Chapter 5 Calibration
DAQCard-1200 User Manual 5-2 © National Instruments Corporation
Calibration at Higher Gains
The DAQCard-1200 has a maximum gain error of 0.8%. This means that if
the card is calibrated at a gain of 1, and if the gain is switched to 100, a
maximum of 32 LSB error may result in the reading. Therefore, when you
are recalibrating the DAQCard-1200, you should perform gain calibration
at all other gains (2, 5, 10, 20, 50, and 100), and store the corresponding
values in the user gain calibration data area of the EEPROM, thus ensuring
a maximum error of 0.02% at all gains. The DAQCard-1200 is
factory-calibrated at all gains, and NI-DAQ automatically loads the correct
values into the calibration DACs whenever you switch gains.
Calibration Equipment Requirements
The equipment you use to calibrate the DAQCard-1200 should have a
±0.001% rated accuracy, which is 10 times as accurate as the
DAQCard-1200. However, calibration with only four times the accuracy as
the DAQCard-1200 and a ±0.003% rated accuracy is acceptable. The
inaccuracy of the calibration equipment results only in gain error; offset
error is unaffected.
Calibrate the DAQCard-1200 to a measurement accuracy of ±0.5 LSBs,
which is within ±0.012% of its input range.
For analog input calibration, use a precision DC voltage source, such as a
calibrator, with the following specifications.
• Voltage approximately 4 V (bipolar), 9 V (unipolar)
• Accuracy ±0.001% standard
±0.003% acceptable
Using the Calibration Function
NI-DAQ contains the Calibrate_1200 function, with which you can
either load the calibration DACs with the factory constants or the
user-defined constants stored in the EEPROM, or perform your own
calibration and directly load these constants into the calibration DACs.
Touse the Calibrate_1200 function for analog input calibration, you
must ground an analog input channel at the front connector, for offset
calibration, and apply an accurate voltage reference to another input
channel, for gain calibration. For analog output calibration, the DAC0 and
DAC1 outputs must be wrapped back and applied to two other analog input
channels.