User's Manual

Chapter 2 Function Reference — Calibrate_DSA
NI-DAQ FRM for PC Compatibles 2-56
© National Instruments Corporation
Using This Function
Your device contains calibration D/A converters (calDACs) that are used for fine-tuning the
analog circuitry. The calDACs must be programmed (loaded) with certain numbers called
calibration constants. These constants are stored in nonvolatile memory (EEPROM) on your
device. To achieve specification accuracy, you should perform an internal calibration of your
device just before a measurement session but after your computer and the device have been
powered on and allowed to warm up for at least 15 minutes. Frequent calibration produces the
most stable and repeatable measurement performance.
Before the device is shipped from the factory, an external calibration is performed and the
EEPROM contains calibration constants that NI-DAQ automatically loads into the calDACs
as needed. The value of the onboard reference voltage is also stored in the EEPROM, and this
value is used when you subsequently perform a self-calibration. The calibration constants are
recalculated and stored in the EEPROM when a self-calibration is performed. When you
perform an external calibration, NI-DAQ recalculates the value of the onboard reference
voltage and then performs a self-calibration. This new onboard reference value is used for all
subsequent self-calibration operations. If a mistake is made when performing an external
calibration, you can restore the board’s factory calibration so that the board is not unusable.
Performing Self-Calibration of the Board
Set operation to ND_SELF_CALIBRATE to perform self-calibration of your device.
Example:
You want to perform self-calibration of your device and you want to store the new set of
calibration constants in the EEPROM. You should make the following call:
Calibrate_DSA (deviceNumber, ND_SELF_CALIBRATE, 0.0)
Performing External Calibration of the Board
Set operation to ND_EXTERNAL_CALIBRATE to externally calibrate your device. The value
of the internal reference voltage will be recalculated and the board will be self-calibrated
using the new reference value.
Before calling the
Calibrate_DSA function, connect the output of your reference voltage to
analog input channel 0.
Example:
You want to externally calibrate your device using an external reference voltage source with
a precise 7.0500 V reference, and you want to store the new set of calibration constants in the
EEPROM. You should make the following call:
Calibrate_DSA (deviceNumber, ND_EXTERNAL_CALIBRATE, 7.0500)