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Strain Gauge Excitation / Voltage Reference


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#1 tristan

tristan
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Posted 04 March 2011 - 08:46 AM

Hi, What's your recommendation for excitation for a load cell strain gauge bridge (say something typical like 2mV/V, 700-ohm bridge, etc..)? I would like to use the U6 because it has the integrated instrumentation amplifiers but I don't see any kind of Vref output (such as on the LJTIA). The only other obvious solution seems to be dedicating one of the analog inputs to measure Vs and just assume everything is ratiometric (since USB power supply voltages are somewhat variable!). Am I missing something obvious? Thanks, Tristan

#2 LabJack Support

LabJack Support
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Posted 04 March 2011 - 09:48 AM

Good bridge circuit topic here:

https://forums.labja...?showtopic=4376

I recommend using a DAC output for excitation on the U6. Set it to perhaps 4.5 volts (something safely away from the minimum VS rail), and due to the 50 ohms of source impedance you will get about 4.2 volts at the bridge. The DAC outputs are reference based and much better than VS for stability and noise.

If you use VS for excitation you really have to read it back on another analog input to get good measurements. If you use a DAC output, you could probably get away with just measuring the actual voltage once with a DMM or whatever, rather than continuously with every signal measurement, but for best measurements you should measure continuously. In fact with any excitation supply, a good reference or a $1000 power supply, you should consider measuring the actual value in real-time as inputs are generally better than outputs.


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