strain gauge calibration with NI9237 and NI9944.

[cgenco]

Sirs,

I have an NI cDAQ9172  with NI9237 and the 1/4 bridge compliant NI 9944. Practically I work on strain gauge matters measurements using a strain 120 Ohm connected to the NI9944 to build the half bridge that goes inside the 9237. I have a continuous doubt how the calibration for the strain gauges is done. The manual speaks about a shunt resistance that in case of NI9944 is already in the system. The manual says I don't nee external shunt resistance. This is clear.

My question is this:

the menu for the calibration asks for a resistance value that I don't know, I leave in the value proposed by the NI menu. The strain gauges takes easily offset so I'm always obliged to recalibrate the channels in the NI9237. Is this normal ? Can an exitation voltage (strain gauge requests 2.0 V) of 2.5 [V] generates a continuous drift in the measurement ?

Strain gauges are:   EA-06-125BT-120

[BROhan · Accepted solution]

Hi cgenco,

Since the NI-9237 with 9944 uses an internal resistor for the shunt calibration, so you do not need to worry about the value for that shunt resistor. Take a look at the following article which specifies how those connections are made. The calibration article will show you basics behind how those operate.

Also, since this is a ratiometric measurement, the excitation voltage being 2.5V should not matter as long as your gage can handle it.