PVDF cantilever

LabVIEW tutorials

for engineering students

PVDF cantilever

LabVIEW tutorials

for engineering students

Background

When I started working for Newcastle University I was assigned to teach LabVIEW as part of two modules on software for engineers and computational modelling. The objective was to prepare the students to the use of this software, which is widely used and convenient for quick data acquisition in the lab. The first year, I used the handouts prepared by a colleague who had taught it for several years before. They were good, but I felt the part of data acquisition was somewhat artificial: voltage signal were generated on one side of the card (a NI USB-6008) and acquired on the other. Students were practicing the use of DAC and ADC, but I felt something more real was needed.

A real application

I therefore looked at potential sensors to connect to the DAQ. I’ve explored light sensors, proximity sensors, etc. It had to be simple but meaningful. I landed on PVDF piezoelectric cantilevers: they naturally generate a voltage signal which is small, but perfectly within the capabilities of the USB-6008 (if properly configured!). So the assignment became not a simple writing of a program per se, but the coding of a slightly simpler program and its use to determine the unknown mass of a little rubber bit I provided. In the process, students were exposed directly to the technique of measuring mass via the frequency-shift it causes on a resonating structure (which is at the basis of most mass-sensing in MEMS, among others).

Implementation

I purchased a good supply of cantilevers, solderless breadboards and self-adhesive rubber feet. Once mounted, it looked like this:

Cantilever with unknown mass

I kept the first tutorial from the old handout, with only minor changes and fixes. The second explained the Power Spectrum and the VIs used to compute it in LabVIEW. The third and fourth tutorials focused on configuring the DAQ correctly, in particular for what concerns the input gain and on the saving of data to disk. The fifth tutorial introduced the piezoelectri cantilever and the acquisition of its signal. Finally, for the assignment, the students were asked to add the unknown mass and modify the program adding some functionality (like data saving).

A typical result is shown below:

Time domain and frequency domain data from the cantilever

Download

The PDF of the handouts can be donwloaded from here.

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Michele Pozzi
Engineer and scientist