Triggered sequencing of continuous signal

[Matle]

Hi,

I am currently trying to build a VI which is able to cut a 1kHz periodic signal on one channel of my BNC box with an external trigger on another channel of my BNC box. This way I want to obtain packages of single periods  which are sequenced during the measurement, not afterwards.

I tried different VIs, but none of them was working properly. The best I got right now, is the one in the attached picture, using "basic level trigger detection.vi" and a get waveform subset vi. The problem is that the chopped sequences are not of the same length, even though I give the number of samples after the trigger signal as an input to the waveform subset vi.   

I hope my problem and the wanted outcome is clear. I would be very thankful for every idea.

Regards,

MaLe

[RupiDo]

Hi MaLe,

finally your aim is to cut a specific amount of samples after a trigger signal is occurred. I would recommend using DAQmx functions, so you can configure the trigger signal and set the acquired data to a specific amount.

I attached a screenshot. Be aware you are able to drag&drop this screenshot in the blockdiagram of LV 2012. So you have already the code.

Kind regards,

RupiDo

[lehrm]

Hey.

Thanks for your answer. The problem is, that data is being lost in between the finite acquisitions of n samples, which is not fitting to my requirements... I need a continuous acquisition.

But thanks anyways.

[RupiDo]

Hi,

now we have modified the example, so the card is continuously acquiring data and the rist 200 samples after the trigger signal are written into a queue.

Now you are also able with array and waveform functions retrieve a specific amount of samples.

Kind regards,

RupiDo

[lehrm]

Hey.

Thank you again...

The problem is still there.

I dont have a trigger to use the "DAQmx start trigger" vi.

I just spent some time trying to make your vi work for my case and i think it is impossible, because i want to use an analog square signal on channel1 of my PXIe-6124 to trigger the analog signal on channel0. 

I think my card cannot do this. I probably need a software solution for my problem. I built one that reads the trigger channel, finds the trigger time and uses the trigger time to sequence the actual signal. It works, but the signal is getting a bit shorter with every chopped sequence... that means it ALMOST works.

any idea how i could solve this problem?

[RupiDo]

Hi Lehrm,

the analog trigger signal shouldn't be the issue. The PXIe-6124 supports an analog trigger
. Check following link:

Which S-Series (61xx) Devices Support Analog Triggering?

http://digital.ni.com/public.nsf/allkb/074CF0F18BB49F9D862570260078DCE0?OpenDocument

Please try to set the trigger to analog and select for source: "DevX/ai1", so the trigger signal will be retrieved from channel1.

Kind regards,

Rupert

[don_Micheal]

I have the same requirement, but my device is different. I acquire signal from NI 9239 module which does not support hardware triggering. I can only use software triggering.

Could you please give me any suggestion!