Ionization-type fire sensing system
US4109240A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Nov 15, 1976 |
| Grant date | Aug 22, 1978 |
| Priority date | — |
| Expiry date | Nov 15, 1996 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B17/11
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
An ionization chamber is exposed to the atmosphere to be supervised, the ionization chamber being so constructed that the electrical resistance thereof changes in the presence of fire particles or aerosols upon occurrence of a fire; to improve reliability of detection, the ionization chamber is connected as a resistance element in a free-running multivibrator oscillator circuit, which includes a pair of cross-coupled field effect transistors (FET's) so that, upon change of the atmosphere to which the ionization chamber is exposed, the pulse frequency of the oscillator changes, which change is detected by a pulse rate detector. If the detector has upper and lower threshold levels, deviation of pulse rate in one direction may be used to sense presence of a fire, and in the other direction may be used to sense incipient trouble in the circuit itself.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.