JP2009205515A - Photoelectric smoke sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately determine occurrence of a fire without being affected by external noise such as hum noise. <P>SOLUTION: When a modulation signal obtained by modulating a rectangular wave signal with a pulse carrier wave signal is applied as a flashing caution signal that is an irradiation light emitted from a light emitting element 10 of a detection part 1, and a scattered light of the flashing caution signal scattered by smoke particles flowing into a detection space A is received by a light receiving element 11, a band pass filter 4 filters a light receiving signal which is received by the light receiving element as a pulse waveform and amplified by a light receiving amplifier 3 with the frequency of the pulse carrier wave signal as a central frequency, whereby an external noise N such as hum noise superimposed on the light receiving signal can be easily removed. Thereby, in determining fire occurrence or not in a light receiving level read circuit 6, determination errors by the external noise such as hum noise can be reduced to perform accurate determination. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photoelectric smoke detector, and more particularly, a light receiving element receives scattered light scattered by smoke particles that are emitted from a light emitting element and flows into a detection space, and has a light receiving level of a light receiving signal. The present invention also relates to a photoelectric smoke detector that determines whether or not a fire has occurred.

  Conventionally, as this type of photoelectric smoke detector, when light is emitted from the light emitting element of the smoke detector at a predetermined cycle, when the light receiving element receives the light scattered by the intrusion of smoke, an alarm is generated. A fire alarm device is disclosed (see, for example, Patent Document 1).

JP-A-5-166080

  Since the fire alarm of Patent Document 1 described in the background art is normally driven by a DC power supply, external noise such as hum noise is superimposed on the light signal (light reception signal) received by the light receiving element. For this reason, there is a possibility that an alarm is issued due to a malfunction.

  The present invention has been made to solve this problem, and has an object to provide a photoelectric smoke detector that can accurately determine the occurrence of a fire without being affected by external noise such as hum noise. Yes.

  In order to achieve the above-described object, the photoelectric smoke detector of the present invention is a smoke detector in which irradiation light emitted from a light emitting element using a modulation signal obtained by modulating a rectangular wave signal with a pulse carrier signal as a light emission signal flows into a detection space. A detector for receiving the scattered light scattered by the particles with the light receiving element, a light receiving amplifier for amplifying a light receiving signal received as a pulse waveform received by the light receiving element of the detecting unit, and amplified by the light receiving amplifier A bandpass filter for filtering the received light signal with the frequency of the pulse carrier signal as the center frequency, a demodulation circuit for demodulating the received light signal output from the bandpass filter, and a received light level of the output signal from the demodulation circuit And a light receiving level reading circuit for determining whether or not a fire has occurred.

  According to the photoelectric smoke detector of the present invention, a light emission signal of a modulation signal obtained by modulating a rectangular wave signal with a pulse carrier signal is applied as a light emission signal that is irradiation light emitted from the light emitting element of the detection unit. When the scattered light scattered by the smoke particles flowing into the detection space is received by the light receiving element as a light receiving signal, the band pass filter receives the light received by the light receiving element and obtains it as a pulse waveform, which is amplified by the light receiving amplifier. Is filtered with the frequency of the pulse carrier signal as the center frequency, it is possible to easily remove external noise such as hum noise superimposed on the received light signal. As a result, when determining whether or not a fire has occurred in the light receiving level reading circuit, a determination error due to external noise such as hum noise is reduced, and accurate determination is possible.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments to which the photoelectric smoke detector of the present invention is applied will be described below with reference to the drawings.

  FIG. 1 is a circuit block diagram showing a specific configuration of a photoelectric smoke detector according to an embodiment of the present invention. The photoelectric smoke detector receives, for example, scattered light that is irradiated as light emitted from a light emitting element 10 constituted by a light emitting diode (LED) and scattered by smoke particles flowing into the detection space A (from the outside). For example, the detection unit 1 for receiving light by a light receiving element 11 configured by a photodiode and the emission of a modulation signal obtained by modulating a rectangular wave signal with a pulse carrier signal as irradiation light emitted from the light emitting element 10 of the detection unit 1 A light-emitting circuit 2 for generating a signal, a light-receiving amplifier 3 for amplifying a light-receiving signal received by the light-receiving element 11 of the detection unit 1 and obtained as a pulse waveform, and a light-receiving signal amplified by the light-receiving amplifier 3 A bandpass filter 4 for filtering the frequency of the pulse carrier signal of the light emission signal generated by the light emission circuit 2 as a center frequency, and the bandpass filter 4 outputs the filtered signal. The demodulating circuit 5 for demodulating the optical signal, the light receiving level reading circuit 6 for reading the light receiving level of the output signal from the demodulating circuit 6 and determining whether or not a fire has occurred, and the light receiving level reading circuit 6 An alarm device 7 for alarming / displaying the determined fire occurrence, and a resistor (stabilizing resistor) 8 connected in parallel between the light receiving element 11 and the light receiving amplifier 3 of the detector 1 are provided. Yes.

