Transmitter unit for the self-monitoring of a device and method for self-monitoring

Abstract

The invention relates to a transmitter unit (100), wherein for fastening the transmitter unit (100) to a measuring insert (2), the transmitter unit (100) can be mechanically connected, in particular in a releasable manner, to an outer casing (21) of the measuring insert (2) at a proximal end region (2a) of the measuring insert (2). The transmitter unit (100) has an electrically conductive fastening element (6), which is used to mechanically fasten the transmitter unit (100) to the measuring insert (2). The transmitter unit (100) is designed such that when the transmitter unit (100) is fastened to the measuring insert (2), as a result of said fastening an electrically conductive connection between the transmitter unit (100) and the outer casing (21) is simultaneously established by means of the electrically conductive fastening element (6). The invention also relates to a device (200) having a transmitter unit (100) according to the invention, and to a method for self-monitoring using a device (200) according to the invention.

Description

[0001] Transmitter unit for self-monitoring of a device and method for self-monitoring

[0002] The invention relates to a transmitter unit for a device for determining and / or monitoring a measured variable, in particular the temperature, of a medium. Furthermore, the invention relates to a device comprising a transmitter unit according to the invention and a method for self-monitoring using a device according to the invention.

[0003] In process and manufacturing automation, field devices are often used as devices for determining and / or monitoring physical or chemical parameters of a medium, especially a fluid—e.g., a liquid and / or a gas—or a solid—e.g., a fine-grained or powdered medium. Field devices essentially refer to all devices used close to the process and that provide, process, and / or display process-relevant information.

[0004] Field devices are used, for example, to record and / or influence measured variables. Measuring devices or sensors are used to record the measured variables. These are used, for example, for pressure and temperature measurement, conductivity measurement, flow measurement, pH measurement, level measurement, etc. and record the corresponding measured variables: pressure, temperature, conductivity, pH value, level, flow, etc. Actuators are used to influence measured variables. These are, for example, pumps or valves that can influence the flow of a fluid medium in a pipeline or the level of a medium in a container. In addition to the measuring devices and actuators mentioned above, field devices also include remote I / Os, wireless adapters, and generally devices that are arranged at the field level. A large number of such field devices are produced and distributed by the Endress+Hauser Group.

[0005] Thermometers are known as field devices in a wide variety of designs from the state of the art, and their underlying measuring principles have also been described in detail. For example, there are thermometers that use the expansion of a liquid, a gas, or a solid with a known coefficient of expansion to measure temperature, or those that relate the electrical conductivity of a material to temperature, such as when using resistance elements (RTD elements, short for resistance temperature detectors) or thermocouples. In contrast, radiation thermometers, especially pyrometers, utilize the thermal radiation of a medium to determine its temperature.

[0006] So-called PTC thermistors (PTC stands for positive temperature coefficient) are often used as resistance elements. PTC thermistors are characterized by the fact that their resistance increases with increasing temperature, especially linearly in the first order. Platinum is widely used among PTC thermistors because platinum's resistance overall has a maximum quadratic dependence on temperature. The resistance elements are usually designed such that they have a certain nominal resistance at a reference temperature, e.g., a reference temperature of 0°C, and are available accordingly under the designations Pt10 (10 ohms), Pt100 (100 ohms), and Pt10000 (1 kOhm), etc. The resistance element can be designed as a so-called wound resistance element or as a resistance layer applied to a substrate, especially a structured one, e.g., using thin- or thick-film technology. In a (thin) film sensor, for example,a resistance structure provided with connecting wires and applied to a carrier substrate is used, whereby the back of the carrier substrate usually has a metal coating.

[0007] With temperature-sensitive sensor elements in the form of thermocouples, the temperature is measured using a thermoelectric voltage generated between thermocouple wires made of different materials connected at one end. Thermocouples according to DIN standard IEC584, e.g., thermocouples of type K, J, N, S, R, B, T, or E, are typically used as temperature sensors. However, other material pairs, especially those with a measurable Seebeck effect, are also possible.

[0008] Numerous thermometers have become known in which the temperature-sensitive sensor element, as well as connecting lines at least partially connected to the sensor element, are arranged in a lumen of an elongated measuring insert enclosing the sensor element. The measuring insert has a distal end region—in particular, one facing the medium and / or immersed in the medium—and a proximal end region—in particular, one facing away from the medium—located longitudinally opposite the distal end region. Preferably, the measuring insert is closed in the distal end region, and in particular, the temperature-sensitive sensor element is arranged in the distal end region.

[0009] This measuring insert is often made of an electrically conductive material, especially a metal, with the sensor element (and its connecting leads) being electrically insulated from the measuring insert. This is achieved with the aid of an electrically insulating material, which is also filled into the lumen of the measuring insert. Thus, the sensor element and at least partially the connecting lead are enclosed and / or encapsulated in the lumen or interior of the measuring insert in the insulating material. The insulating material is, for example, a ceramic powder, such as magnesium oxide (MgO) or aluminum oxide (Al2O3), or a ceramic potting compound, especially a hardening one. The encapsulation / inclusion, e.g. using the ceramic powder, ensures that the connecting leads of the sensor element are insulated from one another even at high temperatures, especially at temperatures of up to approximately 600°C.In addition, the sensor element is additionally fixed by means of the insulating material inside the measuring insert. Measuring inserts with thermal sensor elements are also often arranged inside an immersion body, in particular a protective tube. The immersion body is used, for example, to insert the measuring inserts of field devices into a container containing the medium or a pipe carrying the medium. These are usually immersed bodies that are at least partially immersed in the medium and designed to accommodate the measuring insert. For this purpose, the immersion body has, for example, a central guide, which is designed, in particular, as a bore or a blind hole, into which guide the measuring insert can be inserted. The immersion body then fulfils the function of a housing. Such immersion bodies, which e.g.made of ceramic or metallic materials, are often used to improve the resistance of the measuring insert to chemicals, abrasion, corrosion or extreme temperatures. In process measurement technology, this is particularly important in the chemical or oil industries or in power plants, etc. Depending on the design, it is important that the measuring insert rests against the bottom of the immersion body, particularly for temperature-sensitive sensor elements, in order to ensure sufficiently good and rapid thermal coupling of the sensor element to the medium. Only then is the heat from the medium quickly thermally conducted to the temperature-sensitive sensor element, which is arranged in the measuring insert. In terms of design, the tip of the measuring insert is pressed against the bottom of the protective tube by springs, for example to ensure metal-to-metal contact. The available spring travel is typically around 8-10 mm.The immersion bodies themselves are typically inserted into a nozzle of the container or a measuring tube that can be integrated into the pipeline. If necessary, the measuring insert can be removed from the protective tube, especially repeatedly, for example, for replacement and / or maintenance purposes.

