FR2825176A1 - Long range optical detector for explosion risk areas uses special fibre optic - Google Patents

Abstract

A long range optical detector has electronic components in a safe area (1) with transmission (3) and reception (4) of light to the explosion risk area by fibre optic cables (2, 5). The fibre optic cables have non-electrostatic coatings and large ends to prevent heating and comparison of the sample (6) through special cable (7) that interrupts the light if the cable breaks.

Description

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 The present invention relates to a long-range optical detection device in an explosive atmosphere thanks to the offset of dangerous electrical and optoelectronic elements in a safe area. The signal is transported and used in the danger zone in cold light, driven by specially constructed optical fibers, under safe conditions and without the use of electrical energy.

 The device complies with the safety rules applicable to electrical devices used in potentially explosive atmospheres, in intrinsic safety, according to European standards EN 50 014 and EN 50 020.

 The use of intrinsically safe optical detection is limited by the maximum level of electrical power used in hazardous areas. This limitation does not allow the use of sufficient powers to excite electroluminescent devices to allow optical immaterial detection at decametric distances, or which require a high penetration rate of atmospheres opacified by pollution of the light ray by a fog. or the presence of suspended solid particles. This is also true in the case of optical detection exposed to strong ambient light or parasitic incident light of artificial or natural origin. The constraints imposed by the standards for protection by explosion-proof enclosure (EN 50 018) lead to very large sensor sizes, without any real benefit for optics. The tests and test methods for this protection become even more restrictive as soon as the internal volume exceeds 10 cm3. By imposing individual tests in all cases of welded construction envelope, they almost prohibit assemblies and crimping by ultrasound. The use of protection by internal overpressure of a non-flammable gas also generates significant dimensions by the addition of bulky and very expensive gas supply device. The proposed device thus allows economical miniaturization of the sensors while preserving the possibility of far-reaching far-reaching detection in an explosive atmosphere. The use of optical fibers in an explosive atmosphere is already in itself a way of increasing the level of security. However, this level remains insufficient by the risk of discharging electrical sparks and igniting the gases by heating the optical surfaces. This heating can become dangerous at the point of a break or deep damage to the fiber if the energy loss is significant or concentrated on a very small area. The quality of the polishing of the optical face of the fibers can also become a hot surface element depending on the optical powers required. This same principle is directly reversible at the focal point in the event of direct lighting by a solar ray by simple magnifying effect. Object detection or change of light state by means of optical fibers are today mainly oriented towards applications in which the accessibility or size of a complete detection device is impossible by conventional means.

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 c. In these applications, these devices are sometimes associated with primary optical devices capable of increasing the detection distance but without ever being able to exceed a few decimeters of a reflector.

 The device according to the invention consists in associating and combining four safety factors. Move the optical converter of electrical signals to a safe area, and vice versa of the electrical processing of the optical signal. Ensure the transport of the energy necessary for this light signal in the danger zone, in complete safety without recourse to electric energy and without risking producing electric sparks by electrostatic discharge. Eliminate the risk of surface temperature which can cause self-ignition of the dangerous atmosphere, and constantly monitor the signal transmission between the converter and the optical device for emitting the light signal. It is thus possible to associate geometric optical devices capable of wide-range detection or of strong penetration of polluted atmosphere in complete safety.

 The attached diagrams illustrate the invention.

 Figure 1/4 shows the general diagram of the complete interconnected assembly.

 Figure 2/4 shows the block diagram of the transducer and optical converter.

 Figure 3/4 shows the geometrized optical signal transmission system; Transmitter.

 Figure 4 1 4 shows the reception system by focusing and transmission of the received optical signal; Receiver.

 Referring to Figure 1/4, according to particular manufacturing methods, the device consists of the following functional units: - Reference 1, An electro-optical converter-transducer system and vice versa.

 - Reference 2, An optical fiber for transporting the emitted light.

- Reference 3, Geometry system of the light emitted: Emitter - Reference 4, System of focusing in the fiber reference 5 of the received light:
Receiver - Benchmark 5, An optical fiber for transporting the received light.

 - Reference 6, a device for taking information from the optical signal proportional to the signal transmitted and integrated into the transmitter.

 - Reference 7, an optical fiber for feedback of the optical signal to the converter.

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 Referring to Figure 2 1 4, the device consists of 8 functions that can be integrated into an envelope (item 2-1).

 - An electrical-optical converter (transducer) consisting essentially of a light emitter, visible or not visible to the human eye (item 2-2), such as an electroluminescent component (ED L), LASER emitter or any other device controlled by a electronic (item 2-3). This electronics, by generating suitable electrical currents and or calibrated pulses, possibly allows this light to be coded by a series of extinctions ignitions at a chosen frequency which may vary.

 An optical system for focusing the light beam (item 2-4) which allows the light emitted by the light emitter to be concentrated in a suitable optical fiber (item 2).

 An optical fiber (item 2) ensuring the transport of light to the geometrization device (item 3) of the optical signal which can be placed in a potentially explosive area. This fiber is characterized by a coating of non-electrostatic flexible material incapable of causing an electrical spark. This fiber is optionally protected by a flexible metallic envelope which provides it with high mechanical resistance. According to provisions not shown, the obligation to use this particular fiber and the ban on the use of any optical fibers which do not meet the criteria previously announced is ensured by means of one of the two connection devices particu - following links. Either a definitive and non-removable seal, or a particularly realized removable connection which by presenting a set of mechanical keys prohibits any other connection than that corresponding to the use.

