DE102019108561A1 - Refractometer and method for determining the refractive index of a process medium with a refractometer - Google Patents

Abstract

The invention relates to a refractometer for determining the refractive index of a process medium (PM), having: - several, especially at least two, light sources (21,22; LZ, LD1, LD2), - an optical detector unit (7), - a control / Evaluation unit (4) and a measuring prism (6) with a predetermined refractive index, the light sources (21,22; LZ, LD1, LD2) being separately controllable by the control / evaluation unit (4) and the refractometer in different Operating modes (BM1, BM2; BM3) can be operated in which exactly one of the multiple light sources (21, 22; LZ, LD1, LD2) emits light and is connected to an interface between the process medium (OF) of the measuring prism that is in contact with the medium ( PM) and measuring prism (6) irradiates, - the light undergoes refraction and / or reflection at the interface and generates at least one optical signal (OS) dependent on the refractive index of the process medium (PM), - the optical detector unit (7) generates at least one optical signal (OS) is recorded and transmitted to the control / evaluation unit (4), which stores the optical signal (OS) associated with the operating mode, and the control / evaluation unit (4) is configured to use the totality of the stored optical signals (OS) to determine the refractive index of the process medium (PM) from all operating modes (BM1, BM2; BM3) and based on the specified refractive index of the measuring prism (6). Furthermore, the invention relates to a method for determining the refractive index of a process medium (PM) with a Refractometer.

Description

The invention relates to a refractometer for determining the refractive index of a process medium with at least one light source, an optical detector unit, a control / evaluation unit and a measuring prism with a predetermined refractive index. The invention also relates to a method for determining the refractive index of a process medium using a refractometer according to the invention.

Refractometers are used in many areas of process measurement technology, for example in food technology, water management, chemistry, biochemistry, pharmacy, biotechnology and environmental measurement technology to determine the refractive index of a process medium, for example a process liquid. The refractive index is used, for example, to determine a process variable that can be derived from the refractive index, such as the concentration of a substance in the process medium, for example sugar, or in a purity test.

The measuring principle of a refractometer is based on the fact that light is radiated into an interface between the process medium and the measuring prism that is formed by a surface of the measuring prism in contact with the medium. An optical signal is generated by means of refraction and / or reflection of the light at the interface. The direction and / or intensity of the refracted and / or reflected light on the surface in contact with the medium depends on the refractive index difference between the process medium and the measuring prism. Using the optical signal and the known refractive index of the measuring prism, the refractive index of the process medium can be determined.

So-called Abbe refractometers are known from the prior art, for example, which work with the critical angle of total reflection. Depending on the refractive index difference between the measuring prism and the process medium as well as the angle of incidence, the light irradiated at an interface between the process medium and the measuring prism is partially refracted into the process medium and reflected or completely reflected. The critical angle of total reflection is determined by means of the reflected light intensity as a function of the angle of incidence, and the refractive index of the process medium is determined from this. Abbe refractometers are described in the most varied of configurations in the prior art, for example in DE 1994 47 98 A1 .

In contrast to Abbe refractometers, in transmitted light refractometers (also: transmission refractometers) the measuring prism and process medium are traversed by a preferably collimated beam. The deflection of the beam as it traverses the measuring prism and the process medium is dependent on their refractive index difference. The angle of deflection between the incident beam and the beam passing through it is therefore a measure of the refractive index of the process medium. The deflection angle in turn is determined, for example, on the basis of the position of a focal point of the traversing beam on a detector plane perpendicular to the optical axis of the incident beam. Measuring prisms with surfaces inclined towards one another are often used on the surface of the measuring prism that is in contact with the medium. In this case, two focal points are generated, from the distance between which the refractive index of the process medium can be determined.

The disadvantage of known transmitted light refractometers is that they generally require two accesses to the process medium. A transmitted light refractometer with a one-sided process access is in the patent DE 10 2007 05 07 31 B3 described. In the refractometer described therein, light is radiated in via a single process access, which is collimated by means of illumination optics, is deflected by deflection optics, then crosses the process medium and the measuring prism, and is focused on a detector plane by imaging optics. The detector plane is advantageously arranged on the irradiation side, which enables one-sided access to the process medium.

In the application of the applicant with the application number 102018116409.2, which was still unpublished at the time of the filing date of this application, a transmitted light refractometer with one-sided process access is described, which uses a common imaging and illumination optics. As a result, the diameter of an access to the process medium can advantageously be reduced.

All refractometers have in common that they have a measuring prism, a light source, an optical detector unit for detecting the optical signal and a control / evaluation unit for regulating and / or evaluating the optical signal and then determining the refractive index of the process medium. The measuring range of the refractometer is limited by the fact that the optical signal generated during refraction and / or reflection can be fully detected by the optical detector unit.

For example, if two focus points are generated (see the above-mentioned transmitted light refractometer), both focus points must be detectable by the optical detector unit. In the event that there are often severe restrictions on the dimension of the optical detector unit, for example due to small process accesses, refractometers known from the prior art have a very limited measuring range. It is therefore desirable to specify a refractometer with an enlarged measuring range without enlarging the optical detector unit and / or reducing the sensitivity of the refractometer.

The invention is based on the object of specifying a refractometer which has an enlarged measuring range.

The object is achieved by a refractometer for determining the refractive index of a process medium and by a method for determining the refractive index of a process medium with a refractometer according to the invention.

