Measurement Computing PCI-DAS1002 - Manual (Page 17)

17
Chapter 3
Calibrating the Board
Introduction
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 sensitive to temperature. Pre-measurement calibration
ensures that your board is operating at optimum calibration values.
Calibration theory
The PCI-DAS1002 is shipped fully calibrated from the factory with calibration coefficients stored in nvRAM.
When using Universal Library at run time, these calibration factors are loaded into system memory and are
automatically retrieved each time a different DAC/ADC range is specified.
The analog input circuits are calibrated for both offset and gain (Figure 3).
 Offset calibration for the analog input is performed directly on the input amplifier (PGIA) with coarse and
fine trim DACs acting on the amplifier.
 For input gain calibration, a precision calibration reference is used with coarse and fine trim DACs acting
on the ADC.
PGIA Analog In A/D
Trim DAC
Coarse
Trim DAC
Fine
Pre-Gain
Offset
Variable
Gain
Figure 3. Analog input circuit calibration
The analog output circuits are calibrated for both offset and gain (Figure 4). This circuit is duplicated for both
DAC0 and DAC1.
 Offset adjustments are made in the output buffer section. The tuning range of this adjustment allows for
max DAC and output buffer offsets.
 Gain calibration is performed via DAC reference adjustments.
Trim DAC
Ref
D/A
Gain
Adjust
Analog Out
Offset
Adjust
Trim DAC
Coarse
Trim DAC
Fine
Figure 4. Analog output circuit calibration