Arrangement for optical measurement of a process variable and measuring instrument comprising such an arrangement for optical measurement of a process variable and measuring instrument

Abstract

Arrangement (13) for optical measurement of at least one process variable, in particular an analytical process variable, in a medium (14), comprising - at least one light source (8) for transmitting light, - at least one light receiver (9) for receiving received light, wherein the light receiver (9) converts the received light into an electrical measurement quantity, - an optical sensor element (11), wherein the optical sensor element (11) is at least partially in contact with the medium (14) and converts the transmitted light into the received light, and - at least one data processing unit (7) for controlling and regulating the light source (8) and / or for processing the electrical measurement quantity into the process quantity, characterized by the fact that a light guide (10) is provided, wherein the light guide (10) connects the light source (8) to the optical sensor element (11) and the optical sensor element (11) to the light receiver (9), wherein the optical fiber (10) is designed with at least three arms, comprising a first arm (10.1), a second arm (10.2) and a third arm (10.3), wherein the first arm (10.1) is arranged on the light source (8) such that transmitted light enters the first arm (10.1), wherein the second arm (10.2) is arranged on the light receiver (9) such that received light from the second arm (10.2) enters the light receiver (9), wherein the third arm (10.3) is attached to the optical sensor element (11) in such a way that transmitted light from the third arm (10.3) reaches the optical sensor element (11) and received light from the optical sensor element (11) reaches the third arm (10.3), and wherein the first arm (10.1) and the second arm (10.2) combine to form the third arm (10.3), wherein the power consumption of the arrangement (13), in particular the light source (8) and the data processing unit (7), is less than 1 W.

Description

[0001] The invention relates to an arrangement for the optical measurement of a process variable, in particular an analytical process variable, in a medium, and to a measuring device comprising such a device.

[0002] Although the invention is explained below using an oxygen sensor that operates on the principle of fluorescence quenching, the inventive idea is not limited to such sensors. Rather, other process parameters, in particular concentrations of certain substances such as ions, molecules, gases, or other chemical compounds, pH value, or temperature, can also be measured using such an arrangement with conventional modifications. Measuring instruments suitable for determining the corresponding process parameters are offered and distributed by the Endress+Hauser Group in a wide variety of models.

[0003] The sensor comprises a sensor head containing an optical sensor element, to which a housing containing a data processing unit is attached. The optical sensor element is illuminated by light from a light source. The light is reflected back by the optical sensor element with a specific light characteristic, possibly after conversion, detected by a light receiver, and a signal from the light receiver representing the light characteristic is evaluated by the data processing unit.

[0004] From EP 2 295 953 A1, a device for measuring substance concentrations in solutions based on fluorescence measurement is known. The device comprises a light source that emits transmitted light into the medium under investigation. This transmitted light excites an optical sensor element that is in contact with the medium under investigation. During the fluorescence measurement, the transmitted light is absorbed by the optical sensor element, and light of a different wavelength is reflected back, depending on the process variable, such as the concentration of an analyte. The radiation reflected back by the optical sensor element is received by a light receiver, converted into an electrical measurement, and forwarded to a data processing unit.Depending on the properties of the optical sensor element, the optical sensor reacts to different particle concentrations with different received light intensities, received frequencies, phase angles and / or decay curves.

[0005] DE 37 02 210 A1 describes a method for determining the concentration of substances contained in a substance, in particular oxygen, using a luminescence indicator whose luminescence intensity is reduced or quenched by the substances to be determined. The excitation light reaches the sensor element via a first light guide, and the luminescence light reaches the detector via a further light guide.

[0006] Basically, there are various methods for arranging the light source / light receiver with the optical sensor element, which will be explained below.

[0007] For sensors with sufficient power supply, the light source / light receiver can be positioned directly on the optical sensor element. However, this is difficult to implement with high-temperature sensors, as it results in long and interference-prone connecting cables from the data processing unit, located remotely from the high-temperature measuring point, to the optical components.

