GB2105034A

GB2105034A - Fiber optic impurity detector

Info

Publication number: GB2105034A
Application number: GB08224900A
Authority: GB
Inventors: Bruce Norwood Lenderking
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1981-09-04
Filing date: 1982-09-01
Publication date: 1983-03-16
Also published as: DE3232059A1; JPS5853739A; FR2512552A1

Abstract

A system useful for sensing the presence of an impurity in a hostile or remote environment using an optical waveguide sensor (16) disposed within and coupled to the environment. The waveguide sensor comprises the core of a fiber optic cable with its cladding material removed. The impurity presents an altered refractive index medium about the waveguide and causes a change in light transmission characteristic for the waveguide which is detected, resulting in an output signal indicating the presence of the impurity (i.e. by comparison with the signal generated when impurity is absent). The impurity may be deposited on the sensor as droplets, from a spray or by condensation; or particles may deposit on the sensor. Deposition may be electrostatic. <IMAGE>

Description

SPECIFICATION Fiber optic impurity detector The present invention relates to a system for detecting impurities such as gases, moisture, and particulates and, more particularly, to such system adapted for qualitative identification of the presence of chemical impurities.

The system has the advantage of permitting location of a sensor within the ambient environment under study, with the detector being remotely located with a fiber optic cable connection.

It is well known in the fiber optic art that the relative index of refraction of a core material and a cladding material will determine the transmission characteristic of light along the fiber optic cable core. A critical angle is defined for the interface between the core and cladding indices of refraction such that for angles greater than the critical angle Oc, light will be totally internally reflected along the core. For angles greater than the critical angle, the light will be lost to the cladding as a function of this angle. As the index of refraction of the core approaches that of the cladding, the power distortion in the waveguide changes, resulting in power being lost from the core to the cladding.

There are any number of reasons for remotely sensing the presence of impurities, ranging from difficulty of access for inspection, to the presence of hazardous chemicals.

It is desirable that the sensor be as unobtrusive as possible, i.e., non-reactive, not subject to electromagnetic interference or the like.

Impurity detection systems can be used to determine the need for periodic maintenance as from an impurity buildup, as well as to sense failure conditions, such as a fluid piping failure. The ambient environment under consideration may be hostile due to high electric potentials or explosive constituents.

It is an object of the present invention to provide a novel fiber optic impurity detector for sensing the presence of impurity in an enviroment.

The invention resides in a fiber optic impurity detector for sensing the presence of a predetermined impurity in an ambient environment, comprising an elongated optical waveguide disposed within the ambient environment, said waveguide comprising a core having a predetermined index of refraction with its cladding removed; fiber optic input and output light transmission means optically coupled to each end of the optical waveguide; a light source coupled to the optical waveguide through the input fiber optic light transmission means; a light detector coupled to the optical waveguide through the output fiber optic light transmission means, said light detector generating a signal representative of the light transmitted through the waveguide and received by the light detector; and means for comparing the normal light detector output signal generated by light transmitted through the waveguide disposed in an impurity-free ambient environment with the light detector output signal generated when an impurity is present in the ambient environment and is optically coupled about the waveguide, impurity presenting an altered refractive index medium about the waveguide and causing a change in light transmission through the waveguide resulting in a light detector output signal which indicates the presence of the impurity in the ambient environment.

The sole figure is a schematic representation of an exemplary embodiment of the present invention with a waveguide disposed within a sampling chamber.

The present invention can be best understood by reference to the drawing wherein the impurity detector system 10 comprises a sample chamber 1 2 to which the ambient environment under study can be admitted through sampling aperture or port 14. An elongated optical waveguide 1 6 is disposed within the sample chamber 12, and comprises the core of a conventional fiber optic cable with the cladding material removed. In this embodiment the waveguide 1 6 is a generally Cshaped member, but the waveguide configuration is not critical, and could be a straight member, a coil, or any other configuration which provides sufficient core surface within the sampling chamber to permit measurement of the change in light transmission. The waveguide member 1 6 or core medium has an index of refraction of N1.The ambient environment within the sample chamber 1 2 which may be a gas coupled to the waveguide will exhibit an index of refraction of N2.

