Data acquisition trigger 
Author Message
 Data acquisition trigger

Hi all,

I am new to labview and have (again!) encountered an obstacle where I
need some advise.

I am designing VI for dynamic data acquisition with a sampling rate of
200-400 samples per second.  I will be reading accelerometers on all
12-16 channels.  I will need to trigger the acquisition when one (or
more if possible) accelerometers reach a certain value and then record
data for say 30/60 seconds.  In that 30/60 seconds I want to see the
data that is being recorded, in a graphical display, fair to say in
real time.  How can I do this?

Do I need to use hardware analog triggering? or can I achive this
programatically without any loss in data since I am sampling at such a
high rate?  I used AI Read.vi with conditional retrieval quite
successfully to obtain 30 seconds worth of data at 200samples/s, but I
could not see the data as it was read.  I only saw it after 30seconds,
thus defeating my purpose.

I think my card (PCI 6023E) is not capable of analog triggering.  If
this is true I'd appreciate if you could recommend a card(s) that is.
I will be willing to buy a new card and additional any
hardware/software cost permitting.

Here is the hardware I have:
- PCI-6023E
- SCXI 1000, 1100, 1300
- Labview 6i.

Thanks to any and all who are willing to help.

Regards,
Setu.



Tue, 10 Aug 2004 14:45:44 GMT  
 Data acquisition trigger
1. You need to do Analog Trigger, the triggering signal will be the
signal available at the accelerometer.

2. You need to use a card that supports Analog Triggering or you can
use conditional retrieval too.

3. If you want to acquire 30 sec worth of data, at 200 samples/s, then
set the total number of scans to acquire to 6000 and the scan rate to
200.

4. Please take a look at the examples on Data Acquiistion Analog Input
at National Instruments website. The link is given below:

<a
href=http://zone.ni.com/devzone/devzone.nsf/webcategories/85B7B02F75808C1F...>Data
Acquisition</a>



Wed, 11 Aug 2004 03:34:50 GMT  
 Data acquisition trigger
Setu;

Use the Labview shipping example named Acquire N scans Analog Hardware
Trig.vi, so you can make sure the Software part works. There are a
couple of gotchas though. First, the triggering channel must be the
first channel in the scan list and must also physically be the first
channel in the SCXI module. Second, when the trigger channel control
is left empty in LV, it works perfectly.
Hope this helps.
Filipe



Wed, 11 Aug 2004 05:09:06 GMT  
 Data acquisition trigger
Thanks for the reply guys.
See, I also want to view the data while it is being acquired.
Currently using conditional retrieval the AI Read.vi locks out labview
until 6000 scans are complete.  I want to see every point as it is
being acquired.  Is this possible?


Wed, 11 Aug 2004 09:35:49 GMT  
 
 [ 4 post ] 

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