Thermal flow meter and method for operating such a thermal flow meter

Abstract

The invention relates to a thermal flow meter (100), wherein the thermal flow meter (100) can be operated in a first measuring mode configured as a temperature difference operation (CTA) and in a second measuring mode configured as a constant current operation (CCA), in particular asynchronously with the first measuring mode. The thermal flow meter (100) is switchable between operation in the first measuring mode (CTA) and operation in the second measuring mode (CCA). Furthermore, the invention relates to a method for operating a measuring point (200) with the thermal flow meter (100).

Description

[0001] The invention relates to a thermal flow meter for determining and / or monitoring a mass flow rate of a flowable medium contained in a pipeline, and to a method for operating a measuring point with a corresponding thermal flow meter.

[0002] Thermal flowmeters are used in process automation to determine and / or monitor the mass flow rate of a medium, especially a fluid (e.g., a gas, liquid, or mixture thereof), flowing in a pipe, such as a measuring tube. Thermal flowmeters are known from the prior art and are described, for example, in DE 10 2013 105 992 A1, DE 10 2016 121 110 A1, and DE 10 2019 110 876 A1. A thermal flowmeter comprises at least one, and often at least two, thermal sensor elements.

[0003] Thermal sensor elements of this type include, for example, resistance elements (also known as RTD elements, short for Resistance Temperature Detector), especially so-called PTC thermistors (PTC stands for positive temperature coefficient). The latter are characterized by the fact that their electrical resistance increases with rising temperature, particularly linearly in the first order. Platinum is widely used among PTC thermistors because platinum exhibits a resistance that is at most quadratic in its dependence on temperature. Platinum resistance elements are often designed to have a specific nominal resistance at a reference temperature, such as 0°C. They are available accordingly under the designations Pt10 (10 ohms), Pt100 (100 ohms), and Pt1000 (1 kOhm). The resistance element is implemented, for example, as a wound resistor or as one applied to a substrate, especially...A structured, resistive layer, for example, formed using thin-film or thick-film technology. In a (thin-)film sensor, for example, a resistive structure with connecting wires and applied to a substrate is used, which is electrically insulated by means of a cover layer.

[0004] The thermal sensor elements of a thermal flow meter are interconnected with an electronic measuring / operating circuit, e.g. by forming a bridge circuit, which measuring / operating circuit serves to operate the thermal flow meter.

[0005] At least one of the thermal sensor elements serves as a heating sensor element, which is (actively) heated, and at least one of the thermal sensor elements serves as a temperature sensing sensor element, designed to detect the temperature of the medium. If necessary, the same or multiple thermal sensor elements, especially the two, are designed for both heating and temperature detection and can function—depending on the control by the flow meter's measuring / operating circuit—as the heating sensor element and / or as the temperature sensing sensor element. In this case, the two thermal sensor elements can be essentially identical in design.

[0006] Thermal flow meters are designed, for example, to determine the mass flow rate from the heating power required to maintain a temperature difference between the heated heating sensor element and the temperature sensing sensor element. Such thermal flow meters are also known as CTAs (constant temperature anemometers).

[0007] Furthermore, thermal flow meters configured as so-called CCAs (constant current anemometers) have also become known. These are characterized by the fact that the heating sensor element is supplied with a constant input – for example, a constant heating current or a constant heating power. The temperature of the medium is determined by the temperature sensing sensor element and depends on the mass flow rate. The measured temperature difference between the heating sensor element and the temperature sensing sensor element decreases with increasing mass flow rate, whereas at lower mass flow rates, the measured temperature difference increases. Thermal flow meters configured as CCAs therefore also exhibit high sensitivity at low flow rates.CCA thermal flow meters are operated in a pulsed manner, so that in this case the same thermal sensor element can serve as both the temperature sensing sensor element and the heating sensor element.

[0008] Each of the two aforementioned types of thermal flowmeters has specific advantages and disadvantages. Depending on the application, either a CCA flowmeter or a CTA flowmeter is more suitable. This depends in particular on the design of the measuring point, which includes the thermal flowmeter and a pipeline for containing and / or carrying the medium in which the thermal flowmeter is installed.

[0009] The invention is based on the objective of providing a universally applicable thermal flow meter.

