Calibration

Calibration maximizes the accuracy of the PXIe-4309.

To ensure accuracy, you must perform calibration. The PXIe-4309 uses software calibration to adjust the software scaling of signals it measures and generates. The PXIe-4309 calculates scaling constants for analog input using onboard calibration pulse-width modulated (PWM) sources and an external reference voltage.

The PXIe-4309 supports two types of calibration: external calibration and internal self-calibration.

Factory-calibration constants are permanently stored in an onboard EEPROM and cannot be modified. When you self-calibrate the PXIe-4309, software stores new constants in a user-modifiable section of the EEPROM.

Table 15. Calibration Options
Calibration Option Application Frequency
External calibration Recalibrates for time drift of onboard calibration constants. Every two years
Self-calibration Adjusts for drift over time and temperature with respect to the onboard reference. After installation and when ambient temperature changes more than 1 °C from the last self-calibration.

The PXIe-4309 receives NIST-traceable calibration before shipping.

External Calibration

For information on externally calibrating the PXIe-4309, refer to the PXIe-4309 Calibration Procedure document.

Self-Calibration

Use the self-calibration function to reduce errors caused by time and temperature drift. Self-calibration recalculates certain internal reference values, gains, and offsets to significantly improve accuracy over the full operating temperature range of the device.

Every measurement instrument performs within its specifications over a finite temperature range and time. If the excursions in temperature and time exceed those specified, and you need performance close to the specifications, then you must recalibrate the instrument at the new temperature or after a certain amount of time. The NI-DAQmx self-calibration function allows you to perform a calibration at the temperature you are making your measurements.

Self-calibration fully recalibrates the analog input and analog output calibration constants for all ranges.

Note DAQmx Self Calibrate calls device reset.

The PXIe-4309 incorporates a temperature sensor that you can read to determine how much temperature has drifted from the previous calibration. You can also read the previous self-calibration time and date.

During self-calibration, the internal circuitry is automatically disconnected from the input. Therefore, for the majority of applications, you do not need to disconnect the input signals during self-calibration. However, excessive signal levels may generate a self-calibration error. Disconnecting the input signals during a self-calibration prevents the error from occurring.

When to Self-Calibrate

For optimum performance, use self-calibration when any of the following conditions has been met:

  • After first installing the PXIe-4309 in a chassis.
  • After any module that is in the same chassis as the PXIe-4309 is installed, uninstalled, or moved.
  • When the PXIe-4309 is in an environment where the ambient temperature changes. Refer to the PXIe-4309 Specifications to find the allowable ambient temperature for your instrument.
  • When the PXIe-4309 temperature has drifted outside of the specified Tcal since the last self-calibration. Refer to the PXIe-4309 Specifications to find the allowable difference from Tcal for this instrument.
  • Once 24 hours elapse after a previous self-calibration.