Signal.................................................................... 5-4

Analog Output Data Generation Methods ..................................................................... 5-4

Software-Timed Generations .......................................................................... 5-4

Hardware-Timed Generations......................................................................... 5-4

Analog Output Triggering .............................................................................................5-6

Connecting Analog Output Signals ............................................................................... 5-6

Analog Output Timing Signals...................................................................................... 5-7

AO Start Trigger Signal .................................................................................. 5-7

AO Pause Trigger Signal ................................................................................ 5-8

AO Sample Clock Signal ................................................................................ 5-10

AO Sample Clock Timebase Signal................................................................ 5-11

Getting Started with AO Applications in Software....................................................... 5-12

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

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

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

Using an Analog Source ................................................................... 5-8

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

Using a Digital Source...................................................................... 5-9

Using an Analog Source ...................................................................5-10

Routing AO Pause Trigger Signal to an Output Terminal ............... 5-10

Using an Internal Source .................................................................. 5-10

Using an External Source ................................................................. 5-10

Routing AO Sample Clock Signal to an Output Terminal ............... 5-10

Other Timing Requirements ............................................................. 5-11

Chapter 6 Digital I/O

Static DIO......................................................................................................................6-2

Digital Waveform Triggering........................................................................................ 6-3

Digital Waveform Acquisition ...................................................................................... 6-3

DI Sample Clock Signal.................................................................................. 6-4

Using an Internal Source .................................................................. 6-4

Using an External Source ................................................................. 6-4

Routing DI Sample Clock to an Output Terminal............................ 6-5

Digital Waveform Generation ....................................................................................... 6-5

DO Sample Clock Signal ................................................................................ 6-5

Using an Internal Source .................................................................. 6-6

Using an External Source ................................................................. 6-6

Routing DO Sample Clock to an Output Terminal .......................... 6-6

M Series User Manual viii ni.com

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I/O Protection.................................................................................................................6-7

Programmable Power-Up States....................................................................................6-7

DI Change Detection .....................................................................................................6-8

Connecting Digital I/O Signals......................................................................................6-9

Getting Started with DIO Applications in Software......................................................6-10

Chapter 7 Counters

Counter Input Applications............................................................................................7-2

Counter Output Applications .........................................................................................7-19

Contents

Applications.....................................................................................................6-9

Counting Edges ...............................................................................................7-2

Single Point (On-Demand) Edge Counting ......................................7-2

Buffered (Sample Clock) Edge Counting .........................................7-3

Controlling the Direction of Counting ..............................................7-4

Pulse-Width Measurement ..............................................................................7-4

Single Pulse-Width Measurement.....................................................7-4

Buffered Pulse-Width Measurement.................................................7-5

Period Measurement........................................................................................7-6

Single Period Measurement ..............................................................7-6

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

Semi-Period Measurement ..............................................................................7-8

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

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

Frequency Measurement .................................................................................7-9

Method 1—Measure Low Frequency with One Counter..................7-9

Method 1b—Measure Low Frequency with One Counter

(Averaged)......................................................................................7-10

Method 2—Measure High Frequency with Two Counters............... 7-11

Method 3—Measure Large Range of Frequencies

Using Two Counters ......................................................................7-12

Choosing a Method for Measuring Frequency .................................7-13

Position Measurement .....................................................................................7-14

Measurements Using Quadrature Encoders......................................7-14

Measurements Using Two Pulse Encoders.......................................7-17

Two-Signal Edge-Separation Measurement....................................................7-17

Single Two-Signal Edge-Separation Measurement ..........................7-18

Buffered Two-Signal Edge-Separation Measurement ......................7-18

Simple Pulse Generation .................................................................................7-19

Single Pulse Generation ....................................................................7-19

Single Pulse Generation with Start Trigger ......................................7-20

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

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Contents

Pulse Train Generation.................................................................................... 7-21

Continuous Pulse Train Generation.................................................. 7-21

Frequency Generation ..................................................................................... 7-22

Using the Frequency Generator ........................................................ 7-22

Frequency Division ......................................................................................... 7-24

Pulse Generation for ETS ............................................................................... 7-24

Counter Timing Signals................................................................................................. 7-25

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

Routing a Signal to Counter n Source .............................................. 7-26

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

Counter n Gate Signal.....................................................................................7-27

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

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

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 ...................................... 7-28

Routing Signals to A, B, and Z Counter Inputs................................ 7-28

Routing Counter n Z Signal to an Output Terminal ......................... 7-28

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

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

Routing Signals to Counter n HW Arm Input.................................. 7-29

Counter n Internal Output and Counter n TC Signals..................................... 7-29

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

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

Routing Frequency Output to a Terminal......................................... 7-30

Default Counter/Timer Pinouts ..................................................................................... 7-30

Counter Triggering ........................................................................................................ 7-31

Arm Start Trigger............................................................................................ 7-31

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...................... 7-36

When To Use Duplicate Count Prevention ...................................... 7-37

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

M Series User Manual x ni.com

Page 11

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

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

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

External Source Mode.......................................................................7-39

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 I/Os ...................................................................8-3

Connecting PFI Input Signals ........................................................................................8-4

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

I/O Protection.................................................................................................................8-6

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

Chapter 9 Digital Routing and Clock Generation

Clock Routing ................................................................................................................9-1

80 MHz Timebase ...........................................................................................9-2

20 MHz Timebase ...........................................................................................9-2

100 kHz Timebase...........................................................................................9-2

External Reference Clock................................................................................9-2

10 MHz Reference Clock ................................................................................9-3

Synchronizing Multiple Devices ...................................................................................9-3

Real-Time System Integration (RTSI)...........................................................................9-4

RTSI Connector Pinout ...................................................................................9-4

Using RTSI as Outputs....................................................................................9-6

Using RTSI Terminals as Timing Input Signals .............................................9-6

RTSI Filters .....................................................................................................9-7

PXI Clock and Trigger Signals......................................................................................9-8

PXI_CLK10.....................................................................................................9-8

PXI Triggers ....................................................................................................9-8

PXI_STAR Trigger .........................................................................................9-9

PXI_STAR Filters ...........................................................................................9-9

Contents

Chapter 10 Bus Interface

DMA Controllers and USB Signal Stream ....................................................................10-1

PXI Considerations ........................................................................................................10-2

PXI Clock and Trigger Signals........................................................................10-2

PXI and PXI Express.......................................................................................10-2

Using PXI with CompactPCI ..........................................................................10-3

Page 12

Contents

Data Transfer Methods .................................................................................................. 10-4

Changing Data Transfer Methods ................................................................... 10-5

Chapter 11 Triggering

Triggering with a Digital Source................................................................................... 11-1

Triggering with an Analog Source ................................................................................ 11-2

APFI <0..1> Terminals ................................................................................... 11-2

Analog Input Channels.................................................................................... 11-3

Analog Trigger Actions ....................................................................11-3

Routing Analog Comparison Event to an Output Terminal ........................... 11-3

Analog Trigger Types.................................................................................................... 11-3

Analog Edge Triggering.................................................................................. 11-4

Analog Edge Triggering with Hysteresis........................................................ 11-4

Analog Edge Trigger with Hysteresis (Rising Slope) ......................11-5

Analog Edge Trigger with Hysteresis (Falling Slope) ..................... 11-5

Analog Window Triggering ............................................................................ 11-6

Analog Trigger Accuracy ..............................................................................................11-7

Appendix A Device-Specific Information

NI 6220..........................................................................................................................A-2

NI 6221..........................................................................................................................A-7

NI 6224..........................................................................................................................A-24

NI 6225..........................................................................................................................A-30

NI 6229..........................................................................................................................A-45

NI 6250..........................................................................................................................A-61

NI 6251..........................................................................................................................A-66

NI 6254..........................................................................................................................A-86

NI 6255..........................................................................................................................A-92

NI 6259.......................................................................................................................... A-107

NI 6280.......................................................................................................................... A-129

NI 6281.......................................................................................................................... A-134

NI 6284.......................................................................................................................... A-139

NI 6289.......................................................................................................................... A-145

Appendix B Timing Diagrams

Appendix C Troubleshooting

M Series User Manual xii ni.com

Page 13

Appendix D Upgrading from E Series to M Series

Appendix E Technical Support and Professional Services

Glossary

Index

Device Pinouts

Figure A-1. PCI/PXI-6220 Pinout ............................................................................A-3

Figure A-2. PCI/PXI-6221 (68-Pin) Pinout ..............................................................A-8

Figure A-3. PCI-6221 (37-Pin) Pinout......................................................................A-12

Figure A-4. USB-6221 Screw Terminal Pinout........................................................A-15

Figure A-5. USB-6221 BNC Top Panel and Pinout .................................................A-18

Figure A-13. PCI/PXI-6224 Pinout ............................................................................A-25

Figure A-14. PCI/PXI-6225 Pinout ............................................................................A-31

Figure A-15. USB-6225 Screw Terminal Pinout........................................................A-37

Figure A-16. USB-6225 Mass Termination Pinout ....................................................A-40

Figure A-17. PCI/PXI-6229 Pinout ............................................................................A-46

