Method for testing smoke sensor and a smoke sensor having a function of executing the test

Claim 1

A smoke detector comprising: a sensing space, a main light emitting element disposed within said sensing space, a dust preventing net disposed at an entrance part of said sensing space, an auxiliary light emitting element disposed outside said dust preventing net, a main light receiving element disposed at a position where a light beam emitted from said main light emitting element is not directly incident but receives a stray light in said sensing space and resulting, even in the absence of smoke, from said light beam from said main light emitting element as well as a smoke-scattered light in the presence of smoke in said sensing space and resulting, even in the absence of smoke, from a light beam from said auxiliary light emitting element to the sensing space through the dust preventing net and reflected at an inner wall surface of the sensor, an auxiliary light receiving element provided for receiving directly said light beam from said main light emitting element, means, receiving an output of said auxiliary light receiving element, for generating an alarm indicative of a deterioration in the sensing level due to a clogging of the dust preventing net when said output of the auxiliary light receiving element is outside a predetermined range, means, connected to said auxiliary light receiving element, for attenuating said output thereof to a level close to an alarming level of an output of said main light receiving element, and means, connected to said main light receiving element and to said attenuating means as well, for amplifying said output of the main light receiving element and said output attenuated of the auxiliary light receiving element.