Flow sensor and method using temperature to improve low velocity measurements - Patents.com

Abstract

A flow sensor (1) configured to measure a flow rate (Q) of a fluid (26) flowing through a tubular structure (2) is disclosed. The flow sensor (1) is configured to measure a minimum flow rate (Q) that can be measured by using a first detection unit (34). A ) represents a given low flow level (Q A The flow sensor (1) comprises a first detection unit (34) configured to detect a flow rate (Q) greater than - Ambient temperature (T s a first temperature sensor (12) arranged and configured to detect - temperature of the fluid (26) (T f a second temperature (14) arranged and configured to detect a a data processor (10) connected to the temperature sensors (12, 14). The second detection unit (36) detects a low flow level (Q A The temperature difference is measured by the first temperature sensor (12) and the second temperature sensor (14). The second detection unit (36) is configured to estimate a low flow level (Q) based on one or more measurements (M1, M2) made in the flow area (B2). A ), the flow sensor (1) is capable of detecting the flow rate (Q), and the flow rate (Q) is calculated based on a temperature difference (ΔT sf ) using one or more measurements (M1, M2) made in the flow calibration area (B2), the flow rate (Q) is determined by the temperature difference (ΔT sf Determine the parameters needed to determine how the function depends on

Description

[Technical field]

[0001] The present invention relates generally to flow sensors, and more particularly to clamp-on ultrasonic flow sensors. [Background technology]

[0002] Flow measurement is widely used to measure flow in industries, buildings, and utility grids. Flow rates can be detected by using various types of flow sensors. Prior art flow sensors include mechanical flow sensors and ultrasonic flow sensors. Ultrasonic flow sensors are mainly used in two versions: time-of-flight differential is used to measure pure fluids (water, gas, industrial liquids, etc.) and Doppler effect is used to measure fluids containing many particles (slurries, liquids with bubbles, etc.).

[0003] However, all prior art flow sensors have a certain non-zero low flow level which represents the lowest flow rate that can be measured by using the flow sensor. Below the low flow level, no flow rate can be detected. This is a major drawback. It would therefore be desirable to be able to provide a solution to this problem.

[0004] Prior art flow sensors cannot detect low flow rates (also known as velocity or volume), and therefore often have difficulty or difficulty in detecting relatively low flow rates. At the same time, prior art time-of-flight flow sensors are designed to detect the flow rate of homogeneous media, which leads to measurement errors when the media is inhomogeneous. Thus, it results in, for example, the following A to C. A. Measurement error, B. Limitations on detecting, for example, small leaks that could cause damage to the building or product in which the sensor is installed; C. Difficulties in detecting no-flow conditions (fluid in pipe is stationary) which requires identifying the sensor offset.

[0005] Therefore, there is a need for a method and flow sensor that reduces or even eliminates the above-mentioned disadvantages of the prior art. Summary of the Invention

[0006] The object of the present invention is achieved by a flow sensor as defined in claim 1 and a method as defined in claim 15. Preferred embodiments are defined in the dependent claims, explained in the following detailed description and illustrated in the accompanying drawings.

[0007] A flow sensor according to the invention is a flow sensor configured to measure a flow rate of a fluid flowing through a tubular structure, the flow sensor comprising a first detection unit configured to detect a flow rate above a predetermined low flow level representing a minimum flow rate that can be measured by using the first detection unit, the flow sensor comprising a second detection unit, a first temperature sensor arranged and configured to detect an ambient temperature; a second temperature sensor arranged and configured to detect the temperature of the fluid; a data processor connected to the temperature sensor, The second detection unit is configured to estimate a flow rate below the low flow level based on a temperature difference between the ambient and the fluid, the temperature difference being measured by the first temperature sensor and the second temperature sensor, the second detection unit is configured to estimate a flow rate below the low flow level based on one or more measurements made in a flow calibration area, where the flow sensor is capable of detecting a flow rate dependent on the temperature difference, and the one or more measurements made in the flow calibration area are used to determine one or more parameters necessary to determine how the flow rate depends on the temperature difference in the flow area below the flow calibration area.

[0008] This makes it possible to provide a sensor that is able to detect flow rates over a larger flow range than prior art flow sensors.The flow sensor according to the invention is in particular able to detect flow rates below low flow levels.

[0009] A flow sensor according to the present invention is a flow sensor configured to measure a flow rate of a fluid. In one embodiment, the fluid is a liquid. In one embodiment, the fluid is a water-containing liquid. In one embodiment, the fluid is a gas.

[0010] A fluid flows through the tubular structure. In one embodiment, the tubular structure is a pipe. In one embodiment, the tubular structure is a hose. In one embodiment, the tubular structure is a container. In one embodiment, the tubular structure is a box.

[0011] The flow sensor comprises a first sensing unit configured to detect a flow rate above a predetermined low flow rate level representing the lowest flow rate that can be measured by using the first sensing unit. The first sensing unit can be a positive displacement flow meter configuration that requires the fluid to mechanically displace a component of the mechanical flow sensing unit to provide a flow measurement. In one embodiment, the first sensing unit is a turbine. In one embodiment, the first sensing unit is an impeller.

[0012] The first detection unit may be an ultrasonic flow sensor structure. In one embodiment, the first detection unit comprises one or more ultrasonic transducers.

[0013] In one embodiment, the first detection unit comprises one or more ultrasonic transmitters and one or more ultrasonic receivers.

[0014] The flow sensor includes a second detection unit, the second detection unit being a first temperature sensor arranged and configured to detect an ambient temperature; a second temperature sensor arranged and configured to detect the temperature of the fluid; a data processor connected to a temperature sensor; Equipped with.

[0015] The data processor may be a microprocessor.

[0016] The second detection unit is configured to estimate a flow rate below a low flow level based on a temperature difference between the surroundings and the fluid, the temperature difference being measured by the first temperature sensor and the second temperature sensor.

[0017] In one embodiment, the second detection unit is configured to estimate the flow rate below the low flow level based on a single measurement made in the flow calibration area. In some circumstances, the single measurement may be sufficient to determine one or more parameters necessary to determine how the flow rate depends on the temperature difference in the flow area below the flow calibration area.

[0018] In one embodiment, the second detection unit is configured to estimate a flow rate below a low flow level based on two or more measurements made in the flow calibration area.

[0019] In one embodiment, the second detection unit contains storage containing information about how the flow rate depends on the temperature difference, and the data processor is configured to access and use the information so that the data processor can determine the flow rate based on the temperature difference. In a flow rate range below the low flow level, the second detection unit can detect the flow rate based on the value of the temperature difference. This can be achieved when the relationship between the flow rate and the temperature difference is known and stored in the storage.

[0020] The second detection unit is configured to estimate a flow rate below the low flow level based on one or more measurements made in a flow calibration area, where the flow sensor can detect a flow rate that depends on a temperature difference, and to determine, using the one or more measurements made in the flow calibration area, one or more parameters necessary to determine how the flow rate depends on a temperature difference in the flow area below the flow calibration area, and thus to use the flow sensor itself to calculate one or more parameters that enable the flow sensor to estimate a low flow rate (a flow rate below the low flow level) based on the detected temperature difference.

