阅读说明：本技术 折光计和利用折光计来确定过程介质的折射率的方法 (Refractometer and method for determining refractive index of process medium by refractometer ) 是由 托比亚斯·迈纳特 本雅明·舍雷尔 乔基姆·曼哈特 于 2020-03-12 设计创作，主要内容包括：本发明涉及用于确定过程介质(PM)的折射率的折光计,其具有用于在折光计的运行单元(1)和探头单元(5)之间建立光学连接的至少一个光学的光导(3、31、…)。此外,本发明还涉及利用根据本发明的折光计来确定过程介质(PM)的折射率的方法。(The invention relates to a refractometer for determining the refractive index of a Process Medium (PM), comprising at least one optical light guide (3, 31, …) for establishing an optical connection between a drive unit (1) and a probe unit (5) of the refractometer. The invention further relates to a method for determining the refractive index of a Process Medium (PM) using a refractometer according to the invention.)

1. A refractometer for determining the refractive index of a Process Medium (PM), the refractometer having:

-an operating unit (1) that can be arranged outside the Process Medium (PM) and that has at least one light source (2, 21, 22, … …), an optical detector unit (7) and an adjustment/evaluation unit (4);

-a probe unit (5) that can be introduced at least partially into the Process Medium (PM), said probe unit being equipped with a measuring prism (6) having a predetermined refractive index; and

-at least one optical light guide (3, 31, … …) for establishing an optical connection between the operating unit (1) and the probe unit (5), wherein the light guide (3, 31, … …) opens with its first end section (3a, 31a, … …) into the operating unit (1) and with its second end section (3b, 31b, … …) into the probe unit (5), and wherein the operating unit (1), the probe unit (5) and the light guide(s) (3, 31, … …) are designed such that, when determining the refractive index of the Process Medium (PM),

-the at least one light source (2, 21, 22, … …) emits light,

-the light guide/guides (3, 31, … …) conduct light emitted by the at least one light source (2, 21, 22, … …) to the probe unit (5),

-the light undergoes a light refraction and/or reflection at a boundary surface between a Process Medium (PM) formed by a medium-contacting surface (OF) OF the measuring prism (6) and the measuring prism (6), wherein the probe unit (5) generates at least one Optical Signal (OS) dependent on the refractive index OF the Process Medium (PM),

-the light guide/guides (3, 31, … …) guide the at least one optical signal dependent on the refractive index of the Process Medium (PM) back to the operating unit (1),

-the optical detector unit (7) detects the at least one Optical Signal (OS) and transmits the at least one optical signal to the adjustment/evaluation unit (4),

-the adjustment/evaluation unit (4) determines the refractive index of the Process Medium (PM) from the transmitted at least one Optical Signal (OS) and the predefined refractive index of the measurement prism (6).

2. The refractometer according to claim 1, wherein one/more optical light guides (3, 31, … …) are designed as a Fiber Bundle (FB) with a plurality of fibers (B1; B2; A1, A2), wherein one of the light guides (3; 31, … …) comprises at least one illuminating fiber (B1; B2, … …) connected with the at least one light source (2, 21, 22, … …) and one of the light guides (3; 31, … …) comprises at least two imaging fibers (A1, A2, … …) connected with the optical detector unit (7), and wherein one/more illuminating fibers (B1; B2, … …) are designed such that the light of the at least one light source (2, 21, 22, … …) is guided to the probe unit (5) and the imaging fibers (A1; A2, A2), … …) is designed such that the at least one optical signal is guided from the probe unit (5) to the optical detector unit (7).

3. The refractometer according to claim 2, wherein the light guide (3, 31, … …) or one of the light guides is designed to comprise a Fiber Bundle (FB) of one/more illuminating fibers (B1; B2 … …) and a plurality of imaging fibers (A1; A2, … …), and wherein the Fiber Bundle (FB) branches in a first end section (3a, 31a, … …) leading to the operating unit (1) into a first fiber bundle branch (FB1) with one/more illuminating fibers (B1; B2 … …) and into a second fiber bundle branch (FB2) with the plurality of imaging fibers (A1; A2, … …).

4. The refractometer according to at least one OF the preceding claims, wherein the refractometer relates to a transmission refractometer whose probe unit (5) is equipped with an optical system (8) with an optical axis (z) extending in the longitudinal direction OF the probe unit (5), which is configured to produce a collimated beam (SB) from light conducted by the light guide/guides, wherein the measuring prism (6) has at least two surfaces (OF1, OF2) that are flat and mutually inclined, which are arranged at a surface (OF) OF the measuring prism (6) that contacts a medium, and wherein the two mutually inclined surfaces (OF1, OF2) are respectively inclined about an inclination axis (x) and in opposite directions to each other with respect to a plane perpendicular to the optical axis (z), wherein, the tilt axis (x) is perpendicular to the optical axis (z).

5. The refractometer according to claim 4, wherein the probe unit (5) has a steering element (9) which is arranged along the optical axis (z) in a staggered manner with respect to the optical system (8) such that

-the beam (SB) passes through the measuring prism (6) and the Process Medium (PM) for a first time in a first stroke, wherein the beam (SB) undergoes a first light refraction on the surface (OF) OF the contact medium,

-the beam (SB) is steered at the steering element (9),

-the beam (SB) passes through the measuring prism (6) and the Process Medium (PM) a second time in a second stroke, wherein the beam (SB) undergoes a second light refraction on the surface (OF) OF the contact medium, and

-said optical system (8) then focuses Said Beam (SB) back onto one of said light guides (3, 31, … …), and

-the one of the light guides (3, 31, … …) guides the at least one Optical Signal (OS) dependent on the refractive index of the Process Medium (PM) back to the operating unit (1).

6. The refractometer according to claim 5, wherein the refractometer has exactly one light guide (3) which is designed to conduct the light emitted by the at least one light source (2, 21, 22, … …) to the probe unit (5) and to guide the at least one Optical Signal (OS) dependent on the refractive index of the Process Medium (PM) back to the operating unit (1).

7. The refractometer according to at least one of the preceding claims, wherein the plurality of imaging fibers (a1, a2, … …) are arranged staggered, in particular substantially equally spaced, along a direction (y) substantially perpendicular to the optical axis (z) at the second end section (3b, 31b, … …).