Reverse :
An optical fiber (reference 5) having the same characteristic arrangements as the reference fiber 2 ensures the transport of the optical signal received in the dangerous zone, to an electro-sensitive component to light. The light junction between the fiber and this component can be ensured by direct surface contact or by a particular optical device not shown in the diagram.

 A photo component sensitive to the spectrum of light emitted by the emitter (reference 2-5) such as phototransistor, photodiode, or any other physical material association device, which provides a transformation of an optical signal into an electrical value .

 An electronic device (item 2-6) for recognition, amplification and processing of the electrical signal. The processed signal can be used locally or remotely for information or direct control of automation or safety devices.

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- A control optical fiber (item 7), returning the information that the optical signal received by the transmitter (item 3) corresponds to certain conditions. This fiber has the same characteristic provisions as reference fiber 2.

gereuse ne soit atteinte à l'endroit de la rupture de la fibre optique, même si la gaine de protection n'est pas altérée. - An electronic comparison device (item 2-7) processing the signal transmitted by the optical fiber item 7 by means of a photosensitive component item 2-
8), and which in the absence or a strong reduction of the proportional signal returned, automatically and immediately cuts the light emission of the component reference 2-5 so that at no time a surface temperature in

is not reached at the point where the optical fiber breaks, even if the protective sheath is not damaged.

 Referring to Figure 3/4 the device represents a calibrated signal transmission system.

 - It includes an optical device which ensures the recovery of the light signal transmitted by the reference fiber 2, and directs its emission towards the outside according to a suitable geometry. This device is integrated in a solid envelope which can be fixed and oriented easily. It is characterized by the mechanical connection of the fiber made particularly according to the methods set out previously in the description of Figure 2/4.

 By means of non-detailed arrangements, the end of the marker fiber 2 situated in the danger zone is particularly achieved. While guaranteeing optical continuity and homogeneity, the optical transfer surface of the fiber is increased so that its surface temperature always remains below that which could cause the ignition of the dangerous gas.

 An optical device, shown schematically and not detailed, makes it possible to separate a proportional part of the optical signal transmitted by the reference fiber 2 and returns it to the transducer converter by means of the reference optical fiber 7.

 With reference to FIG. 4/4, the device represents the transmission focusing system of the received optical signal.

 It includes an optical device for focusing the signal received in the reference otic fiber 5. This device is integrated in a solid envelope which can be fixed and oriented easily. It is characterized by the mechanical connection of the fiber made particularly according to the methods set out previously in the description of Figure 2/4.

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 - The same specific provisions as the reference fiber 2 are applied to the ends of the reference fiber 5 so that an incident solar ray cannot cause dangerous surface heating.

 By way of nonlimiting example, the annexed diagrams 1 and 2 show alternative arrangements of the functions placed in dangerous zones.

 The appendix figure 1 represents the use of the general device in reflex mode on a reflector or a mirror.

 The annexed figure 2 represents the use of the general device in optical diffusion mode by detection of the variation of the signal reflected directly on the absorbent surface of an object or on any reflecting surface.

 The device according to the invention is particularly intended for automation and security applications in so-called immaterial, long-distance detection of objects or people in explosive or flammable atmospheres such as encountered in particular in the chemical industry and petroleum, sites for the treatment or storage of flammable or explosive gases and pulverulent materials. Another destination of the device is in automation and security applications in industries using spraying techniques for paints and varnishes, or any other liquid or powdery particles which generate a temporarily explosive atmosphere.

The use of non-electric power in the danger zone allows an interesting penetration of the detection in the presence of fog or dust and particles in suspension in the atmosphere, without compromising safety.

Claims (3)

CLAIMS 1-Large optical detection device which can be used in an intrinsically safe explosive atmosphere characterized by: - The transport of the necessary energy, for the distant detection of an object by establishment, cut or variation an optical signal, without recourse to electrical energy in the danger zone, by means of specially made optical fibers. The generation, control and processing of the optical signal being carried out by an optoelectronic conversion device placed in a safe area. The production of these optical fibers by a particular coating of non-electrostatic flexible material in that they no longer present any risk of creating electrical sparks. The particular embodiment of the optical ends situated in the dangerous zone of the optical fibers in that it increases the optical transfer surface so that the energy of said signal cannot increase the temperature of the surface to a level which can cause the ignition of the dangerous atmosphere considered. The optical device for feedback of the conditions of the signal at the input of the optical device for external emission of the signal at the end of the fiber in that it takes a determined proportion of the energy of said signal and the returns using an optical fiber previously characterized; in that it allows an electronic comparison device integrated with the optoelectronic conversion device to automatically and immediately interrupt the generation of the signal in the event of breakage or damage to the optical fiber and in that it prohibits that the altered parts reach an abnormal surface temperature which may cause ignition of the hazardous atmosphere. 2-Device for connecting the optical fibers by permanently sealing the fibers to the device in that it prohibits any use of standard optical fibers or which do not meet the characteristics specified in claim 1, 3-Device for connecting the fibers optical by a precision mechanical assembly having a particular set of mechanical keys in that it prohibits any use of standard optical fibers or which do not meet the characteristics specified in claim 1. 4-Geometric emission device in direction and in divergence of the optical signal, which comprises an optical device for transmitting the light energy transported by <Desc / Clms Page number 7>  an optical fiber characterized according to claim 1 without recourse to electrical energy, in that it allows a safety design usable in an explosive atmosphere. 5-Device for receiving the optical signal, which comprises an optical device which focuses this signal in an optical fiber characterized according to claim 1 without recourse to electrical energy, in that it allows a safety design usable in the atmosphere explosive.