[0010] For processing and / or forwarding a measurement signal generated by the device, the devices within the meaning of the application often have a (head) transmitter unit, which is mechanically connected to the measuring insert at the proximal end region of the measuring insert. In particular, the transmitter unit and measuring insert can be mechanically connected to one another in such a way that the transmitter unit directly borders the outer casing of the measuring insert, in particular a disk-shaped outer casing end face. The transmitter unit has, for example for processing and / or forwarding the measurement signal generated by the sensor element, measuring electronics with a first circuit board and an electrically insulating transmitter housing. The first circuit board is arranged in a lumen of the transmitter housing. If necessary, the transmitter unit also comprises several circuit boards.

[0011] To ensure that the insulating material maintains its good (electrical) insulation properties and is not adversely affected by chemical and / or physical processes, such as the incorporation of water (which may be promoted by the hygroscopic properties of the insulating material) and / or oxidation processes, the lumen of the measuring insert is often sealed to the environment at the proximal end of the measuring insert, for example, using a potting compound. This is particularly important in such a way that only the connecting cables or rigid connecting wires connected to them protrude from the seal at the proximal end of the measuring insert. The potting compound is, for example, filled into the transmitter housing.

[0012] However, this - often necessary - sealing is problematic for the following reasons: The rigid connecting wires (usually made of nickel or copper) must be passed through the seal and / or a connection between the connecting wires and the connecting cables is located in the seal.

[0013] In the event of (thermo-)mechanical stress on the seal, cracks can occur. This, in turn, leads to the (gradual) accumulation of moisture in the insulation material. As a result, a reduction in the electrical insulation resistance between the connecting cables and the measuring insert can lead to a - usually undetectable - distortion of the measurement signal.

[0014] Often, a reference potential, such as a ground connection (also known as earth), is provided on the device's housing, e.g., the protective tube mentioned above. In the case of a sealed enclosure, where only the connecting leads or the connecting wires connected to them are accessible, this reference potential can lead to unwanted electrical interference currents in the measurement electronics. This is due to the lack of another electrical, unwired access point for the reference potential to the measurement electronics. The reference potential can then no longer be directed to a specific area of ​​the measurement electronics.

[0015] The invention is therefore based on the object of providing an improved transmitter unit for such a device for determining and / or monitoring a measured variable, which overcomes the problems mentioned above.

[0016] The object is achieved by a transmitter unit, by a device with a transmitter unit according to the invention and by a method for self-monitoring with a device with a transmitter unit according to the invention.

[0017] With regard to the transmitter unit, the object is achieved by a transmitter unit for a device for determining and / or monitoring a measured variable, in particular the temperature, of a medium, which device comprises an elongated measuring insert with an electrically conductive, in particular metallic, outer casing, wherein the transmitter unit serves to process and / or forward a measuring signal generated by a sensor element of the device, wherein the transmitter unit has measuring electronics with a first circuit board and an electrically insulating transmitter housing, wherein the first circuit board is arranged in a lumen of the transmitter housing, wherein the transmitter unit is mechanically connectable, in particulardetachably mechanically connectable, and the transmitter unit has a fastening element serving for the mechanical fastening of the transmitter unit to the measuring insert, wherein the fastening element is electrically conductive, and wherein the transmitter unit is designed such that when the transmitter unit is fastened to the measuring insert, an electrically conductive connection is produced between the transmitter unit and the outer casing as a result of the fastening, by means of the electrically conductive fastening element.

[0018] In the context of this application, “electrically conductive” means, for example, an electrical conductivity of more than 10, particularly at a temperature of 20°C. 5 S / m, preferably more than 10 6 S / m.

[0019] In particular, the transmitter unit and measuring insert can be mechanically connected in such a way that the transmitter unit is directly adjacent to the outer casing of the measuring insert, in particular to a disc-shaped outer casing end face.

[0020] The electrically insulating transmitter housing can also be designed as a multi-part transmitter housing and in this case comprises several transmitter housing parts.

[0021] The transmitter unit is designed in particular according to the norm specified in a standard, for example according to the DIN EN 50446 standard.

[0022] In one embodiment of the transmitter unit, the fastening element is at least partially pin-shaped, wherein in particular a fastening element longitudinal axis is such that for the transmitter unit fastened to the measuring insert, a fastening element longitudinal axis is parallel to a measuring insert longitudinal axis.

[0023] The fastening element comprises, for example, at least one fastening screw. In addition, the fastening element may comprise a washer for the fastening screw and / or a spring element. The spring element serves to ensure, when the measuring insert is arranged in a protective tube under thermal stress which is associated, for example, with thermal expansion, an unchanged good thermal contact between the measuring insert and the protective tube and in particular to provide the spring travel mentioned at the beginning to ensure an unchanged good thermal coupling. In one embodiment of the transmitter unit, the transmitter unit has an electrically conductive, in particular metallic, contacting element, with a first contacting element end section and a second contacting element end section, which first contacting element end section and second contacting element end section the contacting element in particular.limit, wherein the first contacting element end section or an adjacent section of the contacting element is electrically contacted with the first printed circuit board, in particular in a contacting connection surface of the printed circuit board, and wherein the second contacting element end section can be contacted with the fastening element, so that the electrically conductive connection between the transmitter unit and outer jacket can be produced in that, when the transmitter unit is fastened to the measuring insert, there is an electrically conductive connection between the printed circuit board and the outer jacket via the contacting element and the fastening element contacted with the second contacting element end section.

[0024] The electrically conductive connection between the circuit board and the outer sheath is provided via the contacting element, the fastening element contacted with the contacting element and the outer sheath contacted with the fastening element in the event that the transmitter unit is attached to the measuring insert.

[0025] The contacting element is contacted and mechanically connected to the circuit board at, for example, the first contacting element end section, e.g., by a material fit, a form fit, and / or a force fit. For example, a material fit can be achieved by soldering the first contacting element end section to the first circuit board to the contacting pad of the circuit board. It is advantageous for soldering if the first contacting element end section has a solderable surface. For example, the contacting element is preferably designed as a THT component that is soldered using a selective soldering process, e.g., wave soldering. The contacting pad can also be designed as a conductor track of the circuit board. Alternatively or additionally, a pressed connection is also provided, e.g., at the first contacting element end section to the circuit board and / or at the second contacting element end section to the transmitter housing.

[0026] If necessary, the transmitter unit also has one or more additional circuit boards arranged in the lumen of the transmitter housing. In this case, the contacting element is electrically contacted with only the first circuit board, or with both the first circuit board and one or more, e.g. all, of the additional circuit boards. For example, with the first circuit board at the first contacting element end section, and with the second circuit board at the section of the contacting element adjacent to the contacting element end section. The contacting element is, for example, manufactured in one piece using a primary forming process, e.g., primary forming from the liquid state of group 1.1 according to DIN 8580, e.g., from a molten metal, or primary forming from the plastic state of group 1.2, e.g., draw forming. The contacting element - especially a one-piece one - is pressed into the transmitter housing with its second contacting element end section, e.g.into a first transmitter housing part of a multi-part transmitter housing. Alternatively, the contacting element is injected into the transmitter housing with its second contacting element end section during the manufacture of the transmitter housing, for example, as part of an injection molding process for producing the transmitter housing.

