Fire detector

• US 5,872,517 A
• Filed: 05/23/1997
• Issued: 02/16/1999
• Est. Priority Date: 05/25/1992
• Status: Expired due to Term

• Current Assignee: Nohmi Bosai Limited (Secom Company Limited)
• Original Assignee: Nohmi Bosai Limited (Secom Company Limited)
• Inventors: Yasukawa, Makoto, Mochizuki, Mikio, Hirooka, Eiji
• Primary Examiner(s): Lefkowitz, Edward
• Application Number:
  US08/862,405
• Time in Patent Office: 634 Days
• Field of Search: 340/630, 340/629, 340/628, 340/527, 340/501, 250/573, 250/574
• US Class Current: 340/630
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke

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.

Claims

1. A heat-photoelectric type fire detector comprising:

a light-emitting section for emitting a pulsed light for detecting smoke;

a light-receiving section, having a first variable resistor for adjusting an output, for receiving a scattering light of the light emitted from said light-emitting section caused by the smoke;

a smoke fire discriminating section, having a second variable resistor for adjusting a reference voltage, for generating a smoke fire discriminating output when the output from said light-receiving section reaches the reference voltage;

a heat-sensitive element for detecting heat;

a heat fire discriminating section for outputting a heat fire discriminating output when a detected output from said heat-sensitive element reaches a predetermined level; and

a fire signal transmitting section, having an operation indicating lamp, for outputting a fire signal when a smoke fire discriminating output or a heat fire discriminating output is generated from at least one of said smoke fire discriminating section and said heat fire discriminating section;

wherein said light-emitting section comprises a light-emitting element for detecting smoke, an oscillating circuit for making said light-emitting section emit light by supplying a pulsed output thereto and supplying the pulsed output as a monitoring power source to said heat fire discriminating section, and a pulse width expanding circuit for expanding a pulse width of the pulsed output from said oscillating circuit and supplying it to said operation indicating lamp.

2. A detector according to claim 1, wherein said heat fire discriminating section comprises:

a fire discriminating circuit for discriminating whether the detected output from said heat-sensitive element has reached the predetermined level;

a discriminating output circuit for supplying the heat fire discriminating output to said fire signal transmitting section on the basis of an output from said fire discriminating circuit;

a wire-snap detecting circuit for detecting any wire-snap in said heat-sensitive element; and

a wire snap indication circuit for indicating a presence of snap on the operation indicating lamp of said fire signal transmitting section when said wire-snap detecting circuit detects any wire-snap of said heat-sensitive element.

3. A detector according to claim 2, wherein said fire discriminating circuit further comprises a first comparator for comparing the detected output from said heat-sensitive element with a first reference voltage.

4. A detector according to claim 2, wherein said wire-snap detecting circuit further comprises a second comparator for comparing the detected output from said heat-sensitive element with a second reference voltage.

5. A detector according to claim 2, wherein said wire-snap indication circuit includes a first transistor, which short-circuits both ends of said operation indicating lamp when said wire-snap detecting circuit detects any wire-snap in said heat-sensitive element.

6. A detector according to claim 1, wherein said heat-sensitive element is a thermistor.

7. A heat-photoelectric type fire detector comprising:

a light-emitting section for emitting pulsed light for detecting smoke;

a light-receiving section for receiving scattered light of the light emitted from said light-emitting section caused by smoke;

a smoke fire discriminating section for providing a smoke fire discriminating output when a light-receiving output from said light-receiving section reaches a reference voltage;

a heat-sensitive element for detecting heat;

a heat fire discriminating section for providing a heat fire discriminating output when a detected output from said heat-sensitive element reaches a predetermined level;

a fire signal transmitting section for transmitting a fire signal when a smoke fire discriminating output or a heat fire discriminating output is output from at least one of said smoke fire discriminating section and said heat fire discriminating section; and

a constant voltage circuit for converting an externally supplied power source voltage into a predetermined voltage, and supplying it to said light-emitting section, said light-receiving section, said smoke fire discriminating section and said heat fire discriminating section;

said constant voltage circuit comprising;

a first transistor having an emitter connected to said light-emitting section, said light-receiving section, said smoke fire discriminating section and said heat fire discriminating section;

a first Zener diode having an end connected to a base of said first transistor; and

a constant current circuit connected between a collector and the base of said first transistor.

8. A detector according to claim 7, wherein said constant current circuit further comprises:

a junction-type FET having a drain and a gate respectively connected to the collector and the base of said first transistor; and

a first fixed resistor connected between a source and the gate of said junction-type FET.

9. A detector according to claim 7, wherein said detector further comprises:

an accumulating circuit for discriminating whether a smoke fire discriminating output or a heat fire discriminating output has been provided from at least one of said smoke fire discriminating section and said heat fire discriminating section in synchronicity with the pulse light from said light-emitting section, and supplying a detected output to said fire signal transmitting section when discriminating that the smoke fire discriminating output or the heat fire discriminating output have been provided for a plurality of predetermined times successively; and

wherein said fire signal transmitting section transmits the fire signal upon receiving the detected output from said accumulating circuit.

10. A detector according to claim 9, wherein said fire signal transmitting section further comprises:

a switching element turning on in response to the detected output from said accumulating circuit; and

an operation indicating lamp connected in series with said switching element.

11. A detector according to claim 10, wherein said light-emitting section further comprises:

a light-emitting element for detecting smoke;

an oscillating circuit for making said light-emitting element emit light by supplying the pulsed output thereto; and

a pulse width expanding circuit for expanding a pulse width of the pulsed output from said oscillating circuit and outputting it to said operation indicating lamp of said fire signal transmitting section.