This works but I need to add control; Help PLEASE!

[Lab Student]

Thank you both!! I have not, as you may be able to tell, been around Labview since 1994! I loved it then because I was using it almost everyday. I have started to use it again for a lot of DAQ apps and am very frustrated, mostly because I don't know how to get LAB to do what I know LAB can do.

I'm glad you're both taking time to assist it makes all the difference. Sorry for the generalization that everyone worked for NI. Without you guys the support would be minimal:-) I'm not sure I follow all you have written but I will try to figure it out and rest assured I'll probably be back:-)

[Ben]

Hi Lab,

Hang in there!

Keep asking!

Ben

[Lab Student]

Thanks!
I am sort of lost (sort of?). The index array will separate the two signals? The result is then fed to a THRESHOLD 1D (Y) Array, then run to a subtract function which subtracts one from the other. output to multiply times dT and viola? Correct?
Does this all occur before my waveform graph? and do I throw out the cursor stuff I had written?

Any assistance would be greatly appreciated.
Signed, poor university faculty:-)

[CoastalMaineBird]

The index array will separate the two signals?
--- In your case, use and INDEX ARRAY function to separate the two WAVEFORMS from the ACQUIRE WAVEFORMS vi you already have. Stretch the INDEX ARRAY so it has TWO index inputs, it will then have TWO outputs.


The result is then fed to a THRESHOLD 1D (Y) Array
--- Since you have a WAVEFORM, you have to use GET WAVEFORM COMPONENTS on each output to get the actual Y data.
then run to a subtract function which subtracts one from the other. output to multiply times dT and viola? Correct?
--- Well, if you shout "viola!" when you're done, people might look strangely at you. You might want to try "voila!" instea
d ;->
Otherwise, that's correct.


There is also a VI called TRANSITION MEASUREMENTS (under Waveform - Analog Waveform - Waveform Measurements - Row 1,Col 1), which operates on waveforms directly. It perhaps might benefit you to study that.


Does this all occur before my waveform graph?
--- It doesn't matter. The number you get (delta Time) should be displayed in a separate indicator, just to verify your procedure. But this is independent of the graphing operation.

and do I throw out the cursor stuff I had written?
--- You don't need it - you get delta time directly from this operation.

You could drive the cursors to the transition points on the graph as a nice UI feature, but that's a separate question.

Get the numeric display working first.

[Lab Student]

Coastal, Fantastic! Thanks. People already look at me strange as I sit in my office and swear at the computer.

This will more than likely be a rather dumb question, but as I am following your advice I am wondering where in the vi does it specify how to trigger on channel 0 and then channel 1? Do I still need to put this in? As in - do I head through the THRESHOLD 1D ARRAY after the GET WAVEFORM and then head for the SUBTRACT?

[CoastalMaineBird]

Not sure what you mean by "trigger".

The INDEX array will take the array of waveforms, and output two separate waveforms. If you stretch it to have two outputs, they will be channels 0 and 1, by default. (You could input a different index, if desired, but you don't need to in this case).

Those two wires go to two GET WAVEFORM COMPONENTS functions, with the output set to Y (not t0 or dt). This gets you two arrays of numbers (the sampled data).

Those two arrays go into two THRESHOLD 1-D ARRAY functions. You will have to wire the THRESHOLD Y inputs to those two functions. Maybe you can use the same value for both, maybe not - it depends on your data.


The output of those is a fractional index - the index where the Y value crosses the threshold going positive.

Those two fractional indexes should be subtracted.
The difference is measured in samples. Convert that difference to time, by multiplying it by 1/Sample rate.

[Lab Student]

Coastal,
Sorry, I forgot what I was doing with the THRESHOLD 1Ds. Duh!!! You have been a tremendous help. I'm going to start putting this together and test it on the actual system. Thanks a bunch. Hopefully I'll only be back to say, "VOILA."