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Chapter 6 Calibration Procedures
AT-MIO-16X User Manual 6-8
©
National Instruments Corporation
It is important to realize that inaccuracy of the internal voltage
reference results only in gain error. Offset error is unaffected. If an
application can tolerate slight gain inaccuracy, there should not be a
need to redetermine the value of the onboard reference.
Calibration DACs
There are eight 8-bit DACs (CALDAC<0..7>) and one 12-bit DAC
(CALDAC8) on the AT-MIO-16X that are used for calibration. These
DACs are described in Table 6-2.
Reference Calibration
The AT-MIO-16X has a stable voltage reference to which gain can be
calibrated. The value of this voltage reference is determined through the
reference calibration routine, which requires a known external voltage
between 5 and 9.99 V to be connected differentially on any desired
input channel. The routine calibrates the circuitry to the external
reference and then reads the internal reference. This value is stored as
Table 6-2.
Calibration DACs
Analog DAC Function Adjustment
Range
Incremental
Effect
Input CALDAC0 Coarse gain trim ±1169 ppm –9.13 ppm
CALDAC1 Fine gain trim ±65.1 ppm –0.509 ppm
CALDAC2 Coarse postgain offset trim ±51.8 ppm 404 µV
CALDAC3 Fine postgain offset trim ±512 µV 4.00 µV
CALDAC8 Pregain offset trim ±1.2 µV 0.586 µV
Output CALDAC4 DAC0 gain trim ±976 ppm 7.62 ppm
CALDAC5 DAC1 gain trim ±976 ppm 7.62 ppm
CALDAC6 DAC0 offset trim ±4.86 mV 38.0 µV
CALDAC7 DAC1 offset trim ±4.86 mV 38.0 µV