NATIONAL INSTRUMENTS AO Waveform Calibration Procedure for NI-DAQmx User Guide

AO Waveform Calibration Procedure for NI-DAQmx

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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>.
---|---
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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.

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 ™  ,  icrosoft 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.

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/673X or the SH68-C68-S with the NI 672X.
• 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/673X short. 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.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 Limits section 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)

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

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

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

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.
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxCreateTask with the following parameters:
   taskName : MyAOVoltageTask
   taskHandle : &taskHandle| LabVIEW does not require this step.
4. Add an AO voltage task using DAQmxCreateAOVoltageChan (DAQmx Create Virtual Channel VI) and configure the channel, AO 0. Use the tables in the AO Device Test Limits section to determine the minimum and maximum values for your device.
   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|
5. Start the acquisition using DAQmxStartTask (DAQmx Start Task VI).
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxStartTask with the following parameters:
   taskHandle : taskHandle|
6. Write a voltage to the AO channel using DAQmxWriteAnalogF64 (DAQmx Write VI) using the table for your device in the AO Device Test Limits section.
   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

|
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 DAQmxClearTask with the following parameter:

taskHandle : taskHandle

|
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.
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxCreateTask with the following parameters:
   taskName : MyCounterOutputTask
   taskHandle : &taskHandle| LabVIEW does not require this step.
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 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|
4. Configure the counter for continuous square wave generation using DAQmxCfgImplicitTiming (DAQmx Timing VI).
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxCfgImplicitTiming with the following parameters:
   taskHandle : taskHandle
   sampleMode : DAQmx_Val_ContSamps
   sampsPerChan : 10000|
5. Start the generation of a square wave using DAQmxStartTask (DAQmx Start Task VI).
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxStartTask with the following parameter:
   taskHandle : taskHandle|
6. The device will begin to generate a 5 MHz square wave when the DAQmxStartTask function completes execution. Compare the value read by your counter to the test limits shown on the device table. If the value falls between these limits, the test is considered to have passed.
7. Clear the generation using DAQmxClearTask (DAQmx Clear Task VI).
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxClearTask with the following parameter:
   taskHandle: taskHandle|
8. Disconnect the counter from your device.
   You have verified the counter on your device.

AO Adjustment Procedure

Use the AO adjustment procedure to adjust the analog output calibration constants. At the end of each calibration procedure, these new constants are stored in the external calibration area of the EEPROM. These values are password-protected, which prevents the accidental access or modification of any calibration constants adjusted by the metrology laboratory. The default password is NI.
To perform adjustment of the device with a calibrator, complete the following steps:

1. Connect the calibrator to the device according to Table 3.
   Table 3. Connecting the Calibrator to the Device 671X/672X/673X Pins| Calibrator
   ---|---
   AO EXT REF (pin 20)| Output High
   AO GND (pin 54)| Output Low
2. Set your calibrator to output a voltage of 5 V.
3. Open a calibration session on your device using DAQmxInitExtCal (DAQmx Initialize External Calibration VI). The default password is NI.
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxInitExtCal with the following parameters:
   deviceName: dev1
   password: NI
   calHandle: &calHandle|
4. Perform an external calibration adjustment using DAQmxESeriesCalAdjust (DAQmx Adjust AO-Series Calibration VI).
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxAOSeriesCalAdjust with the following parameters:
   calHandle: calHandle
   referenceVoltage: 5|
5. Save the adjustment to the EEPROM, or onboard memory, using DAQmxCloseExtCal (DAQmx Close External Calibration). This function also saves the date, time, and temperature of the adjustment to the onboard memory.
   NI-DAQ Function Call| LabVIEW Block Diagram
   ---|---
   Call DAQmxCloseExtCal with the following parameters:
   calHandle: calHandle
   action: DAQmxVal
   Action_Commit|
6. Disconnect the calibrator from the device.

The device is now calibrated with respect to your external source.
After adjusting the device, you may want to verify the analog output operation. To do this, repeat the steps in the AO Verification Procedure section using the 24-hour test limits in the AO Device Test Limits section.

AO Device Test Limits

The tables in this section list the accuracy specifications to use when verifying and adjusting the NI 671X/672X/673X. The tables display the specifications for both 1-year and 24-hour calibration intervals. The 1-year ranges display the specifications that the devices should meet if it has been one year between calibrations. When a device has been calibrated with an external source, the values shown in the 24-hour tables are the valid specifications.
Using the Tables
The following definitions describe how to use the information from the tables in this section.
Range
Range refers to the maximum allowable voltage range of an output signal.
Test Point
The Test Point is the voltage value that is generated for verification purposes. This value is broken down into two columns: Location and Value. Location refers to where the test value fits within the test range. Pos FS stands for positive full-scale and Neg FS stands for negative full-scale. Value refers to the voltage value to be verified and is in volts.
24-Hour Ranges
The 24-Hour Ranges column contains the Upper Limits and Lower Limits for the test point value. That is, when the device is within its 24-hour calibration interval, the test point value should fall between the upper and lower limit values. Upper and lower limits are expressed in volts.
1-Year Ranges
The 1-Year Ranges column contains the Upper Limits and Lower Limits for the test point value. That is, when the device is within its 1-year calibration interval, the test point value should fall between the upper and lower limit values. Upper and lower limits are expressed in volts.
Counters
It is not possible to adjust the resolution of the counter/timers. Therefore, these values do not have a 1-year or 24-hour calibration period. However, the test point and upper and lower limits are provided for verification purposes.
NI 6711/6713—12-Bit Resolution
Table 4. NI 6711/6713 Analog Output Values

Table 5. NI 6711/6713 Counter Values

NI 6722/6723—13-Bit Resolution
Table 6. NI 6722/6723 Analog Output Values

Table 7. NI 6722/6723 Counter Values

NI 6731/6733—16-Bit Resolution
Table 8. NI 6731/6733 Analog Output Values

Table 9. NI 6731/6733 Counter Values

CVI™, LabVIEW™, National Instruments™, NI™, ni.com ™, and NI-DAQ™ are trademarks of National Instruments Corporation. Product and company names mentioned herein are trademarks or trade names of their respective companies. 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.
© 2004 National Instruments Corp. All rights reserved.
All trademarks, brands, and brand names are the property of their respective owners.

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Documents / Resources

| NATIONAL INSTRUMENTS AO Waveform Calibration Procedure for NI- DAQmx [pdf] User Guide
PXI-6733, PCI-6711, PCI-6713, PXI-6711, PXI-6713, DAQCard-6715, 6715, 6731, 6733, PCI-6731, PCI-6733, PXI-6731, PXI-6733, 6722, PCI-6722, PXI-6722, 6723, PCI-6723, PXI-6723, AO Waveform Calibration Procedure for NI-DAQmx, AO Waveform Calibration Procedure, Calibration Procedure for NI-DAQmx, Waveform Calibration Procedure, Calibration Procedure, NI-DAQmx
---|---

References

• Engineer Ambitiously - NI
• National Instruments Patents - NI
• PXI-6733 National Instruments Analog Output Module | Apex Waves

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