Measuring phase angle

Hello,
I require some help with a phase angle measurement.
The circuit I have to measure is attached. I would like to measure the current and phase angle through R3 and C1.
I believe that if I use a wattmeter and measure across them (R3 and C1) then cos^-1 the power factor, I will only get the angle associated with their impedance. (about -37 degrees). I want the angle of current relating to the original voltage not just the shift resulting from that branch.
Can any one recommend a device/ method of connecting to achieve the results I am looking for.
Best regards,
Dan
Message Edited by dan1988 on 12-07-2007 04:38 AM
Attachments:
EEP a1.ms10 ‏48 KB

I calculated either 98.97 degrees or -82.87 depending on whether I used a thevenin or super position analysis. I believe the 98.97 degrees is to be taken from the 180 degree point, thus making them them as good as same answer. (Can't go more than 90 degrees anyway so it can't be taken from 0).
I found an interesting result from playing around with the measurement probes you suggested, whereby I was receivng two readings in the load branch from seperate measurement probes, each referenced to a different supply. The readings were 120 degrees and -60.1 degrees.
Now the combined thevenin and load impedance is -20.93 degrees.
120 - 20.93 = 99.07
-60.1 - 20 = -80.1
Meaningful results? I don't know, I do not have enough understanding of the subject to prove or dissprove it.
Any way its still not what i was looking for because Ive had to use my calculations which is what I'm trying to prove in the first place.
If your interested ive attached the circuit and my calculations. As you can probaly tell its part of an assignment, for my HNC. I handed it in yesterday and just had to explain why i couldn't prove the angle (not that we were expected to). I credited you, Lacy, for the measurement probe idea.
Best regards,
Dan
Attachments:
EEP a1_ measurement probes.ms10 ‏45 KB

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Message Edited by Tom W [DE] on 03-06-2006 01:15 PM
Tom W
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Attachments:
untitled.GIF ‏3 KB

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phasor-1.pdf ‏53 KB

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Message Edited by EuanB on 05-15-2009 01:54 AM
Message Edited by EuanB on 05-15-2009 01:55 AM
Message Edited by EuanB on 05-15-2009 01:57 AM
Message Edited by EuanB on 05-15-2009 01:57 AM
Message Edited by EuanB on 05-15-2009 01:59 AM
Solved!
Go to Solution.
Attachments:
In Phase.jpg ‏835 KB
Out of Phase.jpg ‏857 KB
acquire.jpg ‏33 KB

I did some modifications to my first vi. Now is the amplitude problem removed. At least in then I simulate. You may test in real world:smileytongue:
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[email protected]

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Waveform.JPG ‏38 KB
phase.JPG ‏65 KB

Don't appologize for being ignorant or unexperienced! your learning
and asking questions! I grew up as an electronics technician and have
worked in electronics every day for over 25 years (I'm getting old) and I
STILL learn new stuff every day!
OK so you have a few
misconceptions:
1) MYTH: the power company provides a
stable regulated voltage and frequency with no distortions. REALITY:
the power company has no interest in providing a stable pure 50 Hz. (in
fact, it would be nearly impossible) They do attempt to regulate
frequency and voltage to 48-52Hz at 220 - 240 VAC but, surges, spikes and
failures occur often. Additionally, few -if any- line powered devices fail to work properly if the power source is within 10% of "ideal".
2)MYTH: the Fluke i200s current clamp introduces 0 phase distortion. REALITY: The phase distortion is unspecified in the literature (Follow the link.) while the clamp is "usable" up to 10KHz if you used controlled sources and graphed out the accuracy in amplitude, and spectral purity vs input frequency you'ld see an interesting curve with several non-linear components.
3)MYTH: there is no "noise" on the line. REALITY: TV, Radio, Local radar systems, cell phones and microwave relay towers all broadcast RF that can induce currents on the transmission and distrubution lines (not to mention solar events). Additionally PLC technologies actually intentionally introduce modulation of the line frequency.
so in conclusion: I'm not sure there should be any spectral relationship between random samples of line currents from a residential or comercial power provider near 2KHz. I would suggest you limit your experiment to the first 3-5 harmonics as there seems to be no rationale to compare the phase relations way outside of the 50hz that is of interest.
Perhaps you do need to gain information about these higher freq components. If so you will need some type of AC-AC converter with much tighter regulation than the power company provides.
Jeff

SCR Phase Angle control

Hi All,
I'm trying to produce a chopped sine wave to simulate an SCR controlling
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Greetings Nick:
You should be able to get good results with your technique. (You're essentially doing a poor-man's
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Eric P. Nichols
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North Pole, AK 99705

Three phase Measurament

Hi everyone,
I'm trying to measure the phase and the power factor for a three-phase motor. The problemn is that the motor is running with 480V and the SCXI module that I have can only handles until 300Vrms. I'm thinking about using some voltage transformers to step down the voltage and then connect it to the SCXI module. If I do that, will it affect my phase angle and power factor?
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Kenny Caldas
Solved!
Go to Solution.

Just want to emphasise Lynn's point about 480 nominal volts and what you might actually have.
Get your design and wiring checked by someone certified to do so before connecting.
Some further points:
How is the motor being fed?
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Fault Level: You must have fuses as close to the instrumentation pick-off point as possible. That way, if there is a fault in your wiring the instrumentation fuse pops, and you do not have the full fault current flowing through your instrumentation wiring. Fault current will probably be about 4 times motor start current if the motor is fused correctly, and if it is an induction motor.
I would use isolation amplifiers on the voltage inputs. That way you can use a simple potential divider on the input to scale to the voltage you want, but make sure that the isolation amplifier has a suitable frequency range.
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http://en.wikipedia.org/wiki/Current_transformer

Measuring phase angle

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