Measurement Computing PCI-DAS1602/12 - Manual (Page 20)

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Chapter 4
Calibrating the PCI-DAS1602/12
The PCI-DAS1602/12 is equipped with software auto calibration. The InstaCal software makes gain and offset
corrections to the board using on-board digital potentiometers and trim D/A converters. No user intervention or
external equipment is required. The PCI-DAS1602/16 is shipped fully-calibrated from the factory.
All adjustments are made via 8-bit calibration DACs or 7-bit digital potentiometers that are referenced to an on-
board factory calibrated standard. Calibration factors are stored on the serial nvRAM. At run time, these
calibration factors can be loaded into system memory and can be automatically retrieved when a different
DAC/ADC range is specified
You can recalibrate with respect to the factory-measured voltage standards at any time by selecting the
Calibrate menu in InstaCal. Full calibration requires less than two minutes and requires no external equipment
or user adjustments.
The standard calibration involves calibrating one channel with 0 volts input (offset), and then with a known
input voltage (gain). The PCI-DAS1602/12's on board circuitry first shorts the inputs for offset calibration, then
connects the inputs to the ultra-stable precision voltage reference for the gain calibration.
Analog input calibration
Analog inputs are calibrated for offset and gain. Offset calibration is performed in the instrumentation amplifier
gain stage. Front-end gain adjustment is performed via a variable attenuator/gain stage.
The analog input calibration system is shown in Figure 5.
Calibration
Reference
Analog In
Offset
Adjust
Unipolar/
Bipolar
Trim DAC
ADC
Offset
Adjust
Ref.
Digital Offset
Pot.
Digital Gain
Pot.
Figure 5. Analog input calibration