I am a new user and am confounded by the signal provided by simulated devices in MAX and cannot seem to find an answer anywhere. I am using Labview 8.2, MAX 4.2, DAQmx 8.5, cDAQ-9172 and the DAQ Assistant simulating a 9215 card. I understand that the simulation is a noisy sine wave, but what is the frequency of that wave? It seems that you can change it with the timing settings in the Assistant Configuration panel. It would seem to me that the timing settings would relate to the way the 9215 samples the incoming signal, right? Instead it seems like those timing settings change the frequency of the signal itself. For example, in the DAQ assistant if I run the a test plot acquiring N samples and read 1000 samples at 1k Hz, I see one cycle of a noisy sine wave that takes 1 sec. If I read 100 samples at 1k Hz, I see one cycle of a noisy sine wave (with less resolution) that takes 100 ms. Doesn't this mean my signal frequency has increased 10 fold? I would have expected to see only a portion of a sine wave if the original frequency had stayed the same. Also, when I run using continuous sample acquisition mode it seems like the time it takes to go from peak to peak is different again. Here it doesn't seem to make any difference in what the sample size is, but rather what the sample rate is. At 1k Hz it take about 10 secs and at 2k Hz it takes about 5 secs. Please realize that as a newbie I am not far enough along to completely dissect the DAQ assistant VI to find out what is going on, although that will be next. So, I would appreciate any simple explanations as to why I am seeing what I am.

Hi pfrank, It's not documented, but the period of the simulated sine wave (measured in samples) appears to equal the task's input buffer size, at least for buffered tasks. The input buffer size is based on various factors (finite/continuous, samples per channel, sample rate). These are explained in the NI-DAQmx Help file that is installed on the Start Menu under National Instruments\NI-DAQ. Search for "How Is Buffer Size Determined?" (without the question mark) Selecting N Samples causes the DAQ Assistant to set the sample mode to finite, so the buffer size is exactly equal to the samples per channel. If you select Continuous Samples instead, then the buffer size will be set to 10 kS because the sample rate is between 100 S/s and 10 kS/s, and the sine wave's period will be 10000 samples. If this doesn't make any sense, look at "How Is Buffer Size Determined?" in the NI-DAQmx Help. DAQmx does not support providing your own simulated data for simulated devices. If you want control over the simulated signals, you'll need to add code to your application that replaces the data returned from DAQmx. Brad Message Edited by Brad K on 02-18-2010 12:44 PM

Multifunction DAQ

DAQmx simulation signal

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Give up the DAQ Assistant and use the much more flexible DAQmx functions. A front panel channel control has the ability to select channels. You could also define the tasks in MAX where people can edit them.