Reference Trigger. Continuous Acquisition. Is it possible with a PXI-4472?

[Giulia]

Read what I have found:
"Pretriggered acquisitions are ultimately finite acquisition."
"Although continuous data acquisition with pretrigger samples is not an application that is built into the driver or native to the hardware, it is possibleto code this type of application on MIO boards."
Is PXI-4472 a MIO board? If it is not, does it mean I can't produce this application?

[Russell]

The PXI-4472 is not considered an MIO board, although there are similarities.

I can't think of a really good way to have a pretriggered acquisition be retriggerable (or continuous as you said). I see a couple of options.

1. Reconfigure the acquisition after each trigger. (As long as there is enough time between your triggers, this just might work for you.)

2. Set up a continous acquisition and wire your trigger into one of the other analog channels. You can later compare the two channels' data side by side in software and pick out the datapoints surrounding the triggers.

I hope this helps!

Russell
Applications Engineer
National Instruments
http://www.ni.com/support

[Giulia]

What a bad new!Let's find an appropriate solution.
1)The signal is non-periodic. This means I don't know when the trigger occurs. Probably, we have got 10 events/years, but we could have two close events in few seconds. What does you mean for "enough time between your triggers"?Microseconds? Seconds? Minutes? Hours?
2)I'm not sure if I have understood your suggestion: should I collect and write down all scans, then read them again and select them in software? In this case, what does the trigger is for? I have already tried a Acquire&ProcessScans Example vi. and My Data Processing was writing data to file only if data was over threshold. The problem is that this software processing was not able to collect pre-threshold AND post-threshold data, I mean it can'
t collect both. As a consequence of this bad results, I gave up software and went back to hardware, trying trigger selection, untill I found (as you confirm) that even this one is not a solution...
Thank you for attention, hope to hear from you soon.

Giulia De Bonis
Roma

[AlessioD]

Giulia,

what Russell means when saying that you should acquire your trigger as an analog channel is that this way, you would be able to perform post processing of your acquired data. That is, acquiring your signal and your trigger together, allows you to graphically or digitally see when the trigger occurred and decide how many points you want to save before and after the trigger went off.
Unfortunately the 4472 was not designed for the sort of application your are willing to implement. A MIO Board would do that easily.

AlessioD
National Instruments

[Giulia]

Do you mean acquire the trigger and the data together, view both on the same graph and compare them and compare scans acquired in their "written" form? How can I do that?
Are you italian? If yes, please help me in our language, or write me an e-mail
giulia.debonis@roma1.infn.it

[aldeot]

Giulia,

yes, that is exactly what we mean. The way to implement this depends on what version of LabVIEW you are working with. If you are working on LV 7, then there is a good library of functions called Signal Manipulation that would allow you to easily handle and work with your data once they have been acquired.
Basically you should go through your scans and check when the trigger has come in. Depending on the position of the transition (from 0 to 5 V I guess) you can roll back N samples and save those N + M samples you are interested in (being N the number of pretrigger samples and M the number of posttrigger samples).

I think it would be best if you call directly by phone one of our Engineers at NI Italy and discuss the p
roblem directly with us.

AlessioD
National Instruments

[Giulia]

I looked at Signal Manipulation Library and found Trigger&Gate Express VI. It works perfectly, with every trigger threshold, but it stops working at all if input signal amplitude is less than o.4 V pk-pk.

I have noticed that, if input signal amplitude is less than 0.4 V pk-pk, my VI doesn't work. Is it my fault, or is it a real limit in Trigger&ate VI? How can I solve it? (Data I have to acquire are usually lower that 0.1V)

Same question, in Italian:


Noto che, se l'ampiezza del segnale di ingresso è inferiore a 0.4 V picco-picco, il mio VI non funziona. E' un errore nel mio VI, oppure è un limite reale in Trigger&Gate VI? Come posso risolvere il problema? (I dati che devoo acquisire sono di solito inferior
i a 0.1 V)"

[Giulia]

I have found something quite strange... It doesn't seem Trigger&Gate's fault. Look at the VI. It is the simplist DAQ you can create, it is taken directly from NI Examples (it is ContAcq&Graph (buffered)vi). It can't collect data if input is less than 0.4. This means I can collect noise (no input connected)