GB148480A - Electrical annunciator and alarm devices, particularly for burglar and fire alarms - Google Patents

Abstract

148,480. Schmidt, G., and B÷ker & Co. March 27, 1918, [Convention date]. Alarms, fire &c.-Relates to fire and other alarms operated by a selenium cell when illuminated or shaded contrarily to its normal state. In one method, illustrated in Fig. 1, equal selenium cells S<1>, S<2> adjusting resistances W<1>, W<2> and coils a, a<1> of a differential relay R are connected in two parallel circuits energized by the battery B<1>. When a shadow falls on one of the cells S<1>, S<2> in the day time, or a ray of light at night, the tongue Z of the relay R closes a circuit through the alarm bell F and battery B<3> over conductors 5 and 6, and a hold-on circuit over the conductor 7 ensures continued ringing of the bell. A lamp L can be brought into circuit by means of the switch A' for the purpose of adjusting the contacts K, K<1> which can be turned about pins k, k<1>. The cells S<1>, S<2> may be screened laterally and may be furnished with lenses. In the form shown in Fig. 2 the galvanometer R operates the alarm when the cells S, S<2> are differentially illuminated, as already described. In addition, however, a galvanometer G' is so arranged that during the day time current from the battery B<2> flows through it in series with the cells S, S<2> via the contacts m, n. At nightfall, however, the rise in resistance of the cells causes the needle to make contact at K<2> so as to energize a magnet, attract the armature x and trip the lever o. In consequence, the galvanometer G is cut out of circuit by the breaking of contact at m, n, and the galvanometer G<2> is put in circuit with battery B<2> and cells S, S<2> in series by the making of contact at o &c. Thereafter any general illumination of the cells S, S<2> causes a rise of current through the galvanometer G<2> which thereupon operates the alarm, while a differential illumination of the cells S, S<2> will also cause the galvanometer R to operate the alarm as before. According to the Specification as open to inspection under Sect. 91, the galvanometer R with its associated circuits may be omitted. The galvanometers G<1>, G<2> with their circuits then form an alarm apparatus, which is inactive during the day time but automatically becomes effective after nightfall.