GB2170004A - Apparatus for sensing fluids - Google Patents
Apparatus for sensing fluids Download PDFInfo
- Publication number
- GB2170004A GB2170004A GB08530134A GB8530134A GB2170004A GB 2170004 A GB2170004 A GB 2170004A GB 08530134 A GB08530134 A GB 08530134A GB 8530134 A GB8530134 A GB 8530134A GB 2170004 A GB2170004 A GB 2170004A
- Authority
- GB
- United Kingdom
- Prior art keywords
- light
- light guide
- dew
- sensing
- point
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/85—Investigating moving fluids or granular solids
- G01N21/8507—Probe photometers, i.e. with optical measuring part dipped into fluid sample
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/56—Investigating or analyzing materials by the use of thermal means by investigating moisture content
- G01N25/66—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/56—Investigating or analyzing materials by the use of thermal means by investigating moisture content
- G01N25/66—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point
- G01N25/68—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point by varying the temperature of a condensing surface
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/43—Refractivity; Phase-affecting properties, e.g. optical path length by measuring critical angle
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
- Investigating Or Analyzing Materials Using Thermal Means (AREA)
Abstract
Sensing apparatus, for example for sensing the dew-point, comprises a light guide (3) coupled to receive light from a light-emitting diode (1) and to pass light to a detector (2), for example, a photodiode, arranged to measure the light intensity. An area 3f of the surface of the light guide 3 is damaged, e.g. roughened, to produce an uneven area arranged to scatter light. When this uneven area is dry, this scattering causes light losses, which result in a reduction in the photocurrent measured by the diode (2). However, if the uneven area is wetted by a liquid, for example, by dew, then total reflection occurs to a large extent in this region and an increase in the current of the photodiode 2 results. The change in the photodiode current can be utilized to detect the presence of the liquid. <IMAGE>
Description
SPECIFICATION
Apparatus for sensing fluids
The present invention relates to apparatus for sensing fluids, for example, for indicating the level of a liquid in a container or for use as an optical dewpoint sensor. Dew-point mirror hygrometers are known for measuring dew-point by optical means.
Such hygrometers have a metal plate with a mirror-coated surface, which is irradiated by a light source. The light reflected by the surface is received by a light-sensitive detector disposed opposite the surface. When the dew-point is reached, moisture condensing out of the air is deposited on the mirror-coated surface, and as a result the intensity of the reflected light is reduced. This reduction, detected by the detector, represents a criterion for establishing if the temperature has fallen below the dew-point. Thus, if the surface temperature of the metal plate is measured at this time, it will correspond to the dew-point temperature to be measured.
Sensing apparatus of the invention, uses made of a light guide arrangement of a form as described in DE-OS 2,117,168 which shows a fibreoptic measuring device for determining the refractive index of liquids and gases.
In this known fibre-optic refractometer, a light guide dipping into the medium and having an inhomogeneity is provided as the sensor. The inhomogeneity causes a loss of light intensity, which loss is dependent upon the nature of the medium and is utilised for measurement purposes. In this measuring apparatus, the light in the form of discrete modes is introduced into the light guide which extends through the medium which is preferable. The inhomogeneity is situated within the medium and is arranged to convert the discrete modes into a broad mode spectrum. The intensity of the light coupled out of the light guide or of the light emerging at the other end of the light guide is evaluated as representative of the refractive index of the surrounding medium. However, this apparatus does not serve for detecting or measuring the dew-point.
A process and apparatus for detecting vapour in gas are known from US Patent Specification 3,528,278, which process and apparatus can also be used to determine the dew-point.
In the apparatus shown in this US patent specification, a light-transmitting element, e.g. a rod of quartz glass coated with a highly relective material, acts as a sensor for determining the dew-point.
Light is coupled into the rod by way of its accurately ground end face. The angle of inclination of this end face relative to the radiation direction and the envelope surfaces of the rod is so dimensioned that total reflection of the light coupled into the rod takes place within the interior of the rod, as long as the envelope surfaces of the rod are not wetted by a liquid. The critical angle at which total reflection commences is different in the case of a glassliquid interface from its value in the case of a glass-air interface. This phenomenon is utilized in the apparatus in this US patent specification to enable the dew-point to be determined.The drops of condensate which are deposited on the surface of the glass rod, that is, the dew, cause a substantial proportion of the coupled light to be scattered, so that the intensity of the light emerging at the other end of the rod is substantially reduced once the dew-point has been reached.
