GB1453934A - Electrical weighing systems - Google Patents

Abstract

1453934 Electrical weighing system PROBE ENG CO Ltd 3 Jan 1974 [4 Jan 1973] 466/73 Heading G1N A load sensing transducer comprises a pair of generally flat conductors 1, 2, spaced parallel having leads 14 and separated by a cell or cells which are closed and having flexible side walls as in the plastics or rubber foam 4 and held apart by discrete resilient bodies 4 between which and conductors 1 and 2 an air space is left. Items 4 may be set in grooves in the plates or grooves formed by conducting plates attached to plates 1 and 2. Instead of item 4 a thin walled tube may be bonded to plates 1, 2 or thin strips of metal, plastics or rubber, with, at the edges, bonding, which is insulating if metal is used. Reinforcement by membranes 12 may be used, around or between the edges of plates 1, 2, which bear temperature sensitive elements 18, with leads 19, and are separated by insulators 15 from load-bearing plates 16, 17. Overload is indicated by the short circuit caused by stops 13. In Figs. 6 and 7, O is an oscillator of fixed amplitude and frequency, C the capacitance of plates 1, 2; A, A2 are high gain inverting amplifiers, Z is a stable impedance, # a phase splitter and SD a synchronous detector. Stray capacitances CS1 and CS2 and leakage resistance across C do not affect the circuit. One of the resistors Ro, Ri is an element 18. Negative coefficient thermistors, T, may form, with Rx, Ry, resistance Ri and output O/P 2 may be read on a digital voltmeter. Automatic or manual zero correction for barometric pressure may be applied to the input of A2, but is unnecessary with the circuit of Fig. 9, in which low pass filter F prevents mechanical oscillations of the load from causing voltage oscillation on C1, and charge flows into high gain inverting amplifier A3 until monostable circuit M is triggered causing counter CT to register and charge in Co to be discharged into the input of A3 in opposition. The action is repetitive and the total charge from Co equals the total charge from C1 and is proportional to the number of operations of M. Load removal does not cause counts because diode D conducts, but further loads cause additive counting.