WO2009056328A1

WO2009056328A1 - Active fiber-optic moisture sensor device

Info

Publication number: WO2009056328A1
Application number: PCT/EP2008/009200
Authority: WO
Inventors: Jürgen BÜDDEFELD; Jan Consbruch; Josef Elsbrock; Heinz Hess; Andreas Joschko; Rainer Kufferath
Original assignee: Hochschule Niederrhein
Priority date: 2007-11-02
Filing date: 2008-10-31
Publication date: 2009-05-07
Also published as: DE102007052796A1; DE102007052796B4

Abstract

Disclosed is an active fiber-optic moisture sensor device comprising an input optical waveguide (2) that is effectively connected to a light source (30) at one end while being connected to an optically transparent sensor head (1) at the other end, said sensor head (1) being provided with at least one optical boundary surface (3, 4, 29). The moisture sensor device further comprises an output optical waveguide (5) which is effectively connected to a light detector (35) at one end and is connected to the sensor head (1) at the other end. The input optical waveguide (2) and the output optical waveguide (5) are connected to an electronic evaluation unit (31). The light source (30) allows light to be introduced into the sensor head (1) by means of the input optical waveguide (2). The light can be fed to the light detector (35) from the sensor head (1) by means of the output optical waveguide (5) after being reflected at least once on the at least one optical boundary surface (3, 4, 29). In order to do away with the drawback of thermal inertia in previously known measuring systems while designing the moisture sensor device in a highly sensitive and perturbation-insensitive manner, the at least one optical boundary surface (3, 4, 29) is designed and/or arranged in a temperature-controllable fashion.

Description

Active fiber optic dew sensor device

The invention is directed to an active fiber-optic condensation sensor device comprising an input optical waveguide operatively connected at one end to a light source and at the other end to an optically transparent sensor head having at least one optical interface, and an output optical waveguide connected at one end to a light detector and at the other end to the sensor head. which are connected to an electronic evaluation unit, wherein by means of the light source by means of the input optical waveguide in the sensor head introduced and after at least one reflection on the at least one optical interface from the sensor head by means of the output optical waveguide can be fed to the light detector.

The invention further relates to an active fiber-optic condensation sensor comprising an input optical waveguide operatively connected to a light source at one end and an optically transparent sensor head having at least one optical interface, and an output optical waveguide operably connected to a light detector at one end and to the sensor head at the other end ,

Most dew point measurement systems consist of porous structures that absorb moisture. Among other things, this leads to contamination in the measuring system, which increasingly influences the stability of the characteristic curve. Passive optical measuring systems that work and operate on the principle of refraction at an interface between two media generally have smooth, non-hygroscopic interfaces, which pollute comparatively slightly. Optical measuring systems for level measurement, as described, for example, in GB 2 076 960 A and EP 0 450 175 A1, use a sensor head in the form of a liquid cone-facing circular cone, whose lateral surface forms the optical interface. In addition, from DE 100 41 729 Al a raindrop sensor and from US 6,582,658 Bl fiber optic special fibers are known, which also operate on the principle of refraction. A fiber-optic condensation sensor is known from DE 10 2005 016 640 A1.

A disadvantage of the measuring systems known from the prior art and the measurement methods carried out therewith is the poor thermal conductivity of the optical materials of the sensor head and the resulting thermal "inertia" of the measuring system due to the poor thermal conductivity of the optical materials and materials used for the Sensor head used in these optical sensors, this so-called passive fiber optic dew sensor is a thermally inert sensor that follows only slowly temperature changes.The passive fiber optic dew sensor is generally coupled to an object in which a dew is to be detected then a warning signal is generated and countermeasures, such as heating of the object, are initiated A determination of the dew point generally does not take place with this type of sensor.

There is a need to provide a fiber optic dew point sensor device suitable for use in both atmospheric pressure and atmospheric pressure applications. pressure as well as in the high pressure range at a pressure of several hundred bar is usable. In particular, for applications in the high pressure area, a pressure-stable design of the sensor device is required. Furthermore, it is desirable to provide a fiber-optic condensation sensor device, in particular a fiber-optic condensation sensor, which is distinguished by a compact and miniaturized structure and can be produced and manufactured cost-effectively in high quantities.

The invention has for its object to provide a fiber optic Betauungssensorvorrichtung, by which the above-mentioned disadvantage of the inertia of the measuring system is avoided and which has a high sensitivity with simultaneous noise immunity.

In a fiber optic Betauungssensorvorrichtung of the type described above, this object is achieved in that the at least one optical interface formed tempered and / or arranged.

Advantageous and expedient refinements and developments of the invention will become apparent from the corresponding dependent claims.

The optical fiber-based condensation sensor device according to the invention, which is active on account of the possibility of temperature control of the optical interface, provides an optical measuring system with low susceptibility to electrostatic and magnetic interferences and with a high measuring sensitivity. Due to the temperature of the optical interface, a local condensation of the optical interface is actively brought about, without that the actual dew point sensor surrounding measuring medium itself has the dew point temperature. The detected at the time of the detected by the light detector condensation at the interface and measured according to embodiment of the invention by the temperature sensor temperature of the interface corresponds to the dew point temperature of the condensed on the interface medium, which only selectively reaches this locally there. In this way, the dew point is actively determined even before the dew point is reached by the measuring medium surrounding the dew point sensor itself. This makes it possible to introduce countermeasures to prevent undesired condensation since the dew point temperature of the medium, with possibly unknown composition, can be measured or detected before the measuring medium has reached the dew point temperature outside in the environment of the condensation sensor.

In an advantageous embodiment, the invention therefore provides that the light detector is in operative connection with a temperature sensor measuring the temperature of the temperature-controllable optical interface.

In an advantageous embodiment, the invention provides that the input optical waveguide and the output optical waveguide and the at least one temperature-controllable optical interface are aligned with each other so that the transition from an undetected to a dewy state of at least one temperature-controllable optical interface is detectable.

In a development of the invention, it is also advantageous if the at least one boundary surface can be specifically temperature-controlled by means of a cooling system. By deliberately cooling down, depending on the field of application and the desired accuracy of to be determined dew point temperature, the active fiber optic Betauungssensorvorrichtung be controlled and regulated.