8. The refractometer according to at least one of the preceding claims, wherein the refractometer has a plurality of, in particular at least two, illumination fibers (B1, B2) which are connected to a common light source or a plurality of, in particular at least two, light sources (2; 21, 22, … …), and wherein the illumination fibers (B1, B2, … …) are each designed such that the light of the light source (2; 21; 22, … …) connected thereto is guided from the operating unit (1) to the probe unit (5).

9. The refractometer according to claim 8, wherein the plurality of illumination fibers (B1, B2, … …) are arranged at a second end section (3B, 31B, … …) opening into the probe unit (5) offset along a direction (y) substantially perpendicular to the optical axis (z) and perpendicular to the tilt axis (x).

10. The refractometer according to claim 8 or 9, wherein the refractometer has a plurality of, in particular at least two, light sources (2, 21, … …) which can be individually controlled by the adjustment/evaluation unit (4) and illumination fibers (B1, B2, … …) which are respectively connected to the light sources (2, 21, … …), and wherein the illumination fibers (B1, B2, … …) which are respectively connected to the individually controllable light sources (2, 21, … …) are arranged offset at equal intervals along a direction (y) which is substantially perpendicular to the optical axis (z) and perpendicular to the tilt axis (x) at a second end section (3B, 31B, …) which opens into the probe unit (5).

11. The refractometer according to at least one OF the preceding claims, wherein the probe unit (5) has a sleeve-shaped jacket (10) which is interrupted by at least one clearance (11) by means OF which the Process Medium (PM) can flow on a medium-contacting surface (OF) OF the measuring prism (6) when determining the refractive index OF the Process Medium (PM).

12. The refractometer according to at least one of the preceding claims, wherein the probe unit (5) is applicable within a temperature range defined by a maximum temperature (Tmax), and wherein the maximum temperature is greater than 200 ℃, in particular greater than 250 ℃.

13. The refractometer according to at least one of the preceding claims, having at least one temperature sensor (12) which is designed to know the temperature of the Process Medium (PM), and wherein the adjustment/evaluation unit (4) is designed to determine a process variable of the Process Medium (PM) which can be derived from the refractive index and to take into account the temperature known from the temperature sensor/sensors (12) when determining the process variable of the Process Medium (PM) which is derived from the refractive index.

14. The refractometer according to at least one of the preceding claims, wherein the diameter of the probe unit (5), in particular the diameter of the sleeve-shaped jacket (10), is less than 45mm, in particular less than 20mm, preferably less than 15 mm.

15. The refractometer according to at least one of the preceding claims, wherein the refractometer can be at least partially inserted into a gate valve mounting bracket (13) which can be moved into the Process Medium (PM), especially a probe unit (5) thereof.

16. Method for determining the refractive index of a Process Medium (PM) using a refractometer according to at least one of the preceding claims, wherein,

-emitting light by at least one light source (2, 21, 22, …),

-conducting light emitted by the at least one light source (2, 21, 22, …) by a light guide/guides (3, 31, …) to a probe unit (5),

-refracting light on a boundary surface between a Process Medium (PM) formed by a medium-contacting surface (OF) OF a measurement prism (6) and the measurement prism (6), wherein at least one Optical Signal (OS) dependent on the refractive index OF the Process Medium (PM) is generated by the probe unit (5),

-guiding the at least one Optical Signal (OS) dependent on the refractive index of the Process Medium (PM) back to the running unit (1) by the light guide/guides (3, 31, …),

-transmitting the at least one Optical Signal (OS) by an optical detector unit (7) to an adjustment/evaluation unit (4), and

-determining, by the adjustment/evaluation unit (4), the refractive index of the Process Medium (PM) as a function of the transmitted at least one Optical Signal (OS) and the predefined refractive index of the measurement prism (6).

17. Method according to claim 16, wherein the refractometer has a plurality of, in particular at least two, light sources (2, 21, …) each of which is individually controlled by the adjustment/evaluation unit (4), wherein the refractometer is operated in different operating modes (BM1, BM2, …) in time succession,

-using exactly one of the light sources (2; 21; 22, …) of the refractometer and storing the Optical Signals (OS) belonging to the respective operating modes (BM1, BM2, …), wherein the refractive index of the Process Medium (PM) is determined by the adjustment/evaluation unit (4) from the sum of the stored Optical Signals (OS) from all operating modes (BM1, BM2, …) and from the predefined refractive index of the measuring prism (6).

Technical Field

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

Background

Refractometers are used to determine the refractive index of process media, such as process liquids, in many areas of process measurement technology, for example in food technology, water economy, chemistry, biochemistry, medicine, biotechnology, and environmental measurement technology. The refractive index is taken into account, for example, for determining a process variable that can be derived from the refractive index, such as the concentration of a substance (e.g., a sugar) in the process medium.

The measurement principle of a refractometer is based on the incidence of light at the boundary surface between the process medium, which is formed by the medium-contacting surface of the measuring prism, and the measuring prism. In this case, the optical signal is generated by means of refraction and/or reflection of light at the boundary surface. The direction and/or intensity of the light refracted and/or reflected at the surface of the contact medium depends on the refractive index difference between the process medium and the measurement prism. The refractive index of the process medium can thus be determined from the optical signal and the known refractive index of the measuring prism.

From the prior art, for example, so-called abbe refractometers are known, which operate with a critical angle for total reflection. Depending on the refractive index difference between the measuring prism and the process medium and the angle of incidence, the light incident on the boundary surface between the process medium and the measuring prism is refracted into the process medium and reflected or totally reflected. The critical angle of total reflection and thus the refractive index of the process medium is determined by the intensity of the reflected light as a function of the angle of incidence. Abbe refractometers are described in the prior art in various embodiments, for example in DE 19944798 a 1.

In contrast to abbe refractometers, in the case of transmission-light refractometers (also known as transmission refractometers), the measuring prism and the process medium are traversed by a preferably collimated beam. The deflection of the radiation beam as it passes through the measuring prism and the process medium is dependent on their refractive index difference. The angle of deflection between the incoming and the passing beam is therefore a measure for the refractive index of the process medium. The deflection angle is again known, for example, from the focal position of the passing beam on the detector plane perpendicular to the optical axis of the entering beam. The known transmitted light refractometer is disadvantageous in that: they typically require two access ports to the process media.

