Triggering waveform graph

[SiK]

Hi,

I'm wondering if it's possible to get the signal displayed in waveform graph stable? Waveform graph is in a while-loop and signal scrolls on waveform graph at speed depending on frequency. Now the signal to the waveform graph is coming from Square Waveform.vi in the same while-loop but in the future we are going to use waveform graph as an low frequency oscilloscope with analog input of multifunction DAQ.

Thanks,
-Simo

[Dennis_Knutson]

A graph is nothing more than a fancy array indicator. What you can do is set a trigger in your data acquisition so the start of the waveform is always at the same place. You could also post process the acquired data with the Basic Trigger Detection function (Analyze>Waveform Monitoring palette) to find a trigger point. In your simulation with the Square Waveform.vi, set the reset signal input to true. This creates a new waveform array with each iteration and sets t0 back to zero instead of appending new data to the previous.

[SiK]

Thanks for your answer, it's nice to hear it is possible.  I tried  to set reset signal 'true' and it worked fine with the square waveform generator. I'll try tomorrow with real input signal from PCI 6251 card using 'basic level trigger detection'. I'm just not sure what should I do with trigger detected or trigger location signals, but I'll try something. Advices are really welcome..

Thanks again,
-Simo

[Dennis_Knutson]

Well, if you use hardware triggering for the DAQ board, it will work just like a scope when you set a trigger point. If you use the software to detect a trigger location, you can modify the acquired signal. If you're not interested in the pre-trigger data, you can just delete all of that data from the array. If you get a waveform datatype back from the DAQ board, you can use the Get Waveform Components function to get the Y array and then any of the array functions can be used on it. There are also a lot of functions on the waveform palette to manipulate the data.

[SiK]

Triggering works just fine now, I used DAQmx trigger. Thank you very much for your advices.

-Simo

[damiano.natali]

I feel a bit ashamed to answer since I have myself a little or no experience with Labview, so comments from more experienced users are welcome.

However, since I have lost a couple of hours looking for the answer, I think that may be useful for others!

I'm simulating a signal with the "Simulate signal" box, so for me the solution was to go into the properties (double-click on the box) and, under the "Timing" section, thick the Integer number of cycles" box.

Hope this helps,

Damiano