National Instruments NI-USB-621x User Manual

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DAQ M Series

NI USB-621x User Manual

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NI USB-621x User Manual

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March 2008 371931E-01

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Important Information

Warranty

The NI USB-6210, NI USB-6211, NI USB-6212, NI USB-6215, NI USB-6216, and NI USB-6218 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 du ring the warranty period. This warranty includes parts and labor.

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

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

National Instruments believes that the information in this 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 consu Instruments be liable for any damages arising out of or related to this document or the information contained in it.

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lt National Instruments if errors are suspected. In no event shall National

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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,

About This Manual

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

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

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

Applying Signal Labels to the USB-621x......................................................................1-2

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

Mounting the USB-621x ................................................................................................1-4

Desktop Use.....................................................................................................1-4

DIN Rail Mounting..........................................................................................1-4

Panel Mounting ...............................................................................................1-5

Chapter 2 DAQ System Overview

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

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

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

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

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

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

USB-621x Mass Termination Custom Cabling...............................................2-4

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

Chapter 3 Connector and LED Information

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

+5 V Power ....................................................................................................................3-3

+5 V Power as an Output ................................................................................3-3

+5 V Power as an Input ...................................................................................3-3

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

PWR/ACT LED Indicator .............................................................................................3-5

Contents

Chapter 4 Analog Input

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

Analog Input Ground-Reference Settings ..................................................................... 4-3

Multichannel Scanning Considerations......................................................................... 4-5

Analog Input Data Acquisition Methods....................................................................... 4-8

Analog Input Digital Triggering.................................................................................... 4-10

Field Wiring Considerations.......................................................................................... 4-10

Analog Input Timing Signals ........................................................................................ 4-11

Getting Started with AI Applications in Software ........................................................ 4-22

Connecting Analog Input Signals on USB-6210/6211/6212 Devices .......................... 4-23

Configuring AI Ground-Reference Settings in Software................................ 4-5

AI Sample Clock Signal.................................................................................. 4-14

Using an Internal Source .................................................................. 4-14

Using an External Source ................................................................. 4-14

Routing AI Sample Clock to an Output Terminal............................ 4-14

Other Timing Requirements ............................................................. 4-14

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

AI Convert Clock Signal................................................................................. 4-16

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

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

Routing AI Convert Clock to an Output Terminal ........................... 4-16

Using a Delay from Sample Clock to Convert Clock ...................... 4-17

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

AI Convert Clock Timebase Signal ................................................................ 4-19

AI Hold Complete Event Signal ..................................................................... 4-19

AI Start Trigger Signal.................................................................................... 4-20

Using a Digital Source...................................................................... 4-20

Routing AI Start Trigger to an Output Terminal .............................. 4-20

AI Reference Trigger Signal ........................................................................... 4-21

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

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

AI Pause Trigger Signal.................................................................................. 4-22

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

Connecting Floating Signal Sources ............................................................... 4-25

What Are Floating Signal Sources?.................................................. 4-25

When to Use Differential Connections with Floating

Signal Sources ............................................................................... 4-25

When to Use Referenced Single-Ended (RSE) Connections

with Floating Signal Sources ......................................................... 4-25

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

Connections with Floating Signal Sources .................................... 4-26

Using Differential Connections for Floating Signal Sources ...........4-27

NI USB-621x User Manual vi ni.com

Connecting Ground-Referenced Signal Sources .............................................4-31

Connecting Analog Input Signals on USB-6215/6216/6218 Devices ...........................4-36

Taking Differential Measurements..................................................................4-36

Taking Referenced Single-Ended (RSE) Measurements ................................4-37

Taking Non-Referenced Single-Ended (NRSE) Measurements .....................4-38

Chapter 5 Analog Output

AO Range ......................................................................................................................5-2

Minimizing Glitches on the Output Signal ....................................................................5-2

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

Analog Output Digital Triggering .................................................................................5-3

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

Analog Output Timing Signals ......................................................................................5-4

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

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

AO Sample Clock Signal.................................................................................5-7

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

Getting Started with AO Applications in Software .......................................................5-9

Contents

Using Non-Referenced Single-Ended (NRSE) Connections

for Floating Signal Sources ............................................................4-30

Using Referenced Single-Ended (RSE) Connections for

Floating Signal Sources..................................................................4-31

What Are Ground-Referenced Signal Sources?................................4-31

When to Use Differential Connections with Ground-Referenced

Signal Sources................................................................................4-32

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

Connections with Ground-Referenced Signal Sources ..................4-32

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

Ground-Referenced Signal Sources ...............................................4-33

