| 摘要 |
A passive infra red (PIR) detector assembly (10), for example a movement detector assembly, comprises a PIR detector unit in a casing (12), an external housing (20), and at least one additional interior housing (16) intermediate the detector unit and the external housing (20), the interior housing (16) being spaced from the external housing (20) by an air gap (28), with a width in excess of 10 mm, preferably in the region of 15 mm. The interior and exterior housings (16, 20) are apertured or provided with a window of infrared transmissive material allowing the transmission of infrared radiation from the exterior of the assembly to an infrared reflector element (14) associated with the detector unit (10). Provision of the interior housing (16) reduces thermal and radio frequency disturbance of the detector unit (10), thereby substantially reducing the generation of spurious alarms by the PIR detector assembly incorporating the detector unit. |
