Measurement Computing PCI-DAS6023 - Manual (Page 30)

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Chapter 4
Calibrating the Board
Introduction
We recommend that you calibrate the board using the InstaCal utility after the board has fully warmed up. The
recommended warm-up time is 15 minutes. For best results, calibrate the board immediately before making
critical measurements. The high resolution analog components on the board are somewhat sensitive to
temperature. Pre-measurement calibration insures that your board is operating at optimum calibration values.
Calibration theory
Analog inputs are calibrated for offset and gain. Offset calibration for the analog inputs is performed directly on
the input amplifier, with coarse and fine trim DACs acting on the amplifier.
For input gain calibration, a precision calibration reference is used in conjunction with coarse and fine trim
DACs acting on the ADC. See Figure 29.
Analog In
ADC
Trim DAC
Coarse
Trim DAC
Fine
Trim DAC
Coarse
Trim DAC
Fine
MUX
Gain Adjust
Offset
Adjust
Gain
Calibration
Reference
Figure 29. Analog input calibration
A similar method is used to calibrate the analog output components (PCI-DAS6025 only). A trim DAC is used
to adjust the gain of the DAC. A separate DAC is used to adjust offset on the final output amplifier. The
calibration circuits are duplicated for both analog outputs. See Figure 30.
Trim DAC
Ref
DAC
Gain
Adjust
Analog Out
Trim DAC
Offset
Adjust
Figure 30. Analog output calibration