A transmissive refractometer with a one-sided process access opening is described in patent document DE 102007050731B 3. In the refractometer described therein, light is injected via a single process access port, collimated by means of illumination optics and deflected on deflection optics, then passes through the process medium and the measuring prism and is focused by imaging optics onto the detector plane. The detector plane is advantageously arranged on the input side, so that a one-sided access to the process medium is possible.

A transmissive refractometer with a one-sided process access port, which uses common imaging and illumination optics, is described in the applicant's application (application No. 102018116409.2), which was not yet published at the time of filing date of the present application. The diameter of the access opening for the process medium can thereby be advantageously reduced.

All refractometers have in common here a measuring prism, a light source, an optical detector unit for detecting the optical signal and an adjusting/evaluating unit for adjusting and/or evaluating the optical signal and subsequently ascertaining the refractive index of the process medium.

In the aforementioned industry, process access ports are typically of very small diameter. Since it is common in the prior art to integrate light sources and/or optical detector units (e.g. camera lines) into refractometers, they often have dimensions which are problematic for process access openings having a small diameter, in the case of space-saving arrangement and/or dimensioning of their components.

Disclosure of Invention

The task of the invention is therefore to: a refractometer suitable for small process access ports is described.

This 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 using a refractometer according to the invention.

With regard to a refractometer, this object is achieved by a refractometer for determining the refractive index of a process medium, having:

an operating unit that can be arranged outside the process medium and has at least one light source, an optical detector unit and an adjustment/evaluation unit;

a probe unit that can be introduced at least partially into the process medium, said probe unit being equipped with a measuring prism having a predetermined refractive index; and

at least one optical light guide for establishing an optical connection between the operating unit and the probe unit, wherein the light guides each open with their first end sections into the operating unit and with their second end sections into the probe unit, wherein the operating unit, the probe unit and the light guide/light guides are designed such that, when determining the refractive index of the process medium,

-at least one light source emitting light,

-the light guide/guides conduct the light emitted by the at least one light source to the probe unit,

the light undergoes a light refraction and/or reflection at a boundary surface between the process medium, which is formed by a medium-contacting surface of the measuring prism, and the measuring prism, wherein the probe unit generates at least one optical signal that is dependent on the refractive index of the process medium,

-the light guide/guides at least one optical signal dependent on the refractive index of the process medium back to the running unit,

the optical detector unit detects at least one optical signal and transmits the at least one optical signal to the adjustment/evaluation unit,

the adjustment/evaluation unit determines the refractive index of the process medium from the transmitted at least one optical signal and the predetermined refractive index of the measuring prism.

The invention has the following advantages:

the separation of the refractometer into an active light-emitting, light-receiving and evaluation light-emitting operating unit and a substantially passive measuring probe unit is made possible by means of at least one light guide. Only the probe unit has to be introduced into the process medium. The running unit can be detached from the probe unit or can be arranged spatially separated. Thereby, the probe unit can be realized with a reduced diameter compared to refractometers in the prior art. The refractometer according to the invention can therefore also be used in the case of process access openings with a particularly small diameter, in particular a diameter of less than 45mm, which are thus also accessible for the refractometer according to the invention.

The operating unit can advantageously be arranged in a manner to be stripped from the process. Often with very high temperatures in the aforementioned industries. Very high temperatures may occur, for example, when Cleaning-in-place and/or disinfection (Cleaning-in-place-in-Process, CIP or SIP) is carried out regularly. Here, the temperature exceeded to 140 ℃. In the solution according to the invention, the operating unit is associated with temperature-sensitive components of the refractometer, i.e., components with electronic and/or electrical components, such as a light source, an optical detector unit, and an adjustment/evaluation unit with a microprocessor and software for processing. These temperature-sensitive components can be arranged outside the process medium (in particular outside the process container for the process medium). In this way, temperature-sensitive components can be thermally insulated from the process medium or, for example, the cleaning medium. Otherwise, especially for refractometers with smaller dimensions, i.e. for non-peelable operating units, sufficient thermal insulation would be very difficult.

In principle, the probe unit itself does not have to have electronic components for determining the refractive index. Since the medium-contacting surface of the probe unit is mostly composed of an intrinsically chemically inert and temperature-resistant material, typically glass or sapphire, the measuring prism can be subjected without problems to high temperatures and/or other extreme processes and/or environmental conditions. The same applies to light guides which are exposed to temperatures of up to 260 ℃ at the second end section leading into the probe unit. The refractometer according to the invention can therefore, in principle, withstand these very high temperatures, depending on the design.

There are essentially few restrictions in the geometrical design of the at least one light guide (length, shape, etc.). The light guide can be designed, for example, to be flexible, rigid or rigid-flexible, depending on the specific arrangement. Here, a rigid-flexible light guide has rigid and flexible sections.

By means of the length and/or the course or the guidance of the at least one light guide, the refractometer can be adapted to the spatial conditions existing in the respective field of application of the refractometer. This is advantageous for processes or process vessels that are difficult to access, for example.

The solution according to the invention is suitable for the transmission-light refractometer and the critical-angle refractometer described at the beginning. In the case of at least one optical signal that is dependent on the refractive index of the process medium, in the case of a transmission-light refractometer, for example, the positioning of at least one focal point of the beam that has undergone a light refraction on the surface of the contact medium is involved. In the case of at least one optical signal that is dependent on the refractive index of the process medium, the critical angle refractometer involves, for example, the location of a bright-dark transition in the light intensity of the light reflected at the boundary surface and the angle of incidence of the incident light associated with this location, which angle of incidence corresponds to the critical angle of total reflection.

The at least one light source is, for example, an LED. The optical detector unit comprises, for example, a camera with a predefined number of pixels. It is for example possible that the camera comprises exactly one line of pixels.

In one embodiment of the refractometer, one or more optical light guides are designed as a fiber bundle with a plurality of fibers, wherein one of the light guides comprises at least one illumination fiber connected to at least one light source and one of the light guides comprises at least two imaging fibers connected to an optical detector unit, and wherein the one or more illumination fibers are designed such that light of the at least one light source is guided to the probe unit and the imaging fibers are designed such that at least one optical signal is guided from the probe unit to the optical detector unit.

