Patent GB-393248-A (GB)
Title: Method and means for controlling switches by photo-electric currents
IPC: H03K17/288
Filed: 1931-08-25
Abstract: 393,248. Switching systems for consuming devices. ISENTHAL, A. W., Ducon Works, Victoria Road, North Acton, London.-(Assignee of Geffcken, H. ; 81, Biedermannstrasse, and Richter, H.; 3, Wiederitzscherstrasse, both in Leipsic, Germany.) Aug. 25, 1931, No. 23941. Convention date, Aug. 25, 1930. Void [Published under Sect. 91 of the Acts]. [Class 38 (iv).] The intensity of light is measured by the time taken to discharge a negative bias applied periodically to the grid condensers 3, 4, Fig. 1, of two valves 1, 2. The method is applicable to the switching of lamps as daylight fluctuates. In one case the discharge takes place through a standard resistance 8, and in the other through a photo-electric cell 6. As the grid charge leaks away, the flow of plate current is initiated to energize one or other of the coils 12, 21, which thereupon operate relays 15 or 24 to open or close a main contact 10. Subsidiary contacts in the relays 24, 15 serve to maintain the main contact 10 in whatever position it takes up until the expiration of the next but one discharge period, and also ensures that each discharge nullifies the effect of the other upon the main contact 10. In this way the contact 10 is maintained in one definite position when the incident light falls permanently below a certain value, and is equally retained in the other position when the light intensity permanently exceeds a given value. When plate current flows in valve 2, contact 28 is closed to energize relay 31, thereby closing both the load contact 10 and a holding contact 32. Simultaneously, contact 29 is opened to cut off the high tension supply to valve 1. Further, contact 26 is closed to apply a " clearing" or positive charge through resistance 37 to the grids of both of the valves 1, 2, but since there is no high tension supply to valve 1, only the relay 24 is effected .and is reset to its original state. The electron flow through the valve discharges the positive bias, and both grids assume their original negative charge. If, however, plate current is first initiated in the valve 1, the contact 18 opens to de-energize the coil 31 and open the contacts 32, 10. Simultaneously, the opening of contact 17 prevents subsequent operation of the relay 24 (as the grid charge on valve 2 leaks away) and so energizes the coil 31 and alters the setting. This is ensured by the closure of contact 19, which energizes coil 16 through a resistance 39, independently of contact 14, which opens when the relay is operated; but when the relay 24 has acted and dropped back again, the relay 15 is free to return to its inoperative position. In a modified form, a valve operated relay is maintained in one or other of two definite positions for a time corresponding to two successive charging periods, by means of an auxiliary condenser 59, Fig. 2 (not shown). Alternatively, only the timing valve 2, Fig. 1, or the measuring valve 1, is allowed to effect the operation of the main switch, which otherwise remains in its set position, the premature completion of the ineffective device nullifying the succeeding completion of the effective device. For example, in Fig. 3, the timing interval is indicated by means of a rotating disc 71 which tends to tilt the main switch 10 to right or left under the action of a spring 73 and an eccentric 75, at the moment when a block 77 reaches the insets 78, 82, unless the position of a forked armature 79 operated by the plate current of the valve 64 prevents the movement of the lever 80. If the armature 79 is not attracted by relay 70, the arm 80 can only move upwards, whilst if it is attracted, the arm can only move downwards, rocking the main contact 10 to one or other of its two positions. Pins 81, 83 rock a mercury contact 68 to impart successive new negative impulses to the grid of the valve through a resistance 69 as the preceding ones leak away through the photo-electric cell 67. A modification of this arrangement is described in which the main contact can be set in one or other of three definite positions, so that no operation takes place within certain limits of tolerance. Fig. 8 shows an arrangement in which the power for tilting the switch cam is taken only at the moment when tilting actually occurs, and during a non-measuring interval. The tilting of the main mercury contact 10 takes place when a pin 100 on a lever 99 fulcrumed at 101 overrides a rim 98 on a clockwork-driven disc 97, if it is allowed to do so by the profile piece 102, which is normally held up by a ratchet 106 carried by the armature of a relay similar to 70 in Fig. 3. If the valve relay operates before the pin 100 reaches the gap 110, then the ratchet 106 engages a notch 112 on the profile piece and prevents the lever 99 from tilting, at the same time allowing the pin to pass over the gap. The grid of the valve is charged periodically by means of a finger 114 which tilts the mercury switch 68. In a modified form of the last arrangement, the tilt of the lever carrying the main switch is controlled by a separate cam, which is coupled to the clock-driven disc periodically by a magnetic clutch operated by a relay in the plate circuit of the timing valve.