Use a Counter to Export a Change Detection Event on a PXI-1078e Chassis Using LabVIEW with DAQmx

[anaddaff]

I have 7 counter channels running on the 6614 timer card.  Each channel is triggered by an externally generated digital pulse.  I would like to generate a single back plane trigger if any of these channels are triggered.  There is a lot of information on triggering multiple channels from a single source trigger, but I can't find any information on setting a trigger from multiple sources.  Is this possible?  What degree of timing accuracy can I expect?

[Kevin_Price]

You could do this using a DI task with timing set for "Change Detection".  According to the manual, change detection is supported on both port 0 and port 1.

Be sure the signals that trigger the counters are wired into lines of port 0 or port 1, configure a DI change detect task that's sensitive to the appropriate triggering edge, and then export the "change detect" signal to the PXI backplane. 

There's a shipping example for change detection DI and down below is a LV 2016 snippet of the code that shows how to export the change detection event to the PXI backplane.  (Note that you need to configure this signal export before starting the task, as shown.)

-Kevin P

[anaddaff]

This method worked well.  It was best to use the change detect lines to trigger a counter output to drive the PXI trigger.  There is a good example on the forums.

Use a Counter to Export a Change Detection Event on a PXI-1078e Chassis Using LabVIEW with DAQmx

 

 

by  KyleTTUon 

‎12-05-2011 12:19 PM

 - edited on ‎08-14-2017 12:53 PM by  Example_Scrubber_Nian

https://forums.ni.com/t5/Example-Programs/Use-a-Counter-to-Export-a-Change-Detection-Event-on-a-PXI-...

[Kevin_Price]

Thanks for the helpful follow-up and link!  (The more robust method allows for a longer pulse.  Some PXI chassis models can't propagate the very short "change detect" internal pulse signal (50 nanosec pulse width I think?) to all the slots reliably.)

-Kevin P