Do you want to measure phase angle or power factor? Phase angle is a measurement that is not used very often.
This can be accomplished by using an analogue transducer into a PLC analogue input card. The major problem is that the output of the transducer is not normally linear and calculations have to be made in the PLC to determine the correct value.
Power factor is far more common and the best way to measure this is to use a digital device that will calculate the value constantly. Some form of power monitor is usually the best. The value can then be read on a comms line, normally Modbus RTU, or can be output to an analogue output in the device and then taken into the PLC via an analogue input. This output is normally linear and much easier to handle.
I do not know of a digital unit that measures phase angle but if you really need it there is sure to be something around.
The CM3000/CM4000 PowerLogic Circuit Monitor can read the phase angle and other information.
Please refer to http://www.powerlogic.com for detailed information on the CM3000/4000 Circuit Monitor. You can downlaod the latest Instruction Bulletins, which will give you a detailed description of the infomation available from these meters.
Depending on your communication requirements you can use the Mobus RTU or Modbus TCP/IP Ethernet Connection.
Measurement of phase angle is done by converting the voltage reference signal and current ( or another voltage) signals into square waves. The two signals drive a gate and the output is fed to a precision rectifier from where you can have a phase angle voltage signal. Depending on the gate arrangement you may have maximum voltage represent zero phase angle or vice versa.
Can you tell me what effect a supply voltage with a (a+jb) value will have on a resistive heating load. I have assumed that the true power output from the heating elements will be less, is this so?
BALANCED 3-ph, 3-wire, system! For a delta-connected load, resistive or otherwise, the magnitude of the source is used, i.e., sqrt(a^2+b^2), to determine the current of each phase.
UNBALANCED 3-ph, 3-wire, system! For a delta-connected load, use the delta-wye formula to convert the load impedances to an equivalent wye-connected load impedances. Then the phase currents can be calculated using just two current loops, and two phase voltages, not three.
Regarding the original query! Proper determination of phase angle between source voltage and line current, is relatively easy for a balanced 3-ph load. It is not "easy" for an unbalanced load. It can be determined by calculation or measurement of "POWER" and reactive "VARS" for just two phases.
It shouldn't have any. The current is in phase with the voltage in the resistor, period. It cares not what the current in other branches is doing. The resistive load may change the overall power factor if it is a significant part of the load.
A pure resistor doesn't care about phase angle (by the way, phase angle is measured between voltage and current - so iI don't understand what "a supply voltage with a (a+jb) value" means, i.e., measured versus which reference ?)
> Measurement of phase angle is done by converting the voltage reference signal
> and current ( or another voltage) signals into square waves. The two
> signals drive a gate and the output is fed to a precision rectifier from where
> you can have a phase angle voltage signal. Depending on the gate
> arrangement you may have maximum voltage represent zero phase angle or vice versa.
Do we have any particular instrument to measure it?
