unclearity about analog signals

[Borges]

Greetings,

I am trying to create a small DAQ system that digitalizes a analog signal and displays the waveform and spectral analysis. I know that the analog waveform component receives and array to plot the waveform. However I am having doubts about how many samples I need to collect to create the exact graphs that is annexed to this post.

Could anyone give me some help please?

Thanks

[10Degree]

Borges,

Without a lot of detail on your problem, I would suggest you look at some topic on analog acquisition.  It seems as though you would like to capture an accurate "shape" of your signal, and also to sample at a high enough rate to accuratly capture the component frequencies in your signal as well.  I did a quick search on the NI site and found this intro:  http://zone.ni.com/devzone/cda/tut/p/id/3016.  You may want to do some more looking around to make sure you understand all of your options regarding digitization of your signals.

-cb

[Borges]

 Recently I tried to made this program to aquire the analog data from a serial port based device. I am trying to use the waveform graph from the right in my program instead of the graph from the left. 

I do know that I need to create an array to store the aquired elements and connect to the wave form graph.

Question is: What is the correct way to program that?

My serial device is programmed to receive an character and return a 0-255 number that corresponds to the aquired value.

Message Edited by Borges on 05-13-2009 02:31 PM

[Dennis_Knutson]

If you want to create an array and use a graph instead of the chart and it's history (an array), you can use a shift register with a build array function. The way you are creating an array now is not correct.

Please note that the above solution is only recomended for short acquisitions. The array can quickly become very large and your program will become sluggish.

[Borges]

How I should create a optimized way to make a good aquisition? In principle I should collect 2500 samples and store in array and after that the program should clean the array and collect 2500 samples again... Could you explain to me how to do that, please?

[Dennis_Knutson]

You could simply use an Array Size function and when it reaches the limit you set, clear the shift register with an empty array. Wire the shift register to a case statement. The false case (the one where the limit is not reached), would have the shift register wired straight through. The true case would have the empty array.

[Borges]

I tried to find the shift register component but I still cannot find him even with the search tool. Where is here?

[RavensFan]

Right click on the border of the loop and select "Add Shift Register".

This is fundamental LabVIEW knowledge.  If you weren't aware of it, then you should take some tutorials.  I would recommend you learn more about LabVIEW from here. How to Learn LV

[Borges]

I was not aware about the location of the shift register. However, I already have the basics in the labview and I also made many instruments before. I just not 100% aware in how to build a waveform graph using an array since the LabVIEW is a little diferent from the writed languages.

[JK1]

Look at this example: C:\Program Files\National Instruments\LabVIEW 8.x\examples\general\graphs\gengraph.llb\Waveform Graph.vi to begin with