GB462547A - Improvements in current supply arrangements for operating electromagnetic relays - Google Patents

Abstract

462,547. Electromagnetic switches. AUTOMATIC ELECTRIC CO., Ltd., PREIST, T. P., and THOMPSON, G. W. Sept. 10, 1935, No. 25189. [Class 38 (v)] A current supply arrangement for electromagnetic relays which may be controlled by vehicleactuated pressure - operated switches in road - signalling equipments is arranged so that the potential normally across the pressure-operated switch is, by means of a potentiometer arrangement, made considerably less than the voltage of the D.C. supply mains whilst when this switch is closed a rush of current sufficient to produce reliable operation of the relay is produced by the charging or discharging of a condenser in the circuit. As shown in the Figure, the pressure-operated switch is normally connected in series with a low resistance winding of the relay across a high resistance X, a second high resistance Y of unequal value to X being in series with this combination across the mains, the latter resistance being shunted by a condenser C of high capacity. Normally, only a proportion of the supply voltage is across the switch, the remainder being across the condenser. When the pressure-switch D is closed, however, the sudden rush of charging current to condenser C produces a reliable operation of the relay. The consequent changing over of the relay contact a1 completes a maintaining circuit for a high resistance winding of the relay in series with the resistance X until the pressure switch is opened. In a modified arrangement, Fig. 2 (not shown), the relay is further maintained in the operated position after initial operation in the manner previously described by a second contact of the pressure switch which is closed bv further movement of the vehicle. The arrangement described may be modified so that the relay operates by the discharging and not the charging, of the condenser. Specification 433,624 is referred to.