AO Waveform Calibration Procedure for NI-DAQmx

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
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.
AO Waveform Calibration Procedure for NI-DAQmx
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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.
© National Instruments Corporation
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AO Waveform Calibration Procedure for NI-DAQmx
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.
DMM
Counter
LO
HI
Accessory
AO Device
CTR 0 OUT
AO GND
Shielded Cable
AO x
AO GND
AO EXT REF
HI
LO
Calibrator
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.
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•
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.
© National Instruments Corporation
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AO Waveform Calibration Procedure for NI-DAQmx
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.
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.
Note
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)
AO Waveform Calibration Procedure for NI-DAQmx
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Table 1. Connecting the DMM to AO <0..7> (Continued)
Output Channel
DMM Positive Input
DMM Negative Input
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
© National Instruments Corporation
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)
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AO Waveform Calibration Procedure for NI-DAQmx
Table 2. Connecting the DMM to AO <8..31> on the NI 6723 (Continued)
Output Channel
DMM Positive Input
DMM Negative Input
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)
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:
LabVIEW does not require this step.
taskName: MyAOVoltageTask
taskHandle: &taskHandle
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
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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
© National Instruments Corporation
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AO Waveform Calibration Procedure for NI-DAQmx
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
Call DAQmxCreateTask with the
following parameters:
LabVIEW Block Diagram
LabVIEW does not require this step.
taskName: MyCounterOutputTask
taskHandle: &taskHandle
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
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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.
© National Instruments Corporation
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AO Waveform Calibration Procedure for NI-DAQmx
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
AO Waveform Calibration Procedure for NI-DAQmx
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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: DAQmx_Val_
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.
© National Instruments Corporation
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AO Waveform Calibration Procedure for NI-DAQmx
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.
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NI 6711/6713—12-Bit Resolution
Table 4. NI 6711/6713 Analog Output Values
Range (V)
Test Point
24-Hour Ranges
1-Year Ranges
Minimum
Maximum
Location
Value (V)
Lower
Limit (V)
Upper
Limit (V)
Lower
Limit (V)
Upper
Limit (V)
–10
10
0
0.0
–0.0059300
0.0059300
–0.0059300
0.0059300
–10
10
Pos FS
9.9900000
9.9822988
9.9977012
9.9818792
9.9981208
–10
10
Neg FS
–9.9900000
–9.9977012
–9.9822988
–9.9981208
–9.9818792
Table 5. NI 6711/6713 Counter Values
Set Point (MHz)
Upper Limit (MHz)
Lower Limit (MHz)
5
5.0005
4.9995
NI 6722/6723—13-Bit Resolution
Table 6. NI 6722/6723 Analog Output Values
Range (V)
Test Point
24-Hour Ranges
1-Year Ranges
Minimum
Maximum
Location
Value (V)
Lower
Limit (V)
Upper
Limit (V)
Lower
Limit (V)
Upper
Limit (V)
–10
10
0
0.0
–0.0070095
0.0070095
–0.0070095
0.0070095
–10
10
Pos FS
9.9000000
9.8896747
9.9103253
9.8892582
9.9107418
–10
10
Neg FS
–9.9000000
–9.9103253
–9.8896747
–9.9107418
–9.8892582
Table 7. NI 6722/6723 Counter Values
Set Point (MHz)
Upper Limit (MHz)
Lower Limit (MHz)
5
5.0005
4.9995
© National Instruments Corporation
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AO Waveform Calibration Procedure for NI-DAQmx
NI 6731/6733—16-Bit Resolution
Table 8. NI 6731/6733 Analog Output Values
Range (V)
Test Point
24-Hour Ranges
1-Year Ranges
Minimum
Maximum
Location
Value (V)
Lower
Limit (V)
Upper
Limit (V)
Lower
Limit (V)
Upper
Limit (V)
–10
10
0
0.0
–0.0010270
0.0010270
–0.0010270
0.0010270
–10
10
Pos FS
9.9900000
9.9885335
9.9914665
9.9883636
9.9916364
–10
10
Neg FS
–9.9900000
–9.9914665
–9.9885335
–9.9916364
–9.9883636
Table 9. NI 6731/6733 Counter Values
Set Point (MHz)
Upper Limit (MHz)
Lower Limit (MHz)
5
5.0005
4.9995
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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.
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