GB419006A - Improvements in and relating to electric relay circuits - Google Patents

Abstract

419,006. Switching systems. WESTON ELECTRICAL INSTRUMENT CORPORATION, 614, Frelinghuysen Avenue, Newark, New Jersey, U.S.A.-(Assignees of Lamb, A. H. ; 402, Chilton Street, Elizabeth, New Jersey, U.S.A.) June 24, 1933, No. 18048. Convention date, July 7, 1932. [Class 38 (iv).] A relay control system which may be employed, for example, in an arrangement for turning on the lights at a lighthouse when the normal or solar illumination falls below a predetermined amount, comprises a D.C. operated electromagnetic switch adapted to be included in the circuit to be controlled, the winding of which is connected across the output terminals of an A.C. bridge rectifier, the input terminals of which are connected to the secondary winding of a transformer of the type drawing negligible current when the said secondary circuit is open, a thermal switch energized by a relay being included in the circuit of said secondary winding. Thus, if the relay fails to operate initially owing to welding or sticking of the contacts, current impulses are repeatedly and periodically applied to the relay circuit until correct functioning of the relay takes place. As shown in Fig. 1, in which the relay is arranged to control the illumination of a lighthouse in response to variations of a light sensitive cell 1, the latter is arranged to operate the moving coil 2 of a sensitive relay 3 so as to engage fixed contacts 5 or 6 in accordance with predetermined limits of the illumination of the cell. If, for example, contact 6 is engaged a circuit is completed from a transformer 12 of the type drawing negiligible current when the secondary circuit is open through a bank of rectifiers 14 to the heating coil 19 in series with a movable thermal strip 21. The strip is heated after a short interval and engages a contact carried by a second strip 25 completing a circuit to the operating winding 7 of the relay 9 across the rectifier. If the core 8 of the solenoid 7 is immediately attracted, breaking the controlled circuit at contacts 9, the relay completes a maintaining circuit at contacts 10. The energization of the coil 7 in parallel with the heating coil 19 of the thermal switch reduces the current in the latter sufficiently to cause the strip 21 to disengage the contact carried by strip 25. This has no effect if the relay has operated correctly and completed its maintaining circuit in the manner previously described, but if owing to adhesion or welding between the contacts or any other cause operation of the relay has not taken place the opening of the thermal switch H causes the full heating current to flow in the coil 19 and a new current impulse to be delivered to the electromagnet 7 when the contacts again engage. This cycle is thus repeated continuously at intervals determined by the heating and cooling of the strip while the contact 6 remains engaged and the relay 7 unoperated, the current impulses tending strongly to operate the relay against any resisting forces which may be present. A similar action occurs during the return of the relay to the position shown due to engagement of contact 5 of relay 3 consequent on the reduction of illumination of the cell 1 below a predetermined value. In this case, however, the operation of the relay takes place through a second thermal relay L which is arranged if the return movement of the relay does not take place, to repeatedly short-circuit the bank of rectifiers until the impulses given to the armature 8 cause it to drop open thereby opening the maintaining switch 11. The second thermal switch may, however, be arranged to short-circuit one arm only of the rectifier bridge (Fig. 4, not shown). The Specification as open to inspection under Sect. 91 describes also an arrangement in which the rectifier bridge was omitted altogether. This subject-matter does not appear in the Specification as accepted.