Starting and stopping Elapsed Time

Question

I have some code in LabVIEW 8.2.1 I am writing for Qual test with a customer. The basics of the test are the following: monitor and record pressure (thru transducers), temperatures (fluid and ambient), and monitor the opening and closing a valve. The valve has two light switches orientated in such a way, that mechanical counters will count a cycle when it is fully closed to open to closed.
The problem I am having, is that I need the elapsed time vi to start counting, once it has moved off of the full open switch. It needs to count to 240 seconds, at which time it will pass on to an on bit, which will energize the valve again. I can get it to start running at the right part, but it will stop once
it gets in between the two light switches. It almost seems like the elapsed time vi doesn't have enough flexibility for what I need. That or I need to write a bunch of code that would enable it to do what I want.
I am not sure on how I can post code so it can be viewed in LabVIEW, so here is a word doc.
Attachments:
elapsed timing vi.doc ‏45 KB

Answer 1

Hello Chadius, 
Thanks for posting,
I took a look at your code this morning. We at NI recommend using varibales as one of the last resources when trying to pass data out in cases where this is rseally necesary, when looking at your code I realized that the variables to pass data are not needed and that actually there are some misconceptions about the functionality of the vi funtions, do not be ashamed that is totally understandable when you are new to a concept and more understandable if you are new to labVIEW.
Before proceeding with the code I would like to encourage you to check the Getting started with LV It gives you the basis to start programming in labVIEW and helps us understand better how LV executes.
There is also a lot of good help loaded in Labview that can help us determine what to use and what is expected of each function, you can access this by pressing ""CTRL+H" and accesing the detailed help when hovering over a specific VI and clicking detailed help.
Then if you are a new user to labview and would likely use labview for long term development I will suggest the training.
Now, getting to your code I can see that you are doing a bit more code than what you actually need, so for instance:
-we can eliminate the constants and the selector and just pass the boolean.
-we can also use less while loops so the part where you write to the variables can be done in the same while loop on the right.
-Instead writing to the variable and reading from that same variable you can just wire a cable so you have the same data
-You can use the error wire out/in of the functions to control code execution.
Last but not least, I am asumming here that this application you are coding is most likely to be a state machine where you are making a choice depending of the inputs you have, If "A" then "B"
This is an example of a simple state machine based on user input, you can change that input to be an event, a trigger etc.
Hope this helps, 
Luis
Application Engineer
National Instruments. 
Attachments:
LV_Getting_Started.pdf ‏918 KB
This way looks better.JPG ‏20 KB
Delete constants pass only bbolean.JPG ‏15 KB