Figure A-18. USB-6229 Screw Terminal Pinout........................................................A-52

Figure A-19. USB-6229 BNC Top Panel and Pinout .................................................A-55

Figure A-27. PCI/PXI-6250 Pinout ............................................................................A-62

Figure A-28. NI PCI/PCIe/PXI/PXIe-6251 Pinout.....................................................A-67

Figure A-29. USB-6251 Screw Terminal Pinout........................................................A-71

Figure A-30. USB-6251 BNC Top Panel and Pinout .................................................A-74

Figure A-39. USB-6251 Mass Termination Pinout ....................................................A-82

Figure A-40. PCI/PXI-6254 Pinout ............................................................................A-87

Figure A-41. PCI/PXI-6255 Pinout ............................................................................A-93

Figure A-42. USB-6255 Screw Terminal Pinout........................................................A-99

Figure A-43. USB-6255 Mass Termination Pinout ....................................................A-102

Figure A-44. NI PCI/PCIe/PXI/PXIe-6259 Pinout.....................................................A-108

Figure A-45. USB-6259 Screw Terminal Pinout........................................................A-114

Figure A-46. USB-6259 BNC Top Panel and Pinout .................................................A-117

Figure A-55. USB-6259 Mass Termination Pinout ....................................................A-125

Figure A-56. PCI/PXI-6280 Pinout ............................................................................A-130

Figure A-57. PCI/PXI-6281 Pinout ............................................................................A-135

Figure A-58. PCI/PXI-6284 Pinout ............................................................................A-140

Figure A-59. PCI/PXI-6289 Pinout ............................................................................A-146

Contents

Page 14

About This Manual

The M Series User Manual contains information about using the National Instruments M Series data acquisition (DAQ) devices with NI-DAQ 8.6 and later. M Series devices feature up to 80 analog input (AI) channels, and up to four analog output (AO) channels, up to 48 lines of digital input/output (DIO), and two counters.

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 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.

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,

Page 15

About This Manual

programs, subprograms, subroutines, device names, functions, operations, variables, filenames, and extensions.

Platform Text in this font denotes a specific platform and indicates that the text

following it applies only to that platform.

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.

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 about how to install PCI, PCI Express, PXI, PXI Express, and USB devices, as well as accessories and cables.

Device Pinouts

Refer to Appendix A, Device-Specific Information, for M Series device pinouts.

Page 22

Chapter 1 Getting Started

Device Specifications

Refer to the specifications for your device, the NI 622x Specifications, the NI 625x Specifications, or the NI 628x Specifications, available on the

NI-DAQ Device Document Browser or detailed information about M Series devices.

ni.com/manuals, for more

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

Applying the Signal Label to USB-622x/625x Screw Terminal Devices

(USB-622x/625x Screw Terminal Devices) The supplied signal label can be

adhered to the inside cover of the USB-622x/625x Screw Terminal device with supplied velcro strips as shown in Figure 1-1.

Figure 1-1. Applying the USB-622x/625x Screw Terminal Signal Label

M Series User Manual 1-2 ni.com

Page 23

USB Cable Strain Relief

(USB-622x/625x Screw Terminal and USB-622x/625x Mass Termination Devices)

Use the supplied strain relief hardware to provide strain relief for your USB cable. Adhere the cable tie mount to the rear panel of the USB-622x/625x Screw Terminal or USB-622x/625x Mass Termination device, as shown in Figure 1-2. Thread a zip tie through the cable tie mount and tighten around the USB cable.

Chapter 1 Getting Started

Figure 1-2. USB Cable Strain Relief on USB-622x/625x Screw Terminal and

USB-622x/625x Mass Termination Devices

Page 24

Chapter 1 Getting Started

(USB-622x/625x BNC Devices) Thread a zip tie through two of the strain relief

holes on the end cap to provide strain relief for your USB cable as shown in Figure 1-3. The strain relief holes can also be used as cable management for signal wires to/from the screw terminals and BNC connectors.

Figure 1-3. USB Cable Strain Relief on USB-622x/625x BNC Devices

M Series User Manual 1-4 ni.com

Page 25

DAQ System Overview

Figure 2-1 shows a typical DAQ system, which includes sensors, transducers, signal conditioning devices, 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.

Signal

Sensors and

Transducers

Conditioning

DAQ Hardware

Cables and

Accessories

Figure 2-1. Components of a Typical DAQ System

DAQ hardware digitizes signals, performs D/A conversions to generate analog output signals, and measures and controls digital I/O signals. Figure 2-2 features components common to all M Series devices.

DAQ

Hardware

DAQ

Software

Personal Compute

PXI/PXI Express

Chassis

Page 26

Chapter 2 DAQ System Overview

Analog Input

Analog Output

Digital I/O

I/O Connector

Counters

PFI

DAQ-STC2 and DAQ-6202

The DAQ-STC2 and DAQ-6202 implement a high-performance digital engine for M Series 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, AO, DI, and DO 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

• Digital waveform acquisition and generation

• Static DIO signals

• True 5 V high current drive DO

• DI change detection

• PLL for clock synchronization

• Seamless interface to signal conditioning accessories

• PCI/PXI interface

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

Digital

Routing

and Clock

Generation

RTSI

Figure 2-2. General M Series Block Diagram

Bus

Interface

Bus

M Series User Manual 2-2 ni.com

Page 27

Calibration Circuitry

The M Series analog inputs and outputs have calibration circuitry 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 Help in version

8.0 or later for more information about using calibration constants.

For a detailed calibration procedure for M Series devices, refer to the

B/E/M/S Series Calibration Procedure for NI-DAQmx by clicking Manual Calibration Procedures on

Signal Conditioning

Chapter 2 DAQ System Overview

ni.com/calibration.

Many sensors and transducers require signal conditioning before a measurement system can effectively and accurately acquire the signal. The front-end signal conditioning system can include functions such as signal amplification, attenuation, filtering, electrical isolation, simultaneous sampling, and multiplexing. In addition, many transducers require excitation currents or voltages, bridge completion, linearization, or high amplification for proper and accurate operation. Therefore, most computer-based measurement systems include some form of signal conditioning in addition to plug-in data acquisition DAQ devices.

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).

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

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Chapter 2 DAQ System Overview

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

For more information about sensors, refer to the following documents.

• 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 or the LabVIEW Help in version 8.0 or later.

Signal Conditioning Options

SCXI

SCXI is a front-end signal conditioning and switching system for various measurement devices, including M Series devices. An SCXI system consists of a rugged chassis that houses shielded signal conditioning modules that amplify, filter, isolate, and multiplex analog signals from thermocouples or other transducers. SCXI is designed for large measurement systems or systems requiring high-speed acquisition.

ni.com/sensors.

System features include the following.

• Modular architecture—Choose your measurement technology

• Expandability—Expand your system to 3,072 channels

• Integration—Combine analog input, analog output, digital I/O, and switching into a single, unified platform

• High bandwidth—Acquire signals at high rates

• Connectivity—Select from SCXI modules with thermocouple connectors or terminal blocks

Note SCXI is not supported on PCI-6221 (37-pin) or all variants of USB-622x/625x

devices.

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Chapter 2 DAQ System Overview

SCC

SCC is a front-end signal conditioning system for M Series plug-in data acquisition devices. An SCC system consists of a shielded carrier that holds up to 20 single- or dual-channel SCC modules for conditioning thermocouples and other transducers. SCC is designed for small measurement systems where you need only a few channels of each signal type, or for portable applications. SCC systems also offer the most comprehensive and flexible signal connectivity options.

System features include the following.

• Modular architecture—Select your measurement technology on a

per-channel basis

• Small-channel systems—Condition up to 16 analog input and

eight digital I/O lines

• Low-profile/portable—Integrates well with other laptop computer

measurement technologies

• High bandwidth—Acquire signals at rates up to 1.25 MHz

• Connectivity—Incorporates panelette technology to offer custom

connectivity to thermocouple, BNC, LEMO MIL-Spec connectors

™

(B Series), and

Note PCI Express users should consider the power limits on certain SCC modules without

an external power supply. Refer to the specifications for your device, and the Disk Drive

Power Connector section of Chapter 3, Connector and LED Information, for information

about power limits and increasing the current the device can supply on the +5 V terminal.

Note SCC is not supported on the PCI-6221 (37-pin), USB-622x/625x Screw Terminal, or

USB-622x/625x BNC devices.

5B Series

5B is a front-end signal conditioning system for plug-in data acquisition devices. A 5B system consists of eight or 16 single-channel modules that plug into a backplane for conditioning thermocouples and other analog signals. National Instruments offers a complete line of 5B modules, carriers, backplanes, and accessories.

Note 5B is not supported on the PCI-6221 (37-pin), USB-622x/625x Screw Terminal, or

USB-622x/625x BNC devices.

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Chapter 2 DAQ System Overview

Note For more information about SCXI, SCC, and 5B Series products, refer to

ni.com/signalconditioning.

