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Regarding MSP430F6779 Accuracy

Other Parts Discussed in Thread: MSP430F6779

I have a question regarding the Accuracy of the 3Phase energy meter. I was wondering if anyone have encounter a problem like this one before. 

The energy meter was based on the MSP430F6779.  It had an auto range power supply of 120-480Vac, tapping on Phase A, Outputting at 5Vdc and rectified down to 3.3Vdc to power the Microcontroller.  Also there are separate communication cards such as WIFI and Ethernet that will communicate and send data.  

The meter would run perfectly without any communication cards.  However, when plug in one of the COMM cards, the reading on voltage A dropped.  I figured must be the card that is drawing the voltages. 

I would calibrate the meter again with the COMM card attached.  It would read fine.  However, when I switch over to another panel, going from 120Vac panel to 240Vac panel, the voltages reading from Phase A reads as high as 254Vac. While Phase B and C reads 240Vac.

Have anyone seen this issues before? Is there is any suggestion you recommend? I still don’t understand how the COMM card could have effect the ADC reading of Phase A so much.  

Thanks so much.  

  • Hi Cam,
    I'm getting the right people to jump in on this. We should have an answer for you in 2-3 days. I hope that works for you!

    Best regards,
    Cameron
  • Cam,
    Are you only using phase A to power the board?

    If the anti-alias filters are important for this problem, it would mean RF is getting into the ADCs. That's certainly something we have experienced. However, if this were the issue it would probably hit the ADCs for all the phases, yet only phase A is reported as reading badly. I think its necessary to isolate whether only phase A being affected and only phase A being used to source power is a coincidence or is correlated. My first step to diagnose this would be to power the MCU and the comms modules from batteries, and then reconnect them to the power supply one at a time. By comparing the results it should be possible to isolate whether the problem occurs through the supply.

    Let me know if you see a difference.

    Best regards
    Cameron

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