Patent GB-468222-A (GB)
Title: Improvements in or relating to electromagnetic-relay time-delay circuits
IPC: H01H47/18
Filed: 1935-12-31
Abstract: 468,222. Electromagnetic switches. STANDARD TELEPHONES & CABLES, Ltd., and JACOBSEN, B. B. Dec. 31, 1935, No. 36066. [Class 38 (v)] [Also in Group XXXVIII] An electrical time-delay circuit comprises a source of potential, a relay and a condenser which can polarize in both directions and in which the delay in the operation of the relay obtained equals the sum of the charging and the discharging times of the condenser, the delay obtained being of the order of seconds. As shown in Fig. 2, a condenser CR is normally retained charged through a circuit including resistances Ra and Rc and contacts a2, a3 of a relay A, a relay B being at the same time held operated through contacts a3 and b1. On closure of contact x, however, the relay A is energized and contacts a2, a3 opened so breaking the holding circuit of relay B and the charging circuit of the condenser. The charged condenser, however, is now in series aiding the 130 volt battery connected to the resistance Rb so that it has initially an effective voltage of twice the battery voltage and the condenser will commence to discharge through the relay B and immediately to charge in the opposite direction. Thus the relay is held closed until the successive discharging and charging operations are effected and the charging current falls below the minimum holding current for the relay. If the contact x is opened before the expiration of the time delay thus imposed on the release of relay B, the latter will still be held energized, but if it remains closed for a longer period, the relay B is released. On the subsequent opening of the contact x, the relay A is also released and the circuit of a third relay completed and maintained which in turn completes the operation of a time-lag relay D. The latter completes at contact d1 the circuit of an opposing winding of the relay A which initiates a time lag action in the opening of relay C similar to that previously described. If, however, contact x is reclosed before the relay C is released, the relay A releases in view of the opposition of its two windings and the circuit of a lamp S is completed via a1, cl and d1. The relays are restored to their original positions and the original circuit of the condenser restored only if contact x is allowed to remain open for more than a predetermined time, e.g. 3 seconds. In another arrangement shown in Fig. 4, two sources may be switched on to the relay under the control of contacts a1, a2, the relay B, in series with a rectifier RC, being shunted by the condenser CR. Normally, the rectifier prevents a current flow in the relay B, but when the contacts a1, a2 are changed over, the voltage applied to the condenser is reversed and the relay operates only after the discharge of the condenser followed by its charging in the opposite direction until it reaches the minimum voltage at which the relay will operate. In a modified form the relay and rectifier are permanently in one supply circuit while a reverse potential is applied through a small resistance. Variation of the relay resistance may be employed to vary the time delay in relay operation. Specification 430,824, [Group XXXIX], is referred to.