My textbook mentions the mathematical way to find the phase angle, but how do you find it using an oscilloscope, and how do you find the phase shift with an
oscilloscope. These are applied to RL, RLC, RC circuits are there any methods to do this quickly and easily?

 

On a dual trace scope:
Input on channe 1 with internal trigger rising edge
Output on Channel 2
Use the time cursors to measure the time difference between peaks and conver to an angle.
where tdiff is the time difference between the peaks and tperiod is the period of the waveform. You can convert the phase range [0..2*pi] to [-pi..+pi] if you like after you do the computation.

 

What is the internal trigger rising edge mean? Also, what are time cursors?



I'm using Channel A as a reference to the source, and B is measuring the voltage for the grounded resistor. Then to measure the voltage of the capacitor I have to swap the capacitor and resistor right?

The Maximum frequency is up to 50KHz, my function generator has a 50 ohm impedence, and I'm using 10x probes

I have to find the phase angle and phase shift compared to Vs(source) and Vr(resistor) and Vc Capacitor. In a purely capacitive circuit the phase angle is 90 degrees right?, and when you add resistance the more you add the more it lowers the phase angle towards zero?

Thanks

 

On a real oscilliscope the "event" which "triggers" the sweep can be internally generated by the oscilliscope, or it can come from an external source. When the internal triggering source is used you can select either a "rising" edge or a "falling" edge. The remaining parameter is the trigger "level". The trigger "level" is a voltage on channel #1 or channel #2 or the external source.

 

hmm I still don't understand how to apply this. I know you have to have reference wave. Then you have to count the horizontal and vertical crest difference or something?

 

You have to measure on the scope screen the difference in time between the peaks of the two waveforms (the refrence and and the sample point) You set the oscilloscope to trigger on channle A rising edge to keep both waveforms on the screen and channel B to the right of channel A. It'd probably be easiest to measure phase shift using a triangle wave rather than a sine wave, as the peak will show up quiet easily. The peaks of two sine waves less than a handful of degrees out of phase will be very hard to see.

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I found that on a website What do they mean by "This involves inputting one signal into the vertical system as usual and then another signal into the horizontal system."

 

Inside the oscilliscope there is a set of metal plates that deflect the electron beam of the oscilliscope up and down. This is refered to as the vertical or Y direction. Inside the oscilliscope there is another pair of metal plates that deflect the electron beam of the oscilliscope side to side or lefte to right. This is refered to as the horizontal or X direction.

In the normal mode of operation a linear ramp is applied to the horizontal plates which causes the electron beam to start at the left hand side of the screen and sweep from left to right across the screen. If there is no voltage on the vertical plates then what you see on the screen is a horizontal line. If you apply a voltage to the vertical plates while the beam is sweeping across the screen then the beam traces out a replica of the original waveform applied to the vertical plates.

In the XY mode of operation one channel is applied to the vertical plates and one signal is applied to the horizontal plates. If the two signals are identical the beam traces out a circle. The lissajous figures are difficult to interpret unless the singal frequencies are integral ratios of each other. Forget about lissajous figures for your purposes.

 

Nope.
If the two signals are identical then the beam traces out a straight thin diagonal line.
If the signals have the same frequency and have a 90 degrees phase shift from each other then the beam traces out a circle.

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Uncle $crooge

 

cool, well that helps a lot. What about differences other than in phase and 90 degree out of phase shifts?

 

Look in Google for Lissajous. Lots of pictures of the patterns that are made.
180 degrees phase shift makes the straight diagonal thin line go in the opposite diagonal direction.
Change the amount of phase shift and it goes from a diagonal line going up on one side, then it becomes a leaning oval, then a circle, then an oval leaning the other direction, then a diagonal line going up the other direction.

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Uncle $crooge

 

Well chalk up one for a faulty memory. For me it was never more than a lab curiosity, but I suppose it has its uses in some context. In the case of the OPs problem I doubt that it will provide much in the way of quantitative information.

The other thing he asked about was "cursors". On a real oscilliscope pairs of dotted lines can be painted on the screen in either the horizontal or vertical direction. These dotted lines can be manipulated by a knob either individually or together. As the are manipulated the oscilliscope will display a number on the screen representing voltage or voltage difference for the horizontal lines, or delay or delta time or frequency for the vertical lines. Those dotted lines are called cursors and are most helpful in making the kind of measurements we are talking about.

 

In many years of being associated with the electronics industry, both directly and as an outside user of electronics, I can only ever remember seeing one serious application of Lizzi figures.

An off-air frequency standard had a 3" CRT which was used to display the phase difference between the incoming 200khz off air signal*and the oscillator in the frequency standard.

* From the BBC transmitter at Droitwich, which changed frequency to 198khz some years ago.

JimB

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Experience is directly proportional to the value of the equipment ruined.

 

Like you say, it's commonly used to adjust an oscillator against a standard - it's certainly a technique any scope user should be aware of!.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

For years I had my 'scope set to XY and showing the moving tangle of threads when it was connected to the output of my stereo. Sometimes it produced slowly turning ovals and other interesting displays.

OOPS, a few nights I forgot to turn off the 'scope and the brilliant dot in the center of the screen burned it a little.

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Uncle $crooge