Finite Position Counter acquisition using reference trigger

[tcoppert]

I am using Labview 7.1 Full Development, on Win2000, with a PCI-6251 M-series device, and i'm using DAQmx.

I would like to synchronize the acquisition of analog inputs with a quadrature encoder based on a digitial reference trigger (with a specified # of pretrigger samples) on PFI0.

Everything works well, except that i can't figure out how to use a reference trigger with the position counter.  It keeps giving me the error # -200452 "Specified property is not supported by the device or is not applicable to the task.  Property: Ref.TrigType"

Is it possible to synchronize the position counters with a *triggered* analog input acquisition?

I've searched everywhere and i can't find any documentation on this topic.

If i didn't want to have a triggered acquisition, then the synchronization works great, but my application requires that this acquisition be triggered.

Any advice or workarounds would be greatly appreciated!

Thanks.

[Thaison_V]

Hi tcoppert,

Setting up a start trigger to arm a counter operation is done a bit differently than setting up a start trigger for an analog input task.  Whereas with an analog input task, you would use the DAQmx Start Trigger VI, you actually need to use DAQmx Trigger Property nodes for counter operations, otherwise you will get the error indicating that the property is not supported by this task.  One other thing I should also clear up is that this only performs a start trigger on the counter operations.  A reference trigger with pretriggers is not supported for counter tasks.  To actually add the property you need within the DAQmx Trigger Properties, browse to More>>Arm Start.  Take a look at the attached VI to see an example of how to set this up.

Thaison V

[tcoppert]

Thaison,

I really appreciate the info!  Although DAQmx is a big improvement over the old traditional NI-DAQ, this counter trigger functionality still seems like it wasn't completely thought through. 

I will try the DAQmx Trigger Properties as you suggest.

Thanks again for the help,

Ted

[tcoppert]

Thaison,

I ended up implementing my project using the Arm Start under the DAQmx Trigger Properties as you suggested.  Although this doesn't allow a Reference Trigger (with pretrigger samples), it does allow the counters (position encoders) to by synchronized with the Analog acquisition as i needed.  It will work for now.

Thanks again,

Ted

[Thaison_V]

Hi Ted,

I'm glad the suggestion helped and you were able to get that working how you wanted for now!

Thaison V