Fire alarm system with discrimination between smoke and non-smoke phenomena

An alarm system comprising:

• a control unit;
• a communications link coupled to the control unit;
• a plurality of spaced-apart ambient condition detectors coupled to the communications link wherein the detectors transmit signals indicative of ambient conditions sensed in regions adjacent to the respective detectors and wherein the control unit includes circuitry for determining if a signal received from a selected detector in a predetermined region is indicative of the possible presence of a foreign element in the detector and additional circuitry in the control unit for determining whether a second detector in the same region has transmitted signals to the control unit of a magnitude too low to be indicative of a possible alarm condition for a predetermined time interval;
• and
• circuitry for indicating the presence of an alarm condition in response thereto.

An alarm system comprising:

• a control unit;
• a communications link coupled to the control unit;
• a plurality of spaced-apart ambient condition detectors coupled to the communications link wherein the detectors transmit signals indicative of ambient conditions sensed in regions adjacent to the respective detectors and wherein the control unit includes circuitry for determining if a signal received from a selected detector in a predetermined region is indicative of the possible presence of a foreign element in the detector, additional circuitry in the control unit for determining whether a second detector in the same region is transmitting signals to the control unit indicative of a possible alarm condition;
• circuitry for indicating the presence of an alarm condition;
• and
• wherein the control unit includes circuitry for storage of prior signal values from the selected detector.

A method of determining an alarm condition in response to signals received from a plurality of displaced smoke detectors, the method comprising;

• receiving signals from at least two detectors in a selected region being monitored;
• in response to one of the received signals changing in a way indicative of a possible fire, analyzing the one received signal and then other received signals to differentiate between a fire condition and a non-fire condition;
• and
• which includes storing a history of signals received from at least one of the detectors.

A method of assessing the presence of a fire condition in one or more regions being monitored with an alarm system having a linked plurality of displaced ambient condition detectors, the method comprising:

• receiving signals from the detectors indicative of sensed ambient condition at the respective detectors;
• storing performance histories of at least some of the detectors;
• for at least the signal from a first detector, determining if a possible fire condition may be present in the vicinity of the first detector;
• responsive to said possible fire condition, determining if the performance history of the first detector exhibits a predetermined confirmatory trend during a selected time interval, and, in response to the presence of the confirmatory trend, producing a signal indicative of an alarm condition, but in the absence of the trend, evaluating the signal from another detector, located in the same region as the first detector, and, in the absence of a predetermined signal from the another detector, indicating a fault condition at the first detector.