LabVIEW
LAB VIEW SOFTWARE WITH DAQ NOT PERFORMING
Thank you for attaching your VI. It shows me you have only Express VIs and Dynamic Data Wires in your program, which (probably) means that you need to Learn More LabVIEW. Here is my recommended Course of Action (which will lead you to be able to solve your own problem):
- Do my "Step 5" first. Connect your hardware up to MAX and get MAX to acquire the 9 channels you want and to show them to you. This article will explain how to set up Test Panels to test your devices.
- Next, do Step 4, and Learn 10 Functions in NI-DAQmx and Handle Your Data Acquisition Application. It's been a while since I read it -- I just "revisited" it, and realize that it may be a little more "intimidating" at first than it should be. So here's a Short Cut (there should be, and may there is, a White Paper explaining this Method, but if not, here it is):
- Open MAX (again).
- Create a Test Panel for your Device (as you did in Step 1) and configure it.
- Now click Create Task, choose your Device, and duplicate the setting you did in Test Panel. Name this something sensible (DAQmx might want no spaces in the Task Name).
- Let's assume your task is Analog Input on some Channels, continuous acquisition at some frequency and some # of points. You need three DAQmx functions to acquire one set of samples, and just need to add the Loop of your choice to collect multiple Samples. The functions are DAQmx Start Task, DAQmx Read, and DAQmx Stop Task. Drop them down on your Block Diagram and wire them together (in that order). Since we are assuming Analog Input and multiple Channels, on the DAQmx Read, choose N Channels, N Samples, and I recommend 1D Array of Waveforms for the output.
- Right-click the Task input of Start Task and wire a constant. See the little down-arrow on the (empty) Constant? Click it -- it should show you the Task you created in Step 3. Choose that Task.
- Now look at the DAQmx Read. Read its Help (right-click on the Read and choose Help). You want to wire something to the Number of Channels input -- if you remember how many channels you specified in the Task, wire this number. If you forgot, get the Task to tell you. Wire a DAQmx Timing Node (see the DAQmx Palette) between Start Task and Read, passing the Error Line and Task line through it. Right-click the displayed Property and Select Property "Sample Quantity, Samples per Channel". Right-click again and
- "Change all to Read" (you want to read this Property). Wire the Samples per Channel into the Read VI.
- Wire something to the Output of the Read VI (like a Chart) so you can see the Results.
- Run the VI. It should take one set of samples and stop (which is what you programmed). Think how you would make it take multiple sets of samples.
- If you can't follow these steps, do my Steps 1 and 2 (Learn more LabVIEW).
Here's how the 3 DAQmx Functions + 1 Property Node VI should look, with no Express VIs and none of those awful Dynamic Data Wires --
Bob Schor
P.S. -- after writing the above, in the hopes of teaching you enough that you can do this yourself, I took a look at your code, and noticed that your Express VI is configured for three Strain Gauges. I've not worked with Strain Gauges, and don't know how the Module you are using to collect the samples works, nor what its limitations are (maybe it can't handle 9 signals?). Of course, you need to have sufficient hardware to acquire the signals you need, so provide additional information. Also, you talk about the total length of acqusition time (5 minutes = 300 seconds), but say nothing about the sampling rate you desire. I see you asked the device to take 18 million samples at 1 kHz -- most DAQ devices don't have megabytes of internal memory to store that much data. You need to learn more about Data Acquisition, I think -- go find an engineer who understands Signals, sampling, data sizes, etc. (or someone who has a few months experience with LabVIEW data acquisition to clue you in.
