National Instruments NI 6703 Manuale

NI 6703/6704 Calibration

Procedure for Traditional NI-DAQ

Introduction

This document contains instructions for calibrating the NI 6703/6704 for

PCI/PXI/CompactPCI using Traditional NI-DAQ. Use this calibration

procedure with the ni6704Cal.dll file, which contains specific functions

required for calibrating the NI 6703/6704.

The NI 6703/6704 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.

Note Refer to ni.com/support/calibrat/mancal.htm for a copy of the

ni6704Cal.dll file.

Calibration Options: External Versus Internal

NI 6703/6704 products have two calibration options, an internal or

self-calibration, and an external calibration.

Internal Calibration

The NI 6703/6704 is continuously applying corrections to the output levels

based on previous calibration results. Both the NI 6703 and the NI 6704

have 16 voltage outputs and two voltage calibration channels. The NI 6704

also has 16 current outputs and two current calibration channels. All the

output and calibration channels are scanned and refreshed together. The

outputs of the calibration channels for the NI 6703/6704 are continuously

compared to the onboard reference, and the offset and gain of the 16-bit

digital-to-analog converter (DAC) are adjusted to minimize the error of the

calibration channels. Because the NI 6703 and NI 6704 have excellent

channel-to-channel matching of offset and gain errors, minimizing the error

on the calibration channels also minimizes the error for all of the voltage

and current outputs.

™

NI 6703/6704 Calibration Procedure for Traditional NI-DAQ 2 ni.com

External Calibration

External calibration requires a high-precision digital multimeter (DMM)

to measure error on the NI 6703/6704 outputs. The error is then corrected

with a set of calibration constants that adjust the offset and gain of the

16-bit DAC to ensure that the output voltages and currents are within the

device specifications.

Because of the NI 6703/6704 calibration circuitry, the only calibration

adjustment you must make is to the values of the calibration channels to

account for time- or temperature-related drift of the onboard reference.

Equipment and Other Test Requirements

This section describes the equipment, test conditions, documentation, and

software you need to calibrate the NI 6703/6704.

Test Equipment

To calibrate the NI 6703/6704, you need a high-precision DMM that is at

least 10 ppm (0.001%) accurate. NI recommends that you use the

Hewlett-Packard 3458A DMM for calibration.

If you do not have a Hewlett-Packard 3458A DMM, use the accuracy

specifications to select a substitute calibration standard.

If you do not have custom connection hardware, you may need a connector

block such as the NI CB-68 and a cable such as the SH6868-D1. These

components give you easy access to the individual pins on the 68-pin

I/O connector.

Test Conditions

Follow these guidelines to optimize connections and test conditions during

calibration:

• Keep connections to the NI 6703/6704 short. Long cables and wires

act as antennae, picking up extra noise that 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.

©National Instruments Corporation 3 NI 6703/6704 Calibration Procedure for Traditional NI-DAQ

Software

Because the NI 6703/6704 is a PC-based measurement device, you must

have the proper device driver installed in the calibration system before

attempting calibration. For this calibration procedure, you need the latest

version of NI-DAQ installed on the calibration computer. NI-DAQ,

which configures and controls the NI 6703/6704, is available at

ni.com/downloads.

NI-DAQ supports a number of programming languages, including

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

Basic and Borland C ++. When you install the driver, you only need to

install support for the programming language that you intend to use.

You also need a copy of the ni6704Cal.dll, ni6704Cal.lib, and

ni6704Cal.h files.

The DLL provides calibration functionality that does not reside in NI-DAQ,

including the ability to protect the calibration constants, update the

calibration date, and write to the factory calibration area. The factory

calibration area and the calibration date should only be modified by a

metrology laboratory or another facility that maintains traceable standards.

You can access the functions in this DLL through any 32-bit compiler.

Configuring the NI 6703/6704 in NI-DAQ

The NI 6703/6704 must be configured in NI-DAQ, which automatically

detects the device. The following steps briefly explain how to configure

NI-DAQ. Refer to the PCI/PXI-6703/6704 User Manual for detailed

installation instructions. You can install this manual when you install

NI-DAQ.