A remotely disposed light source and light detector means 1 8 is connected by a fiber optic cable 20 which connects the light source portion of means 1 8 to one end 21 of the waveguide 1 6 through the sampling chamber wall. A second fiber optic cable 22 connects the other end 23 of the waveguide 1 6 to the light detector portion of the means 1 8. The light detector portion of means 1 8 is also connected to an information processor and control means 24, whereby an output light detector signal is fed to means 24 for comparing the signal to a standard or reference signal had from a known ambient environment present in the sampling chamber.

In operation, the sampling chamber 1 2 is disposed in a remote and/or hostile environment, such as within a steam turbine, or an electrical generator housing, or a nuclear steam supply system. The sample port 14 permits periodic change in the atmosphere within the sampling chamber as by diffusion, so that the sampling chamber atmosphere is representative of the ambient environment at a point of time.

Light from the light source portion of means 18 is directed throughf fiber optic cable 20 to the waveguide 16. The atmosphere within sampling chamber 1 2 interfaces or is optically coupled to the waveguide or core by a variety of mechanisms depending on the impurity.

For a vaporized impurity, it could be deposited on the core by evaporation. Other coupling mechanisms include attraction by static charge, and particle fallout for simple particulates. The ambient environment this provides a cladding index of refraction 2, which causes light loss at the core-cladding interface. This transmitted light exits waveguide 1 6 and is transmitted by cable 22 to the light detector portion of means 1 8. The conventional light detector portion of means 1 8 may be a photomultiplier tube which produces an output signal as a function of light reaching the detector.This detector output signal is fed to information control processor means 24 to be compared to a refrer. a signal or set point signal, which is a function of a known ambient environment which represents an impurity-free condition. The means 24 can then be used to generate a control signal which is used to shut down or alter the equipment or system within which the sampling chamber is disposed. The means 24 might also be a meter which informs an operator of the presence of impurity and the need for operator action.

The light source portion of means 1 8 can be a conventional high intensity light source which is collimated and inputted into cable 20. A laser light source can be used also, with the monochromatic source simplifying the light detection requirements, as well as being easily coupled into the cable 20.

By way of an example, the sensor or waveguide 1 6 is a 200 micro-meter diameter cable core, which is fused silica having an index of refraction of 1.46. The normal cable cladding of silicon rubber is stripped from this core which forms the sensor or waveguide portion 16, while the cable is continued as cable links 20 and 22 between the waveguide portion 1 6 and the light source and detector means 18.

When a contaminating fluid, which may be present as a spray or vapor, is present in sampling chamber 12, fluid droplets form on the waveguide surface, and the intensity of light transmitted through the waveguide is reduced. The output signal from the light detector is fed to the signal processor 24 and compared to a set point or reference signal which Is indicative of no contaminant fluid in chamber 1 2. The output signal of processor means 24 can then be used to perform an equipment control function such as valve control or power control.

Claims

1. A fiber optic impurity detector for sensing the presence of a predetermined impurity in an ambient environment, comprising an elongated optical waveguide disposed with the ambient environment, said waveguide comprising a core having a predetermined index of refraction with its cladding removed; fiber optic input and output light transmission means optically coupled to each end of the optical waveguide; a light source coupled to the optical waveguide through the input fiber optic light transmission means: a light detec- tor coupled to the optical waveguide through the output fiber optic light transmission means, said light detector generating a signal representative of the light transmitted through the waveguide and received by the light detector; and means for comparing the normal light detector output signal generated by light transmitted through the waveguide disposed in an impurity-free ambient environment with the light detector output signal generated when an impurity is present in the ambient environment and is optically coupled about the waveguide, said impurity presenting an altered refractive index medium about the waveguide and causing a change in light transmission through the waveguide resulting in a light detector output signal which indicates the presence of the impurity in the ambient environment.

2. A fiber optic impurity detection set forth in claim 1, wherein the elongated optical waveguide is disposed within a substantially light-tight sampling chamber having a sample port to admit the ambient environment to be sampled for the presence of impurities.

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