Question about mixed signal collection and digital trigger

[hanwei]

Hi all :

I want to develop a project basd on the DAQ  analog and digital signals collection. The digital signals is used for triggering (start and stop) the Analog signal sampling.

now I have two solution here, 

the first one is to acquire both analog signal and digital signal, then develop some logics in loop and  use digital signal to control the analog sampling .( like software trigger)

another solution is normal digital trigger issue.  (like hardware trigger)

 1. I am not sure which one is better??

 2. Is it possible, if I want sample mixed signals including analog signal and digital signal??

 3. Can the continuous collection loop in the system  restart, when the next digital rising edge comes, if I choose hardware triggering.

( The basic idea of my program is:  at the begining, the system start, when the digital signals is coming and the system will run with a custom-defined operation time. then the system stop until next digital triggering signal come )

Thanks so lot

regards

[Christian Mergl]

Hey,

to 1: Iit depends on your application. if softwaretiming is fast enough then its easier to use the first solution. I would prefer hardwaretiming.

to 2: It depends on your hardware. If you have e.g. an M-Seriesboard (pxi-62xx) you can use the AI sample clock as timing for the DIOs, so its possible.

to 3: What you mean is called "retriggerable AI", which is described here (with example) http://zone.ni.com/devzone/cda/epd/p/id/5228

        You cannot retrigger the AI for its own in hardware. For that a counter Task will be used which is retriggerable and provides the sample clock for the AI,

        which you can use then also for the DI. But as far as I understood you, the DI signal should only be the trigger.

However, you will find a lot of useful hints under the retriggerable example and also when you search for "synchronization" or "retriggerable" with the LV Examplefinder.

Hope this helps,

Christian

[hanwei]

Hi Christian:

Thanks for your reply.

The measurement hardware I am using now are E series and Scxi-1102 and Scxi-1162HV.

and I just want to implement digital signal trigger.

Actually, the digital signal is from PLC, and it is used for starting and stoping the analog data sampling (by Scxi-1102). 

For example:

1. At the first step, the measurement system(analog signal measurement) is starting when the PLC send a digital signal "1".

2. And then if the digital signal change to "0", the measurement system is going to stop.

3. After that, again, when the digital signal from PLC is "1", the system is going to start again. 

you know, for continuous analog data sampling, I define a data process loop in my program. So my question is : Can data sampling restart, when the next digital triggering signal is coming . 

Here I attached a NI example for Analog DAQ with digital start. I add a loop here, and want to implement continous data sampling.

In this examlp, if the digital is becoming from "0" to "1", the data sampling will start.  but if it is changing from "1" to "0", what's going on?? stop? . 

  if it could stop when digital signal change from 1 to 0, and then next rising edge of digital signal still can restart the data sampling, right??

Thanks again

best regards

[Christian Mergl]

Hey,

Attached you find an example what should be what you need. It is using the pause trigger, which you can set to pause when a digital signal is Low or High. So in your case you cane set it to Low and you acquire data as long as your pulse is high, stop acquiring (pause) when it is low and starts again when it is high.

Christian

[hanwei]

Hi Christian:

I really appreciate your help, your suggestion is very good and useful for me. Thanks a lot.

Here I have a another small question about source of trigger. you know, the NI measment equipment I am using is Scxi series, but it seems I can't use scxi channel as a trigger source, isn't it???

Best regards

Wei

[Christian Mergl]

Hey,

Here is a KB which descripes how to use hardware triggering with SCXI: http://digital.ni.com/public.nsf/allkb/B84AB0F53DEEAEDA86256CFE00782A2E?OpenDocument

Hope this helps,

Christian