• - mehrere, insb. zumindest zwei, Lichtquellen,
• - eine optische Detektoreinheit,
• - eine Regel-/Auswerteinheit und
• - ein Messprisma mit einem vorgegebenen Brechungsindex,

wobei die Lichtquellen von der Regel-/Auswerteinheit jeweils separat ansteuerbar sind und wobei das Refraktometer in verschiedenen Betriebsmodi betreibbar ist, in denen

• - jeweils genau eine der mehreren Lichtquellen Licht aussendet und an eine durch eine mediumberührende Oberfläche des Messprismas gebildete Grenzfläche zwischen Prozessmedium und Messprisma einstrahlt,
• - das Licht an der Grenzfläche Lichtbrechung und/oder Reflexion erfährt und zumindest ein vom Brechungsindex des Prozessmediums abhängiges optisches Signal erzeugt,
• - die optische Detektoreinheit das zumindest eine erzeugte optische Signal erfasst und an die Regel-/Auswerteinheit übermittelt, welche das zu dem Betriebsmodus gehörige optische Signal speichert,

und wobei die Regel-/Auswerteinheit dazu ausgestaltet ist, anhand der Gesamtheit der gespeicherten optischen Signale aus allen Betriebsmodi und anhand des vorgegebenen Brechungsindex des Messprismas den Brechungsindex des Prozessmediums zu bestimmen.With regard to the refractometer, the object is achieved by a refractometer for determining the refractive index of a process medium, having:

• - several, especially at least two, light sources,
• - an optical detector unit,
• - a control / evaluation unit and
• - a measuring prism with a given refractive index,

wherein the light sources can each be controlled separately by the control / evaluation unit and wherein the refractometer can be operated in different operating modes in which

• - in each case exactly one of the multiple light sources emits light and irradiates it at an interface between the process medium and the measuring prism formed by a surface of the measuring prism that is in contact with the medium
• - the light undergoes refraction and / or reflection at the interface and generates at least one optical signal that is dependent on the refractive index of the process medium,
• the optical detector unit detects the at least one generated optical signal and transmits it to the control / evaluation unit, which stores the optical signal associated with the operating mode,

and wherein the control / evaluation unit is designed to determine the refractive index of the process medium on the basis of the entirety of the stored optical signals from all operating modes and on the basis of the specified refractive index of the measuring prism.

Depending on the operating mode i.e. the light source used therein and the refractive index of the process medium, the generated optical signal from the respective operating mode can be mapped onto the optical detector unit, only partially mapped or not mapped. In the invention, for at least one of the operating modes, an optical signal that is dependent on the refractive index of the process medium and generated with the light source used therein can be at least partially detected by the optical detector unit. If, for example, the optical signal comprises two focus points, the position of which depends on the refractive index of the process medium, at least one of these focus points is detected in at least one of the operating modes. When using the optical signals from all operating modes, the refractometer has an enlarged measuring range compared to a refractometer with only one light source, which is otherwise designed in a comparable manner. As a result of this enlargement of the measuring range, the refractometer can be used for a large number of different process media without further structural measures, even with comparatively small process accesses.

The solution according to the invention is suitable for both the transmitted light and critical angle refractometers described above. In transmitted light refractometers, the at least one optical signal that is dependent on the refractive index of the process medium is, for example, the position of at least one focal point of a beam which has undergone refraction on the surface in contact with the medium. In critical angle refractometers, the at least one optical signal that is dependent on the refractive index of the process medium is, for example, the position of a light-dark transition in the intensity of the light reflected at the interface and an angle of incidence of the incident light associated with this position, which is the critical angle corresponds to total reflection.

The at least one light source is, for example, an LED.

The optical detector unit includes, for example, a camera with a predetermined number of pixels. It is e.g. possible that the camera comprises exactly one line of pixels.

In one embodiment of the invention, the refractometer is a transmitted light refractometer, having an optical system, with an optical axis, the optical system and the measuring prism being offset from one another along the optical axis, and the optical system being configured for this purpose to generate a collimated bundle of rays from the light generated by the respective light source, the measuring prism having at least two flat and mutually inclined surfaces, which on the medium-contacting surface of the measuring prism are arranged, and wherein the two mutually inclined surfaces are each inclined in relation to a plane perpendicular to the optical axis about an inclination axis and in opposite directions, the inclination axis being perpendicular to the optical axis.

The two mutually inclined surfaces of the measuring prism generate two focal points as an optical signal, the distance between them representing a measure of the refractive index of the process medium. In particular, the inclination of the two mutually inclined surfaces is essentially symmetrical to the optical axis.

• - das Strahlenbündel in einem ersten Durchgang ein erstes Mal das Messprisma und das Prozessmedium durchquert, wobei das Strahlenbündel an der medienberührende Oberfläche ein erstes Mal Lichtbrechung erfährt,
• - das Strahlenbündel am Umlenkelement umgelenkt wird,
• - das Strahlenbündel in einem zweiten Durchgang ein zweites Mal das Messprisma und das Prozessmedium durchquert, wobei das Strahlenbündel an der medienberührende Oberfläche ein zweites Mal Lichtbrechung erfährt, und
• - das optische System anschließend das Strahlenbündel auf die optische Detektoreinheit fokussiert .