[0010] The problem is solved by a thermal flow meter and by a method for operating a measuring point with such a thermal flow meter. Advantageous embodiments are specified in the dependent claims. All embodiments of the thermal flow meter according to the invention are, of course, mutatis mutandis, encompassed by the method according to the invention, and vice versa.

[0011] Regarding the thermal flow meter, the problem is solved by a thermal flow meter for determining and / or monitoring a mass flow of a flowable medium contained in a pipeline, comprising a thermal flow meter: two thermal sensor elements designed to heat and / or detect the temperature of the medium, and a measuring / operating circuit for operating the thermal flow meter, wherein the thermal flow meter can be operated in a first measuring mode designed as a temperature difference operation and in a second measuring mode designed as a constant current operation, in particular not simultaneously with the first measuring mode, the first measurement operation includes: - Heating one of the two thermal sensor elements and determining the temperature of the heated first thermal sensor element, - Determining the temperature of the second thermal sensor element, especially if it is unheated, - Controls, by adjusting an electrical control variable fed to the first thermal sensor element by the measuring / operating circuit, in particular a heating current and / or a heating power, such that a first temperature difference formed from the determined temperature of the first thermal sensor element and the determined temperature of the second thermal sensor element is regulated to a constant temperature difference value, - Determining a flow rate measurement for the mass flow, based at least on the electrical control variable, in particular the heating current and / or the heating voltage, which is present at the first temperature difference regulated to the constant temperature difference value, and wherein the second measurement operation includes: - Determining the temperature of the medium using the unheated first thermal sensor element and / or the unheated second thermal sensor element, - Heating the first thermal sensor element by supplying it with an electrical input quantity set to a constant target value, in particular a heating current or a heating voltage, and determining the temperature of the heated first thermal sensor element, - Determining a second temperature difference, formed from the determined temperature of the medium and the determined temperature of the heated first thermal sensor element. - Determining a flow measurement value for the mass flow, based at least on the determined second temperature difference, which second temperature difference is present at the electrical input quantity set to the constant setpoint, and wherein the thermal flow meter is switchable between operation in the first measuring mode and operation in the second measuring mode.

[0012] Because the thermal flowmeter can be operated in either the first measuring mode (constant temperature difference operation) or the second measuring mode (constant current operation), it is universally applicable. If the operating conditions for a flowmeter already installed at a measuring point change, such that the second measuring mode is preferred over the first, or vice versa, the thermal flowmeter can be switched between the two modes. Thanks to its universal applicability, replacing the thermal flowmeter, which would otherwise require removing the existing one, is no longer necessary.

[0013] In one embodiment of the thermal flowmeter, it includes a physical or virtual switching element for switching between the first and second measuring modes. This switching element is, for example, a physical switch or a button displayed on the flowmeter's touchscreen. The presence of the switching element is not essential to the invention; for example, switching between the first and second measuring modes can alternatively be achieved using an operating device that communicates with the thermal flowmeter via a communication link.

[0014] In one embodiment of the thermal flow meter, the measuring / operating circuit comprises one or more electronic storage elements, in which a first operating and evaluation algorithm is stored in one or more storage elements, by means of which the first measuring operation is implemented, and a second operating and evaluation algorithm is stored, by means of which the second measuring operation is implemented.

[0015] For example, the first operating and evaluation algorithm is selected from a first memory element, or the second operating and evaluation algorithm is selected from a memory element, depending on a predefined value of a switching variable.

[0016] In one embodiment of the thermal flowmeter, the measuring / operating circuit has an electronic storage element in which a common operating and evaluation algorithm is stored, by means of which both the first measuring operation and the second measuring operation are implemented in such a way that, depending on a predefinable value of a switching variable, the common operating and evaluation algorithm configures the thermal flowmeter to perform either the steps of the first measuring operation or the steps of the second measuring operation.

[0017] The switching variable mentioned in connection with the aforementioned configurations is, for example, a Boolean switching variable whose value can be set to T or F, e.g., CTA=T in which case the first measurement mode (CTA) is selected, or CTA=F in which case the second measurement mode (CCA) is selected. This switching variable may be coupled to the aforementioned switching element in such a way that the value of the switching variable can be set by operating the virtual or physical switching element.

[0018] In one embodiment of the thermal flow meter, the two thermal sensor elements each comprise a cold-conducting material, in particular platinum and / or nickel, and are essentially identical in design.

