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ADS1292: impedance of the 1292 chip in some areas were nonlinear

Part Number: ADS1292

Dear Expert

We are using TI's ADS1292 evaluation board to measure impedance.

Verification block diagram is as follows:

After switching the value of the variable resistance tube, we read the returned voltage value from PC to determine the resistance, and the curve is as follows:.

It can be seen that below 4000Ω, the resistance has a good linearity with the voltage, and the linearity of 5000-9000 is also linear. However, at 4000-5000, the voltage has a significant drop

Repeated for several times, similar results were obtained. The resistance box was tested by external equipment and the resistance value was correct.

I would like to ask if you have encountered such a situation there?What could be causing it?thank you1

  • Hi Gabriel,

    Thanks for the post. 

    For clarification, is it possible to provide further information for your test.

    1. Are you using the AC or DC current leadoff in your test?

    2. Is the variable resistance tube connected across RA and LA in your diagram?

    3. Is the ADS1292 Demo Board in your diagram the ADS1292ECG-FE Evaluation module from TI or your hardware?

    4. Please provide the complete ADS1292 device register setting for the test.

    Thanks

    -TC

  • Thank you for your reply. We answer the questions as below:

    1. Are you using the AC or DC current lead off in your test?

        A: No, we did not use the AC or DC current lead off. The Lead off detection registers are show as below:

       

    1. Is the variable resistance tube connected across RA and LA in your diagram?

        A: Yes,we connected RA and LA to the variable resistance box's two terminals.

    1. Is the ADS1292 Demo Board in your diagram the ADS1292ECG-FE Evaluation module from TI or your hardware?

         A: We use the ADS1292ECG-FE Evaluation module.

    1. Please provide the complete ADS1292 device register setting for the test.

        A:Please refer the table below:

             

  • Hi Gabriel,

    Thanks for the additional information. I will check with the team and get back to you. 

    Thanks

    -TC

  • Dear TCT Expert

    Any suggestion will be  great  hlep!