In this apparatus the critical angles are of great importance, and the glass rod must be accurately ground and accurately disposed relative to the light source. The apparatus is therefore costly and susceptible to interference.
The special properties of light guides are discussed in "Conference Proceedings OFS 84", published by VDE-Verlag GmbH, Berlin-Offenbach, on the occasion of the 2nd International Conference on optical fibre sensors, which took place in Stuttgart during the period from 5th to 7th September, 1984.
In this publication, a light guide whose surface is provided with a defined raster over a predetermined length thereof, is proposed as sensor. This raster consists of a defined optical ruled grating, which, when wetted, couples out a proportion of the light within the light guide. From the reduction in the light intensity, conclusions can be drawn as to the nature of the moisture molecules. A prerequisite for this process of measurement is an optical ruled grating which is applied to the guide in a very accurate manner.
It is an object of the present invention to provide a fluid sensor, for example which may be used to detect the dew-point, but which is less costly to produce and less susceptible than the application shown in U.S. Patent No. 3,528,278 and in the Conference Proceedings.
According to the present invention, there is provided apparatus for sensing fluids comprising a light guide coupled to receive light from a light source and to pass light to a light detecting device, wherein the light guide has in its surface an uneven region arranged to scatter light.
Sensing apparatus of the invention is very simple and therefore cheap to produce. It is particularly suitable for use for detecting the dew-point of gases.
The uneven area of the light guide may be simply produced, for example, by roughening of the surface. The resultant inhomogeneity causes the light intensity of the light emerging at the other end of the light guide surprisingly to increase when the dew-point is reached. This increase is a very noticeable indication of the presence of a fluid and is in contrast to the operation of known sensors. The increase can be used for measurement or alarm purposes. The physical causes of this increase in light intensity are explained below with reference to the drawings.
In a further embodiment, the light-scattering inhomogeneity is produced by a rupture in the light guide. Where the light guide is made of fibres, one or more of the fibres are ruptured.
Sensing apparatus of the present invention can be made to be very sensitive and in the event of the deposit of a liquid be arranged simply to generate a signal.
Sensing apparatus may be incorporated into a measuring device for measuring the dew-point of gases. In this case, cooling means connected with control means, and a temperature sensor connected with temperature measuring means, are arranged in the uneven area of the light guide.
Preferably, the cooling means comprise a Peltier element.
Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 shows a measuring apparatus having a light guide, a transmitting diode and a receiving detector;
Figure la shows a section taken along the line A
B of Figure 1;
Figure 2 shows schematically the path of a light beam which is totally reflected at the boundary surface between the light guide and water or air where the light guide surface is being undamaged;
Figure 3 shows the beam path at the light guide surface in various circumstances, namely::
Figure 3a shows the beam path where the light guide surface is undamaged and has no dew deposit,
Figure 3b shows the beam path where the light guide surface is damaged and has no dew deposit, and
Figure 3c shows the beam path where the light guide surface is damaged and dew has been deposited;
Figure 4 shows a first embodiment of a sensing apparatus of the invention;
Figure 5 shows a second embodiment of a sensing apparatus of the invention;
Figure 5a shows schematically a light beam path which is totally reflected at the boundary surface
between the light guide and water, the light guide
having damaged by a fibre rupture;
Figure 6 shows a first embodiment of a measur
ing apparatus for measuring the dew-point of
gases;
Figure 7 shows a second embodiment of a
measuring apparatus for measuring the dew-point
of gases; and
Figure 8 shows a block diagram of an electrical
circuit for the measuring apparatus of Figures 6
and 7.
The basic construction of a measuring apparatus
suitable for use as a sensor of the present inventiopn is illustrated in Figure 1. The apparatus com
prises an emitting diode 1 arranged to generate
light, which is fed by way of a light guide 3 to a
receiving detector 2. For measurement purposes, the light guide 3, which is situated between cou
pling pieces 3a and 3b, is exposed wholly or partially to the medium to be examined. As is shown
by the enlarged cross-section in Figure la, the light
guide 3 has an inner core 3c made of glass or plas
tics material, which is enclosed by an envelope 3d
made of glass or plastics material. The light guide
is outwardly enveloped by an elastic protective
tube 3e made of rubber or plastics material.
An example of a sensor of the present invention is illustrated in Figure 4 and it will be seen that it has the basic construction of the apparatus shown in Figure 1 but that the light guide 3 is provided with surface damage, which is represented in an exaggerated manner at 3f in Figure 4.
