Measuring Power Factor in AC Circuits

[chakr]

How can one measure power factor in AC circuit? http://www.cnktechlabs.com/index_files/cnkdevelopmentkit.htm

 

[Baluncore]

http://en.wikipedia.org/wiki/Power_factor#Measuring_the_power_factor

 

[chakr]

Thank you. If I use a volt and amp meters I can measure RMS power. To determine power factor I need to know phase shift between the two. Is there a way to determine PF from voltage and current measurements alone?

 

[Baluncore]

There is no simple way. Phase is too important.

The continuously accumulated product of V and I will give you the real power.
The average voltage over a cycle, multiplied by the average current will give you the apparent power.
The difference between real and apparent power is due to the reactive circulating current.

You could use a clamp meter to monitor the current. Then if you have a switched range of bipolar, high voltage capacitors, such as motor start capacitors, since most loads are inductive, you could adjust the parallel capacitance to minimise the total supply current, (when PF = 1). Knowing the AC frequency and voltage you can calculate, (or measure with the clamp meter), the capacitive current, then compare that with the minimum current read from the meter, and you have the reactive and resistive currents. That can give you phase angle and power factor.

 

[chakr]

Thank you for your answer.