Signal Conditioning
Gauge Factor of strain gauges in a Wheatstone bridge
If you have strain gauges with a Gauge Factor of 2.07, and these are arranged in a Wheatstone bridge configuration, what would the resulting Gauge Factor be? Can it be extrapolated like parallel/series resistors?
We are getting low readings from our SCXI-1520/PCI-6221, such as 33% low, and I was wondering if it's due to having 2.07 as a Gauge Factor while reading a bridge.
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@Josh B wrote:
Hi Broken Arrow,
Typically the strain gauges themselves are based on the concept of a Wheatstone Bridge and come in quarter, half, or full-bridge configurations. The configuration of quarter, half, or full-bridge is based on the number of elements in the bridge. The following developer zone discusses this topic in more detail.
Do you have four resistors that you are setting up in a full bridge configuration? If this is the case what type of full-bridge are you configuring? If you go to page 2-6 of the SCXI-1520 user manual you will find information on the different types of full-bridges and how to wire them to the SCXI-1520.
https://www.ni.com/docs/en-US/bundle/372583e/resource/372583e.pdf
Another question I have for you is what excitation voltage are you supplying to the strain gauge?
Regards,
Josh B
Thanks Josh. I have since discovered that LabVIEW is smart enough to know what "happens" to Gauge Factor at the various settings. In other words, set to Full Bridge, the software/hardware knows that the gain is a parallel/series combination of gains. At least that's what my further testing has shown.
My excitation voltage varies with application. 1 volt to 10 volt.
Hi Josh,
Well, if you really want to know the back story: We have a sensor with 4 active gauges in it. I have ran it as Full Bridge III and have gotten very stable, temperature-compensated data from it. However, the mechanical engineers deduced that the output was low. If I set it to Quarter Bridge II, I get the output that they seem happy with - the numbers match an input that they supply (which is only applied in one axis, hence, Quarter bridge makes sense). However, I am not convinced that the real world loads occur in one axis. This is when I started thinking about the Gauge Factor, but have sense scratched that idea.
Even though my numbers are "good" now, I am concerned about temperature effects and side loading of the sensor when set to Quarter Bridge. I am going to monitor ambient temperature and correlate sensor drift that way.
So, yes, the low signals are resolved, for now.
Since you're probably wondering, I perform Offset Bridge Nulling but not Shunt Calibration because our cables are very short. I use the 100Hz hardware filter. 1000S/s.
