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Help! An issue with a cantilever tube instrumented with strain gauges.

  1. Nov 2, 2007 #1
    I am working on the development of an instrument which can be simply thought of as a cantilever tube. This tube is instrumented with strain gauges to measure the X/Y strains and two sets of rosettes, each consisting of two strain gauges at 45 degree. Note that the X/Y are 3-wire half bridge and the rosettes (for torque) are full bridge. I have been having several issues with this instrument and I am trying to figure them out one at a time.

    First of all, when I apply a small load (around 1 N) I get an output of around 12 N if not more. Would anyone know why the gauges seem to be so sensitive to the loads? I have taken into consideration the gains of the amplifier and filter in the circuit. Would lead wire resistance be the culprit despite it being a 3-wire connection (which apparently negates its effect)? What about soldering? That's my first of many questions! Any help is appreciated!
  2. jcsd
  3. Nov 2, 2007 #2


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    The first things I would look at are your zero load null and the gauge factor input into your readout system.
  4. Nov 10, 2007 #3
    Sorry I didn't reply back. I had to work on something else for the past couple of weeks. Thanks for that. I'll look into those things whenever I can.

    I do, however, have a more urgent task at hand and was hoping you could help me out. I am supposed to write a program using C++ that will take data collected by two separate DAQ cards and save them as either a text or spreadsheet file. Now, I'm still new at C++ and I do not even know where to begin. I have been looking for some literature or tutorials that might guide me online but I have had no luck. Would you know of any sites I could look into for that? Thanks.
  5. Nov 11, 2007 #4


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    Sorry. I am not a programmer. I haven't done anything outside of Labview when it comes to DAQ. I don't even think I could tell you what the first line of C++ code should say.
  6. Nov 12, 2007 #5


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    Try the Programming sub-forum...

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