How to output XY values from a graphically produced waveform to control a process

[Dave@Ventec]

I would like to graphically create a waveform and then output the Y values of that waveform on a time selectable basis to control a 0-5 VDC device.  The attached VI, found initially on the forums nicely acomplishes the waveform creation.  How do I then output that calculated wavefroms Y values at selected intervals, say every 10, 100, or 1000 ms to control a device?  Any help is very much appreciated.

[Matthew_Kelton]

You didn't attach the VI.

[Dave@Ventec]

Sorry, here is the VI....

[Amanda_H]

Hi,

Which hardware are you using to acquire data from? You could simply acquire the data, and using the Timing VIs to control the amount of time for each iteration of a while loops, for example. A more thorough discussion of the Timing VIs is in the following KnowledgeBase article:

Difference between Wait (ms) and Wait Until Next Ms Multiple

From what I understand, the VI you've attached is not accomplishing what your intended application is. Do you have another VI that is acquiring data?

[Dave@Ventec]

Amanda,

I am using a PXI based system to acquire data and control the process, BUT that is NOT the point.  My question is:  How do I GRAPHICALLY create a waveform (the attached sample VI does that fine) and then use that GRAPHICALLY created waveform to OUTPUT Y values at a user selected time interval to CONTROL an analog flow valve, that uses a 0-5VDC signal.  I know how to do the control part with the PXI hardware, I do NOT know how to get the Y values out of the spline created by this VI.  Thanks for your or others assistance.  David

[Matthew_Kelton]

There's a comment in the diagram stating where the Y values are.   Pull them out and geenrate them at whatever frequency or timing you desire.




Message Edited by Matthew Kelton on 12-31-2007 07:38 PM

[Dave@Ventec]

Matthew,

Thanks for your help.  I must be missing somethig, your suggestion is where I started, but the values at that point didn't seem to be following the generated curve as I thought they should.  Perhaps I just need to dig deeper.  I will try again.  David

[Matthew_Kelton]

The x values also make up the curve which is the line above it.  If you send the y values out at a different rate, you will not get the spline.  Make sure you generate enough poitns as well so that you don't make too big of a step between points.

[Dave@Ventec]

OK, I am now making progress with your help, just needed to be more persistant I guees.  One question leads to another...The resulting Y array has 1,000 elements containing data, even when I change the ramp to say 1,500 which results in an array size of 1,500, but with Y values only for the first 1,000 elements.  How do I get the array populated with 1,500 Y values?
Thanks.

[Matthew_Kelton]

I'm not sure if I'm misunderstanding your problem.  When I ran the VI and hit the stop button, there were 1500 Y values in the array.  Where you have the array positioned, it only gets updated when you hit the stop button.  Are you sure you didn't run it with a 1000, then 1500, but not hit the stop button.  That is the only way I can think of where you would see 1000 elements.