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ADS1115: Problem in facing current variation

Snart Caleb
Prodigy 30 points
Part Number: ADS1115
Other Parts Discussed in Thread: INA196,

Hey As I am working with 3 different sensor (like temperature, flow meter, pressure sensor) which is connected far away from 2 wire current loop receiver. I am checking the value from sensor and transmitter directly(with multimeter) first and after that while checking it from current loop receiver(with multimeter) the value is slightly lesser from the previous one

For Example:

I have temperature sensor and during 40 degree Celsius I should get the value of 8.266mA but I am getting 7.88mA similarly when temperature Is at 82 degree Celsius we should get value of 16.16mA but actual value is coming out to be 15.66mA

I am not able to understand where I am facing problem

Kindly how to overcome with this problem?

  • 0
    TI__Guru* 94295 points
    Snart,


    It took me a bit to figure out that you've put some of the information in hyperlinks. I did go to the website for the current loop receiver, but unfortunately I think the link to the schematics are broken. Do you have them and are you able to post them?

    Without the schematics, I can only guess what the error is for the measurement. My first thought would be that the error comes from the front end (either the INA196 or the sense resistor). From the photo, it looks a little like there is a 4.99Ω sense resistor at at the input. I would note that the offset error of the INA196 is 0.5mV typ (2mV), which could be a large contribution to the error you see. However, I need to know how the circuit is put together.

    Beyond that, have you tried to measure the actual current from current loop by other means? If you had a precision ammeter you could measure the current, or if you had a precision voltmeter, you could measure both the sense resistor voltage, or the output of the INA196 to confirm that's what the ADS1115 measures. You'll want to compare those voltages with the output code produced by the ADC conversions.


    Joseph Wu
  • 0 in reply to Joseph Wu
    TI__Guru* 94295 points
    Snart,


    I haven't heard from you for a while. If you've figured out your error problem great. If not, let me know if you make measurements to check the front end of the board.

    Regardless, I'll close this post for now. If you haven't finished debugging the board, and have further questions, post back again and we can discuss the circuit again.


    Joseph Wu