National Instruments NI-DAQ mx Manuale

AO Waveform Calibration

Procedure for NI-DAQ mx

Contents

Conventions ............................................................................................ 2

Introduction............................................................................................. 2

Software .................................................................................................. 3

Documentation ........................................................................................ 3

Test Equipment ....................................................................................... 4

Test Considerations................................................................................. 5

Calibration Process ................................................................................. 5

Calibration Process Overview ......................................................... 5

Initial Setup...................................................................................... 6

AO Verification Procedure .............................................................. 6

Analog Output Verification ...................................................... 6

Counter Verification ................................................................. 10

AO Adjustment Procedure............................................................... 12

AO Device Test Limits ........................................................................... 14

Using the Tables .............................................................................. 14

Range ........................................................................................ 14

Test Point.................................................................................. 14

24-Hour Ranges ........................................................................ 14

1-Year Ranges .......................................................................... 14

Counters.................................................................................... 14

NI 6711/6713—12-Bit Resolution................................................... 15

NI 6722/6723—13-Bit Resolution................................................... 15

NI 6731/6733—16-Bit Resolution................................................... 16

™

AO Waveform Calibration Procedure for NI-DAQmx 2 ni.com

Conventions

The following conventions appear in this manual:

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

range of values associated with a bit or signal name—for example,

P0.<0..7>.

»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.

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 and hardware labels.

italic Italic text denotes variables, emphasis, a cross reference, or an introduction

to a key concept. This font also denotes text that is a placeholder for a word

or value that you must supply.

monospace Monospace text denotes text or characters that you should enter from the

keyboard, sections of code, programming examples, and syntax examples.

This font is also used for the proper names of disk drives, paths, directories,

programs, subprograms, subroutines, device names, functions, operations,

variables, filenames, and extensions.

monospace italic

Italic text in this font denotes text that is a placeholder for a word or value

that you must supply.

Introduction

This document contains instructions for calibrating NI 671X/672X/673X

for PCI/PXI/CompactPCI analog output (AO) devices.

This document does not discuss programming techniques or compiler

configuration. The National Instruments DAQmx driver contains help files

that have compiler-specific instructions and detailed function explanations.

You can add these help files when you install NI-DAQmx on the calibration

computer.

AO devices should be calibrated at a regular interval as defined by

the measurement accuracy requirements of your application. National

Instruments recommends that you perform a complete calibration at least

once every year. You can shorten this interval to 90 days or six months.

©National Instruments Corporation 3 AO Waveform Calibration Procedure for NI-DAQmx

Software

Calibration requires the latest NI-DAQmx driver. NI-DAQmx includes

high-level function calls to simplify the task of writing software to calibrate

devices. The driver supports many programming languages, including

LabVIEW, LabWindows™/CVI™, Microsoft Visual C++, Microsoft Visual

Basic, and Borland C++.

Documentation

If you are using the NI-DAQmx driver, the following documents are your

primary references for writing your calibration utility:

• The NI-DAQmx C Reference Help includes information about the

functions in the driver.

• The DAQ Quick Start Guide for NI-DAQ 7.3 or later provides

instructions for installing and configuring NI-DAQ devices.

• The NI-DAQmx Help includes information about creating applications

that use the NI-DAQmx driver.

For more information about the device you are calibrating, refer to the

Analog Output Series Help.

AO Waveform Calibration Procedure for NI-DAQmx 4 ni.com

Test Equipment

Figure 1 shows the test equipment you need to calibrate your device. The

specific DMM, calibrator, and counter connections are described in the

Calibration Process section.

Figure 1. Calibration Connections

When performing calibration, National Instruments recommends that you

use the following instruments for calibrating an AO device:

• Calibrator—Fluke 5700A. If that instrument is unavailable, use a

high-precision voltage source that is at least 50 ppm accurate for

12- and 13-bit boards and 10 ppm for 16-bit boards.

• DMM—NI 4070. If that instrument is unavailable, use a multi-ranging

5.5-digit DMM with an accuracy of 40 ppm (0.004%).

• Counter—Hewlett-Packard 53131A. If that instrument is unavailable,

use a counter accurate to 0.01%.

• Low thermal copper EMF plug-in cables—Fluke 5440A-7002. Do not

use standard banana cables.

• DAQ cable—NI recommends using shielded cables, such as the

SH68-68-EP with the NI 671X/673Xor the SH68-C68-S with the

NI 672X.

HI LO

Calibrator

HILO

DMM

Counter

AO Device

Shielded Cable

Accessory

CTR 0 OUT

AO GND

AO EXT REF

©National Instruments Corporation 5 AO Waveform Calibration Procedure for NI-DAQmx

• One of the following DAQ accessories:

– SCB-68—The SCB-68 is a shielded I/O connector block with

68 screw terminals for easy signal connection to 68- or 100-pin

DAQ devices.

