topic Re: initialize waveform in LabVIEW

initialize waveform

Philipp Kravanja — Wed, 12 Mar 2008 21:59:28 GMT

Hi

I want to acquire data using the acquire waveform waveforms.vi and append them to one long file.
without.jpeg shows how i am doing it. the problem ist, that if i stop the vi and run it again data remains stored in that waveform array.
i would like it to be cleared when starting it again, or in other words i want to initialize the vi when starting it. for a normal array i just connected
an empty array left to the shift register, but this does not work for waveform because i can´t create a constant.
i had the idea to do it as shown in with.peg but i dont think this is a good way to do it.
How can i initialize that waveform when i start the vi.?

Thanks for help

Philipp

Re: initialize waveform

Philipp Kravanja — Wed, 12 Mar 2008 23:01:43 GMT

i just had the idea to initilize with the acquire waveform.vi just with the same settings as in the while loop.
and is the connection of the append waveforms.vi correct or should it be just the other way round
(the wire coming from the shift register on top and the wire coming from the acquire waveform.vi on the bottom) ?
thanks for help

Re: initialize waveform

ASTDan — Wed, 12 Mar 2008 23:06:21 GMT

Hello,

By right clicking on your wavform wire and selecting create constant you can get a blank waveform variable

Dan

Re: initialize waveform

Philipp Kravanja — Thu, 13 Mar 2008 00:20:56 GMT

thanks for your reply.

thats what i wanted to do but i can´t do it. if i right click on the wire constant is light grey and can´t be used.
by the way i am using labVIEW 6.1. so maybe that´s why. what do you think about initializing as i suggested in
the second posting ? or do you have any idea why i can´t get a waveform constant ?

Thanks Philipp

Re: initialize waveform

Dennis_Knutson — Thu, 13 Mar 2008 03:14:24 GMT

LabVIEW 6.1 did not have a waveform constant. I always just used a front panel waveform control (empty of data, of course).

Re: initialize waveform

Philipp Kravanja — Thu, 13 Mar 2008 16:29:44 GMT

you mean like this?

Thanks for help

Re: initialize waveform

Dennis_Knutson — Thu, 13 Mar 2008 16:32:04 GMT

Yes.

Re: initialize waveform

Philipp Kravanja — Thu, 13 Mar 2008 16:55:24 GMT

ok thanks again

Re: initialize waveform

Philipp Kravanja — Fri, 14 Mar 2008 00:15:13 GMT

another problem occured

i want to analyse the data using the FFT-Power Spectral Density.vi so i am basically doing some sort of Fourier Transform. i did this in the past with the FFT-Power Spectral Density.vi in the while loop. now it turns out it is better to save the time domain signal and do the analysis afterwards( to be able to vary parameters of analysis) i want to have a spectrum up to 20 kHz so i sample with 40 kHz as you can see. the problem is, when i initailize as in empty.jpg the FFT-Power Spectral Density.vi does not work the way it should, if i initialize as in waveform.jpg it does.
can you tell me why the FFT-Power Spectral Density.vi does not work properly when initializing as in empty.jpg ?

another thing is storing the time domain signal. if i do it as in the .jpgs, (as .txt using the write waveform to file.vi )i can read them later and perform the analysis with another vi. i can read the calculated spectrum with a normal text editor but i can not read the waveform with a text editor.
when i tried to export the time domain signal (its pretty big though, i am sampling with 40K for about a minute) using the export waveforms to spreadsheetfile.vi nothing happened for a long time and the the message as is in message.jpg occured. how can i export and read the time domain signal ? by the way using LabVIEW 6.1

Thanks a lot

Philipp