So that the cooling does not act on the measuring medium, it is provided in another embodiment of the invention that an insulating layer covers the surfaces of the sensor head with the exception of the at least one boundary surface, so that upon cooling, the at least one interface is the coldest outwardly directed element of the sensor head ,

It is particularly expedient for the use of a cooling system when the temperature control, in particular cooling, takes place on a surface of the sensor head which is not an interface, so that a temperature transfer takes place through the thermally highly conductive part and the at least one optical interface.

In a further development of the invention, it is provided that cooling of the sensor head takes place by means of metal and / or semiconductor structures applied to at least one interface according to the functional principle of the Peltier effect, so that a temperature difference in the form of cooling is produced when current flows through.

In order to determine the dew point temperature as accurately as possible, the invention provides in a further embodiment that the sensor head can be tempered following a step-shaped temperature cycle.

In a further development of the invention, the evaluation unit is in operative connection with a temperature sensor arranged in the measurement medium, so that further weather-related values can be determined by means of the electronic evaluation unit. To increase the compactness and to enable the miniaturization of the active fiber optic Betauungssensor- device, the invention provides in an embodiment that the thickness of the sensor head substantially equal to the diameter of the input and output optical waveguides used, so that the spatial spread of the divergently behaving light in Sensor head is limited.

In order to increase the sensitivity of the active fiber optic condensation sensor device, the invention further provides for the sensor head to be divided into parallel sensor head substructures optically connected to the optical waveguides. Specially shaped sensor head substructures may, for example, use the temperature-dependent refractive index of the sensor head material for temperature determination.

A particularly advantageous embodiment of the invention consists in that intermediate elements made of a thermally highly conductive material, in particular a metal material, are arranged between the sensor head substructures. As a result, the sensor head and in particular the thermally poorly conductive sensor head substructures can be cooled down faster and more effectively.

With further preference, the sensor head substructures have different functional properties, in particular for the detection of different substances in the measuring medium. Thus, the active fiber optic Betauungssensorvorrichtung is universally applicable to detect and compensate for the presence of different substances or groups of substances. In particular, forms of the sensor head that are outside of the influence of the measuring medium, can be used as a reference for the undetached state as well as for the degree of surface contamination of the interface or interfaces.

In a further embodiment, the invention provides that the sensor head or the sensor head substructures consist of a permeable material for selectable wavelengths of light. Due to the selective spectral behavior, individual coupled-out light intensities of sensor head substructures with their specific wavelength can be selectively read out and determined, so that different analytical measuring processes, such as different condensation events of different substances or substance groups, sensor adjustments or also spectral analytical measurements of colored measuring medium or material, with only a single sensor head are possible.

To further increase the sensitivity of the active fiber optic Betauungssensorvorrichtung the invention provides in an advantageous embodiment, that thermally conductive elements and optically conductive elements of the sensor head over a large area, in particular by juxtaposition, are coupled together. Thus, thermally conductive elements and optically conductive elements of the sensor head are connected to each other in such a way that the thermal contact resistance between the two consisting of different materials elements is minimized. In order to produce a better thermal contact, for example, a thermal compound can be used, which increases the sensitivity and thus the reaction speed of the Betauungssensorvorrichtung. A further possibility for increasing the sensitivity of the active fiber-optic condensation sensor device is given in an embodiment of the invention by applying a partially transparent coating of a thermally highly conductive material, in particular an optically transparent metal coating, to the at least one interface of the sensor head or to the surface of the sensor head substructures is. In this way, a uniform temperature distribution and a surface tension compensation of the condensate on, for example, an interface are achieved, which is configured in a mixed structure or consists of sensor head substructures with interposed thermally highly conductive intermediate elements. The condensate formed during condensation forms primarily at the coldest point on the mixed-structured sensor head surface, ie the thermally better conductive structures. On these thermally better conductive structures, a sufficient amount of condensate must first accumulate, so that a wetting jump takes place on the adjacent optical material, ie, so that wetting on the thermally better conductive structures expands and spreads to and across the adjacent optical structure , On a homogeneous surface, such as a metal coating, with the same surface material and lower partial temperature differences is a wetting or their areal distribution over underlying structures temporally faster and more uniform instead, because no more direct material interfaces are available, but covered by the coating and are covered.

A particularly advantageous embodiment of the invention with regard to the compactness of the device is in that each sensor head part structure is assigned in each case an output optical waveguide whose respective diameter substantially corresponds to the thickness of the respective sensor head part structure.

In a further development of the invention, a condensation of the optical sensor head substructures takes place by means of a finely divided mixed structuring of optical sensor head substructures and thermally well-conducting intermediate elements. In this mixed structuring, the thickness of the individual optical sensor head substructures is dimensioned such that it is substantially smaller than a measurement-relevant condensate drop, so that condensation can already be detected on a microscopic scale. The size of a measurement-relevant condensate drop is dependent on the field of application of the active fiber optic Betauungssensorvorrichtung, so that the thickness of the sensor head substructures is set in advance according to the application.

In a further embodiment of the invention, the sensor head or a respective sensor head part structure has a linear shape, a non-linear shape or a semicircular shape. When using sensor head part structures, it is also conceivable to use different shapes for individual sensor head partial structures mixed.

A possible embodiment of the invention also consists in the fact that a shape of the sensor head or of the sensor head part structures is selected and provided, which makes it possible to determine the dew point temperature without the temperature sensor. This special shape then makes it possible to determine from the measured difference of the light coupled into the sensor head and the light coupled out of the sensor head by means of a mathematical calculation by solving a differential equation of n-th order to calculate the dew point temperature, so that a temperature of a tempered interface measuring temperature sensor can be omitted.

A particularly expedient embodiment of the invention consists in that, in the case of a semicircular shape of the sensor head, the light is coupled into a region of the sensor head close to the edge. In the case of a semicircular shape of the sensor head, the effect is utilized that the light coupled into the sensor head propagates only in an optically conductive region close to the edge between an outer optical interface and an inner optical reflection surface.

Due to the fact that the coupled-in light propagates only in an area close to the edge, it is an advantage of the invention if at least part of the sensor head in which light coupled in via the input optical waveguide does not propagate consists of a thermally highly conductive material, in particular a Metal material, consists. As a result, the sensor head can be cooled down more effectively and faster, and the dew point of the measuring medium surrounding the sensor head can be determined more quickly.