Cables and Accessories

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

• Shielded cables and cable assemblies, and unshielded ribbon cables and cable assemblies

• Screw terminal connector blocks, shielded and unshielded

• RTSI bus cables

• SCXI modules and accessories for isolating, amplifying, exciting, and multiplexing signals; with SCXI you can condition and acquire up to 3,072 channels

• Low-channel-count signal conditioning modules, devices, and accessories, including conditioning for strain gauges and RTDs, simultaneous sample and hold circuitry, and relays

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 about 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, 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.

For more information about the connectors used for DAQ devices, refer to the KnowledgeBase document, Specifications and Manufacturers for

ni.com.

M Series User Manual 2-6 ni.com

Page 31

Board Mating Connectors, by going to ni.com/info and entering the info code

rdspmb.

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 7.3 and later 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.

Chapter 2 DAQ System Overview

To locate LabVIEW and LabWindows/CVI examples, open the National Instruments Example Finder. In LabVIEW and LabWindows/CVI, select Help»Find Examples.

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

For additional examples, refer to

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

reference point for single-ended AI measurements in RSE mode and the bias current return point for DIFF measurements. All three ground references—AI GND, AO GND, and D GND—are connected on the device.

AI <0..79> Va ri e s Input Analog Input Channels 0 to 79—For single-ended

measurements, each signal is an analog input voltage channel. In RSE mode, AI GND is the reference for these signals. In NRSE mode, the reference for each AI <0..15> signal is AI SENSE; the reference for each AI <16..63> and AI <64..79> signal is AI SENSE 2.

For differential measurements, AI 0 and AI 8 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 Connecting Ground-Referenced Signal

Sources section of Chapter 4, Analog Input.

AI SENSE, AI SENSE 2

M Series User Manual 3-2 ni.com

— Input Analog Input Sense—In NRSE mode, the reference for

each AI <0..15> signal is AI SENSE; the reference for each AI <16..63> and AI <64..79> signal is AI SENSE 2. Also refer to the Connecting

Ground-Referenced Signal Sources section of Chapter 4, Analog Input

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Chapter 3 Connector and LED Information

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

Signal Name Reference Direction Description

AO <0..3> AO GND Output Analog Output Channels 0 to 3—These terminals

supply the voltage output of AO channels 0 to 3.

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

AO <0..3>. All three ground references—AI GND, AO GND, and D GND—are connected on the device.

D GND — — Digital Ground—D GND supplies the reference

for P0.<0..31>, PFI <0..15>/P1/P2, and +5 V. All three ground references—AI GND, AO GND, and D GND—are connected on the device.

P0.<0..31> D GND Input or

Output

APFI <0..1> AO GND/AI GND Input Analog Programmable Function Interface Channels

+5 V D GND Input or

Output

PFI <0..7>/P1.<0..7> PFI <8..15>/P2.<0..7>

D GND Input or

Output

Port 0 Digital I/O Channels 0 to 31—You can individually configure each signal as an input or output.

0 to 1—Each APFI signal can be used as AO external reference inputs for AO <0..3>, AO external offset input, or as an analog trigger input. APFI <0..1> are referenced to AI GND when they are used as analog trigger inputs. APFI <0..1> are referenced to AO GND when they are used as AO external offset or reference inputs. These functions are not available on all devices. Refer to the specifications for your device.

+5 V Power Source—These terminals provide a fused +5 V power source.

Programmable Function Interface or Digital I/O Channels 0 to 7 and Channels 8 to 15—Each of these

terminals can be individually configured as a PFI terminal or a digital I/O terminal.

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

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

As a Port 1 or Port 2 digital I/O signal, you can individually configure each signal as an input or output.

USER <1..2> — — User-Defined Channels 1 and 2—On USB-62xx BNC

devices, the USER <1..2> BNC connectors allow you to use a BNC connector for a digital or timing I/O signal of your choice. The USER <1..2> BNC connectors are internally routed to the USER <1..2> screw terminals.

Page 35

Chapter 3 Connector and LED Information

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

Signal Name Reference Direction Description

CHS GND

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

USB-62xx Screw Terminal users can connect the shield of a shielded cable to the chassis ground lug for a ground

connection. The chassis ground lug is not available on all device versions.

— — Chassis Ground*—This terminal connects to the

USB-62xx BNC device metal enclosure. You can connect your cable’s shield wire to CHS GND for a ground connection.

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Page 36

Chapter 3 Connector and LED Information

M Series and E Series Pinout Comparison

The pinout of Connector 0 of 68-pin M Series devices is similar to the pinout of 68-pin E Series devices. On M Series devices, some terminals have enhanced functionality or other slight differences. Table 3-2 compares the two pinouts.

Table 3-2. M Series and E Series Device Pinout Comparison

ESeries

Terminal

1 FREQ OUT PFI 14/P2.6 E Series devices drive each of these terminals with one

2 CTR 0 OUT

40 CTR 1 OUT

45 EXT STROBE PFI 10/P2.2

46 AI HOLD COMP

3 PFI 9/CTR 0 GATE

5 PFI 6/AO START

6 PFI 5/AO SAMP CLK

10 PFI 1/AI REF TRIG

37 PFI 8/CTR 0 SRC

38 PFI 7/AI SAMP CLK

41 PFI 4/CTR 1 GATE

42 PFI 3/CTR 1 SRC

43 PFI 2/AI CONV CLK

Te rm in a l

(GPCTR0_OUT)

(GPCTR1_OUT)

(SCANCLK)

(GPCTR0_GATE)

TRIG (WFTRIG)

(UPDATE)

(TRIG2)

(GPCTR0_SOURCE)

(STARTSCAN)

(GPCTR1_GATE)

(GPCTR1_SOURCE)

(CONVERT)

M Series

Terminal

PFI 12/P2.4

PFI 13/P2.5

PFI 11/P2.3

PFI 9/P2.1 As a PFI input, the functionality of E Series and

PFI 6/P1.6

PFI 5/P1.5

PFI 1/P1.1

PFI 8/P2.0

PFI 7/P1.7

PFI 4/P1.4

PFI 3/P1.3

PFI 2/P1.2

particular internal timing signal.

M Series devices can drive each terminal with the same signal as on E Series devices. On M Series devices, you also can route many other internal timing signals to each terminal.

On M Series devices, you also can use these terminals as additional PFI inputs to drive internal timing signals.

On M Series devices, you also can use these terminals as digital I/O signals.

Also refer to Chapter 8, PFI.

M Series devices is similar for these terminals.

E Series devices can drive each of these terminals with one particular internal timing signal.

M Series devices can drive each terminal with the same signal as on E Series devices. On M Series devices, you also can route many other internal timing signals to each terminal.

On M Series devices, you also can use these terminals as digital I/O signals.

Also refer to Chapter 8, PFI.

Differences

Page 37

Chapter 3 Connector and LED Information

Table 3-2. M Series and E Series Device Pinout Comparison (Continued)

ESeries

Terminal

11 PFI 0/AI START TRIG

16 P0.6 P0.6 On both E Series and M Series devices, these terminals

48 P0.7 P0.7

20 AO E XT REF

39 D GND PFI 15/P2.7 On E Series devices, this is one of the D GND terminals.

In NI-DAQmx, National Instruments has revised terminal names so they are easier to understand and more consistent among National Instruments hardware and software products. This column shows the NI-DAQmx terminal names (Traditional NI-DAQ (Legacy) terminal names are shown in parentheses).

Te rm in a l

(TRIG1)

(EXTREF)

M Series Terminal

PFI 0/P1.0 On E Series devices, as an input, this terminal can either

be a PFI input or the analog trigger input.

On M Series devices, as an input, this terminal can only be a PFI input. Analog triggers use the APFI <0..1> terminals.

E Series devices can drive this terminal with the AI START TRIG signal.

M Series devices, as an output, can drive this terminal with the AI START TRIG signal. You also can route many other internal timing signals to this terminal.

On M Series devices, you also can use this terminal as the digital I/O signal, P1.0.

Also refer to Chapter 8, PFI.

are digital I/O signals. You can individually configure each signal as an input or output.

On E Series devices, P0.6 and P0.7 also can control the up/down signal of general-purpose Counters 0 and 1, respectively.

On M Series devices, you have to use one of the PFI terminals to control the up/down signal of general-purpose Counters 0 and 1.

APFI 0 On E Series devices, this terminal is the external

reference input for the AO circuitry.

On M Series devices, this terminal can be used as the external reference input for the AO circuitry, the external offset for the AO circuitry, or the analog trigger input. These functions are not available on all devices. Refer to the specifications for your device.

Note that this terminal is a no connect on some E Series and M Series devices.

On M Series devices, this is the PFI 15/P2.7 terminal.

Differences

Refer to Appendix D, Upgrading from E Series to M Series, for more information about the differences between these two device families.

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Page 38

+5 V Power Source

The +5 V terminals on the I/O connector supply +5 V referenced to D GND. Use these terminals to power external circuitry. A self-resetting fuse protects the supply from overcurrent conditions. The fuse resets automatically within a few seconds after the overcurrent condition is removed.

Caution Never connect the +5 V power terminals to analog or digital ground or to any

other voltage source on the M Series device or any other device. Doing so can damage the device and the computer. NI is not liable for damage resulting from such a connection.

