Operating state indicator for traffic light - uses rectifier and pulse circuits to sense phase shift of supply at lamp transformer primary winding

摘要

A power transformer (2) supplying a traffic light (1) hoists primary winding powered from a source (3) controlled from a control box (4). The control box contains a circuit (5) which includes a detector (6) sensing current in the primary circuit, which comprises a diode rectifier whose output is isolated by a phototransistor to transmit an 'all or nothing' signal. A pulse circuit (7) provides pulses for each half cycle of the same polarity as that in the primary winding. This signal and the current signal are applied to a bistable (8) to produce pulses of duration equal to the phase shift if the polarity is correct or zero if it is incorrect. An integrator (12) output signals that lamp operation is correct.