Moreover, it is in a further embodiment of the invention finally advantageous if a near-edge region of the sensor head is formed of an optically conductive material whose thickness is reduced or reduced so far that the reflection of the coupled via the input fiber in the sensor head light between the outer optical interface and an inner optical reflection surface of the near-edge region takes place. This is one low-cost and simple design for a non-linear sensor head given because the consisting of a thermally highly conductive material existing part or core of the sensor head with a film or a transparent lacquer layer as an interface in which the light can propagate.

Furthermore, the signal transmission to the electronic evaluation unit in pressurized or separable measuring ranges, such as in applications in the high pressure range, by optically transparent and / or permeable to selective wavelengths sealing materials.

A controller-based evaluation allows in the subject invention a self-calibration and error compensation of the active fiber optic Betauungssensorvorrichtung. In addition, it is possible to use a non-electrical and potential-free measuring principle in the measuring medium, ie no electrical components are arranged in the measuring medium during dew point determination. Furthermore, the cooling system is designed for both Peltier elements and other cooling systems. By using a special measuring method and applying a certain temperature cycle while cooling down the sensor head, the sensitivity of the dew sensor device is increased. Due to the specially structured construction of optical and thermally conductive elements, such as the sensor head substructures with interposed intermediate elements or as for example on the existing of an optically conductive material sensor head metal coating, the thermal change behavior of the active fiber optic Betauungssensorvorrichtung is improved , Overall, the active fiber-optic condensation sensor device according to the invention for determining the dew point of a medium or measuring medium is characterized by a compact and miniaturized structure and has a high sensitivity with the possibility of quantitatively determining the wetted measuring surface. A non-hygroscopic, smooth, robust interface allows stable long-term performance and ensures that no foreign matter or contamination can accumulate. Impurities and / or small amounts of, for example, thin oil layers in the measuring medium, which would lead to failure in systems with hygroscopic materials, are compensated by the condensation sensor device. There is no need for adjustment in the manufacture and operation of the active fiber optic dew sensor device, because the measurement-specific angle for refraction of light entering refraction is determined by the shape of the sensor head as it is manufactured. Thus, the condensation sensor device is virtually maintenance-free. The reasonably priced active fiber optic condensation sensor device is long-term stable and, due to the optical measuring principle, not susceptible to interference and is characterized by a robust construction, so that a broad field of applications is possible.

In an active fiber optic condensation sensor of the type described, the above object is inventively achieved in that the at least one optical interface is designed to be tempered.

In this case, the condensation sensor in an advantageous development is further distinguished by the fact that the Sensor head has a temperature of the at least one optical interface measuring temperature sensor.

In a particularly advantageous manner, the dew point sensor can be used in a dewatering device, so that the invention further provides that the dew point sensor is part of a dew point sensor device according to one of claims 1 to 22.

In order to be part of the condensation sensor device according to the invention, it is also expedient if the condensation sensor has the features of the sensor head of the condensation sensor device according to one of claims 1 to 22, which the invention also provides.

The dew point sensor according to the invention has the same advantages as described above in connection with the active fiber optic dew sensor device.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations. The scope of the invention is defined only by the claims.

Further details, features and advantages of the subject matter of the invention will become apparent from the following description taken in conjunction with the drawings in which exemplary preferred embodiments of the invention are shown. In the drawing shows:

1A is a side view of a first embodiment of the active fiber optic Betauungssensorvorrichtung, 1B is a front view of the active fiber optic Betauungssensorvorrichtung of the first embodiment,

FIG. 1C is another front view of the active fiber optic dew sensor device of the first embodiment; FIG.

FIG. ID is another front view of the active fiber optic dew sensor device of the first embodiment; FIG.

2A is a side view of a second embodiment of an active fiber optic dew sensor device,

2B is a front view of the active fiber optic Betauungssensorvorrichtung of the second embodiment,

3A is a side view of a third embodiment of an active fiber optic dew sensor device,

3B is a front view of the active fiber optic Betauungssensorvorrichtung of the third embodiment,

3C is a side view of the third embodiment of an active fiber optic Betauungssensorvorrichtung, FIG. 3D another side view of the third embodiment of an active fiber optic dew sensor device, FIG.

3E is yet another side view of the third embodiment of an active fiber optic dew sensor sensor apparatus;

4 shows an exemplary view of temperature profiles during cooling down of the sensor head,

5A is a schematic representation of a controller-based evaluation,

5B is a schematic representation of another controller-based evaluation,

6 is a side view of an optical sensor head in the form of a prism,

7 is a side and front view of the active fiber optic Betauungssensorvorrichtung of the first embodiment,

FIG. 8 is a side view of the active fiber optic dew sensor device of the second embodiment; FIG.

9 is a side and front view of the active fiber optic dew sensor device of the third embodiment

Embodiment and Fig. 10 exemplary usable basic shapes of sensor heads.

The active fiber optic condensation sensor or the active fiber optic condensation sensor device (a-FoBt) according to the invention is based on a passive fiber optic condensation sensor (p-FoBt), which works on the principle of total reflection. In this principle, the light coupled into a sensor head 1 and originating, for example, from a light source 30 in the unexploded state of the sensor head 1 at an optical interface of two media, in the context of the invention as a contact surface between the surface of the sensor head 1 and the sensor head 1 surrounding Air (measuring medium) is defined, completely reflected. At the onset of condensation, i. when wetting this optical of the interface with liquid molecules or condensate, the coupled into the sensor head 1 light is no longer completely reflected at the interface, but partially refracted at the interface and emitted from the sensor head 1 to the outside. As a result, the light arriving at an output optical waveguide 5 decreases in intensity and indicates incipient condensation on the interface of the sensor head 1. Due to the poor thermal conductivity of the optical materials used for the sensor head 1, a passive fiber-optic condensation sensor is a thermally inert sensor, which only follows the temperature changes in the measuring medium slowly or delayed passively.

Illustrated in FIG. 10 are exemplary basic forms of an optical sensor head 1 of passive fiber optic condensation sensors, some of which are within the scope of the present invention Invention of an active fiber optic Betauungssensor- device (a-foBt) can be used.