A light guide which does not have its surface damaged will conduct light coupled in it by total reflection, and substantially without loss, from the emitting diode to the receiving detector, where the light intensity can be measured. In this procedure, total reflection takes place regardless of whether the light guide is wetted with a liquid or surrounded by gas.
The path taken by the light beam in these circumstances is illustrated in Figure 2. For clarity, in
Figure 2 only the beam path within the fibre core (refractive index nc) has been shown, without consideration of the fibre envelope and of the water layer (index nw) surrounding the light guide. Total reflection takes place at the boundary surface between the water surrounding the light guide and the surrounnding air, while the water layer surrounding the light guide results only in refraction of the emerging light beam.
In general, the following applies with regard to the limiting angle for total reflection: arc sin n/nc n = refractive index nc = refractive index of the light guide
n, = refractive index of air
nw = refractive index of water.
The thin water layer surrounding the core of the light guide defines two boundary surfaces extending parallel to one another, namely the boundary surface between the light guide and the water, and the boundary surface between the water and air.
Double application of the traditional law of refraction leads in turn to the law of refraction applied to a simple interface between the light guide and air.
However, this means that the water waler has no effect on the total reflection, from the optical point of view. The reason for the optical in effectiveness of the water layer is the fact that the two boundary surfaces extend parallel to one another.
The exact conditions are represented in Figure 3a in which the inner core 3c of the light guide 3 and the envelope 3d on one side thereof are shown. The surface of the core 3c is undamaged.
With this arrangement, in a manner similar to that in Figure 2, the beam path which is indicated is produced as a result of total reflection.
A light guide of such a kind is thus unsuitable as a sensor for the determination of dew-point.
Other conditions apply if, as is proposed by the invention, the light guide is damaged at its surface in an appropriate manner, for example is roughened, as is the case in the embodiments shown in
Figures 4 to 7.
The enlarged representations of Figures 3b and 3c illustrate the beam path produced near a damage surface of the light guide.
The surface damage represented by the irregular line in Figures 3b and 3c, which is, for example, a roughened surface on the light guide, presents a multiplicity of differingly oriented surfaces which refract the incident light in a diffuse manner and also part reflect the light.
Surprisingly, the loss in light intensity of a light guide which has a damaged surface but which does not have a deposit of dew thereon is greater than in the case of such a light guide having dew deposited thereon. This can be seen by comparing the beam paths illustrated in Figures 3b and 3c.
The surface damage of the light guide, for example the roughening, produces a multiplicity of differingly inclined surfaces. In contrast to a microscopically smooth surface, with such a surface, the respective angle of incidence of the light beams impinging on the boundary surfaces necessarily varies. Accordingly, it is dependent on chance whether an individual incident light beam is reflected into the light guide or emerges from the latter in the form of scattered light. The microscopically roughened and dry surface of the light guide has so many differingly inclined surfaces that, seen as a whole, in a large proportion of the modes the limiting angle for total reflection is exceeded, that is, have an angle a < 43 , and scattered light emerges from the light guide. This reduces the intensity of the light at the other end of the light guide.
On the other hand, if the surface of the light guide has been wetted by dew, as illustrated in
Figure 3c, then the conditions are similar to those which have been explained with reference to Figure 3a, where the light guide surface is smooth.
Because of its surface tension, a film of water extends over the troughs and peaks of the roughened or damaged surface such that the water does not extend along the individual surfaces of the damaged region, but extends substantially parallel to the axis of the light guide.
As a result, the limiting angle for total reflection at the light guide/water interface is larger, of < 63 , and so a large proportion of the light is scattered into the water film. However, only a proportion of the modes leave the water film through the water film/air interface. Those modes which are totally reflected at the water/air interface pass back into the light guide, provided that the light guide has a lower refractive index than that of the wetting liquid, which is, for example, true for a glass fibre/ water system. Thus, a light guide of the type illustrated and which is wetted by a liquid, will have a larger number of modes remaining in the light guide than if the light guide were not wetted.Thus, the light intensity determined by the detector is significantly greater for the wet light guide than for the dry light guide.
