FLOW METER

Abstract

Flow meter comprising a heater arranged on a channel and heating a fluid flowing through the channel, two temperature output units arranged in series in the direction of fluid flow, between which the heater is positioned and which output first information on the temperature of the fluid near the temperature output unit upstream of the heater and second information on the temperature of the fluid near the temperature output unit downstream of the heater, and a flow measuring unit which switches the flow measurement method of the fluid to be measured by determining the flow of the fluid to be measured according to a first measurement method using the first information.if this is equal to or above a predetermined threshold value and the flow rate of the fluid to be measured is determined by a second measurement method using the output difference between the first and second pieces of information, if this is below the predetermined threshold value.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based on Japanese Patent Application No. 2020-044572, filed with the Japan Patent Office on March 13, 2020, the entire contents of which are incorporated herein by reference. FIELD OF THE INVENTION

[0002] The present invention relates to a flow meter. STATE OF THE ART

[0003] A measurement technique in which a fluid flow is measured using a thermal flow sensor has been disclosed (see, for example, JP 3658321 B2). In detail, JP 3658321 B2 describes that the flow sensor has a heater and two thermopiles, between which the heater is positioned in the flow direction of the fluid. Furthermore, it describes a technique for increasing the sensitivity of the flow sensor by determining the difference in output power of the two thermopiles to determine the fluid flow. The reason given for this is that the output power of the thermopile contains noise components that are conducted through the channel, and these noise components can be compensated for by determining the output difference between the two thermopiles, as described in JP 3658321 B2.In this way, the accuracy of flow measurement can be increased by determining the flow rate of a fluid by determining the output difference. Furthermore, various techniques are disclosed that improve the measurement accuracy of the flow rate of a fluid over a wide range (see, for example, JP 2003-247876 A and JP 2002-277483 A).

[0004] At high fluid flow rates, the output of the upstream thermopile decreases linearly with the flow rate, according to theory, while the output of the downstream thermopile tends to increase non-linearly with the flow rate, contrary to theory. This can be attributed to the fact that the positional relationship between the heat distribution of the heater and the downstream thermopile deviates from an optimal state at high flow rates. In this case, the flow rate determined by determining the output difference between the two thermopiles may be inaccurate compared to the actual flow rate. Consequently, the accuracy of the fluid flow measurement may decrease.

[0005] It is conceivable to increase the cross-section of the main channel through which a fluid flows and measure the resulting reduced flow rate of the fluid passing through the channel. However, this would require a larger measuring device. This makes it difficult to resolve the reduced accuracy of flow measurement in high flow ranges through a structural change. SUMMARY

[0006] The present invention has been made in one aspect in view of these circumstances, and it is an object of the present invention to provide a technique capable of measuring the flow rate of a fluid in a wide range with high accuracy while miniaturizing the apparatus.

[0007] To achieve the above object, the present invention employs the following arrangement.

[0008] A flow measuring device according to one aspect of the present invention comprises a heater arranged on a channel and heating a fluid flowing through the channel, two temperature output units arranged in series in the flow direction of the fluid, between which the heater is positioned and which output first information on the temperature of the fluid in the vicinity of the unit upstream of the heater and second information on the temperature of the fluid in the vicinity of the unit downstream of the heater, and a flow measuring unit that switches the flow measuring method of the fluid to be measured by determining the flow of the fluid to be measured according to a first measuring method using the first information,if it is equal to or above a predetermined threshold value and the flow of the fluid to be measured is determined according to a second measuring method by means of the output difference between the first and the second information if it is below the predetermined threshold value.

[0009] According to this arrangement, when the flow rate of the fluid to be measured is low, its flow is determined using the second measuring method based on the output difference between the first and the second information. This output produces a flow rate at which the noise components conducted through the channel are compensated, thereby improving the accuracy of the flow measurement. In contrast, when the flow rate of the fluid to be measured is high, its flow is determined using the first measuring method based on the first information, which increases the measurement accuracy compared to measurement via the output difference. This arrangement makes it possible to determine the flow rate of a fluid over a wide range with high accuracy, even without having to increase the flow cross-section. This makes it possible to determine the flow rate of the fluid over a wide range with high precision without having to increase the output device.

