Measure strain using quarter bridge

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Vindhyachal Takniki

Joined Nov 3, 2014
594
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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