Thermal flowmeter

Abstract

A thermal flowmeter (10) for measuring the mass flow rate of a medium in a measuring tube, comprising: a measuring tube (11) having a measuring tube wall (11.1); a sensor (12) having four probes (12.2) that project from a main sensor body (12.1) into the measuring tube, the probes being designed to heat the medium to determine the temperature of the medium or to influence the flow of the medium in the measuring tube; an electronic measurement / operation circuit (13) that is designed to operate at least three probes and to generate and provide a flow measurement value by operating the probes, each probe having a main probe body (G) and an active probe body (W), and the active probe body being designed to heat the medium to determine the temperature of the medium and / or to influence the flow of the medium in the measuring tube, characterized in that the main probe body spans a rhombus (R) on the surface of the main sensor body, and the rhombus is defined by the centroid points of the cross-section of the main probe body.

Description

Field of the Invention

[0001] The present invention relates to a thermal flowmeter and a method for operating a thermal flowmeter. Background Art

[0002] Thermal flow measurement is based on the fact that conclusions about the mass flow of a medium can be drawn from the input of energy via a probe into the medium flowing past the probe or from the temperature of a heated probe located in the medium. However, the direction in which the medium flows cannot be determined from the energy input or the temperature of the probe.

[0003] Publication DE102015118123A1 shows a sensor of a thermal flowmeter that is immersed in the measuring tube of the flowmeter and has a plurality of probes that are designed to heat the medium and measure their own temperature or the temperature of the medium. In addition, the flow resistance is configured to affect the direction-dependent incident flow on the heatable probes so that a clear indication of the flow of the medium in the measuring tube can be obtained from the direction dependence of the incident flow. However, it has been shown that at low to medium flow rates, the indication of the flow direction is accompanied by a high degree of uncertainty.

[0004] Therefore, the object of the present invention is to provide a flowmeter that helps to reliably detect the flow direction of the medium in the measuring tube. Summary of the Invention

[0005] A flowmeter for measuring the mass flow of a medium in a measuring tube according to the present invention includes:

[0006] A measuring tube having a measuring tube wall;

[0007] A sensor having four probes that project from a main sensor body into the measuring tube, wherein the probes are designed to heat the medium to determine the temperature of the medium or to affect the flow of the medium in the measuring tube;

[0008] An electronic measurement / operation circuit that is designed to operate at least three of the probes and to generate and provide a flow measurement value by operating the probes,

[0009] wherein each probe has a main probe body and an active probe body, wherein the main probe body is respectively arranged on the side of the corresponding probe facing the main sensor body, and wherein the active body is respectively arranged on the side of the corresponding probe facing away from the main sensor body,

[0010] Wherein, the active probe body is designed to heat the medium to determine the temperature of the medium and / or affect the flow of the medium in the measurement tube.

[0011] Wherein, the main probe body is columnar.

[0012] Wherein, the main probe body spans a rhombus on the surface of the main sensor body, wherein the rhombus is defined by the centroid point of the cross-section of the main probe body and has a first diagonal and a second diagonal.

[0013] Wherein, the first probe is configured to measure the temperature of the medium.

[0014] Wherein, the second probe and the third probe are configured to heat the medium and determine the temperature of the medium respectively.

[0015] Wherein, the first probe is arranged on the first side of the first diagonal, and wherein, the third probe is arranged on the second side of the first diagonal, wherein, the second probe and the fourth probe are arranged on the opposite sides of the second diagonal.

[0016] Wherein, the rotation angle of the first diagonal of the rhombus with respect to the normal of the cross-section of the measurement tube is η.

[0017] Wherein, η is greater than 1 degree, especially greater than 2 degrees, preferably greater than 3 degrees.

[0018] This probe arrangement achieves a high degree of symmetry of the arrangement with respect to the two possible flow directions of the medium in the measurement tube in terms of the flow resistance of the sensor.

[0019] It has surprisingly been shown that a slight rotation of the main sensor body exhibits significantly better flow direction detection in a wide range of speeds. The rotation of the sensor has an advantageous effect, especially at high flow rates greater than 70 m / s.

