DE102019132218B4 - flow cell - Google Patents

Abstract

Flow measuring cell (100), comprising - a housing (105), in which at least a first viewing window (141), a first connection (110) and a second connection (120) are formed, - a channel element (200) which has a first opening (215) and a second opening (225) and a continuous channel (205) between these openings (215, 225) for at least one fluid, and- a holder (300),- wherein the channel element (200) along the channel ( 205) is divided into a first end section (210), a middle section (230) and a second end section (220),- the middle section (230) having a rectangular external cross section and being designed to be optically transparent,- the first end section ( 210) and the second end section (220) each have a round outer cross section,- the first opening (215) being formed in the first end section (210) and being connected to the first connection (110), and the second opening (225) formed in the second end portion (220) and connected to the second port (120),- the bracket (300) being connected to the housing (105) and to the duct member (200) to enclose the duct member (200) on the housing (105) in such a way that the housing (105) surrounds the channel element (200) and a first outer surface (231) of the middle section (230) is aligned parallel to the first viewing window (141),- the holder ( 300) on the channel element (200) only contacts the central section (230) and the channel element (200) is spaced from the housing (105) on all sides.

Description

The invention relates to a flow measuring cell.

Flow measuring cells are used, for example, to monitor crystallization processes. In particular, they can be used to make a continuous measurement of a crystal size distribution. Image-based methods have proven to be advantageous in this context, since they contain information about the crystal size as well as the crystal shape and the individual crystal faces. In particular, online microscopes, which are fed via a bypass with a suspension to be measured, offer the advantage of being able to record a statistically significant number of objects in a short time and with high image quality in terms of particle sharpness and few particle overlaps. In particular, compared to the observation of crystallization processes in large vessels, particles can be viewed in focus and better image quality can be achieved. Online microscopes that have been commercially available to date use flow measuring cells in which the crystals flowing past are recorded from one direction via a viewing window using a light source and a camera.

It has been shown that known flow measuring cells are difficult to construct, for example with regard to the alignment of components or with regard to the provision of connections while at the same time having suitable optical properties.

The document DE 100 16 023 A1 discloses a device for the combined use of spectrometry and polarimetry for the simultaneous determination of several measured variables in physical-chemical and biotechnical processes, and at the same time with several optical layer thicknesses.

The document DE 10 2012 108 158 B4 discloses a capillary cell for receiving a microscopic sample, the capillary cell being adapted to be positioned in a chamber volume and comprising a capillary portion and a bottom closure portion.

The document U.S. 2018/0188154 A1 discloses an improved optical flow cell adapted for use in a flow cytometer for differentiating formed bodies in liquid suspension.

The document DE 36 88 679 T2 discloses a flow cell for analyzing materials having a housing and a passageway through the housing.

The document DE 1 299 136 A discloses a cuvette with a tempering jacket.

The document US 4,730,922A discloses a photometer with a sample cell which has a rectangular absorption cross section for a radiation.

The document US 4,243,883A discloses a system for continuously monitoring blood hematocrit levels using a photometric sensor.

The document DE 11 2011 103 757 T5 discloses a miniature UV sensor with disposable flow cell.

It is therefore an object of the invention to provide a flow measuring cell which is designed alternatively or better than known designs. According to the invention, this is achieved by a flow measuring cell according to claim 1 . Advantageous configurations can be found in the dependent claims, for example. The content of the claims is made part of the content of the description by express reference.

The invention relates to a flow measuring cell. The flow measuring cell has a housing in which at least a first viewing window, a first connection and a second connection are formed. The flow measuring cell has a channel element which has a first opening and a second opening as well as a continuous channel between these openings for at least one fluid. Furthermore, the flow measuring cell has a holder.

The channel element is divided along the channel into a first end section, a middle section and a second end section. The middle section has a rectangular outer cross-section and is designed to be optically transparent. The first end section and the second end section each have a round outer cross section.

The first opening is formed in the first end portion and connected to the first terminal. The second opening is formed in the second end portion and connected to the second port. This can in particular be a respective fluidic connection.

The bracket is connected to the housing and to the channel member to secure the channel member to the housing such that that the housing surrounds the channel member and a first outer surface of the middle section is oriented parallel to the first viewing window.

The design according to the invention makes it possible to use a channel element which provides both a rectangular external cross section through which an optical inspection can take place in a particularly advantageous manner and a transition to round end sections which advantageously can be connected to hoses such as inlet and outlet lines can be connected, which have a round cross-section. It has been shown that a particularly well-functioning flow measuring cell can be produced in this way, which is easy to connect and offers ideal optical conditions for optical measurements or observations through viewing windows.

According to the invention, the channel element is at a distance from the housing on all sides, such a distance being able to be specified in particular by the holder.

In particular, observation by means of a camera or another optical device can be carried out through the viewing window. Other types of measurements are also possible through the viewing window. Targeted illumination is also possible via this viewing window or via another viewing window.

The channel is preferably designed in such a way that fluid can flow between the first opening and the second opening in such a way that it does not leak out of the channel. A fluid can in particular be a liquid or a gas. In this liquid or in this gas, for example, particles such as intermediate or end products of crystallization processes can be present, which can be guided through the channel in this way and thus measured.

The holder is intended in particular to hold the channel element in a specific position in the housing.

The rectangular external cross section of the central section provides a particularly good opportunity for carrying out optical observations or measurements in the central section. The rectangular outer cross-section avoids unwanted deflection of light rays. The rectangular external cross section can in particular also be square.

In contrast, the round external cross sections of the two end sections serve to ensure an advantageous connection to round lines. This allows for easy use and avoids the need for additional adapters, which can complicate the setup and cause unwanted effects or strains.

The orientation of the first outer surface of the middle section parallel to the first viewing window also ensures that a completely or largely unimpeded and unmodified beam path through the first viewing window and the outer surface into the channel and out again is possible. This also avoids unwanted distractions or other disturbances during an optical measurement or observation.

In short, it can be said that the channel element with its different external cross sections is ideally adapted to a measurement (in the middle) and for fluidic connections (at the ends).

According to a preferred embodiment, a second viewing window is also formed in the housing, with a second outer surface of the middle section being oriented parallel to the second viewing window. This enables measurement or observation from two directions, whereby the optical advantages already mentioned above also come into their own with regard to the second viewing window. In particular, a largely or completely unimpeded and distraction-free optical measurement or observation through the second viewing window into the channel is possible.

The first viewing window and the second viewing window can in particular be aligned at right angles to one another. In this way, it can be achieved in particular that the fluid in the channel can be observed from two directions at right angles to one another. However, other designs are also possible, for example the viewing windows can be arranged opposite one another or at other angles to one another.

The first viewing window and the second viewing window can be arranged in an overlapping manner, in particular when viewed along the channel. For example, viewed along the duct, they can reveal the same section or at least overlapping sections of the duct. This can make it possible for a single volume within the channel to be observed and/or illuminated from two different directions. However, it should be understood that other arrangements of the viewing windows are also possible. The same applies if there are more than two viewing windows.

According to a preferred embodiment, the flow measuring cell has a first line and/or a second line. The first opening is preferably connected to the first connection by means of the first line. The second opening is preferably connected to the second connection by means of the second line. The lines create a connection between the openings and the respective connection within the housing, so that the flow measuring cell can be connected to connection lines, which can supply and drain fluid, from outside the housing. No changes need to be made within the housing to change connecting cables. Due to the round external cross-sections of the end sections of the channel element, the openings can be connected to the connections by the lines in a particularly simple manner, since round lines can also be used here.

