Measure strain using quarter bridge

Discussion in 'General Electronics Chat' started by Vindhyachal Takniki, Jan 30, 2015.

  1. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
    348
    6
    I have to measure strain & circuit is attached. I am using ADS1246 to measure strain, its a 24 bit adc from TI.

    For 1K SG
    1. SG nominal = 1000 ohms , with min = 900 ohms during compression & max = 1100 ohms during tension.
    2. I have used R5 to generate Vref for ADS1246. R5 produce Vref = 0.6V.
    3. Minimum resolution I need is = 0.5uV.
    Max voltage = +25.641mV
    Min voltage = -24.39mV
    4. I have used PGA = 64.

    For 350 ohm SG
    1. SG nominal = 350 ohms , with min = 315 ohms during compression & max = 385 ohms during tension.
    2. I have used R8 to generate Vref for ADS1246. R5 produce Vref = 0.6V.
    3. Minimum resolution I need is = 0.13125uV.
    Max voltage = +13.462mV
    Min voltage = -12.805mV
    4. I have used PGA = 128.


    My questions are:

    1. What will be resolution is? Is it:
    resolution = Vref / (2^23 * PGA)
    = 0.6 / (128 * 8388608) = 0.55nV.

    2. In datasheet I have read that noise is in uV with Verf = 2.5V.
    But in my case vref is also small 0.6V.

    3. Will be circuit be able to measure such low voltages

    4. I am using 3 wire quarter brigde.
    It involves error from 1 lead resistance.
    How can I remove error this error?
    (Only option I have to use quarter bridge. I cannot use half brigde, full or dummy gage in quarter bridge. My application is such.)

    Edit: 5. Any other better circuit in someone's mind. This application is battery operated so have to be low power circuit.
     
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