In principle, there is no limit to the number of light guides. For example, two completely separate light guides can be used for the illumination fiber and the imaging fiber. Furthermore, the light guides can be guided onto different inputs of the probe unit. Preferably, the refractometer has a large number of imaging fibers, especially at least three. Preferably, the refractometer has at least twenty, particularly preferably at least forty, imaged fibers. Depending on the design of the optical detector unit and of the imaging fibers, an optimum number of imaging fibers is obtained with which the refractometer has as great a sensitivity as possible. The number of imaging fibers corresponds here to the number of pixels of the optical detector unit. However this is not necessarily the case. Since the light is coupled into the imaging fibers under a defined angular range, the signal-to-noise ratio can advantageously also be optimized with a smart design.

In a preferred embodiment of the refractometer, the light guide or one of the light guides is designed as a fiber bundle comprising one or more illumination fibers and a plurality of imaging fibers, wherein the fiber bundle branches in a first end section leading to the running unit into a first fiber bundle branch with the one or more illumination fibers and a second fiber bundle branch with the plurality of imaging fibers.

In the case of a common light guide comprising illumination and detection fibers, the respective fiber bundles can advantageously be guided separately to the light source/light sources and the optical detector unit by branching into a first and a second fiber bundle branch in the operating unit. The light source/light sources and the optical detector unit can thus be separated from one another, in particular can be arranged sufficiently spaced apart from one another. Thus, the separation between the light source/sources and the optical detector unit is simplified. In this case, the branching begins only at the first end section, so that the illumination fibers and the imaging fiber/fibers are guided in a single, common fiber bundle in the region adjoining them.

In one embodiment of the invention, a transmission refractometer is provided, the probe unit of which is equipped with an optical system having an optical axis extending in the longitudinal direction of the probe unit, which optical system is designed to produce a collimated beam from light conducted by one or more light guides, wherein the measuring prism has at least two flat surfaces inclined to one another, which are arranged at the surfaces of the measuring prism that contact the medium, and wherein the two surfaces inclined to one another are each inclined about an inclination axis with respect to a plane perpendicular to the optical axis and in opposite directions to one another, wherein the inclination axis is perpendicular to the optical axis. The inclination of the two mutually inclined surfaces is substantially symmetrical with respect to the optical axis.

The two focal points are generated as optical signals by measuring two mutually inclined surfaces of the prism, the distance between which represents a measure for the refractive index of the process medium.

In a further embodiment, the probe unit has a deflection element which is arranged along the optical axis with respect to the optical system in such a way that it is oriented in such a way that it is parallel to the optical axis

The beam passes through the measuring prism and the process medium for the first time in a first pass, wherein the beam undergoes a first light refraction on the surface of the contact medium,

-the beam is steered at a steering element,

the beam passes through the measuring prism and the process medium a second time in a second pass, the beam undergoing a second light refraction on the surface of the contact medium, and

the optical system then focuses the beam back onto one of the light guides and

-the one of the light guides at least one optical signal dependent on the refractive index of the process medium back to the running unit.

The deflecting element relates, for example, to a mirror or retroreflector.

The design scheme has the advantages that: (see the not yet published application with application number 102018116409.2.) the optical system serves as a common imaging and illumination optic. The refracted light is turned back into the direction of incidence by means of a turning element. It is possible, for example, to advantageously introduce the imaging and illumination fibers into the probe unit at the same end region of the probe unit.

As an alternative to this embodiment, it is naturally also possible within the scope of the invention to: the probe unit is designed without steering elements and therefore with separate imaging and illumination electronics. In this case, the imaging fiber is initially located on the end region of the probe unit opposite the illumination fiber without further measures. However, due to the possibility of a flexible design of the light guide, the light guide comprising the imaging fiber can be guided, in particular bent, such that it opens into the probe unit at the same end region as the light guide comprising the illumination fiber, in order to guide the imaging fiber at the same end region as the illumination fiber. Thus, a single-sided process access opening can also be realized by using a flexible light guide without the explicit use of a deflection element.

Furthermore, as long as the mutually inclined surfaces of the measuring prism are medium-contacting and, as required, a process medium-measuring prism boundary surface is present, there are no restrictions (with respect to the probe unit with or without a deflection element) with regard to the arrangement of the measuring prism with respect to the process medium.

For example, the probe unit may comprise a process window through which the collimated beam is incident into the process medium in an incident direction before the first stroke, and through which the beam is subsequently emitted from the process medium in an exit direction to the second stroke. The measuring prism, the process window and the deflection element are arranged relative to one another such that the beam passes first through the process medium and then through the measuring prism in a first stroke and passes through the measuring prism and then through the process medium in the reverse order in a second stroke. With regard to the path of the beam of the first stroke, the arrangement in this design is: process window-process medium-measuring prism-turning element.

Naturally, an arrangement of the measuring prism, the process medium and the deflection element is also possible. In an alternative embodiment, the measuring prism and the deflection element are therefore arranged relative to one another such that the beam in a first stroke passes first through the measuring prism and then through the process medium and in a second stroke passes first through the process medium and then through the measuring prism in the reverse order, the collimated beam being incident into the process medium via the measuring prism and emerging from the process medium via the measuring prism. The design scheme has the advantages that: the measuring prism itself serves as a process window. No additional process window is required.

For probe units which do not have a deflection element and therefore make exactly one pass at the boundary surface of the contact medium, an arrangement is possible in which the measurement prism/process medium/process window or the process window/process medium/measurement prism.

In a preferred variant of the aforementioned embodiment, the refractometer has exactly one light guide which is designed to conduct the light emitted by the at least one light source to the probe unit and to guide at least one optical signal, which depends on the refractive index of the process medium, back to the travel unit. Exactly one common light guide comprises an imaging fiber and an illumination fiber.

In a further development of the refractometer, the plurality of imaging fibers is arranged offset, in particular substantially equally spaced, in a direction substantially perpendicular to the optical axis at the second end section leading to the probe unit.

In particular, the plurality of imaging fibers are arranged in a direction that is also substantially perpendicular to the tilt axis.

Since the distance between the focal points in this direction represents a measure for the refractive index for the transmission refractometer, the measuring range of the transmission refractometer is delimited by the diameter and/or arrangement of the imaging fibers at the second end section leading into the probe unit.