The first line can in particular be a flexible line. A flexible line can be designed, for example, as a silicone hose, made of polymer, rubber and/or Teflon. Likewise, the second line can in particular be a flexible line. By using flexible lines, any component tolerances during the production of the flow measuring cell can be compensated for easily and without disadvantages, which means that it is possible to respond in a simple manner to the fact that the channel element may not be completely geometrically straight. For example, the channel element can have an angle of a few degrees, for example less than one degree, less than two degrees, less than five degrees or less than 10 degrees, between the first end section and the middle section and/or between the middle section and the second end section e.g. may be unavoidable due to production. With a direct connection of the openings to the connections without an intermediate flexible element, an exact adjustment of fixed elements would have to take place or tensions would have to be accepted. By using flexible lines, on the other hand, such an adaptation to the specific channel element, which is afflicted with production-related inaccuracies, takes place in a particularly simple manner.

The first line can in particular be attached to the first end section and/or turned over onto the first end section. Likewise, the second line can be attached to the second end section and/or turned over onto the second end section. A secure and permanent connection is achieved by such a fastening. Turning it on is a particularly simple realization of a connection of a line with a respective end section.

In particular, the viewing windows can be flat. The outer surfaces of the middle section can in particular also be flat. A particularly advantageous beam path is made possible by such a planar design.

The housing can be designed in particular to be fluid-tight. In particular, it can form a chamber surrounding the channel element. Such a fluid-tight design or the design of a chamber surrounding the channel element makes it possible to provide temperature control for the channel in the housing. For example, the housing can have an inlet and an outlet for conducting temperature-controlling fluid through the chamber. As a result, tempering fluid can be introduced into the chamber and also discharged again. This fluid can be brought to a desired temperature beforehand, for example, so that the channel can also be brought to a desired temperature.

In particular, the channel can be formed in a straight line. This enables a particularly advantageous and undisturbed flow of fluid. A rectilinear design can preferably also be spoken of when the manufacturing tolerances already mentioned above lead to slight deviations from a strictly rectilinear shape.

Furthermore, it should be understood that a design of the channel other than a rectilinear design is also possible. For example, bends or other elements can be provided.

The middle section can in particular have a rectangular internal cross section. As a result, a particularly advantageous, for example, distortion-free or low-distortion beam path can be made possible.

The first end section and/or the second end section can each have a round internal cross section. This enables a particularly advantageous connection to round connection elements, for example the lines already mentioned above.

A transition between round or angular inner and/or outer cross sections can be realized by the channel element, which has proven to be a simple and reliable construction.

The channel element can in particular be designed in one piece. For example, it can are composed of elements which each form one of the sections and which can be connected to one another by positive connection, for example by fusing. For example, it can be made of glass. In particular, it can be designed to be completely optically transparent, so that a single material can be used for the channel element and the optical transparency desired in particular in the middle section is provided.

According to the invention, the holder on the channel element only contacts the middle section. This has proven to be advantageous since the channel element is thereby held in a defined manner at precisely that section in which particularly precise positioning in relation to the viewing windows is advantageous. Even if the manufacturing tolerances already described above occur in the channel element, no tensions are generated within the channel element, which could occur if the channel element were also fastened outside of the middle section.

In particular, the mount can have a first mount element and a second mount element, which are spaced apart from one another along the channel. As a result, the channel element can be held at two points, which stabilizes its position in space in a particularly advantageous manner. In particular, the holder can only have the two holder elements, but can also have further holder elements or further components.

The first mounting element and the second mounting element can in particular each be designed to be planar transverse to the channel. This achieves a simple design that advantageously fixes the channel element.

The first mounting element and the second mounting element can in particular each be designed in the manner of a lattice. This allows a light and stable design.

The first mounting element and the second mounting element can in particular have a respective groove. The respective groove can, in particular, accommodate the middle section in a contacting manner on three sides. Such an embodiment achieves a planar contacting of the middle section, as a result of which it can be held in position particularly precisely.

The first mounting element and the second mounting element can in particular have a respective bar which covers the groove, so that the central section is accommodated in contact on all sides. As a result, an even better fixation of the channel element can be achieved. The beam may be designed to be removable from the remainder of the respective support member, allowing the channel member to be changed.

It should be understood that the mount can also be designed differently than described here, for example with more than two mount elements or with mount elements designed differently.

It should be understood that further viewing windows can also be present in addition to the first and second viewing windows already mentioned. For example, a third viewing window can be formed opposite the first viewing window, and a fourth viewing window can be formed, for example, opposite the second viewing window. These opposing viewing windows can in particular be aligned parallel to one another. Respective outer surfaces of the middle section can also be aligned parallel to a respective viewing window. As a result, it can be achieved, for example, that a straight beam path is possible between the first and third viewing window, and that a straight beam path is also possible between the second and fourth viewing window. Thereby, for example, a volume in the channel can be illuminated through the third viewing window and viewed from the first viewing window, and likewise the volume can be illuminated through the fourth viewing window and viewed from the second viewing window.

The flow measuring cell just described can be used in particular as part of a system. The system can have a first camera and a second camera and the degrees of freedom first rotation of the first camera about its optical axis, second rotation of the second camera about its optical axis, zoom difference between the first camera and the second camera and height difference between the first camera and the second camera . Such a system can be calibrated in particular using the method described below, which represents an independent aspect of the invention. The system, a flow measuring cell arrangement as an embodiment of such a system and an associated use and an associated storage medium can also be considered as independent aspects of the invention.

According to a further, independent aspect, the invention relates to a method for calibrating a system with a first camera and a second camera. The system reassigns the degrees of freedom of first rotation of the first camera its optical axis, second rotation of the second camera about its optical axis, zoom difference between the first camera and the second camera and height difference between the first camera and the second camera.

Within the framework of the method, a respective number of first rotations, a respective number of second rotations and a number of zoom differences are iterated over.

A number of corresponding reference image pairs are generated for each combination of first rotation, second rotation and zoom difference, and a respective height difference is calculated therefrom. Each reference image pair has a respective first reference image and a respective second reference image. A number of reference objects are depicted in the respective first reference image and in the respective second reference image. One pair of reference images can be used for each combination, or multiple pairs of reference images can be used.

• - Festlegung einer anfänglichen Kerndichtefunktion des Kerndichteschätzers, deren Definitionsbereich in einer ersten Koordinate die Menge aller möglichen Höhendifferenzen umfasst, und deren Wertebereich in einer zweiten Koordinate die Häufigkeit der jeweiligen Höhendifferenz repräsentiert,
• - Erkennen der Referenzobjekte,
• - Berechnen einer jeweiligen Länge für jedes Referenzobjekt,
• - Bilden jeweiliger Referenzobjektpaare aus je einem Referenzobjekt des ersten Referenzbilds und einem Referenzobjekt des zweiten Referenzbilds eines jeweiligen Referenzbildpaars, so dass jedes Referenzobjekt des ersten Referenzbilds mit jedem Referenzobjekt des zweiten Referenzbilds je genau ein Referenzobjektpaar bildet,
• - Aktualisieren der Kerndichtefunktion für jedes Referenzobjektpaar oder zumindest einen Teil der Referenzobjektpaare mit einer Kernfunktion aus dem Definitionsbereich der Kerndichtefunktion, wobei die Kernfunktion von einem Versatz zwischen dem ersten Referenzobjekt und dem zweiten Referenzobjekt abhängt,
• - Festlegen der jeweiligen Höhendifferenz als denjenigen Wert der ersten Koordinate, an welchem die Kerndichtefunktion ihren maximalen Wert hat.

