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MSP430F67791A: TIDM-THDREADING measurements fluctuating too much

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Replies: 17

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Part Number: MSP430F67791A

Hi

I was testing the e-meter app code in MSP430F67791A based design and found voltage rms was reading proper but Fundmental RMS and Voltage THD measurement is fluctuating too much and not getting stable value(erratic readings)(Applied input was 240 V and 10% 3rd Harmonic). What could be the reason for non-consistence reading?Please resolve my query.

Thanks,
Santhosh

  • Hello Santhosh,
    I have reached out to one of our metering experts familiar with this device.
    We will get you an answer shortly.

    Dennis Lehman

  • Hello,

    Are you using our EVM430-F6779 or your own custom board? Have you modified the TIDM-THDREADING source code at all?

    Regards,

    James

    Check out our new Answers to Common Sigma-Delta ADC Questions on MSP MCUs app note!

  • In reply to James Evans:

    Hi James,

     I am using our own custom board. I didn't modified any part of the code except metrology-template.h & metrology-calibration-template.h.

    Rgds,

    Santhosh

  • In reply to SANTHOSH V:

    Hello,

    I would highly recommend that you use our EVM430-F6779 and the original code to see if the behavior goes away. I suspect that custom board doesn't match our EVM430-F6779 or whatever was changed in these two files is causing the issue. What specific changes were made to these two files?

    Regards,

    James

    Check out our new Answers to Common Sigma-Delta ADC Questions on MSP MCUs app note!

  • In reply to James Evans:

    metrology-calibration-template.txt

    metrology-template.txt

    Hi,

    I have modified only default constants and ADC input. Files are attached, please have a look.

    Rgds,

    Santhosh 

  • In reply to SANTHOSH V:

    Hello,

    Thanks for sharing the files. Your modifications are most likely what's causing the issue. I'll look through them, but in the meantime, it would be helpful if you start with the original versions and make incremental changes to these files and then note when the fluctuations start to happen.

    Can you duplicate the issue using our EVM430-F6779? Perhaps this is a hardware issue, not a software issue. Do you observe any issues with the frequency readings when the fluctuations occur? Is the frequency relatively stable? Most importantly, what is the range of fluctuation that you observe? Please be specific.

    Regards,

    James

    Check out our new Answers to Common Sigma-Delta ADC Questions on MSP MCUs app note!

  • In reply to James Evans:

    Also, do you still see the fluctuations with VRMS lowered to 200V or lower?

    Regards,

    James

    Check out our new Answers to Common Sigma-Delta ADC Questions on MSP MCUs app note!

  • In reply to James Evans:

    Hi, 

    Vrms is proper, we face problem only with THD.

    Rgds,

    Santhosh

  • In reply to SANTHOSH V:

    Hi Santosh,

    So VRMS improves when it's below 200V, correct? What about the frequency measurement? Is it stable? How much is the THD fluctuating. Please be specific.

    Regards,

    James

    Check out our new Answers to Common Sigma-Delta ADC Questions on MSP MCUs app note!

  • In reply to James Evans:

    Hi,

    I have attached 2 files that contains measurement results with below inputs:

    1. All three phases 240V, 10A, UPF, 50Hz, 10% 3rd harmonic in all three voltages.

    Watch1-240V.log

    2. All three phases 195V, 10A, UPF, 50Hz, No harmonic.

    Watch2-195V.log

    Rgds,

    Santhosh

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