Measurement Computing PCI-DAS6402/16 - Manual (Page 20)

Chapter 4
Calibrating the PCI-DAS6402/16
Overview
The PCI-DAS6402/16 provides self-calibration of the analog inputs and outputs, eliminating the need for
external equipment and user adjustments. All adjustments are made via 8-bit calibration DACs and digital
potentiometers that are referenced to an on-board factory-calibrated standard. The board is fully calibrated at the
factory with calibration coefficients stored in nvRAM. At run time, these calibration factors are loaded into
system memory and are automatically retrieved each time a different DAC/ADC range is specified.
You can recalibrate any time using factory voltage standards by selecting the Calibrate option in InstaCal. A
full calibration typically requires less than two minutes. We strongly recommend that you turn your computer
on, and allow at least 60 minutes for the internal computer case temperature to stabilize prior to calibrating the
board.
Calibration theory
Offset calibration for the analog front end is performed via adjustments of the ADC itself. Front-end gain
adjustment is performed only via the ADC reference. This strategy was chosen since the gain tolerance of the
in-amp circuit is quite good and there is adequate gain tuning range using only the ADC.
Analog input calibration is shown in . Figure 4-1
Figure 4-1. Analog input calibration
Calibration
Reference
Analog In
Offset
Adjust
Unipolar/
Bipolar
ADC
Offset
Adjust
Ref.
Digital offset
potential
Digital gain
potential
4-1