With the exception of the first sensor head 1 (Rf = I), all the other sensor heads 1 shown (Rf = 2, Rf = 3, Rf = 4,... Rf = n) have a parallel connection of input optical waveguide 2 and output optical waveguide 5 for input and output Coupling of the light in the sensor head 1 on. In the case of linear shapes of the sensor head 1, the number of reflection angles (Rf) corresponds to the number of optical boundary surfaces at which the light coupled into the sensor head 1 is reflected. With only one reflection angle (RF = I), the input optical waveguide 2 and the output optical waveguide 5 are arranged at a specific angle to one another on the sensor head 1. The coupled-in light is reflected in the unexploded state of the sensor head 1 at one boundary surface and coupled out into the output optical waveguide 5. At a number of at least two reflection angles, as mentioned above, the input optical waveguide 2 and the output optical waveguide 5 are arranged in parallel with each other. The coupled-in light is reflected at the interfaces in the unexploded state of the sensor head 1 and coupled out into the output optical waveguide 5.

As the number of reflection angles increases, the shape of the sensor head 1 approaches a circular shape (Rf = n). The peculiarity of the semicircular shape is that the light divergently coupled into the sensor head 1 or the light beam is no longer distributed and propagated in the peripheral region of the sensor head 1 in the entire semicircle, but only reflected at shallow angles along the round boundary surface of the sensor head 1 becomes. In this optical effect, the propagation of the injected light takes place only in a narrow edge region in the manner of a skin effect, in which the current flowing through a line is displaced to the edge of the line. From this multiplicity of different reflection angles, sufficiently many are close to the optical limit angle (42 ° for glass / air), so that this shape of the sensor head 1 also indicates condensation.

It should also be noted that the light is distributed divergently in all forms of the sensor head 1, wherein in the first four representations of FIG. 10 (Rf = I to Rf = 4) only one course of the reflected light beam is shown by way of example.

The sensor head 1 should be as flat as the optical fibers 2, 5 for the sensor head shapes used in the invention. The thickness of the sensor head 1 should correspond substantially to the diameter of the input and output optical waveguides 2 and 5 used, so that the light coupled into the sensor head 1 propagates divergently substantially only in one direction.

As an exemplary shape for a sensor head 1 of the first and second embodiments of the present invention, a triangular shape or a prism (Rf = 2) shown in FIG. 6 is used. The third embodiment uses a semicircular shape for the sensor head 1 and exploits the optical effect occurring in this round shape (Rf = n).

In the triangular shape of the sensor head 1 with two reflection angles (Rf = 2), the above the input light wave propagates Head 2 coupled light divergent in the sensor head 1 off. As can be seen in FIG. 6, the light in the undetached state of the interfaces 3 and 4 is reflected on the latter in such a way that it is fed back into the output light waveguide 5 rotated through 180 °. The angles of the prism-shaped sensor head 1 are selected so that the majority of the divergent light is just below the critical angle of total reflection. With onset of condensation of the sensor head 1 now occurs a media change from air to water at the optical interfaces 3 and 4. As a result, the limiting angle of the total reflection and parts of the light left due to the onset of refraction of the sensor head 1. The light difference occurring, ie the increase in attenuation or the attenuation of the light intensity, is the actual measured variable that indicates a condensation.

The sensor head 1 formed in the form of a prism or a triangle of the first embodiment of the active fiber optic condensation sensor device is shown in FIGS. 1A to 1 and 7 and has two interfaces 3 and 4. However, any other linear shape as well as a non-linear shape may be used for the sensor head 1.

The sensor head 1 of the first embodiment is divided into mutually parallel sensor head substructures 1.1 to ln. Light is guided via an input optical waveguide 2 into an optical input coupler 17, which then propagates through its divergent propagation behavior into the six sensor head substructures 1.1 to ln connected to the optical input coupler 17, which are formed in the form of triangles. The selected number of sensor head substructures is exemplary only and one of them may be different numbers of triangles are selected. The six sensor head substructures 1.1 to ln are arranged one behind the other and adjacent to each other. By reflection of the light beam at the optical interfaces 3 and 4, the coupled into the sensor head substructures 1.1 to ln light is reflected by 180 ° and rotated and passed through an optical output coupler 18 in a second optical waveguide, the output optical waveguide 5. The output optical waveguide 5 collects the light coupled out of the sensor head substructures 1.1 to ln and transfers it in the form of a signal to an electronic or optoelectronic evaluation unit 31, which is shown in FIGS. 5a and 5b.

Parallel to the plan side of the sensor head substructures 1.1 to ln are intermediate elements 8 in the form of triangles, which are thermally connected to a base plate 9. The five illustrated intermediate elements 8 are made of a thermally highly conductive material, such as a metal material, and are disposed between the sensor head substructures 1.1 to ln. In this embodiment, the intermediate elements 8 are made of aluminum, which has a good or high thermal conductivity. However, other materials with a high thermal conductivity can also be used. Accordingly, the sensor head 1 of the first embodiment is sandwiched with thermally highly conductive layers. This sandwich-type construction of the sensor head 1 comprising sensor head substructures 1.1 to ln with intermediate elements 8 arranged therebetween leads to mixed-structured interfaces 3 and 4 which consist of alternately thermally well-conducting sections and optical sections which are arranged adjacent to one another and thus coupled to one another over a large area. The base plate 9 is also made of a thermally highly conductive material. The thermally connected to the base plate 9 five intermediate elements 8 can be specifically controlled via the base plate 9 by means of a cooling unit 10. By way of example, a Peltier element can be used for cooling, which generates a temperature difference when current flows through. Accumulating waste heat can be dissipated, for example via a heat sink 11. In order to cause condensation only on the optical interface 3, all elements of the cooling system 10 and 11 which are not on the optical interface 3, must be airtight and thermally sealed. The demolition edge of insulating layers 12 shown in FIG. 1A, which cover the entire surface of the side surface of the sensor head 1 or of the outer sensor head partial structures 1. 1 and 1 n, is shown correspondingly only for a better insight into the underlying structures. The insulating layers 12 prevent condensation at undesired locations so that the metal structure formed on the interface 3 forms the coldest point in the system, ie, the interface 3 is the coldest outward element of the dew sensor device.

By omitting the interface 4, the entry of the cooling by means of the cooling unit 10 can take place from this point, wherein the sensor head 1 still remains sufficiently sensitive. The interface 3 thus represents an active interface of the sensor head 1, since it is due to the cooling down by means of the cooling unit 10 causes condensation, although in the measuring range of the dew point is not really reached. This active interface 3 is then alternately with a thermally conductive layer, an intermediate element 8 consisting of, for example, aluminum, and an optical layer, a sensor head part structure 1.1 to ln consisting of polymethyl methacrylate (PMMA) or the like, designed.

