RU2173887C1 - Smoke detector - Google Patents

Abstract

FIELD: automatic fire alarm, in particular, smoke detectors. SUBSTANCE: detector preserves the positive qualities of smoke detectors operating both on the principle of detection of scattered radiation and on the principle of monitoring of transmitted light. The detector has a pulse generator with antiphase outputs connected to the radiation sources of two optopairs, the outputs of the photodetectors of the optopairs are connected to the inputs of the measuring transducer representing an arithmetic unit, its third input is connected to the output of the pulse switch, and the output of the arithmetic unit is connected to the output stage. EFFECT: minimized influence of variation of the radiation intensity of the sources and sensitivity of the photodetectors on detector operation. 2 dwg

Description

 The invention relates to the field of automatic fire alarms, and more particularly to fire detectors that detect the appearance of smoke in the area of their installation.

 Smoke detectors operating on the principle of recording scattered radiation are widely known. For example, A. smoke detector USSR N 575672, G 08 B 17/10; Smoke detector USSR N 1265821, G 08 B 17/10; The scheme for detecting a decrease in the sensitivity of the photoelectric smoke detector, Japanese application N 4-60276, N 4-60277, G08B17 / 107.

 In these detectors in a clean atmosphere, the radiation from the source does not reach the photodetector. When smoke appears in the zone of the sensing element (chamber), light is scattered on its particles and enters the photodetector. Upon reaching a certain threshold level of the signal, the detector is triggered, giving a signal about a fire.

 Detectors are also known that act on the principle of monitoring transmitted light, i.e., recording absorption. For example, SECURISTAR Smoke Detector “With passing light to the future!”, SYSTEMSERVICE. Specialized Information and Technical Journal for Fire and Security Protection, Information and Communications, December 1997 / February 1998, p. 13.

 The disadvantage of both types of detectors is that the sensitivity of the detector depends on the instability of the radiation source, the sensitivity of the photodetector, contamination of the optics, etc.

 Closest to the proposed technical essence and the achieved result is a smoke sensor according to AS USSR N 736149, G 08 B 17/10. The smoke detector contains one light source that is optically coupled to one photocell (photodetector) and another light source that is optically coupled to another photocell (photodetector), i.e. two optocouplers: a light source - a photodetector. In this case, the additional light source is on the same axis as the working photodetector, and the additional photodetector is on the same axis as the working source. In standby mode, one radiation source is constantly on, and a fire signal is generated when a predetermined threshold value of the difference between the signals of two photodetectors is reached. When a fire signal is generated to verify its truth, the first radiation source is turned off and the second one is turned on. If, in this case, the absolute value of the signal difference exceeds the threshold level, then the fire signal is considered true. Such a device can reduce the number of false positives. However, his work is affected by a change in the radiation intensity of the sources and the sensitivity of the photodetectors. This can be caused, for example, by their pollution or physical aging.

 The technical problem to which this invention is directed is to reduce the effect on the detector operation of a change in the radiation intensity of the sources and the sensitivity of the photodetectors.

при этом третий из входов арифметического устройства соединен с выходом коммутатора импульсов, а выход арифметического устройства соединен с выходным каскадом,
где: U₁₂ - напряжение в первом полупериоде фотоприемника другой оптопары;
U₂₁ - напряжение во втором полупериоде фотоприемника первой оптопары;
U₁₁ - напряжение в первом полупериоде фотоприемника одной оптопары;
U₂₂ - напряжение во втором полупериоде фотоприемника другой оптопары.This problem is solved in that in a smoke fire detector containing two optocouplers, the radiation source of one of them is connected to the first and the other of them to the second outputs of the pulse switch, the output of the photodetector of one optocoupler is connected to one input of the transmitter, and to the other the input is connected to the output of the photodetector of another optocoupler, the measuring transducer is an arithmetic device that implements the calculation of the magnitude

while the third of the inputs of the arithmetic device is connected to the output of the pulse switch, and the output of the arithmetic device is connected to the output stage,
where: U ₁₂ is the voltage in the first half-period of the photodetector of another optocoupler;
U ₂₁ is the voltage in the second half-period of the photodetector of the first optocoupler;
U ₁₁ is the voltage in the first half-period of the photodetector of one optocoupler;
U ₂₂ is the voltage in the second half-period of the photodetector of another optocoupler.

The invention is illustrated by drawings, where:
FIG. 1 is a block diagram of a proposed detector;
FIG. 2 - dependence of the output signal U on the concentration of smoke C, U _o ~ γ - characterizes a detector operating on the principle of registration of scattered radiation;
U _o ~ β - characterizes a detector operating on the principle of recording light absorption;
U _o ~ γ / 1-β - characterizes the inventive detector.