Each height difference is calculated using a respective kernel density estimator as follows:

• - Determination of an initial kernel density function of the kernel density estimator, whose domain of definition includes the set of all possible height differences in a first coordinate, and whose value range in a second coordinate represents the frequency of the respective height difference,
• - recognition of the reference objects,
• - Calculating a respective length for each reference object,
• - Forming respective reference object pairs from one reference object of the first reference image and one reference object of the second reference image of a respective reference image pair, so that each reference object of the first reference image forms exactly one reference object pair with each reference object of the second reference image,
• - updating the kernel density function for each reference object pair or at least a part of the reference object pairs with a kernel function from the domain of definition of the kernel density function, the kernel function depending on an offset between the first reference object and the second reference object,
• - Specifying the respective height difference as that value of the first coordinate at which the kernel density function has its maximum value.

Finally, the combination of first rotation, second rotation and zoom difference is used to determine the height difference with the largest value of the kernel density function.

Using such a method, a system made up of a first camera and a second camera can be calibrated in a particularly advantageous manner, so that the known degrees of freedom can be taken into account. In particular, it can be avoided that small adjustment errors, which are often unavoidable in experimental setups, lead to errors in measurement results or evaluations. The values obtained can be used, for example, to electronically correct recorded images or to readjust the structure, so that measurements can be taken, for example, without deviations in the rotations from specified initial values and/or without a height difference and/or without a zoom difference.

In particular, the initial kernel density function can be specified such that all values in the second coordinate are zero.

A length can in particular be understood as a length of the reference objects in the direction of a height offset of the cameras and/or along a vertical direction in the system and/or along an axis along which the respective camera is height-adjustable. This can typically easily be taken into account in the image evaluation.

It should be understood that pairs of reference objects are typically formed only between reference images of a respective pair of reference images. If more than one reference image pair is used for a combination of first rotation, second rotation and zoom difference, all reference image pairs can be evaluated separately, with typically only one kernel density estimator with a kernel density function being used for all such reference image pairs that belong to a combination is updated across all reference image pairs.

With each calculation of a height difference, a difference between the length of the first reference object and the length of the second reference object can preferably be calculated for each reference object pair. In this case, the core function also preferably depends on the difference. As a result, the difference can be taken into account, in which case, for example, the core function can have a maximum value that is all the greater or an integral value that is all the greater the smaller the difference is. It can thus be taken into account that small differences in the lengths of the reference objects indicate this show that there is a high probability that it is the same object.

According to one embodiment, each pair of reference images is obtained by converting a respective pair of output reference images with a first output reference image and a second output reference image. A first intermediate reference image can be obtained from the first output reference image by rotating with the first rotation. A second intermediate reference image can be obtained from the second output reference image by rotating with the second rotation. The rotation can be in the direction indicated by the respective rotation, or in the opposite direction. The first intermediate reference image and/or the second intermediate reference image can be scaled depending on the zoom difference. The first intermediate reference image can then be used as the first reference image and the second intermediate reference image can be used as the second reference image. This allows the reference images to be calculated from the initial reference images without having to set the rotation or zoom difference manually.

The output reference images of each pair of output reference images can in particular be recorded or have been recorded simultaneously, and/or they can be extracted or have been extracted from a video stream at the same recording time. This allows easy generation of the initial reference images.

The reference objects can be recognized in particular by means of color recognition and/or by means of grayscale recognition. This has proven advantageous for typical situations. However, other methods can also be used for this purpose, for example other image recognition methods.

According to one embodiment, it can be provided that the kernel density function is only updated if the difference between the length of the first reference object and the length of the second reference object is less than a predefined threshold value. Provision can also be made for a respective offset to be calculated only if the difference between the length of the first reference object and the length of the second reference object is less than a predefined threshold value. As a result, it can be taken into account that typically only when there are differences in the lengths below the threshold value can it be assumed that, given an ideal configuration of the camera degrees of freedom, the same object was actually viewed with sufficient probability. Conversely, it can be achieved that even if the same object was observed in both cameras, the kernel density function remains unaffected, since in this case the configuration of the camera degrees of freedom is insufficient. If the difference in length is larger, it can be assumed that different objects were considered and no further calculations are therefore required. In particular, you can then refrain from updating the kernel density function, since this would not lead to an improvement in the result when considering different physical objects.

In particular, the core function can be a Gaussian function. This has proven to be advantageous for typical applications, since blurring is taken into account. However, other functions can also be used, for example a function can be used which has a value in the value range only at a discrete value of the domain of definition.

The core function can in particular have a maximum and/or an axis of symmetry at the offset. It can also have a maximum value or an integral value that decreases as the difference increases. This allows the kernel function to be ideally adjusted so that it updates the kernel density function in such a way that the height difference is calculated in the best possible way.

When updating the kernel density function, the respective kernel function can be added to the previous kernel density function. This corresponds to a simple procedure that leads to good results. However, other ways of updating are also possible.

The respective kernel function can be determined in particular by scaling an output kernel function with a factor dependent on the respective difference between the length of the first reference object and the length of the second reference object. As a result, it can be taken into account that the lower the difference, the higher the probability that the same physical object is involved. Accordingly, the smaller the difference, the higher the factor can be.

Length and/or offset and/or difference can be determined in particular along the same direction. This corresponds to a suitable course of action. In particular, the same direction with reference to a coordinate system can also be used for all reference images.

The first rotation, the second rotation and the zoom difference, in which the height difference is or was defined with the largest value of the kernel density function, and this height difference can be used in particular as calibration values or calibration values can be generated therefrom. Thus, calibration values for calibrating the system can be provided.

The first camera and the second camera can in particular record a flow measuring cell or a measuring cell which is not a flow measuring cell, for example, or another object from different directions. The method described has proven itself in a special way for such a use with a flow measuring cell. In particular, it can be a flow measuring cell described further above, it being possible to fall back on all the embodiments and variants described herein. However, objects other than a flow cell can be included and the system can still be calibrated as described.

The zoom difference can in particular correspond to a difference between the respective focal lengths of the first camera and the second camera. Such focal lengths typically serve to characterize a zoom of a respective camera. In particular, the height difference can correspond to a vertical distance between the optical axis of the first camera and the optical axis of the second camera. This corresponds to a typical degree of freedom which, when two cameras are set up on an optical table or another base, cannot be set so precisely that it would be identically zero or at least negligible without special calibration. The height difference can thus be determined in an advantageous manner using the method described here, in order to then compensate for it.

In particular, the first rotation can be iterated between a lower limit and an upper limit at equal or variable intervals. In particular, the second rotation can be iterated between a lower limit and an upper limit at equal or variable intervals. The zoom difference can also be iterated between a lower limit and an upper limit at equal or variable intervals. The respective lower limits and upper limits can be set individually. In particular, they can also be the same for the first rotation or the second rotation. Overall, in the manner described or also in other ways, a respective number of values can be specified, which are iterated with regard to the respective degree of freedom. These are then taken into account one after the other.

In particular, the kernel density estimator can be a histogram. This has proven advantageous for typical applications. In particular, the kernel density function can be specified in discrete values of the first coordinate and/or the second coordinate. This has proven workable for typical numerical calculations. However, it is also possible to specify functions represented by formulas.

The method described herein can be carried out in particular on an electronic device, for example a computer or an electronic control device.