In a further embodiment of the transmitted light refractometer, it has a deflecting element, the deflecting element and the optical system being arranged relative to one another along the optical axis in such a way that

• - the bundle of rays crosses the measuring prism and the process medium for the first time in a first pass, the bundle of rays experiencing light refraction for the first time on the surface in contact with the medium,
• - the beam of rays is deflected at the deflection element,
• the bundle of rays traverses the measuring prism and the process medium a second time in a second pass, the bundle of rays experiencing light refraction a second time on the surface in contact with the medium, and
• - The optical system then focuses the beam on the optical detector unit.

The deflecting element is, for example, a mirror or a retroreflector.

One advantage of this configuration is that (see the as yet unpublished application with application number 102018116409.2) the optical system serves as a common imaging and illumination optics. By means of the deflection element, the refracted light is advantageously deflected back in the direction of incidence.

There are no restrictions on the arrangement of the measuring prism in relation to the process medium as long as the mutually inclined surfaces of the measuring prism are in contact with the medium and the process medium-measuring prism interface is present, as required.

E.g. The refractometer can include a process window through which the collimated beam enters the process medium in an entry direction before the first passage and through which the beam subsequently exits the process medium to the second passage in the exit direction. The measuring prism, the process window and the deflecting element are arranged with respect to one another in such a way that the bundle of rays first crosses the process medium and then the measuring prism in the first pass, and in the second pass it crosses the measuring prism and then the process medium in reverse order. In relation to the path of the beam of rays of the first passage, the arrangement in this embodiment is therefore the process window-process medium-measuring prism-deflecting element.

The arrangement of the measuring prism, the process medium deflection element, is of course also possible. In an alternative embodiment, the measuring prism and the deflecting element are therefore arranged with respect to one another in such a way that the bundle of rays first crosses the measuring prism and then the process medium in the first passage, and in the second passage in the reverse order first crosses the process medium and then the measuring prism, whereby The collimated bundle of rays enters the process medium via the measuring prism and exits the process medium via the measuring prism. The advantage of this embodiment is that the measuring prism itself serves as a process window. So there is no need for an additional process window.

In a further development of the transmitted light refractometer, the optical detector unit comprises a camera with at least one pixel line arranged in a detector plane, the pixels of which are arranged along a line direction that is essentially perpendicular to the optical axis and the inclination axis, and wherein the multiple light sources are arranged along a Light source direction are arranged offset, which is substantially parallel to the row direction.

In a further development of the transmitted light refractometer, one of the light sources is designed as a centrally arranged light source, which is essentially arranged at an imaginary intersection of a parallel axis displaced parallel to the optical axis along the inclination axis and the light source direction. In particular, the light emitted by the centrally arranged light source is collimated along the optical axis of the optical system.

In a further development of the transmitted light refractometer, at least one of the light sources is designed as a decentrally arranged light source, which in the light source direction with respect to an imaginary point of intersection of one to the optical Axis parallel axis displaced in parallel with the light source direction is arranged at a distance from the point of intersection in the light source direction.

In one embodiment of this development, the transmitted light refractometer has two decentrally arranged light sources, in particular a first distance between the first decentrally arranged light source and the imaginary intersection point coincides with a second distance between the second decentrally arranged light source and the imaginary intersection point, so that the two decentrally arranged light sources are arranged symmetrically around the imaginary intersection point in opposite directions.

• - zwei äußere Fokuspunkte, deren Position in Zeilenrichtung abhängig von dem Brechungsindex des Prozessmediums ist und
• - einen zwischen den beiden Fokuspunkten zentral angeordneten Fix-Fokuspunkt, dessen Position in Zeilenrichtung unabhängig von dem Brechungsindex des Prozessmediums ist,

wobei die dezentralen Lichtquellen derart angeordnet sind, insbesondere deren Abstand so gewählt ist, dass

• - für alle dezentralen Lichtquellen deren Fix-Fokuspunkt auf die Pixelzeile abbildbar ist und

für alle dezentralen Lichtquellen und alle Brechungsindizes des Prozessmediums aus dem Messbereich des Refraktometers zumindest einer der äußeren Fokuspunkte der dezentralen Lichtquellen auf die Pixelzeile abbildbar ist.In one embodiment of the transmitted light refractometer, each of the light sources generates on the detector plane

• - two outer focus points, the position of which in the line direction depends on the refractive index of the process medium and
• - a fixed focus point located centrally between the two focus points, the position of which in the line direction is independent of the refractive index of the process medium,

wherein the decentralized light sources are arranged, in particular their spacing is chosen so that

• - for all decentralized light sources whose fixed focus point can be mapped onto the pixel line and

for all decentralized light sources and all refractive indices of the process medium from the measuring range of the refractometer at least one of the outer focus points of the decentralized light sources can be mapped onto the pixel line.

• - eine erste der Lichtquellen das Licht auf die mediumberührende Oberfläche des Messprismas unter einem ersten Winkelbereich einstrahlt,
• - eine zweite der Lichtquellen das Licht auf die mediumberührende Oberfläche des Messprismas unter einem zweiten Winkelbereich einstrahlt,
• - wobei der erste Winkelbereich und der zweite Winkelbereich einen Überlapp aufweisen, insbesondere einen Überlapp von zumindest 5% der Spanne des ersten und/oder zweiten Winkelbereichs,
• - und wobei alle Lichtquellen die im Wesentlichen gleiche Fläche auf der mediumberührenden Oberfläche des Messprismas ausleuchten.