– CB-68LP/CB-68LPR/TBX-68—The CB-68LP, CB-68LPR, and

TBX-68 are low-cost termination accessories with 68 screw

terminals for easy connection of field I/O signals to 68-pin DAQ

devices.

Test Considerations

Follow these guidelines to optimize connections and test conditions during

calibration:

• Keep connections to the NI 671X/672X/673Xshort. Long cables and

wires act as antennae, picking up extra noise, which can affect

measurements.

• Use shielded copper wire for all cable connections to the device.

• Use twisted-pair wire to eliminate noise and thermal offsets.

• Maintain a temperature between 18 and 28 °C. To operate the module

at a specific temperature outside this range, calibrate the device at that

temperature.

• Keep relative humidity below 80%.

• Allow a warm-up time of at least 15 minutes to ensure that the

measurement circuitry is at a stable operating temperature.

Calibration Process

This section provides instructions for verifying and calibrating your device.

Calibration Process Overview

The calibration process has four steps:

1. Initial Setup—Configure your device in NI-DAQmx.

2. AO Verification Procedure—Verify the existing operation of the

device. This step allows you to confirm that the device was operating

within its specified range prior to calibration.

3. AO Adjustment Procedure—Perform an external calibration that

adjusts the device calibration constants with respect to a known voltage

source.

4. Perform another verification to ensure that the device is operating

within its specifications after adjustment.

AO Waveform Calibration Procedure for NI-DAQmx 6 ni.com

These steps are described in detail in the following sections. Because a

complete verification of all of the device’s ranges can take some time,

you may wish to verify only the ranges of interest to you.

Initial Setup

NI-DAQmx automatically detects all AO devices. However, for the driver

to communicate with the device, it must be configured in NI-DAQmx.

To configure a device in NI-DAQmx, complete the following steps:

1. Install the NI-DAQmx driver software.

2. Power off the computer that will hold the device, and install the device

in an available slot.

3. Power on the computer, and launch Measurement & Automation

Explorer (MAX).

4. Configure the device identifier and select Self-Test to ensure that the

device is working properly.

Note When a device is configured with MAX, it is assigned a device identifier. Each

function call uses this identifier to determine which DAQ device to calibrate.

AO Verification Procedure

Verification determines how well the DAQ device is meeting its

specifications. By performing this procedure, you can see how your device

has operated over time. You can use this information to help determine the

appropriate calibration interval for your application.

The verification procedure is divided into the major functions of the device.

Throughout the verification process, use the tables in the AO Device Test

Limitssection to determine if your device needs to be adjusted.

Analog Output Verification

This procedure checks the performance of the analog output. Check

measurements using the following procedure:

1. Connect your DMM to AO 0 as shown in Table 1.

Table 1. Connecting the DMM to AO <0..7>

Output Channel DMM Positive Input DMM Negative Input

AO 0 AO 0 (pin 22) AO GND (pin 56)

AO 1 AO 1 (pin 21) AO GND (pin 55)

AO 2 AO 2 (pin 57) AO GND (pin 23)

©National Instruments Corporation 7 AO Waveform Calibration Procedure for NI-DAQmx

AO 3 AO 3 (pin 25) AO GND (pin 59)

AO 4 AO 4 (pin 60) AO GND (pin 26)

AO 5 AO 5 (pin 28) AO GND (pin 61)

AO 6 AO 6 (pin 30) AO GND (pin 64)

AO 7 AO 7 (pin 65) AO GND (pin 31)

Table 2. Connecting the DMM to AO <8..31> on the NI 6723

Output Channel DMM Positive Input DMM Negative Input

AO 8 AO 8 (pin 68) AO GND (pin 34)

AO 9 AO 9 (pin 33) AO GND (pin 67)

AO 10 AO 10 (pin 32) AO GND (pin 66)

AO 11 AO 11 (pin 65) AO GND (pin 31)

AO 12 AO 12 (pin 30) AO GND (pin 64)

AO 13 AO 13 (pin 29) AO GND (pin 63)

AO 14 AO 14 (pin 62) AO GND (pin 28)

AO 15 AO 15 (pin 27) AO GND (pin 61)

AO 16 AO 16 (pin 26) AO GND (pin 60)

AO 17 AO 17 (pin 59) AO GND (pin 25)

AO 18 AO 18 (pin 24) AO GND (pin 58)

AO 19 AO 19 (pin 23) AO GND (pin 57)

AO 20 AO 20 (pin 55) AO GND (pin 21)

AO 21 AO 21 (pin 20) AO GND (pin 54)

AO 22 AO 22 (pin 19) AO GND (pin 53)

AO 23 AO 23 (pin 52) AO GND (pin 18)

AO 24 AO 24 (pin 17) AO GND (pin 51)

AO 25 AO 25 (pin 16) AO GND (pin 50)

AO 26 AO 26 (pin 49) AO GND (pin 15)

Table 1. Connecting the DMM to AO <0..7> (Continued)

Output Channel DMM Positive Input DMM Negative Input

AO Waveform Calibration Procedure for NI-DAQmx 8 ni.com

2. Choose the table from the AO Device Test Limits section that

corresponds to the device you are verifying. This table shows all

acceptable settings for the device. Although NI recommends that you

verify all ranges, you may want to save time by checking only the

ranges used in your application.