According to a further, independent aspect, the invention relates to a system with a first camera and a second camera. The first camera is rotatably mounted about a first rotation. The second camera is rotatably mounted about a second rotation. The first camera and/or the second camera have a variable focal length for establishing a zoom difference. The first camera and/or the second camera are attached in a height-adjustable manner in order to set a height difference between the cameras. The first camera and the second camera are aimed at an optically transparent object from different directions, so that the recording volumes of the cameras at least partially overlap.

The system also has a control device which is configured to carry out a method according to the invention or as described herein. With regard to the method, all of the versions and variants described herein can be used.

The advantages already described above can be achieved by means of the system. In particular, the system can be calibrated in a particularly simple manner using the method.

According to a further, independent aspect, the invention relates to a flow-through measuring cell arrangement with a flow-through measuring cell and a system according to the invention or as described herein. In this case, the flow measuring cell represents the object. In other words, the system can also be referred to as a flow measuring cell arrangement. With regard to the system, all of the versions and variants described herein can be used.

According to a further, independent aspect, the invention relates to the use of a system according to the invention or a system according to the invention dimensional flow cell arrangement for displaying 3D crystals or crystallization processes. It has been shown that flow measuring cells are particularly suitable for displaying such 3D crystals or crystallization processes, in particular if they can be observed by two cameras at the same time. For such a system with two cameras, the calibration method according to the invention has again proven to be particularly suitable. With regard to the system or the flow-through measuring cell arrangement, all of the versions and variants described herein can be used.

According to a further, independent aspect, the invention relates to a non-volatile computer-readable storage medium on which a program code is stored, during the execution of which a processor executes a method according to the invention. With regard to the method, all of the versions and variants described herein can be used.

The viewing windows already mentioned can in particular be made of quartz glass. The channel element can also be made of quartz glass.

The objects entrained in the fluid can be measured in particular using a high-speed camera or two high-speed cameras and associated light sources, for example LED light sources, at the height of the viewing window, for example with variable resolution and/or frequency. For example, both cameras can be controlled together with their light sources in such a way that the corresponding images record the same objects at exactly the same time. This typically requires precise positioning of the cameras in space and axially to the viewing windows and channel member. In order to ensure this, a mounting system can be used, for example, which has a planar base plate and height-adjustable guide rails on which the cameras are mounted. The flow cell can also be mounted in a matching bracket on the base plate, which ensures alignment of the cameras to the cell. A separate calibration block, which can be placed at the position of a cell holder, can also be used to calibrate the recorded image pixels to spatial coordinates via a microscale. It should be mentioned that a high-speed camera can take, for example, more than 40 frames per second, or, for example, 50 frames per second. However, it is not mandatory to use a high-speed camera. For example, a trigger time or an exposure time of a camera used can have a value between 10 and 20 µs, which enables advantageous synchronization with light sources and/or can lead to blurring being reduced to a maximum of a few pixels or just one pixel at typical movement speeds of particles .

In order to quantitatively evaluate the sets of images or videos obtained by the two cameras, it is advantageous to recognize photographed crystals and to identify the detected images of the individual crystals with the image data from the two cameras.

In particular, a camera system with two cameras aligned at right angles allows crystals to be observed from two perspectives oriented at right angles to one another, which in turn makes it possible to reliably reconstruct a three-dimensional crystal shape from the image data obtained. This can be used in software, for example, to automatically determine the three-dimensional geometric shapes of the crystals. This makes it possible, for example, to describe the crystal population by a multivariate crystal shape and size distribution, with which the properties and dynamics of the crystallization process can be quantified and predicted with much greater accuracy.

• Christian Borchert, Erik Temmel, Holger Eisenschmidt, Heike Lorenz, Andreas Seidel-Morgenstern, Kai Sundmacher, „Image-Based in Situ Identification of Face Specific Crystal Growth Rates from Crystal Populations“, Crystal Growth & Design 14(3):952-971, 2014.

Mechanisms that are already known can be used to evaluate images obtained with regard to a crystal size distribution or the shape of crystals flowing through. In this regard, reference is made in particular to the following publication:

• Christian Borchert, Erik Temmel, Holger Eisenschmidt, Heike Lorenz, Andreas Seidel-Morgenstern, Kai Sundmacher, "Image-Based in Situ Identification of Face Specific Crystal Growth Rates from Crystal Populations", Crystal Growth & Design 14(3):952-971 , 2014.

• Christian Borchert, Erik Temmel, Holger Eisenschmidt, Heike Lorenz, Andreas Seidel-Morgenstern, Kai Sundmacher, „Experimental Investigation of Crystal Size and Shape Dynamics“, 4th European Conference on Crystal Growth, 19.06.2012.

In addition, a suitable procedure was published for the following lecture:

• Christian Borchert, Erik Temmel, Holger Eisenschmidt, Heike Lorenz, Andreas Seidel-Morgenstern, Kai Sundmacher, "Experimental Investigation of Crystal Size and Shape Dynamics", 4th European Conference on Crystal Growth, June 19, 2012.

• 1: ein System,
• 2: einen Teil einer Durchflussmesszelle,
• 3: einen Teil einer Durchflussmesszelle in einer Schnittansicht,
• 4: eine Durchflussmesszelle,
• 5: eine Durchflussmesszelle in einer anderen Ansicht,
• 6: ein Ablaufdiagramm,
• 7 bis 16: eine Vorgehensweise bei einer Bestimmung einer Höhendifferenz,
• 17: einen Verlauf eines Gewichtungsfaktors,
• 18: einen Kerndichteschätzer,
• 19: einen weiteren Kerndichteschätzer, und
• 20: ein weiteres Ablaufdiagramm.

The person skilled in the art will find further features and advantages in the exemplary embodiments described below with reference to the attached drawing. show:

• 1 : a system,
• 2 : part of a flow cell,
• 3 : a part of a flow cell in a sectional view,
• 4 : a flow cell,
• 5 : a flow cell in another view,
• 6 : a flowchart,
• 7 until 16 : a procedure for determining a height difference,
• 17 : a history of a weighting factor,
• 18 : a kernel density estimator,
• 19 : another kernel density estimator, and
• 20 : another flowchart.

1 shows a system 1 which can be used, for example, to monitor crystallization processes. The individual components are described in more detail below. The system 1 can also be referred to as a flow cell arrangement.

The system 1 includes an optical table 5 on which other components, described below, are mounted. It should be mentioned that the table 5 is a typical design for such an optical system, but that other types of tables or other bases can also be used.

The system 1 has a first camera 10 and a second camera 20 . The first camera 10 is mounted on the table 5 via a first fastening element 12 . The height of the first camera 10 can be adjusted via the first fastening element 12 . The second camera 20 is mounted on the table 5 via a second fastening element 22 . The height of the second camera 20 can also be adjusted via the second fastening element 22 .

The first camera 10 has a first optical axis 14 . This also defines a longitudinal direction of the first camera 10. The second camera 20 has a second optical axis 24 accordingly. This also defines a longitudinal direction of the second camera 20. The first camera 10 can be rotated about the first optical axis 14, which is referred to as the first rotation. The second camera 20 can be rotated about the second optical axis 24, which is referred to as the second rotation.

The first camera 10 and the second camera 20 each have a zoom setting, by means of which a focal length of the respective camera 10, 20 can be changed. Thus, a zoom difference between the first camera 10 and the second camera 20 can be set as a degree of freedom of the system 1.

The system 1 also has a first light source 30 and a second light source 40 . These are also mounted on the table 5.

