DAQ setup

[Coulton]

Hey guys,

I am currently trying to relearn Labview since I haven't used it in a while. I have a VI created to allow a DAQ (From NI USB-6210) to input data. My goal is to plot the data real-time on the front panel. I then want to export the data to an excel document. I believe I am getting the export part right, but my real-time graphs don't seems to be matching up. Any suggestions? I have attached the VI.

[Charles_CLA]

Um... I don't see any graphs in the attached code? All I see is that the data is collected until you click "Stop" then the data is written to a file.

Charles

[Coulton]

Oops. Now see attached =).

[Charles_CLA]

The graphs look to be setup correctly, keep in mind that you are acquiring 100 points at a time at a 1kHz rate which means that you will always lag the very first point collected by 100ms + whatever time is required for LV to draw 6 different graphs. Updating displays in a loop should only be done if absolutely necessary as updating the GUI is quite the load on the machine. What do you mean by "real-time graphs don't seems to be matching up"?

Thanks,

Charles

[Coulton]

Should I drop the DAQ down to 250Hz or something? As for the "real-time graphs don't seems to be matching up", I am working on a strain gauge/wheatstone bridge config. When I apply a load I am expecting a change in the voltage, but I don't necassarily see the change until I plot the data in excel. Would this be due to the 1kHz issue?

[Charles_CLA]

Actually this could be caused by the fact that you are looking at the data too quickly. You only see 1/10th of a second on the graph, the graph is (unless you explicitly changed it) set to autoscale the y data. so you are probably seeing roughly flat data across the entire graph with only the axis labels changing. You might consider either A. increasing the number of samples or B. Using a gauge indicator where the scales won't change and you will be able to see the needle move more easily in real time. Note: using the gauge requires that you use scalar data, the easiest way to do that is to get the mean of your data, bring up quick drop (CTRL + SPACE) and type "Mean" to find the vi.

[Coulton]

I believe that I am actually seeing the noise of the circuit because every graph is sparatically moving. Let's say I push on my specimen (which has a wheatstone bridge attached to it) the graph really doesn't change (The y-values I mean). Could this be that my voltage change is too small, or something else? Thanks for the ehlp!

[Charles_CLA]

Did you set the range of the DAQ input as low as possible? The higher voltage ranges can be quite noisy if you're looking at a small signal. Also, I am not familiar with wheatstone bridge, is it single ended or differential output? Did you setup the Input Terminal Configuration appropriately?

Charles

[Coulton]

Now that you mention it, my voltage ranges might be too large. A wheatstone bridge measures voltage change when resistors changes it's resistance due to contraction or elongation from the material it is adhered to. I have a positive and negative wire and I placed them in channel 17 and 18 (corresponding to A1) in the USB-6210. I am not sure what you mean by "is it single ended or differential output? Did you setup the Input Terminal Configuration appropriately?" so if this doesn't answer your question let me know.

[Coulton]

I just look in the DAQ and I currently have it setup as differential in the terminal config