Elevator codes established by regulatory agencies in a number of countries require that elevator service includes monitoring whether the elevator cab lights are functioning or not. Heretofore, lighting status has been monitored by intercepting the wiring of the light power supply, and monitoring the current in the light circuits. However, the current sensor is expensive; the installation time is excessive because the circuit employs high voltage so that the wiring and sensor must be in voltage-protective housings; and failure modes of some lights, such as fluorescent lights, cannot be detected accurately by sensing the current. Furthermore, some elevators power the cab fan from the light circuit; this makes it difficult to distinguish fan on/off variations from bulb failure variations. In cabs with the fan always on, bulb current is a lesser part of the total, and detecting partial lighting failure is difficult.
USPTO Backgrounds
USPTO Backgrounds