[0008] To avoid this, the light source and light receiver can be placed far away from the potentially hot medium under investigation. The light can then be guided to the optical sensor element via a single optical fiber. This is not feasible for compact sensors with a small form factor, as a relatively large optical fiber is required.

[0009] Separate optical fibers can also be used for the light source and the light receiver. This is known, for example, from EP 0 940 662 B1. For an optimal measurement signal, the optical fibers must meet at an angle of approximately 45° at the optical sensor element. This, however, is not feasible for compact sensors.

[0010] German patent application DE 102 18 606 A1 describes a digital sensor consisting of two detachably connected components: a sensor-side component (plug-in head) to which a sensor element (in this case, a potentiometric sensor) and a data storage device are permanently connected, and a transmit-side component (a connector coupling or a sensor cable) via which the sensor-side component is coupled to a transmitter or directly to a control system. Digital bidirectional data transfer between the two described sides occurs contactlessly via a magnetically inductively coupled interface. Energy transfer via the contactless, magnetically inductive interface is unidirectional. Due to the energy transfer via a galvanically isolated interface, only a small amount of energy is available to the sensor-side component. The applicant offers and markets corresponding sensors under the name "Memosens".It should be noted that the “Memosens” technology is not only applicable to potentiometric sensors, but that it is in principle applicable to any sensors for determining and monitoring a wide variety of process variables.

[0011] The invention is based on the objective of providing optimal light input and optimal light output for compact, optical and low-energy sensors.

[0012] The problem is solved by an arrangement for the optical measurement of a process quantity, in particular an analytical process quantity, in a medium, comprising at least one light source for emitting transmitted light; at least one light receiver for receiving received light, wherein the light receiver converts the received light into an electrical measurement quantity; an optical sensor element, wherein the optical sensor element is at least partially in contact with the medium and converts the transmitted light into the received light; and at least one data processing unit for controlling and regulating the light source and / or for processing the electrical measurement quantity into the process quantity.The arrangement is characterized in that a light guide is provided, wherein the light guide connects the light source to the optical sensor element and the optical sensor element to the light receiver, wherein the light guide is multi-armed with a first arm, a second arm and a third arm, wherein the first arm is arranged on the light source such that transmitted light enters the first arm, wherein the second arm is arranged on the light receiver such that received light from the second arm enters the light receiver, wherein the third arm is attached to the optical sensor element such that transmitted light from the third arm reaches the optical sensor element and received light from the optical sensor element reaches the third arm, and wherein the first arm and the second arm combine to form the third arm, wherein the power consumption of the arrangement (13), in particular of the light source (8) and the data processing unit (7), is less than 1 W.

[0013] This allows the light source, such as an LED, and the light receiver, such as a photodiode, to be positioned away from the potentially hot medium. In its simplest form, the light guide has a "Y-shape." By using a light guide with multiple arms extending from the LED or photodiode, which merge into a single arm at the optical sensor element, it is possible to maximize the light yield.

[0014] In a first advantageous variant, the light guide is designed as a glass rod. This is a cost-effective solution. The first and second arms of the glass rod are bent in such a way that they together form the third arm. As already mentioned, this can result in a "Y-shape," meaning the glass rod is designed as a branching rod at one end.

[0015] In a second advantageous embodiment, the optical fiber is designed from a fiber bundle formed from a multitude of fibers, wherein a first group of fibers, the transmitting fibers, form the first arm, and a second group of fibers, the receiving fibers, form the second arm. The use of flexible fibers makes it possible to compensate for any differences in length. This problem can arise, for example, due to manufacturing processes or temperature fluctuations.

[0016] In another advantageous embodiment, the optical fiber is designed from multiple fiber bundles, including, in addition to the first and second groups of fibers already mentioned, a third and fourth group of fibers. The third and fourth groups of fibers form a fourth and fifth arm of the optical fiber, respectively. The fourth and fifth arms also merge into the third arm. While the first arm transmits light for a first process variable and the second arm receives light for the same process variable, the fourth arm can transmit light for a second process variable, and the fifth arm can receive light for the same process variable. Examples of the different process variables include oxygen and temperature, as well as the process variables already mentioned.