3. Create a task using DAQmxCreateTask.

4. Add an AO voltage task using DAQmxCreateAOVoltageChan

(DAQmx Create Virtual Channel VI) and configure the channel,

AO0. Use the tables in the AO Device TestLimits section to determine

the minimum and maximum values for your device.

AO 27 AO 27 (pin 14) AO GND (pin 48)

AO 28 AO 28 (pin 13) AO GND (pin 47)

AO 29 AO 29 (pin 46) AO GND (pin 12)

AO 30 AO 30 (pin 11) AO GND (pin 45)

AO 31 AO 31 (pin 10) AO GND (pin 44)

NI-DAQ Function Call LabVIEW Block Diagram

Call DAQmxCreateTask with

the following parameters:

taskName:

MyAOVoltageTask

taskHandle: &taskHandle

LabVIEW does not require this step.

NI-DAQ Function Call LabVIEW Block Diagram

Call

DAQmxCreateAOVoltageChan

with the following parameters:

taskHandle: taskHandle

physicalChannel: dev1/aoO

nameToAssignToChannel:

AOVoltageChannel

minVal:

-10.0

maxVal:

10.0

units: DAQmx_Val_Volts

customScaleName: NULL

Table 2. Connecting the DMM to AO <8..31> on the NI 6723 (Continued)

Output Channel DMM Positive Input DMM Negative Input

©National Instruments Corporation 9 AO Waveform Calibration Procedure for NI-DAQmx

5. Start the acquisition using DAQmxStartTask

(DAQmx Start Task VI).

6. Write a voltage to the AO channel using DAQmxWriteAnalogF64

(DAQmx WriteVI) using the table for your device in the AO Device

Test Limits section.

7. Compare the resulting value shown by the DMM to the upper and

lower limits in the table. If the value is between these limits, the test is

considered to have passed.

8. Clear the acquisition using DAQmxClearTask

(DAQmx Clear Task VI).

NI-DAQ Function Call LabVIEW Block Diagram

Call DAQmxStartTask with

the following parameters:

taskHandle: taskHandle

NI-DAQ Function Call LabVIEW Block Diagram

Call DAQmxWriteAnalogF64

with the following parameters:

taskHandle: taskHandle

numSampsPerChan: 1

autoStart: 1

timeout: 10.0

dataLayout:

DAQmx_Val_GroupByChannel

writeArray: &data

sampsPerChanWritten:

&samplesWritten

reserved: NULL

NI-DAQ Function Call LabVIEW Block Diagram

Call DAQmxClearTask with the

following parameter:

taskHandle: taskHandle

AO Waveform Calibration Procedure for NI-DAQmx 10 ni.com

9. Repeat steps 4 through 8 until all values have been tested.

10. Disconnect the DMM from AO 0, and reconnect it to the next channel,

making the connections as shown in Table 1.

11. Repeat steps 4 through 10 until you have verified all channels.

12. Disconnect your DMM from the device.

You have finished verifying the analog output levels on your device.

Counter Verification

This procedure verifies the performance of the counter. AO devices have

only one timebase to verify, so only counter 0 needs to be checked. It is not

possible to adjust this timebase, so only verification can be performed.

Perform checks using the following procedure:

1. Connect your counter positive input to CTR 0 OUT (pin 2) and your

counter negative input to D GND (pin 35).

2. Create a task using DAQmxCreateTask.

3. Add a counter output channel to the task using

DAQmxCreateCOPulseChanFreq (DAQmx Create

Virtual Channel VI) and configure the channel.

NI-DAQ Function Call LabVIEW Block Diagram

Call DAQmxCreateTask with the

following parameters:

taskName:

MyCounterOutputTask

taskHandle: &taskHandle

LabVIEW does not require this step.

NI-DAQ Function Call LabVIEW Block Diagram

Call

DAQmxCreateCOPulseChanFreq

with the following parameters:

taskHandle: taskHandle

counter: dev1/ctr0

nameToAssignToChannel:

CounterOutputChannel

units: DAQmx_Val_Hz

idleState: DAQmx_Val_Low

initialDelay: 0.0

freq: 5000000.0

dutyCycle: .5

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