SU1188772A1 - Fume detector - Google Patents

Abstract

A SMOKE SENSOR containing a radiation receiver mounted on the same optical axis of the fiber section, an emitter facing the input end of the first fiber section, on the output ends of all fiber sections, except the last, have the first focusing elements that are optically connected to the second focusing elements mounted on the input ends of all sections of the fiber, except for the first, the output end of the last section of the fiber is a reflector, characterized in that, in order to increase the senses itelnosti sensor input end of the first section of the fiber and the output end of the last section of fiber are chamfered with an angle of taper of from 15 to 46 °, radiation receiver is mounted at an angle to the fiber axis of the section, and the optical emitter axis perpendicular to the plane of the entrance end of the first section of the fiber.

Description

The invention relates to an automatic fire alarm and can be used as a smoke detector at facilities associated with the manufacture, processing, storage or transportation of fire-hazardous materials.

The purpose of the invention is to increase the sensitivity of the sensor.

FIG. 1 is a diagram of a smoke sensor for one controlled zone of space; in fig. 2 is a diagram of a smoke detector for several controlled areas of space.

The smoke sensor contains a radiation receiver 1, sections 2 and 3 of the optical fiber, an emitter 4, a focusing element 5, an output end 6 of the last section of the optical fiber, which is a reflector, an input end 7 of the first section 2 of the optical fiber. The space controlled by the smoke detector is indicated by the position 8.

The emitter 4 generates a given luminous flux in the optical fiber 2.

Sections 2 and 3 of the light guide are designed to transmit radiation to the controlled medium 8.

In section 2 of the fiber, the input end 7, facing the emitter 4, is angled at an angle φ exceeding the critical angle of total internal reflection at the interface of two media with different refractive indices.

The bevel angle φ of the input end 7 of section 2 and output end 6 of the last section 3 of the fiber is determined by the ratio

,

P2

where | - refractive index

environment, i.e. air; P2 is the refractive index of the core material of section 2 and 3 of the fiber; Ф is the angle between the optical axis of sections 2 and 3 of the optical fibers and the normal to the surface of the end face 6 and 7. For example, if the core of sections 2 and 3 of the fiber is made of glass (the refractive index is P2 1.53), and the external medium is air ( refractive index P1 1), the bevel angle.

At a bevel angle satisfying relation (1), all the rays propagating through the sections of the optical fiber 2 and 3 experience complete internal reflection and not a single beam comes out through the broadcasted output end 6, which is a reflector of the device.

By the relation (1), we determine the angle for the interval of the refractive indices of Pg from 1.4 to 4, which makes it possible to cover almost the entire interval of the refractive indices of the optical materials used today for the manufacture of fiber elements.

For P2 1,4 we have Sincp -j-, which is corresponding to j

It bends a bevel angle.

one

For P2 4 we have 51pf - which corresponds to a bevel angle of 15 °.

Thus, the bevel angle of the fiber end face, at which full internal reflection is provided at the interface of two air-to-fiber media, is in

ranging from 15 to 46 ° for most materials of which the optical fibers are made.

At bevel angles φ 46 °, the relation (1) is also satisfied, but the conditions for the input of radiation from the radiator 4 through the beveled input end of section 2 of the fiber deteriorate.

The reflector, which is the output end 6 of the last section of the light guide 3, is designed to form a counter-radiation mainstream.

A radiation receiver converts optical radiation scattered by particles into an electrical signal.

Focusing element 5 provides directional transmission of optical radiation.

The smoke sensor reflector is a slanting output end of 6 light guide sections 3 with a bevel angle of 15 to 46 °.

The smoke detector works as follows.

In the absence of smoke in the controlled space, the luminous flux of the radiator 4 propagates through the input end 7 through section 2 of the optical fiber and is transmitted through the controlled medium 8 to the output end 6 of the last section 3 of the optical fiber. Therefore, in sections 2 and 3 of the optical fiber, a luminous flux is created which is opposed to the main one, which passes through the focusing elements 5 and the controlled medium 8 to the beveled input end 7 of the optical fiber section 2, the radiation again experiences total internal reflection, which leads to repeated reflection of radiation in section 2 light guide. Thus, the rays of light, as it were, fall into a trap between the input 7 end of the light guide and the output end 6 of the last section 3 of the light guide.

Thus, in a controlled environment 8, a counter multiple passage of the luminous flux of the radiator 4, which does not reach the radiation receiver 1 due to the concentration of the flux, is provided.

radiation in sections 2 and 3 of the fiber.

When smoke appears in the controlled environment 8, part of the light flux of the radiator 4 is scattered by smoke particles and enters the photodetector 1, and the rest of the light flux of the radiator 4 passes through the elements

focusing 5 and sections 2 and 3 of the light guide and falls on the output end 6 and is reflected back to section 2 and 3 of the light guide.

The radiation reflected from the output end 6 re-passes through sections 2 and 3 of the light guide, focusing elements 5 and the monitored medium 8, where it is again scattered by smoke particles to the radiation receiver 1.

The remaining luminous flux propagates through sections 2 and 3 of the fiber, undergoes total internal reflection and enters a controlled environment 8, where it is scattered by smoke particles on the radiation receiver 1.

Thus, repeated passage of radiation through the controlled medium 8 (smoke) significantly increases the sensitivity of the smoke sensor, i.e., increases the light flux dissipated by smoke detected by radiation receiver 1, whose electrical signal, passing through the processing device, triggers an alarm signal.

In the proposed device, when multiple radiation passes through the smoke, the fraction of the luminous flux scattered by smoke of the radiator 4, registered by the radiation receiver 1, is determined by the formula

infinitely decreasing geometric progression ,,

lim 5 where b is part of the luminous flux of the radiation source 4 dispersed by smoke to the radiation receiver 1 with a single passage of light through the smoke;

q is the attenuation coefficient of light when it passes through once

controlled medium 8. For example, at q 0.975 a fraction of the light flux scattered by smoke to the radiation receiver 1 of the proposed device

equal to 406

The scattering of smoke by particles of two oppositely directed flows ensures that the radiation emitted by the radiation emitter 5 is dispersed by smoke both at sharp and obtuse angles, which makes it possible to achieve approximately equal sensitivity to white and black smoke.

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Claims (1)

A SMOKE SENSOR containing a radiation receiver mounted on one optical axis of a fiber section, a radiator facing the input end of the first fiber section, the first focusing elements are installed on the output ends of all fiber sections except the last one, which are optically coupled through the controlled medium to the second focusing elements, mounted on the input ends of all sections of the fiber, except the first, the output end of the last section of the fiber is a reflector, characterized in that, in order to increase the sensitivity sensor, the input end of the first section of the fiber and the output end of the last section of the fiber are beveled with a bevel angle of 15 to 46 °, the radiation receiver is installed at an angle to the axis of the sections of the fiber, and the optical axis of the emitter is perpendicular to the plane of the input end of the first section of the fiber. figure 1