Using Differential Connections for Ground-Referenced

Signal Sources................................................................................4-33

Using Non-Referenced Single-Ended (NRSE) Connections for

Ground-Referenced Signal Sources ...............................................4-34

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

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

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

Using an Internal Source...................................................................5-7

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

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

Other Timing Requirements..............................................................5-8

Contents

Chapter 6 Digital I/O

Digital I/O on USB-6210/6211/6215/6218 Devices ..................................................... 6-1

Digital I/O on USB-6212/6216 Devices........................................................................ 6-4

Chapter 7 PFI

Using PFI Terminals as Timing Input Signals .............................................................. 7-2

Exporting Timing Output Signals Using PFI Terminals............................................... 7-3

Using PFI Terminals as Static Digital I/Os ................................................................... 7-3

Connecting PFI Input Signals........................................................................................ 7-4

PFI Filters ...................................................................................................................... 7-4

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

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

Static DIO on USB-6210/6211/6215/6218 Devices ....................................... 6-2

I/O Protection on USB-6210/6211/6215/6218 Devices.................................. 6-2

Increasing Current Drive on USB-6210/6211/6215/6218 Devices ................ 6-3

Connecting Digital I/O Signals on USB-6210/6211/6215/6218 Devices....... 6-3

Getting Started with DIO Applications in Software on

USB-6210/6211/6215/6218 Devices ........................................................... 6-4

Static DIO on USB-6212/6216 Devices ......................................................... 6-5

I/O Protection on USB-6212/6216 Devices....................................................6-5

Programmable Power-Up States on USB-6212/6216 Devices....................... 6-6

Increasing Current Drive on USB-6212/6216 Devices................................... 6-6

Connecting Digital I/O Signals on USB-6212/6216 Devices ......................... 6-6

Getting Started with DIO Applications in Software on

USB-6212/6216 Devices.............................................................................. 6-7

Chapter 8 Counters

Counter Input Applications ........................................................................................... 8-2

Counting Edges ............................................................................................... 8-2

Single Point (On-Demand) Edge Counting ...................................... 8-2

Buffered (Sample Clock) Edge Counting......................................... 8-3

Controlling the Direction of Counting.............................................. 8-4

Pulse-Width Measurement.............................................................................. 8-4

Single Pulse-Width Measurement .................................................... 8-4

Buffered Pulse-Width Measurement ................................................ 8-5

Period Measurement ....................................................................................... 8-6

Single Period Measurement.............................................................. 8-6

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

NI USB-621x User Manual viii ni.com

Contents

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

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

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

Frequency Measurement .................................................................................8-9

Choosing a Method for Measuring Frequency .................................8-13

Position Measurement .....................................................................................8-15

Measurements Using Quadrature Encoders ......................................8-15

Measurements Using Two Pulse Encoders .......................................8-17

Two-Signal Edge-Separation Measurement....................................................8-18

Single Two-Signal Edge-Separation Measurement ..........................8-18

Buffered Two-Signal Edge-Separation Measurement ......................8-19

Counter Output Applications .........................................................................................8-20

Simple Pulse Generation .................................................................................8-20

Single Pulse Generation ....................................................................8-20

Single Pulse Generation with Start Trigger ......................................8-20

Retriggerable Single Pulse Generation .............................................8-21

Pulse Train Generation ....................................................................................8-22

Continuous Pulse Train Generation ..................................................8-22

Frequency Generation .....................................................................................8-23

Using the Frequency Generator ........................................................8-23

Frequency Division .........................................................................................8-24

Pulse Generation for ETS................................................................................8-24

Counter Timing Signals .................................................................................................8-25

Counter n Source Signal..................................................................................8-26

uting a Signal to Counter n Source...............................................8-26

Routing Counter n Source to an Output Terminal ............................8-26

Counter n Gate Signal .....................................................................................8-27

Routing a Signal to Counter n Gate ..................................................8-27

Routing Counter n Gate to an Output Terminal................................8-27

Counter n Aux Signal ......................................................................................8-27

Routing a Signal to Counter n Aux ...................................................8-27

Counter n A, Counter n B, and Counter n Z Signals.......................................8-28

Routing Signals to A, B, and Z Counter Inputs ................................8-28

Counter n Up_Down Signal ............................................................................8-28

Counter n HW Arm Signal ..............................................................................8-28

Routing Signals to Counter n HW Arm Input...................................8-29

Cou

nter n Internal Output and Counter n TC Signals .....................................8-29

Routing Counter n Internal Output to an Output Terminal...............8-29

Frequency Output Signal.................................................................................8-29

Routing Frequency Output to a Terminal .........................................8-29