The power rating on most devices is +4.75 to +5.25 VDC at 1 A.

Refer to the specifications document for your device to obtain the device power rating.

Note (NI PCIe-625x Devices Only) M Series PCI Express devices supply less than 1 A of

+5 V power unless you use the disk drive power connector.

Note The NI 6221 (37-pin) device does not have a +5 V terminal.

Chapter 3 Connector and LED Information

USB Chassis Ground

For EMC compliance, the chassis of the USB M Series device must be connected to earth ground through the chassis ground.

Page 39

Chapter 3 Connector and LED Information

Disk Drive Power Connector

(NI PCIe-625x Devices Only) The disk drive power connector is a four-pin

hard drive connector on PCI Express devices that, when connected, increases the current the device can supply on the +5 V terminal.

When to Use the Disk Drive Power Connector

M Series PCI Express devices without the disk drive power connector installed perform identically to other M Series devices for most applications and with most accessories. For most applications, it is not necessary to install the disk drive power connector.

However, you should install the disk drive power connector in either of the following situations:

• You need more power than listed in the device specifications

• You are using an SCC accessory without an external power supply, such as the SC-2345

Refer to the specifications document for your device for more information about PCI Express power requirements and power limits.

Disk Drive Power Connector Installation

Before installing the disk drive power connector, you must install and set up the M Series PCI Express device as described in the DAQ Getting Started Guide. Complete the following steps to install the disk drive power connector.

1. Power off and unplug the computer.

2. Remove the computer cover.

3. Attach the PC disk drive power connector to the disk drive power connector on the device, as shown in Figure 3-1.

Note The power available on the disk drive power connectors in a computer can vary. For

example, consider using a disk drive power connector that is not in the same power chain as the hard drive.

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Chapter 3 Connector and LED Information

1 Device Disk Drive Power Connector 2 PC Disk Drive Power Connector

Figure 3-1. Connecting to the Disk Drive Power Connector

4. Replace the computer cover, and plug in and power on the computer.

5. Self-calibrate the PCI Express DAQ device in MAX by following the instructions in Calibrating DAQ Devices in the Measurement & Automation Explorer Help.

Note Connecting or disconnecting the disk drive power connector can affect the analog

performance of your device. To compensate for this, NI recommends that you self-calibrate after connecting or disconnecting the disk drive power connector.

USB Device Fuse Replacement

M Series USB devices have a replaceable 2A 250V (5 × 20 mm) fuse.

(USB-62xx Screw Terminal Devices) To remove the fuse from the USB-62xx

Screw Terminal, complete the following steps.

1. Power down and unplug the device.

2. Loosen the four Phillips screws that attach the back lid to the enclosure, and remove the lid.

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Chapter 3 Connector and LED Information

3. Replace the fuse while referring to Figure 3-2 for the fuse location.

Fuse

Figure 3-2. USB-62xx Screw Terminal Fuse Location

4. Replace the lid and screws.

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Chapter 3 Connector and LED Information

(USB-62xx BNC Devices) To remove the fuse from the USB-62xx BNC,

complete the following steps.

1. Power down and unplug the device.

Note Take proper ESD precautions when handling the device.

Fuse

Figure 3-3. USB-62xx BNC Fuse Location

2. Remove both end pieces by unscrewing the four sockethead cap screws with a 7/64 in. hex wrench.

Note The end pieces are attached using self-threading screws. Repeated screwing and

unscrewing of self-threading screws will produce a compromised connection.

3. With a Phillips #2 screwdriver, remove the Phillips 4-40 screw adjacent to the USB connector.

4. Remove the nut from the power connector.

5. Remove the four Phillips 4-40 screws that attach the top panel to the enclosure, and remove the panel and connector unit.

6. Replace the fuse.

7. Replace the top panel, screws, nut, and end pieces.

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Chapter 3 Connector and LED Information

(USB-62xx Mass Termination Devices) To remove th e fuse from the USB -62xx

Mass Termination, complete the following steps.

1. Power down and unplug the device.

2. Loosen the four Phillips screws that attach the lid to the enclosure, and remove the lid.

3. Replace the fuse while referring to Figure 3-4 for the fuse location.

Fuse

Figure 3-4. USB-62xx Mass Termination Fuse Location

4. Replace the lid and screws.

RTSI Connector Pinout

Refer to the RTSI Connector Pinout section of Chapter 9, Digital Routing

and Clock Generation, for information about the RTSI connector.

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Page 44

LED Patterns

Note USB-62xx BNC devices also have a POWER (+5 V) LED on the top panel. The

POWER (+5 V) LED indicates device power.

Chapter 3 Connector and LED Information

(USB-62xx Devices Only) All variants of M Series USB devices have LEDs

labeled ACTIVE and READY. The ACTIVE LED indicates activity over the bus. The READY LED indicates whether or not the device is configured. Table 3-3 shows the behavior of the LEDs.

Table 3-3. LED Patterns

POWER (+5 V)

LED

ACTIVE

LED

READY

LED

USB Device State

Off Off Off The device is not powered.

On Off Off The device is powered but not

connected to the host computer.

On Off On The device is configured, but there is

no activity over the bus.

On On On The device is configured and there is

On Blinking On

The POWER (+5 V) LED is available on USB-62xx BNC devices only.

activity over the bus.

Page 45

Analog Input

Figure 4-1 shows the analog input circuitry of M Series devices.

AI <0..n>

AI SENSE

I/O Connector

AI GND

Mux

DIFF, RSE,

or NRSE

AI Terminal

Configuration

Selection

The main blocks featured in the M Series analog input circuitry are as follows:

• I/O Connector—You can connect analog input signals to the M Series

• MUX—Each M Series device has one analog-to-digital converter

• Ground-Reference Settings—The analog input ground-reference

• Instrumentation Amplifier (NI-PGIA)—The NI programmable gain

NI-PGIA

Input Range

Selection

device through the I/O connector. The proper way to connect analog input signals depends on the analog input ground-reference settings, described in the Analog Input Ground-Reference Settings section. Also refer to Appendix A, Device-Specific Information, for device I/O connector pinouts.

(ADC). The multiplexers (MUX) route one AI channel at a time to the ADC through the NI-PGIA.

settings circuitry selects between differential, referenced single-ended, and non-referenced single-ended input modes. Each AI channel can use a different mode.

instrumentation amplifier (NI-PGIA) is a measurement and instrument class amplifier that minimizes settling times for all input ranges. The

AI Lowpass

Filter

Figure 4-1. M Series Analog Input Circuitry

ADC

AI FIFO

AI Data

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Chapter 4 Analog Input

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.

• 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 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 of one ADC code. For example, a 16-bit ADC converts analog inputs into one of 65,536 (= 2

) codes—that is, one of 65,536 possible digital values. These values are spread fairly evenly across the input range. So, for an input range of –10 V to 10 V, the voltage of each code of a 16-bit ADC is:

(10 V – (–10 V))

= 305 μV

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 formula 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 voltage resolution. Choosing a smaller input range improves the voltage resolution, but may result in the input signal going out of range.

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Chapter 4 Analog Input

For more information about setting ranges, refer to the NI-DAQmx Help or the LabVIEW Help in version 8.0 or later.

Tables 4-1, 4-2, and 4-3 show the input ranges and resolutions supported by each M Series device family.

Table 4-1. Input Ranges for NI 622x

Nominal Resolution Assuming

Input Range

5% Over Range

–10 V to 10 V 320 μV

–5 V to 5 V 160 μV

–1 V to 1 V 32 μV

–200 mV to 200 mV 6.4 μV

Table 4-2. Input Ranges for NI 625x

Nominal Resolution Assuming

Input Range

5% Over Range

–10 V to 10 V 320 μV

–5 V to 5 V 160 μV

–2 V to 2 V 64 μV

–1 V to 1 V 32 μV

–500 mV to 500 mV 16 μV

–200 mV to 200 mV 6.4 μV

–100 mV to 100 mV 3.2 μV

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Chapter 4 Analog Input

Table 4-3. Input Ranges for NI 628x

Input Range

–10 V to 10 V 80.1 μV

–5 V to 5 V 40.1 μV

–2 V to 2 V 16.0 μV

–1 V to 1 V 8.01 μV

–500 mV to 500 mV 4.01 μV

–200 mV to 200 mV 1.60 μV

–100 mV to 100 mV 0.80 μV

Analog Input Lowpass Filter

A lowpass filter attenuates signals with frequencies above the cutoff frequency while passing, with minimal attenuation, signals below the cutoff frequency. The cutoff frequency is defined as the frequency at which the output amplitude has decreased by 3 dB. Lowpass filters attenuate noise and reduce aliasing of signals beyond the Nyquist frequency. For example, if the signal of interest does not have frequency components beyond 40 kHz, then using a filter with a cutoff frequency at 40 kHz will attenuate noise beyond the cutoff that is not of interest. The cutoff frequency of the lowpass filter is also called the small signal bandwidth. The specifications document for your DAQ device lists the small signal bandwidth.

