How do I auire data at every third pulse of an external trigger?

Question

I need to aquire 2048 data points where each one is triggered by the third pulse of an external trigger (TTL). Currently I can aquire 2048 data points where each is triggered by every pulse of an external trigger but I need to be able to do this at every third trigger pulse. It seems that I can't do this simply by entering "2" into the "skip count" input of the "Additional Trig Parameters' input of the "AI Start" VI. My attempt is in the VI titled TriggerScanA.
Further more I will need to know the actual trigger scan rate for data analysis. This is also prooving difficult since even when I am triggering off every external trigger pulse the actual scan rate only returns zeros. My attempt is i
n the VI entitled TriggerScanB.
Thankyou.
Attachments:
Trigger_Scan_VI's.llb ‏211 KB

Answer 1

Greetings,
This sounds like an interesting application. I would suggest that you use your external pulse train as a scan clock, not as a start trigger. Furthermore, since you want to acquire data every third pulse, you will need to use one of your device's counters to divide-down this signal. To accomplish this task, you will need to configure the counter for pulse train generation with an external source - your external pulse train. You will then need to choose the correct "raw counts" to generate a pulse train with a frequency that is 1/3 of that of your external signal. I would suggest that you examine the example Generate Pulse Train (DAQ-STC).vi for this purpose. Now, you can perform a finite analog input acquisition of 2048 data points u
sing this pulse train as your scan clock. Finally, to determine the frequency of your scan clock, you will need to us your device's other counter to perform a frequency measurement of either pulse train.
I believe that this will be your best approach to accomplishing this task. Good luck with your application.
Spencer S.