AW: Sampling in LabView

Hello,

Maybe it is easier to use the Comedi for LabVIEW project at OpenG.org
than the VIs provided by NI. They still lack some of the features of
comedi (where the adapting functions are not implemented jet) but maybe
the ones you need are already done: I would recommend the
slow-varying-input functions of the comedi library or do the averaging
yourself by getting the data with the command-interface and processing
it in labview.

Just have a look at the project and see if it helps.

Jan

-----Ursprüngliche Nachricht-----
Von: comedi-admin_at_comedi.org [mailto:comedi-admin_at_comedi.org] Im Auftrag
von Jonathan C Erickson
Gesendet: Donnerstag, 25. März 2004 22:56
An: Ale[x] Garbino
Cc: comedi_at_comedi.org
Betreff: Re: Sampling in LabView


hi alex,
i am assuing you are using the VIs downloaded from ni.com.
yes, it is possible to modify these VIs to gain full control over
scan_begin_arg and other parameters that fit within the comedi_cmd
structure.  it's been some while since i have done this. but if i recall
correctly, you first need to modify the VI to accept that argument as an
input.  then  you need to modify the source for the VI CIN, and the VI
itself. The source for the CIN should be tucked way back in a directory
called lowlevelCIN that you downloaded along with the VIs, the file
might be called something like start_cmd.c or something similar.  change
the appropriate function headers and lines.  there should only be a few
changes. if it's not obvious what to do, email me back and i'll send
over a copy of the source i use the scan_begin_arg controls the timing
between successive scans.  for instance, say you are sampling channels
1,2,3, and 4 at 1 kHz.  Data will be collected at 1kHz for all of these
channels--that is, at periods of 1ms, data will be acquired from all of
these channels "simultaneously"
+/- the A/D conversion time.  see the comedi documentation for more on
this.
alos, i hear there are special function calls for slowly varying
signals, but i don't think 1kHz fits under that heading.  i've never
used slowly varying samples before, so i'm not too knowledgeable about
it.

hope this info helps.
jon
 On Thu, 25 Mar 2004,
Ale[x] Garbino wrote:

> I'm using labview to sample several single ended analog inputs, but 
> I'm unsure of how to deal with noise correction. Is there a way to 
> modifiy scan_begin_arg within the VI? Also, do this simply increase 
> the time between scans, or does it measure an 'average' of that scan 
> period as well? My noise is in the kHz range (I belive most is in 4-24

> kHz; from the ignition coils of the car where the data is being 
> measured); and the signal voltage varies very slowly; I think a 
> sampling rate of 1 kHz would probably be more accurate than I need. Is

> there a way to process the signal with LabView in this way?
>
> Thanks,
>
> A. Garbino
>
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Received on 2004-03-26Z12:32:07