[0010] In the flow meter according to the above aspect, it is also possible for the temperature output units to output both the difference between the first and second information and the first information in the vicinity of the predetermined threshold at which the measuring method is switched.

[0011] This arrangement prevents the information that should be used for the process in the event of a change in the measurement method from being missing because the temperature output units have not provided it. This ensures the continuity of the flow measurement near the predetermined threshold at which the measurement method is switched.

[0012] In a dispensing device according to the above aspect, the channel represents a branch channel extending from a main channel, which in turn has branching channels, one of which represents a high-flow channel on which the heater and temperature dispensing units are arranged and which determines the flow of a high-flow fluid, and the other represents a low-flow channel on which the heater and temperature dispensing units are arranged and which determines the flow of a low-flow fluid. The passage cross-section of the low-flow channel is larger than that of the high-flow channel, and the heater and temperature dispensing units are each arranged on the low / high-flow channel.The flow measuring unit can determine the flow using the output power of the temperature output units arranged on the high flow channel according to the first measuring method and can determine the flow using the output power of the temperature output units arranged on the low flow channel according to the second measuring method.

[0013] With this arrangement, the passage width of the high-flow channel is designed to be relatively small, limiting the amount of fluid flowing through the high-flow channel. This prevents an excessive amount of fluid from flowing into the high-flow channel to be processed by the temperature output units arranged on this channel. This prevents the accuracy of the flow measurement from deteriorating at high flow rates.

[0014] With this arrangement, the passage width of the low-flow channel is designed to be relatively large, reducing the fluid pressure loss caused by the wall of the low-flow channel. This prevents the flow measurement accuracy from deteriorating at low flow rates. Thus, the measurement accuracy is well maintained over a wide range of fluid flow rates. Furthermore, the flow measurement accuracy increases because the low flow rate is measured using the second measurement method and the high flow rate is measured using the first measurement method.

[0015] In the output device according to the above aspect, the branch channel may further comprise: another branching channel as a property detection channel that detects the property of the fluid, a second heater arranged on the property detection channel, and two second temperature output units arranged orthogonally to the flow direction of the fluid in the property detection channel, between which the second heater is positioned and which output third information on the distribution of heat diffused from the second heater in the orthogonal direction.

[0016] The distribution of heat diffusing orthogonally to the fluid flow direction depends on the fluid's properties. Thus, with this arrangement, the fluid's properties can be determined in addition to the fluid's flow rate. Based on the determined fluid properties, the measured flow rate can be corrected, which in turn increases the flow measurement accuracy.

[0017] According to the present invention, a technique capable of measuring the flow rate of a fluid in a wide range with high accuracy while miniaturizing the device can be provided. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exemplary schematic diagram of a flowmeter according to an embodiment. Fig. 2A and Fig. 2B are each an exemplary detailed representation of a detection element arranged on a secondary channel. Fig. 3A - 3C each show an example flow rate dependent change in the output power of the thermopile. Fig. 4 is an example of a circuit arrangement of the flow meter. Fig. Figure 5 is an example flowchart for flow measurement performed by the flowmeter MCU. Fig. 6 is an exemplary plan view of a branch channel on which the flow meter is arranged according to a variant. DETAILED DESCRIPTION

[0018] In the following, embodiments of an embodiment (hereinafter also referred to as "the embodiment") according to one aspect of the present invention will be explained with reference to the drawings. However, the following embodiment is to be regarded in all respects merely as an example. Of course, various improvements and variations are possible without departing from the scope of the invention. Thus, when implementing the invention, specific configurations according to the embodiment may be used as appropriate. 1. Application example

[0019] Based on Fig. 1 describes an example in which the present invention is used. Fig. 1 is an exemplary schematic diagram of a flowmeter 100 according to the embodiment. As shown in Fig. As shown in Figure 1, the flow meter 100 has a detection element 1 arranged on a secondary channel 5 branching off from the main channel 4. The detection element 1 represents a so-called thermal flow sensor and comprises a micro-heater and two thermopiles arranged in the gas flow direction, between which the micro-heater is positioned. At high gas flow through the secondary channel 5, the flow meter 100 determines the flow based on the output of the upstream thermopile, while at low gas flow through the secondary channel 5, the flow meter 100 determines the flow based on the output difference between the upstream and downstream thermopiles. The flow meter 100 thus switches the measuring method between high and low gas flow.

