"high frequency" data logging

[sunny dee]

Hi, I need to write a program that will log my data to disk at a rate of roughly 2000 Hz. I am using Labview 7.1. Can anyone either point me to some example code or give me a general idea of how to do this?

ps. I've written a program for low frequency data logging (just by monitoring the system time) but that was only good for about 2Hz or lower. So I am familiar with Labview, but I've just never written a program to log high speed before.

Thanks!!!

Sunny

[Dennis_Knutson]

A rate of 2000 Hz is not all that high. There's a shipping example called High Speed Data Logger that was written for traditional DAQ but can be easily modified for other applications. What are you using now to get the data, what functions are you using to write the data, how are you storing it (text, binary)?

[m3nth]

If you're using DAQ hardware just look at the examples that ship with LabVIEW.  If you're not, you can't really do high frequency acquisition, and certainly not past 1kHz.

[sunny dee]

I'm using an IOTech Daq card to get the data right now. I want to be able to store it in text so that I can open it with a spreadsheet program.

I found an example of a program and I've modified it a bit, but haven't tested it. Perhaps you can have a look at how I implemented the logger and tell me if there is some huge disadvantage to doing it this way.

Thanks!!

[sunny dee]

Just out of curioisity, does the AI Read.vi timestamp each data point?

[Dennis_Knutson]

A big disadvantage of saving as text is that it takes longer. First you have to do the conversion and then your data is larger. If you need it readable, then you can save as binary and when the program is complete, read the entire binary file back in and save it as text to a new file. The example I mentioned writes a header with timing information and then the data ina binary format. From this, you can post process a text file any way that you want.

It also looks like your write buffer may be getting bigger and bigger. Once data has been written, you can empty the shift register by writing an empty array to it.

Yes, AI Read can include time information if the Waveform data type is selected as the output but it really doesn't matter if you are using an I/O Tech board and their driver.