MSP430F47187: Issue in power calibration at 0.5lag.

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