[0020] The flowmeter is preferably used to measure gas flow.

[0021] In this case, columnar means that the main probe body protrudes from the main sensor body, especially with longitudinal axis symmetry. The following formula applies to the length l along the longitudinal axis and the volume V of the main probe body: (l^3 / V)^(0.5) is greater than 2^(0.5), especially greater than 2.

[0022] In one embodiment, η is less than 20 degrees, especially less than 15 degrees, preferably less than 10 degrees. What is important here is that the probe located in the flow shadow (i.e., the first probe or the third probe, depending on the flow direction) remains completely within the flow shadow formed by the second probe and the fourth probe.

[0023] In one embodiment, the fourth probe is designed to block the flow of the medium in the portion between the first probe and the third probe.

[0024] The heat transfer from the heating probe to the medium is low enough that the first probe very approximately detects the temperature of the medium, unaffected by heat transfer and independent of the flow direction of the medium. The first temperature difference between the first probe and the second probe is suitable for measuring the flow velocity of the medium. The second temperature difference between the first probe and the third probe is suitable for measuring the flow direction. For example, in the case where the heat outputs of the second probe and the third probe are the same, it can be concluded that when the second temperature difference is greater than the first temperature difference, the third probe is in the flow shadow. However, for example, the time curves of the first temperature difference and the second temperature difference can also be used to assign the expected temperature to the flow measurement values for the two flow directions. In this case, the heat output of the third probe can be different from the heat output of the second probe.

[0025] In one embodiment, the active probe body of the fourth probe has a first width along the first diagonal and a second width along the second diagonal, where the second width is at least 1.1 times greater than the first width, in particular at least 1.2 times greater, preferably at least 1.3 times greater.

[0026] And wherein the geometric center of the active probe body of the fourth probe is offset in the direction of the second probe.

[0027] In this way, the heat flow from the third probe to the first probe can be at least partially prevented, which improves the measurement of the flow rate.

[0028] In one embodiment, the outer surface of the active probe body of the fourth probe is symmetric about the second diagonal.

[0029] In one embodiment, each of the first probe, the second probe, and the third probe includes a probe sleeve.

[0030] Wherein, the flowmeter has a resistance thermometer, and the resistance thermometers are respectively arranged in the internal space surrounded by the probe sleeves, and the resistance thermometers are designed to detect temperature or emit heat energy.

[0031] In one embodiment, the fourth probe is solid.

[0032] In one embodiment, the interior angle of the rhombus belonging to the first probe is less than 90°, in particular less than 75°, preferably less than 60°.

[0033] This ensures a reduced flow resistance of the sensor in the measuring tube and a good incident flow of the probe.

[0034] In one embodiment, the centroid point of the cross-section of the main probe body of the fourth probe is separated from the centroid point of the cross-section of the main probe body of the second probe by a second distance.

[0035] Wherein, the minimum distance between the outer surface of the effective probe body of the fourth probe and the outer surface of the effective probe body of the second probe is less than 30% of the second distance, particularly less than 15% of the second distance, and preferably less than 5% of the second distance.

[0036] In one embodiment, the first outer diameter of the first probe, the second probe, and the third probe in the corresponding effective region is at least 1 mm, particularly 1.5 mm, preferably at least 2 mm, and / or at most 7 mm, particularly at most 5 mm, preferably at most 4 mm.

[0037] In one embodiment, the centroid point of the cross-section of the main probe body of the first probe is separated from the centroid point of the cross-section of the main probe body of the third probe by a first distance.

[0038] Wherein, the first distance is at least two times the first outer diameter.

[0039] In one embodiment, the cross-sections of the first probe, the second probe, and the third probe have a circular profile at least in some regions of the effective probe body.

[0040] The circular profile makes production easier and makes the flow resistance independent of the flow direction.