Nominal Resolution Assuming

5% Over Range

On some devices, the filter cutoff is fixed. On other devices, this filter is programmable and can be enabled for a lower frequency. For example, the NI 628x devices have a programmable filter with a cutoff frequency of 40 kHz that can be enabled. If the programmable filter is not enabled, the cutoff frequency is fixed at 750 kHz. If the cutoff is programmable, choose the lower cutoff to reduce measurement noise. However, a filter with a lower cutoff frequency increases the settling time of your device, as shown in the specifications, which reduces its maximum conversion rate. Therefore, you may have to reduce the rate of your AI Convert and AI Sample Clocks. If that reduced sample rate is too slow for your application, select the higher cutoff frequency.

Add additional filters to AI signals using external accessories, as described in the Cables and Accessories section of Chapter 2, DAQ System Overview.

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Analog Input Ground-Reference Settings

M Series devices support the analog input ground-reference settings shown in Table 4-4.

Table 4-4. Analog Input Ground-Reference Settings

AI Ground-Reference

Settings

DIFF In differential (DIFF) mode, the M Series device measures the

difference in voltage between two AI signals.

RSE In referenced single-ended (RSE) mode, the M Series device measures

the voltage of an AI signal relative to AI GND.

NRSE In non-referenced single-ended (NRSE) mode, the M Series device

measures the voltage of an AI signal relative to one of the AI SENSE or AI SENSE 2 inputs.

The AI ground-reference setting determines how you should connect your AI signals to the M Series device. Refer to the Connecting Analog Input

Signals section for more information.

Description

Chapter 4 Analog Input

Ground-reference settings are programmed on a per-channel basis. For example, you might configure the device to scan 12 channels—four differentially-configured channels and eight single-ended channels.

M Series devices implement the different analog input ground-reference settings by routing different signals to the NI-PGIA. The NI-PGIA is a differential amplifier. That is, the NI-PGIA amplifies (or attenuates) the difference in voltage between its two inputs. The NI-PGIA drives the ADC with this amplified voltage. The amount of amplification (the gain), is determined by the analog input range, as shown in Figure 4-2.

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Chapter 4 Analog Input

Instrumentation

Amplifier

in+

AI Ground-Reference

Settings

RSE AI <0..79> AI GND

NRSE AI <0..15> AI SENSE

DIFF AI <0..7> AI <8..15>

PGIA

] × Gain

in–

Vm = [V

in+

– V

Figure 4-2. NI-PGIA

Table 4-5 shows how signals are routed to the NI-PGIA.

Table 4-5. Signals Routed to the NI-PGIA

Signals Routed to the Positive

Input of the NI-PGIA (V

in+

Signals Routed to the Negative

)

Input of the NI-PGIA (V

AI <16..79> AI SENSE 2

AI <16..23> AI <24..31>

AI <32..39>, AI <48..55>,

AI <64..71>

AI <40..47>, AI <56..63>,

AI <72..79>

Measured

Voltage

–

in–

)

Notice that some M Series devices do not support the AI <16..79> signals.

For differential measurements, AI 0 and AI 8 are the positive and negative inputs of differential analog input channel 0. For a complete list of signal pairs that form differential input channels, refer to the I/O Connector Signal

Descriptions section of Chapter 3, Connector and LED Information.

Caution The maximum input voltages rating of AI signals with respect to ground (and for

differential signals with respect to each other) are listed in the specifications document for your device. Exceeding the maximum input voltage of AI signals distorts the measurement results. Exceeding the maximum input voltage rating also can damage the device and the computer. NI is not liable for any damage resulting from such signal connections.

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AI ground-reference setting is sometimes referred to as AI terminal configuration.

Configuring AI Ground-Reference Settings in Software

You can program channels on an M Series device to acquire with different ground references.

Chapter 4 Analog Input

To enable multimode scanning in LabVIEW, use

Virtual Channel.vi

each channel or group of channels configured in a different input mode. In Figure 4-3, channel 0 is configured in differential mode, and channel 1 is configured in RSE mode.

Figure 4-3. Enabling Multimode Scanning in LabVIEW

To configure the input mode of your voltage measurement using the DAQ Assistant, use the Terminal Configuration drop-down list. Refer to the DAQ Assistant Help for more information about the DAQ Assistant.

To configure the input mode of your voltage measurement using the NI-DAQmx C API, set the terminalConfig property. Refer to the NI-DAQmx C Reference Help for more information.

of the NI-DAQmx API. You must use a new VI for

Multichannel Scanning Considerations

NI-DAQmx Create

M Series devices can scan multiple channels at high rates and digitize the signals accurately. However, you should consider several issues when designing your measurement system to ensure the high accuracy of your measurements.

In multichannel scanning applications, accuracy is affected by settling time. When your M Series device switches from one AI channel to another AI channel, the device configures the NI-PGIA with the input range of the new channel. The NI-PGIA then amplifies the input signal with the gain for the new input range. Settling time refers to the time it takes the NI-PGIA to amplify the input signal to the desired accuracy before it is sampled by the

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Chapter 4 Analog Input

ADC. The specifications document for your DAQ device lists its settling time.

M Series devices are designed to have fast settling times. However, several factors can increase the settling time which decreases the accuracy of your measurements. To ensure fast settling times, you should do the following (in order of importance):

• Use Low Impedance Sources

• Use Short High-Quality Cabling

• Carefully Choose the Channel Scanning Order

• Avoid Scanning Faster Than Necessary

Use Low Impedance Sources

To ensure fast settling times, your signal sources should have an impedance of <1 kΩ. Large source impedances increase the settling time of the NI-PGIA, and so decrease the accuracy at fast scanning rates.

Settling times increase when scanning high-impedance signals due to a phenomenon called charge injection. Multiplexers contain switches, usually made of switched capacitors. When one of the channels, for example channel 0, is selected in a multiplexer, those capacitors accumulate charge. When the next channel, for example channel 1, is selected, the accumulated charge leaks backward through channel 1. If the output impedance of the source connected to channel 1 is high enough, the resulting reading of channel 1 can be partially affected by the voltage on channel 0. This effect is referred to as ghosting.

If your source impedance is high, you can decrease the scan rate to allow the NI-PGIA more time to settle. Another option is to use a voltage follower circuit external to your DAQ device to decrease the impedance seen by the DAQ device. Refer to the KnowledgeBase document, How Do I Create a Buffer to Decrease the Source Impedance of My Analog Input Signal?, by going to

ni.com/info and entering the info code rdbbis.

Use Short High-Quality Cabling

Using short high-quality cables can minimize several effects that degrade accuracy including crosstalk, transmission line effects, and noise. The capacitance of the cable also can increase the settling time.

National Instruments recommends using individually shielded, twisted-pair wires that are 2 m or less to connect AI signals to the device. Refer to the Connecting Analog Input Signals section for more information.

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Carefully Choose the Channel Scanning Order

Avoid Switching from a Large to a Small Input Range

Switching from a channel with a large input range to a channel with a small input range can greatly increase the settling time.

Suppose a 4 V signal is connected to channel 0 and a 1 mV signal is connected to channel 1. The input range for channel 0 is –10 V to 10 V and the input range of channel 1 is –200 mV to 200 mV.

When the multiplexer switches from channel 0 to channel 1, the input to the NI-PGIA switches from 4 V to 1 mV. The approximately 4 V step from 4 V to 1 mV is 1,000% of the new full-scale range. For a 16-bit device to settle within 0.0015% (15 ppm or 1 LSB) of the ±200 mV full-scale range on channel 1, the input circuitry must settle to within 0.000031% (0.31 ppm or 1/50 LSB) of the ±10 V range. Some devices can take many microseconds for the circuitry to settle this much.

To avoid this effect, you should arrange your channel scanning order so that transitions from large to small input ranges are infrequent.

In general, you do not need this extra settling time when the NI-PGIA is switching from a small input range to a larger input range.

Chapter 4 Analog Input

Insert Grounded Channel between Signal Channels

Another technique to improve settling time is to connect an input channel to ground. Then insert this channel in the scan list between two of your signal channels. The input range of the grounded channel should match the input range of the signal after the grounded channel in the scan list.

Consider again the example above where a 4 V signal is connected to channel 0 and a 1 mV signal is connected to channel 1. Suppose the input range for channel 0 is –10 V to 10 V and the input range of channel 1 is –200mV to 200mV.

You can connect channel 2 to AI GND (or you can use the internal ground signal; refer to Internal Channels in the NI-DAQmx Help). Set the input range of channel 2 to –200 mV to 200 mV to match channel 1. Then scan channels in the order: 0, 2, 1.

Inserting a grounded channel between signal channels improves settling time because the NI-PGIA adjusts to the new input range setting faster when the input is grounded.

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Chapter 4 Analog Input

Minimize Voltage Step between Adjacent Channels

When scanning between channels that have the same input range, the settling time increases with the voltage step between the channels. If you know the expected input range of your signals, you can group signals with similar expected ranges together in your scan list.

For example, suppose all channels in a system use a –5 to 5 V input range. The signals on channels 0, 2, and 4 vary between 4.3 V and 5 V. The signals on channels 1, 3, and 5 vary between –4 V and 0 V. Scanning channels in the order 0, 2, 4, 1, 3, 5 produces more accurate results than scanning channels in the order 0, 1, 2, 3, 4, 5.