[0020] With the above-mentioned flow meter 100, a flow rate is determined at low gas flow rates at which noise components conducted through the channel are compensated. This increases the accuracy of the flow measurement. At high gas flow rates, the flow rate is determined based on the output power of the upstream thermopile, which, even at high flow rates, strongly correlates with the change in the gas flow rate. This increases the accuracy of the flow measurement. Using such a flow meter 100, the gas flow rate can be determined with high accuracy over a wide range. For this purpose, the cross-section of the secondary channel 5 does not need to be increased. This enables the gas flow rate to be determined with high precision over a wide range without having to increase the size of the device. 2. Configuration exampleHardware configuration

[0021] Next, an example of the flowmeter according to the embodiment will be described. The flowmeter 100 according to the embodiment includes, as shown in Fig. 1, a detection element 1, an MCU (microcontroller unit) 2, a substrate 3 on which the detection element 1 and the MCU 2 are implemented, and an A / D converter 30. The detection element 1 of such a flow measuring device 100 is arranged on a secondary channel 5 branched off from the main channel 4, wherein a gas flows through the main channel 4, as the arrow in Fig. 1. Part of the gas flowing through the main channel 4 branches off to flow into the secondary channel 5.

[0022] Fig. 2A and Fig. 2B are each an exemplary detailed representation of a detection element 1 arranged on the secondary channel 5. In Fig. 2A shows its state without gas flow into the secondary channel 5, while in Fig. 2B, the state of which is shown with gas flow into the secondary channel 5.

[0023] The detection element 1 comprises a micro-heater 6 (an example of the "heater" of the present invention) and two thermopiles 7A and 7B (an example of the "temperature output unit" of the present invention), between which the micro-heater 6 is positioned. The detection element 1 is arranged in the sub-channel 5 such that the thermopile 7A in the sub-channel 5 is located upstream of the micro-heater 6, and the thermopile 7B in the sub-channel 5 is located downstream of the micro-heater 6. Furthermore, the detection element 1 has an insulating layer formed between the micro-heater 6 and the thermopiles 7A and 7B. A cavity 9 is located in the central region of the substrate 3, in which the micro-heater 6 and the thermopiles 7A and 7B are arranged. Flow measuring principle

[0024] The flow measurement principle using the detection element 1 is described below. Without gas flow into the secondary channel 5, as in Fig. As shown in Figure 2A, the heat from the micro-heater 6 diffuses symmetrically around the micro-heater 6. Therefore, there is no difference between the output power of the thermopile 7A and the output power of the thermopile 7B. However, when gas flows into the secondary channel 5, the heat from the micro-heater 6 diffuses, as shown in Figure 2A. Fig. 2B, towards the thermopile 7B located downstream of the secondary channel 5, influenced by the gas flow. Furthermore, the heat from the micro-heater 6, also influenced by the gas flow, diffuses in the insulating thin film 8 towards the downstream thermopile 7B. This means that the heat from the micro-heater 6 does not spread symmetrically around the micro-heater 6, but rather in the direction of the thermopile 7B. The extent of heat diffusion directed downstream of the micro-heater 6 depends on the gas flow. The output power of the thermopile 7A or 7B should therefore theoretically decrease or increase linearly with the gas flow. Due to this phenomenon, the gas flow through the secondary channel 5 can be determined using the output power of the thermopile 7A or 7B.

[0025] Furthermore, the flow in the sub-channel 5 may contain dust, for example, which may cause the output of the thermopiles 7A and 7B to contain noise components. This, in turn, may cause the measured gas flow to contain errors due to the noise components. It is conceivable to determine the gas flow using the difference in the output of the thermopiles 7A and 7B to increase the accuracy of the flow measurement (an example of the "second measurement method" of the present invention). According to this measurement method, the noise contained in the output of the thermopiles 7A and 7B is compensated by determining the output difference between the two thermopiles 7A and 7B. This makes it possible to increase the measurement accuracy of the gas flow.

