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How to find the exact elapsed time?

Hi everyone

 

I'm collecting data using Labview. A part of my task is to measure the pressure at different locations by controlling solenoid valves. The code for controlling the valves placed in a case structure, by using elapsed time function I hold each valves open for 15 sec, while the pressure measurement is continuously acquired.

 I have 4 valves. This mean 4 different set of data(15 sec each, total of 1 minute). My problem is: all the data saved in one file and as the elapsed time has some lag (does not hold the valve exactly 15 sec). I cannot separate the data easily. Is there any way I can estimate the actual elapsed time?, as I've the data already and it's not easy to repeat it the runs.

For future work, I should be grateful if you suggestion a way to work out the exact elapsed time for each case?

 

Regards 

Rajab

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Seeing some code would be helpful.  Does LabVIEW turn the valves on and off?  How are you timing the 15 seconds of data acquisition?  Why do you say that the valve isn't open exactly 15 seconds (unless the user is turning the valve on and off "manually")?

 

LabVIEW has numerous "timing" functions that should help you here.  The basic functions provide a time resolution of 1 millisecond, which should be sufficient for your task, I would think.

 

Post a VI (use the "Save Selection as Snippet" option on the Edit menu and insert the resulting .png as an image) so we can help you.

 

BS

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Bob_Schor wrote: The basic functions provide a time resolution of 1 millisecond, which should be sufficient for your task, I would think.
Resolution of 1ms, but not the accuracy.
What I like to do with these kinds of systems is add to your data acquition channels feedback of your control signals.  Then you can see exactly when each solenoid was commanded to be on/off.

GCentral
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