 The smoke fire detector contains a pulse switch 1, one output of which is connected to one radiation source 2 of one optocoupler, and the other to another radiation source 3 of another optocoupler, 4 - a photodetector of one optocoupler, 5 - a photodetector of another optocoupler, the outputs of which are connected to one and the other the inputs of the arithmetic device 6, respectively, the third of the inputs of which is connected to the third of the outputs of the pulse switch 1, the output of the arithmetic device 6 is connected to the input of the output stage 7.

 Any square-wave pulse generator with two antiphase outputs can be used as a switch (see, for example, Fundamentals of Industrial Electronics. Edited by Prof. V.G. Gerasimov. M., Higher School, 1986, p. 208).

 The arithmetic device can be implemented on the basis of analog-to-digital converters, for converting the output signals of photodetectors into digital form, a microprocessor that implements the necessary calculations, and a digital-to-analog converter that provides inverse conversion (see ibid., Pp. 215–223).

 The output stage of the fire detector is a transistor switch that provides, when the threshold level of the input signal is exceeded, an abrupt decrease in the detector resistance from hundreds of ohms to tens of ohms, which leads to a change in the current in the loop and registration of the Fire signal by the control panel. Similar cascades are used in all active fire detectors (see, for example, F.I.Sharovar, Fire Alarm Devices and Systems. M., Stroyizdat, 1985, p. 47-54).

 Smoke fire detector operates as follows.

на арифметическом устройстве 6, обеспечивающем вычисление величины γ/1-β (пояснение смотри далее по тексту), затем сигнал поступает на выходной каскад, транзисторный ключ которого открывается при достижении заданного порогового значения, и извещатель переходит в состояние срабатывания.The LEDs 2, 3 are alternately turned on by the output signal of the pulse switch 1 and their radiation is detected by photodetectors 4, 5. The output signals from the photodetectors are processed in accordance with the formula

on an arithmetic device 6, which calculates the value of γ / 1-β (see the explanation below), then the signal is fed to the output stage, the transistor switch of which is opened when the specified threshold value is reached, and the detector switches to the operation state.

The radiation of the first radiation source f ₁ , the second - f ₂ . We believe that the characteristics of the photodetectors are linear, this is permissible under the conditions of the initial stage of a fire with small changes in the optical parameters of the medium. The sensitivity of the first photodetector is α ₁ , the second is α ₂ .

In the absence of smoke in the first half-period (the first LED is on), the output signal of the photodetector of one optocoupler: U ₁₁ = α ₁ Ф ₁ , the output signal of the photodetector of another optocoupler: U ₁₂ = 0.

In the second half-cycle, U ₂₁ = 0; U ₂₂ = α ₂ Ф ₂ (the first digit in the designation is the half-period, and the other is the photodetector of the optocoupler).

 When a fire occurs in the area of the optocouplers (optical camera) smoke appears, characterized by the parameters β — attenuation coefficient of radiation and γ — scattering coefficient (see Fig. 2). Since the camera is symmetrical with respect to both optocouplers, the effect of smoke on the output signals of the photodetectors will be identical.

In the first half-cycle: U ₁₁ = Ф ₁ (1-β); U ₁₂ = γα ₂ Ф ₁ .

In the second: U ₂₁ = γα ₁ Ф ₂ ; U ₂₂ = α ₂ Ф ₂ (1-β).

As a result of simple transformations, we obtain:
U ₁₂ / U ₂₂ = γF ₁ / F ₂ (1-β); U ₁₁ / U ₂₁ = Ф ₁ (1-β) / γФ ₂ .

- величина, не зависящая ни от интенсивности излучения источников, ни от чувствительности фотоприемников.Where from

- a value that does not depend on the intensity of the radiation sources, nor on the sensitivity of the photodetectors.

 In the absence of smoke, γ / 1-β = 0.

 With the appearance of smoke and with increasing concentration, the value of γ increases (which is used in detectors based on registration of scattered radiation) and decreases (1- β), on which detectors working on registration of absorption are based.

 Thus, the γ / 1-β dependence has a greater slope than in both types of detectors.

Claims (1)

A smoke fire detector containing two optocouplers, the radiation source of one of them is connected to the first and the other to the second antiphase outputs of the rectangular pulse generator, the output of the photodetector of one optocoupler is connected to one input of the measuring transducer, and the output of the photodetector of the other optocoupler is connected to its other input, different the fact that the measuring transducer is an arithmetic device that implements the calculation of the value

,
wherein the third of the arithmetic device inputs is connected to the output of the rectangular pulse generator, and the arithmetic device output is connected to the output stage of the fire detector,
where U ₁₂ is the voltage in the first half-period of the photodetector of another optocoupler;
U ₂₁ is the voltage in the second half-period of the photodetector of one optocoupler;
U ₁₁ is the voltage in the first half-period of the photodetector of one optocoupler;
U ₂₂ is the voltage in the second half-period of the photodetector of another optocoupler.

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