[0027] In addition, in particular subsequently for the contacting element connected to the transmitter housing element, the contacting element is joined to the circuit board at the first contacting element end section, e.g. soldered onto the contacting connection surface of the circuit board and / or pressed onto the contacting connection surface of the circuit board.

[0028] In one embodiment of the transmitter unit, it has: a first transmitter housing end face region, which first transmitter housing end face region is to face the measuring insert when the transmitter unit is fastened to the measuring insert and a second transmitter housing end face region, which second transmitter housing end face region is to face away from the measuring insert when the transmitter unit is fastened to the measuring insert, wherein the first transmitter housing end face region and the second transmitter housing end face region are arranged opposite one another with regard to a transmitter housing longitudinal axis, wherein the fastening element can be inserted into the transmitter housing from the second transmitter housing end face region and can be locked for fastening, wherein the contacting element has a, in particularflat, contacting surface section, which contacting surface section rests on the second transmitter housing end face region, in particular directly, and wherein the contacting element can be contacted with the fastening element in that the fastening element adjoins the contacting surface section in regions at least with a contact region.

[0029] The two transmitter housing end face areas are preferably flat.

[0030] In particular, the second contacting element end section protrudes from the transmitter housing (part) with the contacting surface section on the second transmitter housing end face. In a further development of the above embodiments of the transmitter unit, the contacting surface section has a recess, particularly an internal one, for receiving the fastening element, so that the fastening element protrudes through the recess of the contacting surface section.

[0031] The recess is preferably an internal recess, which is therefore completely surrounded by the contacting surface section and which is not located at an edge of the second contacting element end section or the contacting surface section. All previously defined specifications or the surface area of ​​the contacting surface section include the entire surface area, without subtracting the surface area of ​​the recess.

[0032] In one embodiment of the transmitter unit, the transmitter housing has a guide extending from the second transmitter housing end face region to the first transmitter housing end face region, which guide serves to receive a portion of the fastening element, in particular the pin-shaped portion of the fastening element.

[0033] In one embodiment of the transmitter unit, the contacting element is designed such that an electrical contact resistance value between the second contacting element end section and the first contacting element end section is less than 100 ohms, in particular less than 50 ohms, preferably less than 10 ohms, particularly preferably less than 1 ohm. This is therefore a highly electrically conductive contacting element, by means of which the best possible electrical contact can be established between the fastening element / outer sheath and the circuit board.

[0034] In one embodiment of the transmitter unit, the contacting element has a current-carrying capacity of at least 100 mA, in particular at least 300 mA, preferably at least 500 mA. The electrically highly conductive contacting element can therefore conduct currents effectively to a specific location on the circuit board even when a reference potential (mentioned below) is applied, due to its sufficiently high current-carrying capacity.

[0035] In one embodiment of the transmitter unit, the contacting element has a conductive and, in particular, corrosion-resistant oxidation-prevention layer, in particular comprising gold or a gold-containing alloy, at least on the second contacting element end section, in particular the contacting surface section. The oxidation-prevention layer serves to ensure that the second contacting element end section, in particular the contacting surface section, which is arranged on the second transmitter housing end face region and is possibly exposed to the environment, continues to have good electrical properties. The oxidation-prevention layer has, in particular, a layer thickness of at least 0.5 pm (micrometers), preferably at least 1 pm. It can also be formed as a coating and / or multi-layer layer and has, for example, a first, less noble layer with a thicker, first layer thickness (e.g. comprising nickel) and a, in particular,a second, more noble layer covering the first layer with a thinner, second layer thickness (e.g. comprising gold), wherein the first layer thickness is in particular at least 5 times as large as the second layer thickness, preferably at least 7 times as large.

[0036] In one embodiment of the transmitter unit, the first printed circuit board has a circuit arrangement comprising conductor tracks, contact surfaces and components, wherein for the transmitter unit fastened to the measuring insert, in which the electrically conductive connection between the printed circuit board and the outer sheath is present, namely via the fastening element and the contacting element, the circuit arrangement is designed to determine an electrical insulation resistance value between at least a first connecting line of the connecting lines and the outer sheath and / or to determine whether the electrical insulation resistance value between at least a first connecting line of the connecting lines and the outer sheath is less than at least a first minimum resistance value.

[0037] In a first variant, the circuit arrangement is configured to determine an electrical insulation resistance value between the first connecting cable and the outer sheath. This is done via the fastening element contacted with the outer sheath and the contacting element contacted with the fastening element and with the circuit board, in the case of the transmitter unit attached to the measuring insert. Additionally or alternatively, in a second variant, the circuit arrangement is configured to determine whether the electrical insulation resistance value is less than a first minimum resistance value. In the second variant, it can, for example, also be just a limit switch that does not output the exact value of the insulation resistance value, but only detects when the first minimum resistance value has been undershot.

[0038] In one embodiment of the transmitter unit, the circuit arrangement has a capacitive element with a capacitance of at least one pF, wherein the capacitive element is connected in series with the contacting pad of the circuit board. The contacting pad serves to make electrical contact with the first contacting element end section. The capacitive element, which is connected in series with the contacting pad of the circuit board, therefore serves to create a high-frequency connection between the circuit board and the measuring insert and, in particular, to provide a path for any potentially present electromagnetic interference current in order to increase the so-called EMC immunity (EMC is short for electromagnetic compatibility).a maximum capacitance of the capacitive element is selected as a function of a maximum useful frequency of an electric current which can be impressed on the electronic unit via the connecting lines: the higher the useful frequency between the connecting lines, the smaller the maximum capacitance should be.

[0039] With regard to the device, the object is achieved by a device for determining and / or monitoring a measured variable, in particular the temperature, of a medium, comprising:

[0040] - a sensor element, especially a temperature-sensitive one, for generating a measurement signal dependent on the measured variable

[0041] - an elongated measuring insert with an electrically conductive, in particular metallic, outer sheath, having a distal end region, wherein the measuring insert surrounds the sensor element and in particular the sensor element is arranged in the distal end region and in particular the measuring insert is closed in the distal end region,

[0042] - connecting cables, in particular at least two, which connecting cables serve to contact the sensor element and lead from the sensor element to a proximal end region of the measuring insert, which proximal end region is arranged opposite the distal end region with respect to a measuring insert longitudinal axis, and

[0043] - a transmitter unit according to the invention, wherein the transmitter unit serves to process and / or forward the measuring signal generated by the sensor element, wherein the transmitter unit is fastened to the measuring insert at the proximal end region of the measuring insert by means of the fastening element, so that the outer sheath is electrically conductively connected to the transmitter unit.

