Weighing scales – Self-positioning – Electrical current generating or modifying
Patent
1996-10-07
1999-06-08
Gibson, Randy W.
Weighing scales
Self-positioning
Electrical current generating or modifying
7386259, G01G 314
Patent
active
059106476
ABSTRACT:
A weighing apparatus includes a base supporting a cantilevered elastic member bearing a load platform. The interior of the elastic member is hollowed and is provided with first and second piezoelectric transducers mounted on respective opposed posts. The transducers are arranged substantially parallel to each other with a small gap between them and are coupled to an amplifier to form a "delay line" and a positive feedback loop, i.e. a natural oscillator. According to various aspects of the invention, one or both substrates is provided with anti-reflection structure; the transducers are arranged on overlapping substrates to further reduce reflection; the transducers are coupled to a thermal sink to reduce the effects of thermal gradients across the transducers; two pairs of transducers are provided and arranged to provide a pair of oppositely polarized signals which doubles the accuracy of measurements and also compensates for the effects of temperature gradients; a thermal transducer channel is provided on the same substrate to measure the effects of temperature gradients and thereby compensate for temperature effects; a pair of differential transducers is arranged to measure the effects of temperature changes in the same acoustic channel in which displacement measurements are made; and a phase shift is applied to the output of the amplifier(s) to improve gain.
REFERENCES:
patent: 4096740 (1978-06-01), Sallee
patent: 4107626 (1978-08-01), Kiewit
patent: 4294321 (1981-10-01), Wittlinger et al.
patent: 4623813 (1986-11-01), Naito et al.
patent: 4858145 (1989-08-01), Inoue et al.
patent: 5476002 (1995-12-01), Bowers et al.
patent: 5663531 (1997-09-01), Kats
"Progress in the Development of SAW Resonator Pressure Transducers" by Cullen et al., 1980 Ultrasonics Symposium, pp. 696-701.
"Pressure and Acceleration Sensitivity of SAW Interferometer" by Staples et al., 1981 Ultrasonics Symposium, pp. 155-158.
Gordon Arnold S.
Kats Vyacheslav D.
Circuits and Systems, Inc.
Gallagher Thomas A.
Gibson Randy W.
Gordon David P.
Jacobson David S.
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