[0026] At high gas flow through the secondary channel 5, the heat distribution near the upstream thermopile 7A may change monotonically with the flow rate, but this will not be the case near the downstream thermopile 7B. Fig. 3A - 3C each show an exemplary flow rate-dependent change in the output power of the thermopile 7A or 7B. Fig. Figure 3A shows an example of the output power of thermopile 7A. Fig. 3B and Fig. 3C correspond to an example of the output power of the thermopile 7B and the output difference between the thermopiles 7A and 7B. As in Fig. As shown in Figure 3A, the output power of the thermopile 7A decreases linearly with the flow rate in the high flow range according to theory. Thus, a strong correlation between the flow rate and the output power of the thermopile 7A can be seen in the high flow range. Therefore, in the upstream thermopile 7A, the influence of the change in the heat distribution of the micro-heater 6 appears to be small even at higher flow rates, and the heat is removed depending on the fluid flow, so that a good correlation between the output power and the change in the flow rate is maintained. In contrast, the output power of the thermopile 7B does not increase linearly with the flow rate in the high flow range, contrary to theory, so that its gradient becomes smaller, as shown in Fig. 3B. As a result, the output difference between the thermopile 7A and 7B does not increase linearly with the flow rate in the high flow range, which always results in a decreasing slope, as in Fig. 3C. Consequently, the flow rate determined in the high flow range from the output difference between thermopiles 7A and 7B would have to contain errors compared to the actual flow rate through the secondary channel 5.

[0027] Subsequently, in this embodiment, the gas flow rate was determined in the low flow range using the output difference between thermopiles 7A and 7B, but in the high flow range using the output of the upstream thermopile 7A (an example of the "first measurement method" of the present invention). This increases the accuracy of the flow rate measurement over a wide flow range.

[0028] Fig. 4 shows an example of a circuit arrangement of the flow meter 100. In the flow meter 100, the output difference between the thermopile 7A and 7B is input as analog information to the A / D converter 30, as shown in Fig. 4. At the same time, the output power of the thermopile 7A alone is also input to the A / D converter 30 as analog information. In the A / D converter 30, the input analog information is then converted into digital information, which in turn flows into the MCU 2.

[0029] Fig. 5 shows an example flowchart for flow measurement performed by the MCU 2 of the flowmeter 100. In the flowchart in Fig. Figure 5 illustrates how the decision is made as to whether the gas flow in secondary channel 5 is high or low and how the measurement method is changed. A gas flow rate of approximately 0.216 to 200 L / min flows through secondary channel 5. Step S101

[0030] In step S101, the difference between the output power of the thermopile 7A located upstream of the micro-heater 6 and the output power of the thermopile 7B located downstream of the micro-heater 6 is measured. The measured output difference is input to the MCU 2. Furthermore, the voltage difference ΔV between the voltage output from the thermopile 7A and the voltage output from the thermopile 7B is expressed as the following formula 1: [Formula 1] ΔV=A⋅(Th−Ta)bVf where T h for temperature of micro heater 6 and T a stands for the ambient temperature of the detection element 1. V f stands for gas flow rate and A and b are a constant. Step S102

[0031] In step S102, the output power of the thermopile 7A arranged upstream of the micro heater 6 is measured. Step S103

[0032] In step S103, it is determined whether the output difference between the thermopile 7A and 7B measured in step S101 is greater than or equal to a predetermined threshold value (an example of the “predetermined threshold value” of the present invention). Step S104

[0033] In step S104, the gas flow is determined based on the output power of the thermopile 7A measured in step S102 if it was determined in step S103 that the output difference between the thermopile 7A and 7B is greater than or equal to the predetermined threshold value. Step S105

[0034] In step S105, the gas flow is determined based on the output difference between the thermopile 7A and 7B measured in step S101 if it was determined in step S103 that the output difference between the thermopile 7A and 7B is smaller than the predetermined threshold value.

