Patent GB-185084-A (GB)
Title: Improvements in devices for indicating the failure of electric lamps
IPC: H05B39/10
Filed: 1922-01-23
Abstract: 185,084. Westinghouse Brake & Saxby Signal Co., Ltd., (Assignees of Lucas, S. M.). Aug. 24, 1921, [Convention date]. Lamp-failure alarm devices; thermionic value luminous signals; semaphore signals; elongated signal lights, horizontal and vertical.-The lamp, failure of which is to be indicated, is formed as a two-electrode valve whose anode-cathode circuit includes a source of alternating current and controls an indication device. The invention is described in connection with interlocking railway signals. In an example, Fig. 1, a " proceed " lamp G and a " stop " lamp R are controlled by a signal lever L. As shown the lever is in the " reverse " position and lamp G is lighted by current from a transformer Ta. When the lever L is pushed in to the " indicating " position the face 21 comes up against the latch 11 and a circuit is completed through contacts 6, 9 to illuminate the filament 3 of lamp R which is formed as a two electrode valve. If the filament is hot enough to radiate enough light, rectified current will flow in its anode-filament circuit in one direction so that the primary transformer Tb is supplied with pulsating unidirectional current. There is thus induced in the stator 14 of an induction motor M current having a component of the frequency of the current in transformer Ta and another twice that frequency. The motor M thus rotates at a speed' between those corresponding to the two frequencies and by the operation of a centrifugal device C is arranged at that speed but not at the speed due to the frequency in the transformer Ta, to lift the latch 11 so that the lever L may be pushed further in to its " normal " position. The motor M then stops but lamp R remains lit. In a modification, tuned circuits are arranged between the transformer Tb and the motor M so that the fundamental frequency is tuned out. In a further modification, the latch 11 is raised by a polarized magnet in the anode-cathode circuit of the lamp R. This cannot be actuated by stray alternating current of any frequency. In a further modification, Fig. 4, the circuits are modified as shown, the motor M being arranged to run the whole time the lamp R is illuminated. The centrifugal device may control the circuits of lamps R<a>, Ga to indicate at any time the state of the signal lamps. In a further modification, the lamp R is arranged to have two anodes so as to rectify both half waves of the supply current and the synchronous motor is consequently supplied with current of twice the fundamental frequency without the use of any tuned circuits. In a modided form of indicating apparatus, Fig. 5. a magnetic switch is provided which in order to be operated requires a current comprising both a uni-directional and an alternating component such as that on the transformer Tb, Fig. 4. This switch comprises two magnetizable cores 29, 30 and two magnetizable bridges 32, 33 the latter of which is laminated and' of comparatively small cross-section. Short circuited copper bands 35, 36, 34 surround one end of cores 29, 30 and the bridge 32. Two armatures 28, 28a are provided so arranged that if one is attracted lamps Ga, Ra are both extinguished and one of the latches 11, 11<a> stops the movement of the lever L to its rormal position, but if both are attracted the lamp R<a> glows and both latches 11, 11<a> are raised'. The construction of the switch ensures that alt rnating current in the winding 31 causes the armature 28 to be attracted but does not affect the armature 28a and that direct current on the other hand operates only the armature 28<a>. In a further example, Fig. 7, the invention is applied to a " position light signal." The three " proceed " lamps G are lighted through contacts 6, 9 from a transformer T<a>. A lamp R<1> common to both groups is constantly lighted from a transformer T<c> and the " stop lamps R under control of the signal lever from a transformer Td. The indicator circuit includes the anode-cathode circuits of all the lamps R and the lamp R<1> in series and the primary of a transformer Tb. The selective device X tunes out the fundamental frequency so that the stator of a motor M receives current at twice that frequency only. The control of the latch 11 is the same as described with reference to Fig. 1.