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MSP430F47187: Issue in power calibration at 0.5lag.

Part Number: MSP430F47187
Other Parts Discussed in Thread: MSP430F6779A

Hi,

we are using three phase capacitive power supply with MSP430F47187.my issue is that when we do calibration in UPF side ie 1.00 upf then meter is calibrated in upf but when are giving 0.5 lag to meter then accuracy is showing 100% .i am following the capacitive supply as given in ti pdf .voltage sensing and current sensing is also same as given reference by ti but problem occuring in 0.5 lag. please revert what is the issue in hardware.

  • Hello Peeyush,

    I don't fully understand the issue. It sounds like an issue with the calibration routine.

    Do you think the issue is coming from the powersupply? Maybe your system is pull more power than the design is delivering. Can you power the board externally?

    Also, Can you link the pdf you refered to?

    Thanks,
    JD
  • Hey Peeyush,

    Thanks for the link. I'm checking with some collegues more familiar with this e-metering offering.

    In the mean time, do you think there is an issue with the power supply or have you been able to rule that out?

    Thanks,
    JD
  • Hi JD,

    my issue with power calibration of meter at 0.5 lagging.

    meter is successfully calibrated at UPF but not calibrating at 0.5 lagging ie 60 degree phase angle so i think there might be something at gain values in firmware so please revert how we adjust gain in firmware.

    at 0.5 lagging(60 degree phase angle) meter is showing 100% error.

    at upf (0 degree)meter accuracy is ok.

    so confirm me how we can correct error at 0.5 lagging(60 degree phase shift).

    i have some doubt in ADC calibration and its related circuit in hardware and gain in firmware.

  • Hello,

    First, the SLAA577 app note that you shared is for the MSP430F6779A family whereas you're using the MSP430F47187. Thus, I would recommend referencing SLAA409 for this device. Unfortunately, you may not be able to find SLAA409 on TI.com because it's been removed due to recommending F6779A for new designs rather than F47187.

    peeyush tyagi said:
    meter is successfully calibrated at UPF but not calibrating at 0.5 lagging ie 60 degree phase angle so i think there might be something at gain values in firmware so please revert how we adjust gain in firmware.

    Normally, the Gain is calibrated at UPF (0 degrees phase angle), and then the Phase is calibrated at PF = 0.5 (60 degrees phase angle). According to Section 4.3.3 Phase Compensation in SLAA409:

    In the current application for input frequency of 60Hz, OSR of 256 and sampling frequency of 4096, the resolution for every bit in the preload register is about 0.02 degrees with a maximum of 5.25 degrees (maximum of 255 steps). Since the sampling of the 7 channels are group triggered. An often method used is to apply 128 steps of delay to all channels and then increasing or decreasing from this base value. This allows +/- delay timing to compensate for phase lead or lag. This puts the practical limit in the current design to +/- 2.62 degrees. When using CTs that provide a larger phase shift than this maximum, an entire sample delay along with fractional delay must be provided. This phase compensation can also be modified on the fly to accommodate temperature drifts in CTs.

    Thus, I suspect that your CT's are introducing a phase angle greater than +/- 2.62 degrees at PF = 0.5. If so, then you'll need to implement whole sample delays (since every bit in the preload register is a fractional sample delay). Here's the delay resoluton equation from SLAA409:

    Regards,

    James