Avoid Scanning Faster Than Necessary

Designing your system to scan at slower speeds gives the NI-PGIA more time to settle to a more accurate level. Here are two examples to consider.

Example 1

Averaging many AI samples can increase the accuracy of the reading by decreasing noise effects. In general, the more points you average, the more accurate the final result. However, you may choose to decrease the number of points you average and slow down the scanning rate.

Suppose you want to sample 10 channels over a period of 20 ms and average the results. You could acquire 500 points from each channel at a scan rate of 250 kS/s. Another method would be to acquire 1,000 points from each channel at a scan rate of 500 kS/s. Both methods take the same amount of time. Doubling the number of samples averaged (from 500 to 1,000) decreases the effect of noise by a factor of 1.4 (the square root of 2). However, doubling the number of samples (in this example) decreases the time the NI-PGIA has to settle from 4 µs to 2 µs. In some cases, the slower scan rate system returns more accurate results.

Example 2

If the time relationship between channels is not critical, you can sample from the same channel multiple times and scan less frequently. For example, suppose an application requires averaging 100 points from channel 0 and averaging 100 points from channel 1. You could alternate reading between channels—that is, read one point from channel 0, then one point from channel 1, and so on. You also could read all 100 points from channel 0 then read 100 points from channel 1. The second method

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switches between channels much less often and is affected much less by settling time.

Analog Input Data Acquisition Methods

When performing analog input measurements, you either can perform software-timed or hardware-timed acquisitions. Hardware-timed acquisitions can be buffered or non-buffered.

Software-Timed Acquisitions

With a software-timed acquisition, software controls the rate of the acquisition. Software sends a separate command to the hardware to initiate each ADC conversion. In NI-DAQmx, software-timed acquisitions are referred to as having on-demand timing. Software-timed acquisitions are also referred to as immediate or static acquisitions and are typically used for reading a single sample of data.

Hardware-Timed Acquisitions

With hardware-timed acquisitions, a digital hardware signal (ai/SampleClock) controls the rate of the acquisition. This signal can be generated internally on your device or provided externally.

Chapter 4 Analog Input

Hardware-timed acquisitions have several advantages over software-timed acquisitions.

• The time between samples can be much shorter.

• The timing between samples is deterministic.

• Hardware-timed acquisitions can use hardware triggering.

Hardware-timed operations can be buffered or non-buffered. A buffer is a temporary storage in computer memory for to-be-generated samples.

Buffered

In a buffered acquisition, data is moved from the DAQ device’s onboard FIFO memory to a PC buffer using DMA or interrupts before it is transferred to application memory. Buffered acquisitions typically allow for much faster transfer rates than non-buffered acquisitions because data is moved in large blocks, rather than one point at a time.

One property of buffered I/O operations is the sample mode. The sample mode can be either finite or continuous.

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Chapter 4 Analog Input

Finite sample mode acquisition refers to the acquisition of a specific, predetermined number of data samples. Once the specified number of samples has been read in, the acquisition stops. If you use a reference trigger, you must use finite sample mode.

Continuous acquisition refers to the acquisition of an unspecified number of samples. Instead of acquiring a set number of data samples and stopping, a continuous acquisition continues until you stop the operation. Continuous acquisition is also referred to as double-buffered or circular-buffered acquisition.

If data cannot be transferred across the bus fast enough, the FIFO becomes full. New acquisitions will overwrite data in the FIFO before it can be transferred to host memory. The device generates an error in this case. With continuous operations, if the user program does not read data out of the PC buffer fast enough to keep up with the data transfer, the buffer could reach an overflow condition, causing an error to be generated.

Non-Buffered

In non-buffered acquisitions, data is read directly from the FIFO on the device. Typically, hardware-timed, non-buffered operations are used to read single samples with known time increments between them.

Analog Input Triggering

Analog input supports three different triggering actions:

• Start trigger

• Reference trigger

• Pause trigger

Refer to the AI Start Trigger Signal, AI Reference Trigger Signal, and

AI Pause Trigger Signal sections for information about these triggers.

An analog or digital trigger can initiate these actions. All M Series devices support digital triggering, but some do not support analog triggering. To find your device triggering options, refer to the specifications document for your device.

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Connecting Analog Input Signals

Table 4-6 summarizes the recommended input configuration for both types of signal sources.

Chapter 4 Analog Input

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Chapter 4 Analog Input

Table 4-6. Analog Input Configuration

Floating Signal Sources

(Not Connected to Building

Ground)

Ground-Referenced

Signal Sources

†

AI Ground-Reference

Setting

Differential

Non-Referenced Single-Ended (NRSE)

Referenced Single-Ended (RSE)

Examples:

• Ungrounded thermocouples

• Signal conditioning with isolated outputs

• Battery devices

Signal Source DAQ Device

AI+

+ –

Signal Source DAQ Device

+ –

Signal Source DAQ Device

+ –

AI–

–

AI GND

–

AI SENSE

AI GND

–

AI GND

Example:

• Plug-in instruments with non-isolated outputs

Signal Source DAQ Device

AI+

+ –

Signal Source DAQ Device

+ –

NOT RECOMMENDED

Signal Source DAQ Device

+ –

AI–

–

AI GND

–

AI SENSE

AI GND

–

AI GND

Ground-loop potential (VA – VB) are added

Refer to the Analog Input Ground-Reference Settings section for descriptions of the RSE, NRSE, and DIFF modes and

to measured signal.

software considerations.

†

Refer to the Connecting Ground-Referenced Signal Sources section for more information.

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Chapter 4 Analog Input

Connecting Floating Signal Sources

What Are Floating Signal Sources?

A floating signal source is not connected to the building ground system, but has an isolated ground-reference point. Some examples of floating signal sources are outputs of transformers, thermocouples, battery-powered devices, optical isolators, and isolation amplifiers. An instrument or device that has an isolated output is a floating signal source.

When to Use Differential Connections with Floating Signal Sources

Use DIFF input connections for any channel that meets any of the following conditions:

• The input signal is low level (less than 1 V).

• The leads connecting the signal to the device are greater than 3 m (10 ft).

• The input signal requires a separate ground-reference point or return signal.

• The signal leads travel through noisy environments.

• Two analog input channels, AI+ and AI–, are available for the signal.

DIFF signal connections reduce noise pickup and increase common-mode noise rejection. DIFF signal connections also allow input signals to float within the common-mode limits of the NI-PGIA.

Refer to the Using Differential Connections for Floating Signal Sources section for more information about differential connections.

When to Use Non-Referenced Single-Ended (NRSE) Connections with Floating Signal Sources

Only use NRSE input connections if the input signal meets the following conditions.

• The input signal is high-level (greater than 1 V).

• The leads connecting the signal to the device are less than 3 m (10 ft).

DIFF input connections are recommended for greater signal integrity for any input signal that does not meet the preceding conditions.

In the single-ended modes, more electrostatic and magnetic noise couples into the signal connections than in DIFF configurations. The coupling is the

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Chapter 4 Analog Input

result of differences in the signal path. Magnetic coupling is proportional to the area between the two signal conductors. Electrical coupling is a function of how much the electric field differs between the two conductors.

With this type of connection, the NI-PGIA rejects both the common-mode noise in the signal and the ground potential difference between the signal source and the device ground.

Refer to the Using Non-Referenced Single-Ended (NRSE) Connections for

Floating Signal Sources section for more information about NRSE

connections.

When to Use Referenced Single-Ended (RSE) Connections with Floating Signal Sources

Only use RSE input connections if the input signal meets the following conditions.

• The input signal can share a common reference point, AI GND, with other signals that use RSE.

• The input signal is high-level (greater than 1 V).

• The leads connecting the signal to the device are less than 3 m (10 ft).

DIFF input connections are recommended for greater signal integrity for any input signal that does not meet the preceding conditions.

In the single-ended modes, more electrostatic and magnetic noise couples into the signal connections than in DIFF configurations. The coupling is the result of differences in the signal path. Magnetic coupling is proportional to the area between the two signal conductors. Electrical coupling is a function of how much the electric field differs between the two conductors.

With this type of connection, the NI-PGIA rejects both the common-mode noise in the signal and the ground potential difference between the signal source and the device ground.

Refer to the Using Referenced Single-Ended (RSE) Connections for

Floating Signal Sources section for more information about RSE

connections.

Using Differential Connections for Floating Signal Sources

It is important to connect the negative lead of a floating source to AI GND (either directly or through a bias resistor). Otherwise, the source may float

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Chapter 4 Analog Input

out of the maximum working voltage range of the NI-PGIA and the DAQ device returns erroneous data.

The easiest way to reference the source to AI GND is to connect the positive side of the signal to AI+ and connect the negative side of the signal to AI GND as well as to AI– without using resistors. This connection works well for DC-coupled sources with low source impedance (less than 100 Ω).