[0021] In one embodiment, the flow sensor periodically or continuously: - carrying out one or more measurements in a flow calibration area; - updating more parameters necessary to determine how the flow rate depends on the temperature difference between the flow rate calibration area and the flow rate area below the flow rate calibration area; The present invention is configured to:

[0022] This provides a reliable flow measurement and allows the parameters to be adjusted periodically in response to changing ambient conditions (e.g., increased ventilation.) The flow sensor is configured to automatically perform the required number of measurements at the flow calibration area to calculate and update more parameters required to determine how they depend on the temperature difference between the flow calibration area and the flow areas below the flow calibration area.

[0023] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once per second.

[0024] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once every 5 seconds.

[0025] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once every 10 seconds.

[0026] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once every 30 seconds.

[0027] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once per minute.

[0028] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once every two minutes.

[0029] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once every five minutes.

[0030] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once every 15 minutes.

[0031] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once every 30 minutes.

[0032] In one embodiment, the term "periodically or continuously" should be understood as an attempt being made to provide one or more measurements in the flow calibration area once per hour.

[0033] When an attempt is made to provide one or more measurements in a flow calibration area, a) in some circumstances it may be possible to provide a useful measurement (this is possible if the flow rate is within the flow rate calibration area), or b) In some circumstances it is not possible to provide a useful measurement (this is the case when the flow rate is not within the flow rate calibration area).

[0034] In one embodiment, the flow rate (Q) and the temperature difference (ΔT sf ) is defined by one of the following equations:

[0035]

number

[0036]

number

[0037] where C1 is constant and ΔT B is the temperature difference corresponding to the basic flow level. In Figure 8, the basic flow level Q B is shown.

[0038] These equations have two unknowns: - Basic flow level Q B The temperature difference ΔT B , - constant C1.

[0039] Therefore, the two measurements taken in the flow calibration area are the flow rate (Q) and the temperature difference (ΔT sf ) to determine dependencies between

[0040] In an embodiment the second detection unit is integrated in the first detection unit, hi an embodiment the second detection unit is provided as a separate unit.

[0041] In one embodiment, the second detection unit is communicatively connected to a storage or external device containing information regarding how the flow rate depends on the temperature difference, and the data processor is configured to access and use the information such that the data processor can determine the flow rate based on the temperature difference.

[0042] In one embodiment, the second temperature sensor is arranged and configured to detect the temperature of the fluid by measuring the temperature outside the tubular structure. This allows the flow sensor to be provided as a clamp-on type flow sensor that can be mounted on the outside of a tubular structure (e.g., a pipe). Thus, there is no need for the second temperature sensor to be in direct contact with the fluid.

[0043] In one embodiment, the data processor and the second temperature sensor are located inside the housing, which allows for a simple, easily installed and robust flow sensor to be provided.

[0044] In one embodiment, the first temperature sensor is disposed within the housing, such that all components of the flow sensor can be provided in a single housing.

[0045] In one embodiment, the first temperature sensor is located outside the housing, which makes it possible to take into account heat transfer caused by convection.

[0046] In one embodiment, the second detection unit comprises an intermediate temperature sensor arranged and configured to detect an intermediate temperature at a location inside the housing, the location being expected to have a temperature between the ambient temperature and the temperature of the fluid, making it possible to provide additional information and thus an improved estimation of the flow rate in the low flow range.

[0047] In one embodiment, the flow sensor is a clamp-on flow sensor configured to measure the flow rate of a fluid from outside the tubular structure.

[0048] In one embodiment, the flow sensor is an ultrasonic flow sensor, and the first detection unit comprises at least one ultrasonic transducer arranged to transmit ultrasonic waves and at least one ultrasonic transducer arranged to receive ultrasonic waves.

[0049] In one embodiment, the data processor comprises: - calculating a predicted sound speed as a function of the detected temperature of the fluid; - comparing the detected sound velocity with a predicted sound velocity as a function of the detected temperature of the fluid; - calculating density and flow rate corrections if the detected sound speed does not match the expected sound speed as a function of the detected temperature of the fluid; The present invention is configured to:

[0050] This allows for improved flow measurement accuracy in the flow range above low flow levels.

[0051] The expected sound speed depends on the temperature of the detected fluid and can be calculated by using a given relationship of the sound speed as a function of the temperature of the fluid. If the fluid is pure water, as an example, the relationship of the expected sound speed as a function of the temperature of the detected fluid may be defined as shown in FIG. 7.

[0052] If the fluid is different from pure water (eg, if it is water that contains salts, sugars, or other substances), a different predetermined relationship for the expected speed of sound as a function of the detected temperature of the fluid can be used.

[0053] The predicted sound speed can be compared to the detected sound speed simply by detecting the sound speed and making a comparison. The detection can be performed by using the following formula (16):

[0054]

number

[0055] where c is the speed of sound, L is the distance traveled by the sound signal, and t1 and t2 are the travel times of the transmitted and reflected sound signals, respectively.

[0056] If the detected sound speed does not match the expected sound speed, calculate the density and flow corrections. The density correction can be calculated by using the following equation (18):

[0057]

number

[0058] where K is the bulk modulus of the fluid and ρ is the density of the fluid.

[0059] In one embodiment, the flow sensor is configured to calculate a correction value for the specific heat capacity of the fluid if the detected sound speed c does not match the expected sound speed c as a function of the detected temperature of the fluid. This allows the flow sensor to be utilized to provide a thermal energy meter that provides improved accuracy. The use of the correction value for the specific heat capacity of the fluid ensures that the thermal energy meter provides the most accurate measurement.

[0060] In one embodiment, the data processor comprises: - Calculating the predicted sound speed as a function of the detected temperature of the fluid The present invention is configured to:

[0061] In one embodiment, the flow sensor is configured to automatically calculate the distance L traveled by the transmitted and received ultrasound waves in the fluid based on the detected speed of sound c and the measured time of flight. This allows the flow rate of a pipe to be measured without knowing the exact dimensions of the pipe. It also allows accurate measurements to be made even if sediment builds up on the inner surface of the pipe over time.

[0062] A method according to the invention is a method for measuring a flow rate of a fluid flowing through a tubular structure by using a first detection unit, the first detection unit being configured to detect a flow rate above a predetermined low flow level representing a minimum flow rate that can be measured by using the first detection unit, the method comprising utilizing a second detection unit to: - detecting an ambient temperature by a first temperature sensor; - detecting the temperature of the fluid using a second temperature sensor; - estimating a flow rate below a low flow level based on a temperature difference between the ambient and the fluid measured by a first temperature sensor and a second temperature sensor; Including, The method comprises the following steps: a) performing one or more flow measurements using a first detection unit in a flow calibration area, where the flow sensor is capable of detecting a flow rate that depends on a temperature difference; b) determining, using one or more measurements, one or more parameters necessary to determine how the flow rate depends on the temperature difference of a flow area below a flow calibration area; c) estimating a flow rate below a low flow level based on two or more measurements made in the flow calibration area; Includes.

[0063] Thereby, the method enables flow measurements to be performed in the low flow range.

[0064] In one embodiment, the fluid is a liquid. In one embodiment, the fluid is a water-containing liquid. In one embodiment, the fluid is a gas.

