FI20205777A1 - Refractometer - Google Patents

Abstract

The Disclosure of the embodiments of the invention concern a cylindrical probe process refractometer that comprises such a prism (500) that is cylindrical and fits snugly into the probe to be inserted into a process liquid to be measured. The prism (500) also comprises two polished plane surfaces (501) that are cut into opposite sides of the prism (500), working as mirrors in the refractometer optics. The end of the prism (500) is processed to a conical surface with the same axis as the cylinder, making a conical sealing surface (501b) around the prism surface against the measured liquid (502). An embodied cylindrical probe process refractometer (REF) further has a probe tip (502) with a built-in temperature sensor (510). An embodied cylindrical probe process refractometer (REF) has the probe fit to a process connection, having a diameter of 12 mm or ½”.

Description

A REFRACTOMETER

FIELD OF THE EMBODIMENTS OF THE INVENTION In general, the disclosure of the presently embodied invention relates to the field of optics but in more specifically to process refractometers, and even in more spe- cifically to a refractometer with its structure that has been disclosed in the pream- ble part of an independent claim directed thereto.

BACKGROUND A process refractometer measures optically the refractive index of a process liquid in line. A prism forms the interface between the optics and the process liquid.

With reference to Fig 1, in general about the operating principle of a refractometer, the refractometer determines the refractive index RI of the process liquid by meas- urement of the critical angle of total reflection. Light from the light source (L) in Fig 1 is directed to the interface between the prism (P) and the process medium (S) by two prism surfaces (M) acting as mirrors bending the light rays so that they meet the interface at different angles.

With a reference to Fig 2A and Fig 2B, to illustrate optical images by refractome- ter, the refractive index RI can then be determined from the position of the shadow edge C, which can be transformed to an electrical signal e.g. with a CCD array camera. The refractive index RI changes with the process solution concentration.

Normally the refractive index RI increases when the concentration increases. From this follows that the concentration of the process liquid can be read from the optical images (Fig 2A, Fig 2B).

S As in Figs 3A and 3B illustration about mounting of refractometer, an in-line re- N fractometer can be wall-mounted (left) in a pipe, or inserted as a probe (right). The 5 25 — probe refractometer can reach a more representative sample, and a faster measure- 5 ment, as it measures in the middle of the stream, not in the liguid clinging to the I pipe walls.

N But the most important advantages of the probe are due to temperature. The probe N has a temperature sensor in the tip measuring the process temperature T. The con- N 30 centration to be measured is a function of the refractive index and temperature N Conc% = F(RLT)

It means the reading is temperature compensated. Clearly, T is a closer measure- ment of the sample temperature for a probe than for a wall-mounted instrument. A refractometer is quite sensitive to the fouling of the measurement prism surface. If the prism is coated by impurities, the refractometer measures the RI of the coat- ing, instead of the process liquid. The probe tip is hotter than the pipe wall, making the coating more soluble. In addition, the probe tip is in the middle of the flow, enhancing mechanical cleaning by the flow. The trend in the pharmaceutical industry is to use cylindrical 12 mm outer diameter probes for measuring instruments. The principal players are adhering to this de — facto standard, providing instruments to measure pH, conductivity, ion concentra- tion, dissolved oxygen and ORP (Oxidation-Reduction Potential) with 12 mm outer diameter probes. As far as the author knows, there is no refractometer on the market conforming to the 12 mm probe diameter reguirement. Yet, eguipment de- livered to pharma industry, such as chemical reactors, are today prepared mainly — for 12 mm measurement probes, by dimensioning the process connections accord- ingly. Probes with larger diameters cannot easily be installed

SUMMARY The purpose of the embodiments of the invention is to make an in-line process refractometer with a probe diameter as small as possible, targeting to 12 mm probe standard, which is a widespread standard for inline sensors in the pharma industry. According to the author's knowledge, no one has yet been able to make a refrac- tometer to conform to this standard. According to the embodiments of the invention, as the embodied cylindrical prism makes a 12 mm probe possible, it provides a decisive advantage on the pharmaceutical instrumentation market. N 25 — A cylindrical probe process refractometer according to the invention is character- . ized in that, the prism is cylindrical and fits snuggly into the probe.

