National Instruments Lab-PC+, User Manual

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© National Instruments Corporation 5-1 Lab-PC+ User Manual
Chapter 5
Calibration
This chapter discusses the calibration procedures for the Lab-PC+ analog input and analog output
circuitry.
The Lab-PC+ is calibrated at the factory before shipment. In order to maintain the 12-bit
accuracy of the Lab-PC+ analog input and analog output circuitry, recalibration at six-month
intervals is recommended. Recalibration is also recommended whenever the input or output
configuration is changed.
Factory calibration is performed with the Lab-PC+ in its default factory configuration:
• -5 to +5 V analog input range (bipolar)
• -5 to +5 V analog output range (bipolar)
Calibration Equipment Requirements
For best measurement results, you should calibrate the Lab-PC+ so that its measurement
accuracy is within
±
0.012% of its input range (
±
0.5 LSB). According to standard practice, the
equipment used to calibrate the Lab-PC+ should be 10 times as accurate, that is, have
±
0.001% rated accuracy. Practically speaking, calibration equipment with four times the
accuracy of the item under calibration is generally considered acceptable. Four times the
accuracy of the Lab-PC+ is 0.003%. You need the following equipment to calibrate the
Lab-PC+ board.
For analog input calibration, you need a precision variable DC voltage source (usually a
calibrator) with these features:
Accuracy
±
0.001% standard
±
0.003% sufficient
Range Greater than
±
10 V
Resolution 100
µ
V in
±
10 V range (5
1
/
2
digits)
For analog output calibration, you need a voltmeter with these features:
Accuracy
±
0.001% standard
±
0.003% sufficient
Range Greater than
±
10 V
Resolution 100
µ
V in
±
10 V range (5
1
/
2
digits)