1. Power off the computer.

2. Install the NI 6703/6704 in an available slot.

3. Power on the computer.

4. Launch Measurement & Automation Explorer (MAX).

5. Configure the NI 6703/6704 device number.

6. Click the Test Resources button to ensure that the NI 6703/6704 is

working properly.

The NI 6703/6704 is now configured.

Note After a device is configured in MAX, the device is assigned a device number.

This number is used in each of the function calls to identify which DAQ device is to

be calibrated.

NI 6703/6704 Calibration Procedure for Traditional NI-DAQ 4 ni.com

Writing the Calibration Procedure

The calibration procedure in the Calibrating the NI 6703/6704section

provides instructions for calling the appropriate calibration functions.

These calibration functions are C function calls from NI-DAQ that are also

valid for Visual Basic programs. Although LabVIEW VIs are not discussed

in this procedure, you can program in LabVIEW using the VIs that are

named similarly to the NI-DAQ function calls in this procedure. Refer to

the Flowcharts section for illustrations of the code used at each step of the

calibration procedure.

Often you must follow a number of compiler-specific steps to create an

application that uses NI-DAQ. Refer to the NI-DAQ User Manual for PC

Compatibles at ni.com/manuals for details about the required steps for

each of the supported compilers.

Many of the functions listed in the calibration procedure use variables that

are defined in the nidaqcns.h file. To use these variables, you must

include the nidaqcns.h file in the code. If you do not want to use these

variable definitions, you can examine the function call listings in the

NI-DAQ documentation and the nidaqcns.h file to determine what input

values are required.

Documentation

For information about NI-DAQ, refer to the following documentation:

• Traditional NI-DAQ Function Reference Help (Start»Programs»

National Instruments»NI-DAQ»Traditional NI-DAQ Function

Reference Help)

• NI-DAQ User Manual for PC Compatibles at ni.com/manuals

These two documents provide detailed information about using NI-DAQ.

The function reference help includes information about the functions in

NI-DAQ. The user manual provides instructions on installing and

configuring DAQ devices and detailed information about creating

applications that use NI-DAQ. These documents are the primary references

for writing the calibration utility. For further information about the products

you are calibrating, you may also want to install the PCI/PXI-6703/6704

User Manual.

Calibrating the NI 6703/6704

To calibrate the NI 6703/6704, complete the following steps:

1. Verify the performance of the NI 6703/6704. This step, which is

covered in the Verifying the Performance of the NI 6703/6704 section,

confirms whether the device is in specification prior to adjustment.

©National Instruments Corporation 5 NI 6703/6704 Calibration Procedure for Traditional NI-DAQ

2. Adjust the NI 6703/6704 calibration constants with respect to a

known voltage source. This step is described in the Adjusting the

NI 6703/6704 section.

3. Reverify the performance to ensure that the NI 6703/6704 is operating

within its specifications after adjustment.

Verifying the Performance of the NI 6703/6704

Verification determines how well the device is meeting its specifications.

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

Throughout the verification process, refer to the tables in the Specifications

section to see if the device needs to be adjusted.

Verifying Voltage Output

This procedure verifies whether the output of voltage channel 0 is within

specifications. Because of the channel-to-channel matching of the

NI 6703/6704 voltage channels, if voltage channel 0 is operating within

specifications, all the voltage channels should be operating within

specifications.

If you want to verify the channels individually, this procedure can be easily

expanded to verify all the voltage channels. Perform the procedure once for

each value of the channel parameter from 0 to 15. Each time you repeat the

procedure, you also need to connect the appropriate channel to the DMM.

Refer to the PCI/PXI-6703/6704 User Manual at ni.com/manuals for the

pin numbers corresponding to each channel. To verify the voltage output,

read the Equipment and Other Test Requirements section, and complete the

following steps:

1. Call the Get_Cal_Date function contained in ni6704Cal.dll to

determine the previous calibration date of the NI 6703/6704.

2. Connect the DMM to the NI 6703/6704 as shown in the following

table.

3. Place the DMM in voltage mode.

4. Call AO_VWrite to generate 9.9 V on voltage channel 0. Set the

following parameters:

•chan: 0

•voltage: 9.9

Signal Name Description NI 6703/6704 Output DMM Input

VCH0 Voltage Channel 0 Pin 34 High

AGND0 Analog Ground 0 Pin 68 Low

NI 6703/6704 Calibration Procedure for Traditional NI-DAQ 6 ni.com

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

lower limits listed in Table 1 in the Specifications section. If the value

is between these limits, the device passes the test.

