06-28-2012 01:52 PM
I am wanting to use my NI USB-6008 DAQ to take a voltage data point on four channels once every 10 minutes for a few days at a time. I have changed the timeout to -1 seconds and turned off automatic exporting of log file. I am also using the save to ASCII step. When I go to stop the run, it hangs up. My computer is pretty bad, but I can do the same operation with a much faster sample rate no problem. Does the 6008 have a lower limit to sampling rate? I just started messing with this program yesterday so I'm still learning.
06-29-2012 12:20 PM
So I did some more searching through the expansive knowledge base and found that the minimum sample rate for the USB 6008 is 5.587935 mHz (source).
I ditched the save to ASCII step for now, and have gotten the program to collect some data at 10 mHz, currently trying it at 6 mHz now.
The main cause to my problem so far has been with what seems to be an error with the continuous data collection option. I discovered that eventhough the sample size is supposed to be treated as buffer size in this mode, for me it was not. I would set it to 20k 'buffer' at something like 1 kHz samples and it would 'freeze' on stop. I let it go like this for a while once and to my suprise it came out of it and I was able to view the log. When I did I saw that the log went to exactly 20k samples, eventhough I had stopped it within ~5 seconds. So during that time it was 'stopping' it was actually finishing the program and getting 20k samples. This is why I always had a problem trying to record at low sample rates with what I thought was a 1k buffer - but was actually 1k samples.
So..... why is this happening? I want to actually collect continuously, but also stop it whenver I want (eg. continuous up until I stop it). I might try the 'n-sample' mode now, considering the rest of the problems with this program, they could very well be flipped.
Assuming I figure out how to get it into true continous mode, will I be able to stop the logging at my will? And what should I set the buffer to with a sample rate of 6 mHz?