DE3232059A1 - GLASS FIBER DETECTOR - Google Patents

Description

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Fiber optic detector

The invention relates to a fiber optic detector for determining contamination in an environment with one or more elongated optical fibers arranged in the environment.

With the help of such a fiber optic detector can qualitatively chemical Impurities are detected in the environment, the detector has the advantage that its sensor part is directly in the area to be checked Environment can be arranged, whereas the evaluation can take place in a remote station to which a transmission path with an insensitive fiber optic cable.

It is generally known that optical fibers suitable for light transmission have a refractive index between the fiber core and the fiber cladding which determines the transmission characteristics along the optical fiber or, in the case of several optical fibers, along the optical cable. _{A critical angle e c is} defined at the boundary layer between the fiber core and the fiber cladding, so that there is total reflection for the light introduced into the glass fiber if the angle of incidence is greater than the critical angle. If the angle of incidence is smaller than the critical angle, light emerges through the fiber cladding and is lost. When the refractive index of the fiber core approaches that of the fiber cladding, the power distribution in the light guide changes, with the power being lost from the fiber core to the fiber cladding.

There are a variety of monitoring processes that require remote monitoring it is desirable, be it that the area to be monitored is difficult to access or that dangerous chemical substances are present are. It is desirable that the actual sensor so

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has as little influence as possible, d. H. neither chemically reacts nor z. B. electromagnetic fields o. The like. Influences.

Such a detection system for determining contamination can for periodic monitoring purposes or to detect functional failures, e.g. B. in a fluid transfer in a pipeline system to serve. The environments to be monitored or the environment to be monitored can be very aggressive or potentially explosive be and z. B. are also under a very high electrical potential.

The invention is therefore based on the object of a detector device to create, with which contamination in an environment or in the environment can be determined, with the sensor the occurring Detect contamination with the highest possible sensitivity, but on the other hand not affect or affect the environment to be monitored. this does not bother.

According to the invention, this object is achieved using one or more Optical fibers solved in that the optical fibers have a core with a predetermined Have a refractive index from which the fiber cladding or cladding layer is removed,

that at the ends of the optical fibers input and output side optical Transmission lines connected. are via which a ■ Light source and a light detector on the output side are coupled, and that comparison devices are connected to the light detector, with which the light signals transmitted via the optical fiber on the one hand in a pollution-free and on the other hand in a polluted environment are comparable to detect contamination due to the change in the refractive index of the optical fibers.

The invention with its advantages and features is based on a an embodiment referring to a single figure is explained in more detail, which shows a light guide arranged as a sensor in a chamber.

WS340P-2528 In the drawing

In the drawing, a detector device 10 according to the invention is shown, which is provided with a measuring chamber 12 which is arranged in the environment to be checked and has an opening 14 through which the atmospheric conditions prevailing in the environment or environment can be seen in can expand the interior of the measuring chamber. In the measuring chamber 12, an elongated light guide is arranged, which can consist of one or more optical fibers and from which the fiber sheath or the cladding is removed. This light guide runs approximately C-shaped in the chamber, but S-. other configurations such as B. an annular or coil-shaped

Course be provided. It should thereby be ensured that the light guide has a sufficiently large surface and the change in light transmission triggered by the contamination is measurable Size supplies. The fiber core of the light guide 16 has a refractive index Nj. The effective environment in the measuring chamber, which the Surrounding light guide should have a refractive index N2.

The light guide 16 is at one end 21 with an optical transmission line 20 is connected to a light source and has its other end 23 via an optical transmission line 22 with detector devices in connection, which are housed in a block marked 18. The light source and the light detector are with one Comparison device 24 connected, which controls both the measurement process and the comparison of the received light signal with the transmitted one or a standard or reference light signal, which characterizes a known environment in the measuring chamber.

In use, the measuring chamber 12 is in the desired environment or environment introduced, which is for example within the flow of a steam turbine or within an electrical generator housing or an inaccessible area in a nuclear power plant. In a nuclear power plant, for. B. an undesirable change in chemical composition in a radioactive flow circuit or chemical components are monitored. Through the opening 14

WS340P-2528 results

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diffusion influences the inside of the measuring chamber located atmosphere, so that this atmosphere is representative of the environment to be checked and an actual time measurement can be carried out can. From the light source of the detector devices is via the transmission line 20 the light guide 16 is supplied with a light signal. The atmosphere within the measuring chamber 12, which at the boundary layer too the light guide acts on its surface, whereby a variety of mechanisms are effective depending on the nature of the contamination could be. For a dull-shaped contamination, for example form a deposit on the fiber core. However, there can also be a build-up of particles due to static charge build-up and thus result in a static attraction. These impurities from the environment thus form a fiber cladding on the fiber core or a cladding layer, the refractive index of which corresponds to the value N2 and triggers a loss of light at the boundary layer. The transferred Light is passed on from the light guide 16 via the transmission line 2 2 to the light detector. A conventional Find photoelectron multiplier use, which provides an output signal as a function of the received light signal. This output signal is transmitted to the comparison devices 24 for further processing and compared with a reference signal or an actual signal, which can be determined on the basis of a known pollution-free ambient atmosphere. The comparison devices 24 can also can be used for control purposes by emitting a control signal which switches the system on and off for test monitoring. In the end The comparison devices can also comprise display devices in order to allow an operator to recognize the occurrence of contamination close.

The light source is a high intensity light source with a blanked one Use of the bundle of rays placed on the transmission line 20. In this context, a laser light source is considered special to be considered advantageous because it provides a monochromatic light and thus simplifies the detector devices. Such a laser light

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is also relatively easy to get into and out of the transmission lines decoupling.

For the light guide, for example, a light guide cable with 200 μm Find diameter use, which consists of fused quartz glass and has a Breehnungsidex of 1.46. The usual fiber sheath made of silicon rubber is removed in the area of the light guide 16 inside the measuring chamber so that the outside of the measuring chamber Sections as transmission lines 20 and 22 to the light source and the light detector can be used. For example, if the measuring chamber in a polluted flow, e.g. B. a steam stream, is arranged, flow particles are deposited on the surface of the waveguide 16 and influence the transmission of light, the intensity of the transmitted light being reduced. The output signal that the Light detector receives is processed in the comparison unit 24 and compared with a reference signal or actual signal which characterizes an uncontaminated flow in the measuring chamber 12. With the help of The comparison device then turns the measurement results into monitoring functions and control functions triggered, which in a known manner, for example, on the power control or on an auxiliary control Can influence.

WS340P-2528

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Claims (2)

Claims (lΛ Glass fiber detector for the detection of contamination in an environment or an environment with one or more elongated guide fibers arranged in the environment or environment, characterized in, - That the guide fibers (16) have a core with a predetermined refractive index and have been freed from the fiber sheath or the cladding layer, - That at the ends of the optical fibers input and output side optical Transmission lines (20, 23) are connected, via which a light source is coupled on the input side and a light detector is coupled on the output side are, - and that comparison devices (24) are connected to the light detector are, with which the via the optical fiber on the one hand with contamination-free and on the other hand, light signals transmitted in a polluted environment are comparable to determine contamination due to the change in the refractive index of the guide fibers. WS340P-2528 2. Glass fiber detector according to claim 1, characterized in that - That the light guide (16) within a substantially light-tight Measuring chamber (12) is arranged, in which the atmosphere of the environment to be monitored acts through an opening (14). WS340P-2528