Electronic weighing apparatus utilizing surface acoustic waves

摘要

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 sealed from moisture; an hermetically sealed temperature transducer is provided to compensate 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.