start a counter with digital trigger

[zhengw80]

I want to use a counter in my DAQ card to count TTL pulses and I want this counter is started by a external trigger.

I run the example progrem 'counter-count edges.vi' provided by Labview and choose the tag of "Digital Arm Start". There is a error message which shows "Specified property is not supported by the device or is not applicabel to the task".

My DAQ card is PCI 6733 and my labview version is 2012 service pack1.

Does that mean the counter in my DAQ card cannot be triggered by external pulse? How can I do if I want to start a counter by external trigger? Thanks

[WenR]

Hi zhengw80!

That's correct, if DAQmx tells you that the feature is not supported, that means that your card is not able to handle triggering for that type of task. That is a common limitation for M Series cards. When that happens, there is a good workaround that consists of using 2 tasks, one that supports triggering and the one that you really want to use. The one that supports triggering is only used as a dummy task to get a triggerable clock, you share the clock from the dummy task to the actual task, and that way you get your task to start when the trigger arrives, both tasks will do.

This workaround is known as "Correlated Tasks", here is some documentation about it:

M Series FAQ  What is correlated digital I/O and how does it work?  

Community Example Performing Correlated Digital IO with an M Series Device in LabVIEW

Community Example Correlated Digital Input Using Analog Input Task in DAQmx

Hope it helps!

WenR

[zhengw80]

Thank you very much

It is helpful