In an alternative embodiment to the transmitted light refractometer, the refractometer is a critical angle refractometer which is designed such that

• - a first of the light sources radiates the light onto the medium-contacting surface of the measuring prism at a first angular range,
• - a second of the light sources radiates the light onto the medium-contacting surface of the measuring prism at a second angular range,
• - wherein the first angular range and the second angular range have an overlap, in particular an overlap of at least 5% of the span of the first and / or second angular range,
• - and wherein all light sources illuminate essentially the same area on the medium-contacting surface of the measuring prism.

• - mehrere, insb. zumindest zwei, Lichtquellen,
• - eine optische Detektoreinheit,
• - eine Regel-/Auswerteinheit und
• - ein Messprisma mit einem vorgegebenen Brechungsindex,

wobei die Lichtquellen von der Regel-/Auswerteinheit jeweils separat ansteuerbar sind und wobei das Refraktometer in verschiedenen Betriebsmodi betreibbar ist,
und wobei das Refraktometer zeitlich aufeinanderfolgend in verschiedenen Betriebsmodi betrieben wird, in denen

• - jeweils von genau einer der mehreren Lichtquelle Licht ausgesandt und an eine durch eine mediumberührende Oberfläche des Messprismas gebildete Grenzfläche zwischen Prozessmedium und Messprisma eingestrahlt wird,
• - das Licht an der Grenzfläche gebrochen und/oder reflektiert wird, wobei zumindest ein vom Brechungsindex des Prozessmediums abhängiges optisches Signal erzeugt wird,
• - das zumindest eine erzeugte optische Signal von der optischen Detektoreinheit erfasst und an die Regel-/Auswerteinheit übermittelt, wird, wobei das zu dem jeweiligen Betriebsmodi gehörige optische Signal gespeichert wird,

und wobei von der Regel-/Auswerteinheit anhand der Gesamtheit der gespeicherten optischen Signale aus allen Betriebsmodi und anhand des vorgegebenen Brechungsindex des Messprismas der Brechungsindex des Prozessmediums bestimmt wird.With regard to the method, the object is achieved by a method for determining the refractive index of a process medium with a refractometer, in particular a refractometer according to the invention, having:

• - several, especially at least two, light sources,
• - an optical detector unit,
• - a control / evaluation unit and
• - a measuring prism with a given refractive index,

wherein the light sources can each be controlled separately by the control / evaluation unit and wherein the refractometer can be operated in different operating modes,
and wherein the refractometer is operated successively in time in different operating modes in which

• - Light is emitted from exactly one of the multiple light sources and irradiated to an interface between the process medium and the measuring prism formed by a surface of the measuring prism that is in contact with the medium
• - the light is refracted and / or reflected at the interface, with at least one optical signal dependent on the refractive index of the process medium being generated,
• the at least one generated optical signal is detected by the optical detector unit and transmitted to the control / evaluation unit, the optical signal associated with the respective operating mode being stored,

and wherein the control / evaluation unit determines the refractive index of the process medium based on the entirety of the stored optical signals from all operating modes and based on the specified refractive index of the measuring prism.

The invention is explained in more detail with reference to the following figures, which are not true to scale, wherein the same reference symbols denote the same features. If it is necessary for clarity or if it appears to be useful in some other way, the already mentioned reference symbols are dispensed with in the following figures.

• 1: Eine erste Ausgestaltung des erfindungsgemäßen Refraktometers als Durchlichtrefraktometer in einer Schnittansicht;
• 2a, 2b: Ein Detail einer weiteren Ausgestaltung des erfindungsgemäßen Refraktometers in einer weiteren Ansicht;
• 3: Ein Grenzwinkelrefraktometer nach dem Stand der Technik;
• 4, 4a, b, c: Eine weitere Ausgestaltung eines erfindungsgemäßen Refraktometers als Grenzwinkelrefraktometer;
• 5: Eine weitere Ausgestaltung eines erfindungsgemäßen Refraktometers als Grenzwinkelrefraktometer.

Show it:

• 1 : A first embodiment of the refractometer according to the invention as a transmitted light refractometer in a sectional view;
• 2a , 2 B : A detail of a further embodiment of the refractometer according to the invention in a further view;
• 3 : A critical angle refractometer according to the prior art;
• 4th , 4a, b , c : Another embodiment of a refractometer according to the invention as a critical angle refractometer;
• 5 : Another embodiment of a refractometer according to the invention as a critical angle refractometer.

In 1 is a first embodiment of a refractometer according to the invention for measuring the refractive index of a process medium PM shown. This has two light sources 21st , 22nd which are arranged offset along a light source direction y '. In a first operating mode BM1 becomes the light of a first light source 21st by means of an optical system 8th along its optical axis z collimates and then crosses the measuring prism 6th . This points to a surface that comes into contact with the medium in a measuring operation OF two around an axis of inclination x surfaces inclined against each other OF1 , OF2 on. The beam of the collimated light has a first component SB1 on that on the first surface OF1 Refraction experiences, and a second part SB2 on that on the second surface OF2 Experiences light refraction.