Furthermore, as mentioned before, there is an optimum number of imaging fibers, which are arranged offset in this direction at the second end section. Furthermore, in order to reduce the calibration of the components of the probe unit or the deflecting element and the requirements for its temperature stability, the imaging fiber can be additionally designed twice, three times or n times in the oblique direction.

The same applies to the illumination fiber. In a further development of the refractometer, therefore, the refractometer has a plurality of, in particular at least two, illumination fibers, which are connected to a common light source or a plurality of, in particular at least two, light sources, and the illumination fibers are each designed such that the light of the light source connected thereto is guided from the operating unit to the probe unit.

In a further development of the aforementioned embodiment, the plurality of illumination fibers is arranged offset in a direction substantially perpendicular to the optical axis and the tilt axis at the second end section leading into the probe unit.

In a further embodiment of the refinement, the refractometer has a plurality of, in particular at least two, light sources that can each be individually controlled by the adjustment/evaluation unit and illumination fibers that are each connected to a light source.

In particular, the illumination fibers connected to the individually controllable light sources are arranged offset at equal intervals in a direction substantially perpendicular to the optical axis and the tilting axis at the second end section leading into the probe unit.

The extension of the measuring range of the folded light meter is achieved by means of individually controllable light sources, wherein reference is made here to the embodiments mentioned below.

In a further embodiment of the refractometer, the probe unit thereof has a sleeve-shaped jacket, which is interrupted by at least one recess, by means of which the process medium can flow on the medium-contacting surface of the measuring prism when the refractive index of the process medium is determined.

The sleeve-shaped jacket preferably has a high chemical and/or mechanical resistance and/or a high resistance to temperature fluctuations of the process medium. For this purpose, the sleeve-shaped casing is made, for example, of steel, in particular stainless steel, or else of glass or teflon.

In a further embodiment of the refractometer, the probe unit can be used in a temperature range defined by a maximum temperature, wherein the maximum temperature is greater than 200 ℃, in particular greater than 250 ℃. The probe unit or refractometer can be used with a process medium and/or subjected to ambient conditions, wherein high temperatures in excess of 260 ℃ are reached. The maximum temperature is less than 1000 ℃ in one embodiment.

In one embodiment of the refractometer, the refractometer has at least one temperature sensor which is designed to acquire the temperature of the process medium, and the adjustment/evaluation unit is designed to determine a process variable of the process medium which can be derived from the refractive index and to take into account the temperature acquired by the temperature sensor/sensors when determining the process variable derived from the refractive index.

The temperature sensor is preferably arranged in the region of the probe unit adjoining the recess in order to detect the temperature of the process medium. The derivable process variable of the process medium relates, for example, to a material concentration, such as a sugar concentration. The temperature sensor is designed, for example, as a resistance-based thermometer, for example Pt100 or Pt1000, or as a thermo-voltage-based thermometer or thermocouple, or as another temperature sensor known from the prior art. Such sensors usually only have to be connected to a conductor loop in order to supply the temperature sensor with electrical energy and in order to transmit the measurement signals generated by the temperature sensor to the operating unit. The connecting wires of the conductor loops required for this purpose are therefore guided substantially parallel to the light guide or light guides.

In a further embodiment, the temperature sensor is designed to measure the relative humidity. And thus advantageously relates to a combined temperature and humidity sensor. In an alternative embodiment, an additional humidity sensor is used. The measurement of the humidity (with a combined temperature and humidity sensor or an additional humidity sensor) is used, for example, to detect a leakage of the process medium at the region of the probe unit adjoining the recess.

In one embodiment of the refractometer, the diameter of the probe unit, in particular the diameter of the sleeve-shaped sheath, is less than 45mm, in particular less than 20mm, preferably less than 15 mm.

In one embodiment of the refractometer, at least part of the refractometer, in particular the probe unit thereof, can be inserted into a gate valve mounting (Schleusenarmatur) which can be moved into the process medium.

In the industry mentioned at the outset, gate valve mounting brackets, in particular so-called telescopic mounting brackets, are widely used, by means of which, for example, electrochemical sensors are moved manually or automatically in the axial direction between a process position and a service position. Since the telescopic mounting bracket closes the process container for the process medium in a fluid-tight manner in the process position and in the service position, the electrochemical sensor can be introduced and/or removed without having to interrupt the process in progress.

With regard to the method, this object is achieved by a method for determining the refractive index of a process medium, which method makes use of a refractometer according to the invention, wherein,

-emitting light by at least one light source,

-conducting light emitted by the at least one light source to the probe unit by the light guide/guides,

refracting light at a boundary surface between the process medium and the measuring prism, which boundary surface is formed by a medium-contacting surface of the measuring prism, wherein at least one optical signal dependent on the refractive index of the process medium is generated by the probe unit,

-guiding at least one optical signal dependent on the refractive index of the process medium back to the running unit by the light guide/guides,

-transmitting at least one optical signal by the optical detector unit to the adjustment/evaluation unit, and

the refractive index of the process medium is determined by the adjustment/evaluation unit as a function of the transmitted at least one optical signal and the predefined refractive index of the measuring prism.

In one embodiment of the method, the refractometer has a plurality of, in particular at least two, light sources each of which is individually controlled by the adjustment/evaluation unit, wherein the refractometer is operated in different operating modes in time succession, in which different operating modes,

exactly one of the plurality of light sources using refractometers, respectively,

-storing the optical signals belonging to the respective operating modes,

and wherein the refractive index of the process medium is determined by the adjustment/evaluation unit from the sum of the stored optical signals from all operating modes and from the predefined refractive index of the measuring prism.

The measurement range of the refractometer is increased by the refractometer operating in different operating modes with the respective light source of the plurality of individually controllable light sources, wherein reference is made here to the exemplary embodiments mentioned below.

Drawings

The invention is explained in detail in the following, not to scale, drawings, wherein like reference numerals identify like features. Where required for clarity or for other meaningful reasons, reference numerals already mentioned in the following figures are cancelled. Wherein:

FIGS. 1a to 1e show various embodiments of a refractometer according to the invention in a sectional view;

FIG. 2 shows a perspective view of a design of a refractometer according to the invention;

fig. 3a, b show different arrangements of the illumination fibers and imaging fibers in different embodiments of the refractometer according to the invention;

fig. 4a, b show the design of a refractometer according to the invention with individually controllable light sources.