[0017] In a first advantageous variant of the fiber arrangement, the transmitting fibers and receiving fibers are distributed in the third arm such that in the cross-section of the third arm the transmitting fibers form a first partial circle, and the receiving fibers form a second partial circle, completing the first partial circle, wherein the area of ​​the first partial circle is smaller than that of the second partial circle.

[0018] In a second advantageous variant of the fiber arrangement, the transmitting fibers and receiving fibers are equally distributed in the third arm.

[0019] In a third advantageous variant of the fiber arrangement, the receiving fibers form an inner circle and the transmitting fibers form a coaxial, outer ring around the inner circle.

[0020] To further increase the light output and reduce the number of light-reflecting interfaces, at least one optical filter and / or lens is preferably provided in the light guide, in particular at the interface between the light source and the first arm, the light receiver and the second arm, and the optical sensor element and the third arm.

[0021] In an advantageous embodiment, the ends of the optical fibers facing the optical sensor element are cut at an angle of less than 90° to their longitudinal axes. This makes it possible to further maximize the light yield, since the transmitted light strikes the optical sensor element at an angle and, after being converted by the optical sensor element, is then received as light in the receiver.

[0022] In a preferred embodiment, the optical sensor element is configured as a photoluminescence sensor, in particular as a fluorescence or phosphorescence sensor, wherein the optical sensor element emits received light after excitation with the transmitted light, depending on the process parameter. The received light in the light receiver can be analyzed in various ways and thus determined as a function of the process parameter. Possible methods include different intensity, phase angle, response time, etc.

[0023] In a further preferred embodiment, the optical sensor element comprises at least one layer which, upon contact with the process variable, changes at least one property, in particular changes color, and absorbs transmitted light depending on the process variable.

[0024] Preferably, the optical fiber is an optical fiber with a numerical aperture greater than 0.1.

[0025] The problem is further solved by a measuring device comprising an arrangement as described above, wherein the measuring device includes a sensor-side component and a transmitter-side component; wherein the arrangement is positioned on / in the sensor-side component; wherein energy is transmitted unidirectionally from the transmitter-side component to the sensor-side component, and data is transmitted bidirectionally, in particular the electrical measured quantity and / or the process quantity; and the sensor-side component and the transmitter-side component are coupled to each other via a galvanically isolated connection, in particular an inductive connection, or the sensor-side component and the transmitter-side component are galvanically coupled and connected to a control system via a galvanically isolated connection.

[0026] The measuring device is, for example, a measuring instrument for measuring a process variable from the field of process automation, such as an analytical process variable, for example the concentration of an analyte, such as the oxygen concentration.

[0027] The invention is explained in more detail with reference to the following figures. They show Fig. 1 a measuring instrument according to the invention, Fig. 2 an arrangement according to the invention, and Fig. 3a-c Cross-sectional designs of the third arm of the optical fiber.

[0028] In the figures, identical features are marked with the same reference symbols.

[0029] First, the measuring device 1 according to the invention will be described. The measuring device 1 is not to be understood as a single device, but rather as a combination of a transmitter-side component and a sensor-side component. The transmitter-side component is, for example, a higher-level unit 2, such as a transmitter or a control center. The higher-level unit 2 comprises at least one data processing unit 10. The sensor-side component is a consumer 4, such as a sensor, connected via a cable 3. The connection between the higher-level unit 2 and the consumer is established via interfaces 5 and 6. The interfaces 5 and 6 are designed as galvanically isolated, and in particular inductive, interfaces.