[0044] The longitudinal axis of the transmitter housing is arranged parallel to the longitudinal axis of the measuring insert, in particular with the transmitter unit attached to the measuring insert. As mentioned above, the device, in particular for the temperature-sensitive sensor element, can also have the components mentioned above, including the insulating material, the seal, and / or the immersion body, in particular the protective tube. The sensor element is operated by means of the at least two connecting cables, which are, for example, soldered or welded to the sensor element, in a two-, three-, or four-wire circuit, etc., depending on the number of connecting cables. In particular, the transmitter unit is free of any further supply lines / connections, in addition to the connecting cables for operating the sensor element in the aforementioned two-, three-, or four-wire circuit. Therefore, only the (wired) connecting cables are accessible through the seal.

[0045] In one embodiment of the device, the outer casing has, at the proximal end region, a particularly disc-shaped outer casing end face facing the transmitter unit. This outer casing end face has a receptacle for the fastening element corresponding to the fastening element, so that when the fastening element is inserted into the receptacle, the fastening element is electrically conductively connected to the outer casing. The receptacle is, for example, a thread for a screw as a fastening element. The fastening element's longitudinal axis is preferably parallel to the measuring insert's longitudinal axis. In particular, the first end face of the transmitter unit directly borders the outer casing end face.

[0046] In one embodiment of the device, a reference potential, preferably zero, is provided to the fastening element and / or the outer casing, for example, a ground. The reference potential is provided, for example, via a ground connection. The reference potential is used in connection with EMC.

[0047] With regard to the method, the object is achieved by a method for self-monitoring a device according to the invention. The method comprises:

[0048] - Determining an electrical insulation resistance value between the outer sheath and at least one first connecting cable and issuing a first warning message in the event that the electrical insulation resistance value is less than a first minimum resistance value, or

[0049] - Determining whether the electrical insulation resistance value between the outer sheath and at least one first connecting cable is less than a first minimum resistance value and issuing a first warning message in the event that the electrical insulation resistance value is less than the first minimum resistance value.

[0050] In one embodiment of the self-monitoring method, this comprises: - issuing a second warning message, in particular for the measuring electronics, in the event that the electrical insulation resistance value is less than a second minimum resistance value, wherein the second minimum resistance value is less than the first minimum resistance value.

[0051] In one embodiment of the method, the first minimum resistance value is at least 0.2 megaohms, in particular at least 0.5 megaohms, preferably at least 1 megaohm and / or the second minimum resistance value is at least 0.1 megaohms, in particular at least 0.2 megaohms, preferably at least 0.5 megaohms.

[0052] Alternatively or in addition to the above-mentioned absolute limits, the first and / or second minimum resistance value may also depend on a maximum measuring resistance that the sensor element can assume within the measuring range specified for the device. The first minimum resistance value is, for example, at least 1000 times, in particular at least 5000 times, preferably at least 10,000 times the maximum measuring resistance, and the second minimum resistance value is, for example, at least 500 times, in particular at least 1000 times, preferably at least 5000 times the maximum measuring resistance.

[0053] In one embodiment of the method, the sensor element is a

[0054] Resistance element, wherein during the generation and / or processing of the measurement signal, an electrical measuring resistance dependent on the electrical resistance value of the resistance element is detected by means of a first connecting line and at least one second connecting line, and wherein the method comprises:

[0055] Determining an electrical insulation resistance value between the outer sheath and the first connecting cable;

[0056] Determining the electrical measuring resistance by means of the first connecting line and at least the second connecting line; and

[0057] Determine the electrical resistance value of the resistance element based on the determined electrical measuring resistance and the determined insulation resistance value

[0058] For example, the device is designed such that the electrical connection between the outer sheath and the first connecting cable, which has the electrical insulation resistance value, is connected in parallel with the resistance element. Thus, a corrected value for the electrical resistance value of the resistance element can be determined based on the measured resistance and the measured insulation resistance.

[0059] All configurations of the transmitter unit also apply mutatis mutandis to the device or method, and vice versa. Without limiting its generality, the invention is explained in connection with a thermometer as a field device or as a device for determining and / or monitoring the measured variable. Naturally, the invention encompasses, mutatis mutandis, transmitter units for other devices or devices for determining and / or monitoring other measured variables, including in particular the measured variables mentioned above.

[0060] The invention is explained in more detail with reference to the following figures, which are not to scale. Like reference numerals denote like features. For reasons of clarity or where otherwise expedient, previously mentioned reference numerals have been omitted in the following figures.

[0061] They show:

[0062] Fig. 1 a: A schematic sectional view of an embodiment of a transmitter unit 100 according to the invention;

[0063] Fig. 1 b: A schematic sectional view of an embodiment of a device 200 according to the invention with a transmitter unit 100;

[0064] Fig. 1 c: A detailed view of an embodiment of a device 200 according to the invention with a transmitter unit 100; Fig. 2a: A schematic sectional view of a contacting element 7 in an embodiment of a transmitter unit 100 according to the invention;

[0065] Fig. 2b: A perspective view of a multi-part transmitter housing 5, having a plurality of fastening elements 6, in an embodiment of a transmitter unit 100 according to the invention;

[0066] Fig. 2c: A perspective view of the second transmitter housing end face region SF2 and the contacting surface section 7-KF, in an embodiment of a transmitter unit 100 according to the invention;

[0067] Fig. 3a-c: equivalent circuit diagrams for a circuit arrangement 41, in embodiments of the transmitter unit 100 according to the invention;

[0068] Fig. 4: Steps of the method according to the invention in an embodiment of the method according to the invention.

[0069] The sectional views in Figs. 1a and 1b show a transmitter unit 100 according to one embodiment of the invention. The transmitter unit 100 is attached to a measuring insert 2. Fig. 1a essentially shows only the transmitter unit 100, whereas Fig. 1b also shows the device 200 or the field device 200 with the transmitter unit 100.

[0070] The transmitter unit 100 is attached to a measuring insert 2 by means of an electrically conductive fastening element 6. The fastening element 6 has a pin-shaped section that runs along a fastening element longitudinal axis BE-LA, which here is parallel to a transmitter housing longitudinal axis TG-LA. The fastening element longitudinal axis BE-LA is also preferably parallel to the measuring insert longitudinal axis ME-LA. A first transmitter housing end face region SF1 directly borders the outer casing end face AM-SF.

[0071] In this embodiment, the fastening element e comprises a screw with a spring element and a washer. The spring element serves to provide the spring travel mentioned above. Further fastening elements 6, which are naturally encompassed by the invention mutatis mutandis, include, for example, a part of a bayonet lock engaging a corresponding receptacle of the measuring insert 2, or an eccentric lever for fastening, etc.