[0019] The applicant refers here to the RTD resistance elements mentioned at the outset, whereby the invention mutatis mutandis also includes RTD resistance elements other than those mentioned in this embodiment, e.g., thermistors.

[0020] In one embodiment of the thermal flowmeter, the device has an elongated probe element in which the two thermal sensor elements are arranged, and which probe element serves for at least partial immersion in the pipeline, in particular in the medium contained in the pipeline, for determining and / or monitoring a mass flow, wherein the probe element has a proximal end region and a distal end region opposite the proximal end region along a longitudinal axis of the probe element, at which distal end region the probe element is terminated, and wherein the first thermal sensor element, which is heated in the first measuring operation and the second measuring operation, is arranged in the distal end region.

[0021] In one embodiment of the thermal flow meter, the second thermal sensor element is spaced apart from the first thermal sensor element along the longitudinal axis of the probe element and is offset from the first thermal sensor element along the longitudinal axis in the direction of the proximal end region.

[0022] In one embodiment of the thermal flow meter, the two thermal sensor elements are arranged in a probe section, which probe section has a length in the direction of the longitudinal axis of at most 2 / 3, in particular at most 1 / 2 of a total length of the probe element in the direction of the longitudinal axis of the probe element.

[0023] The heating sensor element, which is actively heated in both measurement modes, is located in the distal end region through which the probe element immerses in the medium. The second thermal sensor element, which serves as the temperature sensing sensor element in the first measurement mode, is, however, positioned offset from the first thermal sensor element in the probe element towards the proximal end region.

[0024] The probe element can be designed as a single or multi-part component, in particular as a two-part component. The latter, for example, involves the probe element having a sensor cap at its distal end to close the probe element at this end, which contains the first thermal sensor element. This is, for example, preferred from a manufacturing perspective.

[0025] In one embodiment of the thermal flow meter, the first thermal sensor element has: - a measuring element for measuring temperature; and - a heating element for heating the thermal sensor element and / or the probe element, wherein the heating element has a temperature-independent electrical resistance which in linear order is at most 0.2 × 10 -3 / Kelvin, in particular at most 0.1 × 10 -3 / Kelvin, preferably at most 0.05 × 10 -3 / Kelvin.

[0026] Regarding the procedure for operating a measuring station, the problem is solved by a procedure for operating a measuring station comprising the measuring station: - A thermal flow meter according to the invention; and - a pipeline for containing and / or conveying a medium; wherein the thermal flow meter is installed in the pipeline in such a way that the probe element of the thermal flow meter protrudes into the pipeline, in particular into a medium contained in the pipeline, at least section by section.

[0027] In one embodiment of the procedure, this includes a recommendation operation, which includes the following recommendation operations: - Determining and / or transmitting a value for one or more characterizing parameters of the measuring point; - Recommending either the first measurement operation or the second measurement operation as preferred, based on the value of one or more characterization variables, whereby the recommended operation is carried out in particular during the commissioning of the measuring point.

[0028] The characterization parameter is determined, for example, by the thermal flow meter itself or by another device, such as an operator panel or another field device. Alternatively, the characterization parameter is transmitted if it is known by a user and is transmitted directly, for example, by input on-site at the thermal flow meter itself or via input on an operator panel. Whether the characterization parameter is determined or transmitted depends on the specific design, in particular the type of characterization parameter.

[0029] The thermal flow meter or an operating device is then, for example, designed to recommend either the first or the second measuring mode based on one or more characterization parameters. Based on this recommendation, the thermal flow meter can then be switched to the (currently) recommended measuring mode automatically or by active input or release from a user, depending on the design of the method. This could be done, for example, by a corresponding input at the aforementioned switching element of the thermal flow meter or by input at the operating device.

[0030] In one embodiment of the procedure, the one or more characterization parameters include at least one of the following: - Immersion depth of the probe element that is immersed in the pipeline, at least in sections; - An installation position of the thermal flow meter, in relation to a predetermined and / or current flow direction of the medium flowing in the pipeline.

[0031] The installation position in relation to a given and / or current flow direction is known to the user and can be entered by them.

[0032] In one version of the procedure, the recommendation process includes: - Determining or transmitting the immersion depth of the probe element that is immersed in the pipeline, at least in sections; - Recommend the first measurement operation if at least the immersion depth of the probe element is greater than a specified minimum immersion depth; and - Recommend a second measurement operation, otherwise.

