# Measuring phase between voltage and current(HELP!!)

#### lamela110

Joined Jun 18, 2015
5
Hey guys! I'm stuck with my project(assignment) and I'm required to measure voltage, current and phase from an AC source with any equipment that is connected.
I've heard from my supervisor it's difficult to measure the phase angle and I've googled a lot but I'm still stuck.
I'll have to draw out the circuit connection schematic first before doing the actual connection(hardware).

Really appreciate if you guys can help me with the sourcing of phase angle, any samples or guidance will help too!
Thank you!

#### WBahn

Joined Mar 31, 2012
30,067
What does your circuit look like?

What measurement tools do you have available?

#### WBahn

Joined Mar 31, 2012
30,067
You will be sampling the voltage and current waveforms. What do you know about the relationship between the phase angle and when the waveforms cross zero?

#### lamela110

Joined Jun 18, 2015
5

#### WBahn

Joined Mar 31, 2012
30,067
This: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/phase.html
There is no voltage when the waveforms cross zero?
You have two waveforms -- one for the voltage and one for the current. If there is a phase difference other than 0° or 180°, then the voltage will not be zero when the current waveform crosses zero.

Depends one what you want your phase measurement to mean. Usually you want the phase angle of the current relative to the voltage. So you use the voltage waveform as your reference. You can pick any point you want, but you need to be able to detect it and then detect the corresponding point on the current waveform.

#### lamela110

Joined Jun 18, 2015
5

#### WBahn

Joined Mar 31, 2012
30,067
Draw the voltage waveform. Now pick a value of the phase by which the current is delayed relative to the voltage. Pick 30°. Now draw the current waveform delayed from the voltage waveform by 30°. Identify the time difference between when the voltage crosses zero and when the current crosses zero (going in the same direction). Identify the period of the waveforms. Can you figure out a relationship between these times and the phase of the current relative to the voltage?

#### lamela110

Joined Jun 18, 2015
5
Draw the voltage waveform. Now pick a value of the phase by which the current is delayed relative to the voltage. Pick 30°. Now draw the current waveform delayed from the voltage waveform by 30°. Identify the time difference between when the voltage crosses zero and when the current crosses zero (going in the same direction). Identify the period of the waveforms. Can you figure out a relationship between these times and the phase of the current relative to the voltage?
Is there any device or components to easily measure the phase angle difference?

#### WBahn

Joined Mar 31, 2012
30,067
Is there any device or components to easily measure the phase angle difference?
For heaven's sake, you are using a mircroprocessor that is getting the raw voltage and current data. A few lines of code and you have your phase angle measurement. Why won't you even attempt to figure out what the key relationships are?