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Original question:

ADS114S08: Random ADC values when one of the RTD is not connected in Two channel of 3-wire RTD Sensor with the ADS114S08B...

ADS114S08: Spindle disturbs ADC readings

fm. rd18
Prodigy 20 points
Part Number: ADS114S08

Tool/software:

Hello everyone,

I am currently designing a circuit using the ADS114S08 to measure temperature in a four 3-wire RTD configuration.

I asked the question before https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1458574/ads114s08-random-adc-values-when-one-of-the-rtd-is-not-connected-in-two-channel-of-3-wire-rtd-sensor-with-the-ads114s08b-system. Now there are new problems. My RTD is located at the spindle bearing. When the spindle is not rotating, the ADC reading is stable, but when the spindle is rotating, the ADC reading fluctuates. This question has been cross-tested with the same results.

Thanks in advance for your professional advice. I look forward to your insights.

CH1 Should remain stable

  • 0
    TI__Guru 52496 points

    Hi fm. rd18,

    It sounds like you are picking up noise from the machinery around the ADC. You will need to identify how this noise is making its way into the system (maybe through the RTD cable?) and then find a way to remove this noise

    You might be able to remove it by post processing your data through a digital filter in your controller, as it sounds like the ADC digital filter is not removing it. Seeing an FFT would help identify what frequencies are being passed into the system. But this is something you will need to explore on your own

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 20 points

    The noise comes in through the RTD cables. The 4 RTD cables are shielded. When the shield of the RTD cable is connected to the safety ground of the chassis, the noise will be reduced, but the noise impact is still too much for me.

  • 0 in reply to fm. rd18
    TI__Guru 52496 points

    Hi fm. rd18,

    Thanks for clarifying. Then you can put heavy filtering on the inputs, depending on the frequency of the noise. Note that low cutoff filters affects settling time of the circuit

    You can also attempt to postfilter the captured digital data using a digital filter you create in your controller. Again, this depends on the noise frequencies you are trying to reject

    -Bryan