[0041] The present invention will now be described with reference to schematic exemplary embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Shows the effective regions of two exemplary probe arrangements according to the present invention for a thermal flowmeter and the orientation of the probes in the measuring tube;

[0043] Figure 2a ) Shows a cross-sectional view through an exemplary first, second, or third probe;

[0044] Figure 2b ) Shows a side view of an exemplary fourth probe;

[0045] Figure 3 Shows a side view of a sensor according to the present invention; and

[0046] Figure 4 Outlines the structure of an exemplary schematic thermal flowmeter according to the present invention. DETAILED DESCRIPTION

[0047] Figure 1 shows the active regions of two probe arrangements according to the invention in a measuring tube 11 with a measuring tube wall 11.1, each probe arrangement having a first probe 12.21, a second probe 12.22, a third probe 12.23 and a fourth probe 12.24. The active region is the region in which the active probe body W (see Figure 2a ), Figure 2b ) and Figure 3 )) is effective. Each active probe body is connected to the main probe body G of the corresponding probe, which is connected to the main sensor body 12.1 (see Figure 2a ), Figure 2b ) and Figure 3 ). The function of the active probe body is to heat the medium, determine the temperature of the medium and / or influence the flow of the medium in the measuring tube.

[0048] The main probe bodies of the probe arrangement span a rhombus R, where the rhombus is defined by the centroid points of the cross-sections of the main probe bodies and has a first diagonal D1 and a second diagonal D2. The first probe 12.21 is designed to measure the temperature of the medium,

[0049] where the second probe 12.22 and the third probe 12.23 are designed to heat the medium and determine the temperature of the medium respectively,

[0050] where the first probe is arranged on the first side of the first diagonal, and where the third probe is arranged on the second side of the first diagonal, and where the second probe and the fourth probe 12.24 are arranged on opposite sides of the second diagonal,

[0051] According to the invention, the first diagonal D1 of the rhombus has a rotation angle η with respect to the normal 11.3 of the measuring tube cross-section 11.2, where η is greater than 1 degree, in particular greater than 2 degrees, preferably greater than 3 degrees.

[0052] Surprisingly, it has been shown that a slight rotation of the main sensor body exhibits significantly better flow direction detection in a wide range of speeds. The rotation of the sensor has an advantageous effect, especially at high flow rates greater than 70 m / s.

[0053] In one embodiment, η is less than 20 degrees, in particular less than 15 degrees, preferably less than 10 degrees. It is important here that the probe located in the flow shadow (i.e., the first probe or the third probe, depending on the flow direction) remains completely within the flow shadow formed by the second probe and the fourth probe.

[0054] The interior angle β associated with the first probe is less than 90 degrees, such that the probe arrangement has a low flow resistance.

[0055] In the first probe arrangement according to the invention, the fourth probe 12.24 has a circular profile in its active region like the other probes. In this way, a sensor with probes can be manufactured cost-effectively. In the second probe arrangement according to the invention, the fourth probe 12.24 has a non-circular profile in its active region, wherein the probe has a first width B1 parallel to the first diagonal D1 and a second width B2 parallel to the second diagonal D2, wherein the second width is at least 10% greater than the first width. The geometric center GS4 of the active probe body of the fourth probe (see Figure 2b )) is offset in the direction of the second probe. As a result, a partial blocking effect on the flow of the medium through the measuring tube is achieved along the second diagonal D2 in the active area of ​​the probe. As a result, the influence of the third probe 12.23 of the heating medium on the first probe can be reduced, thereby improving the measurement accuracy of the sensor. As a result, the centroid point of the cross section of the main probe body of the fourth probe is at a second distance from the centroid point of the cross section of the main probe body of the second probe. The minimum distance between the outer surface of the active probe body of the fourth probe and the outer surface of the active probe body of the second probe is less than 30% of the second distance, in particular less than 15% thereof, and preferably less than 5% thereof.

[0056] Figure 2a ) shows a longitudinal section through an exemplary first, second or third probe, wherein the probe sleeve SH defines an inner space IR of the probe, in which the probe has a resistance thermometer WT. The resistance thermometer is thus thermally and mechanically coupled to the probe sleeve via a contact device. For example, the contact device can be a molten material that is melted during the production of the probe and subsequently processed after solidification.

