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Surface acoustic wave scale that automatically updates calibration information

  • US 9,477,638 B2
  • Filed: 01/16/2013
  • Issued: 10/25/2016
  • Est. Priority Date: 06/12/1995
  • Status: Active Grant
First Claim
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1. An electronic weighing apparatus comprising:

  • a) a displaceable elastic member that receives a load is displaced by the load such that the displacement of said elastic member is related to the weight of the load;

    b) a first piezoelectric transducer having a first substrate and one of a first surface acoustic wave (SAW) transmitter and a first SAW receiver, said first piezoelectric transducer being coupled to said elastic member;

    c) a second piezoelectric transducer having a second substrate and the other of said first SAW transmitter and said first SAW receiver, said second piezoelectric transducer being mounted in close proximity to said first piezoelectric transducer such that said displacement of said elastic member causes a corresponding displacement of one of said first and second piezoelectric transducers relative to each other;

    d) a first amplifier having an input and an output, said input of said first amplifier being coupled to said first SAW receiver and said output of said first amplifier being coupled to said first SAW transmitter such that said first SAW receiver, said first amplifier and said first SAW transmitter form a first oscillator having a first output, said first oscillator adapted to operate in a plurality of modes including a first mode and a second mode adjacent said first mode;

    e) a second SAW receiver;

    f) a second SAW transmitter;

    g) a second amplifier having an input and an output, said input of said second amplifier being coupled to said second SAW receiver and said output of said second amplifier being coupled to said second SAW transmitter such that said second transducer, said second amplifier, and said second SAW transmitter form a second oscillator having a second output, and said second amplifier output being indicative of environmental factors of said electronic weighing apparatus;

    h) a processor coupled to said output of said first amplifier and to said output of said second amplifier, said processor storing initial calibration information for said electronic weighing apparatus, said processor determining from said initial calibration information and from indications of said first oscillator output and said second oscillator output an indication of the weight (P) of the load at a first time, said processor further adapted to determine that the load is static and to receive indications of said first oscillator output in each of said first and second modes and indications from said second oscillator output and to generate therefrom updated calibration information which is stored by said processor and used to determine an indication of the weight of the load at a subsequent second time.

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