[0030] The sensor 4 is powered via cable 3. Furthermore, data is exchanged bidirectionally between sensor 4 and transmitter 2. Some of the functions of transmitter 2 have been transferred to sensor 4, specifically to a data processing unit 7, such as a microcontroller. Sensor-specific data, such as designation, serial number, manufacturing date, device data, calibration data, firmware version, manufacturer information, device driver information, sensor data, historical data, and process data, are stored in the microcontroller 7, or rather in its memory.

[0031] The evaluation of the measurement data from sensor 4 is divided between transmitter 2 and sensor 4. Preprocessing of the measurement data from sensor 4 takes place in the data processing unit 7. In particular, the light source 8 and the light receiver 9 (see Fig. 2) controlled by the microcontroller. In one embodiment, the tasks mentioned above are also performed by another microcontroller located in the cable.

[0032] Sensor 4 is a process automation sensor, specifically an optical sensor. Examples include pH, temperature, pressure, oxygen, or carbon dioxide sensors; sensors for determining the number of cells and cell structures; sensors for monitoring specific organic or metallic compounds; or sensors for determining the concentration of a chemical substance, such as a specific element or compound.

[0033] Transmitter 2 is either connected to a control system or is itself part of a control system. In the latter case, sensor 4 is directly connected to a control system, for example via HART, 4-20 mA, Profibus, Modbus, Ethernet, etc.

[0034] Alternatively, sensor 4 can also include an integrated transmitter and thus have transmitter functions and, if necessary, be directly connected to a control system. The sensor and integrated transmitter are then galvanically coupled. Galvanic isolation is then achieved through the connection to a control system.

[0035] Fig. Figure 2 shows an arrangement 13 according to the invention in detail. In the Fig. Figure 2 on the right shows an optical sensor element 11. The optical sensor element 11 is connected to a light source 8 or a light receiver 9 by a light guide 10. The light source 8 or the light receiver 9 are connected to the data processing unit 7. As already mentioned, the light source 8 is controlled by the data processing unit 7.

[0036] The light source 8 is implemented as an LED; the light receiver 9 is implemented as a photodiode. As already mentioned, the power supply to the arrangement 1 is provided via inductive interfaces 5, 6, which do not allow for high energy densities. The total energy consumption or the total power dissipated by the arrangement 13, i.e., in particular by the data processing unit 7, the light source 8, and the light receiver 9, and generally by the sensor electronics, should be less than 1 W.

[0037] A first arm 10.1 of the optical fiber 10 is connected to the light source 8. A second arm 10.2 of the optical fiber 10 is connected to the light receiver 9. These connections are made by gluing, joining, or similar methods, with the respective method meeting the optical requirements such as transparency at the corresponding wavelength, etc.

[0038] In one embodiment, an optical filter and / or a lens is provided at the interface between light source 8 and first arm 10.1 or light receiver 9 and second arm 10.2, as well as at the interface between third arm 10.3 and optical sensor element 11 (see below).

[0039] The first arm 10.1 and the second arm 10.2 combine to form a third arm 10.3. The third arm 10.3 is connected to the optical sensor element 11, the optical sensor element 11 being in contact with the medium 14.

[0040] Sensor 4 is designed as an optical sensor, the operation of which will be briefly explained. The light source 8 transmits light via the optical fibers 10.1 and 10.3 to the optical sensor element 11. The optical sensor element 11 modifies a property of the transmitted light and emits received light. The received light takes the reverse path via the arms 10.3 and 10.2 to the light receiver 9. The change in property involves, for example, the intensity, phase angle, wavelength, etc. The magnitude of the change is then directly related to the process variable to be measured in the medium, such as the concentration of a specific analyte, for example, oxygen concentration. The optical sensor element 11 is thus designed as a fluorescent or phosphorescent element.

[0041] As an alternative to the described fluorescence sensor, the optical sensor element 11 comprises at least one layer which, upon contact with the process variable in the medium 14, changes at least one property, for example, changes color, and absorbs transmitted light depending on the process variable.

[0042] As already mentioned, sensor 4 is powered via an inductive interface 5, 6. By definition, only small amounts of energy can be transmitted. The sensor typically has a diameter of 12 mm.