[0035] In the flowchart in Fig. 5, in step S102, the output power of the thermopile 7A arranged upstream of the microheater 6 is always measured. However, it is also possible to perform step S102 when the output difference between the thermopiles 7A and 7B measured in step S101 is greater than or equal to a predetermined second threshold value, which is less than or equal to the predetermined threshold value (step S103). According to such a flow meter 100, the measurement process is simplified because the measurement of the output power of the thermopile 7A in step S102 is omitted at low flow rates, where the output difference is less than the predetermined second threshold value. Effect

[0036] With the above-mentioned flow meter 100, the flow rate is measured at low gas flow rates using the output difference between the thermopiles 7A and 7B. This determines a flow rate at which the noise components conducted through the branch channel 5 are compensated, thus improving the accuracy of the flow rate measurement. At high gas flow rates, the flow rate is measured using the output of the upstream thermopile 7A, which shows a strong correlation with the flow rate even at high flow rates (see Fig. 3A). This increases their measurement accuracy compared to the measurement based on the output difference. Using such a flow meter 100, the gas flow can be determined with high accuracy over a wide range. For this purpose, the cross-section of the secondary channel 5 does not need to be increased. This allows the gas flow to be determined with high accuracy over a wide range without having to increase the size of the device.

[0037] Furthermore, in the above-mentioned flow meter 100, both the output difference between the thermopile 7A and 7B and the output power of the thermopile 7A alone are measured in steps S101 and S102. This prevents the flow rate determination from being made difficult due to failure to measure the output difference when the measurement method is to be switched from determining the flow rate based on the output power of the thermopile 7A in step S104 to determining the flow rate based on the output difference in step S105, for example, because the flow rate estimated as high in step S103 turns out to be low. Consequently, the continuity of the flow rate measurement near the threshold value is ensured in step S103 by switching the measurement method. 3. Variant

[0038] The embodiment of the invention has been described in detail as above. However, this description is to be considered merely as an example in every respect. Naturally, various improvements and variations can be made without departing from the scope of the invention. For example, the following modifications are possible. In the following, the same components as in the aforementioned embodiment are provided with the same reference numerals, and similar points have been omitted where appropriate. The following variants can be combined if necessary. 3.1

[0039] Fig. 6 shows an exemplary plan view of a secondary channel 5A (an example of the “branch channel” of the present invention) on which a flow meter 100A is arranged according to a variant. As in Fig. 6, the secondary channel 5A has two adjacent channels 71 and 81. An inlet 34A is provided on the secondary channel 5A, into which the gas flows from the main channel 4, wherein the inlet 34A communicates with the channels 71 and 81. This arrangement allows the gas from the main channel 4 to flow into the channels 71 and 81 via the inlet 34A. Furthermore, an outlet 35A is provided on the secondary channel 5A, via which the gas flows into the main channel 4, wherein the outlet 35A communicates with the channels 71 and 81. This arrangement allows the gas to flow into the main channel 4 via the outlet 35A after passing through the channels 71 and 81.Here, the channel 81 is provided such that its passage cross section is larger compared to a position upstream side at which the detection element 1B (described below) is arranged than the passage cross section of the channel 71 compared to a position upstream side at which the detection element 1A (described below) is arranged.

[0040] Furthermore, a detection element 1A and 1B are provided on each channel 71 and 81. The detection element 1A and 1B are of the same type as the detection element 1 and are arranged so that their two thermopiles are lined up parallel to the gas flow direction, just like the detection element 1. Consequently, the gas flow through the channels 71 and 81 can be measured using the output power of the thermopiles provided on the detection element 1A and 1B, respectively.

[0041] When the gas flow rate through the main channel 4 is low, the gas flowing through the channel 71 with a smaller passage area is greatly affected by friction with the channel wall surface. This may result in a larger pressure loss of the gas flowing through the channel 71 due to the effect of the wall surface of the channel 71, and therefore the flow value measured by the detection element 1A arranged on the channel 71 may contain a larger error than the actual flowing amount. Therefore, when the gas flow rate is low, the flow meter 100A outputs a gas flow rate measured by the detection element 1B arranged on the channel 81 with a larger passage area as the gas amount flowing through the main channel 4.This arrangement enables flow measurement with high accuracy because the low flow gas flowing through the channel 81 with a larger passage cross section experiences relatively small pressure loss through the channel wall surface.