[0033] If the thermal flow meter has an insufficient immersion depth, preventing the second thermal sensor element (which serves as the temperature sensing element in the first measurement mode and is positioned offset towards the proximal end), from maintaining adequate thermal contact with the medium, the second measurement mode is recommended. In this second measurement mode (CCA), which can be configured as a pulsed mode, only the first thermal sensor element at the distal end of the probe element is used to determine the mass flow rate. A sufficiently large immersion depth of the probe element is a necessary (but, depending on the design, potentially not sufficient) condition for recommending the first measurement mode.

[0034] In one version of the procedure, the recommendation process includes: - Determining or transmitting the thermal conductivity of the medium; - Comparison of the determined or provided thermal conductivity with a specified minimum thermal conductivity; - Recommend the first measurement operation if the determined thermal conductivity is less than the specified minimum thermal conductivity.

[0035] In one version of the procedure, this includes a review operation, the review operation being comprehensive: - Determining an initial verification temperature of the medium using the first thermal sensor element, with the first thermal sensor element unheated; - Determining a second verification temperature of the medium with the second thermal sensor element, with the second thermal sensor element unheated; - Determining the temperature difference between the first verification temperature and the second verification temperature; - Recommending the first measurement operation (CTA) if at least the determined temperature difference is smaller than a specified maximum temperature difference; and - Recommend the second measurement operation (CCA), otherwise.

[0036] The immersion depth mentioned above can, if known, be specified in the inventive method, for example, by a user input on the thermal flowmeter itself or on the operating device. If necessary, the sufficient immersion depth is additionally or alternatively determined, particularly at least indirectly, by the thermal flowmeter itself, for example, based on the aforementioned temperature difference determined during the verification process.

[0037] The thermal conductivity can also be entered if known, or determined by the thermal flowmeter itself. The latter is possible, for example, if the flow rate is known, such as in the case of a stagnant medium, and / or if the immersion depth is known, especially if it is greater than a required minimum immersion depth. Otherwise, the thermal conductivity can be determined, for example, by another field device.

[0038] In one embodiment of the procedure, the verification operation is carried out within the framework of the recommendation operation, in particular during the commissioning of the measuring point and / or alternates with an operation to measure the flow rate, namely an operation in the first measuring operation or an operation in the second measuring operation.

[0039] The invention is explained in more detail with reference to the following figures, which are not to scale, where identical reference numerals denote identical features. Where clarity requires it or it otherwise appears appropriate, previously mentioned reference numerals are omitted in subsequent figures.

[0040] They show: Fig. 1a: A sectional view of a measuring point 200 comprising a measuring tube 2 with a thermal flow meter 100, in an embodiment of the invention; Fig. 1b: An embodiment of the first thermal sensor element 1a; and Fig. 2: A flowchart showing the steps of the inventive method for operating a measuring point 200 with an inventive thermal flow meter 100, according to an embodiment of the invention.

[0041] Fig. Figure 1a shows a schematic side view of a measuring point 200, comprising a pipeline 2 for conveying a medium whose flow rate is to be determined and / or monitored by a thermal flow meter 100, and the thermal flow meter 100 installed in the pipeline 2. The thermal flow meter 100 includes a measuring / operating circuit 3, which is, for example, arranged in a housing 8 for enclosing the measuring / operating circuit 3. The electronic measuring / operating circuit 3 is configured to operate the thermal sensor elements 1a, 1b and to provide flow rate measurements Φ.

[0042] The thermal flow meter 100 comprises a first thermal sensor element 1a and a second thermal sensor element 1b, which are arranged together inside a probe element 7. The probe element 7 has sufficiently high thermal conductivity and simultaneously sufficiently high chemical and / or mechanical resistance to the requirements of the measuring point 200, e.g., the medium. For example, it is a metallic probe element 7, in particular made of stainless steel. The probe element 7 projects at least partially into the pipeline 2 via a process connection from a distal end region 71. The housing of the measuring / operating circuit 3 connects to the probe element 7 at the proximal end region 72, which is opposite the distal end region 71 along a longitudinal axis LA of the elongated probe element 7.Depending on the immersion depth ET of the probe element 7, the proximal end region 72 is located outside the pipeline 2.

[0043] The first thermal sensor element 1a, which is heated in both the first measurement operation CTA and the second measurement operation CCA, is arranged in the distal end region 71, e.g. adjacent to or inside a probe element cap that closes off the probe element 7 at its distal end.