As the sensor head 1 cools down by means of the cooling unit 10, condensation first occurs on the surface of the thermally conductive intermediate elements 8, which then settles on the surfaces of the thermally inert sensor head substructures 1.1 to 1.n, i. of the optical PMMA layers. To improve the distribution of condensate on the optical PMMA layers, i.e., the condensation caused by the cooling down. the sensor head substructures 1.1 to 1.n, between the struts-formed aluminum layers, i. To reach the intermediate elements 8, on the interface 3, the surface of the interface 3 with an optically transparent metal coating 13 can be occupied.

In this regard, coating trials with gold plating (by so-called sputtering) on the PMMA layer were successfully carried out on the dewing surface or the interface 3. It was recognized that structures can be applied by previously covering and partially transparent to light-tight coatings. Using the example of a prism transparent to the sensor surfaces coated prism, the side surfaces were gilded more to provide a better thermal transition for a foreign temperature.

So that the thermally slower sensor head substructures 1.1 to 1 respond more quickly to a cooling down, We recommend a large-scale coupling of thermally conductive elements and optically conductive elements. An improvement in the reaction rate of the thermally inert sensor head substructures can be achieved, for example, by the intermediate elements 8 completely covering the side surfaces of the respective sensor head substructures 1.1 to ln. In addition or alternatively, a large-area coupling can also be realized in that by means of the cooling element 10 and the base plate 9, the cooling is introduced into the sensor head 1 on the entire surface of the interface 4.

In order to achieve a uniform distribution of the condensate formed on cooling down on the surface of the interface 3, so that the thermally inert sensor head substructures 1.1 to l.n are wetted, a fine-grained mixed structuring of optical sensor head substructures 1.1 to 1.n and thermal intermediate elements 8 is desirable. In this case, the thickness of the respective sensor head substructures 1.1 to 1n and intermediate elements 8 should preferably be dimensioned such that they are smaller than a condensate droplet generated by the cooling down.

A division of the active fiber optic Betauungssensor- device in sensor head part structures 1.1 to ln, as shown in Fig. IC, opens up the possibility to provide them with special properties. Thus, the presence of other substances or substance or condensate groups in the measuring medium can be detected or compensated by different forms of the individual sensor head substructures 1.1 to 1, ie by prior determination of the critical angle for a particular condensate. Forms of sensor head substructures 1.1 to ln which are outside of an flow through the measuring medium, can be used as a reference for the undetached state and for the degree of surface contamination. Specially shaped sensor head substructures 1.1 to 1 can, for example, use the temperature dependence of the material used to determine the temperature. Materials with selective spectral behavior enable further analytical measurements. As materials, for example, plastics come into consideration, which cloud in moisture absorption and thus decrease in their translucency. It is also possible to use materials with dyes that change color when exposed to moisture or temperature changes. When such a material is used and applied, for example, to the interface of the sensor head or sensor head substructure, it reflects certain wavelengths which it absorbs upon color change. Thus, with different sensor head substructures, one obtains a platform which can be extended with other functions so that the sensor can be used as a combination sensor or combination sensor.

In addition, the coupling-out and coupling-in of the light into the sensor head substructures 1.1 to ln can be done both via additional input optical fibers 5.1 to 5.n, as shown in FIG. 1C, and with the aid of filter masks 27, as shown schematically in FIGS. ID and 5B , respectively. Furthermore, only a certain spectral region of the light can be coupled into the sensor head substructures 1.1 to ln, in which a sensor head substructure 28 consisting of a spectrally selective material itself acts as a kind of filter which transmits only a certain portion of the light and thus couples in, as in FIG Figures ID and 5B is shown. The different spectral components that over the common output optical waveguide 5 are guided to the optoelectronic evaluation unit 31 can then be separated again by means of optical filter 34 or wavelength-specific filter 34 in front of the light detector 35 and evaluated individually by the evaluation unit 31, as shown schematically in Fig. 5B.

The second embodiment of the active fiber optic condensation sensor device is shown by way of example in FIGS. 2A, 2B and 8. As mentioned above, the illustrated sensor head 1 has a triangular shape or the shape of a prism. In the second embodiment as well, light is coupled into the sensor head 1 via the input optical waveguide 2. By reflections at the optical interfaces 3 and 4, the light beam is rotated by 180 ° and passed into the output optical waveguide 5 and evaluated by an opto-electronic evaluation unit 31, which is shown in FIGS. 5A and 5B.

The sensor head 1 of the second embodiment is entirely made of an optically conductive material such as polymethyl methacrylate (PMMA) and has no sensor head part structures. The thickness 20 of the sensor head 1 shown in FIG. 2B should substantially correspond to the diameter of the input and output optical waveguides 2 and 5 used, so that the light coupled into the sensor head 1 propagates divergently substantially only in one direction.

The cooling unit 10 of the second embodiment consists of a p-, n-doped semiconductor pair 6, which is connected via a metal strip 7 with the optical interface 3 of the sensor head 1. To get a better thermal Contact of interface 3 and metal strip 7 produce, for example, a thermal paste can be used. This additionally prevents condensate 19 from getting under the contact surface. Alternatively, the metal strip 7 may be a metal coating applied to the interface 3, the cross-section of which is designed for the corresponding current intensity of the cooling unit 10 or of a Peltier element.

The semiconductor pair 6 has at one of its two end faces 14 a contact surface (positive pole) to the n-doped semiconductor and at the end face 15 a contact surface (negative pole) to the p-doped semiconductor. If a current is now passed through the upper end faces 14 and 15 of the semiconductor pair 6, the coldest point in the system, at which condensate 19 forms when the dew point temperature is reached, is formed at the contact surface with the sensor head 1 in the form of a prism. When exceeding a certain amount of condensate and the interface 3 is wetted and parts of the injected light by refraction of the sensor head 1 withdrawn. By means of an optically transparent metal coating 13, this wetting of the optical interface 3 is considerably improved on account of the same material, the dipole property of water and the same temperature level. A condensation of the interface 4 will be delayed in time wetting of the interface 3, because the interface 3 is due to the cooling unit 10 arranged there in the form of the semiconductor pair 6, the coldest point in the measuring system.