[0065] In one embodiment, the method includes estimating a flow rate below a low flow level based on a single measurement made in a flow calibration area. In some circumstances, the single measurement may be sufficient to determine one or more parameters necessary to determine how the flow rate depends on a temperature difference in a flow area below the flow calibration area.

[0066] In one embodiment, the method includes estimating a flow rate below a low flow level based on two measurements made in a flow calibration area.

[0067] In one embodiment, the method includes estimating a flow rate below a low flow level based on two or more measurements made in a flow calibration area.

[0068] In one embodiment, the method comprises the following steps: - storing information about how the flow rate depends on the temperature difference; - using said information to determine a flow rate based on a temperature difference; Includes.

[0069] This allows the stored information to be used to provide flow rate estimates in a simple and reliable manner. The information may be stored in an external device. In one embodiment, the information is stored in a web-based service.

[0070] In one embodiment, the method includes periodically or continuously: - performing one or more measurements in a flow calibration area; - updating more parameters necessary to determine how the flow rate depends on the temperature difference between the flow rate calibration area and the flow rate area below the flow rate calibration area; Includes.

[0071] This allows for reliable flow measurements and for parameters to be adjusted periodically in response to changes in ambient conditions (e.g. increased ventilation), and allows for an improvement in the method by automatically taking the required number of measurements in the flow calibration area and then calculating and updating more parameters required to determine how they depend on the temperature difference between the flow calibration area and the flow areas below the flow calibration area.

[0072] In one embodiment, the flow rate (Q) and the temperature difference (ΔT sf ) is defined by one of the following equations:

[0073]

number

[0074]

number

[0075] where C1 is constant and ΔT B is the temperature difference corresponding to the base flow level.

[0076] In one embodiment, the method comprises the following steps: - storing information about how the flow rate depends on the temperature difference in a second detection unit; - using said information to determine a flow rate based on a temperature difference; Includes.

[0077] This allows the stored information to be used to provide an estimate of flow rate in a simple and reliable manner.

[0078] In one embodiment, the second temperature sensor is positioned and configured to detect the temperature of the fluid by measuring the temperature outside the tubular structure, which may eliminate the need for the temperature sensor to be in contact with the fluid.

[0079] In one embodiment, the method is performed with the flow sensor including a data processor, the data processor and the second temperature sensor being disposed inside the housing.

[0080] In one embodiment, the method is performed by using a flow sensor and a first temperature sensor is disposed within the housing.

[0081] In one embodiment, the method is performed by using a flow sensor and the first temperature sensor is located outside the housing.

[0082] In one embodiment, the method includes detecting an intermediate temperature using an intermediate temperature sensor disposed at a location inside a housing that contains the second temperature sensor and the intermediate temperature sensor, the intermediate temperature being expected to have a value between the ambient temperature and the temperature of the fluid.

[0083] In one embodiment, the method includes measuring an estimate of the density and / or non-uniformity of the fluid prior to measuring the flow rate.

[0084] This allows for improved flow measurements and allows for consideration of fluid density and / or non-uniformity.

[0085] In one embodiment, the method comprises the following steps: - performing one or more measurements on a sample of the fluid; - calculating an estimate of the density and / or non-uniformity of the fluid prior to measuring the flow rate using one or more measurements; Includes.

[0086] In one embodiment, the estimate of fluid inhomogeneity corresponds to the content of one or more substrates in the fluid, which may be one of the following more substances: sugars, salts, ethylene glycol, glycerol, or propylene glycol.

[0087] In one embodiment, the method is performed by using a clamp-on flow sensor configured to measure the flow rate of the fluid from outside the tubular structure.

[0088] In one embodiment, the method is performed using an ultrasonic flow sensor, and the first detection unit comprises at least one ultrasonic transducer arranged to transmit ultrasonic waves and at least one ultrasonic transducer arranged to receive ultrasonic waves.

[0089] In one embodiment, the method comprises the following steps: - calculating the predicted sound speed as a function of the detected temperature of the fluid; - comparing the detected sound velocity with an expected sound velocity as a function of the detected temperature of the fluid; - calculating density and flow rate corrections if the detected sound speed does not match the expected sound speed as a function of the detected temperature of the fluid; Includes.

[0090] This allows for improved flow measurement accuracy in the flow range above low flow levels.

[0091] In one embodiment, the method includes calculating a correction value for the specific heat capacity of the fluid if the detected sound speed c does not match an expected sound speed c as a function of the detected temperature of the fluid. This allows the flow sensor to be utilized to provide a thermal energy meter that provides improved accuracy. The use of the correction value for the specific heat capacity of the fluid ensures that the thermal energy meter provides the most accurate measurement.

[0092] In one embodiment, the method includes automatically calculating the distance L (the distance the transmitted and received ultrasound waves travel in the fluid) based on the detected speed of sound c and the measured time of flight. This allows the flow rate of the pipe to be measured without knowing the exact dimensions of the pipe. It also allows accurate measurements to be made even if sediments are introduced to the inner surface of the pipe over time.

[0093] In one embodiment, the method includes a step of estimating thermal energy in a heating or cooling system, which makes it possible to provide an improved (more accurate) method of detecting thermal energy in a heating or cooling system.

[0094] A thermal energy meter according to the invention is a thermal energy meter comprising a sensor according to the invention.

[0095] The present invention will be more fully understood from the detailed description given herein below. The accompanying figures are given by way of example only and are therefore not limiting of the present invention. [Brief description of the drawings]

[0096] [Figure 1A]1 shows a graph depicting the temperature difference between the surroundings and the fluid passing through the pipe as a function of the flow rate through the pipe. [Figure 1B] 1B shows the low flow portion of the graph shown in FIG. 1A. [Figure 2A] 1 shows a schematic diagram of a clamp-on type flow sensor according to the present invention. [Figure 2B] 1 shows a schematic diagram of another clamp-on type flow sensor according to the present invention. [Figure 3A] 1 shows a schematic diagram of a flow sensor according to the present invention. [Figure 3B] 2 shows a schematic diagram of another flow sensor according to the present invention. [Figure 4A] 1 shows a schematic diagram of a clamp-on type flow sensor according to the present invention mounted on the outside of a pipe. [Figure 4B] 2 shows a schematic diagram of another flow sensor according to the present invention. [Figure 5A] 1 shows a schematic diagram of a flow sensor according to the present invention. [Figure 5B] 2 shows a schematic diagram of another flow sensor according to the present invention. [Figure 6A] 1 shows a schematic diagram of a flow sensor according to the present invention. [Figure 6B] 2 shows a schematic diagram of another flow sensor according to the present invention. [Figure 7] 1 shows a graph depicting the speed of sound in water as a function of water temperature. [Figure 8] The flow rate is shown as a function of the temperature difference. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0097] Referring now in detail to the drawings for the purposes of illustrating a preferred embodiment of the invention, the temperature difference ΔT between the surroundings and the fluid passing through the pipe as a function of the flow rate Q through the pipe shown in FIG. sf Graph 28 showing the above is shown.

