| 摘要 |
<p>PURPOSE:To perform secure detection without causing malfunction even in case of a change in environmental state by comparing a preset prescribed reference voltage with the quantity of variation in detected value within a prescribed time. CONSTITUTION:Infrared rays in a monitor area 5 are gathered on the sensing part of a sensing means 1 through a reflecting mirror 2. A 1st comparing circuit 10 which compares the quantity of variation corresponding to an increase in the quantity of infrared rays with a prescribed voltage E0, a 2nd comparing circuit 15 which compares the quantity of variation corresponding to a decrease in the quantity of infrared rays with the prescribed voltage E0, and a holding circuit 11 which receives the output of the 1st comparing circuit 10 and varies the output value, and holds the output value until the output of the 2nd comparing circuit 15 is received. Consequently, when the absolute value of the difference voltage between a detection voltage and an environmental voltage is larger than the previously set reference voltage value, the presence of a person is decided, so even if the environmental state changes, the presence of the person is securely detected.</p> |