Embodiments of indicators for the detection of liquid phases, for example, of dew-point, are shown in Figures 4 and 5. In the sensor shown in
Figure 4, light is coupled by means of a light-emitting diode 1 into the light guide 3, which is provided at its exit end with a photodiode 2 which forms the detector and measures the intensity of the light received. At an arbitrary position 3f along its length, the light guide 3 is roughened. If the roughening is unwetted, for example, there is no condensed phase such as dew present, a considerable proportion of the light coupled into the light guide emerges out of the roughened area 3f, so that the photodiode 2 generates only a very small, and even virtually null, current. However if the roughened area 3f is wetted, for example because the temperature has fallen below the dew-point, then the photocurrent of the photodiode 2 greatly increases.This change in the photocurrent can be used to give a qualitative indication of the liquid deposited. The same arrangement can also be employed to monitor the level of a liquid within a container.
Figure 5 shows a modification of the apparatus of Figure 4, in which light is again coupled into the light guide by an emitting diode 1 and detected by a receiving diode 2. However, in this apparatus, the light guide 3 is communicated by way of a light divider in the form of a Y splitter 4 with light guide limbs 3g and 3h. The light guide limb 3g is coupled to receive the light from the emitting diode 1 and feed it to the light guide 3 whereas the limb 3h couples the light in the guide 3 to the receiving diode 2. In this embodiment, instead of a roughened area, the light 3 has a rupture 3f, which, as described with reference to Figure 5a, has a similar effect.The end of the light guide 3 is provided with a mirror coating 5, which reflects the incident light, so that the latter must once again pass the rupture 3f of the light guide 3, and be fed via the Y splitter 4 and the light guide limb 3h to the receiving diode 2. The mode of operation of the apparatus of Figure 5 is the same in principle as that of Figure 4.
However, as in this embodiment the light is double coupled at this embodiment the light is double coupled at the rupture, this embodiment is far more sensitive, than that shown in Figure 4. Consequently, one would not use this embodiment for measurement, but only to provide a qualitative indication of moisture deposited.
The enlarged beam path in Figure 5a shows that initially the light is conducted within the core 3c by total reflection without loss. In the region of a rupture 3f', which can be produced in any manner required, the protective tube 3e has been removed.
When this ruptured region is not bridged by a film of water, the light will emerge in the same manner as shown in Figure 3b for a roughened area. However if, as indicated in Figure 5a, the ruptured area 3f' is covered by a film of water 8, then total reflection again takes place, in a manner similar to that shown in Figure 3c.
If the intention is to measure the dew-point, i.e.
the temperature at which in a gas-vapour mixture the gas is just saturated with the quantity of the vapour which is present and below which condensation of the vapour takes place because of supersaturation, then apparatus of the kind schematically shown in Figures 6 and 7 will be required. In these arrangements, the damaged surface of the light guide is situated directly on a cooling element 7 constructed in a suitable manner, for example in the form of a Peltier element.
In the surface of the cooling element 7 a temperature sensor 6 is integrated which is arranged to determine the associated temperature when the dewpoint is exceeded.
The quantitative measurement of the dew-point is performed in a manner known per se, for example, as described in detail in United States Patent
Specification No. 3,528,278.
In Figure 8 there is illustrated a block circuit diagram for measuring apparatus of the invention.
The circuit is made up of two banked regulating circuits which cooperate with the optical dew-point sensor 3.
By means of a dew regulator 12, the light intensity detected by the receiver of the sensor 3 is used in any suitable manner to determine the theoretical value at which the deposit of dew takes place. This theoretical value is compared, at 13, with the temperature detected by the temperature measuring arrangement 6 located at the region of the surface damage. In this procedure, the cooling or heating element 7 is set by means of a temperature regulator 10 such that the theoretical value and the actual value coincide. When the theoretical value and the actual value do so coincide, the dewpoint has been reached, and this is indicated or recorded by display device 11.
Claims (8)
1. Apparatus for sensing fluids comprising a light guide coupled to receive light from a light source and to pass light to a light detecting device, wherein the light guide has in its surface an uneven region arranged to scatter light.
2. Apparatus as claimed in Claim 1, wherein said uneven region is an area of roughened surface.
3. Apparatus as claimed in Claim 1, wherein said uneven region is formed by a rupture in said light guide.
4. Apparatus as claimed in any preceding claim, wherein the light source and the light detecting device are disposed at opposite ends of the light guide.
5. Apparatus as claimed in any of Claims 1 to 3, wherein the light guide is connected to a Y-shaped light divider, a first limb of which is connected to the light source and the second limb of which is connected to the light detecting device, and wherein at its free end the light guide has an internal mirror coating.
