Combining analog input and frequency counter

[Gisle]

I am trying to measure a voltage as a function of a frequency. The application must be trigged by a signal at the apfi input. I have not found any way of trigging the counter from the apfi input. It is important that the frequncy is measured at the same point as the voltage, or at least at a constant delay. It would also be appreciable to acquire pretrigger-samples. The card I am using is ni-usb 6259.

[Christian Mergl]

Hey,

You can trigger an AI Task with a analog signal connecte to APFI. However a counter task for frequency measurements cannot be triggered.

Also I assume that when talking about a trigger you understand to use a external signal as kind of sample clock. A trigger at DAQmx is unique event to e.g. start an acquisition.

Christian

[kikiduu]

What you can try is to configure AI's trigger to use level triggering at APFI line and then set the Counter's trigger settings (using 'DAQmx Trigger' property node)  as follows

ArmStart.TrigType: Digital Edge

ArmStart.DigEdge.Src: DevName/ai/StartTrigger

ArmStart.DigEdge.Edge:  Rising

After doing this start the Counter task first and then the AI start task.

Even though I have used triggering of counter with AI starttrigger, I have not yet tried cascade triggering that I have suggested above. So may be you can just give it a shot. 

Please let me know what happened.

Message Edited by kikiduu on 02-05-2009 04:48 AM

[Christian Mergl]

@kikidu:  you cannot set a trigger for a frequency counter task.

[kikiduu]

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Christian_M wrote:
@kikidu:  you cannot set a trigger for a frequency counter task.

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May be you are right, I have used it for edge counting using counter not for frequency measurement using counter.

Message Edited by kikiduu on 02-05-2009 09:53 AM

[Christian Mergl]

@kikidu: No, I'm sorry, you where right, you can use an arm.start trigger with this bord. It just does not work with E-Series boards.

Christian