Default Counter/Timer Pinouts......................................................................................8-30

Counter Triggering ........................................................................................................8-31

Contents

Other Counter Features.................................................................................................. 8-32

Sample Clock .................................................................................................. 8-32

Cascading Counters......................................................................................... 8-33

Counter Filters................................................................................................. 8-33

Prescaling ........................................................................................................ 8-34

Duplicate Count Prevention ............................................................................ 8-35

Example Application That Works Correctly

(No Duplicate Counting) ............................................................... 8-35

Example Application That Works Incorrectly

(Duplicate Counting) ..................................................................... 8-36

Example Application That Prevents Duplicate Count...................... 8-36

Enabling Duplicate Count Prevention in NI-DAQmx...................... 8-37

Chapter 9 Isolation and Digital Isolators on USB-6215/6216/6218 Devices

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

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

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

Creating an AC Return Path............................................................................9-3

Isolated Systems ............................................................................... 9-4

Non-Isolated Systems ....................................................................... 9-4

Chapter 10 Digital Routing and Clock Generation

80 MHz Timebase ......................................................................................................... 10-1

20 MHz Timebase ......................................................................................................... 10-1

100 kHz Timebase......................................................................................................... 10-1

Chapter 11 Bus Interface

USB Signal Stream........................................................................................................ 11-1

Data Transfer Methods .................................................................................................. 11-1

Changing Data Transfer Methods ................................................................... 11-2

Chapter 12 Triggering

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

NI USB-621x User Manual x ni.com

Appendix A Device-Specific Information

USB-6210 ......................................................................................................................A-2

USB-6211/6215 .............................................................................................................A-4

USB-6212/6216 Screw Terminal...................................................................................A-6

USB-6212/6216 Mass Termination ...............................................................................A-8

USB-6218 ......................................................................................................................A-13

Appendix B Troubleshooting

Appendix C Technical Support and Professional Services

Glossary

Index

Contents

Device Pinouts

Figure A-1. USB-6210 Pinout ..................................................................................A-2

Figure A-2. USB-6211/6215 Pinout .........................................................................A-4

Figure A-3. USB-6212/6216 Screw Terminal Pinout...............................................A-6

Figure A-4. USB-6212/6216 Mass Termination Pinout ...........................................A-9

Figure A-5. USB-6218 Pinout ..................................................................................A-13

About This Manual

The NI USB-621x User Manual contains information about using the National Instruments USB-621x data acquisition (DAQ) devices with NI-DAQmx 8.7.1 and later. NI USB-6210, USB-6211, USB-6212, USB-6215, USB-6216, and USB-6218 devices feature up to 32 analog input (AI) channels, up to two analog output (AO) channels, two counters, and up to eight lines of digital input (DI) and up to eight lines of digital output (DO), or 32 bidirectional static DIO lines.

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

About This Manual

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 NI-DAQmx for USB Devices Getting Started Guide, which you can download from instructions for installing software and hardware, configuring channels and tasks, and getting started developing an application.

Installing Other Software

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

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

Installing the Hardware

The NI-DAQmx for USB Devices Getting Started Guide contains non-software-specific information about how to install USB devices.

Device Pinouts

Refer to Appendix A, Device-Specific Information, for USB-621x device pinouts.

Chapter 1 Getting Started

Device Specifications

Refer to the NI USB-621x Specifications, available on the NI-DAQ Device Documentation Browser or from

ni.com/manuals, for more detailed

information about USB-621x devices.

Applying Signal Labels to the USB-621x

Your USB-621x kit includes labels for the combicon connectors on USB-621x Screw Terminal devices. You can choose labels with pin numbers or signal names, or blank labels. Choose one of the labels, align the correct label with the terminals printed on the top panel of your device or the 16-position combicon connector, and apply the label, as shown in Figure 1-1.

P/N 19XXXX REVX

msi 6000

1 Terminal Number Label 2 Single-Ended Signal Name Label

3 Differential Signal Name Label 4 User-Defined Custom Label

Figure 1-1. USB-621x Signal Labels

NI USB-621x User Manual 1-2 ni.com

USB Cable Strain Relief

You can provide strain relief for the USB cable in the following ways:

• Cable Strain Relief Groove Method—Press the USB cable into one

of the two grooves on the underside of the USB-621x. Choose the USB cable groove that matches your USB cable size, as shown in Figure 1-2a.

• Zip Tie Method—Thread a zip tie through the zip tie bar on the

underside of the USB-621x and tighten around the USB cable, as shown in Figure 1-2b.

