Datasheet
Installation and Operation
2010 Microchip Technology Inc. DS51915A-page 19
The appropriate Phase Delay register value is determined by the measurement of the
indication variation during the following calibration routine.
As calibration is initiated, the values of the Active Power Scaling Factor, RMS Current
Scaling Factor, and RMS Voltage Scaling Factor at a Power Factor of 1 are determined
through the following process:
1. Supplying the meter with the following values: 110 of V
RMS
, 5 A
RMS
, and Phase
at 0 degrees
The meter takes a few seconds (maximum 20 s) to get stable readings, then the
PC virtual port sends the character “c” from the PC to the power monitor. The
pulse output LED stops blinking for a few seconds, and the LCD shows “Calibrat-
ing 110V 5A PF=1”. The three constants will be computed and saved to the
EEPROM of the MCU. Power can be interrupted without losing this calibration
information.
2. Powering the monitor with 110V of U
RMS
, 5V of I
RMS
and a Phase at -45 degrees
The meter takes a few seconds to get stable readings, then the PC virtual port
sends the character “n” (negative phase) from the PC to the power monitor. The
the pulse output LED is forced ON for a few seconds, while the LCD shows “Cal-
ibrating for -45 degrees”. The results collected during this step are not saved into
the EEPROM of the MCU. It is important that power is not lost until after Step 3
is complete.
3. Powering the meter with 110V of U
RMS
, 5A of I
RMS
and Phase at 45 degrees.
The meter takes a few seconds to get stable readings, then the PC virtual port
sends the character “p” (positive phase) from the PC to the power monitor. The
pulse output LED is forced ON for a few seconds, while the LCD shows “Calibrat-
ing for +45 degrees”. When this step finishes, the calibration parameters are
saved into the EEPROM. Now power can be disconnected from the meter.
The two power values measured at -45 and +45 degrees are inserted into the equation
in Figure 2-8, and the result is the Phase Delay register value required to compensate
for the power factor variation.