DAQ Assistant: Reading samples that are no longer available

[bcglaxer]

I'm trying to use the DAQ Assistant to read in some voltage data, but I keep getting "Error -200279 occured at DAQmc Read (Analog 1D Wfm NChan NSamp).vi:2. The error message suggests increasing the buffer size, reading the data more frequently, or specifying a fixed number of samples to read instead of reading all available samples. My timing settings are as follows: Continuous Samples for Acquisition Mode, 1K Samples to Read, 1K Sample Rate (Hz). I'm curious what would be the optimal settings for this. If I set the mode to 1 Sample (On Demand), would that simply take a sample each time the loop runs? Please help.

Thanks,

Brian

[AdnanZ]

Buffer overflow errors occur when data is written to the buffer faster than it is being read off of it. Buffer underflow errors occur when data is being read off the buffer faster than new data is being added. In order to avoid either of these, a general rule of thumb for NI devices is to acquire around 1/10th of a second of data. For example, for a sample rate of 1000 Hz, set samples to read at 100 samples.

[Aaron_W. · Accepted solution]

Brian,

Thank you for posting on the NI Forums.  Adnan is right about why you are getting this error. If you use On Demand sampling you will only get a value returned for every iteration of the loop. If you only need to sample every so often and it does not need to be highly consistent then this could work for your applications, but it depends on what type of application you have. At what speed do you need to sample? 

[bcglaxer]

Thanks for the general rule of thumb. I'll give it a try.

Brian

[bcglaxer]

Thanks for the general rule of thumb. I'm trying to implement the data acquisition within a simulation loop from the Control Design & Simulation Toolkit to control a custom actuator, and I'm still getting buffer overflow errors. Could that be because the rest of my .vi is too slow to keep up?

[bcglaxer]

Thanks, Aaron. On Demand seems to have fixed this particular problem, though I'm sure more will pop up 🙂

Brian