The system 1 also has a flow measuring cell 100 . The flow cell 100 is also mounted on the table 5 and is described below with reference to FIG 2 until 5 be described in more detail.

In particular, a fluid which is to be observed by means of the two cameras 10 , 20 can be conducted through the flow measuring cell 100 . For this purpose, viewing windows are provided in the flow measuring cell 100, which below with reference to FIG 2 until 5 be described in more detail. The cameras 10, 20 are there as in 1 seen arranged so that their optical axes 14, 24 are at right angles to each other. Both cameras 10, 20 thus view part of the fluid flowing through the flow measuring cell 100 from two directions at right angles to one another.

The first light source 30 is arranged opposite the first camera 10 with respect to the flow measuring cell 100 . Likewise, the second light source 40 is arranged opposite the second camera 20 with respect to the flow measuring cell 100 . The cameras 30, 40 can thus illuminate respective parts of the fluid flowing through the flow measuring cell 100, which are observed by the respective opposite camera 10, 20. In particular, the cameras 10, 20 can observe the same volume of fluid.

The system 1 also has an electronic control device 2, shown only schematically, which is configured to carry out a method as described further below, for example.

2 shows a part of the flow measuring cell 100 in a perspective view. All components of the flow cell 100 are shown with the exception of a cover, which only in the 4 and 5 is shown.

The flow measuring cell 100 has a housing 105 . A first connection 110 and a second connection 120 are arranged in the housing 105 . The first port 110 and the second port 120 are oppositely arranged along a longitudinal direction as shown. The connections 110, 120 are used for the inlet and outlet of fluid.

A channel element 200 is arranged in the housing 105 . The channel element 200 is formed in one piece from a transparent material, here glass. The channel element 200 is divided into a first end section 210, a second end section 220 and an intermediate central section 230. A channel 205 is arranged in the channel element 200 and is designed as an elongated cavity between a first opening 215 and a second opening 225. The channel 205 runs through the channel element 200 completely along its longitudinal direction and thus offers the possibility of conducting a fluid through the channel 205 . The first opening 215 is formed in the first end portion 210 and the second opening 225 is formed in the second end portion 225 .

As shown, the first end portion 210 and the second end portion 220 each have a circular outer cross-section. Their internal cross-sections are also round. In contrast, the central section 230 has a rectangular external cross section, with an internal cross section of the central section 230 also being rectangular. Here, the cross-sections of the middle section 230 are not only rectangular, but square, which corresponds to a preferred embodiment. In other words, the middle section 230 of the channel element 200 here has a square inner cross-section and a square outer cross-section.

Due to the rectangular design of the outer cross section of the central section 230, it has a total of four outer surfaces which are aligned at right angles to one another. On the outer surfaces, reference is made to 3 to be dealt with in more detail.

The channel element 200 is attached to the housing 105 by means of a bracket 300 . The mount 300 is divided into a first mount element 310 and a second mount element 320 which are spaced apart from one another along the channel 205 . Both the first mounting element 310 and the second mounting element 320 only contact the middle section 230 of the channel element 200.

Both the first holding element 310 and the second holding element 320 are designed in the form of a lattice, as shown.

The first mounting element 310 has a first groove 312 which receives the central section 230 of the channel element 200 in a contacting manner on three sides. The first mounting element 310 also has a first bar 314, which covers the first groove 312, so that the middle section 230 with its rectangular outer cross section is held in contact on all sides. A play between the middle section 230 and the first mounting element 310 is therefore not provided.

The second mounting element 320 has a second groove 322 which receives the middle section 230 of the channel element 200 in a contacting manner on three sides. The second mounting element 320 also has a second bar 324, which covers the second groove 322, so that the middle section 230 with its rectangular outer cross section is held in contact on all sides. A play between the middle section 230 and the second mounting element 320 is therefore not provided.

Beams 314, 324 are presently removably attached, allowing channel member 200 to be interchanged.

The design of the first mounting element 310 and the second mounting element 320 of the mounting 300 ensures that the channel element 200 is only held at its middle section 230 and is fixed there with regard to its spatial orientation relative to the housing 105 . This allows a very precise alignment of the middle section 230 to in 2 not to be seen viewing windows, which are formed in the housing 105 and a cover to be described and which will be discussed in more detail below. As a result, particularly good optical properties can also be achieved in connection with the viewing windows in the middle section 230 of the channel element 200 .

The first end section 210 and the second end section 220 can be arranged on the middle section 230 with small angles of their respective longitudinal directions relative to a longitudinal direction of the middle section 230 due to production. In this case, the channel 205 is not exactly straight, but has slight bends of, for example, a few degrees at the transitions between the first end section 210 and the middle section 230 and/or between the middle section 230 and the second end section 220.

To accommodate such manufacturing variations, the first end portion 210 is connected to the first connector 110 via a first flexible line 115 and, correspondingly, the second end portion 220 is connected to the second connector 120 via a second flexible line 125 . The flexible lines 115, 125 are each slipped over the respective end section 210, 220.

As already mentioned, the position of the channel element 200 in the housing 105 is determined in a particularly advantageous manner by the described embodiment such that the optical properties in the middle section 230 are ideal, and at the same time the channel element 200 already ensures that a transition to round connections takes place . A conversion of a round internal or external cross-section, which is typically used at the connections 110, 120 for connection to external connection lines, into a rectangular internal or external cross-section outside of the channel element 200 is therefore no longer necessary. At the same time, the flexible lines 115, 125 allow for the production-related variations already mentioned, which can lead to the channel 205 possibly not running completely straight, without fear of warping of the channel element 200 or a particularly precise positioning of the connections 110, 120 would be required. The combination described has proven to be particularly advantageous since it can be implemented very easily with the best possible optical properties.

Surrounding the channel element 200, a chamber 130 is formed in the flow measuring cell 100, into which temperature-controlling fluid can be introduced. This allows direct temperature control of the channel element 200 and thus also of a fluid flowing through the channel 205 .

Overall, a fluid can thus be conducted through the channel 205, which fluid can be introduced, for example, through the first connection 110 and discharged again through the second connection 120, or vice versa. By means of already referring to 1 With the cameras 10, 20 described and the light sources 30, 40, it is thus possible to observe crystallization processes, or other evaluations are also possible, which can be carried out using the system 1 shown.

3 shows a part of the flow measuring cell 100 in a sectional view. First mounting element 310 of mount 300 in particular can be seen particularly well, and it is also clear to see that middle section 230, with its square outer cross-section in the present case, is accommodated without play in first groove 312 of first mounting element 310 and likewise without play from the first beam 314 of the mounting element 310 is contacted from above. The channel element 200 is thus held without play in the first holding element 310 . This allows a particularly precise positioning. It should be mentioned that the second mounting element 320, which is 3 is not shown, is constructed accordingly and acts.

Furthermore, in 3 Also seen are three viewing windows, namely a second viewing window 142, a third viewing window 143 and a fourth viewing window 144. These are formed in the housing 105 and each has a planar shape. Furthermore, a first viewing window 141 is formed in the flow measuring cell 100, but this is in 3 is not visible and only in the 4 is shown.