[0072] According to the invention, the transmitter unit 100 is designed such that, when attached to an outer casing 21 of the measuring insert 2, an electrically conductive connection is simultaneously established between the transmitter unit 100, here a first circuit board 4 (see Fig. 1 b, or a first circuit board 4 and a second circuit board 4, as shown in Fig. 1 a) of the transmitter unit 100, and the outer casing 21, namely by means of the electrically conductive fastening element 6.

[0073] In the embodiments shown in Fig. 1a, b, this is achieved in that the transmitter unit 100 has a contacting element 7, which is contacted with the first printed circuit board 4 by a first contacting element end section 7a. The first contacting element end section 7a is contacted, for example, with a contacting connection surface 4-KF (see Fig. 1c), for example, soldered using a selective soldering process such as wave soldering and optionally subsequently, or alternatively, pressed. The contacting element 7 is thus designed as a THT component of the transmitter unit 100. The second contacting element end section 7b protrudes from the transmitter housing 5 such that the fastening element e can be pressed onto a contacting surface section 7-KF, namely with a contacting surface of the fastening element 6 corresponding to the contacting surface section 7-KF (see Fig. 2c).By pressing the contacting surface section 7-KF and the corresponding contacting surface of the fastening element 6 together, the fastening element 6 is contacted with the contacting element 7 and thus also with the first printed circuit board 4. In the case of contacting with two printed circuit boards 4, as shown in Fig. 1a, the contacting element 7 is contacted with a first printed circuit board (see the contact with the lower printed circuit board in Fig. 1a) at the first contacting element end section 7a, and with a second printed circuit board at a section arranged between the first contacting element end section 7a and the second contacting element end section 7a (see the contact with the upper printed circuit board in Fig. 1a).

[0074] On the other hand, when attached to the measuring insert 2, the fastening element 6 engages in a receptacle 8 corresponding to the fastening element. The receptacle 8 serves to receive the fastening element 6 and is arranged at a proximal end region 2a of the measuring insert 2, which adjoins the transmitter unit 100. At the proximal end region 2a, the outer casing 21 has a disk-shaped outer casing end face AM-SF facing the transmitter unit 100, in which the receptacle 8 is arranged. The receptacle 8 is, for example, a thread for a screw as the fastening element 6. As a result, when the fastening element 6 is inserted into the receptacle 8, the fastening element 6 is electrically conductively contacted with the outer casing 21.Since the fastening element 6 is in turn contacted with the printed circuit board 4 via the contacting element 7, the electrically conductive connection between the outer jacket 21 and the printed circuit board 4 of the transmitter unit 100 is ultimately established via the interaction of the contacting element 7 and the fastening element e during fastening. A major advantage of the solution according to the invention, implemented here by means of the contacting element 7, is that the electrically conductive connection or contact is established automatically, namely simultaneously with the fastening of the.

[0075] Transmitter unit 100 on the measuring insert 2.

[0076] The field device 200 with the transmitter unit 100 is shown in more detail in Fig. 1b. It comprises the transmitter unit 100 attached to the proximal end region 2a of the measuring insert 2, wherein the measuring insert 2 further contains a sensor element 1 in its lumen, for example, an RTD resistance element such as a Pt100 as a temperature-sensitive sensor element 1 for a thermometer as the field device 200.

[0077] The sensor element 1 is preferably arranged in a distal end region 2b, which lies opposite the proximal end region 2a along the measuring insert's longitudinal axis ME-LA. The sensor element 1 is contacted by means of connecting lines 3a, 3b, 3c, 3d (here, four connecting lines 3a, 3b, 3c, 3d for implementing a four-wire circuit), which lead from the sensor element 1 to the transmitter unit 100 or the circuit board 4. In this case, an electrical resistance Rmess measured by means of the four-wire circuit represents a measurement signal for the temperature-dependent electrical resistance of the resistance element RRTD.

[0078] Furthermore, as mentioned at the beginning, an insulating material 9, for example, is filled into the measuring insert 2. The insulating material surrounds the sensor element 1 and, at least in sections, the connecting lines 3a, 3b, 3c, 3d connected to it. As mentioned at the beginning, it serves to electrically insulate the connecting lines 3a, 3b, 3c, 3d or the sensor element 1 from the, for example, metallic and thus electrically conductive measuring insert 2 and from one another, as well as to stabilize the sensor element 1 in the measuring insert 2. Furthermore, an earth connection for providing a reference potential 11 is connected to the measuring insert 2. When using an additional immersion body, in particular a protective tube, the earth connection is optionally also provided directly on the fastening element 6 itself. A seal 10, for example in the form of a potting compound, is also arranged on the proximal end region 2a of the measuring insert 2, adjacent to the insulating material 9.The seal 10 seals the insulating material 9 liquid-tight and / or airtight against the environment.

[0079] Fig. 1c further shows a detail of an embodiment of the field device 200, which is indicated in Fig. 1b with a dashed circle. The first contacting element end section 7a is electrically contacted with the contacting connection surface 4-KF of the printed circuit board 4, for example by soldering and / or pressing the contacting element 7 onto the contacting connection surface 4-KF. In this embodiment, a circuit arrangement 41 of the printed circuit board 4 comprises a capacitive element 12, which is connected in series with the contacting connection surface 4-KF. As mentioned above, the capacitive element 12 serves to provide a path for a potentially present electromagnetic interference current. By means of the transmitter unit 100 according to the invention, the measured electrical resistance Rmess of the sensor element 1 is now determined via the four-wire circuit.On the other hand, the insulation resistance Riso can also be measured directly via the electrically conductive connection, or only its undershoot can be determined, and / or the insulation resistance Riso can be related to the measured electrical resistance Rmess. For this purpose, the measuring insert 2, in particular, is completely electrically conductive (e.g., made of a metal), so that the electrical potential at the outer sheath 21 also corresponds to the electrical potential at the inner sheath, which inner sheath is in direct contact with the insulating material 9.

[0080] Determining when the insulation resistance Riso falls below the threshold is an important measure for self-monitoring of the field device 200. This is implemented, for example, as part of so-called "predictive maintenance" measures and, if necessary, logged in a so-called Heartbeat Technology protocol; see also Fig. 4 explained below.

[0081] Furthermore, by means of the electrically conductive connection, the reference potential 11 applied to the outer jacket 21 can now be conducted to a dedicated location of the transmitter unit 100 or the circuit board 4, for example to the capacitive element 12 shown in Fig. 1 c. Without the electrically conductive connection, the reference potential 11 would otherwise lead, via parasitic capacitances, for example, to undesired interference currents in the transmitter unit 100 or in the field device 200.

