how to solve delay in a program with data aquisition and processing

[Alberta]

Hello, I am a starter in Labview programing. I am working on a system which contains a roller, a piston and a A/D cart which is from Data Translation Inc (DT304). I am using labview to get speed data of the roller (which is voltage first then be converted into speed) from Analog Input Channels, and then using Analog Output Channels to control the friction force being appylied to the roller by using a piston.

I am using a Waveform Chart to show the speed of roller. However, as I am adding more components to the program, I always get delay in the speed display and also the output control of the piston. Also, as I spent more time using the program eg. from morning to night, it became slower too.

My question is, how does labview store data and how are the data been stored and released in the buffer.Is it because I am loading too much data in the buffer so that it became slower? And also how to solve these delays?

I am using the "save to file" function to write data to a ".lvm" file, but I did some changes to the saving by using a button to enable and disable saving. So I don't think the problem is because I am always saving the data into a file.

Thank you very much.

Jessie

[SnowMule]

I'm betting it's two things:

1. Program Architecture

and 2. Dynamically resizing arrays.

With the program architecture... if you have one do-while loop that acquires data from teh DAQ, processes it, opens/indexes/writes/closes a file, then comes back around... as your arrays and files increase in size, the loop is going to take longer to execute.  A Producer-Consumer loop (a good tutorial on them can be found here) has one loop that acquires data and stuffs the data into a queue.  This will buffer the data while it's in transition between acquisition and processing.  A second loop in parallel takes data in from the queue, processes it, then comes back around.  The two loops operate independently of each other, so even if the consumer loop takes longer as the files or math gets more complex, the producer loop continues to run full speed.

Second is the arrays.  Every time you append data into an array, LabVIEW has to make a copy of the data that's in the array.  If you append small amounts of data to an array over and over and over again, eventually LabVIEW is going to be copying very large amounts of data over and over and over again.  The producer-consumer architecture can alleviate this problem.