detecting a change to a numerical control

[dbarr]

Hi. I am fairly new to Labview and I was wondering if I could get some advice. My question is how do you detect a change to a numerical control. I believe I need to use a property node or a invoke node but I am not sure which one I need to uses or if it is possible.

Thanks again

[Jorge_Amaral]

Hello,

It seems that you're very new to labview. Because there's some ways of doing that.

1- shift registers in a cycle and compare the actual value with the pass.
2 - use an event case and then, choose an event associated with the numeric control.

Or else, tell me your labview version and I can made you a small example

[parthabe]

You can use trhe Value Change event of the Numeric control.

See the attached VI in LV 7.1...

[dbarr]

Thank for that. I am very new to lab view only been using it for two weeks so a very quick learning curve.

Thanks again

[Wiebe@CARYA]

Use the event structure.

Regards,

Wiebe.

[dbarr]

 

Hi again. Sorry for asking another question but I have managed to get stuck again.

I have managed to get an event structure working to detect a change to an input of a controller which I have turned into a sub-VI. However I now have a new problem. What I actually need to do is create a high Boolean output if there is a change to the input control, and a low if there is no change. The problem with the event structure is that it needs a change to happen before it will allow the dataflow to continue. If anyone has any advice on how to achieve this I would be very grateful

Thanks again

[GerdW]

Hi dbarr,

that's easy:
create a second event case (using the same structure!) with event "timeout". Set a nice timeout-time of maybe 200ms. Wire a TRUE constant from value.changed-event and a FALSE constant from timeout case. You can also set the wire tunnel to "default if unwired", then you don't need the FALSE constant.

[dbarr]

Thanks for that 🙂

dbarr