Apparatus and method for detecting tampering with an infra-red motion sensor

摘要

An infra-red motion detector for monitoring motion in a monitored space is described. The motion detector includes, within a housing, an infra-red radiation sensor sensitive to infra-red radiation incident through a window. A refractive optical system within the housing selects incident infra-red radiation for redirection onto the infra-red sensor. An external light source mounted externally of the housing directs external light through the window providing a recognizable light input. A refractive Fresnel patch mounted externally to the window selects incident light from the external light source and redirects it to a tamper sensor within the housing. A detection controller processes signals output by both sensors in monitoring the space. The detection controller detects incident light from the external light source and trips a tamper alarm in failing detection, and further detects changes in infra-red radiation in the monitored space and trips an intrusion alarm upon detecting changes.

主权项

1. An infra-red motion detector Fresnel lenslet body comprising:
an array of Fresnel lenslets provided on said Fresnel lenslet body, each of said Fresnel lenslets corresponding to a motion detection zone for collecting and focusing light onto a passive infrared sensor target, said array of Fresnel lenslets being provided on a first side of said body to act as internal side Fresnel lenslets; and at least one anti-masking optical structure provided on said Fresnel lenslet body within said array of Fresnel lenslets, said at least one anti-masking optical structure having an optical property that changes in the presence of a masking material, said at least one anti-masking optical structure is provided on a second side of said body to act as at least one external side anti-masking optical structure.