[0043] With the arrangement in Fig. 2. It is possible to meet these energy and space requirements.

[0044] The optical fiber 11 is designed as a multi-armed, in this example two-armed, optical fiber. The arms merge into a single arm at the sensor-side end.

[0045] One possible design of the light guide 11 is its realization as a glass rod. The glass rod is bent, drawn, etc., into shape as appropriate. The two individual arms then join to form a single glass rod.

[0046] An alternative is to design the optical fiber 11 as a fiber bundle, wherein the fiber bundle is formed from a multitude of fibers. A first group of fibers, the transmitting fibers 12.1, form the first arm 10.1; a second group of fibers, the receiving fibers 12.2, form the second arm 10.2.

[0047] In one variant, the optical fiber 11 comprises, in addition to the first arm 10.1 and the second arm 10.2, a fourth and fifth arm (not shown). The fourth and fifth arms also merge into the third arm 10.3. While the first arm 10.1 transmits light for a first process variable, as already mentioned, and the second arm receives light for the first process variable, the fourth arm can transmit light for a second process variable, and the fifth arm can receive light for the second process variable. Examples of the different process variables are oxygen and temperature.

[0048] Care must be taken to ensure that the area on the optical sensor element 11, which is covered by the receiving fibers 12.2, is also illuminated by the transmitting fibers 12.1.

[0049] The fibers in question are, for example, fibers made of glued, joined or similarly shaped glass fibers (air / glass), thick core fibers (quartz / quartz), polymer-coated glass (air / polymer), plastic (POF-air / polymer) or photonic crystalline fibers (glass / air, polymer / air).

[0050] On the side of the optical fiber 10 or the third arm 10.3 facing the optical sensor element 11, the fibers can be arranged differently.

[0051] Fig. Figure 3 shows a selection. Fig. 3a The fibers in the third arm 10.3 are distributed such that, in the cross-section of the third arm 10.3, the transmitting fibers 12.1 form a first partial circle, and the receiving fibers 12.2 form a second partial circle, completing the first partial circle. In one embodiment, the area of ​​the first partial circle is smaller than that of the second partial circle. Thus, a "crescent-shaped", "half-moon-shaped", or similar cross-section can be formed for a group of fibers.

[0052] In Fig. In 3b, fibers 12.1 and 12.2 are arranged in a uniform distribution. This can result in a symmetry, but arbitrary distributions are also possible.

[0053] Fig. Figure 3c shows an arrangement in which receiving fibers 12.2 form an inner circle and transmitting fibers 12.1 form a coaxial, outer ring around the inner circle.

[0054] To increase the light yield, the ends of the fibers of the optical guide 11 facing the optical sensor element are cut at an angle of less than 90° to their longitudinal axes. This allows the received and transmitted light to be guided even more effectively.

[0055] To meet the requirements for explosion protection, the assembly 13 may be at least partially potted. In particular, the potting of data processing unit 7 should be mentioned. Reference symbol list 1 measuring device 2. Parent unit 3 cables 4 consumers 5 Interface 6 Interface 7 Data processing unit 8 Light source 9 light receivers 10 fiber optic cables 10.1 First arm of 10 10.2 Second arm of 10 10.3 Third arm of 10 11 Optical sensor element 12 fibers 12.1 LED fiber 12.2 Photodiode fiber 13. Arrangement 14 Medium

