Weighing scales – Self-positioning – Electrical current generating or modifying
Patent
1995-06-12
1997-09-02
Gellner, Michael L.
Weighing scales
Self-positioning
Electrical current generating or modifying
177211, G01G 314
Patent
active
056635311
ABSTRACT:
An electronic weighing apparatus includes a base which supports a cantilevered elastic member upon which a load platform is mounted. The free end of the elastic member is provided with a first piezoelectric transducer and a second piezoelectric transducer is supported by the base. Each transducer includes a substantially rectangular piezoelectric substrate and a pair of electrodes imprinted on the substrate at one end thereof. The transducers are arranged with their substrates substantially parallel to each other with a small gap between them and with their respective electrodes in relatively opposite positions. The electrodes of the second transducer are coupled to the input of an amplifier and the output of the amplifier is coupled to the electrodes of the first transducer. The resulting circuit is a positive feedback loop with a "delay line" in which a surface acoustic wave in one substrate is effectively induced into the other. When a load is applied to the load platform, the free end of the cantilevered elastic member moves and causes the first transducer to move relative to the second transducer. The movement of the first transducer relative to the second transducer causes a change in the frequency at the output of the amplifier which is used to determine the displacement of the elastic member and thus the weight of the applied load.
REFERENCES:
"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.
Circuits and Systems
Gellner Michael L.
Gordon David P.
Mai Anh
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