When exiting the measuring prism 6th over the media-contacting surfaces OF1 , OF2 finds a first, from the refractive index of the process medium PM dependent refraction takes place. Now by means of a deflection element 9 each the refracted bundle of rays SB1 , SB2 reflects and experiences a second transition between process medium PM and measuring prism 6th again refraction. Then the bundles of rays SB1 , SB2 by means of the optical system 8th on an optical detector unit arranged on the incident side of the light 7th with a camera 5 focussed back, with focal points in a detector plane FF , FP1 , FP2 be generated.

Thereby each of the operating modes BM1 , BM2 , BM3 ,. ,, two outer focus points FP1 , FP2 generated, their spacing in line direction y a measure of the refractive index of the process medium PM represents. Furthermore, there is a between the two focal points FP1 , FP2 , centrally arranged fixed focus point FF its position in line direction y regardless of the refractive index of the process medium PM is.

The fixed focus point FF is through one in the middle of the beam SB arranged portion generated, which in the first pass on a first of the two mutually inclined surfaces OF1 ; OF2 the first time light refraction and the second pass on the second of the two mutually inclined surfaces OF2 ; OF1 experiences refraction the second time. These two refractions cancel each other out for the case of one about the optical axis z symmetrical measuring prism 6th each other up.

The distance between the two focal points FP1 , FP2 in one to the tilt axis x and the optical axis z essentially vertical line direction y thus represents a measure of the refractive index of the process medium PM Here the camera comprises at least one line of pixels PZ (see. 2a , 2 B) running along the line direction y is arranged which is perpendicular to the optical axis z and to the slope axis x is. The above-mentioned light source direction y ' is again parallel to the row direction y .

In the embodiment shown here, the material is for the measuring prism 6th chosen such that its refractive index nG is greater than all values for the refractive index of the process medium from the measuring range of the refractometer nM. The upper limit of the measuring range is therefore limited by the choice of material for the measuring prism, which typically comprises a glass or sapphire.

The smaller the refractive index of the process medium PM the greater the distance between the outer focus points FP1 , FP2 . This can be used for small refractive indices of the process medium PM the case that occur in the first operating mode BM1 generated focus points FP1 , FP2 can no longer be detected by the camera. It will then only be the one between the focal points F1 , F2 arranged fixed focus point FF detected.

In another operating mode BM2 with the further light source offset in the light source direction y ' 22nd can add more focus points FP1 , FP2 , FF are generated, whereby the measuring range of the refractometer according to the invention is enlarged downwards, compared to an otherwise identically designed refractometer, which only the first light source 21st having. This enlargement of the measuring range by means of the separately controllable light sources 21st , 22nd is below related to a transmitted light refractometer 2a , 2 B explained in detail.

In 2a a centrally arranged light source is shown as a black-filled point in a view which is related to that in FIG 1 shown view by 90 ° around the line axis y is rotated. The centrally arranged light source LZ is at an intersection SP between a parallel axis z 'and the light source direction y ' arranged with the parallel axis z ' in the direction of inclination x parallel to the optical axis z is shifted. The centrally arranged light source LZ essentially corresponds to the in 1 shown first light source 21st .

The refractometer also has two decentrally arranged light sources LD1 , LD2 on that along the light source direction y ' are arranged offset and each with a distance y1 , y2 from the centrally arranged light source LZ are spaced. The decentralized light sources LD1 , LD2 are in 2a shown as different hatched circles. The first distance is preferably correct y1 with the second distance y2 match. With the optical detector unit 7th it is about the camera 5 with a line of pixels PZ running along the line direction y is arranged. The pixels are shown here as unfilled circles.

Is the refractometer like in 1 shown are configured in each of the operating modes BM1 , BM2 , BM3 the two outer focus points FP1 , FP2 in the plane of the optical detector unit 7th generated whose distance in the y-direction is a measure of the refractive index of the process medium PM represents. The first decentralized light source LD1 is in this embodiment in the second operating mode BM2 and the second decentrally arranged light source LD2 in the third operating mode BM3 used. For better identification of the focus points FP1 , FP2 , FF with the operating modes BM1 , BM2 , BM3 are in 2 B in the lower half of the picture the respective focus points FP1 ; FP2 ; FF according to the light source used in their creation LZ ; LD1 ; LD2 shown, namely as filled black or as differently hatched circles. The distance y1 , y2 is now chosen so that for all light sources LZ ; LD1 ; LD2 their fixed focus point FF on the pixel line PZ the camera 5 can be mapped and for all decentralized light sources LD1 , LD2 and all refractive indices of the process medium PM at least one of the outer focus points from the measuring range of the refractometer FP1 , FP2 of decentralized light sources LD1 , LD2 on the pixel line PZ the camera 5 is mappable.

Those in the first mode of operation BM1 in the plane of the optical detector unit 7th generated outward focus points FP1 , FP2 the central light source LZ no longer necessarily have to be used for all refractive indices of the process medium PM from the measuring range of the refractometer to the pixel line PZ the camera 5 be mappable. Depending on the refractive index of the process medium, only one outer focal point may be possible FP1 ; FP2 from the second and third operating mode BM2 , BM3 on the pixel line PZ the camera 5 be mappable.

This is here for the first mode of operation BM1 shown. Here are those in the plane of the optical detector unit 7th generated outward focus points FP1 , FP2 the central light source LZ no longer on the pixel line PZ the camera 5 mapable so that in the first operating mode BM1 only the centrally arranged fixed focus point FF from the optical detector unit 7th is captured. Because the two outer focus points FP1 , FP2 (filled black circles) no longer on the pixel line PZ the camera 5 can therefore be mapped from the first operating mode BM1 alone no longer the refractive index of the process medium PM determine.

