Telephone warning system for railway repair gangs - has optical as well as acoustic alarm to attract attention of lookout

摘要

The telephone warning system, for building site workers and esp. railway repair gangs, uses an optical system in addition to an acoustic signal to draw the attention of the lookout to the fact that there is a telephone call. The optical signal may occur at the same time or after the acoustic signal and is switched off by the lookout after acknowledgment. The main bus (3) has couplers at intervals along it. Each coupler is connected to the next coupler along the bus, to a distant telephone terminal and to the telephone terminal associated with the coupler.