topic Re: Event Structure in LabVIEW

Event Structure

pnam — Sat, 03 Sep 2011 03:16:22 GMT

I have attached a simple code (test.vi) with a case structure. Is it possible replace the case structure with an event structure (testvi.vi)( using user event?)

If yes please let me know the solution . I am trying to modify an already existing code with an event structure and am running into problems.

Thanks in advance,

-P

Re: Event Structure

RavensFan — Sat, 03 Sep 2011 03:28:22 GMT

Anything is possible. But a case structure has a completely different purpose than an event structure. A case structure is to take one of two or more different actions based on a condition. An event structure is designed to wait for something to happen than take an action.

We can't answer your question without know what it is you are really trying to do here.

Re: Event Structure

stevem181 — Sat, 03 Sep 2011 20:06:10 GMT

It appears that you are simulating checking the level in a Tank and you want to perform an action when the level reaches a certain point.

Assuming this is correct, it is usually best to do the data acquisition and level check in a loop that is separate from your Event Structure loop.

This is called a Producer/Consumer design pattern.

See the attached example "test1vi mod.vi".

For extremely simple situations or a quick test, the Timeout Event can be used for what I call a "Poor man's Producer/Comsumer".

See the attached example "test1vi mod 1.vi".

Re: Event Structure

Citabria — Sat, 03 Sep 2011 21:17:25 GMT

The Answer is most definitely yes, you can use user events. In fact, it is my preferred method of communication between processes. You will need 2 while loops one will hold the event structure, the other will fire off a user event whenever a condition is met. Look up some examples of user events. There are many, many other ways to accomplish what you are trying to do (queues, local variables, etc.). It's all a matter of preference and need.

Re: Event Structure

Citabria — Sat, 03 Sep 2011 21:17:25 GMT

Re: Event Structure

Citabria — Sat, 03 Sep 2011 21:51:11 GMT

I re-wrote your test1.vi using User Events. Take a look. Hope it helps!

Re: Event Structure

pnam — Mon, 05 Sep 2011 13:18:45 GMT

Thanks everyone for the response. Here is what I am actually trying to do.
I have a Labview code (attached) which 'sends out a trigger and saves data from 4 channels every time we hit F8 or a button on the front panel.
('Triggering' in the Event structure)

I would now like to modify the code as follows:

1) Press F8 and the very first time one of the channel signal crosses (yet to determine which channel) a user defined threshold, I would like
to 'sends out a trigger and saves data from 4 channels'

2) I would like to make minimum modification to the structure of the code and use the event structure that already exists.

I am working with somebody else's code and am not an expert in labiview. Any help will be highly appreciated

Re: Event Structure

pnam — Tue, 06 Sep 2011 15:09:02 GMT

Thank you.

Re: Event Structure

pnam — Tue, 06 Sep 2011 15:09:39 GMT

Could you plesae convert it to 8.2 and send it to me please .

Thanks

Re: Event Structure

stevem181 — Tue, 06 Sep 2011 17:23:59 GMT

Here are my examples converted to 8.2.

Re: Event Structure

pnam — Tue, 06 Sep 2011 18:39:25 GMT

@stevem181 test1vimod.vi is perfect for my application. Thanks you. I would like to make one more modification to the code. I would like to have a button in the front panel. I want the indicator to light up (or the event to occur) only once after the button has been pressed. ie Everytime I press the button, the first time the condition (comparison) is satisfied I want the event to occur (indicator to light up) Can this modification be made without changing the structure of the program . Thanks again for your help.

Re: Event Structure

stevem181 — Tue, 06 Sep 2011 19:27:24 GMT

There are many ways this could be done. Here is one way.

Re: Event Structure

pnam — Wed, 07 Sep 2011 12:55:17 GMT

Perfect! Thank you!

Re: Event Structure

pnam — Wed, 14 Sep 2011 16:58:19 GMT

Hi , I am trying to integrate the new piece of code in the main program. The main program is 'TMS Trigger and Save_modified.vi' In this progam, currently, the trigger is being sent when We press 'F8' or the 'Trigger button'. I would like to replace this trigger with the output of the indicator 'Limit?'. I tried doing this but ended up with an error message. I think this was mainly due to the fact that I'm trying to replace one type of input with another. -Priya

Re: Event Structure

pnam — Fri, 16 Sep 2011 18:48:00 GMT

How do we take a variable outside the while loop. The indicator Limit? lights up, but Limit?2 does not.

-P