Patent GB-1310889-A (GB)
Title: Electrical measuring device
IPC: G01G19/12
Filed: 1969-12-04
Abstract: 1310889 Measuring weight of vehicle, electrically P W RICH and D J SADDLER 4 Dec 1970 [4 Dec 1969] 59266/69 Heading G1N The load on each axle and the gross vehicle weight of a vehicle having leaf springs is measured using transducers incorporated in the leaf springs, each transducer comprising resistance strain gauge elements connected in a bridge circuit and bonded to the major faces of a resilient metal plate having a resiliency characteristic the same as or better than the spring. The transducer may be interposed between the saddle plate and the spring Fig.1A, (not shown) or on top of the spring Fig.1B, (not shown) or may be substituted for one of the leaves of the spring Fig.1C, (not shown). Preferably four strain gauge elements are arranged, two at each end, on opposite faces of the plate to compensate for axle twist. As shown in Figs. 3A and 3B, four strain gauge elements 3 are bonded to plate 2 in recesses 17 and are connected in a bridge by wires laid in grooves 19 and passing through holes 18. A protective silicone coating 20 is applied over the elements 3, and metal cover plates 4 further protect the elements on the exposed face of the plate. A central hole 16 is provided for a locating bolt. In a modified form Figs.4A and 4B, (not shown) for mounting in the position shown in Fig.2, screws 14 can be tightened to contact spring 12. In the form shown in Figs. 5A and 5B, four strain gauge elements 35 are bonded to reduced thickness portions 29, bridge connections being made via grooves 34 and cut-out 36. Screws 31 are for tightening against spring 12 as shown in Fig.2. The thickness of portions 29 may be different for front and rear axles so that the transducers can give the same output when the axles are carrying their maximum loads even though the spring characteristics and loads are different. The thickest part of the plate 28 lies entirely within the boundary of the saddle plate so that variations in saddle plate length have no effect on the transducer output. In Fig.7, nearside and offside front axle strain gauge bridges B1 and B2 are arranged so that their outputs are zero at maximum permitted load. Their outputs are summed at A3 and fed to comparators C1, C2, C3 which respond when the axle load reaches 97%, 100% and 90% of the maximum respectively whereby amber lights come on at 90%, red at 97%, and the amber go off at 100%. Similar circuits are provided for the other axle(s). The Gross Vehicle Weight (of which the allowable maximum value may be less than the sum of the allowable axle loads) is measured by summing at the input to amplifier A4 the outputs of all the axle sum amplifier through scaling resistors R29, R30, R31, R32. Centre zero meters M1, M2 are calibrated from 80% to 100% G.V.W., 100% being at the scale centre. Red lights come on at 100%. Calibration adjustments. RV 3 , RV 4  are adjusted to give zero output from Al, A2 when S1, S2 are closed. R9, R12 are equal to half R10, R11; RV5 and RV6 are adjusted with S3 in CAL N/S and CAL O/S positions respectively. Closing S5 alters the threshold of C3 from 90% to 80%, allowing calibration to be effected over the range 80%-100%. Calibration is effected on the increasing load part of the hysteresis curve of the leaf springs.