6. Apparatus for measuring the dew-point of gases including sensing apparatus as claimed in any preceding claim, said measuring apparatus further comprising cooling means and temperature sensing means connected at said uneven region of the light guide, control means for said cooling means, and a temperature measuring means.
7. Apparatus as claimed in Claim 6, wherein said cooling means comprises a Peltier element.
8. Apparatus for sensing fluids substantially as hereinbefore described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3444830 | 1984-12-08 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8530134D0 GB8530134D0 (en) | 1986-01-15 |
| GB2170004A true GB2170004A (en) | 1986-07-23 |
| GB2170004B GB2170004B (en) | 1989-05-10 |
Family
ID=6252250
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8530134A Expired GB2170004B (en) | 1984-12-08 | 1985-12-06 | Dew point sensor |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS61198040A (en) |
| FR (1) | FR2574552B1 (en) |
| GB (1) | GB2170004B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2183344A (en) * | 1985-10-08 | 1987-06-03 | Sharp Kk | Sensor |
| GB2256270A (en) * | 1991-05-31 | 1992-12-02 | De Beers Ind Diamond | Determination of the condition of or change in state of an environment |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6228640A (en) * | 1985-07-31 | 1987-02-06 | Tomoo Matsuo | Damping light quantity sensor |
| JP2004108940A (en) * | 2002-09-18 | 2004-04-08 | National Institute Of Advanced Industrial & Technology | Dew point measuring device using optical waveguide |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1289146A (en) * | 1969-10-07 | 1972-09-13 | ||
| GB2105034A (en) * | 1981-09-04 | 1983-03-16 | Westinghouse Electric Corp | Fiber optic impurity detector |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2733594A (en) * | 1956-02-07 | dew-point detecting device | ||
| US3528278A (en) * | 1967-09-05 | 1970-09-15 | Technology Inc | Method and apparatus for determining the presence of vapor in a gas |
| FR2058851A5 (en) * | 1969-09-30 | 1971-05-28 | Amelkin Anatoly | |
| JPS4934850U (en) * | 1972-06-24 | 1974-03-27 | ||
| US3856404A (en) * | 1973-06-06 | 1974-12-24 | Phys Chem Res Corp | Method and apparatus for measuring vapor pressure |
| ZA745115B (en) * | 1973-09-07 | 1975-08-27 | Clupak Inc | Apparatus for compacting a nonwoven fabric to improve hand and drape |
| GB1463910A (en) * | 1975-08-21 | 1977-02-09 | Standard Telephones Cables Ltd | Liquid level sensor |
| US4311048A (en) * | 1980-02-21 | 1982-01-19 | Trw, Inc. | Liquid level sensing means |
| DE3217168C2 (en) * | 1982-05-07 | 1986-10-30 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., 8000 München | Fiber optic refractometer |
| JPS59137844A (en) * | 1983-01-27 | 1984-08-08 | Showa Electric Wire & Cable Co Ltd | Humidity sensor |
| GB8422910D0 (en) * | 1984-09-11 | 1984-10-17 | Lucas Ind Plc | Liquid level gauge |
-
1985
- 1985-12-04 JP JP27168685A patent/JPS61198040A/en active Pending
- 1985-12-06 GB GB8530134A patent/GB2170004B/en not_active Expired
- 1985-12-06 FR FR8518082A patent/FR2574552B1/en not_active Expired
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1289146A (en) * | 1969-10-07 | 1972-09-13 | ||
| GB2105034A (en) * | 1981-09-04 | 1983-03-16 | Westinghouse Electric Corp | Fiber optic impurity detector |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2183344A (en) * | 1985-10-08 | 1987-06-03 | Sharp Kk | Sensor |
| GB2183344B (en) * | 1985-10-08 | 1990-03-14 | Sharp Kk | Sensor |
| GB2256270A (en) * | 1991-05-31 | 1992-12-02 | De Beers Ind Diamond | Determination of the condition of or change in state of an environment |
| GB2256270B (en) * | 1991-05-31 | 1995-04-19 | De Beers Ind Diamond | Determination of the condition of or change in state of an environment |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2574552A1 (en) | 1986-06-13 |
| JPS61198040A (en) | 1986-09-02 |
| GB2170004B (en) | 1989-05-10 |
| GB8530134D0 (en) | 1986-01-15 |
| FR2574552B1 (en) | 1989-01-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |