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Need a Poteniometer value soldered on board

  1. Feb 22, 2007 #1
    I am not really a circuits guru, but I am trying to find out the value of a potentiometer on a signal conditioning circuit board that consists of a Wheatstone bridge and an amplifier.

    I have attached the circuit diagram and an image of the board.

    I need to know the exact value of the potentiometer (R3) that determines the gain of the amplifier. It is the blue box in the upper right of the board image.

    The circuit takes a strain gauge as the input of the board, so it is a variable resistance, and the output goes to an oscilloscope.

    I am not sure how to measure, where to measure, simulate anything like that to figure out that potentiometer value and I dont have to means to solder/reattach the pot itself. I know technically the pot has to be removed to measure its value.

    Any quick and easy suggestions

    I appreciate it.
     

    Attached Files:

  2. jcsd
  3. Feb 22, 2007 #2

    turbo

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    The pot is R3 with a max resistance of 50 ohms. If you need to know its present setting, you can de-solder one leg of the pot - (lead 3 or lead 12 to the IC) and measure the resistance across the legs. I don't know of another way to reliably determine the present resistance of that pot. Since it is a pot and not a fixed-value resistor, I assume that it has to be variable to allow calibration of the equipment.
     
  4. Feb 22, 2007 #3

    dlgoff

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    You could estimate if you don't want to desolder it. It is probably a 3/4 turn pot. So mark where it is currently set then rotate the setter to estimate what percent of this 3/4 turn it's adjusted to. Then calculate how much resistance this would represent. Now move it back to the original setting.
     
  5. Feb 23, 2007 #4

    AlephZero

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    Look at the data sheet of the op amp it is connected to. http://focus.ti.com/lit/ds/symlink/ina163.pdf page 6

    I can't see any obvious reason why you shouldn't just measure it in circuit (with the circuit powered off, of course).
     
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