Why Should I Use External and Internal Excitation When Calibrating NI 9219?

Updated Mar 26, 2018

Reported In

Hardware

  • NI-9219

Issue Details

I am following the calibration procedure in the NI 9219 calibration manual for full bridge accuracy verification. The instructions say to use an external excitation source as well as internal excitation on the NI 9219. It appears that I could remove the external source and still get reasonable measurements. Why is this necessary?

Solution

The 9219 is a ratiometric device meaning it is constantly dividing the voltage from a sensor by the excitation voltage to get a reading. This allows the device to have consistent readings without a consistent excitation supply.

The calibration procedure mimics this ratiometric behavior by using two DMMs for this measurement. However, the DMMs are not synchronized and may be taking readings at different times. As the internal excitation voltage of the 9219 may not be consistent, these readings may vary. 

An external source regulates the voltage and reduces inconsistencies in voltage being supplied. This removes any need for synchronization between DMMs and increases accurate measurements. 
 

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