The heat generated in the region of the power supply at the ends of the semiconductor pair 6 waste heat must over the

Heatsink 11 are derived, which, for example by means of a holder for the semiconductor pair 6 can be made, which serves the heat dissipation and the power supply.

The arranged between the semiconductors of the semiconductor pair 6 insulating layer 12 prevents a metrologically unrecognizable condensate formation in the bottom region between the two semiconductors of the semiconductor pair 6. The arrangement and number of heatsink 11 can be varied accordingly on both sides of the semiconductor pair 6. Also, a plurality of semiconductor pairs 6 may be arranged on an interface 3 or on both interfaces 3 and 4, so that a large-area coupling of thermal and optical elements of the Betauungssensorvorrichtung is achieved. It should be noted that this design is designed for both the high pressure and the normal pressure range.

In the first and second embodiments, a change of the optical measurement signal is caused by accumulation of condensate on at least one of the optical interfaces 3 and 4. When the dew point temperature is reached, this condensation starts at the coldest point on the surface of the sensor head 1, ie the corresponding boundary surface 3 and / or 4. If the sensor surface and thus the boundary surface 3 and 4 consist of thermally differently conducting, mixed-structured materials (PMMA 1.1-ln and aluminum 8 or PMMA and metal plate 7) as in the first and second embodiments, only the better thermally conductive structures stiffen. A signal change only starts when the amount of condensate is sufficient to wet adjacent optical structures as well. This delay in wetting can be achieved by the application of optically semi-transparent, thermally conductive layers (eg by sputtering), which has only one exit into the Sensor head substructures 1.1 to 1-n coupled light and no entry of light from the measured medium in the sensor head substructures 1.1 to ln enable reduced.

Further improvement of the responsiveness of the mixed-structured interfaces as they are in the first and second embodiments can be achieved by utilizing the different thermal inertia of the materials used. By way of example, FIG. 4 shows the method for determining the dew point by means of the condensation sensor device of the first and second embodiment by the step-shaped measuring profile when the sensor head 1 or the sensor head partial structures 1.1 to 1 are cooled down. The line 26 corresponds to the temperature that assumes the optical material of the sensor head 1 when cooling down, whereas the line 21, the temperature of the thermally highly conductive material when cooling down the sensor head 1 reflects. By cooling the sensor head 1, the temperature T or the damping D of the thermally better conductive material (characteristic curve 21) decreases faster than that of the sensor head 1 or its sensor head substructures 1.1 to ln optical material (characteristic 26). If now the cooling unit 10 is switched off briefly after reaching a first stage 25, then the thermally better conductive material heats up faster than the optical material. If both materials have fallen below the characteristic curve of the dew point temperature 22 at this point in time, the condensate formed on the thermally better conducting structure is released by heating and can be absorbed by the briefly cooler optical structure drop. As a result, the fed back optical power characteristic 23 or optical attenuation characteristic 23 abruptly, because the onset of refraction reduces the amount of light returned. When cooling down both materials, the falling temperature of the optical material will follow the thermally more conductive material at a time interval. Now, if the cooling is suspended after both materials have fallen below the dew point, the thermally better conductive material heats up faster. This will make the bound

Condensate released at the thermally better conductive material and condenses instantaneously on the still colder

(slower) optical material. This is the moment which, due to the drop of the feedback optical power characteristic 23 or attenuation characteristic 23 at point 24, indicates condensation of the interface 3, 4 which is detected by the light detector 35. By means of a coupled to the corresponding interface 3, 4 and in operative connection with the evaluation unit 31 and the light detector 35 temperature sensor 38, which is shown schematically in Figures 5A and 5B, the dew point temperature is detected at this moment, the thus by means of the targeted and controlled cooling. The temperature sensor 38 forwards the information of the dew point temperature to the evaluation unit 31. A processor (CPU) of the evaluation unit 31 controls and / or controls, for example, the supply of coolant from a cooling periphery 32 to the cooling unit 10. Further, the processor can control and / or regulate the step-shaped temperature cycle 25. A fast but also rough determination of the dew point is possible by large temperature intervals or stages when cooling down. A more precise determination of Dew point temperature is in contrast possible by small temperature intervals or temperature levels.

The temperature sensor 38 has the task of determining and / or measuring the temperature of the surface of the sensor head 1 at the moment of the condensation detected by the light detector 35 and determined optically. This determined and / or measured value of the temperature then corresponds to the dew point temperature of the substance condensed on the sensor surface. The dew point temperature determined in this way is an important measured value and specifies the condensation. As temperature sensor 38 is any measuring system into consideration, which can display and determine the surface temperature. A sensible temperature sensor 38 is an electronic, semiconductor, or resistance change based temperature sensor 38 cooperating and operating with electronic evaluation 31 and the CPU. The terminals of such a temperature sensor 38 must be isolated from the condensate and air. The quality of the mechanical and thermal connection and coupling of the temperature sensor 38 to the Betauungssensoroberflache or to the interfaces 3 and / or 4 is crucial for the accuracy of the dew point measurement and can be improved, for example by means of a thermal paste.

The third embodiment of the active fiber optic condensation sensor device is shown by way of example in FIGS. 3A to 3E and 9 and exploits the special optical effect which occurs only at roundish interfaces. In this semi-circular shape of the sensor head 1, the injected light does not propagate in the entire semicircle when irradiated in the edge region of the sensor head 1, but is only propagated at shallow angles along the reflected round optical interface 29 of the sensor head 1.

The sensor head 1 shown in Fig. 3A is made of an optically conductive material such as polymethylmethacrylate (PMMA), and like the second embodiment has no sensor head part structures. The input optical waveguide 2 and the output optical waveguide 5 are arranged in the region near the edge of the sensor head 1. The light is thus coupled in via the input optical waveguide 2 in an area near the edge of the sensor head 1, so that the above-mentioned effect predominates and in the undetached state of the sensor head 1 the coupled light only in a narrow edge section along the interface 29 at shallow angles along the round boundary surface 29 is reflected and coupled via the output optical waveguide 5. When condensation of the interface 29 sets in, the coupled-in light is refracted at the interface and comes out of the sensor head 16. The right of the two condensate droplets 19 shown in FIG. 9 is small with respect to the left condensate droplet 19, so that the coupled-in light is only slightly refracted and the light intensity of the coupled-out light decreases only slightly. In contrast, the larger of the two condensate drops causes a stronger refraction of light of the coupled light at the optical interface 29, so that the intensity of the coupled-out light with respect to the coupled-in light decreases more.