  As the alarm device 7, for example, an intercom device in the dwelling unit in which the photoelectric smoke detector is installed, or a server installed in a fire department or a security company as an alarm transfer destination is suitable.

  In the photoelectric smoke detector according to the embodiment of the present invention configured as described above, the specific operation will be described below with reference to the circuit block diagram of FIG. 1 and the waveform diagrams of FIGS. 2 (A) to 2 (G) ( A time characteristic waveform diagram and a frequency characteristic waveform diagram) will be described respectively.

  In the photoelectric smoke detector shown in FIG. 1, the light emitting circuit 2 is a pulse carrier signal that converts a rectangular wave signal having a period (time width) T at a time interval t as shown in the time characteristic waveform diagram of FIG. A light emission signal S1 of the modulated modulation signal is generated, and the light emitting element 10 of the detection unit 1 is caused to emit light. Since the light emission signal S1 is a modulation signal having a continuous pulse shape having a period (time width) T at a time interval t, the DC voltage supplied to the light emission circuit 2 can be reduced to save power. It is assumed that the time interval t and the period (time width) T have a relationship of “2t <T”.

  Further, the light emission signal S1 shown in FIG. 2A irradiated as light by the light emission of the light emitting element 10 of the detection unit 1 is received from the scattered light scattered from the smoke particles flowing into the detection space A (from the outside). The signal S2 is received by the light receiving element 11 in a pulse waveform.

  The light receiving amplifier 3 amplifies the light receiving signal S2 received by the light receiving element 11 of the detecting unit 1, so that the bandpass filter 4 has a time characteristic waveform diagram of FIG. 2B and a frequency of FIG. 2C. As shown in the characteristic waveform diagram, a received light signal S3 on which external noise N such as hum noise is superimposed is input. Here, the light reception signal S3 having a period (time width) T at a time interval t shown in FIG. 2B is a DC component of the light reception signal and an external frequency at a period of 1 / t, as shown in FIG. 2C. Each DC component of noise N is represented by a peak output.

  The band pass filter 4 is a pulse carrier signal of the light emission signal S1 generated by the light emission circuit 2 as shown in the frequency characteristic waveform diagram of FIG. Is filtered with the center frequency 1 / T and the filtered received light signal S4 is sent to the demodulating circuit 5, so that external noise N such as hum noise can be easily removed from the received light signal S4.

  The demodulating circuit 5 demodulates the light reception signal S4 filtered by the bandpass filter 4 so that the period (time width) shown in the time characteristic waveform diagram of FIG. 2E and the frequency characteristic waveform diagram of FIG. ) A light reception signal S5 of T is generated and sent to the light reception level reading circuit 6.

  As shown in the time characteristic waveform diagram of FIG. 2 (G), the light reception level reading circuit 6 uses the light reception level of the light receiving element 11 in a state where the light emitting element 10 of the detection unit 1 is not emitting light as a reference value Lv0. A comparison is made with the received light level Lv5 of the received light signal S5 demodulated by the demodulation circuit 5 within the light emission time of the element, and a fire occurs when the calculated value of “Lv5−Lv0” exceeds a predetermined threshold value. The alarm device 7 can perform a predetermined alarm issue / display. On the other hand, when the calculated value of “Lv5−Lv0” is less than a predetermined threshold, it can be determined that no fire has occurred. As a result, when the light reception level reading circuit 6 determines whether or not a fire has occurred, an external noise N such as a hum noise superimposed on the light reception signal S4 is easily removed to reduce a determination error due to the external noise. Accurate judgment is possible.

  Finally, the photoelectric smoke detector of the present invention has been described with a specific embodiment. However, the present invention is not limited to this embodiment, and any configuration known so far as long as the effect of the present invention is exhibited. It goes without saying that even photoelectric smoke detectors can be used.

FIG. 1 is a circuit block diagram showing a specific configuration of a photoelectric smoke detector according to an embodiment of the present invention. 2A to 2G are waveform diagrams (time characteristic waveform diagram and frequency characteristic waveform diagram) showing an example of signal processing in the photoelectric smoke detector according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Detection part 10 ... Light emitting element 11 ... Light receiving element A ... Detection space 3 ... Light receiving amplifier 4 ... Band pass filter 5 ... Demodulation circuit 6 ... Light reception level reading circuit

Claims (1)

Scattered light scattered by the smoke particles in which the irradiation light emitted from the light emitting element (10) using the modulated signal obtained by modulating the rectangular wave signal with the pulse carrier signal as the light emission signal is scattered into the detection space (A) is received by the light receiving element (11). ) To detect light (1),
A light receiving amplifier (3) for amplifying a light receiving signal received by the light receiving element of the detection unit and obtained as a pulse waveform;
A bandpass filter (4) for filtering the light reception signal amplified by the light reception amplifier with the frequency of the pulse carrier signal as a center frequency;
A demodulating circuit (5) for demodulating the light receiving signal output from the bandpass filter, and a light receiving level reading circuit for reading the light receiving level of the output signal from the demodulating circuit and determining whether or not a fire has occurred. (6) and a photoelectric smoke detector.

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