[0082] The contacting element 7 and its interaction with the transmitter housing 5 is shown in more detail in Fig. 2a-c. Fig. 2a shows the contacting element 7, which has an elongated section with a contacting element longitudinal axis. This is (cf. Fig. 1a, 1b) particularly parallel to the transmitter housing longitudinal axis TG-LA. The first contacting element end section 7a is arranged at a first end region of the elongated section. The contacting surface section 7-KF, which is flat, adjoins the elongated section. An included angle between the contacting element longitudinal axis and a straight line running in the plane of the contacting surface section 7-KF is, for example, between 80° and 100°.

[0083] The contacting surface section 7-KF is preferably flat, namely in that the thickness in the direction of the surface normal is at most 0.2, preferably 0.1, times the diameter of the surface of the contacting surface section. A diameter of the surface of the contacting surface section is defined, for example, as a maximum diameter of the surface or a diameter of a circular area corresponding to the surface, which corresponding circular area has the same area as the surface. The contacting surface section preferably has a surface area of ​​0.1 cm. 2 up to 6 cm 2 , especially 0.5 cm 2 up to 3 cm 2The contact surface section preferably has a maximum thickness of 0.2 cm, preferably 0.1 cm, in a direction of a surface normal. Fig. 2b shows a perspective side view of a transmitter unit 100 with a multi-part transmitter housing 5, with a first transmitter housing part 51 and a second transmitter housing part 52. In the embodiment shown here, two fastening elements 6 are provided, wherein the invention encompasses, mutatis mutandis, all embodiments presented in connection with only one fastening element e. The fastening elements 6 engage in the transmitter housing 5 starting from a second transmitter housing end face region SF2. The first transmitter housing end face region SF1 preferably corresponds to the entire flat end face of the transmitter housing 5.

[0084] Fig. 2c again shows a top view of the second transmitter housing end face region SF2, rotated by 90° compared to Fig. 2b, in which the transmitter housing's longitudinal axis TG-LA points into the image plane. The second transmitter housing end face region SF2 of the top view shown in Fig. 2c preferably corresponds to only one region of the end face. This region, see also Fig. 2b, is offset from other regions of the end face of the transmitter housing 5 facing away from the measuring insert 2, in the direction of the first transmitter housing end face region SF1.

[0085] The electrically conductive contact surface section 7-KF of the contacting element 7 lies directly against the second transmitter housing end face region SF2, for example, is pressed thereon. The contact surface section 7-KF has an internal recess 71, through which recess 71 the fastening element 6, in particular with its pin-shaped section, protrudes during fastening. The electrical contact between the contact surface section 7-KF and the fastening element 6 is then ultimately established by a corresponding contact surface of the fastening element 6—for example, a screw head, with or without a washer (see Fig. 1a)—pressing onto the contact surface section 7-KF. The contacting element 7 preferably has a current-carrying capacity of at least 500 mA and a contact resistance value of less than 10 μm.

[0086] The insulation resistance Riso shown in Fig. 1b can be determined and / or monitored by means of the transmitter unit 100 according to the invention. The insulation resistance Riso or the undershoot of the minimum resistance value Mini is preferably determined purely by circuitry in the circuit arrangement 41 of the printed circuit board 4, as shown in more detail in Figs. 3a-c.

[0087] Fig. 3a shows an equivalent circuit diagram for a first embodiment of the circuit arrangement 41 in order to determine a value for the insulation resistance Riso in terms of circuitry. For this purpose, the electrically conductive connection having the insulation resistance Riso is connected in series with a reference resistance element 16 having the electrical resistance value Rref (e.g. by appropriately connecting the contact surface section 7-KF of the circuit arrangement 41 which is in contact with the contacting element 7). The electrically conductive connection having the insulation resistance Riso is symbolically represented here as a single resistance element and, for the sake of clarity, is now and hereinafter referred to as the insulation resistance element 18. An A / D converter 14 is connected in the circuit arrangement 41 between the insulation resistance element and the reference resistance element 16. The output of the A / D converter 14 is then, for example,to an input of a microcontroller.

[0088] If necessary, the reference resistance element 16 can also be replaced by a current source 15 which provides a measuring current Imess, as shown in Fig. 3b.

[0089] The design as a limit switch is implemented, for example, in circuitry by the circuit arrangement 41 having at least one reference resistance element 16 with an electrical reference resistance value Ref, which reference resistance value Ref depends, for example, on the first minimum resistance value Mini. In Fig. 3c, for example, the reference resistance element 16 is connected in series with the insulation resistance element 18, wherein the voltage dropped across the insulation resistance element 18 is fed to a non-inverting first input of a differential amplifier 17 and a reference voltage Vref is provided at the inverting second input of the differential amplifier 17. The output signal of the differential amplifier 17 is then fed to a digital input of a microcontroller. The differential amplifier in the circuit arrangement shown here serves as a comparator.

[0090] The embodiments shown in Fig. 3a-c represent only examples of a determination and / or monitoring of the insulation resistance Riso implemented at least partially by circuitry; further embodiments obvious to a person skilled in circuit technology are of course also encompassed by the invention.

[0091] Finally, Fig. 4 shows a flowchart of steps of the inventive method for self-monitoring of an inventive device 200.

[0092] In a step A), a measured value for the insulation resistance Riso is determined for a field device 200, as shown in Fig. 1 b

[0093] In step B) it is checked whether the insulation resistance Riso is smaller than a first minimum resistance value Mini.

[0094] Step A) is optional. If only step B) and not step A) is implemented, the device is configured as a limit switch; this is implemented in circuitry, for example, as shown in Fig. 3c or similarly. If the insulation resistance Riso falls below the first minimum resistance value Mini (arrow y), a first warning message W1 is output during step C) and / or stored in a log, e.g., as part of the so-called heartbeat technology.

[0095] However, if the insulation resistance Riso does not fall below the first minimum resistance value Mini (arrow n), a good message “OK1” is output and / or stored in a protocol as part of step B1).

[0096] In step D), it is checked whether the insulation resistance Riso is less than a second minimum resistance value Min2. The second minimum resistance value Min2 is less than the first minimum resistance value Mini. The detection of the undershoot of the second minimum resistance value Min2 can also be implemented, mutatis mutandis, using circuitry, as previously explained in connection with Fig. 3c.

[0097] If the insulation resistance Riso also falls below the second minimum resistance value Min2 (arrow y), a second warning message W2 is issued and / or stored in a log as part of step E). This second warning message W2 can, for example, signal to a user that it is advisable to switch off the field device 200 or to interrupt the power supply to the field device 200.

[0098] If the insulation resistance Riso does not fall below the second minimum resistance value Min2 (arrow n), a further good message “OK2” is output and / or stored in a protocol as part of step D1).