O = A refractometer according to an embodiment of the invention has two polished I plane surfaces are cut into opposite sides of the prism, working as mirrors in the N refractometer optics. 3 30 A refractometer according to an embodiment of the invention comprises such an N end of the prism that is processed to a conical surface with the same axis as the N cylinder, making a conical sealing surface around the prism surface against the measured liquid.

A refractometer according to an embodiment of the invention, comprises such a probe tip that has a built-in temperature sensor. A refractometer according to an embodiment of the invention has as the outer di- ameter of the probe to fit to a 12 mm diameter process connection. A refractometer according to an embodiment of the invention has the outer diam- eter of the probe that fits to a half inch (12.7 mm) diameter process connection.

FIGURES Embodiments of the invention are described in the following in a further detail with reference to the examples shown in Figures 2A to 14. Fig 1 illustrates known techniques as such, Figs 2A and 2B illustrate optical images by a refractometer in general as such, Figs 3A and 3B illustrate refractometer mounting positions in general as such, Fig 4 illustrates an example detail of refractometer optics according to an embod- iment as such, Fig 4B illustrates an embodied prism cut along the plane of the optical light rays as such, Figs 5A, 5B, and 5C illustrates examples of details in embodiments, such as ex- amples of prisms according to embodiments of the invention, Figs 6 and 7 illustrate examples of details in embodiments, such as examples of prisms according to embodiments of the invention,

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QA & Fig 8 illustrates an embodied refractometer in combination of a thermowell,

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O - Fig 9 illustrates bending problem of a refractometer probe,

O E Fig 10 illustrates a solution to the Fig 9 problem, S Fig 11 illustrates an optional camera-based solution to detect the Fig 9 prob- S 25 lem,

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N Fig 12 illustrates an image conduit implementation examples for image con- veying in an embodiment,

Fig 13 illustrates an example of an embodiment, and Fig 14 illustrates embodiment example of the invention with splitable optics.

EXAMPLES ON EMBODIMENTS OF THE INVENTION In the following figures (Fig) same reference numerals are used to denote to the similar objects in the Figs, if expressly otherwise indicated. The objects with the same reference numeral do not need necessarily to be exactly the same as a skilled person in the art knows on the basis of the embodiments.

Fig 4 illustrates a larger picture of the reflected rays in an embodied refractometer, from the prism 500 to the CCD element, as been illustrated in the Fig 4, to form the image (A Cf B) into digital form for further processing by a computer’s micro- processor up, for example. A lens 802 can be used in focusing the image to the CCD element’s window.

With reference to Fig 5A, in embodiments of the invention, the prism 500 of the refractometer (REF) is basically cylindric, made to fit snuggly to the inner diame- — ter of the probe. A conical part is grounded at the end of the cylinder, to make a sealing surface to the probe tip. It fits a conical hole in the probe tip. The seal is typically cut out of a 0.1 mm Teflon sheet 501b (i.e. as in Figs 4, 5A, 5B and 5C). Moreover, two flat mirrors 501 are grounded in two opposite sides of the cylinder, to work as mirrors in the refractometer optics.

— The cylindrical form of the prism makes it possible to make the probe diameter of the refractometer small. A primary objective, crucial for the pharmaceutical indus- try, is an embodiment with an outer probe diameter of 12 millimeter.

There is a limit to how small the prism can be. The interfacing surface 502 in N contact with the process liguid must have an adeguate area, that the optics can . 25 integrate over reasonable sample size. Fig 4B shows the prism cut along the plane O of the optical light rays. Interfacing surface 502 is a surface between the prism 500 © and the medium, i.e. the liquid when the embodied refractometer REF with the E prism 500 is in use. N Figure 5A illustrates an example of a refractometer prism 500 as in a scaled (by 5 30 the dimensions in suitable part) example of embodied details of the refractometer ON according to the disclosure of the embodiments, with shown exemplary measures. N . . . .

The embodiment can be combined to one or more embodiments of the invention.

According to an embodiment, the prism 500 is a sapphire prism having a cylindri- cal form. According to an embodiment variant, the sapphire prism 500 is con- structed to measure Refractive Index (RI) in rangel.31 — 1.53, for the embodied refractometer. According to an embodiment, the sapphire prism is manufactured 5 to fit snuggly into a 12 mm Outer Diameter (OD) and 10 mm Inner Diameter (ID) pipe of the refractometer probe.

