(19)
(11) EP 0 507 025 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
24.02.1993 Bulletin 1993/08

(43) Date of publication A2:
07.10.1992 Bulletin 1992/41

(21) Application number: 91307782.2

(22) Date of filing: 23.08.1991
(51) International Patent Classification (IPC)5: G08B 13/19, G08B 29/04
(84) Designated Contracting States:
DE FR GB IT

(30) Priority: 04.04.1991 GB 9107062

(71) Applicant: GUARDALL LIMITED
Newbridge, Midlothian EH28 8LP (GB)

(72) Inventors:
  • Henness, Alan
    Grangemouth FK3 9BT (GB)
  • Galloway, John Lindsay
    Edinburgh EH10 5NJ (GB)
  • Owers, Ian Alexander
    Aberdour, Fife, Scotland (GB)

(74) Representative: Bibby, William Mark et al
Mathisen, Macara & co. The Coach House 6-8 Swakeleys Road
Ickenham Uxbridge UB10 8BZ
Ickenham Uxbridge UB10 8BZ (GB)


(56) References cited: : 
   
       


    (54) Intruder detection arrangements and methods


    (57) An intruder detection arrangement has a passive infra-red sensor (10) for detecting the presence of an intruder in a predetermined zone of protection and an IR anti-masking detection unit (20) for detecting the presence of masking material M in view of sensor (10). A signal processing circuit (30) is responsive to outputs from the sensor (10) and the detection unit (20) producing an intruder alarm signal in response to an output from sensor (10) and an anti-masking alarm signal in response to an output from unit (20). The signal processing circuit is arranged to cancel the anti-masking alarm signal in response to an output from sensor (10) produced after the output from unit (20) that gave rise to the anti-masking alarm signal.






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