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

Discussion in 'Homework Help' started by lamela110, Jun 18, 2015.

1. ### lamela110 Thread Starter New Member

Jun 18, 2015
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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!

2. ### WBahn Moderator

Mar 31, 2012
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4,788
What does your circuit look like?

What measurement tools do you have available?

Jun 18, 2015
5
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4. ### WBahn Moderator

Mar 31, 2012
17,720
4,788
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?

5. ### lamela110 Thread Starter New Member

Jun 18, 2015
5
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This: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/phase.html
There is no voltage when the waveforms cross zero?
Thank you!

6. ### WBahn Moderator

Mar 31, 2012
17,720
4,788
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.

Jun 18, 2015
5
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8. ### WBahn Moderator

Mar 31, 2012
17,720
4,788
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?

9. ### lamela110 Thread Starter New Member

Jun 18, 2015
5
0
Is there any device or components to easily measure the phase angle difference?

10. ### WBahn Moderator

Mar 31, 2012
17,720
4,788
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?

JoeJester and panic mode like this.