As in 3 Also shown is the central portion 230 of channel member 200 having a first exterior surface 231 , a second exterior surface 232 , a third exterior surface 233 , and a fourth exterior surface 234 . These are each flat, since the middle section 230 of the channel element 200 has, as already mentioned, a rectangular external cross section. The first outer surface 231 is aligned parallel to the first viewing window 141 in the assembled state. The second outer surface 232 is aligned parallel to the second viewing window 142 . The third outer surface 233 is aligned parallel to the third viewing window 143 . The fourth outer surface 234 is oriented parallel to the fourth viewing window 144 . Due to the parallel alignment of the outer surface and the respective viewing window, a particularly advantageous undisturbed beam path through the viewing windows 141, 142, 143, 144 and the middle section 230 of the channel element 200 is achieved. Deflections of light rays are not to be feared due to the parallel orientation. It has been shown that precisely this parallel alignment can be implemented in a particularly advantageous manner by the design of the holder 300 shown.

4 shows the complete flow measuring cell 100 in a perspective view. It can be seen that the housing 105 is closed with a cover 106 . The chamber 130 is thus designed to be fluid-tight. The cover 106 can be understood as part of the housing 105 .

The already mentioned first viewing window 141 is formed in the cover 106 . In the arrangement which 1 is shown, the first viewing window 141 faces the first camera 10 and the second viewing window 142 faces the second camera 20 .

An inlet 132 and an outlet 134 are also formed in the cover 106 . As a result, as already mentioned, tempering fluid can be introduced into the chamber 130 and also discharged again. This enables a reliable temperature control of the channel element 200 and thus also of the fluid flowing through the channel 205 .

In the present case, the cover 106 can be removed in order to be able to carry out maintenance work inside the flow measuring cell 100 .

5 shows the flow cell 100 of FIG 4 in a different view. In this case, only the perspective has changed, so that the third viewing window 143 is also visible.

6 shows a schematic of a calibration process. However, before the figure is described in more detail, general aspects relating to the calibration of the system 1 should be explained.

It is particularly desirable for the in 1 system 1 shown, with both cameras 10, 20 to photograph an identical volume of the channel 205 simultaneously and automatically. In this case, the simultaneous and preferably also automated triggering of both cameras 10, 20 can be ensured via hardware that is used. It is advantageous if both cameras 10, 20 are mechanically precisely aligned with one another in order to ensure that the same volume of the duct 205 is photographed. As already mentioned above, the two cameras 10, 20 can differ in their zoom and the rotation of the image plane and also in terms of their height. If, for example, the zoom of the second camera 20 is determined relative to the zoom of the first camera 10, this results in a total of four degrees of freedom, the values of which are to be determined experimentally. For example, once these values are known, either the images can be recalculated so that they actually depict the same volume of the channel 205, or the cameras 10, 20 can be readjusted manually so that they observe the same volume. The latter variant saves the computing effort required to convert the images.

In order to determine corresponding parameters, for example, videos can first be recorded, for which purpose test particles are guided through the channel 205 . For example, an equidistant grid can be generated in which values for the parameters of the relative zoom (in the present case the second camera 20 relative to the first camera 10) and for both rotations are scanned. For example, the grid points can be run through systematically in three nested for loops. With each run, i.e. for each constellation of three varied parameters, the individual images can be converted according to the current camera configuration. In detail, the images can, for example, be rotated counter to the rotation angle currently being examined and the images of the second camera 20 can be compressed or stretched according to the zoom value currently being examined. Furthermore, an estimated value for the height difference of the cameras can be calculated in order to determine the optimal camera configuration, for example via the best estimate of the height difference.

In an ideal configuration, the two cameras 10, 20 have the same zoom and no difference in height from one another, and the angle of rotation of the image planes is zero. In this case, the objects that can be seen in the respective image sets have identical maximum and minimum coordinates in the vertical direction, which is also referred to below as the z-direction. In case the cameras have a height offset, but an identical zoom and rotation angle of 0°, the maximum and minimum coordinates of identical objects have a constant offset equal to the height difference of the cameras. In this case, identical particles can be identified based on their identical length in the z-direction, i.e. height direction.

The properties of the second case are used to determine a height difference. Here you can search for objects that have an identical or at least very similar length in the z-direction in both images. If this is the case, the height offset of the object is saved in a histogram in both images. The more object pairs have an identical height offset, the more likely it is that this height offset is the true offset, ie the height difference of the cameras 10, 20.

The generation of a histogram, which can also be referred to as a kernel density estimator, is discussed below with reference to FIG 7 until 16 be described in more detail. In the configuration shown with three objects, an exemplary procedure is illustrated, assuming an identical zoom, camera rotations of 0° and a height difference of 100 pixels. Every possible object combination, i.e. three times three combinations, is checked here. In the case where both checked objects have an identical or similar length in the z-direction, a weighted Gaussian distribution is added to the existing histogram. In the present case, this distribution has a fixed standard deviation of ten pixels and a mean value which corresponds to that of the height offset of the object pair. It should be understood that other values are also possible here.

The illustrated procedure can be repeated for each object combination and the histogram can be successively expanded. When all object combinations have been processed, the maximum of the histogram is sought. The position of the maximum then gives the estimated value for the height difference, which of the currently examined parameter combinations (relative zoom, both camera rotations). The larger the maximum value, the more pairs of objects with identical z-length and height offset have been identified, and the better the estimate of the height difference.

Within the framework of three for loops for varying the zoom and the camera rotations, the parameter combination can be searched for that has the largest maximum value in the respective histograms. This combination of parameters, together with the value of the height difference associated with the maximum, then yields the estimated values for the camera parameters.

Determining the maximum and minimum z-coordinates of the individual objects, which form the basis for the entire calibration procedure, can be subject to inaccuracies. Such inaccuracies can come from the image recording and the image processing, for example, and are typically in the range of a few pixels. The presence of such inaccuracies can affect the creation of the histogram in two main ways. On the one hand, a height offset between the objects in both images can only be determined up to a certain level of accuracy. In addition, the values determined for the length of the objects in the z-direction are also subject to error.

An iterative update of the histogram in the sense of H(dz)=H(dz)+1 is, in the presence of measurement inaccuracies, only partially effective in many situations, since it is not possible to completely distinguish between height differences that are close together. For example, a height difference of 100 pixels cannot be significantly distinguished from a height difference of 104 pixels using a pair of objects. For this reason, instead of a point estimator, a Gaussian distribution can advantageously be added to the already existing histogram in order to take possible measurement errors into account in the evaluation.

As part of the histogram update, it is also possible to distinguish between pairs of objects whose length difference is too large, which indicates that they are not identical objects, or is sufficiently small, which indicates that they are the same object acts. In the case of existing measurement errors, this distinction typically cannot be made in absolute terms. For this reason, a weighting factor can advantageously be introduced that preferentially weights small differences in length, but also allows larger differences in length, albeit with a lower weighting factor. An example of a possible course of a weighting factor is given in 17 shown. Furthermore, in 18 an exemplary histogram is presented, which was obtained with an optimal combination of camera parameters, and in 19 shows an example histogram obtained with an incorrect combination of camera parameters. It should be mentioned again that the term kernel density estimator can also be used instead of the term histogram.

Below is the procedure according to a possible procedure with reference to 6 described. It should be understood that this is just an example implementation and other implementations are possible accordingly.

In step 10, the process is first started. In step 12, the test videos mentioned above are loaded. In addition, pairs of reference images are generated, each pair of reference images having a first reference image and a second reference image. In each reference image there are respective reference objects. The first reference images originate from the first camera 10, the second reference images originate from the second camera 20. In step 14 grids for camera rotations and camera zooms are specified.