Detailed Description

Fig. 1a to 1e show various embodiments of a refractometer according to the invention for measuring the refractive index of a process medium PM. The refractometer has a probe unit 5, which is connected to the operating unit 1 by means of at least one light guide (fig. 1 a: exactly one light guide). In the operating unit 1, at least one light source 2 (see fig. 2) is arranged, the light of which is guided via a light guide 3 (fig. 1a) or one of the light guides (fig. 1b to d) onto the probe unit 5. The probe unit is equipped with a measuring prism 6 with a surface OF that contacts the medium (see fig. 2). In the measuring operation, that is to say for the case OF a probe unit 5 introduced or penetrating into the process medium PM, the medium-contacting surface OF can be flowed through by the recess 11 on the probe unit 5. The probe unit 5 is stable here against extreme operating conditions, for example high process temperatures.

After reflection and/or refraction OF the further guided light on the medium-contacting surface OF, the probe unit 5 generates an optical signal OS which is guided back to the travel unit 1 via the first light guide 3 (fig. 1a) or one OF the further light guides 31 (fig. 1 b-d), where it is detected and reprocessed. The probe unit 5 is essentially passively measured, while the operating unit is used to actively operate the refractometer when measuring the refractive index of the process medium.

Depending on the measurement principle of the refractometer or the design of the probe unit 5, different possible arrangements for one or more light guides 3, 31 are possible. Thus, as is shown in fig. 1b for a transmitted light refractometer, for example, light can be guided by means OF a first light guide 3 on a first end region OF the probe unit 5 and, after refraction on the surface OF the measuring prism 6, the optical signal OS generated during the refraction can be guided back to the operating unit by means OF a second light guide 31, the second light guide 31 being connected to the probe unit 5 at a second end OF the probe unit 5 opposite the first end region.

If necessary, this second light guide 31 can also be guided or bent in the interior of the probe unit 5, so that it opens into the same end region as the first light guide 3, as shown in fig. 1 c.

For a transmissive refractometer (see the still unpublished application with application number 102018116409.2 of the applicant, which relates to a transmissive refractometer with a one-sided process access) with a deflecting element (see the design in fig. 2) in the probe unit 5, or for a critical angle refractometer, the optical signal OS is again guided back in the direction of the incident side, so that the design shown in fig. 1c or 1a (for the case of a single light guide 3 with different fibers) is possible. One or more light guides 3; 31 can be designed flexibly (fig. 1a to 1c), rigidly (fig. 1d) or rigidly-flexibly (not explicitly shown).

If desired, the refractometer also has a cover that encloses the light guide/guides 3; 31 of the guide member 14. The light guides 3, 31 enable a variable length of the region of the refractometer adjoining the sensor unit 5 and thus enable a simple thermal insulation between the sensor unit 5 and the operating unit 1.

The length of the probe unit 5 is typically between 3cm and 30cm, depending on the design. The diameter thereof is preferably selected to be the standard diameter that is usual in process automation, for example 40mm or 12 mm.

A refractometer built into the gate valve mounting bracket 13 is shown in fig. 1 e. The refractometer is preferably inserted into the gate valve mounting carrier 13 in such a way that the probe unit 5 or its end section with the recess 11 is brought into contact with the process medium PM in the moved-in position of the gate valve mounting carrier 13.

In conjunction with the perspective view of the design of the refractometer shown in fig. 2, further details of the probe unit 5 and the operating unit 1 are shown. The operating unit 1 (at the edge of the lower drawing) comprises a light source 2, here an LED, and an optical detector unit 7 with a camera. The optical detector unit 7 and the light source 2 are connected to an adjustment/evaluation unit 4 of the operating unit 1, which is used to adjust the light source 2 and/or to evaluate the optical signal OS and then to ascertain the refractive index of the process medium PM. In this embodiment, a single light guide 3 is preferably used. The light guide is designed flexibly here, but as already mentioned can also be designed rigidly- (flexibly). In a first end section 3a of the light guide 3, which opens into the operating unit 1, the light guide branches into a first fiber bundle branch FB1 and a second fiber bundle branch FB 2. The first fiber bundle branch FB1 comprises in this embodiment an illumination fiber B1 and is connected in the operating unit 1 to a light source 2 which is designed as an LED. The second fiber bundle branch FB2 comprises in this embodiment a plurality of imaging fibers a1, a2, A3, a4 and is connected to the camera of the optical detector unit 7. By branching into two fiber bundle branches FB1, FB2, the light source 2 and the camera of the optical detector unit 7 can be arranged separately from each other. Thereby, undesired effects on the optical detector unit 7 due to e.g. scattered light of the light source 2 are preferably avoided. The design of such a Y-splitter for separating the illumination from the detection on the side of the operating unit 1 is advantageous, but not absolutely necessary.

The second end section 3B opens into the probe unit 5 at a fiber head on the second end section 3B of the light guide 3 opposite the first end section 3a, wherein the illumination fiber B1 and the imaging fibers a1, a2, A3, a4 are arranged at the fiber front side FS of the fiber head. For the sake of overview, four imaging fibers a1, a2, A3, a4 are shown here. There is no limitation in the present invention with respect to the number of fibers. Further details regarding the arrangement or design of the fibers are shown in connection with fig. 3a, b to be set forth next.

The light of the illumination fiber B1 is collimated along its optical axis z by means of an optical system 8 and then passes through the measuring prism 6. The measuring prism has two surfaces OF1, OF2 inclined to each other about the tilt axis x at the surface contacting the medium. In the case OF introduction or penetration OF the probe unit 5 into the process medium PM, the process medium can flow via the clearance 11 over surfaces OF1, OF2 OF the contact medium.

The first light refraction, which depends on the refractive index OF the process medium, occurs upon exit from the measuring prism 6 via the surfaces OF1, OF2 OF the contact medium. In the variant shown here (see fig. 1a), the refracted beam SB is currently reflected by means of the deflection element 9 and undergoes a renewed refraction of light at the second transition between the process medium PM and the measuring prism 6. And then focused back to the fiber front side FS by means of the optical system 8. The measuring prism 6 and the process medium PM can also be arranged in the reverse order relative to one another, as already mentioned above and shown, for example, in application 102018116409.2, wherein in this case an additional process window is required.

