> Load cells, i.e. those operating under high pressure, have the additional
> problem of making sure the load is evenly distributed, needing such items
> as case-hardened steel plates. This makes the cells not only expensive,
but
> hard to maintain calibration.

> >The kitchen scales I see use a variable capacitor sensor. Never seen a
> >kitchen scale using a strain gage.

The ones I have definitely use a formal separately mounted load cell.
Many of the smaller load cells I have seen (up to around 50 kg AFAIR - maybe
more) use what the trade callss a single point mounting. They use typically
2 x M6 bolts to mount the cell to the base plate and another 2 at the other
end of the cell to mount the platform (or load point). In small scales this
supports the weighing platform directly on the cell with the M6 bolts. I
imagine there are some assumptions made re centrailty of distribution. of
the load on the platform :-).  Such an arrangement should be easy enough to
use for my purpose (dynamometer). Applying the load to a point intermediate
between the 2 x M6 holes (possibly with an adaptor) should be mechanically
easy.


>  Bathroom scales often use the half
> >bridge strain gage method. I think that supplying a strain gage like that
> >would be problematic because in my experience 95% of the strain gage
> >problems have to do with using the proper adhesive and curing it properly
> >in place.

Yes. If possible I want to buy made up units which can be simply bolted into
place. Rolling your own looks easy in theory but there are many lifetimes of
practical experience involved in making it work well.

Indicative price so far is around 9 euros in 1000's for a cell that
handsomely exceeds my accuracy specs.
It will have to be substantially cheaper to be viable. The price and
performance of my kitchen scales indicates this is achievable.


Russell McMahon

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