6. Call AO_VWrite to generate 0.0 V on voltage channel 0. Set the

following parameters:

•chan: 0

•voltage: 0.0

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

lower limits listed in Table 1 in the Specifications section. If the value

is between these limits, the device passes the test.

8. Call AO_VWrite to generate –9.9 V on voltage channel 0. Set the

following parameters:

•chan: 0

•voltage: –9.9

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

lower limits listed in Table 1 in the Specifications section. If the value

is between these limits, the NI 6703/6704 passes voltage verification.

10. Disconnect the DMM from the NI 6703/6704.

You have now verified the voltage output of the NI 6703/6704.

Verifying Current Output (NI 6704 Only)

This procedure verifies that the current output of channel 16 is within

specifications. Because of the channel-to-channel matching of the NI 6704

current channels, if current channel 16 is operating within specifications,

all the current channels should be operating within specifications.

However, you can verify the channels individually for each current

channel. Perform the procedure once for each value of the channel

parameter from 16 to 31. You also need to connect the appropriate channel

to the DMM each time you repeat the procedure. Refer to the

PCI/PXI-6703/6704 User Manual for the pin numbers corresponding to

each channel.

To verify current output, complete the following steps:

1. Call the Get_Cal_Date function to determine the previous calibration

date of the NI 6704.

2. Connect the DMM to the NI 6704 as shown in the following table.

Signal Name Description NI 6704 Output DMM Input

ICH16 Current Channel 16 Pin 67 High

AGND16 Analog Ground 16 Pin 68 Low

©National Instruments Corporation 7 NI 6703/6704 Calibration Procedure for Traditional NI-DAQ

3. Place the DMM in current mode.

4. Call AO_VWrite to generate 0.1 mA on current channel 16. Set the

following parameters:

•chan: 16

•voltage: 0.1

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

lower limits listed in Table 2 in the Specifications section. If the value

is between these limits, the device passes the test.

6. Call AO_VWrite to generate 20.0 mA on current channel 16. Set the

following parameters:

•chan: 16

•voltage: 20.0

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

lower limits listed in Table 2 in the Specifications section. If the value

is between these limits, the device passes current verification.

8. Disconnect the DMM from the NI 6704.

You have now verified the current output of the NI 6704.

Adjusting the NI 6703/6704

At the end of each calibration procedure, new constants are stored in

the user calibration area of the NI 6703/6704, ensuring that the device

stores a permanent record of the calibration constants. Storing the

calibration constants here also ensures that the constants automatically load

when the NI 6703/6704 is powered on.

Adjusting Voltage Output

For the voltage outputs, you need to make offset and gain adjustments.

Adjust offsets first, followed by gains. Adjust offset and gain again to

ensure accuracy. This second set of offset and gain adjustments is

necessary because a large initial change in one of the calibration channels

can affect the accuracy of the other calibration channel.

The following table lists the offset and gain channel numbers.

Calibration Channel NI 6703 Channel Numbers NI 6704 Channel Numbers

Voltage Offset 16 32

Voltage Gain 17 34

NI 6703/6704 Calibration Procedure for Traditional NI-DAQ 8 ni.com

To measure voltage outputs, complete the following steps:

1. Call Set_DAQ_Device_Info to configure the NI 6703/6704 so that

you can access the calibration channels. Set the following parameters:

•infoType: ND_CALIBRATION_ENABLE

•infoValue: ND_YES

2. Connect the DMM to the NI 6703/6704 as shown in the following

table.

3. Place the DMM in voltage mode.

4. Call AO_VWrite to generate 0.0 V on voltage channel 0. Set the

following parameters:

•chan: 0

•voltage: 0.0

5. Call AO_VWrite with the channel set to the voltage offset channel.

Adjust the voltage parameter until the DMM reads as close to 0.0 V as

possible. The value you write to the voltage offset channel is close to

0.0 V. Increasing the voltage value lowers the magnitude of the voltage

on voltage channel 0. Decreasing the voltage value increases the

magnitude of the voltage on voltage channel 0.