In diamond 20, an iteration over each camera rotation to be used begins first. In step 22, all reference images of the first camera 10 and the second camera 20 are rotated according to the current rotation. In step 24 respective frames for all reference objects in all reference images of the second camera 20 are calculated. In step 26 these borders are stored.

An iteration over each zoom difference begins in lozenge 30 , which in the present case is implemented in the form of a variable zoom of the first camera 10 . In step 32, the resolution or scaling of the images of the first camera 10 rotated with the current camera rotation is adjusted according to the zoom difference that is currently present. In step 34 frames of all objects in the rotated and scaled reference images of the first camera 10 are calculated. In step 36 these frames are stored.

At diamond 38 the iteration over camera zooms ends and at diamond 28 the iteration over camera rotation ends.

At diamond 40, an iteration over the second rotation of the second camera 20 begins, and at diamond 50, iteration over the first rotation begins tion of the first camera 10. In lozenge 60, an iteration over reference image pairs also begins.

In step 62 maximum and minimum z-coordinates of all objects in the rotated second reference images of the second camera 20 are determined. In step 64, a kernel density estimator is defined as an empty kernel density estimator, which is then used.

In diamond 70 an iteration over all camera zooms begins. In step 72 all minimum and maximum z-coordinates of all objects in the currently rotated and zoomed reference image of the first camera 10 are determined.

In diamond 80 an iteration over each reference object in the second reference image of the second camera 20 begins. In step 82 the differences of the minimum and maximum z-coordinates of the current reference object in the current reference image of the second camera 20 are compared with all minimum and maximum z-coordinates in the current reference image of the first camera 10 is calculated. In lozenge 90, an iteration over all reference objects in the current reference image of the first camera 10 begins again.

In step 92 deviations from differences in the minimum and maximum z-coordinates between current reference objects in the reference images of the first camera 10 and the second camera 20 are calculated. In step 94, a scaling factor is assigned for the object configuration currently under consideration. In step 96, a Gaussian distribution is defined, which has the mean z-deviation as mean value. In step 97 the Gaussian distribution is multiplied by the scale factor and is then added to the kernel density function.

The iteration over the reference objects in the first reference image of the first camera 10 ends in lozenge 98. The iteration over reference objects in the second reference image of the second camera 20 ends in lozenge 88. The iteration over camera zooms ends in lozenge 78.

In step 100 the maximum value of the kernel density function is determined. In the diamond displayed below, it is first determined whether this value F is greater than the previously largest measured value Fmax. If this is not the case ("0"), the iteration over the reference object pairs is ended in diamond 125 . In diamond 130 the iteration over the first rotation of the first camera 10 is ended and in step 140 the iteration over the second rotation of the second camera 20 is ended. In step 150 the determined best camera configuration is saved and in step 160 the process is ended.

However, if the maximum value in the above-mentioned decision diamond after step 100 is greater than the largest value measured so far ("1"), the largest measured maximum value Fmax so far is set as the maximum value just measured, in step 110 the current camera orientations or camera rotations are stored and in step 120 the best camera zoom and the optimal difference in z-coordinates between the two cameras 10, 20 are identified. The process then proceeds to diamond 125 as just described.

In the 7 until 16 it is described in more detail below how a kernel density estimator is used multiple times based on two reference images of a reference image pair, i.e. a first reference image shown in the respective figure a) and a second reference image shown in the respective figure b), based on three reference objects 1, 2, 3 contained therein can be updated to determine a height difference. The reference objects 1, 2, 3 are also referred to below as objects for the sake of simplicity. In 7a) and 7b) the reference objects are shown with respective dashed frames, which can be used to determine the respective extent of the respective object in the z-direction, which is also shown. This is a simulated image set with three objects each, the data set being simulated with an identical camera zoom, rotations of the two cameras 10, 20 of 0° each and a height offset of 100 pixels.

Both 8th until 16 is still in the respective c ) the kernel density estimator generated in each case is given, which can also be referred to as a histogram, for example.

At 8th the object 1 of the first reference image is compared with the object 1 of the second reference image. The former has a length of 226 pixels, the latter has a length of 277 pixels. Both objects therefore have a significantly different length, so if the camera is configured correctly, they cannot be the same object. Thus, the kernel density estimator is not updated.

At 9 object 1 of the first reference image is compared with object 2 of the second reference image. Both objects have a length of 226 pixels each. This is identical, so there is a high probability that it is the same object. The offset that is also shown, which is denoted by v in this and the following figures, is +100 pixels. Accordingly, the kernel density estimator is used with a Gaussian Updated function which has a maximum at 100 pixels.

At 10 object 1 of the first reference image is compared with object 3 of the second reference image. The former has a length of 226 pixels, the latter has a length of 230 pixels. They are therefore of similar length and have an offset of +498 pixels. The four pixel difference in length could also be due to inaccurate image processing. The kernel density estimator is therefore updated with a weighted Gaussian distribution, the maximum of which is 498 pixels and which is weighted with a factor of 0.841 in order to take account of the poorer fit of the lengths.

At 11 object 2 of the first reference image is compared with object 1 of the second reference image. The former has a length of 230 pixels, the latter has a length of 277 pixels. Both objects therefore have a significantly different length, so if the camera is configured correctly, they cannot be the same object. The kernel density estimator is therefore not updated.

At 12 object 2 of the first reference image is compared with object 2 of the second reference image. Both objects are of similar length, with an offset of -298 pixels. The four pixel length difference could also be due to inaccurate image processing. The kernel density estimator is thus updated with a weighted Gaussian distribution, the maximum of which is at -298 pixels, and which was multiplied by a weighting factor of 0.841 in order to take account of the poorer fit of the lengths.

At 13 object 2 of the first reference image is compared with object 3 of the second reference image. Both objects have an identical length of 230 pixels. The offset is +100 pixels. The kernel density estimator is thus updated with a Gaussian function whose maximum is at +100 pixels and which was not multiplied by a weighting factor.

At 14 object 3 of the first reference image is compared with object 1 of the second reference image. Both objects have an identical length of 277 pixels, with an offset of +100 pixels. The kernel density estimator is thus updated with a Gaussian function that is not scaled and has a maximum of +100 pixels.

At 15 object 3 of the first reference image is compared with object 2 of the second reference image. The former has a length of 277 pixels, the latter has a length of 226 pixels. Both objects therefore have a significantly different length, so if the camera is configured correctly, they cannot be the same object. The kernel density estimator is therefore not updated.

At 16 object 3 of the first reference image is compared with object 3 of the second reference image. The former has a length of 277 pixels, the latter has a length of 230 pixels. Both objects therefore have a significantly different length, so if the camera is configured correctly, they cannot be the same object. The kernel density estimator is therefore not updated.

How out 16c ) clearly shows, the largest value in the kernel density estimator is +100 pixels. For the camera configuration mentioned at the beginning with a zoom difference of 0 and respective rotations of 0°, a height difference of +100 pixels was correctly determined, as also shown in 16c ) can be seen with a maximum value of the kernel density function of 0.12.

A sensible procedure for determining the actual existing height difference, rotation and zoom difference of the two cameras 10, 20 of the system 1, which in 1 is shown, it can be done in particular by iterating over respective predetermined values of the first rotation, second rotation and zoom difference and in each case as with reference to the 7 until 16 described an associated height difference is determined. One pair of reference images can be used in each case, or a plurality of pairs of reference images can also be used in each case. That height difference which was determined with the largest value of the kernel density estimator is then assumed to be the actual height difference, and the associated values of first rotation, second rotation and zoom difference are also assumed to be the respective actual values of system 1. This has proven to be a sensible and reliable procedure for typical configurations. A manual adjustment can then be made to correct rotations, zoom difference and height difference, for example, so that both cameras 10, 20 actually see the same volume, or the determined values can be used to measure without changing the physical structure and the determined values can be used as Calibration are used, which is taken into account in a subsequent computational evaluation. For example, images can be determined according to the th rotations and scaled according to the determined zoom difference. Likewise, the height difference can be taken into account by shifting the respective image in the z-direction.