By using the outer focus points FP1 , FP2 from one of the other operating modes BM2 , BM3 a distance d3 = 2 * d31 or d3 = 2 * d32 to the respective central fixed focus point can be achieved FF from this operating mode BM2 ; BM3 determine. The distance d3 then represents a measure of the refractive index of the process medium PM If necessary, you can also use the two operating modes BM2 and BM3 are averaged, and a distance d3 = ½ (2 * d31 + 2 * d32) = d31 + d32 is used.

In the event that the process medium is cloudy PM the central fixed focus point FF , depending on the refractive index of the process medium PM , only of low light intensity and therefore very weak. So as not to be on the central fixed focus point FF Alternatively or additionally, a distance d3 'between the outer focal points can also be instructed FP2 , FP1 from different operating modes BM2 , BM3 be used. The distance d3, which is the measure of the refractive index of the process medium PM is now obtained from d3 = d3 '+ y1 + y2. In this case, the distance between the decentralized light sources must be LD1 , LD2 from each other, ie y1 + y2, must be known very precisely, since every drift of this distance is reflected in the measurement result.

Notwithstanding the fact that in the embodiment the invention with three light sources LZ , LD1 , LD2 has been explained, two light sources are sufficient for the design as a transmitted light refractometer with an extended measuring range, for example a central light source LZ and a decentralized light source LD1 or two decentralized light sources LD1 , LD2 .

In the in 1 The embodiment shown as a transmitted light refractometer can use the measuring prism 6th and the process medium PM As shown, for example, in 102018116409.2, they can also be arranged in the reverse order to one another, in which case an additional process window is required.

Furthermore, the refractometer can optionally also include a temperature sensor not explicitly shown here and configured, for example, as a Pt100. This also measures the temperature of the process medium PM and transmits this to the control / evaluation unit 4th . The temperature measured by the temperature sensor is advantageous, for example, when calculating a sugar concentration in the process medium that is dependent on the refractive index PM considered.

Even in the embodiment as a critical angle refractometer, the use of several separately controllable light sources 21st , 22nd , 23 , especially at least two light sources, an expansion of the measuring range can be achieved. This is in the 3 to 5 shown in more detail.

3 explains the measuring principle of a critical angle refractometer known in the prior art, in which the light from a light source, for example by means of an optical system 81 , at different angles α on a process medium PM - contacting interface OF a measuring prism 6th is irradiated. The lighting (i.e. light source 21st and the optical system 81 ) are designed in such a way that the light hits the interface at different locations at different angles OF hits (spatially resolved angular spectrum). At a light-dark transition of the reflected light is the critical angle of total reflection and from this the refractive index of the process medium PM determinable. In the example shown here, light is irradiated at the angles α, which is between the angles α1 and α2 lie. In the example in 3 the angle of incidence α increases from left to right within the illuminated area. In order to determine the critical angle, this angle of incidence α must be between α1 and α2 lie. The angles α1 and α2 thus limit the measuring range of the refractometer. An extension of the measuring range in which the illuminated interface OF does not have to be enlarged, is achieved in that separately controllable light sources 21st , 22nd , 23 be used. These illuminate essentially the same area on the interface OF , but from different angular ranges α1-α2 , β1-β2 and γ1-γ2 . A slight overlap of adjacent angular ranges (i.e., for example, where α2> β1 and β2> γ1) ensures that there are no gaps in the measuring range, the overlap being at least 5%, for example. In the event that the angular ranges α1- α2 , β1- β2 and γ1- γ2 are of different sizes, the largest angular range, for example, is to be taken as the reference value for the relative information for the overlap.

Would you be in 3 as in the in 1 embodiment shown several light sources arranged offset in a light source direction 21st , 22nd , 23 use, overlapping angular ranges would be used as intended α1- α2 , β1- β2 and γ1- γ2 occur, but at the same time a shift in the spatial area would occur, ie at the same time a larger camera 5 are needed. This can be done, for example, through a cover 10 avoid. In 4th , 4a , 4b an example with 3 LEDs is shown. These are LED chips without collimator optics, which can be described as Lambert radiators, ie they emit in all directions, but only a certain part of the light with angles from a certain range of the angular spectrum passes the aperture 10 , the rest of the light is absorbed. Will now be the aperture 10 by means of an optical system 81 on the interface OF of the measuring prism 6th pictured can be about the position of the light source 21st , 22nd , 23 in relation to the aperture 10 the angular range α1- α2 , β1- β2 , or. γ1- γ2 can be set. The position of the light source 21st , 22nd , 23 in terms of aperture 10 determines what part of the original angular spectrum of the light source 21st , 22nd , 23 the aperture 10 happens. The position of the light spot remains constant, however, since it is determined by the position of the diaphragm fixed in the local area 10 is defined. The angular range α1- α2 the first light source 21st is in 4th , 4a with the aid of a dotted-dashed line, the angular range β1-β2 of the second light source 22nd is in 4th , 4b with the help of a solid line, and the angular range γ1- γ2 the third light source 23 is in 4th , 4c shown with the help of a dashed line.

A disadvantage of using a diaphragm 10 is the lower light output. To without a bezel 10 The light sources have to get by 21st , 22nd , 23 not only shifted to each other, but also tilted to each other (not explicitly shown here).

