Logging data in a file using Labview VIs vs. Mathscript functions.

Question

Hello,
 I'm working on a data logger at 200 Hz frequency. I wanted to log the data to a file after eace sample received. When I used (fopen,fprintf,....) on Mathscript, the Labview started to log the data at a slower rate. I then used the Labview file VIs and it is working fine up till now.
My questions are as follows:
1- Are the file functions in the Mathscript slower than the Labview VIs ?
2- Is saving the data to a file after each sample is received a good idea or is there a better idea ? I just don't want to keep the data in the memory and after all the data is logged, I flush them to a file ... because, it seems that the PC will run out of memory.
Thank you,
 Walid

Answer 1

wfarid wrote:
Hello,
 I'm working on a data logger at 200 Hz frequency. I wanted to log the data to a file after eace sample received. When I used (fopen,fprintf,....) on Mathscript, the Labview started to log the data at a slower rate. I then used the Labview file VIs and it is working fine up till now.
My questions are as follows:
1- Are the file functions in the Mathscript slower than the Labview VIs ?
Yes. That's because you're going through another layer of software. Why were you trying to use MathScript to log data to file in the first place? Are you a Matlab "aficionado"? 
2- Is saving the data to a file after each sample is received a good idea or is there a better idea ? I just don't want to keep the data in the memory and after all the data is logged, I flush them to a file ... because, it seems that the PC will run out of memory.
It doesn't make sense to save data after each sample. File I/O is an expensive operation in terms of time, and you have the operating system to deal with, so while you may be able to keep up the rate for some time, eventually it will be thrown off. You can do as suggested which is to wait until you have a certain amount and then write that to file, or you can set up a producer-consumer or master-slave architecture. Let one process/loop collect the data and put into a buffer, like a queue, and the other process/loop can stream it to disk at a more reasonable rate. You just have to make sure the buffer is large enough so that if the file I/O gets hung up you won't reach the buffer's limit.