User`s manual

Calibration 51
5 Calibration
This chapter introduces the calibration process to minimize AD
meas-urement errors and DA output errors.
DAQ/PXI-2500 SERIES is factory calibrated before shipment.
The on-board high precision band-gap voltage reference together
with TrimDAC compensates for unwanted offsets and gain errors,
caused by environment variation or component aging.
5.1 Auto-calibration
The auto-calibration feature of DAQ/PXI-2500 SERIES facilitates
users completing a calibration process, without the necessities for
any external voltage references or measurement devices.
The on-board auto-calibration circuitry is composed of a precision
band-gap voltage reference, an ADC and a TrimDAC. TrimDAC is
a multi-channel DAC that generates DC offsets that counteract the
offsets from the main DACs. Digital codes for the TrimDAC, as
well as the tem-perature and the date of the calibration, are stored
in the onboard EEPROM. We do not recommend end-users to
adjust the onboard band-gap voltage reference in anyway, unless
an ultra-precision calibrator is available.
Due to temperature, humidity variations, and component aging,
the preci-sion of DAQ board may degrade over time. It is sug-
gested that users pe-riodically calibrate the DAQ board. The user
calibration constants can also be stored in the on-board EEPROM.
NOTE:
1. Before auto-calibration procedure starts, it is recom-
mended to warn up the board for at least 15 minutes.
2. Please remove the cable before auto-calibration,
because the D/A outputs would be changed in the pro-
cess.