AI+

Floating

Signal

Source

Inpedance <100 Ω

–

AI–

AI SENSE

AI GND

Figure 4-4. Differential Connections for Floating Signal Sources without Bias Resistors

However, for larger source impedances, this connection leaves the DIFF signal path significantly off balance. Noise that couples electrostatically onto the positive line does not couple onto the negative line because it is connected to ground. This noise appears as a DIFF-mode signal instead of a common-mode signal, and thus appears in your data. In this case, instead of directly connecting the negative line to AI GND, connect the negative line to AI GND through a resistor that is about 100 times the equivalent source impedance. The resistor puts the signal path nearly in balance, so that about the same amount of noise couples onto both connections, yielding better rejection of electrostatically coupled noise. This configuration does not load down the source (other than the very high input impedance of the NI-PGIA).

Floating

Signal

Source

R is about 100 times source impedance of sensor

–

AI+

AI–

AI SENSE

AI GND

Figure 4-5. Differential Connections for Floating Signal Sources

with Single Bias Resistor

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Chapter 4 Analog Input

Floating

Signal

Source

Bias

Current

Return

Path s

–

You can fully balance the signal path by connecting another resistor of the same value between the positive input and AI GND, as shown in Figure 4-6. This fully balanced configuration offers slightly better noise rejection, but has the disadvantage of loading the source down with the series combination (sum) of the two resistors. If, for example, the source impedance is 2 kΩ and each of the two resistors is 100 kΩ, the resistors load down the source with 200 kΩ and produce a –1% gain error.

AI+

Bias Resistors (see text)

Instrumentation

Amplifier

PGIA

AI–

–

Measured

Voltage

–

Input Multiplexers

AI SENSE

AI GND

I/O Connector

M Series Device Configured in DIFF Mode

Figure 4-6. Differential Connections for Floating Signal Sources

with Balanced Bias Resistors

Both inputs of the NI-PGIA require a DC path to ground in order for the NI-PGIA to work. If the source is AC coupled (capacitively coupled), the NI-PGIA needs a resistor between the positive input and AI GND. If the source has low-impedance, choose a resistor that is large enough not to significantly load the source but small enough not to produce significant input offset voltage as a result of input bias current (typically 100 kΩ to

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Chapter 4 Analog Input

1MΩ). In this case, connect the negative input directly to AI GND. If the source has high output impedance, balance the signal path as previously described using the same value resistor on both the positive and negative inputs; be aware that there is some gain error from loading down the source, as shown in Figure 4-7.

AC Coupled

Floating

Signal

Source

AC Coupling

–

AI+

AI–

AI SENSE

AI GND

Figure 4-7. Differential Connections for AC Coupled Floating Sources

with Balanced Bias Resistors

Using Non-Referenced Single-Ended (NRSE) Connections for Floating Signal Sources

It is important to connect the negative lead of a floating signals source to AI GND (either directly or through a resistor). Otherwise the source may float out of the valid input range of the NI-PGIA and the DAQ device returns erroneous data.

Figure 4-8 shows a floating source connected to the DAQ device in NRSE mode.

Floating

Signal

Source

–

AI SENSE

AI GND

Figure 4-8. NRSE Connections for Floating Signal Sources

All of the bias resistor configurations discussed in the Using Differential

Connections for Floating Signal Sources section apply to the NRSE bias

resistors as well. Replace AI– with AI SENSE in Figures 4-4, 4-5, 4-6, and 4-7 for configurations with zero to two bias resistors. The noise

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Chapter 4 Analog Input

rejection of NRSE mode is better than RSE mode because the AI SENSE connection is made remotely near the source. However, the noise rejection of NRSE mode is worse than DIFF mode because the AI SENSE connection is shared with all channels rather than being cabled in a twisted pair with the AI+ signal.

Using the DAQ Assistant, you can configure the channels for RSE or NRSE input modes. Refer to the Configuring AI Ground-Reference Settings in

Software section for more information about the DAQ Assistant.

Using Referenced Single-Ended (RSE) Connections for Floating Signal Sources

Figure 4-9 shows how to connect a floating signal source to the M Series device configured for RSE mode.

AI <0..

Programmable Gain

Floating

Signal

Source

–

I/O Connector

Input Multiplexers

AI SENSE

AI GND

Selected Channel in RSE Configuration

Instrumentation

PGIA

–

Amplifier

Measured

Voltage

–

Figure 4-9. RSE Connections for Floating Signal Sources

Using the DAQ Assistant, you can configure the channels for RSE or NRSE input modes. Refer to the Configuring AI Ground-Reference Settings in

Software section for more information about the DAQ Assistant.

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Chapter 4 Analog Input

Connecting Ground-Referenced Signal Sources

What Are Ground-Referenced Signal Sources?

A ground-referenced signal source is a signal source connected to the building system ground. It is already connected to a common ground point with respect to the device, assuming that the computer is plugged into the same power system as the source. Non-isolated outputs of instruments and devices that plug into the building power system fall into this category.

The difference in ground potential between two instruments connected to the same building power system is typically between 1 and 100 mV, but the difference can be much higher if power distribution circuits are improperly connected. If a grounded signal source is incorrectly measured, this difference can appear as measurement error. Follow the connection instructions for grounded signal sources to eliminate this ground potential difference from the measured signal.

When to Use Differential Connections with Ground-Referenced Signal Sources

Use DIFF input connections for any channel that meets any of the following conditions:

• The input signal is low level (less than 1 V).

• The leads connecting the signal to the device are greater than 3 m (10 ft).

• The input signal requires a separate ground-reference point or return signal.

• The signal leads travel through noisy environments.

• Two analog input channels, AI+ and AI–, are available.

DIFF signal connections reduce noise pickup and increase common-mode noise rejection. DIFF signal connections also allow input signals to float within the common-mode limits of the NI-PGIA.

Refer to the Using Differential Connections for Ground-Referenced Signal

Sources section for more information about differential connections.

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Chapter 4 Analog Input

When to Use Non-Referenced Single-Ended (NRSE) Connections with Ground-Referenced Signal Sources

Only use non-referenced single-ended input connections if the input signal meets the following conditions.

• The input signal is high-level (greater than 1 V).

• The leads connecting the signal to the device are less than 3 m (10 ft).

• The input signal can share a common reference point with other signals.

DIFF input connections are recommended for greater signal integrity for any input signal that does not meet the preceding conditions.

With this type of connection, the NI-PGIA rejects both the common-mode noise in the signal and the ground potential difference between the signal source and the device ground.

Refer to the Using Non-Referenced Single-Ended (NRSE) Connections for

Ground-Referenced Signal Sources section for more information about

NRSE connections.

When to Use Referenced Single-Ended (RSE) Connections with Ground-Referenced Signal Sources

Do not use RSE connections with ground-referenced signal sources. Use NRSE or DIFF connections instead.

As shown in the bottom-rightmost cell of Table 4-6, there can be a potential difference between AI GND and the ground of the sensor. In RSE mode, this ground loop causes measurement errors.

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Using Differential Connections for Ground-Referenced Signal Sources

Figure 4-10 shows how to connect a ground-referenced signal source to the M Series device configured in DIFF mode.

Ground-

Referenced

Signal

Source

Common-

Mode

Noise and

Ground

Potential

I/O Connector

–

AI–

–

Input Multiplexers

AI SENSE

AI GND

M Series Device Configured in DIFF Mode

Instrumentation

Amplifier

PGIA

–

Measured

Voltage

–

Figure 4-10. Differential Connections for Ground-Referenced Signal Sources

With this type of connection, the NI-PGIA rejects both the common-mode noise in the signal and the ground potential difference between the signal source and the device ground, shown as V

in the figure.

AI+ and AI– must both remain within ±11 V of AI GND.

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Chapter 4 Analog Input

Using Non-Referenced Single-Ended (NRSE) Connections for Ground-Referenced Signal Sources

Figure 4-11 shows how to connect ground-reference signal sources in NRSE mode.

I/O Connector

Ground-

Referenced

Signal

Source

Common-

Mode Noise

and Ground

Potential

AI <0..15>

or AI <16..

–

Input Multiplexers

AI GND

–

M Series Device Configured in NRSE Mode

AI SENSE

or AI SENSE 2

Instrumentation

Amplifier

PGIA

–

Measured

Voltage

–

Figure 4-11. Single-Ended Connections for Ground-Referenced Signal Sources

(NRSE Configuration)

AI+ and AI– must both remain within ±11 V of AI GND.

To measure a single-ended, ground-referenced signal source, you must use the NRSE ground-reference setting. Connect the signal to one of AI <0..15> and connect the signal local ground reference to AI SENSE. You also can connect the signal to one of AI <16..79> and connect the signal local ground reference to AI SENSE 2. AI SENSE (or AI SENSE 2) is internally connected to the negative input of the NI-PGIA. Therefore, the ground point of the signal connects to the negative input of the NI-PGIA.

Any potential difference between the device ground and the signal ground appears as a common-mode signal at both the positive and negative inputs of the NI-PGIA, and this difference is rejected by the amplifier. If the input circuitry of a device were referenced to ground, as it is in the RSE ground-reference setting, this difference in ground potentials would appear as an error in the measured voltage.

