JPH0542560Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a dimming type smoke detector for monitoring the presence or absence of smoke over a relatively long distance.

[Background technology] In general, in large areas where smoke easily spreads, such as in tunnels, large warehouses, or building exhaust ducts, it may be difficult to detect fires early with light scattering type or ion type smoke detectors. It is often advantageous to use dimming smoke detectors that can see over long distances. However, in this method, since the light emitter and receiver are installed separately, the sunlight and other temperature conditions are different, and the effects of temperature often do not cancel each other out. Therefore, it is necessary to perform temperature compensation for both the light emitter and receiver. On the other hand, this type of dimming type smoke detector modulates at a higher frequency to prevent the influence of ambient light such as car lights and various lighting equipment, especially power-saving high frequency lighting equipment (several + KHz). However, in this case, although the temperature compensation of the light emission output of the light emitter can be easily performed using a thermistor or the like, there is a problem in that it is not easy to compensate for the temperature characteristics of the detection section of the light receiver.

[Purpose of the invention] The present invention has been developed in consideration of the above-mentioned problems, and aims to provide a smoke detector with separate emitter and receiver that uses a high-frequency modulated optical signal to prevent external noise, by reliably compensating for the temperature characteristics of the receiver including the detection unit, thereby always maintaining accurate sensitivity.

[Disclosure of the invention] The attenuation type smoke detector of the present invention detects the presence or absence of smoke in the optical path by installing the light emitting part and the light receiving part separately and measuring the attenuation rate of the received light beam. In this configuration, the light emitter intermittently emits an optical signal modulated at a high frequency, and the light receiver alternately outputs the output of the light receiving element and the output of the reference voltage signal oscillator having the same frequency as the modulation frequency. It is characterized in that the temperature compensation of the amplification and detection circuit is performed by switching the detection output to the amplification and detection circuit and comparing both detection outputs.
This eliminates the influence of changes in temperature characteristics after the switching element.

The figure shows an embodiment of the dimming type smoke detector of the present invention. In the figure, a light emitting unit 1 and a light receiving unit 2 are installed, for example, 100 m apart in a tunnel, etc., and a power supply current is constantly supplied from a receiver 4 through a signal line 3 that sends a line short circuit signal when smoke is detected. Supplied. A power supply current is intermittently supplied to the light projecting section 1, so that an optical signal modulated by the high frequency oscillator 5 is intermittently emitted from the light emitting element 6. Q is a modulation transistor, R ₁ , R ₂
is a current limiting resistor, and TH is a temperature compensation thermistor. In the light receiving section 2, the output of the light receiving element 7 and the reference voltage oscillator 8 are alternately switched by a switch element 9 and inputted to an amplifier circuit 10 and a detection circuit 11. Here, the reference voltage oscillator 8 generates a constant output regardless of temperature changes, and uses a temperature compensating element such as a temperature compensating capacitor or a thermistor to keep the output constant. The output of the detection circuit 11 is determined by a control circuit 12 using a microprocessor, and if the output is below a certain level, a smoke detection signal is sent to the receiver 4. In addition, the control circuit 12 sends a control signal to the switch element 9 every time the received light signal is determined, switches the input of the amplifier circuit 10 to the reference voltage oscillator 8, and compares the detected outputs. In reality, like the emitter 1, the light receiver is intermittently supplied with power supply current (pulse current with a width of several tens of milliseconds every 5 seconds), which stabilizes the amplifier circuit and clock within one pulse period. The light reception signal and the reference voltage signal are measured and judged.

Now, the reference signal voltage is Ai, the received light signal voltage is Xi,
If the gain of the amplifier circuit 10 is α, the detection efficiency of the detection circuit 11 is φ, and the outputs after amplification and detection of the reference signal voltage and light reception signal voltage are Ao and Xo, respectively, Xo=Xi・α・φ…(1) Ao =Ai・α・φ…(2), and from equations (1) and (2), Xi=(Ai/Ao)×Xo…(3) is obtained. Here, equation (3) means that it is possible to obtain a light-receiving signal output that is not affected by variations in the gain of the amplifier circuit 10 and variations in the detection efficiency of the detection circuit 11 due to temperature changes. Here, the above calculation is performed by the control circuit 12.
will do. Note that it is difficult to keep the output of the reference voltage oscillator 8 completely constant even with temperature compensation;
If it is constant to some extent, it is possible to maintain accurate sensitivity to the extent that it does not pose a problem as a characteristic of a dimming type smoke detector.

[Effects of the invention] As described above, the present invention provides a smoke attenuation type in which the light emitting part and the light receiving part are arranged separately, and the presence or absence of smoke in the optical path is detected by measuring the attenuation rate of the received light flux. In the sensor, a light emitter that intermittently emits an optical signal modulated with a high frequency is used, and a light receiving element that receives the optical signal from the light emitter is the same as the optical signal emitted from the light emitter. A reference voltage generating means for generating a signal modulated by frequency and having a substantially constant level regardless of temperature changes; a switching means for alternately switching outputs between the output of the reference voltage generating means and the output of the light receiving element; The output of the reference voltage generation means is divided by the output of the amplification and detection means for amplifying and detecting the output, and the output of the reference voltage generation means is multiplied by the output of the light receiving element. The light receiving section is provided with a calculating means for calculating the light receiving element output that cancels out the temperature characteristics of the means, and a determining means for determining the presence or absence of smoke in the optical path based on the determined output of the light receiving element. The output of the light receiving element is obtained by dividing the output of the reference voltage generating means by the output obtained by amplifying and detecting the output of the light receiving element. It is possible to obtain an output of the light-receiving element that offsets temperature changes in the means, and it is possible to maintain accurate sensitivity unaffected by temperature changes.

[Brief explanation of the drawing]

The figure is a block circuit diagram showing one embodiment of the dimming type smoke detector of the present invention. 1 is a light emitter, 2 is a light receiver, 3 is a signal line, 4 is a receiver, 5 is a high frequency oscillator, 6 is a light emitting element, 7 is a light receiving element, 8 is a reference voltage oscillator, 9 is a switch element, 10 is an amplification circuit, 11 is a detection circuit, 12 is a control circuit, TH is a thermistor, R ₁ and R ₂ are resistors, and Q is a transistor.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A dimming type smoke detector in which a light emitting part and a light receiving part are arranged separately, and the attenuation rate of the received light beam is measured to detect the presence or absence of smoke in the optical path. , a light projecting section that intermittently emits an optical signal modulated at a high frequency, a light receiving element that receives the optical signal from the light projecting section, and a light receiving element that receives the optical signal from the light projecting section at the same frequency as the light signal emitted from the light projecting section. A reference voltage generating means that generates a modulated signal at a substantially constant level regardless of temperature changes, a switching means that alternately switches between the output of the reference voltage generating means and the output of the light receiving element, and an output of the switching means. The output of the reference voltage generation means is divided by the output of the amplification detection means for amplification and detection and the output of the reference voltage generation means is multiplied by the output of the amplification and detection of the output of the light receiving element. A light-reducing smoke detector comprising a light-receiving section provided with a calculation means for obtaining a light-receiving element output that cancels temperature characteristics, and a determining means for determining the presence or absence of smoke in an optical path based on the obtained output of the light-receiving element. (2) The attenuation type smoke detector according to claim 1, which is a utility model registration, characterized in that a thermistor for temperature compensation is connected in series with the light emitting element of the light projecting part.