Alternatively, in combination with the designs shown in fig. 1b to 1e as mentioned above, variants OF the invention without a deflecting element are also possible in which the beam undergoes only one refraction at the surface OF the contact medium.

The distance between the two focal points FP1, FP2 (produced on the fiber front side FS of the imaging fibers a1, a2, A3, a 4) in the direction y substantially perpendicular to the tilt axis x and the optical axis z represents a measure of the refractive index of the process medium PM in the embodiment illustrated in fig. 2.

The temperature sensor 12, which is designed here as Pt100, additionally measures the temperature of the process medium PM and transmits it to the control/evaluation unit 4 via a measurement transmission path which is guided parallel to the light guide 2. The temperature measured by the temperature sensor 12 is advantageously taken into account, for example, in the calculation of the refractive-index-dependent sugar concentration of the process medium.

The probe unit 5 has a sleeve-shaped sheath 10 made of steel, preferably stainless steel, into which a recess 11 is introduced. As a result, only the sleeve-shaped casing 10, the measuring prism 6 and, if appropriate, the process window and/or the deflecting element 9 come into contact with the process medium PM and, if appropriate, the cleaning medium. The probe unit 5 can thus advantageously be subjected without problems to extreme process and/or environmental conditions.

The illumination fibers B1 and the imaging fibers a1, a2, … … can have the same or different diameters. The fibre head is usually ground flat. However, the fiber head can also be spherically ground or ground into a free-form surface in order to correct, for example, field curvature.

All commonly used refractometers (based on total reflection and transmitted light) are constructed from: a light source 2 (e.g. an LED), an optical system 8, a measuring prism 6 and a detector unit 7 with preferably one line scanning camera. This means that: the invention described above can in principle be used in all conventional refractometers. In the embodiment illustrated in fig. 2, the light source 2 and the detector must be in the same plane in order to be able to replace the light guide 3 with the fiber bundle. This is not the case with all refractometers, but can be achieved by optical matching. Alternatively, the two separate light guides 3, 31 can be used as a fiber bundle FB with the imaging fibers a1, a2, … … and the illumination fibers B1, … … or the ends of the fiber bundle FB can be designed (that is to say on the fiber front side FS) such that the ends of the illumination fibers B1, … … and of the imaging fibers a1, … … are on different planes.

Different variants are also conceivable for the detailed arrangement of the imaging fibers a1, a2, … …, which are now further explained in conjunction with the embodiments shown in fig. 3a to 3b and fig. 4. Fig. 3 a-3 b show a cross-section of a light guide 3 designed as a fiber bundle FB. The fiber front FS, i.e. the cross section of the fiber head of the fiber bundle FB at the second end section 3b of the fiber bundle FB leading into the probe unit 5 and the cross section of the fiber bundle FB at the first end section 3a of the fiber bundle FB leading into the operating unit 1, are shown in each case. In the cross-sectional views of fig. 3a, B, all illuminating fibers B1, B2, … … are shown as unfilled circles and all imaging fibers a1, a2, … … are shown as hatched circles, respectively.

As shown in the left-hand half of the drawing in fig. 3a, the imaging fibers a1, … …, A8 are arranged at the second end section 3b leading to the probe unit 5 in the direction y, i.e., for example in a direction y substantially perpendicular to the tilt axis x and the optical axis z, the distance of the two focal points FP1, FP2 in this direction representing a measure for the refractive index of the process medium.

The illumination fibers B1 can also be integrated into the rows of imaging fibers a1, … …, a8 in the y direction (left graphic half, upper graphic of fig. 3 a) by means of the fiber bundle FB. It is very interesting to design the refractometer as a transmissive refractometer with a retro-reflector as the turning element 9, since the spatial separation of illumination and detection is often difficult. In addition (left figure half, lower figure of fig. 3 a), the illumination fibers B1 may also be arranged slightly offset in the oblique direction x with respect to the imaging fibers a1, … …, a 8.

On the side of the running unit 1, that is to say at the first end section 3a of the light guide 3 (fig. 3a, figure half on the right, figure half below), the imaging fibers a1, … …, A8 can also be arranged in a row, for example for the case of using an optical detector unit 7 with a camera row. In this case, the fibers may be classified or unclassified. In the unclassified case, the mapping must be performed by the adjustment/evaluation unit 4, for example by means of software designed for this purpose. The coupling of the optical detector unit 7 to the imaging fibers a1, … …, A8 may be realized via optics. Alternatively, the camera chip can be contacted directly or introduced at a small distance from the ends of the imaging fibers a1, … …, a8 in the second fiber bundle branch FB 2.

In the case of the use of a separate illumination fiber B1, this illumination fiber is coupled with a separate light source 2 or LED of a coupling fiber (fig. 3a, figure half on the right, figure above).

In order to reduce the calibration of the steering and the requirement for its temperature stability, the illumination and/or detection can be designed twice, three times or n times, where n > 3. This is shown in detail in fig. 3 b. Here, a plurality of lighting fibers B1, … …, B6 (left, top, figure) coupled to the same or different light sources are used. In this case, a plurality of lighting fibers B1, … …, B6 can be arranged in the first fiber bundle branch FB1 at the first end section 3a, for example, with as little space as possible (right-hand, upper pattern). Thereby, a coupling of the individual LEDs to the respective large chip area is made possible. In order to avoid crosstalk of the imaging fibers a1, … …, A8 when coupled to the optical detector unit 7, the imaging fibers a1, … …, A8 can be arranged at a greater pitch on one side of the optical detector unit 7 in the second fiber bundle branch FB2 than at the fiber front side FS of the optical detector unit (FB2, right, lower diagram). It is also conceivable that: the circular arrangement of imaging fibers shown in FB2 in the diagram below fig. 3b is implemented and coupled to a typical camera (i.e., not a line scan camera). It is also necessary in this case for the adjustment/evaluation unit 4 to map the imaged fibers, for example by means of software. In principle, any arrangement via such a mapping is possible.

The imaging fibers a1, … …, a16 may also be designed in multiples. This is shown in the lower left graph of fig. 3 b. A total of 16 imaging fibers a1, … …, a16 are used, which are divided into two rows in the y direction parallel to each other in the oblique direction x. Thus, calibration is also simplified or temperature stability is improved for the imaging fibers a1, … …, a 16.

