THERMAL FLOW METER AND METHOD FOR OPERATING A THERMAL FLOW METER

Description

[0001] This invention relates to a thermal flow meter and a method for operating a thermal flow meter.

[0002] Thermal flow measurement is based on the principle that the mass flow rate of a medium can be inferred from the energy input via a probe into the medium flowing past it, or from the temperature of a heated probe located in the medium. However, the direction of flow of the medium cannot be determined from the energy input or the temperature of the probe.

[0003] German patent DE102015118123A1 describes a sensor for a thermal flowmeter, which is immersed in a measuring tube of the flowmeter and has several probes. These probes are configured either to heat the medium and measure their own temperature or to measure the temperature of the medium. Furthermore, a flow resistance is provided to create a direction-dependent flow towards a heated probe, so that a clear direction of flow within the measuring tube can be derived from this direction. However, it has been shown that at low to medium flow velocities, determining the flow direction is subject to high uncertainties.

[0004] DE102018105046A1, US 2021 / 055145 A1 and WO2020244856A1 disclose further sensors of thermal flow meters with flow direction detection, in which high uncertainties in the flow direction indication still exist at low flow velocity.

[0005] The object of the invention is therefore to propose a flow meter which enables reliable detection of the flow direction of the medium in the measuring tube.

[0006] The problem is solved by a thermal flow meter according to independent claim 1 and by a method according to independent claim 9.

[0007] A thermal flow meter according to the invention for measuring the mass flow rate of a medium in a measuring tube comprises A measuring tube with a measuring tube wall and a measuring tube axis; a sensor with four probes, which probes extend from a sensor base into the measuring tube, wherein the probes are configured to heat the medium, determine its temperature, or influence the flow of the medium in the measuring tube; an electronic measuring / operating circuit, which is configured to operate at least three probes and to generate and provide flow measurement values ​​by means of their operation, wherein each probe has a probe base and a probe active element, wherein the probe base is arranged on a side of the respective probe facing the sensor base, and wherein the probe active element is arranged on a side of the respective probe facing away from the sensor base, and wherein the probe active element is configured to heat the medium.to determine the temperature of the medium and / or to influence the flow of the medium in the measuring tube, wherein the probe bodies are column-shaped, wherein the probe bodies span a rhombus on a surface of the sensor body, wherein the rhombus is defined by the centroids of cross-sections of the probe bodies, wherein a first diagonal of the rhombus is parallel to the measuring tube axis, and wherein a second diagonal lies in a measuring tube cross-section, wherein a first probe and a second probe are configured to heat the medium, wherein at least a third probe is configured to determine a temperature of the medium, wherein the first probe and the second probe are arranged on the first diagonal, and wherein the at least one third probe is arranged on the second diagonal.

[0008] In this way, the power coefficients determined by the electronic measuring / operating circuit between one probe designed as a heating element and a third probe can be advantageously used for direction detection, since in both flow directions one probe designed as a heating element is directly exposed to the flow, and another probe designed as a heating element is located in the flow shadow. Because both probes designed as heating elements are positioned on the first diagonal parallel to the measuring tube axis, the first probe and the second probe exhibit identical measuring behavior.

[0009] In one embodiment, the electronic measuring / operating circuit is configured to select a first group member and a third probe from a group comprising the first probe and the second probe to form a probe pair for measuring the mass flow rate, and to select the other group member for determining the flow direction, wherein the electronic measuring / operating circuit is configured to exchange the group members for measuring the mass flow rate and for determining the flow direction upon detection of a change in flow direction.

[0010] In one embodiment, the first probe, the second probe and the at least one third probe each comprise a probe sleeve, wherein the flow meter has resistance thermometers, wherein at least one resistance thermometer is arranged in the interior spaces of the first, second and third probes enclosed by the probe sleeves, which resistance thermometer is configured to detect a temperature or to emit heat energy.

[0011] In one embodiment, an interior angle β of the rhombus belonging to the first probe is less than 90° and in particular less than 75° and preferably less than 60°.

[0012] In one embodiment, the outer diameter of the probes in the respective operating areas is at least 1 mm and in particular 1.5 mm and preferably at least 2 mm and / or at most 7 mm and in particular at most 5 mm and preferably at most 4 mm.

[0013] In one embodiment, a centroid of a cross-section of the probe base body of the first probe has a first distance to a centroid of a cross-section of the probe base body of the second probe, wherein the first distance is at least two outer diameters.

[0014] In one embodiment, the cross-sections of the probes have a round outline, at least in areas of the probe working body.

[0015] In an inventive method for operating an inventive flow meter In a first process step, a first group member with a third probe forms a probe pair for measuring the mass flow rate from a group comprising the first probe and the second probe, wherein the other group member is used to determine the flow direction, characterized in that, in a second process step for measuring the mass flow rate and determining the flow direction, the group members are exchanged upon detection of a change in flow direction.

[0016] In one embodiment, the electronic measuring / operating circuit determines a first power coefficient using the first probe and at least a third probe and a second power coefficient using the second probe and at least a third probe, wherein the electronic measuring / operating circuit infers a change in flow direction from a temporal progression of a difference in the power coefficients, in particular from a change in the sign of the difference.

