Timer to generate on/off signal every 20 mins for 10 sec

Question

I need to create a simple timer. It comes on every 20 minutes for 10 seconds, then switches off until another 20 minutes has passed, and so it repeats itself. I want to open a valve with this every 20 mins for 10 secs, then close it. This is to work with a field point device that we have on our shelves.

Answer 1

Here is a simple solution.
Create a while loop, inside the while loop put a sequence in step 1 place a wait vi and set the value to 20 min (remember this input is in ms so 20 min = 1200000) in step two place the code to send the on signal (hardware output I assume) in the third step of the sequence place another wait for 10 seconds (10000 ms) and finally place the off sequence last. This solution is very processor friendly. If you just compair time stamps inside a loop, the loop will be continiously checking the time and your CPU use will max out. You can place an inherent wait in the loop but the responsivness (accuracy of your timming) will be reduced. The wait statment will pause your program until the timer (I believe it is linked to the OS interupt system) expires. This solution allows for multiple threads (loops) to run cuncurrently with little extra overhead. I have used timers to generate alarms in the past where the sequence after the time expiring fires an occurance to drive code in other loops. Hope this helps
-Paul
Paul Falkenstein
Coleman Technologies Inc.
CLA, CPI, AIA-Vision
Labview 4.0- 2013, RT, Vision, FPGA