After performing gain calibration, if the accuracy at low currents is not acceptable, perform offset calibration. Offset calibration removes any crosstalk, such as the crosstalk to the current channels of a phase from the line voltages.

To perform active power offset calibration for a phase, simply add the offset to be subtracted from the active power reading (in units of mW) to the current value of the active power offset (labeled Voltage AC off in Figure 4-3) and then enter this new value in the Voltage AC offset field in the Manual Calibration window. As an example, if the Voltage AC off has a value of 200 (0.2W) in Figure 4-3, and the desire is to subtract an additional 0.300mW, then enter a value of 500 in the Voltage AC offset field in the Manual Calibration window. After entering the value in the Voltage AC offset field in the Manual Calibration window, press the Update meter button for the changes to take effect.

To perform reactive power offset calibration for a phase, a similar process is followed as the process used to perform active power offset calibration. Add the offset to be subtracted from the reactive power reading (in units of mvar) to the current value of the reactive power offset (labeled Current AC offset in Figure 4-3) and then enter the value in the Current AC offset field in the Manual Calibration window. After entering the value in the Current AC offset field in the Manual Calibration window, press the Update meter button.