According to an example of embodiment, the prism 500 has two opposite side positioned mirrors 501 to form a mirror pair, that are polished, the prism tip 502, that is embodied with a blunt planar shape in the example, the tip 502 being pol- ished. The prism 500 has also two mounting formations 503, embodied at the op- posite sides of the prism 500. Such formations can be used to provide the prism 500 to the same position as intended at the manufacturing, which is useful espe- cially if the prism is to be meant in the refractometer that require prism change to another same or similar prism.

In an example, the plane and the angle in respect to the prism’s central, rotational axel has been indicated in Fig SA. In the same example, the sealing of the prism to probe’s cylindrical pipe has been indicated by 501b as been illustrated, with an example value in respect to the plane of the planar tip 502 at the interface of the prism 500 and the medium.

In Figs 5A and 6 item 505 has been used to indicate a prism’s 500 polished surface, which is in plane perpendicular to the optical axis of the prism 500, opposite to the tip plane 502, which is thus parallel to the surface 505 of the prism 500.

Figs 5B and 5C as well as Figs 6 and 7 illustrate examples of an embodied detail of the refractometer of Fig 5A according to the disclosure of embodiments, as viewed from the tip direction (Fig 5B), and from a direction of diagonally sideways N (Figs 5C, 6), the embodiment examples to be combinable to one or more embodi- . ments of the invention. ? By making the prism 500 cylindrical, the diameter of the probe can be minimized 2 (Fig 5B). E 30 It’s a geometrical fact that the probe diameter is minimized for a cylindrical prism S 500 (Fig 5B) with a given optics (Figs 4, 4B). The area on the mirrors reflecting S the light rays 507 (Fig 6), is embodied as a straight line that stretches all the way S from the conical seal to the inner diameter of the probe.

The thin 12 mm diameter probe has advantage over probes with larger diameters; — the temperature sensor 510 (Fig 7) in the 12 mm probe tip measures temperatures faster.

The temperature reading will always be close to the temperature of the pro- cess liquid, when in such use.

A dashed line indicated optional temperature sensor 510 indicates an example of an embodied temperature sensor position on prism’s mantel, to measure the temperature at the location from an additional position.

The optical measurement of refractive index is practically instantaneous.

A delay in the temperature impairs the temperature compensation.

Temperature measurement by the 12 mm probe synchronizes with the optical measurement, making the temper- ature compensation more accurate.

According to an embodiment, the mirrors 501 can be provided respectively pair- — wise to different mutual objecting positions at the prisms surface as illustrated in Fig 7. According to an embodiment example of Fig 7, the prism can have two optical planes for the rays to be used in the refractometer for the incident and reflect rays perpendicular position in respect to the prism perimeter, at the objecting positions, — so to provide two optical planes of reflection, embodied perpendicular to each other.

Although perpendicular directions embodied as an example, there can be also other positions of the mirror pairs (501, 501) for the related optical planes of incident and reflected light rays.

Numbers related to dimensions of size of the objects as well as particular measures of them has been shown as examples, in millimeters.

Although the geometric ratios in the examples may be applicable as such, the measures has been used for illus- trative purposes.

According to an embodiment, the embodied refractometer (REF) using an embod- ied prism (500) meets a pharma standard of 12 mm. o 25 Withreference to Fig 8, as all refractometers contain a temperature measuring el- O ement, anyhow, it is often the wish to use the refractometer to make also the meas- K urement of the process temperature.

The refractometers on the market have probe ? diameters above 1", having too much mass, making a large time constant.

It leads 2 generally to a disappointingly sluggish measurement.

If the temperature instead = 30 would be measured with a separate dedicated probe, the usual temperature meas- N urement probe is about 12 mm outer diameter (Fig 8). This is considered the right 5 balance between sturdiness and speed of measurement.

Hence an embodied refrac- ON tometer REF with 12 mm outer diameter probe has the advantage to also handle N the process temperature measurement as well as a dedicated temperature measure- ment probe.

Thereby it is possible to save the cost of installing an additional tem- perature measurement probe.

That the 12 mm refractometer probe tip temperature is adjacent to the process tem- perature, makes it less prone to fouling.

But there are cases where prism wash must be used.

An in-line nozzle, mounted on the refractometer tip, blows steam or high- pressure water directly on the prism at regular intervals can be employed.

But, one cannot blow steam or water into a pharma reactor for example.