[0044] One embodiment of the first thermal sensor element 1a is shown in Fig. 1b shown in more detail. For example, the first thermal sensor element is constructed from a device comprising a substrate 12, a heating layer arranged on the substrate 12 (forming the heating element 11), an insulating layer 13 arranged on the heating layer for electrical insulation, and a measuring layer arranged on the insulating layer 13 (forming the measuring element 10), wherein the arrangement or sequence of the measuring element 10 and the heating element 11 in the device is not essential.

[0045] Preferably, the heating element 11 in this case has a substantially temperature-independent electrical resistance. For example, at a reference temperature, the heating element 11 has an electrical resistance-temperature coefficient that is at most 0.2 × 10⁻⁶ on a linear order. -3 / Kelvin, in particular at most 0.1 × 10 -3 / Kelvin, preferably at most 0.05 × 10 -3 / Kelvin.

[0046] The measuring element 10, however, exhibits a temperature-dependent electrical resistance, as is typical for an RTD, e.g. with a temperature coefficient of at least 1 × 10 in linear order. -3 / Kelvin is, in particular, at least 3 × 10 -3 / Kelvin, so that the temperature can be measured by measuring the electrical resistance of the measuring element 10. For example, the aforementioned Pt / Ni measuring elements have an electrical resistance-temperature coefficient that is approximately 3.85 × 10 on a linear order. -3 / Kelvin.

[0047] This has the advantage that the device is easier to operate from a measurement perspective. Since the electrical resistance of the heating element 11 remains essentially constant even under changing temperatures, the thermal flow meter 100 can be operated with constant heating power in the second measurement mode CCA, because with constant electrical resistance and constant electrical current, the electrical voltage also remains constant.

[0048] Alternatively, the two thermal sensor elements 1a, 1b can of course also be designed as a combined heating / measuring element, such as a Pt100 or a Pt1000, which in turn offers manufacturing advantages.

[0049] According to the invention, the thermal flow meter 100 can be operated either in a first measuring mode CTA (constant temperature difference operation) or in a second measuring mode CCA (constant current operation) in order to measure the mass flow rate of a flowable medium through the pipeline 2. Both the first measuring mode CTA and the second measuring mode CCA are known per se and are only briefly outlined here and in the following.

[0050] In the first measurement mode CTA, the first thermal sensor element 1a is heated in the medium flowing through the measuring tube 2 such that a first temperature difference relative to the medium temperature remains constant. The second thermal sensor element 1b serves to measure the temperature of the medium. Assuming constant medium properties (e.g., density or composition), a flow rate Φ for the mass flow can be determined from the heating current and / or the heating power Q required to maintain the first temperature difference. For example, a power coefficient PC is considered, which is proportional to the amount of heat Q supplied via the heating power divided by the first temperature difference: PC - Q / |T 1a - T 1b |

[0051] The second measuring mode, CCA, designed as a constant current operation, operates in a pulsed mode. In the first pulse, the temperature of the medium, especially the unheated one, is determined. This is done, for example, using the unheated first thermal sensor element 1a, and / or using the unheated second thermal sensor element 1b. If the immersion depth ET is insufficient, only the first thermal sensor element 1a is used, and the temperature of the medium is determined solely by the unheated first thermal sensor element 1a.

[0052] A second temperature difference is then determined. This second temperature difference is formed from the determined temperature of the medium and the determined temperature of the heated first thermal sensor element 1a. The flow rate measurement Φ for the mass flow is then provided, based at least on the determined second temperature difference, which is present when the electrical input is set to the constant setpoint. Typically, the pulsed operation of the second measurement mode CCA includes a third pulse following the second pulse, with a cooling phase. Subsequently, all pulses—namely the first, second, and third—of the pulsed operation are repeated cyclically to provide current flow rate measurements Φ for the mass flow.

[0053] The constant temperature difference value, to which the first temperature difference in the first measurement operation CTA is regulated, is stored, for example, together with an operating and evaluation algorithm 6 in one or more memory elements 5; 51; 52 ... . The constant setpoint value, to which the electrical feed-in quantity in the second measurement operation CCA is regulated, is also generally predefined and stored as a hard-coded value in one or more memory elements 5; 51; 52 ... . The procedure then includes, in particular, reading the predefined constant temperature difference value (first measurement operation CTA) and / or reading the predefined constant setpoint value (second measurement operation CCA) from the one or more memory elements 5; 51; 52.

