GB1114207A - Improvements in or relating to electrical weighing apparatus - Google Patents

Abstract

1, 114, 207. Measuring weight electrically. GIRLING Ltd. Jan. 3,1967 [Jan. 3, 1966], No.47/66. Heading G1N. In a weighing apparatus wherein a voltage from a platform supporting strain gauge load cells is balanced by a voltage related to a servomotor driven potentiometer position, the non-linear relationship of the strain gauge output signal to the applied weight is partly compensated by adding a voltage which is selectively adjustable in steps to the voltage level of the potentiometer circuit. A load weight representative voltage from parallel connected resistance strain gauge load cells 51 to 54 (Fig. 7), is compared in a differential amplifier 64 with a voltage from a circuit including a potentiometer 62 the slider position of which at balance gives an indication of load weight, the slider being driven by a servomotor 65 one winding of which is energized by the differential amplifier output and the other by an A. C. source 57. The junction point of series resistors 73, 74, which are connected in parallel with the potentiometer 62 provides an artificial zero for the potentiometer 62 and between this junction and an output line from the load cell circuit at the slider of a resistor 79, a voltage is added to the potentiometer circuit voltage. This voltage is adjustable by selectively switching, by means of servomotor driven cam operated switches 67, 68, resistors 81, 82 into the circuit at certain portions of the weighing range to give an indicated applied weight characteristic (7) Fig. 5 (not shown) within desired tolerance limits of linearity. The variable resistors 78,79 provide respectively, coarse and fine adjustment of the voltage added and are adjusted to bring the voltage across the resistor 80 in series with parts of potentiometers 78, 79, to approximate 90% of the dead weight of the unladen weighbridge.