3.1.23 Per-Channel Phase Calibration Constants
Phase calibration constants are provided for each channel to equalize relative phase differences across all channels after an appropriate calibration procedure was exercised. All active input channels, both voltage and current, require final calibration to ensure full accuracy. All phase-correction amounts are in BAMS units.
In cases where neither phase-phase vector transformation nor optimal phase-phase voltage measurement are not required, phase correction values may be set for only current channel, and voltage phase correction values are set to zero. However, if phase-phase equalization is also desired, voltage channel phase correction values may be used.
Input requested phase correction values are relative values that may be internally adjusted with an internally computed offset to achieve proper phase shifts for use within the phase correction DSP filters. Any internal offset adjustment made by the DSP is available in the PH_OFFSET status register (see PH_OFFSET). This internal offset phase adjustment is made to shift all requested phase correction values to ≤ -1.35° (at 60 Hz). The maximum phase correction capability among the different channels is 32.39º (at 60Hz) or 26.99º (at 50Hz).
The requested input phase correction values may change dynamically and will be used to compute new phase correction filter coefficients at the start of each integration period. If phase correction values do change dynamically and, if it is preferable to keep coefficients as stationary as possible (change as little as possible), then set the phase correction value of an unused channel to a value slightly larger (more positive) than the expected maximum value of the range of allowable phase correction values. Otherwise, all unused channel’s phase correction values must be set to zero.
For example, the top row of hex values represents the phase corrections as input into the phase correction registers:
| CAL_PH_IA | CAL_PH_VA | |
|---|---|---|
| Input phase corr. values (hex) | 0xFFEDCBAA | 0x00000000 |
| Input phase corr. values (dec) | -0.10º | -0.00º |
| Internally computed offset | -1.35º | — |
| Actual internal phase delays | -1.45º | -1.35º |
If it is preferable to correlate the phase delays of internal signals with the phase delays of outside world signals, simply compute the actual phase delay values by adding the value of PH_OFFSET to the raw input phase correction values.
All phase correction angles entered must be normalized to 60 Hz. For example, if a phase correction factor of -0.31° is measured at 50 Hz, the value at 60 Hz is easily calculated as:
and to convert to the proper BAMS input format:
At the start of every integration period, the input phase calibration constants are used to compute the proper phase correction filter coefficients. If a requested set of phase-corrections is not possible, an error will be returned in the status register STATE_FLAG: PC_OUT_OF_RANGE.
Refer to “PIC32CXMTx Metrology User Guide” for a more detailed description.
| Name: | CAL_PH_Ix, CAL_PH_Vx |
| Offset: | Metrology_Reg_In[38-44] |
| Property: | Read-Write |
| Bit | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | |
| CAL_PH_Ix, CAL_PH_Vx[31:24] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | |||||||||
| Bit | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | |
| CAL_PH_Ix, CAL_PH_Vx[23:16] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | |||||||||
| Bit | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | |
| CAL_PH_Ix, CAL_PH_Vx[15:8] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | |||||||||
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| CAL_PH_Ix, CAL_PH_Vx[7:0] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | |||||||||