Calibrating The Pci-Das1602/16; Analog Input Calibration - Measurement Computing PCI-DAS1602/16 User Manual

Calibrating the PCI-DAS1602/16

The PCI-DAS1602/16 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-DAS1602/16'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 directly on the input amplifier
with trim DACs acting on the amplifier. Input gain calibration is performed with the precision voltage
reference.
Front-end offset corrections are typically performed at the gain stage and/or the ADC input. Offset calibration
is performed in the instrumentation amplifier gain stage. Front-end gain adjustment is only performed via the
ADC reference, 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 input calibration system is shown in Figure 5.
Calibration
Reference
Trim DAC
Analog In
Offset Unipolar/
Adjust Bipolar
Figure 5. Analog input calibration
18
ADC
Offset
Ref.
Adjust
Digital Offset Digital Gain
Pot. Pot.
Chapter 4