[0054] For switching between the first measuring mode CTA and the second measuring mode CCA, the thermal flow meter 100 has, for example, a switching element 4. The switching element 4 is, for example, a switch or a button displayed on a touchscreen of the flow meter. The presence of the switching element 4 is not essential for the invention – for example, switching between the first measuring mode CTA and the second measuring mode CCA can also be carried out using an operating device 9, which communicates with the thermal flow meter 100 via a communication link KV. Of course, the operating device 9 can also be used only to display the currently selected first measuring mode CTA (as in Fig. 1a shown) or serve as the second measurement operation CCA.

[0055] For example, the operating device is like the one in Fig. Figure 1a depicts a mobile device and / or a control unit, such as a smartphone, tablet, smart glasses, or a mobile device specifically designed for process automation, such as the FieldXpert distributed by the Endress+Hauser Group. Within the scope of this application, the term "operating device" also includes all other mobile or non-mobile operating devices that are configured for communication with the thermal flowmeter 100 via a communication link (preferably wireless). Thus, the term "operating device" can also include a process control system assigned to a higher-level unit, such as a PLC (Programmable Logic Controller).

[0056] Fig. Figure 2 shows a flowchart of the steps in the method for operating a measuring point 200, in one embodiment of the method according to the invention. In step A), one or more characterization parameters CG of the measuring point 200 are first recorded. These include, for example, the aforementioned immersion depth ET of the probe element 7 in the pipeline 2, a thermal conductivity λ of the medium carried in the pipeline 2, etc., or an installation position EL with respect to a flow direction. Depending on the embodiment and / or type of characterization parameter CG1, CG2, the (current) values ​​for the one or more characterization parameters CG1, CG2 are known to the user and can be directly entered by the user, or they are additionally or alternatively determined, for example, by the thermal flowmeter 100 itself.

[0057] In step B), for example, it is checked whether the immersion depth ET is greater than a minimum immersion depth ETmin. If not (arrow n of box B in Fig. 2) The first measurement operation CTA is not selected, e.g., by suggesting the value of the Boolean variable CTA=F. If so (arrow y in Fig. In step C, the installation position in relation to the flow direction is additionally checked (see box B). If this does not correspond to the installation position required for the first CTA measurement operation (arrow n in box B), the installation position is checked again. Fig. 2 of box C), the first measurement operation CTA is not selected, e.g. by again proposing to set the value of the Boolean variable CTA=F.

[0058] If yes (arrow y in Fig. In step D), the thermal conductivity λ of the medium is then checked to see if it is less than a minimum thermal conductivity λmin (see box E). For low thermal conductivities λ, the first measurement operation is CTA (see box E). Fig. 2, preferably (arrow y in Fig. 2 of box D to box E). For thermal conductivities λ greater than or equal to the minimum thermal conductivity λ min, both the first measurement operation CTA and the second measurement operation CCA can be selected.

[0059] In this way, either the first measurement mode, CTA, or the second measurement mode, CCA, is recommended via a recommendation mode. The recommended measurement mode, CTA or CCA, can be set automatically or (preferably) by user authorization.

[0060] Typically, the recommended operation is performed during the commissioning of measuring point 200 to select the first CTA or second CCA measurement operation recommended for measuring point 200 before the first measurement. Some of the characterization parameters CG, such as the immersion depth ET, then generally remain constant for measuring point 200. However, if a different medium is introduced, its physical properties change (e.g., temperature and / or pressure), or the flow direction changes, the thermal conductivity and / or the installation position relative to the flow direction can also change. Therefore, depending on the application, repeating the recommended operation after the initial commissioning of the thermal flowmeter 100 is certainly possible.

