how to synchronise two digital output lines?

[olga99]

I need to control two electrical valves using two digital outputs. I want to send a true signal during 20 minutes, and them a false signal during 20 minutes and them a true signal during 20 minutes, and so... all the time, to use it in a automated analytical system. How should I do it?

[Dennis_Knutson]

Do you have a DIO or multi-function DAQ board? If so, it's just a matter of using one of the digital functions on the DAQ palette like Write to Digital Port. For the timing function, what you don't want to do is use the Wait (ms) function unless you don't card about interupting or quitting the program quickly. Get a start time at the beginning of a loop with Tick Count or Get Date Time in Seconds and periodically check the elasped time.

[olga99]

I have a multi-function DAQ board (a PCI 6024 E (NI)). My problem isn't how to comunicate with the digital output lines, but how to use the timing function. How can I check the elapsed time? Thank's for your help.

[Dennis_Knutson]

Subtract current time from start time ans with a reset of current time when your condition is met. The attached VI should give you a hint.