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08-05-2011 08:29 AM

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I am metering an AC voltage signal using a cRIO and 9206. The signal is a triangular wave and I need to get the RMS of this triangle wave. It seems the Cycle Average RMS VI in labview only does sinusoidal wave forms. There is an option between peak/histogram/auto where auto gives a "reasonable answer" for a triangle wave. I need a more precise answer. I can write a custom vi grabbing the peaks of the triangle wave then dividing by sq.rt(3), but this is a lot of work. Was hoping Labview had one programmed already. Thanks for your help.

-phdieum

Solved! Go to Solution.

smercurio_fc

Knight of NI

08-05-2011 08:48 AM - edited 08-05-2011 08:49 AM

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Why do you say the VI only works on sinusoids? Did you test it?

What does your "triangle" wave actually look like?

08-05-2011 08:53 AM - edited 08-05-2011 08:54 AM

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Hello,

Cycle Average RMS VI is calculating RMS of the one selected period of the given signal (unless specified differently with number of cycles) - if you have a lot of data to analyze and want to calculate RMS of all data, I recommend you to use RMS VI. VI takes array of Double, and make an RMS calculation on them, outputting RMS in double.

Please let me know if this solution was appropriate for your problem.

Best Regards,

Gregor Černe

08-05-2011 10:32 AM

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08-05-2011 10:50 AM

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smercurio_fc

Knight of NI

08-05-2011 02:10 PM

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When you say the "RMS" VI are you still referring to the Cycle and Average RMS, or to the RMS VI? Either way, neither of these VIs does any sort of dividing by the sqrt(2). It calculates the RMS value based on the definition of RMS. Please read the Help on those functions before claiming a VI works a certain way.

Please post an example of what your waveform looks like. No pictures - actual data.

08-05-2011 04:52 PM

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08-08-2011 12:55 PM

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smercurio_fc:

Attached you will find the AC signal that I am trying to capture. Using a Klein CL2000 DMM, I am able to accurately read the TRUE RMS voltage of this signal. My question is how to program Labview to accurately interpret this signal. Using RMS.vi does not work on this signal. I am able to get close by extracting the peaks from the signal, averaging them, then dividing by sq.rt(3). Is there a better more accurate way to measure the TRUE RMS of this signal? Again, I appreciate your help and time.

-JLG

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08-08-2011 01:10 PM

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08-08-2011 01:13 PM

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@phdieum wrote:

No this is not correct.It takes the sqrt of the sum of the squares of the elements divided by n

"Should be" isn't "Is" -Jay