[0098] Graph 28 (shown by the solid line) is the low flow level Q A It can be seen that the flow rate exceeds the low flow level QA represents the lowest flow rate that can be measured using the prior art flow sensor. However, this low flow level Q A , the graph 28 is extrapolated. This lower area 30 is illustrated by the dotted oval.

[0099] FIG. 1B illustrates the low flow portion 30 of the graph 28 shown in FIG. 1A. Prior art flow sensors detect low flow levels Q A Although it is not possible to detect flows below this low flow level Q, the flow sensor and method according to the present invention A This makes it possible to provide flow measurements below .

[0100] Basic flow level Q B If the temperature difference ΔT sf is constant and hence independent of the flow rate Q.

[0101] Low Flow Level Q A and the basic flow level Q B In the flow calibration area B2 between sf increases as a function of the flow rate Q. In this flow calibration area B2, a first flow sensor measurement M1 and a second flow sensor measurement M2 are illustrated.

[0102] Using one or more measurements by the flow sensor made in the flow calibration area B2, the flow rate Q is determined to be the temperature difference ΔT between the flow calibration area B2 and the flow area B1 below the flow calibration area B2. sf It is then possible to determine the parameters necessary to determine how the .DELTA..times ...

[0103] Temperature difference ΔT sf is given by the following equation (1) as a function of flow rate Q:

[0104]

number

[0105] In the formula, ΔT B is the basic flow level Q B is the temperature difference corresponding to C1, and C1 is constant.

[0106] By taking two measurements M1 and M2, we can obtain the two unknowns ΔT B and C1 can be determined from equation (1).

[0107] Therefore, the flow rate Q in the flow area B1 where the flow sensor cannot provide any measurement M3 It becomes possible to determine the flow rate Q M3 is the temperature difference ΔT detected by the flow sensor M3 The flow rate Q can be determined based on the measured value. M3 is expressed as equation (1), or the detected temperature difference ΔT sf This can be determined by using the following equation (2), which defines the flow rate Q as a function of

[0108]

number

[0109] where C1 is constant and ΔT B is the basic flow level Q B is the temperature difference corresponding to

[0110] The flow sensor and method according to the present invention detects the temperature difference ΔT between the surroundings and the fluid passing through the pipe. sf By measuring the low flow level Q A The estimation is possible because one or more flow measurements M1, M2 made in the flow calibration area B2 are used to determine the unknowns in equation (1) or equation (2). Therefore, by using equation (2), any flow rate Q in the flow area B1 can be calculated.

[0111] In Figure 1B, it can be seen that a first flow rate Q1 is determined based on a measurement of a first temperature difference ΔT1. Similarly, Figure 1B shows that a second flow rate Q2 is determined based on a measurement of a second temperature difference ΔT2.

[0112] Low Flow Level Q A is the temperature difference ΔT A Similarly, the basic flow level Q B is the temperature difference ΔT B corresponds to a higher measured value of

[0113] By using the temperature sensor of the sensor according to the invention, a temperature difference can be detected, which is shown in and will be explained with reference to Figures 2A, 2B, 3A, 3B and 4B.

[0114] In one example, in flow calibration area B2, a flow sensor according to the present invention used to measure water at 20° C. was used to obtain a flow rate of 2 ml / s (0.000002 m 3 / s) M2 and a temperature difference of 10°C ΔT M2 A measurement point M2 corresponding to is created.

[0115] Temperature difference ΔT between the surroundings and the fluid and flow rate Q sf The relationship is given by equation (2).

[0116]

number

[0117]

number

[0118] and dt B = 10.02°C, the following values ​​can be calculated:

[0119] [Table 1]

[0120] In another example, the low flow level Q A If the temperature difference is less than ΔT sf The relationship between the flow rate Q and the pressure is given by equation (2), where C1 = 4.88 and dt B = 12.54°C, the following values ​​can be calculated:

[0121] [Table 2]

[0122] 2A illustrates a schematic diagram of a clamp-on type flow sensor 1 according to the present invention. The flow sensor 1 is arranged to detect the flow rate of a fluid 26 (e.g., a liquid) in a pipe 2. The flow sensor 1 comprises a data processor 10.

[0123] The flow sensor 1 comprises a first temperature sensor 12 arranged to detect the ambient temperature of the pipe 2. The flow sensor 1 comprises a second temperature sensor 14 arranged to detect the temperature of the fluid 26. The flow sensor 1 comprises a first ultrasonic wave generator 4 and a second ultrasonic wave generator 4'. The wave generators are formed as piezoelectric transducers 4, 4' arranged and configured to generate ultrasonic waves that are introduced into the fluid 26 at an angle to the direction of the flow Q. The flow sensor 1 can be either a Doppler effect type flow sensor 1 or a transit time measurement type flow sensor 1. Both ultrasonic waves 6, 8 are shown to travel a distance ½L. Thus, the total travel distance is L.

[0124] The piezoelectric transducers 4,4' act as transducers and detect the flow rate Q through the pipe by using sound waves 6,8. In one embodiment, the flow sensor 1 comprises several piezoelectric transducers 4,4' in order to make the flow rate Q profile independent of the pipe 2. The operating frequency depends on the application and can be in the frequency range of 100-200 kHz for gases and in the higher MHz frequency range for liquids.

[0125] In one embodiment, the flow sensor 1 is a Doppler effect type flow sensor 1. In this embodiment, the flow sensor 1 comprises only a single piezoelectric transducer. In this case, the second piezoelectric transducer 4' can be omitted, and the first piezoelectric transducer 4 is used for both transmitting ultrasonic waves 6 and receiving ultrasonic waves 8. In a Doppler effect type flow sensor 1, when the transmitted wave 6 is reflected by particles or bubbles in the fluid, its frequency is shifted due to the relative velocity of the particles. The higher the liquid flow velocity, the higher the frequency shift between the emitted wave and the reflected wave.

[0126] In one embodiment, the flow sensor 1 is a Doppler effect flow sensor 1 comprising several piezoelectric transducers 4, 4'. In this case, one piezoelectric transducer 4 can be used to transmit ultrasonic waves 6, while another piezoelectric transducer 4' can be used to receive reflected ultrasonic waves 8.

[0127] In one embodiment, the flow sensor 1 is a propagation type flow sensor 1. In this embodiment, the flow sensor 1 utilizes two piezoelectric transducers acting as both transmitters and receivers arranged at an angle to the direction of the flow Q. The transmission of ultrasonic waves in a flowing medium results in a superposition of the sound propagation speed and the flow velocity. The flow velocity is proportional to the inverse of the difference in the propagation time in the direction and against the flow Q. The sound propagation type measurement method is independent of the sound propagation speed and therefore also independent of the medium. Therefore, it is possible to measure different liquids or gases using the same setup.

[0128] The temperature sensors 12, 14 and the piezoelectric transducers 4, 4' are connected to the data processor 10. The data processor 10 can therefore process the data from the temperature sensors 12, 14 and the piezoelectric transducers 4, 4' and thereby detect the flow rate based on the data.

[0129] 2A, the second temperature sensor 14 is disposed outside the pipe 2. The second temperature sensor 14 is thermally connected to the pipe 2. Thus, the second temperature sensor 14 is able to measure the temperature of the pipe 2. The temperature of the pipe 2 will typically match or be very close to the temperature of the fluid 26 in the pipe 2.

