| 摘要 |
PURPOSE:To prevent malfunction based on fine particles stuck to the detection means of the degree of pollution by changing over a flow path by the selection means thereof so that the air clarified by a clarification means is introduced into the detection means of the degree of pollution. CONSTITUTION:When the clean air passed through a filter 4 is introduced into a duet sensor 6 provided as the detection means of the degree of pollution by changing over a solenoid valve 8 provided in a housing 1 as the selection means of a flow path in a proper time, fine particles stuck on the inner surface of a dust sensor 6 are removed by the clean air. In other words, when a time for changing over the solenoid valve 8 is suitably set, fluctuation of sensitivity of the dust sensor 6 is diminished in a long period and malfunction is prevented. |
