power measurement using field point

[sumi]

I want to measure the power and power factor in an ac circuit using field point module cFP-AI-100 I tried to measure the same using cross power spectrum.vi by applying voltage signal and current signal to channel no:2 and channel no:3 of module CFP-Ai-100. But didnt get the result.When tried with other vi's in the power spectrum measurement some error codes generated. What is the method? Can i get the sample code of power measurement using FIELD POINT vi's?

[Henrik_Volkers]

I assume you want to measure 50/60Hz AC Power.

How fast do you sample your U and I ?

How synchron are your measurements?

I'm not that familar with the FP specs, so I can't tell you if that kind of measurement is possible with FP Hardware.

Some powermeters I used had at least 4800 samles/s and had big errors when switched power consumers where measured.

PowerFactor = RMS(U*I) / RMS(U)*RMS(I)

[sumi]

Sir,
    Thank you for your immediate help.

I am trying with analog input.vi. The sample rate is kept as 100 ms.  The current and voltage signals were applied to the x input and y input of crooss power spectrum.vi.  The output indicators for magnitude and phase are wired. But it didn't display any result.

Can i get some sample code for measuring the power and power factor with FIELD POINT?

[unclebump]

I like using these to measure power with an analog input.

http://www.loadcontrols.com/products/products.html

[Ching_F.]

Hi sumi,

To start off with, I'd like to say that cFP is asynchronous, so you will not be able to achieve a sampling rate of exactly 100 ms.  You may be able to achieve a sampling rate of around 100 ms, but it will not always be exactly that much time between samples.

Have you tried using the Cross Power Spectrum Pt By Pt.vi?  Take a look at that, and let me know if you have any other questions.

Best of luck on your application, and have a great day!!

[Wayne.C]

sumi,

In order to accurately measure power, you need to be able to calculate the phase angle and power factor.  See this post for more info.  http://forums.ni.com/ni/board/message?board.id=170&message.id=171419&view=by_date_ascending&page=1

The example from rpursley8 is probably the best candidate for a cFP. 

I think that you will find that the AI-100 does not sample fast enough for what you need to do.  You need to be able to take many samples during one ac line cycle.  I'm assuming 50/60 Hz.  The cycle time for 60Hz is 16.66 mS.  A cFP-AI-110 would be fast enough to get you 60 samples per 60Hz line cycle.

If you are stuck with the AI-100, I suggest you look at third party devices that measure the power for you.

[sumi]

I tried to measure the power and power factror by using the sample programs given here in the site.
The idea used was:

                               power factor= RMS (V*I)/ RMS (V)*RMS(I)

The program was ok. But i didnt get the answer. The power factor value is indicated as unity throughout. But if waveform generation or simulation vi's are used the power factor and power values are ok. But coming to the real time situations using signal acquisition using field point the anwser is different.

What to do?

Can i get a sample program to measure power and power factor with FIELD POINT?

[sumi]

I tried to measure the power and power factror by using the sample programs given here in the site.
The idea used was:

                               power factor= RMS (V*I)/ RMS (V)*RMS(I)

The program was ok. But i didnt get the answer. The power factor value is indicated as unity throughout. But if waveform generation or simulation vi's are used the power factor and power values are ok. But coming to the real time situations using signal acquisition using field point the anwser is different.

What to do?

Can i get a sample program to measure power and power factor with FIELD POINT?

[sumi]

The main problem that i face in all these measurement is that the rms value of the measuring signal is varying at sample rate.

When i tried to measure the rms value of a voltage which is the secondary voltage of a transformer (230 / 6 V) at different sample rates ranging from very small value upto fairly high values the rms value was the MAGNITUDE OF DIFFERENT SAMPLES.    Actually the rms is expected to be 6V or very near to it. i got values ranging from 0V to 8.24 V ( which is peak value of the waveform ).

I tried to measure the rms value with different vi's such as RMS.VI,  AVERAGE/RMS.VI, BASIC RMS.VI, etc. and the result was the same


Similarly when i tried to measure the peak of the signal the same result obtained. The peak value is varying !!. It was also the instantaneous sample values. 

The output was displayed through indicators, waveform graphs, charts etc.

What is the problem with me? I tried all the examples given in site.

Can i get some example codes prepared SOLELY FOR FIELD POINT ?

All the examples you given are based on signal simulation vi's or  waveform generation vi's. These are running nicely.  I like to know about REAL TIME PROBLEMS?

[unclebump]

Could you make a drawing of your measuring hardware and attach your vi.