Infra-red radiation detecting device for use in alarm system, has mirrors system with mirrors that focus radiation towards sensor and that has different focal lengths and detection or vision field provides different angular openings

摘要

The device has an additional mirrors system with central, secondary and tertiary mirrors (25,27,29) focusing an infra-red radiation towards an infra-red sensor (15), where the radiation comes from detection or additional vision fields and does not pass via a lens system (19). The mirrors have different focal lengths and angular openings in their respective detection or vision fields.