National Instruments Low-Cost Multifunction I/O Board for ISA Lab-PC+ User Manual download pdf (Page 74)

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 µV in ±10 V range (5

/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 µV in ±10 V range (5

/2 digits)

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National Instruments Low-Cost Multifunction I/O Board for ISA Lab-PC+ User Manual Page 74