Claims

[1] Arrangement (13) for optical measurement of at least one process variable, in particular an analytical process variable, in a medium (14), comprising - at least one light source (8) for transmitting light, - at least one light receiver (9) for receiving received light, wherein the light receiver (9) converts the received light into an electrical measurement quantity, - an optical sensor element (11), wherein the optical sensor element (11) is at least partially in contact with the medium (14) and converts the transmitted light into the received light, and - at least one data processing unit (7) for controlling and regulating the light source (8) and / or for processing the electrical measurement quantity into the process quantity, characterized by , that a light guide (10) is provided, wherein the light guide (10) connects the light source (8) to the optical sensor element (11) and the optical sensor element (11) to the light receiver (9), wherein the optical fiber (10) is designed with at least three arms, comprising a first arm (10.1), a second arm (10.2) and a third arm (10.3), wherein the first arm (10.1) is arranged on the light source (8) such that transmitted light enters the first arm (10.1), wherein the second arm (10.2) is arranged on the light receiver (9) such that received light from the second arm (10.2) enters the light receiver (9), wherein the third arm (10.3) is attached to the optical sensor element (11) in such a way that transmitted light from the third arm (10.3) reaches the optical sensor element (11) and received light from the optical sensor element (11) reaches the third arm (10.3), and wherein the first arm (10.1) and the second arm (10.2) combine to form the third arm (10.3), wherein the power consumption of the arrangement (13), in particular the light source (8) and the data processing unit (7), is less than 1 W. [2] Arrangement (13) according to claim 1, wherein the light guide (10) is designed as a glass rod. [3] Arrangement (13) according to claim 1, wherein the optical fiber (10) is designed as a fiber bundle formed from a multitude of fibers, wherein a first group of fibers, the transmitting fibers (12.1), form the first arm (10.1), and a second group of fibers, the receiving fibers (12.2), form the second arm (10.2). [4] Arrangement (13) according to claim 3, wherein the transmitting fibers (12.1) and receiving fibers (12.2) in the third arm (10.3) are distributed such that in the cross-section of the third arm (10.3) the transmitting fibers (12.1) form a first partial circle, and the receiving fibers (12.2) form a second partial circle, completing the first partial circle, where the area of ​​the first partial circle is smaller than that of the second partial circle. [5] Arrangement (13) according to claim 3, wherein the transmitting fibers (12.1) and receiving fibers (12.2) are equally distributed in the third arm (10.3). [6] Arrangement (13) according to claim 3, wherein the receiving fibers (12.2) form an inner circle and the transmitting fibers (12.1) form a coaxial, outer ring around the inner circle. [7] Arrangement (13) according to at least one of claims 1 to 6, wherein at least one optical filter and / or lens is provided in the light guide (10), in particular at the interface between light source (8) and first arm (10.1), light receiver (9) and second arm (10.2), and optical sensor element (11) and third arm (10.3). [8] Arrangement (13) according to at least one of claims 1 to 7, wherein the ends of the fibers of the optical fiber (10) facing the optical sensor element (11) are cut off at an angle of less than 90° to their longitudinal axes. [9] Arrangement (13) according to at least one of claims 1 to 8, wherein the optical sensor element (11) is configured as a photoluminescence sensor, in particular as a fluorescence sensor or phosphorescence sensor, wherein the optical sensor element (11) emits the received light depending on the process quantity after excitation with the transmitted light. [10] Arrangement (13) according to at least one of claims 1 to 9, wherein the optical sensor element (11) comprises at least one layer which, upon contact with the process variable in the medium (14), changes at least one property, in particular changes color, and absorbs transmitted light depending on the process variable. [11] Arrangement (13) according to at least one of claims 1 to 10, wherein the optical fiber (10) is an optical fiber (10) with a numerical aperture greater than 0.

1. [12] Measuring instrument (1), comprising an arrangement (13) according to at least one of claims 1 to 11, wherein the measuring device (1) comprises a sensor-side component (4) and a transmitter-side component (2), wherein the arrangement (13) is positioned on / in the sensor-side component (4), wherein energy is transmitted unidirectionally from the transmitter-side component (2) to the sensor-side component (4), and data is transmitted bidirectionally, in particular the electrical measurement quantity and / or the process quantity, and the sensor-side component (4) and the transmitter-side component (2) are coupled to each other via a galvanically isolated connection (5, 6), in particular an inductive connection, or the sensor-side component (4) and the transmitter-side component (2) are galvanically coupled and are connected to a control system via a galvanically isolated connection (5, 6).

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