[0017] The invention is described below using schematic embodiments. Fig. 1 shows the effective ranges of an exemplary probe arrangement according to the invention for a thermal flow meter; Fig. 2 shows a cross-section through an exemplary first, second, or third probe; and Fig. 3 shows a side view of a sensor according to the invention; and Fig. 4 outlines a structure of an exemplary schematic thermal flow meter according to the invention; and Fig. 5 outlines the process of a method according to the invention.

[0018] Fig. 1 Figure 1 shows the effective ranges of a probe arrangement according to the invention in a measuring tube 11 with a measuring tube wall 11.1, each with a first probe 12.21, a second probe 12.22, a third probe 12.23, and a fourth probe 12.24. The effective ranges are the areas in which probe active elements W (see Figure 1) are located. Figs. 2 and 3) exert their effect. The probe active elements each connect to a probe base body G of the corresponding probe, which probe base bodies are connected to a sensor base body 12.1. The effect of the probe active elements is to heat the medium, determine the temperature of the medium, and / or influence the flow of the medium in the measuring tube. The first probe 12.21 and a second probe 12.22 are configured to heat the medium, with at least a third probe 12.23 being configured to determine the temperature of the medium. The fourth probe can be solid. Alternatively, another third probe can be used instead of the fourth probe.

[0019] The probe bodies of a probe arrangement span a rhombus, with a first diagonal D1 of the diagonal being aligned parallel to a measuring tube axis 11.2. Fig. 1 The orientation of the measuring tube axis is shown in the diagram. A second diagonal D2 lies within a cross-section of the measuring tube. This achieves a high degree of symmetry and independence of the sensor's flow resistance from the flow direction of the medium. An internal angle β, assigned to the first probe, is less than 90 degrees, resulting in a low flow resistance for the probe arrangement.

[0020] According to the invention, the first probe and the second probe are arranged on the first diagonal, and the at least one third probe is arranged on the second diagonal.

[0021] In this way, the electronic measuring / operating circuit (see Fig. 4 The power coefficients determined between a heating element probe and a third probe can be advantageously used for direction detection, since in both flow directions, one heating element probe is directly exposed to the flow, while the other heating element probe is positioned in the flow shadow. Because both heating element probes are located on the first diagonal parallel to the measuring tube axis, the symmetry of the diamond arrangement results in identical measurement behavior for the first probe when approached from a first direction and for the second probe when approached from a second direction opposite to the first. This arrangement proves particularly advantageous with regard to measurement accuracy, even at low flow velocities, and measurement stability with respect to flow direction detection.

[0022] For example, an electronic measuring / operating circuit determines 13, see Fig. 4 , a first power coefficient using the first probe and at least a third probe and a second power coefficient using the second probe and at least a third probe, wherein the electronic measuring / operating circuit infers a change in flow direction from a temporal progression of a difference in the power coefficients, in particular from a change in sign of the difference.

[0023] Fig. 2 Figure 1 shows a longitudinal section through an exemplary first, second, or third probe, where a probe sleeve SH defines an interior IR of the probe, within which the probe has a resistance thermometer WT. The resistance thermometer is thermally and mechanically coupled to the probe sleeve via a contact medium. This contact medium can, for example, be a molten material melted during probe manufacturing and subsequently processed after solidification. Alternatively, a contacting process such as explosive plating of the probe sleeve onto the contact medium, followed by processing, can be applied. The examples given here are not to be interpreted restrictively.

[0024] Fig. 3 Figure 2 shows a schematic side view of a sensor 12 of a thermal flow meter, which sensor has a sensor base body 12.1 and probes 12.2, wherein the probes each comprise a probe base body G and a probe active body W as described in Figures 2 a) and b).

[0025] Fig. 4 Figure 1 outlines a schematic structure of a thermal flowmeter 10 according to the invention, comprising a measuring tube 11 with a measuring tube wall 11.1 and a measuring tube axis 11.2, a sensor 12 with a sensor base 12.1 and probes 12.2, and an electronic measuring / operating circuit 13 for operating the sensor and providing flow measurement values. The sensor base is mounted in the measuring tube wall in a media-tight manner. The effective areas of the probes are preferably arranged in a flow region of the medium in which the local mass flow rate deviates by less than 10%, and in particular less than 5%, and preferably less than 2%, from an average value formed over a flow cross-section.

[0026] Fig. 5 outlines the process of an exemplary method according to the invention 100.

[0027] In a first process step 101, a group consisting of the first probe 12.21 and the second probe 12.22 forms a probe pair with a third probe 12.23 for measuring the mass flow rate, with the other group member being used to determine the flow direction, and in a second process step 102, the group members are exchanged for measuring the mass flow rate and for determining the flow direction.