[0042] On the other hand, when the gas flow rate through the main channel 4 is high, a gas flow rate exceeding the measuring range of the detection element 1B arranged on the channel 81 flows into the channel 81 with a larger flow area. This makes it difficult for the detection element 1B arranged on the channel 81 to accurately measure the flow rate. Therefore, when the gas flow rate is high, the flow meter 100A outputs the gas flow rate measured by the detection element 1A arranged on the channel 71 with a smaller flow area as the gas flow rate through the main channel 4. This arrangement prevents the flow measurement accuracy from deteriorating.

[0043] Furthermore, at high flow rates, the flow meter 100A outputs the measured value at the detection element 1A as the measured flow rate, which is determined based on the output of the upstream thermopile of the detection element 1A. At low flow rates, the flow meter 100A outputs the measured value at the detection element 1B as the measured flow rate, which is determined based on the output difference between the upstream and downstream thermopiles of the detection element 1B. This measurement method further improves the accuracy of the respective detection elements 1A and 1B for flow measurement.

[0044] Furthermore, the decision as to whether the flow is high or low and the switching between the above-mentioned measuring methods based on this decision is carried out in the same way as in the flow chart in Fig. 5. First, the output difference between the upstream and downstream thermopiles is measured at the detection element 1B. Then, the output of the upstream thermopile is measured at the detection element 1A. If the output difference measured by the detection element 1B is equal to or greater than the threshold value, the flow rate is judged to be high, so the flow meter 100A determines a flow rate value based on the output of the upstream thermopile of the detection element 1A and outputs the measured flow rate.On the other hand, if the output difference measured by the detection element 1B is smaller than the threshold value, the flow rate is judged to be low, so that the flow meter 100A determines a flow rate value based on the output difference between the upstream and downstream thermopiles of the detection element 1B and outputs the flow rate as the measured flow rate.

[0045] In addition, on the sub-channel 5A of the flowmeter 100A, a channel 91 (an example of the “characteristic detection channel” of the present invention) is provided so as to communicate with the channel 71 and 81 as shown in Fig. 6. At the channel 91, a detection element 1C is arranged, which is an element of the same type as detection element 1. However, the detection element 1C is arranged so that its two thermocouples are arranged in such a way that the type is as shown in Fig.6 (an example of the "second temperature output unit" of the present invention). By arranging the detection element 1C in this way, the heat distribution diffusing around the micro-heater (an example of the "second heater" of the present invention) of the detection element 1C orthogonally to the gas flow direction can be detected based on the output power of the two thermopiles. This heat distribution changes depending on the properties of the gas, such as temperature or concentration. Information about the properties of the gas can thus be obtained based on the output power of the two thermopiles of the detection element 1C. Effect

[0046] According to the above-mentioned flow meter 100A, the passage cross-section at channel 71 is made smaller, which restricts the gas flow through channel 71. This, in turn, prevents a quantity of gas exceeding the measurable range of the detection element 1A arranged at channel 71 from flowing into channel 71. Thus, the reduction in the accuracy of the flow measurement at high flow rates is prevented.

[0047] Furthermore, according to the above-mentioned flow meter 100A, the passage area at the channel 81 is made larger, so that the pressure loss of the gas due to the effect of the channel wall of the channel 81 is reduced. This prevents the reduction in the accuracy of the flow measurement at low flow rates measured by the detection element 1B. This means that the reduction in measurement accuracy is prevented over a wide range of gas flow rates. In addition, the flow rate at high gas flow rates is measured based on the output of the upstream thermopile of the detection element 1A, while the flow rate at low gas flow rates is measured based on the output difference between the upstream and downstream thermopiles of the detection element 1B. This further increases the accuracy of the flow measurement.

[0048] Furthermore, according to the above-mentioned flowmeter 100A, in addition to the gas flow rate, the properties of the gas can be determined using the detection element 1C. This allows the measured flow rate to be corrected based on the gas properties. This further improves the accuracy of the flow measurement.

[0049] The embodiment and variant disclosed above can each be combined.