[0061] Not in Fig.As described in more detail in Figure 2, but of course also included in the invention, are embodiments in which temperature measurements obtained during a test operation with the two thermal sensor elements 1a, 1b in an unheated state are compared. This allows verification of whether the two thermal sensor elements 1a, 1b at measuring point 200 are in sufficiently good thermal equilibrium, i.e., exposed to the same temperature. This test operation can also be carried out within the framework of the aforementioned recommended operation, or independently thereof. Reference signs and symbols 100 thermal flow meter 200 measuring points 1a, 1b thermal sensor elements 10 measuring element 11 Heating element 2 Pipeline 3 Measuring / Operating Circuit 4 switching element 5, 51, 52 storage elements 6. Operation and evaluation algorithm 7 probe element 71 distal end 72 proximal end region 8 cases 9 Control unit 12 Substrat 13 Insulation layer CTA first measurement operation CCA second measurement operation LA Longitudinal axis Φ Flow rate measurement CG Characterization Size ET immersion depth ETmin Minimum immersion depth λ Thermal conductivity λ min minimum thermal conductivity KV communication link QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2013 105 992 A1

[0002] DE 10 2016 121 110 A1

[0002] DE 10 2019 110 876 A1

[0002]

Claims

[1] Thermal flow meter (100) for determining and / or monitoring a mass flow rate of a flowable medium contained in a pipeline (2), comprising the thermal flow meter (100): two thermal sensor elements (1a, 1b) which are designed for (active) heating and / or for detecting the temperature of the medium, and a measuring / operating circuit (3) for operating the thermal flow meter, wherein the thermal flowmeter (100) can be operated in a first measuring mode designed as a temperature difference operation (CTA) and in a second measuring mode designed as a constant current operation (CCA), in particular asynchronously to the first measuring mode, the first measurement operation (CTA) includes: - Heating one of the two thermal sensor elements (1a, 1b) of the first thermal sensor element (1a) and determining the temperature of the heated first thermal sensor element (1a), - Determining the temperature of the second, especially unheated, thermal sensor element (1b), - Controls, by adjusting an electrical control variable supplied by the measuring / operating circuit to the first thermal sensor element (1a), in particular a heating current and / or a heating power, such that a first temperature difference formed from the determined temperature of the first thermal sensor element and the determined temperature of the second thermal sensor element is regulated to a constant temperature difference value, - Determining a flow rate measurement (Φ) for the mass flow, based at least on the electrical control variable, in particular the heating current and / or the heating voltage, which is present at the first temperature difference regulated to the constant temperature difference value, and where the second measurement operation (CCA) includes: - Determining the temperature of the medium using the unheated first thermal sensor element (1a) and / or the unheated second thermal sensor element (1b), - Heating the first thermal sensor element (1a) by supplying it with an electrical input quantity set to a constant target value, in particular a heating current or a heating voltage, and determining the temperature of the heated first thermal sensor element (1a), - Determining a second temperature difference, formed from the determined temperature of the medium and the determined temperature of the heated first thermal sensor element (1a) - Determining a flow rate measurement (Φ) for the mass flow, based at least on the determined second temperature difference, which second temperature difference is present when the electrical input quantity is set to the constant target value, and wherein the thermal flowmeter (100) is switchable between operation in the first measuring mode (CTA) and operation in the second measuring mode (CCA). [2] Thermal flow meter (100) according to claim 1, comprising a switching element (4), in particular physical or virtual, for switching between the first measuring operation (CTA) and the second measuring operation (CCA). [3] Thermal flow meter (100) according to at least one of the preceding claims, wherein the measuring / operating circuit (3) comprises one or more electronic storage elements (51, 52;..) in which a first operating and evaluation algorithm (51a) is stored in one or more storage elements (51, 52;..) by means of which the first measuring operation (CTA) is implemented and a second operating and evaluation algorithm is stored by means of which the second measuring operation (CCA) is implemented. [4] Thermal flow meter (100) according to at least one of the preceding claims 1 to 3, wherein the measuring / operating circuit (3) has a storage element (5,...) in which storage element (5) a common operating and evaluation algorithm is stored, by means of which both the first measuring operation (CTA) and the second measuring operation (CCA) are implemented such that, depending on a predefinable value of a switching variable, the common operating and evaluation algorithm (6) implements the thermal flow meter to perform either the steps of the first measuring operation (CTA) or the steps of the second measuring operation (CCA). [5] Thermal flow meter (100) according to at least one of the preceding claims, wherein the two thermal sensor elements (1a,1b) each comprise a cold-conducting material, in particular platinum and / or nickel, and