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Topic: Measuring the weight of a beehive (Read 13 times) previous topic - next topic

gardner


my 200kg load cell have been standing on my kitchen bench with a constant load for over a week, and it is only drifting like +/- 20g (a little worse when the temperature changes, but not to bad).


Interesting, that's a good start.  It sounds more stable than I would have guessed.  What % of load capacity is on there?

How about outside in the weather?  For a year?

If you could demonstrate ~ +/- 1% of full scale accuracy, while sitting with 50% of rated load for 10 months across temperature changes of +30C to -20C, then I'll be convinced.

LEGO-lars

Hi
In my load-cell test I used a 20kg load. I am not sure if using a higher load will make a difference since it is the offset of the load-cell and not the gain which is causing the error.

For my next tests of the load-cell, I will probobly leave it outside for a month or two, logging the load and temperature. Maybe I can give you some better answers then :)

gardner

Load cell is actually a strain gauge attached to a beam, in such a way as to measure the elastic deformation of the beam under load.  A higher load will accelerate the effects of creep, which will be one of the modes of long term reading drift.  Affects like work-hardening, corrosion and fatigue will also be there.

My working assumption is that those effects are going to make long term readings from a constantly loaded load-cell drift in such a way that you can't really trust the reading you get, until you, at least, re-tare the load cell to a known load.  If you can prove I'm crazy, that would be great.

Ickmund

Very interesting project, would love to know how it has progressed!

I'm doing the very same thing, environmental monitoring of beehives, including weight. Just as you have, we've identified the weight to be the biggest issue. From what I've heard, constant weight higher than 10% on a load cell will strain it over time. I'm hoping to get to testing this within the next few weeks, but I don't know if testing will be done in time for this season.

On the electronic side of things I've ordered Moteino:s. They sell for $16, including radio at 434MHz, and should be Arduino-compatible. It will probably be a couple of weeks before they arrive, but I'll come back with some details once I've gotten to play with them a bit.

http://lowpowerlab.com/blog/2012/12/20/moteino-the-wireless-low-power-low-cost-arduino-clone/

I should mention that this will be my first "Arduino" project, very excited!  :D

Clemens

Hi Lars, what is going on in your project? I'm interested in hive scales also and did some research. Nice to see that cheap load cells seams to work. Do you have some new recommendations for the amplifier? 

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