Abstract: Fire alarm system utilizing an aerosol detector of the type formed by outer and inner interconnected ion chambers with a single particle source located within the inner chamber. The particle source radiates charged particles emitted therefrom into the inner chamber as well as through the path of chamber interconnection into the outer ion chamber. The outer chamber communicates directly with atmosphere to be monitored and operates as a sensing ion chamber. The inner chamber, operates as a reference ion chamber, is only interconnected with the outer chamber, and is otherwise totally isolated from outside atmosphere to avoid contamination of the particle source therein. Two embodiments of aerosol detector are disclosed.

Abstract: Attempts to pilfer or tamper with condition detector structures such as smoke detectors, intrusion detectors or the like are discouraged by incorporating switch apparatus within the enclosure for the condition detector device. This switch is directly associated with the hardware required for attaching the housing to a wall, ceiling or other structure so that the normal condition alarm signal generated, such as, when smoke, intruders or other sensed conditions are present is simulated by the attempts at removal of the mounting hardware. The invention is particularly useful in conjunction with condition detecting devices having self-contained internal apparatus.

Abstract: An alarm condition detection apparatus and method is embodied in the form of a combustion products detector for detecting fire. The detector generates a difference voltage signal proportional to the degree of combustion products in the atmosphere being monitored. The difference signal is employed to generate an alarm signal to indicate when the condition reaches an alarm state. The detector is adjustable to control the level of a reference voltage which in turn controls the difference signal voltage change needed to cause generation of an alarm signal. Thereby, detector sensitivity is set. The detector includes circuitry operable to generate in response to the difference signal a series of perceptible pulses having a pulse rate proportional to the magnitude of the difference signal. Thereby, with the condition normal, the pulse rate provides a perceptible indication of detector sensitivity.

Abstract: A fire alarm system utilizes an ionization type aerosol detector having first and second intercommunicating and electrically in series ionization regions or chambers irradiated by a particle source. Electrodes are provided which operate in conjunction with a DC voltage source to establish a relatively large voltage gradient across the first region and a relatively small voltage gradient in the second region. Also, the location of the ion source and the effective volumes of the regions are arranged to establish a comparatively high ion density in the first region. In operation, the impedance or resistance of the first region to ion current flow is substantially uninfluenced by the presence of combustion or smoke aerosols due to the relatively high field gradient while the impedance or resistance of the second region is measurably changed thereby. The insensitivity of the first region to the presence of smoke is due to the high voltage gradient therein, as well as to the high ion density therein.