[0057] Figure 2b ) shows a plan view perpendicular to the measuring tube cross section of an exemplary fourth probe which is widened in its active region W and thus has an enlarged outer surface AWK. The geometric center GS4 of the active probe body of the fourth probe is thereby offset from the longitudinal axis of the body.

[0058] Figure 3 1 shows a schematic side view of a sensor 12 of a thermal flow meter, the sensor having a main sensor body 12.1 and a probe 12.2, wherein Figure 2a )and Figure 2b ) as described above, each probe comprises a main probe body G and a working probe body W.

[0059] Figure 4The schematic structure of a thermal flowmeter 10 according to the present invention is outlined. The thermal flowmeter has: a measuring tube 11, which has a measuring tube wall 11.1; a sensor 12, which has a main sensor body 12.1 and a probe 12.2; and an electronic measurement / operation circuit 13 for operating the sensor and providing a flow measurement value. The main sensor body is attached to the measuring tube wall in a medium-sealed manner. Preferably, the active area of the probe is arranged in the flow area of the medium, where the local mass flow rate deviates from the average value formed on the flow cross-section by less than 10%, especially less than 5%, and preferably less than 2%.

[0060] List of reference numerals

[0061] 10 Thermal flowmeter

[0062] 11 Measuring tube

[0063] 11.1 Measuring tube wall

[0064] 11.2 Measuring tube cross-section

[0065] 11.3 Normal

[0066] 12 Sensor

[0067] 12.1 Main sensor body

[0068] 12.2 Probe

[0069] 12.21 First probe

[0070] 12.22 Second probe

[0071] 12.23 Third probe

[0072] 12.24 Fourth probe

[0073] 13 Electronic measurement / operation circuit

[0074] G Main probe body

[0075] W Active probe body

[0076] SH Probe sleeve

[0077] R Rhombus

[0078] AWK Outer surface of the active probe body

[0079] D1 First diagonal

[0080] D2 Second diagonal

[0081] GS4 Geometric center of the active probe body of the fourth probe

[0082] WT Resistance thermometer

[0083] IR internal space

[0084] β internal angle

[0085] B1 First width

[0086] B2 Second width

[0087] η Rotation angle

Claims

1. A heat flow measuring device (10) for measuring the mass flow of a medium in a measuring tube, the flow measuring device (10) comprising: A measuring tube (11), the measuring tube (11) having a measuring tube wall (11.1); A sensor (12), the sensor (12) having four probes (12.21, 12.22, 12.23, 12.24), the probes (12.21, 12.22, 12.23, 12.24) protruding from a main sensor body (12.1) into the measuring tube (11), wherein the probes (12.21, 12.22, 12.23, 12.24) are designed to heat the medium to determine the temperature of the medium or to influence the flow of the medium in the measuring tube (11); An electronic measuring / operating circuit (13), the electronic measuring / operating circuit (13) being designed to operate the at least three probes and to generate and provide a flow measurement value by operating the probes, Wherein each probe (12.21, 12.22, 12.23, 12.24) has a main probe body (G) and an active probe body (W), wherein the main probe body (G) is respectively arranged on the side of the corresponding probe (12.21, 12.22, 12.23, 12.24) facing the main sensor body (12.1), and wherein the active probe body (W) is respectively arranged on the side of the corresponding probe (12.21, 12.22, 12.23, 12.24) facing away from the main sensor body (12.1), Wherein the active probe body (W) is designed to heat the medium to determine the temperature of the medium and / or to influence the flow of the medium in the measuring tube (11), Wherein the main probe body (G) is columnar, Wherein the main probe body (G) spans a rhombus (R) on the surface of the main sensor body (12.1), wherein the rhombus (R) is defined by the centroid points of the cross-section of the main probe body (G) and has a first diagonal (D1) and a second diagonal (D2), Wherein the first probe (12.21) is designed to measure the temperature of the medium, Wherein the second probe (12.22) and the third probe (12.23) are designed to heat the medium and to determine their own temperatures respectively, Wherein the first probe (12.21) is arranged on a first side of the first diagonal (D1), and wherein the third probe (12.23) is arranged on a second side of the first diagonal (D1), wherein the second probe (12.22) and the fourth probe (12.24) are arranged on opposite sides of the second diagonal (D2), Characterized in that, The rotation angle of the first diagonal (D1) of the rhombus (R) with respect to the normal (11.3) of the cross-section (11.2) of the measuring tube (11) is η, Wherein the rotation angle η is greater than 1 degree. Wherein, the fourth probe (12.24) is designed to prevent a portion of the medium from flowing between the first probe (12.21) and the third probe (12.23). Wherein, the active probe body (W) of the fourth probe (12.24) has a first width (B1) parallel to the first diagonal (D1) and a second width (B2) parallel to the second diagonal (D2), and wherein the second width (B2) is at least 1.1 times greater than the first width (B1). And wherein, the geometric center (GS4) of the active probe body of the fourth probe (12.24) is offset in the direction of the second probe (12.22).