In the case of the use of a plurality of light sources 2, 21 which can be controlled separately from one another by the control/evaluation unit 4, the measurement range can be extended by using different operating modes BM1, BM2, BM 3. This function can also be achieved by a further splitting of the first fiber bundle branch FB1, wherein a separate interface is used for each lighting fiber B1, … …, B6. As already shown in fig. 3a, B, in fig. 4a all illumination fibers B1, … …, B6 are respectively represented as unfilled circles and all imaging fibers a1, … …, a8 are represented as hatched circles. The enlargement of the measuring range by means of the individually controllable light sources 2, 21 is explained in detail below in conjunction with fig. 4B for a transmission refractometer, wherein three illumination fibers B1, B2, B3 are shown in the upper diagram on the fiber front side FS, by means of which light is conducted to the probe unit 5 in each case in a temporally successive operating mode BM1, BM2, BM 3. In particular, two lighting fibers B3, B2 arranged non-centrally at the fiber front side FS and one lighting fiber B1 arranged centrally between them are involved. The centrally arranged lighting fiber B1 is shown in fig. 4B as a black filled circle, while the first/second non-centrally arranged lighting fibers B3/B1 are differently hatched.

Preferably, the first spacing y1 between the non-centrally arranged first lighting fibers B3 and the centrally arranged lighting fibers B1 and the second spacing y2 between the non-centrally arranged second lighting fibers B2 and the centrally arranged lighting fibers B1 coincide. The imaging fibers (unfilled circles) a1, … …, a9 are arranged as already shown in fig. 3a, 3b in a row ZA at the fiber front side FS.

If the probe unit 5 is designed as already in fig. 2, in each of the operating modes BM1, BM2, BM3 two outer focal points FP1, FP2 are produced in the plane of the fiber front side FS, the distance between which in the y direction represents a measure for the refractive index of the process medium PM. Furthermore, a fixed focal point FF arranged centrally between the two focal points FP1, FP2 results, the positioning of which in the y direction depends on the refractive index of the process medium PM. The fixed focus FF is produced by the fraction arranged in the center OF the beam, which fraction passes through two mutually inclined surfaces OF1 for the first time; the first surface in OF2 undergoes a first refraction OF light and passes through two mutually inclined surfaces OF2 a second time; the second surface in OF1 experiences a second refraction OF light. These two refractions cancel each other out in the case of a measuring prism which is symmetrical with respect to the optical axis.

In order to better recognize the foci FP1, FP2, FF with the operating modes BM1, BM2, BM3, in the lower half of the graph in fig. 4b the respective foci FP 1; FP 2; FF corresponds to the illumination fiber B1 used in the case of producing them, respectively; b2; b3 is hatched. The spacings y1, y2 are currently selected such that for all illumination fibers B3, B2, B1, their fixed focus FF can be imaged on a row ZA of imaging fibers a1, … …, a9 (unfilled circle) of the fiber front FS, and for all refractive indices of the non-central illumination fibers B3, B2 and of the measuring range of the refractometer of the process medium PM, at least one of the outer foci FP1, FP2 of the non-central illumination fibers B3, B2 can be imaged on a row of imaging fibers a1, … …, a9 at the fiber front FS.

In this case, the outer focal points FP1, FP2 of the central illumination fiber B1 in the plane of the fiber front side FS in the first operating mode BM1 are not necessarily imageable onto the rows of imaging fibers a1, … …, a9 for all refractive indices of the measuring range of the refractive index meter of the process medium PM. Depending on the refractive index of the process medium, if necessary only the outer focal point FP1 of the second and third operating modes BM2, BM 3; FP2 can be imaged onto the rows of imaged fibers a1, … …, a9, respectively, at the fiber front side FS.

This is shown in the lower diagram of fig. 4b for the first operating mode BM 1. Here, the outer focal points FP1, FP2 of the first illumination fiber, which are produced in the plane of the fiber front side FS, can no longer be imaged onto the row of imaging fibers a1, … …, a9, so that in the first operating mode BM1 only the centrally arranged fixed focal point FF is detected by the imaging fibers a1, … …, a 9. Therefore, the refractive index of the process medium PM can no longer be determined from the first operating mode BM1 alone, since the two outer focal points FP1, FP2 (black filled circles) can no longer be imaged onto the fiber front side. By using the outer focal points FP1, FP2 of the further operating modes BM2, BM3, the distance d 3-2 × d31 or d 3-2 × d32 from the central fixed focal point FF of the operating modes BM2, BM3 can be determined. The spacing d3 represents a measure for the refractive index of the process medium PM. If necessary, it can also be detected via two operating modes BM2 and BM3, and the distance d3 is 1/2(2 × d31+2 × d32) ═ d31+ d32 is used.

For the case of a turbid process medium PM, the central fixed focus FF may have only a small light intensity and is therefore very weak, depending on the refractive index of the process medium PM. In order not to have to rely on a central fixed focus FF, it is alternatively or additionally also possible to use the distance d 3' between the outer foci FP2, FP1 of the different operating modes BM2, BM 3. The distance d3, which represents a measure for the refractive index of the process medium PM, is currently determined via d3 ═ d 3' + y1+ y 2. However, in this case, the distance between the outer lighting fibers B1, B3, i.e. y1+ y2, from one another must be known very precisely, since a drift in this distance can be reflected in the measurement result.

Of course, combinations of the embodiments shown in fig. 3b and 4a are also possible within the scope of the invention.

List of reference numerals

1 operating unit

2. 21, 22 light source

3. 31 light guide

3a/3b first/second end section

4 adjustment/evaluation unit

5 Probe unit

6 measuring prism

7 optical detector unit

8 optical system

9 steering element

10-sleeve jacket

11 hollow part

12 temperature sensor

13 gate valve mounting bracket

14 guide piece

PM process medium

OS optical signal

z optical axis

x-oblique axis

y an axis perpendicular to the optical axis and the tilt axis

OF surface OF contact medium

OF1, OF2 mutually inclined surfaces

FB fiber bundle

FB1, FB2 first and second fiber bundle branches

B1, B2, … … lighting fiber

A1, A2, … … imaging fibers

BM1, BM2, … … mode of operation

FF. FP 1; FP2 focal point

Front side of FS fiber

Tmax maximum temperature