Strain Guage Drift Problem

Discussion in 'The Projects Forum' started by tkpatel, Jun 22, 2010.

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  1. tkpatel

    Thread Starter New Member

    Jun 22, 2010
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    Hi all,

    I am having the drift issue with the strain gauge measurements. I have two strain gauges on my sample (one on the compression side and other on the Tension side). I am using two individual channels to measure two individual strains from each gauge and using quarter bridge connection with "dummy" resistor.

    When I use the gauge alone. The results are nice and steady; and am able to nullify the output at some point. But, as soon as I place (glue) the gauge on my sample the voltage starts to drift and reaches to the higher limit.

    Assuming the possibility of the defective gauge, I tried using brand new gauge on my sample but the drift continued as soon as the sample comes in the picture. I also changed the sample with brand new gauges but couldn't get rid of the drift. Just to avoid any possible temperature affect, I changed the room where the room temperature was monitored, but the drift continued.

    When, I interchanged the position of the gauges on the bridge I and II, the drift became negative and continued to -ve 5 volts in merely 10 mins.

    As all these indicate the gauge on the sample may be the cause, I checked the resistance on the gauge (with sample) and it comes out to be 120 ohms as it should be.

    Any hint what could be the trouble here.

    Thanks in advance,

    Tkp
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What kind of adhesive are you using?
    Cyanoacrylate aka Superglue aka Krazy Glue shrinks as it dries, which will stress your gauge.

    Use a filled epoxy.

    You don't mention what you're using for an amplifier; I hope it's an instrumentation amplifier.
     
  3. tkpatel

    Thread Starter New Member

    Jun 22, 2010
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    0
    Thanks for your reply,

    Yes, we are actually using superglue but we have been using it since past few years and never had any problem until recently. But I would really love to use filled epoxy and see that changes the story.

    Actually, I am using the NI SCXI-1321 module that connects to the SCXI 1121 (Isolation Amplifier). The only wires in my configuration is the two quarter bridge connections. One of that connects to the Dummy resistor (Quarter Bridge connection I) and other connects to the strain gauge on the sample (Quarter Bridge Connection II). Interestingly everything works fine with simple gauge (prior the placing on the sample).

    Thanks again,

    Tkp
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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