Weighing scales – With testing
Patent
1986-12-12
1987-12-15
Miller, Jr., George H.
Weighing scales
With testing
177 1, 73 1B, G01G 1952, G01L 2500
Patent
active
047126272
ABSTRACT:
A platform weight scale comprising a capacitative load cell sensing means configured to be insensitive to off center loading of the horizontal platform regardless of load amount or location on the platform. The platform is supported by a plurality of springs selected for equal spring rates. The load cell is electrically connected into a FET (Field Effect Transistor), CMOS (Complementary Metal Oxide Semiconductor) or Bi-Polar semiconductor multivibrator circuit selected and designed to sense electric currents on the order of 10.sup.-13 amperes. In one preferred embodiment the load cell comprises a grounded hemispherical surface opposing a flat charged plate. In alternate embodiments the load cell comprises a differential capacitor or a parallel plate capacitor suspended in a manner that is insensitive to off center loading. An additional embodiment for the load cell comprises a spherically concave surface opposing the above grounded hemisperical surface.
A method for two point calibration of the scale without the use of calibration weights is provided. The method provides for weighing the empty weight table or platform for the zero point, weighing the scale without the platform and without disassembly by turning upside down and then recalibrating the scale at the two points or settings. The differential capacitor load cell embodiment utilizes an alternating switch circuit as a part of the multivibrator circuit. As a third alternative, a frequency modulated system clock circuit that is modulated by the load cell capacitance or differential capacitance may be utilized as the weight sensing circuit and driver for peripheral attachments to the scale circuit.
REFERENCES:
patent: 4343373 (1982-08-01), Stadler et al.
patent: 4425975 (1984-01-01), Luchinger
patent: 4660663 (1987-04-01), Amacher et al.
Harrington Richard H.
Krapf Charles W.
Deimen James M.
Measuretek, Inc.
Miller Jr. George H.
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