are in particular substantially identical in design. [6] Thermal flow meter (100) according to at least one of the preceding claims, comprising an elongated probe element (7) in which the two thermal sensor elements (1a, 1b) are arranged and which probe element (7) serves to be immersed at least sectionally in the pipeline (2), in particular in the medium contained in the pipeline (2), for determining and / or monitoring a mass flow rate, wherein the probe element (7) has a proximal end region (71) and a distal end region (72) opposite the proximal end region along a longitudinal axis (LA) of the probe element, at which distal end region (72) the probe element is terminated, and wherein the first thermal sensor element (1a), which is heated in the first measurement operation (CTA) and the second measurement operation (CCA), is located in the distal end region (71). [7] Thermal flow meter (100) according to claim 6, wherein the second thermal sensor element (1b) is spaced apart from the first thermal sensor element (1a) along the longitudinal axis (LA) of the probe element (7) and is offset from the first thermal sensor element (1a) along the longitudinal axis (LA) in the direction of the proximal end region (72). [8] Thermal flow meter (100) according to claim 7, wherein the two thermal sensor elements (1a, 1b) are arranged in a probe section, which probe section has a length in the direction of the longitudinal axis (LA) of at most 2 / 3, in particular at most 1 / 2 of a total length of the probe element (7) in the direction of the longitudinal axis (LA) of the probe element (7). [9] Thermal flow meter (100) according to at least one of the preceding claims, wherein the first thermal sensor element (1a) comprises: - a measuring element (10) for measuring the temperature; and - a heating element (11) for heating the thermal sensor element (1a) and / or the probe element (7), wherein the heating element (11) has a temperature-independent electrical resistance and an electrical resistance-temperature coefficient which, in linear order, is at most 0.2 × 10 -3 / Kelvin, in particular at most 0.1 × 10 -3 / Kelvin, preferably at most 0.05 × 10 -3 / Kelvin. [10] Method for operating a measuring point (200) comprising the measuring point (200): - a thermal flow meter (100) according to at least one of the preceding claims; and - a pipeline (2) for containing and / or conveying a medium; wherein the thermal flow meter (100) is installed in the pipeline (2) in such a way that the probe element (7) of the thermal flow meter (100) projects into the pipeline (2), in particular into a medium contained in the pipeline (2), at least section by section. [11] The method of claim 10, comprising a recommendation operation which includes: - Determining or transmitting a value for one or more characterization parameters (CG) of the measuring point (200); - Recommend either the first measurement operation (CTA) or the second measurement operation (CCA) as preferred, based on the value of one or more characterization quantity(s) (CG), wherein the recommended operation is carried out in particular during commissioning of the measuring point (200). [12] Method according to claim 11, wherein the one or more characterization quantity(s) (CG) comprises at least one of the following: - An immersion depth (ET) of the probe element (7) which is immersed at least sectionally in the pipeline (2); - An installation position (EL) of the thermal flow meter (100), in relation to a predetermined and / or current flow direction of the medium flowing in the pipeline (2). [13] The method of claim 12, wherein the recommendation operation comprises: - Determining or transmitting the immersion depth (ET) of the probe element (7) which is immersed at least sectionally in the pipeline (2); - Recommend the first measurement operation (CTA) if at least the immersion depth (ET) of the probe element is greater than a specified minimum immersion depth (ETmin); and - Recommend a second measurement operation, otherwise. [14] Method according to at least one of claims 11 to 13, wherein the recommendation operation comprises: - Determining or transmitting the thermal conductivity of the medium; - Comparison of the determined or provided thermal conductivity (λ) with a specified minimum thermal conductivity (λmin); - Recommend the first measurement operation (CTA) if the determined thermal conductivity is less than the specified minimum thermal conductivity (λmin). [15] Method according to at least one of claims 10 to 14, comprising a verification facility, comprising: - Determining an initial verification temperature of the medium using the first thermal sensor element (1a), with the first thermal sensor element (1a) unheated; - Determining a second verification temperature of the medium with the second thermal sensor element (1b), with the second thermal sensor element (1b) unheated; - Determining the temperature difference between the first verification temperature and the second verification temperature; - Recommending the first measurement operation (CTA) if at least the determined temperature difference is smaller than a specified maximum temperature difference; and - Recommend the second measurement operation (CCA), otherwise. [16] Method according to claim 15, wherein the verification operation is carried out within the framework of the recommendation operation, in particular during commissioning of the measuring point (200) and / or alternately with an operation to measure the flow rate, namely the first measuring operation (CTA) or an operation in the second measuring operation (CCA).

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