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Thanks Louis. Typical weight range for my project about 500 to 1,500 lbs. I sourced an amplifier chip specially made for load cells, but I found good load cells were expensive - so much so that a scales built with load cells would not be much cheaper than just buying cattle scales. Hydraulics and pressure transducers were much less expensive.
JPL, first of all it is gratifying to me that you actually built the device from my instructions. Regarding your question, I also found the scale does not hold absolutely on 0, but I assumed it was the error inherent in the pressure transducers I used. I think my pressure transducers are 500 psi 1% FS error where maybe I should have used 300 psi to reduce the error. In actual practice by weighing cattle and then seeing the official weight at the sale barn I believe my device is accurate to about 7 lbs, but the weights on my ticket at the sale always are multiples of 5.
I don't think I've had the problem with shifting weight, but you can adjust the ratio in the function if you like. I seem to recall in course of design and testing I felt like I did revise it toward a more permissive ratio, but I suppose you could take it further based on experience.