Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1984-04-16
1987-03-03
Wan, Gene
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250564, 356432, G01N 2185
Patent
active
046477861
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED CASE
This application is related to the commonly assigned, copending U.S. application Ser. No. 06/606,828, filed Apr. 16, 1984, entitled "SCATTERED RADIATION SMOKE DETECTOR", and listing as the inventors HANNES GUTTINGER and GUSTAV PFISTER.
BACKGROUND OF THE INVENTION
The present invention broadly relates to smoke detectors and, more specifically, pertains to a new and improved construction of a photoelectric smoke detector.
Generally speaking, the photoelectric smoke detector of the present invention relates to a photoelectric smoke detector having a source of radiation driven intermittently by a control circuit and a radiation receiver which is connected to an evaluation circuit which is able to transmit a smoke alarm signal when the radiation receiver receives radition that has been affected by smoke particles in synchronous operation with the radiation source.
In other words, the photoelectric smoke detector of the present invention comprises a radiation source, a control circuit for intermittently driving the radiation source and a radiation receiver. The radiation receiver is connected to an evaluation circuit capable of outputting an alternating smoke alarm signal having at least one phase when the radiation receiver receives radiation influenced by smoke particles in synchronization with operation of the radiation source.
That is, the photoelectric smoke detector of the present invention is of the type comprising a source of radiation for emitting radiation, a control circuit for generating an alternating signal exhibiting a phase and for intermittently driving the source of radiation in synchronism with the phase of the altnerating signal, a radiation receiver for receiving a portion of the radiation influenced by smoke particles and for generating an output signal indicative of the received portion and exhibiting a polarity as well as an evaluation circuit connected to the radiation receiver and to the control circuit for generating a smoke alarm signal when the radiation receiver receives the portion of the radiation influenced by smoke particles in synchronism with the radiation intermittently emitted by the source of radiation.
The present invention also relates to a fire alarm device for detecting smoke particles generated by a fire and comprising a photoelectric smoke detector of the inventive type.
The smoke detector can, for example, be structured as a scattered radiation detector in which the radiation scattered from smoke particles is evaluated, or as a radiation extinction detector which exploits the diminution of radiation or its absorption by smoke particles, or as a photo-acoustic smoke detector in which the smoke particles emit acoustic pulses upon absorbing radiation pulses and an acoustical-electrical converter transforms them into electrical pulses, such as is described in European Patent Application EP No. 14,251. The smoke detector can also serve as a smoke sensor in which the value of the emitted smoke alarm signal is an indication of the smoke intensity. It can also serve as a smoke alarm which gives warning of a prescribed intensity of smoke.
In such smoke detectors, such as for example the scattered radiation smoke detector described in PCT Application WO No. 80/01326, which are preferably employed as fire alarms, electromagnetic radiation is radiated into a measuring volume, for instance by means of a light-emitting diode (LED) and the radiation scattered from smoke particles in the measuring volume is received by a scattered radiation receiver disposed outside of the radiating zone of the radiation source. An evaluation circuit outputs a smoke alarm signal when the level of scattered radiation exceeds a prescribed threshold. Electromagnetic radiation is to be understood as including visible light, infrared radiation or ultraviolet radiation.
A key problem in the art is to assure that a smoke alarm signal only be initiated by radiation scattered from smoke particles and not by interference radiation penetrating into the measuring volume which
REFERENCES:
patent: 4206454 (1980-06-01), Schapiia
Guttinger Hannes
Labhart Martin
Cerberus AG
Kleeman Werner W.
Wan Gene
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