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Using the DAQ Assistant, you can configure the channels for RSE or NRSE input modes. Refer to the Configuring AI Ground-Reference Settings in

Software section for more information about the DAQ Assistant.

Field Wiring Considerations

Environmental noise can seriously affect the measurement accuracy of the device if you do not take proper care when running signal wires between signal sources and the device. The following recommendations apply mainly to AI signal routing to the device, although they also apply to signal routing in general.

Minimize noise pickup and maximize measurement accuracy by taking the following precautions.

• Use DIFF AI connections to reject common-mode noise.

• Use individually shielded, twisted-pair wires to connect AI signals to the device. With this type of wire, the signals attached to the positive and negative input channels are twisted together and then covered with a shield. You then connect this shield only at one point to the signal source ground. This kind of connection is required for signals traveling through areas with large magnetic fields or high electromagnetic interference.

Chapter 4 Analog Input

Refer to the NI Developer Zone document, Field Wiring and Noise Considerations for Analog Signals, for more information. To access this

document, go to

ni.com/info and enter the info code rdfwn3.

Analog Input Timing Signals

In order to provide all of the timing functionality described throughout this section, M Series devices have a flexible timing engine. Figure 4-12 summarizes all of the timing options provided by the analog input timing engine. Also refer to the Clock Routing section of Chapter 9, Digital

Routing and Clock Generation.

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Chapter 4 Analog Input

PFI, RTSI

PXI_STAR

Analog Comparison

Event

20 MHz Timebase

ai/SampleClock

Timebase

PFI, RTSI

PXI_STAR

Analog Comparison Event

Ctr

Internal Output

SW Pulse

Programmable

Clock

Divider

ai/SampleClock

100 kHz Timebase

PXI_CLK10

PFI, RTSI

PXI_STAR

ai/ConvertClock

Timebase

Analog Comparison Event

Internal Output

Ctr

Programmable

Clock

Divider

ai/ConvertClock

Figure 4-12. Analog Input Timing Options

M Series devices use ai/SampleClock and ai/ConvertClock to perform interval sampling. As Figure 4-13 shows, ai/SampleClock controls the sample period, which is determined by the following equation:

1/Sample Period = Sample Rate

Channel 0

Channel 1

Convert Period

Sample Period

Figure 4-13. Interval Sampling

ai/ConvertClock controls the Convert Period, which is determined by the following equation:

1/Convert Period = Convert Rate

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Typically, this rate is the sampling rate for the task multiplied by the number of channels in the task.

Note The sampling rate is the fastest you can acquire data on the device and still achieve

accurate results. For example, if an M Series device has a sampling rate of 250 kS/s, this sampling rate is aggregate—one channel at 250 kS/s or two channels at 125 kS/s per channel illustrates the relationship.

Posttriggered data acquisition allows you to view only data that is acquired after a trigger event is received. A typical posttriggered DAQ sequence is shown in Figure 4-14. The sample counter is loaded with the specified number of posttrigger samples, in this example, five. The value decrements with each pulse on ai/SampleClock, until the value reaches zero and all desired samples have been acquired.

ai/StartTrigger

ai/SampleClock

ai/ConvertClock

Sample Counter

Figure 4-14. Posttriggered Data Acquisition Example

13042

Pretriggered data acquisition allows you to view data that is acquired before the trigger of interest, in addition to data acquired after the trigger. Figure 4-15 shows a typical pretriggered DAQ sequence. ai/StartTrigger can be either a hardware or software signal. If ai/StartTrigger is set up to be a software start trigger, an output pulse appears on the ai/StartTrigger line when the acquisition begins. When the ai/StartTrigger pulse occurs, the sample counter is loaded with the number of pretriggered samples, in this example, four. The value decrements with each pulse on ai/SampleClock, until the value reaches zero. The sample counter is then loaded with the number of posttriggered samples, in this example, three.

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Chapter 4 Analog Input

ai/StartTrigger

ai/ReferenceTrigger

ai/SampleClock

ai/ConvertClock

Scan Counter

Figure 4-15. Pretriggered Data Acquisition Example

n/a

012

10222

If an ai/ReferenceTrigger pulse occurs before the specified number of pretrigger samples are acquired, the trigger pulse is ignored. Otherwise, when the ai/ReferenceTrigger pulse occurs, the sample counter value decrements until the specified number of posttrigger samples have been acquired.

M Series devices feature the following analog input timing signals.

• AI Sample Clock Signal

• AI Sample Clock Timebase Signal

• AI Convert Clock Signal

• AI Convert Clock Timebase Signal

• AI Hold Complete Event Signal

• AI Start Trigger Signal

• AI Reference Trigger Signal

• AI Pause Trigger Signal

AI Sample Clock Signal

Use the AI Sample Clock (ai/SampleClock) signal to initiate a set of measurements. Your M Series device samples the AI signals of every channel in the task once for every ai/SampleClock. A measurement acquisition consists of one or more samples.

You can specify an internal or external source for ai/SampleClock. You also can specify whether the measurement sample begins on the rising edge or falling edge of ai/SampleClock.

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Using an Internal Source

One of the following internal signals can drive ai/SampleClock.

• Counter n Internal Output

• AI Sample Clock Timebase (divided down)

• A pulse initiated by host software

A programmable internal counter divides down the sample clock timebase.

Several other internal signals can be routed to ai/SampleClock through RTS I. Refe r to Device Routing in MAX in the NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for more information.

Using an External Source

Use one of the following external signals as the source of ai/SampleClock:

• PFI <0..15>

•RTSI <0..7>

•PXI_STAR

• Analog Comparison Event (an analog trigger)

Routing AI Sample Clock Signal to an Output Term inal

You can route ai/SampleClock out to any PFI <0..15> or RTSI <0..7> terminal. This pulse is always active high.

You can specify the output to have one of two behaviors. With the pulse behavior, your DAQ device briefly pulses the PFI terminal once for every occurrence of ai/SampleClock.

With level behavior, your DAQ device drives the PFI terminal high during the entire sample.

All PFI terminals are configured as inputs by default.

Other Timing Requirements

Your DAQ device only acquires data during an acquisition. The device ignores ai/SampleClock when a measurement acquisition is not in progress. During a measurement acquisition, you can cause your DAQ device to ignore ai/SampleClock using the ai/PauseTrigger signal.

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Chapter 4 Analog Input

A counter on your device internally generates ai/SampleClock unless you select some external source. ai/StartTrigger starts this counter and either software or hardware can stop it once a finite acquisition completes. When using an internally generated ai/SampleClock, you also can specify a configurable delay from ai/StartTrigger to the first ai/SampleClock pulse. By default, this delay is set to two ticks of the ai/SampleClockTimebase signal. When using an externally generated ai/SampleClock, you must ensure the clock signal is consistent with respect to the timing requirements of ai/ConvertClock. Failure to do so may result in ai/SampleClock pulses that are masked off and acquisitions with erratic sampling intervals. Refer to AI Convert Clock Signal for more information about the timing requirements between ai/ConvertClock and ai/SampleClock.

Figure 4-16 shows the relationship of ai/SampleClock to ai/StartTrigger.

ai/SampleClockTimebase

ai/StartTrigger

ai/SampleClock

Delay

From Start

Trigger

Figure 4-16. ai/SampleClock and ai/StartTrigger

AI Sample Clock Timebase Signal

You can route any of the following signals to be the AI Sample Clock Timebase (ai/SampleClockTimebase) signal:

• 20 MHz Timebase

• 100 kHz Timebase

•PXI_CLK10

•RTSI <0..7>

• PFI <0..15>

•PXI_STAR

• Analog Comparison Event (an analog trigger)

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ai/SampleClockTimebase is not available as an output on the I/O connector. ai/SampleClockTimebase is divided down to provide one of the possible sources for ai/SampleClock. You can configure the polarity selection for ai/SampleClockTimebase as either rising or falling edge.

AI Convert Clock Signal

Use the AI Convert Clock (ai/ConvertClock) signal to initiate a single A/D conversion on a single channel. A sample (controlled by the AI Sample Clock) consists of one or more conversions.

You can specify either an internal or external signal as the source of ai/ConvertClock. You also can specify whether the measurement sample begins on the rising edge or falling edge of ai/ConvertClock.

With NI-DAQmx 7.4 and later, the driver chooses the fastest conversion rate possible based on the speed of the A/D converter and adds 10 µs of padding between each channel to allow for adequate settling time. This scheme enables the channels to approximate simultaneous sampling and still allow for adequate settling time. If the AI Sample Clock rate is too fast to allow for this 10 µs of padding, NI-DAQmx chooses the conversion rate so that the AI Convert Clock pulses are evenly spaced throughout the sample.

Chapter 4 Analog Input

With NI-DAQmx 7.3, the driver chooses a conversion rate so the AI Convert Clock pulses are evenly spaced throughout the sample. This allows for the maximum settling time between conversions. To approximate simultaneous sampling, manually increase the conversion rate.

To explicitly specify the conversion rate, use AI Convert Clock Rate DAQmx Timing property node or function.

Caution Setting the conversion rate higher than the maximum rate specified for your

device will result in errors.

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