[0130] In the low flow area, below the low flow level of the flow sensor 1, the flow sensor 1 determines the flow rate based on the temperature measurements made by the first temperature sensor 12 and the second temperature sensor 14. In fact, below the low flow level of the flow sensor 1, the flow sensor 1 determines the flow rate based on the temperature measurements made by the first temperature sensor 12 and the second temperature sensor 14. sf Based on this, the flow rate is determined.

[0131] (9)ΔT sf =|T s -T f | In the formula, T s is the ambient temperature measured by the first temperature sensor 12, and T f is the temperature of the fluid 26 measured by the second temperature sensor 14.

[0132] Figure 2B illustrates a schematic diagram of a clamp-on type flow sensor 1 according to the present invention. The flow sensor 1 shown in Figure 2B basically corresponds to that shown in Figure 2A. However, the temperature sensor 14 is in contact with the fluid 26 inside the pipe 2. The structure extends through the wall of the pipe 2. The temperature sensor 14 is connected to the data processor 10 via wires that extend through the structure. Both ultrasonic waves 6, 8 are shown traveling a distance 1 / 2L. The total traveling distance is therefore L.

[0133] 3A illustrates a schematic diagram of a thermal energy meter 5 according to the present invention. The thermal energy meter 5 comprises a flow sensor 1 according to the present invention. The flow sensor 1 comprises a housing 20 which is mounted in a pipe 2. The flow sensor 1 is arranged and configured to detect a flow rate Q of a fluid 26 (e.g. a water-containing liquid) in the pipe 2.

[0134] Flow sensor 1 is connected to the ambient temperature T s The flow sensor 1 comprises a first temperature sensor 12 arranged to detect the temperature T f The flow sensor 1 includes a second temperature sensor 14 arranged to detect an intermediate temperature T i a third temperature sensor 16 arranged to detect an intermediate temperature T i is the ambient temperature T s and the temperature T of fluid 26 f It is expected to have a value between

[0135] The flow sensor 1 comprises a first ultrasonic generator 4 and a second ultrasonic generator 4' formed as piezoelectric transducers 4, 4' arranged and configured to generate ultrasonic waves transmitted into the fluid 26 at an angle to the direction of the flow Q. The piezoelectric transducers 4, 4' are used in the same manner as shown in Figures 2A and 2B and will be described with reference to those figures.

[0136] The flow sensor 1 comprises a data processor 10 connected to the piezoelectric transducers 4, 4' and the temperature sensors 12, 14, 16. The data processor 10 is therefore able to process data from the temperature sensors 12, 14 and the piezoelectric transducers 4, 4' and thereby detect the flow rate based on the data.

[0137] The third temperature sensor 16 is positioned to provide a temperature measurement that can be utilized to provide an improved estimate of flow rate below the low flow level of the flow sensor 1. The improved estimate can be achieved by using the difference between two temperatures: - Difference ΔT between the surroundings and the fluid 26 sf : (10)ΔT sf =|T s -T f |, - temperature difference ΔT between the midpoint of the housing 20 and the fluid 26 if : (11)ΔT if =|T i -T f |.

[0138] The thermal energy meter 5 comprises an external temperature sensor 17 thermally connected to the pipe 3. By measuring the temperature of the fluid in the supply pipe 3 and the temperature of the fluid 26 in the return pipe 2 it is possible to calculate the consumed heat (thermal energy). The external temperature sensor 17 can be connected to the data processor 10 by a wired connection as shown in figure 3A or by a wireless connection as shown in figure 3A.

[0139] Fig. 3B illustrates another schematic diagram of a thermal energy meter 5 according to the invention. The thermal energy meter 5 comprises a flow sensor 1 according to the invention. The flow sensor 1 basically corresponds to the one shown in Fig. 3A. However, the first temperature sensor 12 is installed on the outer surface of the housing 20. The thermal energy meter 5 comprises an external temperature sensor 17 attached to the outer surface of the pipe 3. The temperature sensor 17 is thus thermally connected to the supply pipe 3. By measuring the temperature of the fluid in the supply pipe 3 and the temperature of the fluid 26 in the return pipe 2, it is possible to calculate the consumed heat (thermal energy).

[0140] 4A illustrates a schematic diagram of a clamp-on type flow sensor 1 according to the present invention. The flow sensor 1 is mounted on the outside of a pipe 2. The flow sensor 1 comprises a housing 20 having a junction structure that matches the outside geometry of the pipe 2. A thermal connection structure (e.g., a metal layer) is attached to the junction structure. The thermal connection structure thereby reduces the thermal resistance and thus improves and makes the heat transfer between the pipe 2 and a temperature sensor (not shown) of the flow sensor 2 more efficient.

[0141] In one embodiment, the thermal connection structure is a metal foil coated with a thermal adhesive on each side. Such a thermal connection structure can provide a permanent bond and reduce thermal resistance by filling microvoids at the contact surface. In one embodiment, the thermal connection structure is a thermally conductive aluminum tape. In one embodiment, the thermal connection structure can be a thermally conductive double-sided structural adhesive aluminum tape.

[0142] 4B illustrates a schematic diagram of a flow sensor 2 according to the present invention. The flow sensor 2 comprises a mechanical flow sensing unit 24 that is placed inside the pipe 3 and thus submerged in the fluid 26.

[0143] The flow sensor 1 is a positive displacement flow meter that requires the fluid to mechanically displace components of a mechanical flow sensing unit 24 to provide a flow measurement. The mechanical flow sensing unit 24 may be a turbine or impeller. The activity and rotational speed of the turbine or impeller can be measured either by using a direct connection to the data processor 10 or with a sensing member (not shown) arranged and configured to measure the angular velocity of the turbine or impeller. The flow sensor 1 may be, by way of example, a turbine flow meter, a single jet meter, or a paddle wheel flow meter. The mechanical flow sensing unit 24 constitutes a first sensing unit 34. The data processor 10 and the temperature sensors 12, 14 constitute a second sensing unit 36.

[0144] The flow sensor 1 comprises a first temperature sensor 12 arranged and configured to detect the temperature of the surroundings (ambient temperature). The flow sensor 1 comprises a second temperature sensor 14 arranged and configured to detect the temperature of the fluid 26 inside the fluid 3. The second temperature sensor 14 bears against the exterior of the wall of the pipe 3. In another embodiment, however, the second temperature sensor 14 may be located inside the pipe 3. In a further embodiment, the second temperature sensor 14 may be integrated into the exterior of the wall of the pipe 3.

[0145] The flow sensor 1 comprises a pipe 3 provided with a first flange 18 and a second flange 18'. These flanges 18, 18' are configured to be mechanically connected to corresponding flanges 19, 19' of two pipes 2, 2'. In one embodiment, the flanges 18, 18' are replaced with similar mounting structures designed to attach the flow sensor 1 to the pipes 2, 2'.

[0146] In one embodiment, the distal portions of the pipes 2, 2' are provided with an external thread, while the distal portion of the pipe 3 of the flow sensor 3 is provided with a corresponding internal thread allowing the pipe 3 to be screwed onto the pipes 2, 2'.