Chapter 1 Getting Started

1 USB Cable Strain Relief Groove (Large) 2 USB Cable Strain Relief Groove (Small) 3 USB Cable

4 Zip Tie 5 Zip Tie Bar

Figure 1-2. USB Cable Strain Relief Options

Chapter 1 Getting Started

Mounting the USB-621x

You can use the USB-621x on a desktop or mount it to a standard DIN rail or a panel.

Desktop Use

You can use the USB-621x on a desktop. The USB-621x has grooves on the underside that allow it to be stacked with other like-sized USB-621x

devices.

For secure desktop use. adhere the supplied rubber non-skid feet to the underside of the device, as shown in Figure 1-3.

Note Do not apply the rubber feet if you are panel mounting the USB-621x or stacking the

device on another USB-621x device.

Figure 1-3. Applying Rubber Feet to the USB-621x

DIN Rail Mounting

The DIN rail mounting kit (part number 779689-01, not included in your USB-621x kit) is an accessory you can use to mount the USB-621x family of products to a standard DIN rail.

Note Apply strain relief, as described in the USB Cable Strain Relief section, before

mounting the USB-621x to a DIN rail.

NI USB-621x User Manual 1-4 ni.com

Panel Mounting

Chapter 1 Getting Started

To mount the USB-621x to a board or panel, complete the following steps while referring to Figure 1-4.

Figure 1-4. Mounting the USB-621x on a Panel

Note

Do not apply the rubber feet to the USB-621x when panel mounting the device.

Note Apply strain relief, as described in the USB Cable Strain Relief section, before panel

mounting the USB-621x.

1. Download and print the panel mounting template PDF attached in the KnowledgeBase document, USB-621x Panel Mounting Template. Go to

ni.com/info and enter the info code ex3x98 to locate the

KnowledgeBase.

2. Using the template, mark the bottom point and top point on the panel.

(USB-621x Screw Terminal Devices) The points will be 171.45 mm

(6.75 in.) from each other.

(USB-621x Mass Termination Devices) The points will be 182.56 mm

(7.188 in.) from each other.

Chapter 1 Getting Started

3. Remove the USB cable from the connector on the USB-621x.

4. Screw a #8 or M4 screw into the bottom point on the panel.

5. Set the USB-621x on the screw by fitting it into the bottom screw notch on the underside of the USB-621x.

6. Screw a #8 or M4 screw through the USB-621x top screw hole into the panel.

NI USB-621x User Manual 1-6 ni.com

DAQ System Overview

Figure 2-1 shows a typical DAQ system, which includes the USB-621x device, programming software, and PC (DAQ systems involving the USB-621x Mass Termination device can also include signal conditioning devices and a cable for accessory connection). The following sections contain more information about the components of a typical DAQ system.

DAQ

Hardware

Figure 2-1. Components of a Typical DAQ System

DAQ

Software

Personal Computer

or Laptop

DAQ Hardware

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 USB-621x devices.

Chapter 2 DAQ System Overview

Analog Input

Analog Output

Digital I/O

I/O Connector

Counters

PFI

DAQ-STC2

The DAQ-STC2 implements 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, and CTR FIFOs

• Generation and routing of internal and external timing signals

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

• Static DI, DO, and DIO signals

• USB Hi-Speed 2.0 interface

•Up to four USB Signal Streams for acquisition and generation

Digital

Routing

and Clock

Generation

functions

Isolation

Barrier

(USB-6215/

6216/6218

devices only)

Digital

Isolators

Figure 2-2. USB-621x Block Diagram

Bus

Interface

Bus

Calibration Circuitry

The USB-621x 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.

NI USB-621x User Manual 2-2 ni.com

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 re t urn 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 USB-621x devices, refer to the B/E/M/S Series Calibration Procedure for NI-DAQmx by clicking Manual Calibration Procedures on

Signal Conditioning

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.

Chapter 2 DAQ System Overview

ni.com/calibration.

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

ni.com/sensors.

Chapter 2 DAQ System Overview

•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.

Cables and Accessories

Cable and accessory options for USB-621x devices are as follows:

• Combicon Accessory for USB-621x Screw Terminal Devices (Optional)—Your USB-621x kit includes combicon connectors with screws and signal labels. The NI USB-621x Accessory Kit (part number 779807-01) contains four additional combicon connectors with screws, a screwdriver, and additional signal labels. You can use the combicon accessory to create custom connection solutions for USB-621x Screw Terminal devices.

• Cables and Accessories for USB-621x Mass Termination Devices—Refer to the USB-6212/6216 Mass Termination Cables and

Accessories section of Appendix A, Device-Specific Information, for a

list of cables and accessories for USB-621x Mass Termination devices.

