External calibration is the most involved calibration procedure and it requires a highly precise voltage source. When an external calibration is performed, the EEPROM calibration constants are physically overwritten and new ones are applied. This procedure requires using a high-precision voltage source to verify and adjust calibration constants. Because the external calibration procedure changes all EEPROM constants, it invalidates the original calibration certificate. If an external calibration is done with a NIST-certified voltage source, a new NIST traceability certificate can be issued. External calibration is typically performed by a metrology lab, but can be performed in LabVIEW.
The Calibration Procedure Manual
article provides specific guidelines for performing an external calibration for specific measurement hardware. The calibration procedure manuals do not discuss programming techniques or compiler configuration.
Additionally, NI-DAQmx includes high-level function calls to simplify the task of writing software to calibrate devices. DAQmx Calibration VIs and Functions are available in LabVIEW to perform both internal and external calibrations. For information on these VIs, refer to the Help Manual information: DAQmx Manual: DAQmx Calibration VIs and Functions.
Figure 1 - DAQmx Calibration Functions Palette in LabVIEW
As the calibration procedure manuals describe, the DAQmx Intialize External Calibration VI, DAQmx Adjust Y-Series Calibration (where Y is series of the device), and DAQmx Close External Calibration VI are used to perform the calibration using LabVIEW. More information about these VIs can be found in DAQmx Help and LabVIEW Help.