Passive-type infrared sensor system for detecting human body

摘要

A passive-type infrared sensor system includes first and second sensor units each including a first or second light receiving element and a first or second optical system. The first sensor unit has a "viewing" direction oriented towards an upper half of a human body so as to define a first watch area clear of a ground surface. The second sensor unit has a similar "viewing" direction oriented diagonally downwardly towards a point on the ground surface spaced a predetermined watch distance away from where it is installed so as to define a second predetermined watch area below the first watch area. This passive-type infrared sensor system also includes first and second level detecting circuits each operable to output a detection signal only when the level of an electric output signal from the associated first or second sensor unit exceeds a predetermined reference level, and a human detecting circuit for outputting, when the detection signals are outputted respectively from the first and second level detecting circuits, a human detection signal indicative of entry of a human body within a monitoring zone including the first and second watch areas.