USB-621x Mass Termination Custom Cabling

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 Board Mating Connectors, by going to code

rdspmb.

NI USB-621x User Manual 2-4 ni.com

ni.com/info and entering the info

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.

USB-621x devices use the NI-DAQmx driver. 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. Yo u can use examples to develop a new application or add example code to an existing application.

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

• In LabVIEW, select Help»Find Examples.

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

Chapter 2 DAQ System Overview

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

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

–

MeasurementStudio\VCNET\Examples\NIDaq

– MeasurementStudio\DotNET\Examples\NIDaq

• NI-DAQmx examples for ANSI C are in the

NI-DAQ\Examples\DAQmx ANSI C Dev directory

For additional examples, refer to

zone.ni.com.

Connector and LED Information

The I/O Connector Signal Descriptions and +5 V Power sections contain information about NI USB-621x connectors. The PWR/ACT LED Indicator section contains information about the NI USB-621x PWR/ACT LED. Refer to Appendix A, Device-Specific Information, for device I/O connector pinouts. Refer to the Applying Signal Labels to the USB-621x section of Chapter 1, Getting Started, for information about applying signal labels.

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..31> Va ri e s Input Analog Input Channels 0 to 31—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..31> signal is AI SENSE.

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:

<AI1,AI9>, <AI2,AI10>, <AI3,AI11>, <AI4,AI12>, <AI5,AI13>, <AI6,AI14>, <AI7,AI15>, <AI16,AI24>, <AI 17, AI 25>, <AI 18, AI 26>, <AI 19, AI 27>, <AI 20, AI 28>, <AI 21, AI 29>, <AI 22, AI 30>, <AI 23, AI 31>

AI SENSE — Input Analog Input Sense—In NRSE mode, the reference for each

AI <0..31> signal is AI SENSE.

Chapter 3 Connector and LED Information

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

Signal Name Reference Direction Description

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

voltage output of AO channels 0 to 1.

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

AO <0..1>. 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

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

+5 V D GND Input or

Output

PFI <0..3>, PFI <8..11>/P0.<0..7>

D GND Input (USB-6210/6211/6215/6218 Devices) Programmable

+5 V Power—These terminals provide a +5 V power source or can be used to externally power the digital outputs.

Function Interface or Static Digital Input Channels 0 to 7—Each PFI terminal can be used to supply an

external source for AI, AO, or counter/timer inputs.

Yo u also can use these terminals as static digital input lines.

PFI <4..7>, PFI <12..15>/P1.<0..7>

P0.<0..15> D GND Input or

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

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

D GND Output (USB-6210/6211/6215/6218 Devices) Programmable

Output

D GND Input or

Output

Function Interface or Static Digital Output Channels 0 to 7—You can route many different internal AI,

AO, or counter/timer outputs to each PFI terminal.

Yo u also can use these terminals as static digital output lines.

(USB-6212/6216 Devices) Port 0 Digital I/O Channels 0 to 15—You can individually configure each signal

as an input or output.

(USB-6212/6216 Devices) Programmable Function Interface or Digital I/O Channels 0 to 15—Each of these terminals can

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

As a PFI input, each 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.

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National Instruments NI-USB-621x User Manual

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Worldwide Technical Support and Product Information

National Instruments Corporate Headquarters

Worldwide Offices

Important Information

Warranty

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Trademarks

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WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS

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Contents

About This Manual

Conventions

Related Documentation

NI-DAQmx for Windows

NI-DAQmx Base (Linux/Mac OS X/LabVIEW PDA 8.x)

LabVIEW

LabWindows/CVI

Measurement Studio

ANSI C without NI Application Software

.NET Languages without NI Application Software

Device Documentation and Specifications

Training Courses

Technical Support on the Web

Installing NI-DAQmx

Installing Other Software

Installing the Hardware

Device Pinouts

Device Specifications

Applying Signal Labels to the USB-621x

Figure 1-1. USB-621x Signal Labels

USB Cable Strain Relief

Figure 1-2. USB Cable Strain Relief Options

Mounting the USB-621x

Desktop Use

Figure 1-3. Applying Rubber Feet to the USB-621x

DIN Rail Mounting

Panel Mounting

Figure 1-4. Mounting the USB-621x on a Panel

Figure 2-1. Components of a Typical DAQ System

DAQ Hardware

DAQ-STC2

Figure 2-2. USB-621x Block Diagram

Calibration Circuitry

Signal Conditioning

Sensors and Transducers

Cables and Accessories

USB-621x Mass Termination Custom Cabling

Programming Devices in Software

I/O Connector Signal Descriptions

Table 3-1. I/O Connector Signals