The condensation sensor device of the third embodiment also has, for cooling down the sensor head 1, the cooling unit 10, resulting waste heat being dissipated via the cooling body 11. Cover insulating layers 12 the side surfaces and the base of the sensor head 1, so that a non-technically usable condensation is prevented at undesirable locations and the interface 29 is the coldest outwardly facing element of the Betauungssensorvorrichtung. In this embodiment as well, the thickness of the sensor head 1 should substantially correspond to the diameter of the input and output optical waveguides 2 and 5 used, so that the light coupled into the sensor head 1 propagates divergently substantially only in one direction.

In order to improve the response speed of the sensor of the third embodiment in cooling down, at least a part 16 or the core 16 of the sensor head 1, in which the coupled light does not propagate and which consists of the thermally inert PMMA material, has been removed is shown in Fig. 3C. The core 16 of the sensor head 1 is replaced by a thermally highly conductive material, such as aluminum, whereas the remaining edge region of the sensor head 1 consists of the optically highly conductive material (PMMA), as shown in Fig. 3D. This structure of the sensor head 1 of optically and thermally conductive materials or structures also designates a mixed-structured sensor head 1. If now light via the input optical waveguide 2 in the optical edge structure of the sensor head 1, ie in a region near the edge in the vicinity of the optical interface 29, coupled this light is reflected along the optical interface 29 of the edge structure and passes via the output optical waveguide 5 to the optoelectronic evaluation unit 31, which is shown in Figures 5A and 5B. Thus, the coupled into the sensor head 1 light propagates only in an optically conductive, near the edge region between the outer optical Interface 29 and an inner optical reflection surface 33 from. The core 16 of the sensor head 1 can be specifically controlled via the cooling unit 10, for example by a Peltier element, so that the corresponding dew point temperature can be reached on the boundary surface 29. The insulating layers 12 prevent condensation outside of the interface 29, whereby cooling-related waste heat is dissipated, for example via the heat sink 11.

Instead of replacing the core 16 of the sensor head 16 with a thermally highly conductive material, it is also conceivable instead to make a semicircular base body of a thermally highly conductive material and this with a thin film or a transparent lacquer layer as an interface 29, as in Fig. 3E shown to be provided. In the film or the film area and the transparent lacquer layer, the coupled-in light can propagate in accordance with the above explanations. The advantages of this alternative embodiment of the third embodiment are that the cold created during cooling down can only escape through the thin film region or through the thin lacquer layer, which forms the coldest region in the measuring field. By using a film or a transparent lacquer layer, a reflective surface structure is thus already given. In this case, this optically conductive surface structure or its thickness is reduced or reduced to such an extent that the reflection of the light coupled into the sensor head takes place between the outer optical interface 29 and the inner optical reflection surface 33. Furthermore, this embodiment has a simple and inexpensive construction. Also, the dew sensor is the third Easy to clean embodiment and used in high pressure areas.

The method for determining the dew point described for the first and second embodiments can of course also be used in the third embodiment, for which reason reference is made to the above explanations of the method. The temperature sensor 38 used here corresponds to the temperature sensor 38 used in the first and second embodiments, so that reference is also made to the relevant explanations.

The evaluation of the measurement signals, which is carried out by the light detector 35 of the optoelectronic evaluation 31 and which is determined by means of one of the three embodiments of the active fiber optic condensation sensor device described above, is based on the differential measurement of the light intensity of light coupled in and out of the sensor head between dew and non-dew. The light detector 35 measures the light intensity and detects dewing when the light intensity decreases, the dew point temperature being detected by the temperature sensor 38 at the moment of the detected condensation. Due to the active cooling of the sensor head 1 or its sensor head substructures 1.1 to 1.n defined operating states are adjustable, which allow a recalibration of the sensor and a deduction of contamination or other influences.

Likewise, in all three exemplary embodiments explained above, by means of an additional temperature sensor 37, which is arranged in the measuring medium as shown in FIGS. 5A and 5B, due to the knowledge of temperature and dew-point temperature, further weather-related Values can be calculated using the optoelectronic evaluation 31. Examples would be relative and absolute humidity, partial pressure of water vapor, saturation vapor pressure.

The invention improves the thermal conductivity of the optical sensor head and the change behavior while maintaining the optical functionality for detecting incipient condensation by means of a specially structured construction of optical and thermally conductive elements. By means of the cooling system 10, 11 in the form of the Peltier element and the temperature sensor 38 coupled to the interface 3, 4 or 29, an accurate determination of the dew point is possible. But even without the described cooling system 10, 11, the sensor head 1 according to the invention will be due to its structured structure of thermally highly conductive structures and optically conductive structures compared to a passive fiber optic Betauungssensor less thermal, because the sensor head by means of thermally well conductive structures "faster In addition, with the aid of the controller-controlled electrical or optoelectronic evaluation unit 31, further weather-related data, such as, for example, the relative and the absolute humidity, the partial pressure of water vapor and the saturation vapor pressure, can be calculated The special features of the active fiber optic condensation sensor device as measuring system are the simple and robust construction, so that no adjustment during production and operation is necessary ive fiber optic Betauungssensorvorrichtung with measuring system is thus long-term stable and due to their optical measuring principle against interference relatively unreliable.

With light, the input optical waveguide 2 is fed by light emitted by the light source 30 or emitted electromagnetic radiation, in particular of human electromagnetic radiation visible.

Claims

claims

1. Active fiber optic Betauungssensorvorrichtung comprising a one end with a light source (30) in operative connection and at the other end with an optically transparent, at least one optical interface (3, 4, 29) having sensor head (1) connected input optical waveguide (2) and one end with a light detector (35) in operative connection and at the other end with the sensor head (1) connected output optical waveguide (5), which are connected to an electronic evaluation unit (31), wherein by means of the light source (30) light by means of the input optical waveguide (2) in the sensor head (1 ) and after at least one single reflection at the at least one optical interface (3, 4, 29) from the sensor head (1) by means of the output optical waveguide (5) to the light detector (35) can be supplied, characterized in that the at least one optical interface (3, 4, 29) tempered trained and / or arranged.