There are devel- oped solutions to such situations; installation devices, that automatically withdraw a sensor probe into an isolated chamber, where the probe can be regularly washed without letting wash media into the process.

There are known devices as such that are able to take a measurement probe, e.g. for pH, out of the process flow automat- ically for an automatic flush or purge of the fouling-based substances from the probe tip, but they are all for 12 mm probes.

Hence, according to the author at the priority date of the present document, there is no in-line refractometer on the mar- ket that has the advantage of being able to be used in combination with such auto- matic flushing device. — According to an embodiment, the embodied refractometer can be used in such a system with such automatic flushing device.

A well-known problem with a probe type refractometer, is that flow forces bends the probe.

Even a hardly perceptible bending causes a significant error in the meas- urement (Fig 9). The situation has been illustrated with reference to Fig 9. The geometry between the light source L, prism 500 and the image sensor CCD would change because of the flow forces.

The optical image can be transferred by an Image conduit, a glass rod consisting of a coherent bundle of optical fibers.

Each fiber corresponds to one pixel of the image.

The image is transferred from one end surface to the other, and the bending — of the probe has no influence on the position of the shadow edge in the image.

S According to an embodiment with flexible image conduits 801, 804 embodied as N optical fibers in as Fig 10, especially.

Item E illustrates an object in the liguid.

S The same effect, that the shadow edge position isn’t influenced by probe bending, © can also be reached by using a miniature camera (CMOS) close to the prism’s 500 E 30 (Fig 11) surface 505 as embodied in Fig 11, to transfer the image to the imaging N device, such as a CCD-image sensor for example. 3 The optical image can also be transferred with a row of a number of lenses (or one N lens). The lenses maybe normal thin lenses or rod lenses as embodied in Fig 12. N Graded index (GRIN) lenses can also be employed.

In those cases, when used as image conduits, the lens row must be mechanically decoupled from the bending of the probe.

The cylindric prism has the best possible thermal contact by conduction with the probe inner wall. It means that the prism reaches temperature equilibrium quickly. Thereby the optical distortion by temperature gradients is eliminated. The embodied refractometer REF according to an embodiment of the invention can also be used for turbidity measurements. Instrument suppliers are providing turbidity sensors to the pharmaceutical industry with a 12 mm outer diameter probe. A turbidity sensor as such works with an optical fiber, sending light into the process liquid and measuring the light scattered back by particles. Alternatively using two fibers (Fig 13), one sending light (Ray incident) and the other receiving (Al, A2, Fig 13). If the turbidity meter optical plane is perpendicular to the refractometer optical plane, (according to a prism embodiment example shown in Fig 7, showing two mirror pairs of mirrors 501) the two measurements can be independently made, provided their respective light sources alternate. The turbidity meter arrangement — can also be made a particle analyzer, if the receiving fiber optics is exchanged to an image conduit. Item F illustrates such an object in the liquid. A single-use version of the refractometer prism 500 can be built on the refractom- eter according to an embodiment of the invention. A single-use bioreactor or dis- posable bioreactor is with a disposable bag instead of a culture vessel. All wetted parts have to be discarded after a single use. This refractometer can be separated in two enclosed compartments, as illustrated in Fig 14 by the shown embodiment. The prism part is sealed by the cylindrical prism, the other part for example by an additional window (Fig 14). The connec- tion/detachment can be made by the means 13. A lens, such as item 802 can be > 25 used in the embodiment. O For the single-use version above, merely the prism part has to be discarded. The = optical other part can be removed and used repeatably. = i

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Claims (6)

1. A cylindrical probe process refractometer characterized in that, the prism is cylindrical and fits snuggly into the probe.

2. The refractometer of claim 1, wherein two polished plane surfaces are cut into opposite sides of the prism, working as mirrors in the refractometer optics.

3. The refractometer of claim 2, wherein the end of the prism is processed to a conical surface with the same axis as the cylinder, making a conical sealing surface (501b) around the prism surface against the measured liquid (502).

4. The refractometer of claim 3, wherein the probe tip has a built-in temperature — sensor.

5. The refractometer of claim 4, wherein the outer diameter of the probe fits a 12 mm diameter process connection.

6. The refractometer of claim 4, wherein the outer diameter of the probe fits a half inch (12.7 mm) diameter process connection.

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