The procedure described is simplified in 20 shown schematically, which will be described in more detail below.

17 shows, as already mentioned above, a function of a weighting factor p as a function of a length difference Δz of the two objects. This was, for example, when referring to the 7 until 16 procedure described is used. It can be seen that the weighting factor is higher, the smaller the difference in length Δz of the objects is. The greater the difference in length, the smaller the weighting factor, and the less the correspondingly generated Gaussian function will contribute to the overall result.

18 shows an example of a kernel density estimator with a combination of values, i.e. rotations and zoom difference, which lead to a clearly recognizable height difference. In view of the clear maximum, it can be assumed that the values used are good or even ideal. 19 in contrast, shows an example of a kernel density estimator for ill-fitting values, with no pronounced maximum being recognizable. The values should therefore not be used.

20 shows a typical procedure for calibration according to a compared to 6 modified embodiment.

In lozenge 10, an iteration starts over predetermined values of the first rotation. In lozenge 20 an iteration starts over given values of the second rotation. In lozenge 30, an iteration over predetermined values of the zoom difference starts. In this case, the iterations can, for example, each run from a predefined minimum value to a predefined maximum value, specifically with a predefined distance between respectively adjacent values. However, other designs are also possible here.

In step 40, a number of one or more reference image pairs are generated for each current combination of first rotation, second rotation and zoom difference, each reference image pair having a respective first reference image and a respective second reference image. For all reference image pairs, in step 42, a procedure corresponding to that which is used with reference to the 7 until 16 was explained, carried out. It should be mentioned here that the kernel density estimator can in principle be updated using a number of reference image pairs, and that the procedure described can be adapted for any number of respective objects.

In step 44 the maximum of the kernel density estimator is then determined and the associated value on the horizontal axis is determined as the height difference which belongs to the combination of the first rotation, second rotation and zoom difference.

The respective iterations end in diamonds 38, 28 and 18. When all iterations have been carried out, it is determined in step 50 which of the height differences was determined with the largest absolute value of the kernel density estimator. The associated combination of first rotation, second rotation, zoom difference and height difference thus forms a calibration of the system. This procedure has proven to be very reliable for typical configurations, i.e. it determines the correct values for the first rotation, second rotation, zoom difference and height difference in almost all conceivable constellations.

It should be understood that the procedure shown here can also be modified, and that in particular variations in the actual implementation of the procedure are possible, which do not lead outside the scope of protection of the claims. This applies in particular if the same effect or the same result is achieved.

Mentioned steps of the method described herein can be carried out in the order given. However, they can also be executed in a different order, as far as this is technically reasonable. The method described herein can be carried out in one of its implementations, for example with a specific combination of steps, in such a way that no further steps are carried out. In principle, however, further steps can also be carried out, including those which are not mentioned.

It should be noted that in the claims and in the description features can be described in combination, for example to facilitate understanding, although they can also be used separately. The person skilled in the art recognizes that such features can also be combined independently of one another with other features or combinations of features.

Back-references in dependent claims can identify preferred combinations of the respective features, but do not exclude other combinations of features.

Claims (17)

Flow cell (100), comprising - a housing (105) in which at least a first viewing window (141), a first connection (110) and a second connection (120) are formed, - a channel element (200) which has a first opening (215) and a second opening (225) and a continuous channel (205) between these openings (215, 225) for at least one fluid, and - a bracket (300), - wherein the channel element (200) is divided along the channel (205) into a first end section (210), a middle section (230) and a second end section (220), - wherein the central section (230) has a rectangular external cross section and is designed to be optically transparent, - wherein the first end section (210) and the second end section (220) each have a round outer cross section, - wherein the first opening (215) is formed in the first end portion (210) and is connected to the first port (110), and wherein the second opening (225) is formed in the second end portion (220) and is connected to the second port (120 ) connected is, - wherein the bracket (300) is connected to the housing (105) and to the channel element (200) in order to attach the channel element (200) to the housing (105) in such a way that the housing (105) has the channel element ( 200) and a first outer surface (231) of the middle section (230) is aligned parallel to the first viewing window (141), - Wherein the bracket (300) on the channel element (200) only contacts the middle section (230) and the channel element (200) is spaced from the housing (105) on all sides. Flow cell (100) according to claim 1 , - wherein a second viewing window (142) is also formed in the housing (105), and - wherein a second outer surface (232) of the middle section (230) is oriented parallel to the second viewing window (142). Flow cell (100) according to claim 2 , - wherein the first viewing window (141) and the second viewing window (142) are aligned at right angles to one another, and/or - wherein the first viewing window (141) and the second viewing window (142) are arranged overlapping as seen along the channel (205). Flow measuring cell (100) according to any one of the preceding claims, - wherein the flow measuring cell (100) has a first line (115) and a second line (125), - wherein the first port (215) is connected to the first port (110) by means of the first line (115) and wherein the second port (225) is connected by the second line (125) to the second port (120). Flow cell (100) according to claim 4 , - wherein the first line (115) is a flexible line, and/or - wherein the second line (125) is a flexible line. Flow cell (100) according to one of Claims 4 or 5 , - wherein the first line (115) is attached to the first end section (210) and/or turned over onto the first end section (210), and/or - wherein the second line (125) is attached to the second end section (220) and / or is placed on the second end section (220). Flow measuring cell (100) according to any one of the preceding claims, - The viewing windows (141, 142) and/or the outer surfaces (231, 232) of the middle section (230) being flat. Flow measuring cell (100) according to any one of the preceding claims, - The housing (105) being fluid-tight and forming a chamber (130) surrounding the channel element (200). Flow cell (100) according to claim 8 - Wherein the housing (105) has an inlet (132) and an outlet (134) for the passage of tempering fluid through the chamber (130). Flow measuring cell (100) according to any one of the preceding claims, - wherein the channel (205) is formed in a straight line. Flow measuring cell (100) according to any one of the preceding claims, - wherein the middle section (230) has a rectangular internal cross-section, and/or - wherein the first end portion (210) and the second end portion (220) each have a round internal cross section. Flow measuring cell (100) according to any one of the preceding claims, - The channel element (200) being formed in one piece and/or completely optically transparent. Flow measuring cell (100) according to one of the preceding claims, - wherein the holder (300) has a first holder element (310) and a second holder element (320) which are spaced apart from one another along the channel (205). Flow cell (100) according to Claim 13 - wherein the first mounting element (310) and the second mounting element (320) are each formed planar transversely to the channel (205). Flow cell (100) according to one of Claims 13 or 14 - Wherein the first mounting element (310) and the second mounting element (320) are each formed like a lattice. Flow cell (100) according to one of Claims 13 until 15 , - wherein the first mounting element (310) and the second mounting element (320) have a respective groove (312, 322), - wherein the respective groove (312, 322) receives the middle section (230) in contact with three sides. Flow cell (100) according to Claim 16 - wherein the first mounting element (310) and the second mounting element (320) have a respective bar (314, 324) which covers the groove (312, 322), so that the middle section (230) is accommodated in contact on all sides.

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