while loop: execution time and continuos updated - elapsed time VI back to false?

[fabbro12]

Dear all, 

I want to control the execution time of a while loop. I want the user to have the possibility to decide for how long he wants to execute the while loop. THe while loop is used to update some values, so it should continuosly run, not just run once and then wait (which I could easily do using the timing functions).

I used the elapsed time VI like suggested in this post:

http://forums.ni.com/t5/LabVIEW/How-to-create-a-time-control-for-while-loop/m-p/2530212/highlight/fa...

and works ok, but the while loops are integrated into another for loop, and when the for goes to next iteration, the elapsed time boolean output is fixed to true and it does not execute the while (I think this is the problem). 

Is it possible to set the boolean output of the elapsed time VI back to false once the time target has been reached? This would solve my problem, I think...

I attach a part of my VI, even if I don't know it could be useful to you...

Thanks for your help

[GerdW]

Hi fabbro,

read the help for ElapsedTime and use all of it's options…

[fabbro12]

Dear gerdW,

I did read the help of the function vi but i did not find it well explained. Is the reset button that i have to use? I also tried to wire a boolean constant set to true into the reset and into the autoreset, but the vi is still not working as expected...

[GerdW]

Hi Fabbro,

to quote the help:

Dialog Box Options

Parameter	Description
Automatically reset after time target	Resets the elapsed time marker.

I think this is what you are asking for…

[crossrulz · Accepted solution]

Use the iteration counter for the While loops and a Equal To Zero? node.  While the output of the comparison to the Reset input of the Elapsed Time functions.  The idea is that you reset on the first iteration (when i = 0).

[fabbro12]

Thanks crosslrutz... Now it works great, even if I still did not understand the logic of the thing! The most important is that it works 🙂

[billko]

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@fabbro12 wrote:

Thanks crosslrutz... Now it works great, even if I still did not understand the logic of the thing! The most important is that it works 🙂

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Actually, understanding it is just as important because you may run into this same kind of issue in slightly different forms in the future.

When [i] = 0 (the first time through the loop), the output of Equal To Zero? will be true.  The timer is reset to zero.

For any other value of [i], the output will be false and the timer will NOT be reset - it will keep counting.

This is a fairly important concept to learn because there are all kinds of situations where you would employ this logic.

[fabbro12]

Ok, I understood of course that we reset the Elapsed time starting from the first iteration (i=1....).

The only thing I did not get (and still I continue not to completely understand because  the help is not written clearly) is WHAT this reset does... Does it turn the boolean variable of output to FALSE when the Elapsed time function is recalled? 

I don't think the reset put to zero the start,time because I also wire a true constant to the auto reset terminal (means that the start time will be "Present" any time the VI is called)....

So, according to me, NI should provide a better description of what RESET does.... 

[GerdW]

Hi fabbro,

beside the (maybe) needed better description:

ElapsedTime is an ExpressVI. You can open ExpressVIs (with a right-click) and look what they do inside!

[Liu9079]

Hi!! 

I am having the same problem now, what did you do to solve the problem? Did you use the auto reset or reset?