| 摘要 |
A proximity detector has four main sensors (5a to 5d) located at spaced intervals along a door edge at positions suitable for detecting a predetermined class of objects. Two differential amplifiers (7a and 7b) compare the outputs from alternate pairs of sensors (5a, 5c and 5b, 5d) and produce a control signal if the compared outputs differ by more than a threshold value. An auxiliary sensor (6) is situated at or towards the door edge at a position where it is substantially unaffected by the approach of the objects intended to be sensed by the main sensors but where it is affected by the surface against which the door closes. The output from the auxiliary sensor (6), is used as the space between the door and other surface varies, to alter the threshold value to which the differential amplifiers (7a, 7b) respond. Sensors (5a to 5d) are capacitive sensors and sensor (6) may be a capacitive, infrared or acoustic sensor. Sensors (5a to 5d) may be mounted in a guard channel. <IMAGE> |
