Multi-element ionization chamber

摘要

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. The detector operates by the method of employing the second region as a signal or sensing ion chamber and the first region as a reference chamber, thereby to develop electrical signals on the electrodes representative of detected smoke aerosols for driving the associated fire alarm circuitry. The ion collecting electrode in the second region defines a sensing volume which communicates with the surrounding atmosphere to be monitored and which is located at the optimum distance from the particle source to maximize ion production and collection.