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dan1988
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measuring phase angle

[ Edited ]
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
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dan1988
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Re: measuring phase angle

Additionally if I perform a Thevenin analysis on the circuit and then measure it I do not believe the wattmeter takes into consideration the initial phase shift present in the supply thus still not providing me with the result I am looking for.

Many thanks,

Dan

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lacy
Posts: 1,233
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Re: measuring phase angle

I have an option for you to try if you have it available to you. It is called the Measurement Probe. You only have to click on it and place it on a wire in your circuit that you want to measure.

In order for it to measure the phase of a signal you must have 2 of them in your circuit and in the properties box have one seklected as the reference. I will post your original circuit with these in it to let you see if that is what your after. I not sure it this is what you need or not. The only other thing is the Bode Plotter. You will have to look at the bode plotter to see how you could hook this up to your circuit, but it does have a phase measurement capability.

Hope this helps some as I do not have any other suggestions.

Here's the circuit with the two probes for you to experiment with.

Kittmaster's Component Database
http://ni.kittmaster.com

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lacy
Posts: 1,233
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Re: measuring phase angle

I have an option for you to try if you have it available to you. It is called the Measurement Probe. You only have to click on it and place it on a wire in your circuit that you want to measure.

In order for it to measure the phase of a signal you must have 2 of them in your circuit and in the properties box have one seklected as the reference. I will post your original circuit with these in it to let you see if that is what your after. I not sure it this is what you need or not. The only other thing is the Bode Plotter. You will have to look at the bode plotter to see how you could hook this up to your circuit, but it does have a phase measurement capability.

Hope this helps some as I do not have any other suggestions.

Here's the circuit with the two probes for you to experiment with.

Kittmaster's Component Database
http://ni.kittmaster.com

Have a Nice Day
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dan1988
Posts: 13
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Re: measuring phase angle

Many thanks Lacy,

I have tried some different combinations of the probes with little success. I had previously been using the wattmerter and bode plotter but I think they / I have trouble due to there being two power supplies thus no fixed reference, other than gorund but then I end up not meaasuring across anything, or only across the load.

Alternatively I could be getting great reults form all equipment and my calculations are off.

 

Anyways,

Thank you for you suggestion

Best regards,

Dan 

 

 

 

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lacy
Posts: 1,233
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Re: measuring phase angle

Here's another suggestion that I just tried. Use the bode plotter and just hook up the "OUT" side across the components. With this hook up I read a phase angle of 149.371 degrees.

What phase angle did you calculate? Let me know if this does it or not.

Kittmaster's Component Database
http://ni.kittmaster.com

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lacy
Posts: 1,233
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Re: measuring phase angle

Other than what I suggested in the last post, I don't see a way of doing this. This doesn't mean that it isn't possible just that I can't find a way of doing it.

Maybe the NI support Team has a better suggestion. I am sorry I could come up with a good answer for you.

Kittmaster's Component Database
http://ni.kittmaster.com

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dan1988
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Re: measuring phase angle

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

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dan1988
Posts: 13
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Re: measuring phase angle

Should read:

'Now, the combined thevenin and load impedance is -20.93 degrees.'

Also the calcs should be attached now. The file was quite big so i zipped it.

 

Best regards,

Dan

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lacy
Posts: 1,233
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Re: measuring phase angle

I wish there would have been something better on this, but like you said I believe the two sources are throwing the instruments off. I don't like mathmatics very much (namely because I'm not that good at it) or I would try them out to see what I came up with. I might do this on the weekend, because I have been working 9 hour days at my job which is fairly physical. So by the time I get home I am mentally and physically wore.

I know that it may be too late for what you were needing it for, but I will contine examining this and if I would find something I will post it. It may help both of us in the fututre.

 

Kittmaster's Component Database
http://ni.kittmaster.com

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