How to stretch a waveform

[james_p_martin]

Hello,

I have a waveform from which I am generating upper and lower limits...but at some points where the band is narrow is there any way so that I can stretch the waveform at those points to widen the gap.

                  Thus I am looking for a way such that after reading the file if a user wants to change the waveform , he should be able to stretch the waveform using mouse cursor, and by doing so the points also get updated in the waveform points array.

Is there any way.....to do this.

(for waveform file just remove the .txt extension)

Thanks & Regards
James

[becktho]

Hi James

Maybe you should let us know a little bit more. What is this app used for? Why do you create a limit just by multiplying a value?

To get rid of the small limit difference you could for instance just add or subtract a fixed value. So instead of multiplying with 1.2 you could add 0.1.

If you want to use the limits to test a signal, have a look at the examples. LV provides some limit-functions.

So give us some more information and we can give you a better answer.

If you really just want to change a point, add a cursor to the graph. Then place a numeric control to define which value of the limit has to be modified. You also need a button to trigger the replacement of the value.

Just have a look at the attaced example.

[james_p_martin]

Thanks becktho ,

Actually I have to test the current of a motor within a band and for that first I have to generate that band as the way I am doing it.(multiplying by the factors 1.2 and 0.8 to get upper and lower limits respectively), by doing so I have got a band now.

But at some points the band will be narrow so , if user feels that at some points it needs to be adjusted a bit so he could be able to do that.....thats all I wanted to do.

                    Another thing I would like to discuss is that I want to display the upper and lower limits on the chart and then I show the acquired values within those limits...what is happening currently is that my acquired value and upper and lower limits update point by point.....so I want upper and lower limits shown on the chart before the acquired value is being plotted.

Thanks & Regards

[becktho]

Hi James

The generation of you test band is ok, but you have to be aware, that if the user has to manipulate these limits, he has to select the correct point. If you generate the test band based on data with e.g. 1000 values, the user has to change not only one but several points to widen the narrow area. I also use a limit mask in a application but these limits consist of only 5 points each. As mentioned in my last post, there's a good example showing this method. Search the examples for the term "limit mask testing" and then you should find the vi "Limit Testing Measurement" in the list.

To descend to the display topic - use a graph instead of a chart. I really never use charts, because in my opinion graphs are much more easier to control or modify. There you can easily display your limits and add the measured values at a later point.

Thomas