Omega PCI-DAS1602/16, User Manual, Page: 12 / 39

7.0 Self-Calibration of the PCI-DAS1602/16
The PCI-DAS1602/16 provides self-calibration of the analog source and measure systems
thereby eliminating the need for external equipment and user adjustments. All adjustments are
made via 8-bit calibration DACs or digital potentiometers referenced to an on-board factory
calibrated standard. The PCI-DAS1602/16 is shipped fully-calibrated from the factory with cal
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. The
user has the option to recalibrate with respect to the factory-measured voltage standards at any
time by simply selecting the "Calibrate" option in InstaCal. Full calibration typically requires
less than two minutes and requires no user intervention.
7.1 Analog Input Calibration
A variety of methods are used to calibrate the different elements on the board. The analog front-
end has several "knobs" to turn. Offset calibration is performed in both the instrumentation
amplifier gain stage and 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.
The analog output circuits are calibrated for gain and offset as well. 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.
Figure 1 below is a block diagram of the analog front-end calibration system:
Analog-In
ADC
Cal
Ref
T r i m D a c
O f f s e t
Ref Offset Adj
Offset Adj Uni/Bip
Digital Gain Pot Digital Offset Pot
Figure 1
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