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Load cell and wheatstone bridge

Discussion in 'Beginner Electronics' started by James Dill, Sep 29, 2006.

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  1. James Dill

    James Dill Guest

    Need therory help.!!!!!

    I work with load cells to weigh the weight in hoppers. These load cells are
    wheatstone bridge-type strain gauges. I can find the formulas to work out
    the resistence and voltage drops of the gauges. But, when you parallel the
    load cells, the voltage output is addative or as the scale book says "summed
    together". This is where the problem lies...... I have never run into the
    situation where parallel voltages are added togetrher in DC this only
    happens in series circuits like voltage dividers. Can someone tell me how
    or where to find the information about summing parallel voltages together.
    Thanks for any suggestions to this problem.

    P. S. I have Googled this problem and come up with a blank.
     
  2. James Dill

    James Dill Guest

    These are electrically in parallel not mechanically. I built two Wheatstone
    Bridge circuits out of resisters. After applying voltage to one of these, I
    had 15 MV output. I then soldiered the second bridge on top of the first
    bridge and I got a 31 MV output. I then soldiered 4 resisters between the
    bridges to make a box like circuit. I was looking for some kind of strange
    recirculating curcuit. I came up blank.

    I know the two bridges in parallel double the output voltage or summed as
    the scale books say but I have no ideal why.
     
  3. James Dill

    James Dill Guest

    Yes I agree with your above equations but I think I have led you off track.
    My experimental circuit was to just prove that the output voltages of the
    bridges were additive (yes I used 5% resistors) a balanced bridge should
    have 0 output. The two bridges had the same basic current draw and roughly
    the same output. When I paralleled them, the current was additive and the
    voltage was also????

    Please look at the following link. This is similar to the summing box that
    I used. There are no active parts. All the connections are in parallel on
    the back of the circuit board. We have three load cells in parallel on our
    scale. If one of them is removed the other two will continue to sum
    weight??

    ..http://cooperinst.thomasnet.com/item/accessories/xaa-911-load-cell-summing-box/xaa-911?&forward=1





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