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MSP430FR6047: Captured ADC Waveform has asymmetrical positive and negative amplitude peaks

Shubhendra Singh
Intellectual 845 points
Part Number: MSP430FR6047

Hi,

I am using EVM430FR6047 for water meter application with standard Audio-well pipe mentioned by TI. 

we are getting asymmetrical ADC capture as shown below. if we change the TX resistor from 200E to 270E, wave become symmetrical but received signal amplitude decreases.

I have following queries:

1> Is this wave form correct?

2>How to tune the Sensor Interfacing circuit? (value of resistance and capacitance)

Configuration setting

Attached ADC Capture csv

ADC Capture.csv

Below is the attached ADC capture.

Below is Attached Frequency Sweep

  • 0
    TI__Mastermind 28286 points

    Hi,

    For Q1: this is normal.

    For Q2: You don't need to change the R&C unless you can't get good measurement accuracy via djust the parameters.

     And you need to decrease GAIN to keep amplitude of ADC value is about 900 ~ 10000.

    Thanks!

    Best Regards

    Johnson

  • 0 in reply to Johnson He
    Intellectual 845 points

    Hi Johnson,

    First of all, thanks for your quick response.

    Johnson He said:
     And you need to decrease GAIN to keep amplitude of ADC value is about 900 ~ 10000.

    I am using lowest gain setting from GUI side but still ADC amplitude on positive side is crossing 1100 mV and on Negative side it is around -900 mV. At different frequency it is going up to 1200 mV. This was the reason I tried with 270E but in that case Amplitude has gone down drastically and I have to use a very High gain setting. I could not find any document related to fine tuning of R&C Could you please throw some light on that.

    On this,

    Johnson He said:
    For Q1: this is normal.

    We could not understand why Positive Peaks are going up to 1100 mV but negative are only reaching up to -900 mV. To us it feels like unmatched interface circuit, or saturation.

  • 0 in reply to Shubhendra Singh
    TI__Mastermind 28286 points

    Hi,

    Have you try to capture the waveform use oscilloscope? Does this waveform also asymmetrical?

    Thanks!

    Best Regards

    Johnson

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