Mean value of a wave form

[MogaRaghu]

I have a trapezoidal waveform. The period is about 15 sec. In this waveform there is a spike at the beginning of both the +ve and -ve cycles and which lasts for about 1 sec in each case. Please see the enclosed gif file for details.

I am supposed to find out the mean amplitude of the segment A-B and C-D ignoring the initial peak. The user will define this peak as a percentage of the semi-period of the waveform. ( Fortunately both the +ve and -ve transitions have symmetrical durations ).

I have been going through the waveform measurement tools in the functions palatte. There are VIs for Min,Max and amplitude measurements. However in my case, ignoring the user definable peak seems to be the issue.

I would be happy to know if anyone can throw some light on the modality to do this. ( Find out the mean of a waveform ignoring the user defined peak )

Thanks

Raghunathan

[GerdW]

Hello Raghunathan,

the easiest could be to cut out the parts to evaluate.
So you just cut out part A-B and get mean/whatever and the cut out C-D and process it...

[DFGray]

Use Amplitude and Levels.vi. Set the method to histogram. You may want to set more levels in the histogram, but that depends on how accurately you need to know the level and what your data acquisition device is. If you are using an NI-SCOPE device, you can use the measurements functions to fetch the value directly from the waveform. If you prefer Express, you can try the Amplitude and Level Measurements in the Analysis palette, but it won't offer all the customization of the basic VI.

If I remember correctly, this function first appeared in LV7.0. You need the full version or better. Do a search to find it or... In LV7.1, the basic VI is located in Analyze->Waveform Measurements, the right end of the second row of icons, provided you have the Advanced palette enabled.

[MogaRaghu]

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@GerdW wrote:
the easiest could be to cut out the parts to evaluate.

The question is HOW ?

Thanks

Raghunathan

[GerdW]

Hello Raghunathan,

as I don't have much experience with waveforms I would do the following:
seperate your waveform into components with "Get wavefrom components" and process the resulting "Y" array with normal array operations (like subset etc.).

[DFGray]

Get Waveform Subset.vi in the Waveform palette will extract a subset of a waveform based on index or time. I would not recommend you go this route, however. It is a somewhat fragile algorithm. The histogram-based one I mentioned in my earlier post is more robust, given your data set. If you don't have the required LabVIEW version, you can still use the algorithm.

What version of LabVIEW are you using (5.1 base, 7.1 pro, etc.)? I can give you a better answer if I know this.

[MogaRaghu]

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@DFGray wrote:
Get Waveform Subset.vi in the Waveform

What version of LabVIEW are you using (5.1 base, 7.1 pro, etc.)? I can give you a better answer if I know this.

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I am using LV 7.1 full development pack. Waiting for further inputs to proceed. Thanks for your concern.

Regards

Raghunathan

[DFGray]

Use the Amplitude and Levels.vi as I mentioned in the earlier post. It should take care of you. It you have problems, post your code and/or an example data set and I will try to be more specific.