[0099] The warning messages W1, W2, and / or the pass messages are transmitted to a higher-level unit 4, depending on the communication connection of the field device 200, by which the field device 200 is connected to the higher-level unit 4. For example, if an analog measurement transmission path is used, particularly according to the 4-20 mA standard, the warning messages W1, W2 are transmitted, for example, via a fault current. When using a wired fieldbus (or a wireless version of a fieldbus, particularly 802.15.4-based standards such as WirelessHART), the warning messages W1, W2, and / or the pass messages are transmitted via the fieldbus.

[0100] In a step A1), in the event that a value for the insulation resistance Riso is determined as shown in step A), an improved value for an electrical resistance value RRTD of a resistance element as the sensor element 1 can be determined using the determined insulation resistance Riso, as will be explained in more detail below.

[0101] For example, the device 200 is such (see Fig. 1) that the electrical connection between

[0102] Outer sheath 21 and the first connecting cable 3a, which has the electrical insulation resistance value Riso (the insulation resistance element 18), is connected in parallel to the resistance element 1. The measuring resistance Ri iess determined by means of the connecting cables 3a, 3b, 3c, 3d corresponds in this case

[0103] 1 / RM ess — 1 / RRTD + 1 / R|SO (1)

[0104] Only in the case where the electrical insulation resistance value Riso is very large compared to the electrical resistance value RRTD of the resistance element 1, the insulation resistance value Riso can be set to infinite. In this case, the electrical resistance value of the measuring resistor Riviess essentially corresponds to the electrical resistance value

[0105] RRTD of resistance element 1 : Riviess « RRTD.

[0106] If the determined insulation resistance value Riso is sufficiently reduced, e.g., due to the water retention mentioned above, it makes a noticeable contribution to the determined measurement resistance Riviess. The point at which the insulation resistance value's contribution becomes noticeable depends on the specific design, such as the actual range of the electrical resistance value RRTD of the resistance element 1, which the device 200 can assume within a measuring range specified for the measured quantity.

[0107] Using, for example, equation (1), a more accurate value for the electrical resistance value RRTD of the resistance element 1 can then be determined based on the determined measuring resistance Riviess and the determined insulation resistance Riso as follows:

[0108] Reference signs and symbols

[0109] 100 transmitter unit

[0110] 1 sensor element

[0111] 2 measuring insert

[0112] 21 Outer jacket

[0113] 2a, 2b proximal, distal end area

[0114] 3a, 3b, 3c, 3d connecting cables

[0115] 4 circuit board

[0116] 41 Circuit arrangement

[0117] 4-KF contacting connection surface

[0118] 5 Transmitter housing

[0119] 51 , 52 first, second transmitter housing part

[0120] 6 Fastening element

[0121] 200 device

[0122] 7 Contacting element

[0123] 7a, 7b first, second contacting element end section

[0124] 7-KF contact surface section

[0125] 71 recess

[0126] 8 Recording

[0127] 9 Insulating material

[0128] 10 Sealing

[0129] 11 Reference potential

[0130] 12 capacitive element

[0131] 13 Reference resistance element

[0132] 14 A / D converters

[0133] 15 Power source

[0134] 16 Reference resistance

[0135] 17 differential amplifiers

[0136] 18 Insulation resistance element

[0137] ME-LA measuring insert longitudinal axis

[0138] BE-LA Fastener longitudinal axis

[0139] TG-LA T ransmitter housing longitudinal axis

[0140] AM-SF outer sheath end face

[0141] SF1 , SF2 first / second transmitter housing end face area

[0142] Riso insulation resistance

[0143] RRTD Resistance of the resistance element

[0144] Rmess measured resistance Mini, Min2 first, second minimum resistance value

[0145] W1 , W2 first, second warning message

[0146] Imess measuring current

[0147] Vref reference voltage VCC supply voltage

[0148] Rref resistance of the reference resistance element

Claims

Patent claims 1. T ransmitter unit (100) for a device (200) for determining and / or monitoring a measured variable, in particular the temperature, of a medium, which device (200) comprises an elongated measuring insert (2) with an electrically conductive, in particular metallic, outer casing (21), wherein the transmitter unit (100) serves to process and / or forward a measuring signal generated by a sensor element (1) of the device (200), wherein the transmitter unit (100) has measuring electronics with a first printed circuit board (4) and an electrically insulating transmitter housing (5), wherein the first printed circuit board (4) is arranged in a lumen of the transmitter housing (5), wherein the transmitter unit (100) is mechanically connectable, in particulardetachably mechanically connectable, and the transmitter unit (100) has a fastening element (6) serving for the mechanical fastening of the transmitter unit (100) to the measuring insert (2), wherein the fastening element (6) is electrically conductive, and wherein the transmitter unit (100) is designed such that when the transmitter unit (100) is fastened to the measuring insert (2), an electrically conductive connection is produced between the transmitter unit (100) and the outer casing (21) as a result of the fastening, by means of the electrically conductive fastening element (6).

2. Transmitter unit (100) according to claim 1, wherein the fastening element (6) is at least partially pin-shaped, and in particular a fastening element longitudinal axis (BE-LA) is such that for the transmitter unit (100) fastened to the measuring insert (2), a fastening element longitudinal axis (BE-LA) is parallel to a measuring insert longitudinal axis (ME-LA).

3. T ransmitter unit (100) according to at least one of the preceding claims, wherein the transmitter unit (100) has an electrically conductive, in particular metallic, contacting element (7) with a first contacting element end section (7a) and a second contacting element end section (7b), which first contacting element end section (7a) and second contacting element end section in particular delimit the contacting element (7b), wherein the first contacting element end section (7a) or an adjacent section of the contacting element (7) is electrically contacted with the first printed circuit board (4), in particular in a contacting connection surface (4-KF) of the printed circuit board (4), and wherein the second contacting element end section (7b) can be contacted with the fastening element (6), so that the electrically conductive connection between the transmitter unit (100) and the outer casing (21) can be established in that, when the transmitter unit (100) is fastened to the measuring insert (2), an electrically conductive connection is present between the printed circuit board (4) and the outer casing (21) via the contacting element (7) and the fastening element (6) which is contacted at the second contacting element end section (7b).

4. T ransmitter unit (100) according to at least one of the preceding claims, wherein the transmitter housing (5) has: a first transmitter housing end face region (SF1), which first transmitter housing end face region (SF1) is to be turned towards the measuring insert (2) when the transmitter unit (100) is fastened to the (2) measuring insert, and a second transmitter housing end face region (SF2), which second transmitter housing end face region (SF2) is to be turned away from the measuring insert (2) when the transmitter unit (100) is fastened to the measuring insert (2), wherein the first transmitter housing end face region (SF1) and the second transmitter housing end face region (SF2) are arranged opposite one another with respect to a transmitter housing longitudinal axis (TG-LA), wherein the fastening element (6) is insertable into the transmitter housing (5) from the second transmitter housing end face region (SF2) and for Fastening can be determined,wherein the contacting element (7) has a, in particular flat, contacting surface section (7-KF) at its second contacting element end section (7b), which contacting surface section (7-KF) rests on the second transmitter housing end face area (SF2), in particular directly, and wherein the contacting element (7) can be contacted with the fastening element (6) in that the fastening element (6) borders on the contacting surface section (7-KF) in some areas at least with a contact area (61).

