Abstract: A smoke detector of the type that depends on the scattering of light by smoke particles comprising a chamber (301) configured to receive smoke particles from an environment in which the smoke detector is required to detect smoke, a source of light (202) configured to project light therefrom such that light that is received by the chamber is scattered by the smoke particles, an optical element (207) configured to receive light as has been scattered by the smoke particles, and, a photodetector (208) configured to detect at least some of the received scattered light, the smoke detector characterized in that upon receiving the scattered light, the optical element (207) is configured to selectively differentiate between required scattered light that is derived from a subset of predefined directions with respect to the angle of incidence upon the optical element and scattered light that is derived from other directions in order to thereby filter out the light that is not required and thereby redirect the required s

Abstract: A correction system for a detector of a fire system, the correction system comprising: a calculation unit operable to calculate the n+1th order differential (wherein n is a whole number and n?1) of an output of a sensor of the detector with respect to time; a measurement unit operable to measure the n+1th order differential to determine the extent of an initial curvature of a line of the output of a sensor of the detector with respect to time and a correction unit operable to correct an output of the sensor based on the measurement. The correction system can compensate for impairment of the sensor and results in more accurate sensor readings (and accordingly a more useful fire system).

Abstract: An audio distribution system comprises a plurality of individual signal conditioning circuits connected in series. Each circuit comprises a signal conditioning unit to which an audio input (13) is fed. The output from the unit is fed to a precision signal addition device. Each circuit also comprises a balanced line level input (11), which is fed to a balanced to unbalanced precision signal converter the output of which is connected to the precision signal addition device. The output from the precision signal addition device is fed to an unbalanced to balanced converter which provides at its output a balanced line level signal (12). As compared with a conventional distribution system, the system enables only one balanced line level input to amplification equipment eliminating any mixing or control means that equipment and obtaining the need for a conventional mixer.

Abstract: A fire alarm system comprises one or more fire alarm addressable modules (3), which interface with a fire alarm loop (1) along which data and power may be transmitted, and a voice alarm system comprising one or more amplifiers (6) connected to respective speakers (7) for transmitting voice alarm messages. The or each fire alarm module comprises a message store (22), means for interfacing with an amplifier (6) of the voice alarm system, means for interfacing with the fire alarm loop (1) and means for interpreting signals from the loop (1) and for selecting an appropriate message for transmission from the message store (22).