Patent GB-345636-A (GB)
Title: Improvements in and relating to light-sensitive relay systems
IPC: H01H47/24
Filed: 1929-12-13
Abstract: 345,636. Railway signals. BASELER, W., 21, Wallhallastrasse, and HOFFMAN, F., 3, Voitstrasse, both in Munich, Germany. Dec. 13, 1929, No. 38307. Convention date, Dec. 24, 1928. [Class 105.] Relates to a signal -receiving system which may be used in connection with train-control systems employing tetrahedral mirrors as described in Specification 337,976, [Class 105, Railway signals &c.], and comprises a main photoelectric cell and a compensating-cell arranged in a bridge, a shuntinductance or series condenser being provided to ensure that the system will be unaffected by slowly varying illumination of the main cell. In Fig. 1 the main cell 52 and compensating cell 53 are arranged in a bridge so that the relay 55 is energized when a signal beam falls upon the main cell, but not when extraneous light affects both cells equally. The relay 55 is in series with a condenser 54, which ensures that while the system will react to rapidly-changing signal-illumination it will not react to slowly-changing illumination. Alternatively the relay may be in parallel with an inductance and may be associated with a valve amplifier (Fig. 2, not shown) ; or it may be placed, together with the condenser 54, in a diagonal of a Wheatstone bridge of which the cells form two arms (Fig. 3, not shown) ; or the connection 63, Fig. 1, may be made to the negative pole, instead of the mid point of the battery 51 (Fig. 4, not shown). The cells may normally determine a mean value of the anode current, the current being increased or decreased so as to energize one relay or another according as one cell or the other is illuminated. (Fig. 5, not shown). Two relays, 69, 70, Fig. 6, may be so arranged that when a normal current flows in the plate circuit, the point e is connected to both points f, g, as shown. If the cell 52 or 53 is illuminated the plate current rises or falls, cutting the point e off from the point g or f as the case may be. If the signal is of long duration the grid loses or acquires a negative charge, and the arrangement shown in Fig. 6 prevents this charge from causing a reverse signal on the cessation of the light signal. A separate valve and condenser may be provided for each relay (Fig. 7, not shown), and the relay windings 69, 70 may control a single' core and armature (Fig. 9, not shown). The arrangement may be such that the relays 74, 76, Fig. 8, are respectively operated (by de-energization and energization respectively) when the corresponding signal cells F, H are illuminated, the compensating cells F<1>, H<1>, having no effect if they should be illuminated when the main cells are not illuminated. The above arrangements restrict the range over which the characteristics of the cells have to be similar to one another. In another arrangement the compensating cell 53, Fig. 10, sets up in the resistance 80, when illuminated, a potential drop which neutralizes the change of resistance set up by simultaneous illumination of the signal cell 52, thus " locking " this cell, whereas if the latter cell be illuminated alone, the armature 73 falls off. Impedances 82, 83, may be added to delay the action of the signal cell until the compensating cell has had time to take effect. The compensating cell 53 may be associated with a thermionic amplifier and may co-operate with a plurality of main or signal-receiving cells (Fig. 11, not shown). The compensating cell may be associated with a separate amplifier which is coupled through a condenser to the grid of the main cell (Fig. 12, not shown). For use in connection with slowly moving trains the signal light may be chopped. The condenser 54 may be replaced by a filter circuit (Fig. 13, not shown).