combine triggers

[JackTK]

Ladies and Gentlemen

Is there a way to combine two different triggers. I have an analog signal that happens every 50msec that is 10usec wide alternating positive and negative. I have a trigger for each half. One for the positive portion and one for the negative portion. I am using a USB-6251 DAQ. Although I would like to collect all the data, it is not important. what I would like to do though is collect adjacent pulses. A positive and negative pair. Any suggestions?

[J-Barticus]

Hi JackTK,

Are you triggering off the analog signal, as in using an analog trigger? Or are you also sending digital triggers along with the analog signal that correlate to the positive and negative cycles of the signal? Could you perhaps provide an image of a period or two of the signal in question?

From what I have gathered, a solution to your problem maybe to use only a single trigger at the start or positive cycle of your signal and then read a specific number of samples from that point such that it encompasses both the positive and negative portions of the signal.

Is there a reason that you think you can not collect all of the data? How long are you planning to record this signal for?

-Jake B.

[John_P1]

You could configure a dummy digital input task with change detection timing.  Change detection lets you sample the task off of the rising and/or falling edge of one or more lines.  Whenever a sample is taken, it generates a "change detection event" which you would use as the consolidated trigger signal.

Or like Jake said, you could just acquire the entire signal and parse it down in software.

Best Regards,

[JackTK]

Hi Jake

I have a hardware digital trigger that I generate for the positive and negative thresholds. To collect the entire event, would be about 30,000 points. Most of it is not useful. I collect 100 to 1000 cycles. To make things worse, the period could change plus or minus 50%. And there's probably 10% jitter.

Jack TK

[JackTK]

Hi John

I'm interested in the Dummy Digital Input Task. What is it and how would I use it as a trigger.

Jack TK

[John_P1]

The digital input task would be configured something like this.  The inputs have to be 0-5V TTL though.  There is a signal called "ChangeDetectionEvent" that would occur whenever one of the specified edges occurs--you can use this to trigger your analog input task.  

However, analog input tasks are not inherently retriggerable on M Series.  You can get around this by using counters as in this example.

Best Regards,

[JackTK]

Hi Jake

This approach (collecting both pulses with one trigger and parsing) actually works pretty good. I don't collect every pulse pair but I do collect adjacent pulses. Like I said, it's more important to collect adjacent pulse pairs. I think I may tinker with John's suggestions to increase the throughput but right now this works for me.

Thanks a bundle

Jack TK

[JackTK]

Hi John

Thanks for the suggestions. I plan on implementing this at least to test it out to see if it is what I need. Sounds very promising. I implemented Jakes suggestion and it works pretty good although I would like to utilize the 2 triggers. I have some sensors that use 2 analog channels and I would like this software to handle it all.

Thanks

Jack TK