# phase or frequency?

#### suzuki

Joined Aug 10, 2011
119
Hello all,

In a resonator circuit, when applying a voltage, the phase difference between the voltage and current will vary depending on the frequency of the voltage source.

How do I physically measure the phase difference between the input and output of the resonator circuit with a high degree of accuracy?

Could we also measure the frequency somehow? I know that

frequency = phase/time

therefore, Δf = Δphase /Δtime.

So, in practical applications, does this mean I would find the difference in frequency of the two signals and multiply by the time frame?

#### NLightNMe

Joined Apr 20, 2011
16
Couldn't you just connect the input to one channel of an oscilloscope and connect the output to the another channel? Then, measuring the phase between the two signals would be simple.

#### DickCappels

Joined Aug 21, 2008
7,703
You can buy sensitive, high frequency current probes from Tektronix, allowing you to look at both current and voltage when driving your resonator. Many oscilloscopes measure frequency, or if you prefer, you can measure the interval of a cycle visually or with the use of cursors and then calculate the frequency.

#### suzuki

Joined Aug 10, 2011
119
hmm, what I actually want to do is sense the voltage and current, and find the phase difference between them so that I can send that information to a microcontroller, so I cannot use a scope.

I suppose i just wanted to know if my above formula is correct. I.E. if i sensed the changes in frequency in a certain time period (of the voltage and current), if i could get the phase difference between the voltage and current. But i would also be curious to know what other methods are possible for doing this as well.

#### wayneh

Joined Sep 9, 2010
17,153
So, in practical applications, does this mean I would find the difference in frequency of the two signals and multiply by the time frame?
I might be all wet but that doesn't sound right. At steady state I would expect the voltage and current to have the same frequency, regardless of the phase shift between them.

If you have a fast enough data acquisition device, fast enough to resolve where a peak is with reasonable precision, I think it would be "easy" to have a calculation of the time delta between two peaks. It might be easier to resolve a zero-crossing, now that I think about it.