Surface Acoustic Wave Scale That Automatically Updates Calibration Information

摘要

Apparatus and related methods are provided for automatically recalibrating a SAW scale for changing environmental factors. During a period of time when there is no change to a weight applied to the scale, readings of SAW transducers which relate to weight indications and environmental factor indications are taken for two adjacent operating modes of the scale, and two calibrated weight calculations are made utilizing those readings. The difference in calibrated weight calculations is then related to a variable utilized to transform the readings into weights, which is updated, thereby recalibrating the scale.

主权项

1. A transducer for a surface acoustic wave (SAW) weighing device, comprising:
a lithium niobate substrate; at least one electrode attached to said lithium niobate substrate by glue; and a holder attached to said lithium niobate substrate by a bond, wherein said at least one of said substrate and said holder is adapted to reduce stress on said bond when an ambient temperature in which said transducer is located changes significantly, by either (i) said lithium niobate substrate having a thickness between 0.25 mm and 0.1 mm, and said holder having a thickness at least ten times the thickness of said lithium niobate substrate, (ii) said holder and said lithium niobate substrate having a thickness such that said lithium niobate substrate and said holder bend together like a bimetallic strip when said ambient temperature changes significantly, (iii) said holder having a front face to which said lithium niobate substrate is coupled, said front face defining a cantilevered beam, and said bond between said lithium niobate substrate and said holder located on said cantilevered beam and a second surface displaced from said cantilevered beam such that when said ambient temperature changes significantly said beam accommodates thermal stress, (iv) further comprising an intermediate plate between said lithium niobate substrate and said holder, said intermediate plate having a coefficient of thermal expansion (CTE) that closely matches that of said lithium niobate substrate, an adhesive bond located between said lithium niobate substrate and said intermediate plate along a bonding line, and two pins connecting said intermediate plate to said holder, said two pins laterally offset from said bonding line such that when said ambient temperature changes significantly, said intermediate plate stretches or shrinks along with said lithium niobate substrate to prevent overstressing said bonding agent between said lithium niobate substrate and said intermediate plate, and (v) further comprising an intermediate plate between said lithium niobate substrate and said holder, said intermediate plate having a coefficient of thermal expansion (CTE) that closely matches that of said lithium niobate substrate, an adhesive bond located between said lithium niobate substrate and said intermediate plate along a bonding line, said holder having a front face defining a cantilevered beam, and first and second pins, said first pin extending through said intermediate plate and into said cantilevered beam of said holder, and said second pin extending through said intermediate plate and into said front face, said pins provided on opposite sides of lithium niobate substrate, such that when said ambient temperature changes significantly, such that when said ambient temperature changes significantly said beam accommodates thermal stress.