Measurement Computing PCI-DAS1200 - Manual (Page 16)

15
Chapter 3
Calibrating the board
Calibrate the board using InstaCal 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-DAS1200 is shipped fully calibrated from the factory. Calibration coefficients are stored in nvRAM.
When using the Universal Library at run time, these calibration factors are loaded into system memory and
automatically retrieved each time you specify a different DAC/ADC range.
The analog input circuits are calibrated for 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 diagram
The analog output circuits are calibrated for both gain and offset (Figure 4). This circuit is duplicated for both
DAC0 and DAC1.

Offset adjustments for the analog output are made in the output buffer section. The tuning range of this
adjustment allows for max DAC and output buffer offsets.
 Gain calibration of the analog outputs are 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 diagram