Hi,
I am curently trying to acquire 2 voltages thanks to a PCI-4472 DAQmx card at a high sampling rate (51200 S/s). Basically, I display the power spectrum of the two inputs in "real-time" (every 40ms) as well as the ratio of their spectrum. I would like to be able to save the incoming signals in a matrix (each column correspond to one input) that I want to use in MATLAB order to do some further off line calculation.
I have been able to display the spectrums and their ratio. I have saved some data into the MATLAB format BUT when I look at what I have actually saved, using MATLAB there is a problem. Instead of a continuous signal, it looks like I have saved a juxtaposition of chunks of 2048 samples (which is actually the "number of samples per channel" argument of the DAQmx read vi I had used for this example). In other words, there is a discontinuity every 2048 points in the graph (which will ruin my frequency analysis in MATLAB). I have interpreted it as a loss of data during the reading process, probably due to the high sampling rate (between 25600 S/s and 51200 S/s) and the relatively long time it takes to perform the different processing tasks ( mainly calculating the power spectrums).
Hence, I have tried to act on the "Relative to" and "Offset" properties of the DAQmx read vi but it produced no improvement: I still had discontinuitues in my saved files.
I have attached my acquisition VI and a subVI linked to it. If someone can tell me what to do, I would greatly appreciate.
Thanks
Bertrand.