Receiver for light-flash signalling system

摘要

746,030. Photo-electric signalling systems. FRUNGEL, F. Dec. 18, 1952 [Jan. 2, 1952], No. 32101/52. Class 40 (3). In a system for signalling by light flashes, e.g. for warning a vehicle in front that it is to be overtaken, means are provided which will respond only to light flashes which (1) occur in regular succession, (2) are of a duration of between 10-5 to 10-7 seconds, and (3) have a luminous flux which rises at a rate of 100 lumen per microsecond. Light flashes of the kind referred to above from a source of the type described in Specification 742,396 are received on a photo-electric cell 1 situated behind a lens 29 and a blue filter 30. This cell is situated on the rear of the vehicle and pulses developed at its anode are fed through condenser 2 which with the grid leak 3 of amplifier valve 4 has such a time constant as to eliminate all pulses of more than 5 x 10-6 seconds duration. The anode resistors of this stage and the subsequent two stages are relatively low so as to make the circuit an efficient high-frequency amplifier. Tube 6 forms with tube 7 and a common cathode resistor 13, a relaxation oscillator. A negative input signal causes the cathode of tube 6 to go negative and the anode positive. The positive anode pulse increases the conductivity of valve 7 which, due to the increased current sends the cathode of valve 6 positive so that valve 6 blocks, remaining so until the charge on the grid condenser 14 has leaked away. During this period a relay 16 and, if required, a glow tube 34 are energized. The anode relay of the oscillator may operate a further relay which is delayed by a parallel condenser the arrangement being such that a warning signal is operated if pulses arrive at intervals of less than one second. If the photo-cell is situated at the rear of the vehicle and the amplifier near the driver, they may be connected through a lowcapacity cable (Fig. 3, not shown). Pulse transformers may be used at the transmitting and receiving ends of the cable (Fig. 4, not shown) and a preamplifier comprising a transistor may be situated adjacent the photo-cell.