2. Active fiber optic Betauungssensorvorrichtung, characterized in that the light detector (35) with a temperature of the temperature-controllable optical interface (3, 4, 29) measuring the temperature sensor (38) is in operative connection.

3. Active fiber optic Betauungssensorvorrichtung according to claim 1 or 2, characterized in that the input optical waveguide (2) and the output optical waveguide (5) and the at least one temperature-controlled optical interface (3, 4, 29) are aligned with each other so that the transition from an undetected to a dewy state of at least one temperature-controllable optical interface (3, 4, 29) is detectable.

4. Active fiber optic Betauungssensorvorrichtung according to any one of the preceding claims, characterized in that the at least one boundary surface (3, 4, 29) by means of a cooling system (10, 11) is specifically temperature controlled.

5. Active fiber optic condensation sensor device according to claim 4, characterized in that an insulating layer (12) covers the surfaces of the sensor head (1) with the exception of the at least one interface (3, 4, 29), so that upon cooling, the at least one interface ( 3, 4, 29) is the coldest outwardly directed element of the sensor head (1).

6. Active fiber optic Betauungssensorvorrichtung according to claim 4 or 5, characterized in that the temperature, in particular cooling on a surface of the sensor head (1), which is not an interface (3, 4, 19), so that a temperature transfer by the thermally good conducting part (8, 16) and the at least one optical interface (3, 4 29) is carried out therethrough.

7. Active fiber optic Betauungssensorvorrichtung according to one of claims 4 to 6, characterized in that a cooling of the sensor head (1) by means of at least one interface (3, 4) applied metal and / or semiconductor structures (6, 7) according to the principle of operation Peltier effect takes place.

8. Active fiber optic Betauungssensorvorrichtung according to one of claims 4 to 7, characterized in that the sensor head (1) following a step-shaped temperature cycle is temperature controlled.

9. Active fiber-optic condensation sensor device according to one of the preceding claims, characterized in that the evaluation unit is in operative connection with a temperature sensor (37) arranged in the measuring medium, so that further weather-related values can be determined by means of the electronic evaluation unit (31).

10. Active fiber optic Betauungssensorvorrichtung according to any one of the preceding claims, characterized in that the thickness of the sensor head (1) substantially corresponds to the diameter of the input and output light waveguides used (2, 5).

11. Active fiber optic Betauungssensorvorrichtung according to any one of the preceding claims, characterized in that the sensor head (1) in parallel, optically with the optical waveguides (2, 5, 5.1-5.n) connected sensor head part structures (1.1-l.n) is divided.

12. An active fiber optic Betauungssensorvorrichtung according to claim 11, characterized in that between the sensor head part structures (1.1-ln) thermally conductive intermediate elements (8) made of a thermally highly conductive material, in particular a metal material, are arranged.

13. Active fiber optic Betauungssensorvorrichtung according to claim 11 or 12, characterized in that the sensor head part structures (1.1-l.n) have different functional properties, in particular for the detection of different substances in the measuring medium.

14. An active fiber optic condensation sensor device according to one of the preceding claims, characterized in that the sensor head (1) or the sensor head part structures (1.1-l.n) consist of a permeable to selectable wavelengths of light material.

15. Active fiber optic Betauungssensorvorrichtung according to any one of the preceding claims, characterized in that thermally conductive elements (7, 8, 9, 13) and optically conductive elements (1.1-ln) of the sensor head (1) over a large area, in particular by juxtaposition, are coupled together ,

16. An active fiber-optic condensation sensor device according to claim 11, characterized in that a partially transparent coating (13) of a thermally highly conductive material, in particular a metal coating, on the at least one interface (3) of the sensor head (1) or on the Surface of the sensor head part structures (1.1-ln) is applied.

17. An active fiber optic condensation sensor device according to one of claims 10 to 16, characterized in that each sensor head substructure (1.1-ln) is assigned in each case an output optical waveguide (5.1-5.n), the respective diameter of which substantially corresponds to the thickness of the respective sensor head substructure (1.1-ln).

18. Active fiber-optic condensation sensor device according to one of claims 12 to 17, characterized in that a dewing of the optical sensor head substructures (1.1-1.n) takes place by a delicate mixed structuring of optical sensor head substructures (1.1-l.n) and thermally highly conductive intermediate elements (8).

An active fiber optic condensation sensor device according to any one of the preceding claims, characterized in that the sensor head (1) or a respective sensor head part structure (1.1-l.n) has a linear shape, a non-linear shape or a semicircular shape.

20. An active fiber-optic condensation sensor device according to one of the preceding claims, characterized in that, in the case of a semicircular shape of the sensor head (1), the light is coupled into an area near the edge of the sensor head (1).

21. Active fiber-optic condensation sensor device according to claim 20, characterized in that at least a part (16) of the sensor head (1) in which light coupled in via the input optical waveguide (2) does not propagate, consists of a thermally highly conductive material, in particular a metal material, consists.

22. An active fiber optic Betauungssensorvorrichtung according to claim 20 or 21, characterized in that a near-edge region of the sensor head (1) is formed of an optically conductive material whose thickness is reduced or reduced so far that the reflection of the input via the optical waveguide (2) in the sensor head (1) coupled light between the outer optical interface (29) and an inner optical reflection surface (33) of the near-edge region takes place.

23. Active fiber-optic condensation sensor comprising a one-end with a light source (30) operatively connected and the other end with an optically transparent, at least one optical interface (3, 4, 29) having sensor head (1) connected input optical waveguide (2) and a one end with a Light detector (35) can be brought into operative connection and at the other end with the sensor head (1) connected output optical waveguide (5), characterized in that the at least one optical interface (3, 4, 29) is formed tempered.

24. Active fiber-optic condensation sensor according to claim 23, characterized in that the sensor head (1) has a temperature of the at least one optical interface (3, 4, 29) measuring temperature sensor (38).

25. An active fiber optic condensation sensor according to claim 23 or 24, characterized in that the Betauungs- sensor is part of a Betauungssensorvorrichtung according to any one of claims 1 to 22.

26. Active fiber-optic condensation sensor, characterized in that the condensation sensor has the features of the sensor head (1) of the condensation sensor device according to one of claims 1 to 22.