[0147] In one embodiment, the distal portions of the pipes 2, 2' are provided with an internal thread, while the distal portion of the pipe 3 of the flow sensor 3 is provided with a corresponding external thread allowing the pipe 3 to be screwed onto the pipes 2, 2'.

[0148] Figure 5A illustrates a schematic diagram of a flow sensor 1 according to the invention. The flow sensor 1 basically corresponds to the one shown in Figure 3A.

[0149] Figure 5B illustrates a schematic diagram of a flow sensor 1 according to the invention. The flow sensor 1 basically corresponds to the one shown in Figure 3B.

[0150] 5A and 5B, however, the housing 20 includes a portion that bears against the pipe 2 while the second temperature sensor 14 and the piezoelectric transducer 4, 4' extend through that portion of the housing 20 for direct connection to the exterior of the pipe 2 when the flow sensor 1 is attached to the pipe 2. A clamping structure such as a cable tie or hose clamp may be used to clamp the flow sensor to the pipe 2.

[0151] The piezoelectric transducers 4, 4' constitute a first detection unit 34. The data processor 10 and the temperature sensors 12, 14, 16 constitute a second detection unit 36.

[0152] For the flow sensor 1 according to the invention, in most cases, exploitation is made of the fact that the fluid 26 transfers heat between the physical zones through which it flows, and these physical zones have different temperatures. By detecting the temperature difference between these zones, it is possible to provide an alternative measurement of flow rate.

[0153] Therefore, the flow sensor 1 and the method according to the invention can detect flow rates in a low flow range, where the prior art flow sensors cannot detect any flow rates.

[0154] Furthermore, the flow sensor 1 and the method according to the present invention in general can provide improved (more accurate) flow detection by using the temperature differences of the above-mentioned zones.

[0155] The rate of heat transfer from a fluid to the surroundings, q (the rate corresponding to E / t), is defined by the following equation (12): (12)q = UAΔT sf ΔT sfは、 is the temperature difference between the surroundings and the fluid 26, A is the surface area over which heat transfer takes place, and U is the heat transfer coefficient.

[0156] The heat transfer coefficient U is defined by the following equation (13).

[0157]

number

[0158] where k is the thermal conductivity of the material through which heat transfer occurs and s is the thickness of the material through which heat transfer occurs.

[0159] The operating principle of the Doppler flow sensor 1 is shown in FIG. 6A and will be briefly described with reference to FIG. 6A. The Doppler flow sensor is affected by changes in the speed of sound of the fluid 26. Thus, the Doppler flow sensor can detect changes in density and temperature of the fluid 26. Therefore, many prior art Doppler flow sensors are unsuitable for highly accurate measurement applications. However, the present invention makes it possible to detect the temperature and speed of sound of the fluid 26 to compensate for temperature and fluid (density) changes and thus provide improved accuracy. Similarly, the present invention makes it possible to detect the density of the fluid 26 (by measurements made on a sample of the fluid 26) to compensate for temperature and / or fluid (density) changes to further improve the accuracy of the flow sensor 1.

[0160] The Doppler flow sensor 1 is a time-of-flight ultrasonic flow sensor that measures the time it takes for sound to travel between a transmitter 4 and a receiver 4'. In a typical setup, similar to that shown in Figure 6A, two transducers (transmitter / receiver) 4,4' are placed on each side of a pipe 2 where the flow rate Q is to be measured. The transmitters 4,4' transmit pulsating ultrasonic waves 6 at a given frequency from one side to the other. The average flow velocity V is proportional to the difference in frequencies.

[0161] Therefore, the flow velocity V can be expressed as (14).

[0162]

number

[0163] where t1 is the transmission time in the downstream direction, t2 is the transmission time in the upstream direction, L is the distance between the multiple transducers, and φ is the relative angle between the transmitted ultrasonic beam 6 and the flow rate Q.

[0164] The flow rate Q is calculated using (15) based on the flow velocity V and the cross-sectional area A of pipe 2. pipe It can be calculated as the product of (15) Q = VA pipe

[0165] At the same time, the speed of sound c is given by the following equation (16):

[0166]

number

[0167] The flow sensor 1 shown in Figure 6A comprises a first temperature sensor 12 arranged to detect the ambient temperature of the pipe 2. The flow sensor 1 comprises a second temperature sensor 14 arranged to detect the temperature of the fluid 26. The flow sensor 1 comprises a data processor 10. Although not shown in Figure 6B, the temperature sensors 12, 14 and the two transducers 4, 4' are connected to the data processor 10. The data processor 10 is thus able to process data from the temperature sensors 12, 14 and the two transducers 4, 4' and calculate the flow rate Q based on the data.

[0168] The operating principle of the Doppler effect flow sensor 1 for measuring the flow rate of a fluid containing a fluid of particles 32 is shown in and will be briefly explained with reference to FIG. 6B.

[0169] The flow velocity V can be calculated by using the following equation (17):

[0170]

number

[0171] fr is the frequency of the received wave, ft is the frequency of the transmitted wave, φ is the relative angle between the transmitted ultrasonic beam and the flow rate Q, and c is the speed of sound in the fluid 26.

[0172] The flow rate Q is calculated using (15) based on the flow velocity V and the cross-sectional area A of pipe 2. pipe It can be calculated as the product of (15) Q = VA pipe Equations 15 and 16 can also be used when calculating flow rates by using the flow sensors shown in Figures 2A, 2B, 3A, and 3B.

[0173] 7 shows a graph representing the speed of sound in water c as a function of the temperature T of the water. However, similar graphs can be made for other liquids. In the following, water simply represents a possible fluid and water can be replaced by another liquid.

[0174] The dimensions of a tubular structure (e.g. a pipe through which a flow rate Q of water flows) are not known and an estimation of the distance L that sound travels in water is necessary. This problem is particularly relevant for ultrasonic clamp-on sensors. Over time, sediments may be brought to the inner surface of the pipe, which causes the distance L to gradually decrease. The present invention therefore allows the estimation of the distance L under such conditions.

[0175] Determining the speed of sound in water c makes it possible to estimate the distance L, thereby improving the accuracy of the detected velocity V and water flow rate Q. Thus, the change in the speed of sound in water c is of considerable relevance.

[0176] When the speed of sound c is known, it becomes possible to calculate the distance L that sound travels in water.

[0177] At the same time, the speed of sound c is given by the following equation (12):

[0178]

number

[0179] where K is the bulk modulus and ρ is the density.

[0180] Because the density of water depends on the temperature T, the speed of sound c depends on the temperature T. In addition, the speed of sound c depends on the concentration of substances (e.g., glycol) in the water.

[0181] When the tilt angle α is known, the average water velocity V in the tube (measured by time-of-flight difference) can be found by using the following equation (19):

[0182]

number

[0183] When the speed of sound c is known, L can be calculated or estimated (after t1 and t2 are measured) by using the following equation (16):

[0184]

number

[0185] Therefore, the flow rate Q is calculated using (15) based on the average water velocity V and the cross-sectional area A of pipe 2. pipe It can be calculated as the product of (15) Q = VA pipe

[0186] Using measurements of the fluid temperature T and the time of flight, the density ρ can be determined and, by using equation (18), the speed of sound c is solved for.