[0028] In one embodiment, the electronic measuring / operating circuit determines a first power coefficient using the first probe and at least one third probe, and a second power coefficient using the second probe and at least one third probe. The electronic measuring / operating circuit infers a change in flow direction from the temporal profile of a difference in the power coefficients, in particular from a change in the sign of the difference. In this way, a high degree of independence of the measurement characteristic of sensor 12 (e.g., Fig. 1 ) are achieved by a flow direction of the medium in the measuring tube. Bezugszeichenliste

[0029] 10 Thermal flow meter 11 Measuring tube 11.1 Measuring tube wall 11.2 Measuring tube axis 12 Sensor 12.1 Sensor base 12.2 Probe 12.21 First probe 12.22 Second probe 12.23 Third probe 12.24 Fourth probe 13 Electronic measuring / operating circuit G Probe base W Probe active element SH Probe sleeve R Diamond D1 First diagonal D2 Second diagonal WT Resistance thermometer IR Interior β Interior angle

Claims

1. A thermal flowmeter (10) for measuring the mass flow of a medium in a measuring tube, comprising: a measuring tube (11) with a measuring tube wall (11.1) and a measuring tube axis (11.2); a sensor (12) with four probes (12.2), said probes extending into the measuring tube starting from a sensor basic body (12.1), wherein the probes are configured to heat up the medium, determine its temperature or influence a flow of the medium in the measuring tube; an electronic measuring / operating circuit (13) which is configured to operate at least three probes, as well as to both prepare and make available the measured flow values attained through their operation, wherein each probe has one probe basic body (G) and one active probe body (W), wherein the probe basic body is arranged on a side of the corresponding probe facing toward the sensor basic body, and wherein the active probe body is arranged on a side of the corresponding probe facing away from the sensor basic body, wherein the active probe body is configured to heat up the medium, determine the temperature of the medium, and / or influence a flow of the medium in the measuring tube, wherein the probe basic bodies have a column-shaped design, wherein the probe basic bodies are spread out on a surface of the sensor basic body in a rhombus shape (R), wherein the rhombus is defined by centroids of cross-sectional areas of the probe basic bodies, wherein a first diagonal (D1) of the rhombus is parallel to the measuring tube axis (11.2), and wherein a second diagonal (D2) is located in a measuring tube cross-section, wherein a first probe (12.21) and a second probe (12.22) are configured to heat up the medium, wherein at least one third probe (12.23) is configured to determine a temperature of the medium, wherein the first probe and the second probe are arranged on the first diagonal, and wherein the at least one third probe is arranged on the second diagonal, characterized in that the probes on the first diagonal parallel to the measuring tube axis are designed as a heating element, wherein the electronic measuring / operating circuit is configured to determine coefficients of performance between each probe designed as a heating element and a third probe so that the coefficients of performance determined by the measuring / operating circuit in this way can be used to identify the direction, since a probe designed as a heating element is directly exposed to the flow in both flow directions and the other probe designed as the heating element is arranged away from the flow.

2. The flowmeter as claimed in claim 1, wherein the electronic measuring / operating circuit is configured, from a group comprising the first probe and the second probe, to use a first member of the group and a third probe to form a pair of probes for measuring the mass flow, and to use the other member of each group to determine the flow direction, wherein the electronic measuring / operating circuit is configured to swap the members of the group for measuring the mass flow and the members of the group for determining the flow direction if a change in the flow direction is detected.

3. The flowmeter as claimed in claim 1 or 2, wherein the first probe, the second probe, and the third probe each comprise a probe sleeve (SH), wherein the flowmeter has resistance thermometers (WT), wherein at least one resistance thermometer, said resistance thermometer being configured to detect a temperature or dissipate thermal energy, is arranged in each of the interior spaces (IR) of the first, second, and third probes encapsulated by the probe sleeves.

4. The flowmeter as claimed in one of the preceding claims, wherein a fourth probe (12.24) is solid.

5. The flowmeter as claimed in one of the preceding claims, wherein an internal angle ß of the rhombus belonging to the first probe is less than 90°, in particular less than 75°, and preferably less than 60°.

6. The flowmeter as claimed in one of the preceding claims, wherein an external diameter of the probes in the respective active areas is at least 1 mm, in particular 1.5 mm, and preferably at least 2 mm, and / or a maximum of 7 mm, and in particular a maximum of 5 mm, and preferably a maximum of 4 mm.

7. The flowmeter as claimed in one of the preceding claims, wherein a centroid of a cross-sectional area of the probe basic body of the first probe has a first distance from a centroid of a cross-sectional area of the probe basic body of the second probe, wherein the first distance is at least two times the external diameter.

8. The flowmeter as claimed in one of the preceding claims, wherein cross-sections of the probes have a round shape at least in areas of the active probe bodies.

9. A method for operating a flowmeter as claimed in one of the preceding claims, wherein in a first process step, from a group comprising the first probe and the second probe, a member of the group is used with a third probe to form a pair of probes for measuring the mass flow, wherein the other member of each group is used to determine the flow direction, characterized in that in a second process step the members of the group for measuring the mass flow and the members of the group for determining the flow direction are swapped if a change in the flow direction is detected.

10. The method as claimed in claim 9, wherein the electronic measuring / operating circuit determines a first coefficient of performance using the first probe and at least one third probe, and determines a second coefficient of performance using the second probe and at least one third probe, wherein the electronic measuring / operating circuit deduces a change in the flow direction from a chronological course of a difference in the coefficients of performance, in particular from a change in the sign in front of the difference.