Optical probe

Details Optical probe Optical probe

1984-12-24

1987-12-15

LaRoche, Eugene R.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

73293, G01N 2149

Patent

active

047135522

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to an optical probe. This optical probe is used in the detection of the interface separating two media having different optical indices contained in an enclosure and more particularly to the detection of the level of the water in the enclosure of a nuclear power station steam generator. It also applies to the detection of the compositions of two-phase media on the basis of their optical refractive indices.
It is known that the detection of the separating interface of two media having different optical indices contained in an enclosure is difficult, particularly when the latter is sealed and the medium is hostile. This is for example the case that in steam generators in pressurized light water nuclear power stations, in which the water passage zone from the liquid phase to the vapour phase fluctuates and is not well known. Thus, it is also known that it is difficult to detect compositions of two-phase media contained in an enclosure.
The separating interface between two media having different optical indices and more particularly the level of the water in the enclosure of an e.g. steam generator can be defined, on the basis of the difference of static pressures recorded by a probe incorporating pressure detectors located at two different levels, on the same generatrix of the cylindrical enclosure of the generator. One of these detectors is positioned below the level of the water, whilst the other is positioned above said level in the part of the enclosure containing the steam. The pressure measurements can be disturbed in a temporary or permanent manner by secondary flow phenomena of the water between these two detectors. Moreover, the measurements obtained on the basis of these detectors can be relatively unreliable, in the case of an accidental depressurization of the generator.
Other probes making it possible to detect the separating interface of a liquid medium and a gaseous medium are known and a description will now be provided thereof.
Thermal probes are constituted by a system of heating elements. For example, the level of the water in a steam generator is detected by a measurement of the thermal conductivity of these heating elements, said conductivity varying as a function of the position of the heating element, which may be located within the liquid or outside it. These thermal probes are very quickly damaged by high temperature liquids and do not supply accurate measurements.
Electrical probes comprise a series of electrodes, the measurement of resistance variations between two successive electrodes giving a level indication. These probes are fragile and very sensitive to inteference.
Acoustic probes are often used for measuring liquid levels, but they are difficult to use in liquids having high temperatures, as well as in high pressure gases.
The operation of nuclear probes is based on the absorption of nuclear radiation in a liquid medium and rapidly become damaged at high temperatures.
The recent appearance of optical fibres and optoelectronic components has made it possible to develop optical probes for the detection of the separating interface between two media having different optical indices. These probes comprise an optical means generally constituted by a glass prism able to refract or reflect an incident light beam. This prism is placed in the enclousre containing two media having different refactive indices, e.g. a liquid and a gas. When the prism is located in the liquid, any incident light beam is refracted by the prism, whereas when the prism is located above the surface of the liquid, any incident light beam is reflected by the prism. An optical emission illuminated by a light source makes it possible to transmit an incident light beam up to the prism, whilst an optical reception fibre makes it possible to transmit the light beam, optionally reflected in the prism, to an optoelectronic detector. The presence or absence of reflected beams consequently makes it possible to detect the separating interface between the liquid and the gas and with the knowl

REFERENCES:
patent: 3834235 (1974-09-01), Bouton et al.
patent: 4286464 (1981-09-01), Tauber et al.
patent: 4304462 (1981-12-01), Baba et al.

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