[0187] When the flow sensor is calibrated with pure water at a temperature T2 of 26°C, Figure 7 shows that the sound speed c(T2) is 1500 m / s. When a lower temperature T1 of 21.5°C is detected, the sound speed c(T1) is 1485 m / s. Therefore, by calibrating the flow sensor by using a fluid (e.g., a liquid such as water) with a known temperature T and density ρ, a simple temperature measurement is sufficient to detect the sound speed c by using equation (18).

[0188]

number

[0189] The specific heat capacity of a fluid (eg, water) depends on the content of additional substances (eg, sugars, salts, ethylene glycol, glycerol, or propylene glycol).

[0190] When the sound speed c is known, it becomes possible to calculate the specific heat capacity of a fluid (e.g. water) with additional substances based on the detected fluid density, which makes the thermal energy meter with the flow sensor 1 according to the present invention more accurate.

[0191] It may be advantageous to measure the content of additional substances (e.g. sugars, salts, ethylene glycol, glycerol or propylene glycol), which would make it possible to calibrate the flow sensor based on the measurement.

[0192] Example 1 When a flow sensor used with pure water detects a flow rate Q of 1 liter / min at a temperature T2 of 26° C., FIG. 7 shows that the sound speed c(T2) is 1500 m / s.

[0193] When the speed of sound c (1500 m / s) is known, L can be calculated or estimated (after t1 and t2 are detected by the flow sensor) by using the following equation (16):

[0194]

number

[0195] When the flow sensor is used at a later time, the expected sound speed c will be 1500 m / s at the same temperature T2 of 26° C. However, if the detected sound speed c is 1485 m / s, which is calculated by using equation (16) and the known L, the reduction in sound speed is about 1%. This can be caused by the change in density ρ of water. If we assume that the bulk modulus K is constant, equation (18) results in an increase in density ρ of about 2% (this using equation 18).

[0196] When using a flow sensor in a thermal energy measuring instrument, it will be possible to correct the specific heat capacity of the water based on the detected density of the water. It may be concluded that the content of additional substances (e.g. sugars, salts, ethylene glycol, glycerol, or propylene glycol) is increasing. It will therefore be possible to improve the accuracy of the thermal energy measuring instrument. This is relevant because the content of additional substances (e.g. sugars, salts, ethylene glycol, glycerol, or propylene glycol) may change as a function of time. If the flow sensor is configured to automatically detect changes in the density of the fluid, it will be possible for the flow sensor to be used in the thermal energy measuring instrument to provide high accuracy even when the content of additional substances changes over time.

[0197] Figure 8 shows the temperature difference ΔT sf 4 shows a graph representing the flow rate Q detected by means of a flow sensor according to the invention as a function of

[0198] Low Flow Level Q A represents the lowest flow rate that can be measured by using the prior art flow sensor. Prior art flow sensors have a low flow level Q A Although it is not possible to detect flows below this low flow level Q, the flow sensor and method according to the present invention A This makes it possible to provide flow measurements below .

[0199] Basic flow level Q B If the temperature difference exceeds ΔT sf is constant and hence independent of the flow rate Q.

[0200] Low Flow Level Q A and the basic flow level Q B In the flow calibration area B2 between sf increases as a function of the flow rate Q. In this flow calibration area B2, a first flow sensor measurement M1 and a second flow sensor measurement M2 are illustrated.

[0201] The measurements M1 and M2 by these flow sensors are performed in the flow calibration area B2, which means that the flow rate Q is determined by the temperature difference ΔT between the flow calibration area B2 and the flow area B1 below the flow calibration area B2. sf This is done to determine the parameters needed to determine how the flow rate Q and temperature difference ΔT depend on sf The relationship between is given by equation (2).

[0202] TIFF2024527311000023.tif1770

[0203] Temperature difference ΔT1, ΔT M3 By measuring ΔT2 and ΔT2, it is possible to calculate the flow rate Q using equation (2). [Explanation of symbols]

[0204] 1 Flow Sensor 2,2',3 pipe 4,4' Ultrasonic transducer (piezoelectric transducer) 5. Thermal energy measuring instruments 6. Ultrasonic vibration waves 8. Reflected ultrasonic vibration waves 10 Data processor (e.g., microprocessor) 12 Temperature Sensor 14 Temperature Sensor 16 Temperature Sensor 17 Temperature Sensor 18,18' flange 19,19' flange 20. Housing 22 Thermal connection structure (e.g. metal layer) 24 Mechanical flow detection unit 26 Fluid 28 Graphs 30 Low flow area 32 particles 34,36 Detection unit T s Ambient temperature T f fluid temperature ΔT temperature difference ΔT sf Temperature difference between the surroundings and the fluid ΔT1,ΔT2 temperature difference ΔT A ,ΔT B temperature difference T1,T2 temperature M1,M2,M3 flow measurement B1 flow area B2 Flow Calibration Area c p Specific heat capacity k Thermal conductivity U heat transfer coefficient A surface area W Volume t Flight time t' temperature compensated flight time Δt difference in flight time t1,t2 flight time ΔT1,ΔT2 temperature difference ΔT A ,ΔT B temperature difference ΔT M1 ,ΔT M2 temperature difference ΔT M3 temperature difference d Thickness Q flow rate Q1,Q2 flow rate Q A ,Q B flow rate Q M1 ,Q M2 flow rate Q M3 flow rate V flow velocity α angle L distance

Claims

1. A flow sensor (1) configured to measure the flow rate (Q) of a fluid (26) flowing through a tubular structure (2), wherein the flow sensor (1) has a minimum flow rate (Q Ａ that can be measured by using a first detection unit (34). The flow rate (Q) above a predetermined low flow rate level (Q Ａ ) is detected by a first detection unit (34) configured to detect the flow rate (Q). The flow sensor (1) includes a second detection unit (36), and the second detection unit (36) - The first temperature sensor (12) arranged and configured to detect the ambient temperature (peripheral temperature) (T ｓ ) and - a second temperature sensor (14) arranged and configured to detect the temperature (T ｆ ) of the fluid (26); -A data processor (10) connected to the temperature sensors (12, 14), The second detection unit (36) estimates the flow rate (Q) below the low flow rate level (Q) based on the temperature difference (ΔT) between the surroundings and the fluid (26). ｓｆ ), and is configured to estimate the flow rate (Q) below the low flow rate level (Q) based on the temperature difference (ΔT Ａ ), where the temperature difference (ΔT ｓｆ ) is measured by the first temperature sensor (12) and the second temperature sensor (14). The second detection unit (36) is configured to estimate the flow rate (Q) below the low flow rate level (Q) based on one or more measurements (M ２ , M １ , M ２ ) performed in the flow rate calibration area (B Ａ ). The flow rate sensor (1) can detect the flow rate (Q) that depends on the temperature difference (ΔT ｓｆ ), and uses the one or more measurements (M ２ , M １ , M ２ ) performed in the flow rate calibration area (B ２ ) to determine one or more parameters necessary to determine how the flow rate (Q) depends on the temperature difference (ΔT ２ ) between the flow rate calibration area (B １ ) and the flow rate area (B ｓｆ ) below the flow rate calibration area (B). A flow rate sensor (1) characterized by this.

