Last few months I am working on personal project -- I want to measure weight of beehive during the year and then save the results. Beehives has usually from 100 to 200 kg and during one day, the weight can change from -5 to +5 kg. The ideal precision should be 100 g.
I have working prototype with MCU, amplifier and one 20 kg load cell. I put beehive on mechanical platform and weight is scaled down in 1:10 ratio -- thus I can measure 200 kg weight. The precision has to be 10 g.
The results from my prototype are:
- My cheap load cell changes its output with temperature (I expected this, I can correct the results when I save temperature together with weight).
- The output of load cell drifts with time. I put 3 kg weight directly on load cell and after few days, the output was much lower than first day. I think this is called creep?
The second issue is problem, because load cell has to measure weight during whole year so it will be under permanent pressure.
Should I buy more expensive load cell? Are load cells designed for permanent load? Or should I look for another method how to measure weight?
I was thinking about precision multi turn potentiometer. I am not mechanical engineer, but if I can easily change weight into movement, I may be able to use potentiometer as weight sensor.
Or maybe use spring instead of load cell. But how can I convert spring deformation into electrical signal? Spring compress with more weight, so maybe some kind of distance sensor?