Collision avoidance system

Abstract

A collision avoidance system adapted for railroad use comprising a track having connected thereto a plurality of first signal transmitters exciting the track by a first control signal within a first frequency bandpass range and a plurality of second signal transmitters interspaced between the first signal transmitters in an alternating arrangement, such second transmitters exciting the track by a second control signal within a second frequency bandpass range. While the first and second control signals are respectively within the first and second bandpass range, individual ones thereof are separated by frequency increments from the other control signals within the corresponding bandpass range such that any beats therebetween are of a relatively high frequency. A train riding the track includes a front and rear pickup selectively connected to a dual frequency amplifier across a two-position switch where the amplifier, at its output, connects to a first and second bandpass filter respectively centered at the first and second frequency bandpass. The outputs of the respective filters are rectified and fed to corresponding comparators wherein the signals are compared against a preselected level. The outputs of the comparators are then combined in a logical AND circuit which, across a delay network having a long time constant in the direction of brake engagement and a short time constant in the direction of brake disengagement, operates the brakes of the train. Included also in the train, intermediate the front and rear pickups, is a shunt circuit including the motor of the train, whereby the control signals are attenuated. Thus, the next succeeding train will not receive the shunted control signals and will therefore engage the brakes.