6. Call AO_VWrite to generate 10.0 V on voltage channel 0. Set the

following parameters:

•chan: 0

•voltage: 10.0

7. Call AO_VWrite with the channel set to the voltage gain channel.

Adjust the voltage parameter until the DMM reads as close to 10.0 V

as possible. The value you write to the voltage gain channel is close to

10.0 V. Increasing the voltage value lowers the magnitude of the

voltage on voltage channel 0. Decreasing the voltage value increases

the magnitude of the voltage on voltage channel 0.

You have now adjusted the voltage output.

Adjusting Current Output (NI 6704 Only)

For the current outputs, you need to adjust offset and gain. Adjust offset

first, followed by gain. Adjust both offset and gain again to ensure

accuracy. This second set of offset and gain adjustments is necessary

Signal Name Description NI 6703/6704 Output DMM Input

VCH0 Voltage Channel 0 34 High

AGND0 Analog Ground 0 68 Low

©National Instruments Corporation 9 NI 6703/6704 Calibration Procedure for Traditional NI-DAQ

because a large initial change in one of the calibration channels can affect

the accuracy of the other calibration channel. Refer to the offset and gain

channel numbers in the following table.

To adjust current output, complete the following steps:

1. Call Set_DAQ_Device_Info to configure the NI 6704 so you can

access the calibration channels. Set the following parameters:

•infoType: ND_CALIBRATION_ENABLE

•infoValue: ND_YES

2. Connect the DMM to the NI 6704 as shown in the following table.

3. Place the DMM in current mode.

4. Call AO_VWrite to generate 0.1 mA on current channel 16. Set the

following parameters:

•chan: 16

•voltage: 0.1

5. Call AO_VWrite with the channel set to the current offset channel.

Adjust the voltage parameter until the DMM reads as close to 0.1 mA

as possible. The value you write to the current offset channel is close

to 0.01 mA. Increasing the voltage value lowers the magnitude of the

current on current channel 16. Decreasing the voltage value increases

the magnitude of the current on current channel 16.

6. Call AO_VWrite to generate 20.0 mA on current channel 16. Set the

following parameters:

•chan: 16

•voltage: 20.0

Calibration Channel NI 6704 Channel Numbers

Current Offset 33

Current Gain 35

Signal Name Description NI 6704 Output DMM Input

ICH16 Current Channel 16 Pin 67 High

AGND16 Analog Ground 16 Pin 68 Low

NI 6703/6704 Calibration Procedure for Traditional NI-DAQ 10 ni.com

7. Call AO_VWrite with the channel set to the current gain channel.

Adjust the voltage parameter until the DMM reads as close to 20.0 mA

as possible. The value you write to the current gain channel is close to

19.608 mA. Increasing the voltage value lowers the magnitude of the

current on current channel 16. Decreasing the voltage value increases

the magnitude of the current on current channel 16.

You have now adjusted the current output.

Saving Calibration Values

After you have adjusted the calibration constants, you must store the new

calibration constants in the user calibration area of the NI 6703/6704

EEPROM to ensure that the new calibration values are permanently saved

and automatically loaded when the NI 6703/6704 is powered on. If the

calibration is being performed by a metrology laboratory or another facility

that maintains traceable standards, the calibration values should also be

stored in the factory calibration area. Calibration constants stored in the

factory calibration area cannot be overwritten by the user.

To save the calibration constants and update the calibration dates, complete

the following steps:

1. Call AO_Calibrate to store the new calibration constants in the user

calibration area of the EEPROM. Set the following parameters:

•operation: 2

•calibrationArea: 1

2. Call Set_DAQ_Device_Info to configure the NI 6703/6704 so it is

no longer possible to access the calibration channels. Set the following

parameters:

•infoType: ND_CALIBRATION_ENABLE

•infoValue: ND_NO

3. If the calibration is being performed by a metrology laboratory or

another facility that maintains traceable standards, call the Copy_Cal

function in the ni6704Cal.dll. Calling this function copies the

calibration values to the factory calibration area and updates the

calibration date to match the system clock of the calibration computer.

The NI 6703/6704 is now adjusted.

Verifying the New Calibration Constants

You can verify the new calibration constants by repeating the Verifying the

Performance of the NI 6703/6704 section.

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