stabilizing frame rate

[kirkland4]

I'm using PCI 1428 card with latest labview and vision software to capture and save images to hard drive.

I've got a great computer with 4 gigs memory and right now my VI is wuth a while loop to capture images and a voltage reading with a daq card and then save the images to hard drive. Images are roughly 700k.

I usually capture about 11000 images per test and for the most part get 25-30 FPS (capturing and saving). However often once out of 50 images my process bogs down and my frame rate drop to single digits. my initial thought is that the hard drive may have its own memory buffer which gets filled and I experience the burp when it is dumping, however I'm unable to observe a predictable interval at which this occurs, so I'm unsure if that's the case.

CPU usage is at roughly 25%, and my memory usage is very low since i'm going non buffered and straight to disc.

I have 2 questions.

1. what could be the possible source of this slowing down?

2. How may I setup my loop so that I can perhaps set the frame rate to be constant at each frame.

I can attach a VI if necessary.

thanks

[VuD]

Hi kirkland4,

Have you tried saving the images to an AVI file?  This will allow you to capture images at a high rate which you can then post process afterwards by extracting the frames.  There is a Grab and Save to AVI.VI in the LabVIEW Example Finder under the Hardware Input and Output >> IMAQ >> File Input and Output folder which you can look at.  When you remove the DAQ portion of the application and simplify your code to just acquire and save images, do you still see the frame rate drop?  Here are a couple of documents regarding saving images to file that I would suggest looking over:

Reading and Writing Image Files

Streaming Images to Disk with NI Vision

Hopefully these will help explain the file types, rates, and limitations for saving images to the hard drive.  I hope this helps.

Vu