5. Transmitter unit (100) according to claim 4, wherein the contacting surface section (7-KF) has a recess (71), in particular an internal one, for receiving the fastening element (6), so that the fastening element (6) projects through the recess (71) of the contacting surface section (7-KF).

6. Transmitter unit (100) according to claim 4 or 5, wherein the transmitter housing (5) has a guide (51) extending from the second transmitter housing end face region (SF1) to the first transmitter housing end face region (SF1), which guide (51) serves to receive a portion of the fastening element (6), in particular the pin-shaped portion of the fastening element (6).

7. T ransmitter unit (100) according to at least one of the preceding claims, wherein the contacting element (7) is designed such that an electrical contact resistance value between the second contacting element end section (7b) and the first contacting element end section (7a) is less than 100 ohms, in particular less than 50 ohms, preferably less than 10 ohms, particularly preferably less than 1 ohm.

8. T ransmitter unit (100) according to at least one of the preceding claims, wherein the contacting element (7) has a current carrying capacity of at least 100 mA, in particular at least 300 mA, preferably at least 500 mA.

9. T ransmitter unit (100) according to at least one of the preceding claims, wherein the contacting element (7) has, at least on the second contacting element end section (7b), in particular the contacting surface section (7-KF), a conductive and in particular corrosion-resistant oxidation prevention layer, in particular comprising gold or a gold-containing alloy.

10. T ransmitter unit (100) according to at least one of the preceding claims, wherein the first printed circuit board (4) has a circuit arrangement (41) comprising conductor tracks, contact surfaces and components, and wherein for the transmitter unit (100) fastened to the measuring insert (2), in which the electrically conductive connection between the printed circuit board (4) and the outer casing (21) is present, namely via the fastening element (6) and the contacting element, the circuit arrangement (41) is designed to to determine an electrical insulation resistance value (Riso) between at least one first connecting line (3a) of the connecting lines (3a; 3b; 3c, 3d) and the outer sheath (21) and / or to determine whether the electrical insulation resistance value (Riso) between at least one first connecting line (3a) of the connecting lines (3a; 3b; 3c, 3d) and the outer sheath (21) is less than at least a first minimum resistance value.

11. T ransmitter unit according to at least one of the preceding claims, wherein the circuit arrangement (41) has a capacitive element (12) with a capacitance of at least one pF (picofarad), and wherein the capacitive element (12) is connected in particular in series with the contacting connection surface (4-KF) of the printed circuit board (4).

12. Device (200) for determining and / or monitoring a measured variable, in particular the temperature, of a medium, comprising: - a sensor element (1), in particular a temperature-sensitive one, for generating a measurement signal dependent on the measured variable - an elongated measuring insert (2) with an electrically conductive, in particular metallic, outer sheath (21), having a distal end region (2b), wherein the measuring insert (2) surrounds the sensor element (1) and in particular the sensor element (1) is arranged in the distal end region (2b) and in particular the measuring insert (2) is closed in the distal end region (2b), - connecting lines (3a; 3b, 3c, 3d), in particular at least two, which connecting lines (3a; 3b, 3c, 3d) serve to contact the sensor element (1) and lead from the sensor element (1) to a proximal end region (2a) of the measuring insert (2), which proximal end region (2a) is arranged opposite the distal end region (2b) with respect to a measuring insert longitudinal axis (ME-LA), and - a transmitter unit (100) according to at least one of the preceding claims 1 to 11, wherein the transmitter unit (100) serves to process and / or forward the measurement signal generated by the sensor element (1), wherein the transmitter unit (100) is fastened to the measuring insert (2) at the proximal end region (2a) of the measuring insert (2) by means of the fastening element (6), so that the outer casing (21) is electrically conductively connected to the transmitter unit (100).

13. Device (200) according to claim 12, wherein the outer casing (2) has, at the proximal end region (2a), an outer casing end face (AM-SF) facing the transmitter unit (100), in particular a disc-shaped, outer casing end face (AM-SF), which outer casing end face (AM-SF) has a receptacle (8) for the fastening element (6) corresponding to the fastening element (6), so that when the fastening element (6) is inserted into the receptacle (8), the fastening element (6) is electrically conductively connected to the outer casing (21).

14. Device (200) according to one of claims 12 or 13, wherein a reference potential (11), in particular a zero reference potential, for example a ground, is provided on the fastening element (6) and / or on the outer casing (21).

15. A method for self-monitoring a device (200) with a device (200) according to at least one of claims 12 to 14, comprising: - determining an electrical insulation resistance value (Riso) between the outer sheath (2) and at least one first connecting cable (3a) and issuing a first warning message in the event that the electrical insulation resistance value (Riso) is less than a first minimum resistance value (Mini), or - Determining whether the electrical insulation resistance value (Riso) between the outer sheath (2) and at least one first connecting cable (3a) is less than a first minimum resistance value (Mini) and issuing a first warning message (W1) in the event that the electrical insulation resistance value (Riso) is less than the first minimum resistance value.

16. A method for self-monitoring according to claim 15, comprising: - Output of a second warning message (W2), in particular for the measuring electronics, in the event that the electrical insulation resistance value (Riso) is less than a second minimum resistance value (Min2), whereby the second minimum resistance value (Min2) is less than the first minimum resistance value (Mini).

17. The method according to at least one of claims 15 or 16, wherein the first minimum resistance value (Mini) is at least 0.2 megaohms, in particular at least 0.5 megaohms, preferably at least 1 megaohm and / or wherein the second minimum resistance value (Min2) is at least 0.1 megaohms, in particular at least 0.2 megaohms, preferably at least 0.5 megaohms.

18. Method according to at least one of claims 15 to 17, wherein the sensor element (1) is a resistance element, wherein in the generation and / or processing of the measurement signal a signal derived from the electrical Resistance value (RRTD) of the resistance element dependent, electrical measuring resistance (Rmess) is detected by means of a first connecting line (3a) and at least one second connecting line (3b; 3c; 3d), and wherein the method comprises: Determining an electrical insulation resistance value (Riso) between the outer sheath (2) and the first connecting cable (3a); Determining the electrical measuring resistance (Rmess) by means of the first connecting line (3a) and at least the second connecting line (3b); and Determine the electrical resistance value (RRTD) of the resistance element based on the measured measuring resistance (Rmess) and the measured insulation resistance value (Riso)

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