Ultrasonic warning system for rail and road vehicles - operates with Doppler discriminator control loop for approach indicator and has power amplifier for pulses

摘要

The ultrasonic warning system for rail and road vehicles is designed to prevent collisions at crossings. The railway vehicle is fitted with an oscillator running at constant frequency and amplitude in th 20-30 kHz range, which drives a pulse modulator (2). The pulses are amplified in a power amplifier and are fed to the radiator (4). As a standby, the locomotive is also fitted with a Galton pipe of the same frequency. The road vehicle is fitted with a receiver comprising a pick-up (5), high-pass filter and amplifier (6). The amplifier output passes to a divider (8) and to a discriminator (7). The discriminator converts the Doppler frequency-shift into a voltage which is used to control a variable-gain amplifier (9). The output of the amplifier drives an alarm (10) which signals the approach speed of the locomotive.