[0050] In the following, components of the present invention are described together with reference numerals of the drawing in order to be able to compare the components of the invention and the arrangement of the embodiment. (Appendix 1)

[0051] A flow meter (100, 100A) comprising a heater (6) arranged on a channel (5, 5A) and heating a fluid flowing through the channel (5, 5A), two temperature output units (7A, 7B) arranged in series in the flow direction of the fluid, between which the heater (6) is positioned and which output first information on the temperature of the fluid in the vicinity of the unit upstream of the heater (6) and second information on the temperature of the fluid in the vicinity of the unit downstream of the heater (6), and a flow measuring unit that switches the flow measuring method of the fluid to be measured by determining the flow of the fluid to be measured according to a first measuring method using the first information,if it is equal to or above a predetermined threshold value and the flow of the fluid to be measured is determined according to a second measuring method by means of the output difference between the first and the second information if it is below the predetermined threshold value. (Appendix 2)

[0052] A flow meter (100, 100A) according to Annex 1, wherein the temperature output units (7A, 7B) output both the difference between the first and second information and the first information in the vicinity of the predetermined threshold at which the measuring method is switched. (Appendix 3)

[0053] A flow meter (100A) according to Annex 1 or 2, wherein the channel (5, 5A) represents a branch channel (5A) leading from the main channel (4), which in turn has branching channels (71, 81), one of which represents a high-flow channel (71) on which the heater (6) and the temperature output units (7A, 7B) are arranged and which determines the flow of a fluid with a high flow, and the other represents a low-flow channel (81) on which the heater (6) and the temperature output units (7A, 7B) are arranged and which determines the flow of a fluid with a low flow, and the passage cross-section of the low-flow channel (81) is larger than that of the high-flow channel (71) and the heater (6) and the temperature output units (7A,7B) are each arranged on the low / high flow channel (81 / 71), and the flow measuring unit determines the flow by means of the output power of the temperature output units (7A, 7B) arranged on the high flow channel (71) according to the first measuring method and by means of the output power of the temperature output units (7A, 7B) arranged on the low flow channel (81) according to the second measuring method. (Appendix 4)

[0054] A flow meter (100A) according to Annex 3, wherein the branch channel (5A) further comprises: another branching channel (91) as a property detection channel (91) which detects the property of the fluid, a second heater (6) arranged on the property detection channel (91), and two second temperature output units (7A, 7B) arranged orthogonally to the flow direction of the fluid in the property detection channel (91), between which second temperature output units (7A, 7B) is positioned and which output third information on the distribution of heat diffused from the second heater (6) in the orthogonal direction.

Claims

[1] A flow measuring device comprising a heater arranged on a channel and heating a fluid flowing through the channel, two temperature output units arranged in a row in the flow direction of the fluid, between which the heater is positioned and which output a first item of information on the temperature of the fluid in the vicinity of the temperature output unit upstream of the heater and a second item of information on the temperature of the fluid in the vicinity of the temperature output unit downstream of the heater, and a flow measuring unit which switches the flow measuring method of the fluid to be measured by determining the flow of the fluid to be measured according to a first measuring method using the first item of information,if it is equal to or above a predetermined threshold value and the flow of the fluid to be measured is determined according to a second measuring method by means of the output difference between the first and the second information if it is below the predetermined threshold value. [2] The flowmeter according to claim 1, wherein the temperature output units output both the output difference between the first and second information and the first information in the vicinity of the predetermined threshold at which the measurement method is switched. [3] Flow meter according to claim 1 or 2, wherein the channel represents a branch channel leading from a main channel, which in turn has branching channels, one of which represents a high-flow channel on which the heating and temperature output units are arranged and which determines the flow of a fluid with a high flow rate, and the other represents a low-flow channel,on which the heater and the temperature output units are arranged and which determines the flow of a fluid with a low flow rate, and the cross-section of the low flow channel is larger than that of the high flow channel, and the heater and the temperature output units are each arranged on the low / high flow channel, and the flow measuring unit determines the flow on the one hand by means of the output power of the temperature output units arranged on the high flow channel according to the first measuring method and on the other hand by means of the output power of the temperature output units arranged on the low flow channel according to the second measuring method. [4] The flowmeter according to claim 3, wherein the branch channel further comprises: another branching channel as a property detection channel that detects the property of the fluid, a second heater arranged on the property detection channel, and two second temperature output units arranged orthogonally to the flow direction of the fluid in the property detection channel, between which the second heater is positioned and which output third information on the distribution of heat diffused from the second heater in the orthogonal direction.

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