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INA827: Loadcell Instrumentation Amplifier Calibration

Part Number: INA827

Hi All,

I am using INA827 along with load cell for my ADC frontend. I would like to calibrate my ADC using external mV source. How can I achieve the same? I have shared my ciruit below.

https://ibb.co/mRrGk7L

Thanks!

  • I would like to calibrate my circuit using external mV source.

  • Hi Smit, 

    Q:  I would like to calibrate my ADC using external mV source. How can I achieve the same? I would like to calibrate my circuit using external mV source.

    Let me see if I understood your inquiry correctly. 

    You have ADC and Loadcell circuit at its front end. You want to calibration the ADC's output vs. Loadcell_range. 

    If this is the case, you have two linear circuit. You can calibrate both circuit in one calibration approach, such as 2 points calibration. 

    1. You calibrate an low-end of loadcell measurement and ADC in one measurement, say X Volts vs. low_end strain_gauge reference load condition. 

    2. You calibrate an high-end of loadcell measurement and ADC in one measurement, say Y Vo;ts vs. high_end strain_gauge reference load condition. 

    3. You make a linear fit in ADC_Vout vs. Load_cell (e.g. grams), which is the calibration curve of the system. 

    4. If you want to go further, place a known load within the load_cell range and check for ADC's Vout response. 

    If you want to have multiple load_cell calibration, you can perform the above tasks with multiple known load conditions and perform the linear fit across the entire range (in general, this approach is not necessary, unless the sensor behaviors are not exactly linear). 

    Alternatively, you can calibrate two linear circuits individually and/or combine the calibration results. With an external mV calibration source, you can certain calibrate your ADC performance in Vadc_out vs. input_analog_signal. 

    You can also calibrate in INA827_Vout with external input calibration source in mV at its input. This approach may work, but you are unable to calibrate out the offset issues or nonlinearity issues in the load_cell sensor or Wheatstone bridge sensing circuit. 

    INA827 Loadcell 08242021.TSC

    Please let me know if I answered your questions. 

    Best,

    Raymond

  • Hi Raymond,

    As you mentioned in last point, calibrating my circuit using external mV source is what I want to do. We usually use load cells of high capacity i.e. greater than 1Ton. So, calibrating my circuit using 2 point calibration is difficult because we cannot place a deadweight of 1Ton for calibration. If we use less weight like 10 or 25 kg for calibration, then the output is not linear for higher weights.


    My approach:

    Loadcell output: 2mV/V Excitation: 5V Total output: 10mV

    1. Short differential input of INA827 and record zero point of circuit.

    2. Apply external differential 10mV to INA827 and record span point.

    3. Connect loadcell to the system and record new zero point.

    Is there a better approach to solve the problem?

  • Hi Smit,

    Is there a better approach to solve the problem?

    I see the dilemma you have.

    Your calibration approach is really calibrating the DAQ part of the electronic circuit. It will certainly be better than no calibration, but you left out the load_cell calibration in the process. 

    I do not know how accurate your system is going to be. If you are able to make/buy a compression jig and apply 2 point calibration method, then it will be certainly an improvement over the current calibration procedure. 

    Here is what I am thinking. You can get a pneumatic cylinder/piston and apply a load to the DUT of load cell (e.g. similar to piston to lift a vehicle). You adjust air pressure to control a compression of load until a known load is made  You can calibrate the load_cell via the approach. I think that it will be more accurate way than the current method. I do think that you want to calibrate the load_cell as well, which there is an error between applied load vs. voltage output at Wheatstone bridge sensor. 

     If you have other questions, please let me know. 

    Best,

    Raymond