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US 5,670,948 AGranted
Fire detector
AssigneeNohmi Bosai Ltd.
InventorsMikio Mochizuki, Eiji Hirooka, Makoto Yasukawa
Life of this patent
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Abstract
A fire detector capable of readily and accurately adjusting the sensitivity thereof and of not erroneously outputting any fire signal is provided with a first-stage amplifying circuit having an output adjusting variable resistor and a fire discriminating section having a reference voltage adjusting variable resistor. As a result, it is possible to adjust the amplified output to a predetermined value by the switching level of the fire discriminating section to a predetermined value by the reference voltage adjusting variable resistor.
Claims21
A photoelectric type fire detector comprising:
- a light-emitting section for emitting a pulse light for detecting smoke;
- a light-receiving section, including a light-receiving element for receiving scattered light of the pulse light emitted from said light-emitting section caused by smoke, and an amplifying section for amplifying an output from said light-receiving element to generate a light-receiving output, said amplifying section having a first variable resistor for adjusting said light-receiving output to a predetermined value in a state in which there is an absence of smoke;
- a constant voltage circuit for supplying power to said light-emitting section, said light-receiving section, and a fire discriminating section;
- said fire discriminating section including a series resistance circuit composed of at least one fixed resistor and a second variable resistor for adjusting a reference voltage, both of which are coupled between an output end of said light receiving section and an end of a Zener diode of said constant voltage circuit, and a first switching element having a base and an emitter connected to both ends of said fixed resistor, said fire discriminating section generating a fire discriminating output when said light-receiving output from said light-receiving section reaches said reference voltage;
- a sensor output section for detecting the voltage between the ends of said series resistance circuit and for outputting the detected voltage as a sensor output to an outside of said fire detector;
- and
- a fire signal transmitting section for transmitting a fire signal based on said fire discriminating output from said fire discriminating section;
- wherein said first variable resistor is adjusted such that said light-receiving output, in the state without smoke and outputted through said sensor output section, becomes the predetermined value so as to correct differences in said light-receiving outputs, among a plurality of photoelectric type fire detectors, which are due to dispersions of characteristic values of circuit components in said plurality of photoelectric type fire detectors.
5 more elements
A photoelectric type fire detector comprising:
- a light-emitting section for emitting a pulse light for detecting smoke;
- a light-receiving section, having a first variable resistor for setting a light-receiving output from said light-receiving section to a predetermined value in the presence of smoke of a predetermined density, said light-receiving section receiving scattered light of the light emitted from said light-emitting section caused by smoke;
- a fire discriminating section, having a second variable resistor for adjusting a reference voltage, for generating a fire discriminating output when a light-receiving output from said light-receiving section reaches the reference voltage;
- and
- a fire signal transmitting section for transmitting a fire signal based on the fire discriminating output from said fire discriminating section;
- wherein said detector further comprises a constant voltage circuit for converting an externally supplied power source voltage into a predetermined voltage and for supplying the converted voltage to said light-emitting section, said light-receiving section and said fire discriminating section;
- wherein said constant voltage circuit comprises:
- a first transistor having an emitter connected to said light-emitting section, said light-receiving section and said fire discriminating section;
- a first Zener diode having an end connected to a base of said first transistor;
- and
- a constant current circuit coupled between a collector and the base of said first transistor;
- wherein an external power source voltage is applied between the collector of said first transistor and the other end of said first Zener diode.
9 more elements
Dependencies are inferred from the claim text.