A possibility to achieve the same effect without explicitly tilting the light sources 21st , 22nd , 23 to achieve is the use of a light guide 11 comprising multiple fibers F1 , F2 , F3 , each of the fibers F1 , F2 , F3 with one of the separately controllable light sources 21st , 22nd , 23 connected is. One such example is in 5 shown. The exit surfaces of the outer fibers F1 , F2 , F3 are beveled in such a way that the light is in a certain angular range α1- α2 , β1- β2 , or. γ1- γ2 exit. It should be noted that the bevelling of the fibers F1 , F2 , F3 in terms of the cone of light coming from the fibers F1 , F2 , F3 exiting light is coordinated so that a slight overlap of the angular ranges α1- α2 , β1- β2 and γ1- γ2 is guaranteed. Second, the fiber spacing must be d be chosen so that for all light sources 21st , 22nd , 23 or fibers F1 , F2 , F3 essentially the same area on the media-contacting surface OF of the measuring prism 6th is illuminated. As above, in 5 the angular range α1- α2 the first light source 21st represented by a dotted-dashed line, the angular range β1- β2 the second light source 22nd represented by a solid line, and the angular range γ1- γ2 the third light source 23 shown with the help of a dashed line.

In the embodiment as a critical angle refractometer, the invention thus also comprises an arrangement of at least 2 separately controllable light sources 21st , 22nd ; 23 . These are used on the interface in contact with the media OF through each of the light sources 21st ; 22nd , 23 generates a light spot which has a spatially resolved angular spectrum. Depending on the critical angle, the light source is 21st , 22nd , 23 with the corresponding angular range used for determination.

The light spots of the individual light sources 21st , 22nd ; 23 overlap almost completely in the local area and are shifted in the angular space, each with a slight overlap. This enables the critical angle to be determined continuously. Depending on the refractive index of the process medium PM is the critical angle in one (or two, if in the overlapping area, for example between β1 and α2 ) the angular ranges α1- α2 , β1- β2 and γ1- γ2 , each in one of the operating modes BM1 , BM2 , BM3 be used. The corresponding operating mode / i BM1 ; BM2 ; BM3 is then used to determine the refractive index. In order to achieve the simultaneous overlap in the spatial space and the shift in the angular space, a diaphragm is used, for example, as mentioned above 10 , a tilting of the light sources 21st , 22nd , 23 or a light guide 11 used with beveled exit surfaces.

In the embodiment explained here, an expansion of the angle range on the part of the lighting was discussed. Of course, the optical detector unit must also 7th be designed for an extended measuring range. In the ideal case, the image field remains identical, the aperture (ie the angles recorded by the imaging optics or the “image field in angular space”) must therefore be expanded accordingly.

List of reference symbols

21,22,23

Light sources

4th

Control / evaluation unit

5

camera

6th

Measuring prism

7th

optical detector unit

8th

optical system

81

optical system

9

Deflection element

10

cover

11

Light guide

PM

Process medium

OS

optical signal

z

optical axis

z '

Parallel axis

x

Slope axis

y to

optical axis and tilt axis vertical axis

y '

Light source direction

PZ

Pixel line

OF

media-contacting surface

OF1, OF2

surfaces inclined against each other

SB, SB1, SB2

Beams, first / second portion of beams

SP

Intersection

LZ

centrally arranged light source

LD1, LD2

decentrally arranged light sources

BM1, BM2, BM3

Operating modes

FF, FP1; FP2

Focus points

α1- α2, β1- β2, γ1 - γ2

Angular ranges

F1, F2, F3

Fibers

d

Fiber spacing

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 19944798 A1 [0004]
• DE 102007050731 B3 [0006]

Claims (10)

