strain VI

[Aquaphire]

Hello all,

For those who already know me... "know", i've been posting here for a bit anyways.

I created a loop that would make a timestamp, and record elapsted time etc...at the click of a button. I'm not trying to continue on with the program by incorporating into this a DAQ for strain. I'm completely clueless when it comes to DAQ. This is the first VI i've ever made, and the Data Aquisition part of it just seems real complicated.

With my Data Aquisition box came a VI that scans through channels 0 and 7, to take a reading and convert it into strain. I've attached the VI down here.

what I would like to do would be to measure the strain, on channel X, for every press of the button. However, the VI is so complex that I can't even know where to start! If anyone can just explain the use of each individual part of the STRAIN reader, so that I could try to recreate it in my VI, I would be infinately happy!

thanks a lot

[Ryan_V[DE]]

Aquaphire,

The best place to look for help on all of our shipping examples is under "File >> VI Properties" and then "Documentation". Here is the documentation for this VI:

DESCRIPTION:
This VI shows how to use the SCXI-1520 module to measure data from strain gauges.  It also shows how to perform offset nulling and shunt calibration on the strain gages.  The acquistion takes place in a loop that runs until an error occurs OR the stop button is clicked.   This is a timed acquisition, meaning that a hardware clock is used to control the acquisition rate for fast and accurate timing.  It is also a buffered acquisition, meaning that the data are stored in an intermediate memory buffer after they are acquired from the DAQ board.  Once the data have been acquired, LabVIEW retrieves the data from that buffer, processes it, and displays it. 


INSTRUCTIONS:
1.  Enter the device number and the channels you intend to scan.
2.  Select the input limits that pertain to your sensor(s), if the default values configured in the Measurement and Automation Explorer (MAX) are not suitable.
3.  Enter the filter and excitation values you want for your strain gauge(s).
4.  Enter the value of the resistor(s) you are using for shunt calibration (you should use the SCA terminals for all your shunt resistors).  Ignore if you do not intend to perform shunt calibration.
5.  Enter the gauge resistance, gauge factor, and bridge type of the strain gauge(s) you are using and the poisson ratio of the surface on which they are mounted.

NOTE: All the above controls MUST be set before the VI is run.

7.  Run the VI.



The first 4 NI-DAQ VIs in "SCXI-1520 Strain.vi" set the configuration for the acquisition. The Context Help provides a good explanation about how these VIs work. Next, the "AI Parameter" VI is used to set the Voltage excitation level, filter settings, and bridge type. Finally, inside the loop, the only two DAQ VIs that do not deal with calibration are the AI Start and AI Read. These start the acquisition and read in the resulting data.

Hope this helps!
Ryan V.

[Aquaphire]

Hello Ryan,

Thanks for the answer. What I would like to know though, is that assuming I wanted to simplify the program to ONLY calculate the strain, and write it to a txt file, which part of the VI would be essential...

In other words, where exactly is the "output" so that I could wire it to an array premade and integarte it with information I already have. I would like a reading of the strain to be measured everytime a button is pressed, meaning that I would have to loop this program too.

thanks.

Message Edited by Aquaphire on 07-12-2005 02:29 PM

[Aquaphire]

Oh, if possible... just converting it to a sub-vi might be easier... I'm fiddling around with it now, but if anyone has any tips how to do it...

[Ryan_V[DE]]

Aquaphire,

The parts of the VI that I explained are essential for what you plan to do. The actual data will come out of the "AI Read" VI inside the while loop as a 2D double array called "scaled data." If you would rather use this VI as a sub VI, you need to create a connector pane for it. An explanation of this process cab be found in the LabVIEW User Manual (attached) on page 2-4. You can also get there in LabVIEW by going to "Help >> Search the LabVIEW Bookshelf >> LabVIEW User Manual." Have a great day!

Ryan

[Aquaphire]

thanks guys, I managed it ^^