AI Acquire Waveform takes up alot of processor time

[Dean390]

Hi,

This is the first time I have used the AI acquire waveform vi's and I
have found that once it is running, the computer is not at all useful
for anything else. The processor goes to 100%. There is still about
150Mb of memory available. I have set execution priority to the lowest
level. This is a problem as I am communicating with this computer via
pcanywhere on direct dialup and it is now so slow that it is pretty
much impossible to control it remotely. Once the program is stopped,
communication is very good.

Is there a fix or alternative way of doing this to get some of the
processor back? I am trying to log 5 channels at 100 samples per
second. I am collecting 2 minute blocks and then writing ascii data to
disk.
I have found that lowering the sample rate or number of samples
has little effect.

Windows 2000, Labview 6.02. I have tried it on a couple of different
computers. A P3 500, 327Mb RAM, 6036E DAQcard and a P4 2.4Ghz, 500Mb
RAM, 6071E Card.

Thanks in advance for any advice

Dean

[Alexander J.]

Hi,

I do not know how you developed your VI, but one thing possible is if your acquire waveform AI is inside the loop, you must give some delay in your loop. Just put 50mil sec or 100mil sec delay inside the loop. Hope this will help.

Best Regerds,
LV Lover

[Dean390]

On Sat, 27 Sep 2003 09:58:04 -0500 (CDT), SawNaingAye
wrote:

>Hi,
>
>I do not know how you developed your VI, but one thing possible is if
>your acquire waveform AI is inside the loop, you must give some delay
>in your loop. Just put 50mil sec or 100mil sec delay inside the loop.
>Hope this will help.
>
>Best Regerds,
>LV Lover

Yes, I have discovered this in the past when I have used the single
point acquire VI's. Unfortunately, in this case, I can not achieve the
required sample rates using single point acquire so I am using the
waveform acquire.

I have the AI multi point VI acquiring 2 minutes worth of data at a
time so most delays are inside the AI multi point VI. This is inside a
loop but it only loops every 2 minutes so a delay here does no
t do
much for performance. I suppose I could take apart the acquire multi
point VI and add a delay in there but I would be worried about
disturbing the timing.

Thanks for the suggestion!

Dean

[Jonnie_5]

Could you upload your vi so we can have a look?

Buffered acquisition shouldn't take a lot of processor time as the buffering is done on the hardware of the acquisition card, especially at 100 Hz. When you read the card, that's when the processor (and hard drive) are kicking in, so you may be reading/writing too often. You shouldn't have to fiddle with the AI scan vi. Likely, you have a loop somewhere that's eating all your CPU time or you're writing every point as it comes in. Acquire in blocks and write in blocks. I;ve got a 6036 acquiring at 2000 Hz running on an AMD 300 Mhz w/ 96 Mb of RAM that usues minimal processor time.

[Dean390]

On Sun, 28 Sep 2003 08:44:28 -0500 (CDT), Jonnie 5 wrote:

>Could you upload your vi so we can have a look?

Absolutely

>
>Buffered acquisition shouldn't take a lot of processor time as the
>buffering is done on the hardware of the acquisition card, especially
>at 100 Hz. When you read the card, that's when the processor (and
>hard drive) are kicking in, so you may be reading/writing too often.
>You shouldn't have to fiddle with the AI scan vi. Likely, you have a
>loop somewhere that's eating all your CPU time or you're writing every
>point as it comes in. Acquire in blocks and write in blocks. I;ve
>got a 6036 acquiring at 2000 Hz running on an AMD 300 Mhz w/ 96 Mb of
>RAM that usues minimal processor time.

I was hoping for performance like
that. I appreciate your having a
look at this. The default values are what I am primarily running it
with.

Thanks
Dean

[Jonnie_5]

Methinks the upload failed.

[Dean390]

On Sun, 28 Sep 2003 18:27:15 -0500 (CDT), Jonnie 5 wrote:

>Methinks the upload failed.

Not sure why but it showed up for me as a separate message with the
same subject. I'll give it some time before sending it again. It is
220kb in size. There isn't a size limit is there?

[Jonnie_5]

Are you doing this via ni.com or a news group. Try either via the web forum:
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=50650000000800000021A40000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0

or you can ship direct to me (although no one else will get to input):
jshackman.at.yahoo.com

[Dean390]

I was doing it by newsgroup. I didn't know this forum was also on the ni site. Let's see if this works.

[Alexander J.]

As I mentioned earlier, just put 50ms delay in your outside while loop and that will solve the problem.

Best Regerds,
S.N.Aye