Refractometer for determining the refractive index of a process medium (PM), having: - several, especially at least two, light sources (21,22; LZ, LD1, LD2), - an optical detector unit (7), - A control / evaluation unit (4) and - A measuring prism (6) with a predetermined refractive index, the light sources (21,22; LZ, LD1, LD2) being separately controllable by the control / evaluation unit (4) and the refractometer being in different operating modes (BM1, BM2; BM3) is operable in which - in each case exactly one of the multiple light sources (21, 22; LZ, LD1, LD2) emits light and radiates it onto an interface between the process medium (PM) and the measuring prism (6) formed by a surface (OF) of the measuring prism (6) in contact with the medium, - the light undergoes refraction and / or reflection at the interface and generates at least one optical signal (OS) that is dependent on the refractive index of the process medium (PM), - The optical detector unit (7) detects the at least one generated optical signal (OS) and transmits it to the control / evaluation unit (4), which stores the optical signal (OS) associated with the operating mode (BM1; BM2; BM3), and wherein the control / evaluation unit (4) is designed to use the totality of the stored optical signals (OS) from all operating modes (BM1, BM2; BM3) and the specified refractive index of the measuring prism (6) to determine the refractive index of the process medium (PM) to determine. Refractometer Claim 1 , which is a transmitted light refractometer, comprising an optical system (8) with an optical axis (z), the optical system (8) and the measuring prism (6) being arranged offset from one another along the optical axis, and that optical system is designed to generate a collimated beam (SB) from the light generated by the respective light source (21; 22; LZ; LD1: LD2), the measuring prism (6) having at least two flat surfaces (OF1, OF2), which are arranged on the surface of the measuring prism (6) in contact with the medium, and wherein the two mutually inclined surfaces (OF1, OF2) each in relation to a plane perpendicular to the optical axis (z) about an axis of inclination (x) and in directions opposite to each other are inclined, the inclination axis (x) being perpendicular to the optical axis (z). Refractometer Claim 2 , having a deflecting element (9), wherein the deflecting element (9) and the optical system (8) are arranged along the optical axis (z) to one another in such a way that - the beam (SB) in a first pass the measuring prism ( 6) and traverses the process medium (PM), whereby the bundle of rays experiences light refraction for the first time at the interface, - the bundle of rays (SB) is deflected at the deflecting element (5), - the bundle of rays (SB) in a second passage a second time Measuring prism (6) and the process medium (PM) traverses, whereby the beam is refracted a second time at the interface, and - the optical system (8) then focuses the beam (SB) on the optical detector unit (7). Refractometer according to at least one of the Claims 2 or 3 , wherein the optical detector unit (7) comprises a camera (5) with at least one pixel line (PZ) arranged in a detector plane, the pixels of which are along a line direction that is essentially perpendicular to the optical axis (z) and the inclination axis (x) ( y) are arranged, and wherein the plurality of light sources (LZ, LD1, LD2) are arranged offset along a light source direction (y ') which is essentially parallel to the row direction (y). Refractometer Claim 4 , wherein one of the light sources (LZ; LD1; LD2) is designed as a centrally arranged light source (LZ) which is essentially at an imaginary point of intersection (SP) of a parallel axis displaced parallel to the optical axis (z) along the inclination axis (x) (z ') is arranged with the light source direction (y'). Refractometer according to one of the Claims 2 to 5 , wherein at least one of the light sources (LZ; LD1; LD2) is designed as a decentrally arranged light source (LD1, LD2) which in the light source direction (y ') with respect to an imaginary point of intersection (SP) of a to the optical axis (z ) is arranged along the inclination axis (x) parallel axis (z ') with the light source direction (y') of the intersection (SP) in the light source direction at a distance (y1, y2). Refractometer Claim 6 , having two decentrally arranged light sources (LD1, LD2), wherein in particular a first distance (y1) between the first decentrally arranged light source (LD1) and the imaginary intersection point (SP) with a second distance (y2) between the second decentrally arranged light source ( LD2) and the imaginary point of intersection (SP) coincides, so that the two decentrally arranged light sources (LD1, LD2) around the imaginary point of intersection (SP) are arranged symmetrically in opposite directions. Refractometer according to at least one of the previous ones Claims 2 to 7th , whereby each of the light sources (LZ, LD1, LD2) on the detector plane - two outer focus points (FP1, FP2), the position of which in the line direction (y ') depends on the refractive index of the process medium (PM) and - one between the two focus points (FP1, FP2) centrally arranged fixed focus point (FF), the position of which in line direction (y ') is independent of the refractive index of the process medium (PM), and the decentralized light sources (LD1, LD2) are arranged in this way, in particular whose distance (γ1; γ2) is chosen so that - for all decentralized light sources (LD1; LD2) their fixed focus point (FF) can be mapped onto the pixel line and - for all decentralized light sources (LD1; LD2) and all refractive indices of the process medium (PM) from the measuring range of the refractometer at least one of the outer focus points of the decentralized light sources (LD1; LD2) can be mapped onto the pixel line. Refractometer Claim 1 This is a critical angle refractometer which is designed in such a way that - a first of the light sources (21) radiates the light onto the surface (OF) of the measuring prism (6) in contact with the medium in a first angular range (α1- α2), - a second of the light sources (22) irradiates the light onto the medium-contacting surface (OF) of the measuring prism (6) at a second angular range (β1- β2), - the first angular range (α1 - α2) and the second angular range (β1- β2) have an overlap, in particular an overlap of at least 5% of the span of the first (α1- α2) angle range and / or second angle range (β1- β2), - and wherein all light sources (21,22) have essentially the same area illuminate the surface (OF) of the measuring prism (6) in contact with the medium. Method for determining the refractive index of a process medium (PM) with a refractometer, in particular a refractometer according to one of the previous ones Claims 1 to 9 , comprising: several, in particular at least two, light sources (21,22, LZ; LD1; LD2), -an optical detector unit (7), - a control / evaluation unit (4) and - a measuring prism (6) with a predetermined refractive index, the light sources being separately controllable by the control / evaluation unit (4) and the refractometer being operable in different operating modes (BM1, BM2; BM3), and the refractometer being operated in different operating modes (BM1, BM2; BM3) is operated in which - light is emitted from exactly one of the multiple light sources and irradiated to an interface between the process medium and the measuring prism (6) formed by a surface (OF) of the measuring prism (6) in contact with the medium, - the light at the interface is refracted and / or reflected, with at least one optical signal (OS) dependent on the refractive index of the process medium (PM) being generated, the at least one generated optical signal (OS) from the optical detector unit (7) is recorded and transmitted to the control / evaluation unit (4), the optical signal (OS) associated with the respective operating mode (BM1; BM2; BM3) being stored, and the control / evaluation unit ( 4) using the totality of the stored optical signals (OS) from all operating modes (BM1, BM2; BM3) and using the specified refractive index of the measuring prism (6), the refractive index of the process medium (PM) is determined.

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