Current transformers introduce a phase angle error between the current being measured and the voltage signal they generate. Most CTs have a leading phase angle error, where the voltage signal from the CT leads the actual current waveform by a small amount, typically 0.5° to 2.0° (larger for some models). This CT phase angle error results in an error in the reported power. The error is negligible at unity power factor and grows as the power factor gets lower. See Measurement Errors Due to CT Phase Shift for details.
In 2012, with the introduction of the Accu-CT® family of CTs, which have a near zero phase angle error, the phase angle error correction programmed into WattNode® meters was changed from one degree to zero degrees.
There are cases when you might wish to fine tune this adjustment to improve the measurement accuracy at lower power factors. This is possible on some WattNode meter models. Contact CCS if you want more detailed information about the phase angle error of particular current transformer models.
WattNode BACnet® and Modbus®
The WattNode BACnet and Modbus meters provide parameters (PhaseAdjustA, PhaseAdjustB, and PhaseAdjustC) which allow adjustment to the phase angle correction in units of millidegrees. The default value is zero degrees. To change the correction value to 1.0 degree write 1000 to the Phase Adjust Registers.
WattNode® for LonWorks®
The WattNode Plus for LonWorks and WattNode Logger for LonWorks (WNC series) can have the phase angle adjusted, but the process is more difficult. The UCPT (user configuration property type) values UCPTphaseAdjA, UCPTphaseAdjB, and UCPTphaseAdjC adjust the phase angle correction in units of millidegrees. The default value is zero degrees.
In order to change these on LonWorks models, you must unlock the WattNode meter to allow calibration changes, because these variables are treated as protected calibration variables. If you need to do this, contact CCS for details.
WNB Series, Option B Versions
The older WNB series LonWorks WattNode meters and the WNC series WattNode for LonWorks meters with Option B (which emulate the older WNB series models) can also have the phase angle adjusted – contact CCS for assistance.
The WattNode Pulse (WNB series) meters have the phase angle correction factory programmed to zero degrees. This cannot be changed in the field. Contact CCS if you would like models manufactured with a different correction value.