Hi, I want to know a measure of a deformation of a tube. I bought this: http://www.ebay.com/itm/4pc-40kg-Portable-weighing-sensor-weight-sensor-micro-bridge-/262886360708?hash=item3d353f8684:g:66cAAOSw~AVYwCqJ But this not works very well because before of deformation the value is 0 but after of defformation the value is different 0 Anyone know any sensor that works very well?
Add an amplifier. eg HX711
The problem with buying on eBay, Aliexpress or many of the Chinese suppliers is you get no support or documentation. That's the second time I've typed that today and the 4th time this week. Maybe I should make that my signature.
The output of a strain gauge is very small. You need an amplifier. Sparkfun has a tutorial about using strain gauges and load cells. Other do to, probably.
I hope your set up worked after adding an amplification circuit. I have been working on a project that is close to what you were doing and adding an amplification circuit has helped to enhance the accuracy of my system. In my case, I have used a difference op-amp amplification circuit.
Its standard to use the instrumentation-amplifier configuration for strain-guages, you need very good
common-mode rejection for a strain guage. The one-chip solutions are basically instrumentation amps.
You should consider fact about electrical resistance in connection with strain gauge formula as whitestone bridge circuit. This type of strain gauge is most common.