GB811821A - Improvements in or relating to railway classification systems - Google Patents

Abstract

811,821. Railway classification systems. GENERAL RAILWAY SIGNAL CO. May 1, 1957, No. 13877/57. Class 103 (1). Control apparatus for a railway classification system comprises means, such as a radar type scanner, adapted to provide a beat-frequency output signal on the Doppler principle, the frequency being proportional to the speed of the car rolling over a track section, such section being provided with at least one car retarder, and retarder control means operable under the joint control of said speed measuring means and of release speed computing circuit means providing a continuously variable output proportional for each car to the desired release speed of such car from the retarder. The amplitude of beat frequency output signal is made proportional to the proximity of an approaching car and includes circuit means operable for a predetermined period in response to a predetermined amplitude of signal output from the speed measuring means. The circuit means includes an amplifier comprising tubes 47 and 52, Fig. 3A, which are interconnected to form what is commonly known as a Schmitt amplifier circuit. This applies output signals to operate a relay when the amplitude of such signals exceeds a predetermined level. A gate circuit comprising a triode 71 passes the output signals received from the speed-measuring means to a pulse-forming circuit including the one-shot multi-vibrator 81. This generates a pulse for each cycle of beat frequency oscillation received, and the positive going of these pulses are inverted by the amplifier 85 with the result that the input to diode 86 included in the speed relay control circuit 87 comprises negative-going pulses. The speed relay control circuit 87 thus receives negative-going voltage pulses from amplifiers 85, all the pulses being of the same amplitude and width, but their frequency varying with car speed. An anticipation relay control circuit operated in a similar manner to the speed relay control circuit but the control voltage applied to the cathode of diode 111, i.e. of a somewhat higher value than that to diode 86 so that the relay A1 drops at a slightly higher car speed than the relay S1, causing the retarder to be partially released. The exit relay control circuit, i.e. operated as a function of the proximity of the car to the transmitting antenna, and is independent of actual car speed.