Differences in strain gauge measuring grids

Discussion in 'General Electronics Chat' started by beedees, Apr 19, 2015.

  1. beedees

    Thread Starter Member

    Mar 29, 2015
    37
    0
    Hi to all!! :)
    Maybe it would be a stupid question, but according to me it would be interesting to learn more about strain gauges and how these work! There are many types of strain gauge, different form, temperature compensation for different materials and so on.
    I have to use a biaxial (two perpendicular axis) rosette with three terminals i.e. a rosette in half-bridge configuration and then instead of four terminals there are three terminals because two are the same.
    The measuring grids are in constantan. Because I have to calculate the maximum initial offset of the bridge can I be sure that the two measuring grids have the same characteristics? That is tolerances and temperature coefficient of resistance? For example initial offset could increase if one grid increases its resistance and the other decreases due to temperature. Otherwise if both increase or decrease due to temperature then it isn't a problem: the initial offset (without stress) should be zero or near zero!
    So how do usually strain gauge work? Can I be sure that the temperature coefficient of both measuring grids is the same?
    Thanks everybody!
     
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Could you draw a diagram so and label the nodes A, B, C etc so we have something to talk about?
     
  3. Reloadron

    Active Member

    Jan 15, 2015
    969
    235
    To learn just about everything about strain gauges I would start here. Vishay Precision bought the old Micro Measurements group and retained all of their online data and information. Note the Knowledge Bases on the right side of the linked page.

    Ron
     
  4. beedees

    Thread Starter Member

    Mar 29, 2015
    37
    0
    Thanks Reloadron!
    For studiot, to be more precise the strain gauge I mean is like that in the attached image.
    wgeco_xy7x.jpg
    It is a half arm of wheatstone bridge.
    Suppose grids have different Temperature Coefficient of Resistance (TCR), for example the grid on the left have a positive TCR and that on the right a negative TCR. So if the temperature increase or decrease then the voltage output of the bridge is wrong. So I suppose grids have the same TCR and specially with the same sign, both positive or both negative.
    Maybe it could be an unknown question that only manufacturers know! :)
     
  5. Reloadron

    Active Member

    Jan 15, 2015
    969
    235
    You may want to check out Technical Note TN-504-1 Strain Gage Thermal Output and Gage Factor with Temperature. The gauge you intend to use is a pretty common 90 degree type gauge and the right and left sides of the gauge will have the same temperature coefficient. The data sheet for the exact gauge should have the creep data.

    Ron
     
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