2. The flow measurement device (10) according to claim 1, Among them, The rotation angle η is greater than 3 degrees.

3. The flow measurement device (10) according to any one of the preceding claims, Among them, The rotation angle η is less than 20 degrees.

4. The flow measurement device (10) according to claim 1 or 2, Among them, The rotation angle η is less than 10 degrees.

5. The flow measurement device (10) according to claim 1 or 2, Among them, The second width (B2) is at least 1.3 times greater than the first width (B1).

6. The flow measurement device (10) according to claim 1, Among them, The outer surface (AWK) of the active probe body (W) of the fourth probe (12.24) is symmetric about the second diagonal (D2).

7. The flow measurement device (10) according to claim 1 or 2, Among them, Each of the first probe (12.21), the second probe (12.22) and the third probe (12.23) includes a probe sleeve (SH), Wherein, the flow measurement device (10) has a resistance thermometer (WT), and wherein at least one resistance thermometer (WT) is respectively arranged in the internal space (IR) surrounded by the corresponding probe sleeves (SH) of the first probe (12.21), the second probe (12.22) and the third probe (12.23), and the resistance thermometer (WT) is designed to detect temperature or emit heat energy.

8. The flow measurement device (10) according to claim 1 or 2, Among them, The fourth probe (12.24) is solid.

9. The flow measurement device (10) according to claim 1 or 2, Among them, The interior angle β of the rhombus (R) belonging to the first probe (12.21) is less than 90°.

10. The flow measurement device (10) according to claim 9, Among them, The interior angle β is less than 60°.

11. The flow measurement device (10) according to claim 1 or 2, Among them, The centroid point of the cross-section of the main probe body (G) of the fourth probe (12.24) is at a second distance from the centroid point of the cross-section of the main probe body (G) of the second probe (12.22). Among them, the minimum distance between the outer surface of the active probe body (W) of the fourth probe (12.24) and the outer surface of the active probe body (W) of the second probe (12.22) is less than 30% of the second distance.

12. The flow measurement device (10) according to claim 1 or 2, Among them, The first outer diameter of the first probe (12.21), the second probe (12.22) and the third probe (12.23) in the corresponding active region is at least 1 mm.

13. The flow measurement device (10) according to claim 12, Among them, The first outer diameter of the first probe (12.21), the second probe (12.22) and the third probe (12.23) is at least 2 mm and / or at most 7 mm.

14. The flow measurement device (10) according to claim 12, Among them, The first outer diameter of the first probe (12.21), the second probe (12.22) and the third probe (12.23) is at most 4 mm.

15. The flow measurement device (10) according to claim 1 or 2, Among them, The centroid point of the cross-section of the main probe body (G) of the first probe (12.21) is separated from the centroid point of the cross-section of the main probe body (G) of the third probe (12.23) by a first distance, wherein the first distance is at least two first outer diameters.

16. The flow measurement device (10) according to claim 1 or 2, Among them, The cross-sections of the first probe (12.21), the second probe (12.22) and the third probe (12.23) have a circular profile at least in some regions of the active probe body (W).

Images