RMS measuring implementation in LabVIEW. Cycle RMS measuring methods research.

[konstunn]

I'm carrying out a little educational research on estimating and comparing cycle RMS measuring methods accuracy.

The methods under this scope are: direct calculation method and filtering method.

Direct calculation is perfomed according to well-known trivial formula:

RMS = sqrt( sum(x[k])^2 )

Filtering method is perfomed by extracting waveform subset with duration equal to waveform period

and perfoming the following operations on it:

1. calculating square of the waveform elements

2. perfoming lowpass filtering of the waveform

3. taking square root of the waveform elements

4. calculating mean of resulting sequence. This mean would be cycle RMS

That's why I need to know how these VIs are implemented:

Basic Averaged DC-RMS

Averaged DC-RMS

Cycle Average and RMS

Built-in help is not sufficient to suit my needs.

Block diagrams of these VIs are too complicated for me to undestand.

And, however, the most important implementation details might be encapsulated in DLLs.

[Michel_Gauvin]

You can dig into the subVI of these functions and find the help for the "primive" function.  Here's an example of the help for the primitive "RMS.vi".

[Michel_Gauvin]

[konstunn]

Michel_Gauvin, but if we have a look at the Cycle Average and RMS VI hierarchy, we'll see that

there is no primitive RMS VI there, but a CycleRMSAverage function call from a corresponding DLL.

Thus, this VI works somehow different. In particular, I've experimentally found out, that it can calculare RMS of periodic waveform with better accuracy. Although, it was expected to do so according to its' name "Cycle <...> RMS".

[Michel_Gauvin]

Can you provide your experiment code that provides better accuracy compared to what? so I can run it? I'd like to see the parameters that you input to this function.

 Also, here's the help for "Cycle Average and RMS.vi":

[crossrulz]

The Cycle RMS first does some calculations to actually find a cycle start and cycle end and then do the RMS caluclation on that cycle.  Yes, this will be more accuract than the standard RMS unless you have exactly and whole number of cycles (no extra points outside of a complete cycle).