Basic problem with timing 1 DO

[marc france]

Hi everyone,

I am using a 6229 PCI card and Labview 8.5 with XP.

 I need to generate every 10 secs a Digital Output that is  low for 3 secs low and high the rest of the time. I have attached the VI that works fine with my previous values (500 ms and 2000 ms). However I get a low state for 1 sec, 2secs or 3 secs but not continously 3 secs when I used it with the 3secs/10secs values.

It works if I use the values 3secs/15secs  (15 secs or higher).

There must be a problem with my looping but I don't understant what the problem is, since the outside loop should be waiting for the inside loop to finish before starting a new loop. I don't get why my low state time is affected by the exterior time loop...

This is probably a basic pb for you, but any help would be great,

Regards,

Marc 

[Dennis_Knutson · Accepted solution]

It seems overly complex. Below is an alternative. I used the Delay function since it has the error in/error out connections to enforce data flow. I also changed the type of DAQmx Write since you seem to be only writing to a single line.

Message Edited by Dennis Knutson on 11-20-2008 09:03 AM

[mehdi.afif]

Hello.

The best solution is to use a counter rather than a digital out line, and to set a frequency of 0.1Hz and a duty cycle of 0.7 . You would have in this case a better timing accuracy for your generated signal.

Regards

Message Edité par mehdi.afif le 11-21-2008 08:27 AM

Message Edité par mehdi.afif le 11-21-2008 08:28 AM

Message Edité par mehdi.afif le 11-21-2008 08:29 AM

[marc france]

Hi Dennis and Mehdi,

Thank you for your help. Dennis, you solution works out fine and I will use it. However, if anybody could tell me why my VI has this strange behaviour. I would like to understand what  the problem is.....?

Mehdi, I know the 2 output counters are more accurate, but I don't need any very accurate outputs for the moment. I prefer to leave them available in case I need them in the futur.

 Best regards,

Marc