How can I synchronize the start of a measurement with a AO cycle......?

[marc france]

Hi everyone,

I need some advice for a labview program :

I need to generate a square wave form signal to control a heater ( high level from 10 ms to 2 or 3 seconds ). At the same the time I need to acquire data ( impact of the heater on the value of a voltage ) up to 1 sample every  1 ms. They work fine seperatly. However, since I don't need to acquire the data alway through, but I need to keep the heater cycle going, I would like to know how can I launch the measurement( lets say to save 2000 samples ) and then acquire again something like 10 minutes after ( doens't need to be precise ) but it has to start at the same place on the heating cycle each time. (

Should I trigger my AI with a AI trigger wired to the AO of the heater?

What is the best Solution?

Thanks a lot for you help,

Regards,

[falkpl]

What card are you using?  if you have a counter opened you can trigger both the AI and AO on the edges of a pulse out.  This is nice since you can set the AO to trigger on the rising edge and the AI to trigger on the falling edge allowing for precise timing of a measurment seperated by the high time of the square wave.  Triggering on the same edge will allow you to synchronize collection.  This technique also allows to do pre triggering measurments as well.

Paul

[marc france]

Hi Paul !

Thanks a lot for your help. I am using a 6221 PCI card. Would you have any example on how to use the counter solution? In order to see how I can fit it in my program....? I do'nt seem to find any example that triggers measures or generations....

regards,

Marc

[falkpl]

I dont know if there is an example but essentially there are 3 tasks.  AI, configure the points to read and rate, set the trigger to a pfi line.  AO set the out task and configure the trigger with the same pfi.  Task 3 is a pulse train with the outlien equal to the same pfi as the trigger lines, so no extra wiring.  start ai and ao THEN start pulse out task.  everything will be synchronized.  if this is a repeting measurment set up the retrigerable? property of the AI and AO and make your Pulse out a pulse train continious.

Paul

[marc france]

Thanks again for your help Paul. I'll try and follow your advice...

regards,

Marc