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Chapter 5 Calibration

Voltage Output Calibration

There are two adjustments to make for the voltage outputs: offset and gain.

You should perform offset adjustment first. It is a good idea to calibrate

twice, because a large change in the voltage gain channel value could

impact the accuracy of the offset calibration.

Offset Adjustment

To calibrate the offset, set one of the voltage output channels to 0 V and

measure it with a precise voltmeter. Then, change the voltage offset

channel value until the output is zero. The voltage you write to the voltage

offset channel will be close to zero, and increasing it will lower the voltage

you measure.

Gain Adjustment

To calibrate the gain, set the voltage output channel to a voltage near

full-scale, such as +10 V. Then, change the voltage gain channel value until

the output that you measure is as close as possible to the voltage that you

wrote to the output channel. The voltage you write to the voltage gain

channel will be close to +10 V, and increasing it will lower the magnitude

of the voltage you measure.

You can also calibrate using several output channels, instead of just one, by

averaging channels together. Do this by writing the values to all the

channels you wish to average and using a resistive averaging circuit to

average the outputs. This will reduce the sensitivity of the calibration

process to interchannel mismatch—the slight differences in the output

characteristics of the channels—by averaging out these differences.

Current Output Calibration for the 6704

There are two adjustments to make for the current outputs: offset and gain.

You should perform offset adjustment first. It is a good idea to calibrate

twice, because a large change in the current gain channel value could

impact the accuracy of the offset calibration.

Offset Adjustment

To calibrate the offset, set one of the current output channels to 100 µA and

measure it with a precise ammeter. Then, change the current offset channel

value until the output is as close as possible to 100 µA. The current you

National Instruments PCI-6703 User Manual

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