2. The second detection unit (36) is based on two or more measurements (M ２ , M １ ) performed in the flow rate calibration area (B ２ ) to estimate the flow rate (Q) below the low flow rate level (Q Ａ ). The flow rate sensor (1) according to claim 1, which is configured as such.

3. The flow sensor (1) is configured to perform periodically or continuously, - Flow correction area (B ２ ) to perform the one or more measurements (M １ , M ２ ), and - the flow rate (Q) is more parameters necessary to determine how it depends on the temperature difference (ΔT ２ ), between the flow calibration area (B ２ ) and the flow area (B １ ) below the flow calibration area (B ｓｆ ), to update The flow sensor (1) according to claim 1.

4. The dependence between the flow rate (Q) and the temperature difference (ΔT ｓｆ ) is defined by the following equation, 【Number 1】 Or 【Number 2】 where C １ is constant and ΔT Ｂ is the temperature difference corresponding to the basic flow rate level, the flow sensor (1) according to claim 1.

5. The second temperature sensor (14) is arranged and configured to detect the temperature (T ｆ ) of the fluid (26) by measuring the temperature outside the tubular structure (2). The flow rate sensor (1) according to claim 1.

6. The data processor (10) and the second temperature (14) sensor are arranged inside the housing (20), the flow sensor (1) according to claim 1.

7. The first temperature sensor (12) is arranged inside the housing (20), the flow sensor (1) according to claim 6.

8. The first temperature sensor (12) is arranged outside the housing (20), the flow sensor (1) according to claim 6.

9. The second detection unit (36) is, - an intermediate temperature sensor (16) arranged and configured to detect an intermediate temperature (T ｉ ) at a position inside the housing (20), the position being expected to have a temperature between the ambient temperature (T ｓ ) and the temperature (T ｆ ) of the fluid (26), the flow rate sensor (1) according to claim 1.

10. The flow sensor (1) is a clamp-on flow sensor (1) configured to measure the flow rate (Q) of the fluid (26) from the outside of the tubular structure (2), the flow sensor (1) according to claim 1.

11. The flow sensor (1) is an ultrasonic flow sensor (1), and the first detection unit (34) includes at least one ultrasonic transducer (4, 4') arranged to transmit ultrasonic waves (6) and at least one ultrasonic transducer (4, 4') arranged to receive ultrasonic waves (8), the flow sensor (1) according to claim 1.

12. The flow sensor (1) is configured to, - Determine the flight time (t, t １ , t ２ ) of the ultrasonic waves (6, 8), and calculate the change in the speed of sound based on the flight time (t, t １ , t ２ ); - calculating a change in the predicted speed of sound (c) as a function of the detected temperature (T ｆ ) of the fluid (26); - determining whether the change in the predicted speed of sound (c) matches the change in the speed of sound calculated based on the flight times (t, t １ , t ２ ); The flow sensor (1) according to claim 11.

13. The ultrasonic flow sensor (1) is configured to calculate a correction value for a change in the density (ρ) of the fluid (26) based on a change in the speed of sound calculated based on the flight time (t, t １ , t ２ ) when the predicted speed of sound (c) does not match the change in the speed of sound calculated based on the flight time (t, t １ , t ２ ). The flow sensor (1) according to claim 1

14. The ultrasonic flow sensor (1) is configured to calculate a corrected value of the specific heat capacity (c) of the fluid (26) based on the corrected value of the density (ρ) when the change in the predicted speed of sound (c) does not match the change in the speed of sound calculated based on the flight time (t, t １ , t ２ ). The flow sensor (1) according to claim 13. ｐ )

15. The ultrasonic flow sensor (1) is configured to calculate a correction value of the flow rate (Q) of the fluid (26) based on a change in the speed of sound calculated based on the change in the predicted speed of sound (c) not matching the change in the speed of sound calculated based on the flight time (t, t １ , t ２ ), when the flight time (t, t １ , t ２ ). The flow sensor (1) according to claim 13.

16. The data processor (10) is configured to automatically calculate the distance (L) traveled by the transmitted ultrasonic wave (6) and the received ultrasonic wave (8) in the fluid (26) based on the detected value of the speed of sound (c), the flow sensor (1) according to claim 12.

17. A method for measuring the flow rate (Q) of a fluid (26) flowing through a tubular structure (2) by using a first detection unit (34), wherein the first detection unit (34) has a minimum flow rate (Q Ａ ) that can be measured by using the first detection unit (34), and is configured to detect a flow rate (Q) exceeding a predetermined low flow rate level (Q Ａ ), and the method utilizes a second detection unit (36) to - A step of detecting the ambient temperature (peripheral temperature) (T ｓ ) by the first temperature sensor (12); - Using the second temperature sensor (14), the temperature (T ｆ ) of the fluid (26) is detected; - estimating the flow rate (Q) below the low flow rate level (Q) based on the temperature difference (ΔT) between the ambient and the fluid (26) measured by the first temperature sensor (12) and the second temperature sensor (14), ｓｆ ) based on the Ａ ), and including the step of The method is, a) In the flow rate calibration area (B ２ ), a step of performing one or more flow rate measurements (M １ , M ２ ) using the first detection unit (34), wherein in the flow rate calibration area (B ２ ), the flow rate sensor (1) can detect the flow rate (Q) that depends on the temperature difference (ΔT ｓｆ ); b) One or more measurements (M ２ ), M １ ), M ２ ) performed in the flow rate correction area (B ２ ) are used to determine how the flow rate (Q) depends on the temperature difference (ΔT ２ ) between the flow rate correction area (B １ ) and the flow rate area (B ｓｆ ) below the flow rate correction area (B ), and determining one or more parameters necessary for this purpose; c) A step of estimating the flow rate (Q) below the low flow rate level (Q) based on two or more measurements (M ２ , M １ ) performed in the flow rate correction area (B ２ ). ２ ), M １ １ , M ２ ), and Ａ a step of estimating the flow rate (Q) that is below the low flow rate level (Q). Characterized by including, a method.

18. The method according to claim 17 includes the step of performing flow rate measurements two or more times in the flow calibration area.

19. The method is periodically or continuously, - Flow correction area (B ２ ) to perform the one or more measurements (M １ , M ２ ) and a step of executing; - the flow rate (Q) is the temperature difference (ΔT ２ ) between the flow rate calibration area (B ２ ) and the flow rate area (B １ ) below the flow rate calibration area (B ｓｆ ), and updating more parameters necessary to determine how it depends Including, the method according to claim 17.

20. The dependence between the flow rate (Q) and the temperature difference (ΔT ｓｆ ) is defined by the following equation, [Number 3] Or 【Number 4】 where C １ is constant, and ΔT Ｂ is the temperature difference corresponding to the basic flow rate level, the method according to claim 17.

21. The second temperature sensor (14) is arranged and configured to detect the temperature (T ｆ ) of the fluid (26) by measuring the temperature outside the tubular structure (2). The method according to claim 17

22. The method uses an intermediate temperature sensor (16) disposed at a position inside a housing (20) that houses the second temperature sensor (14) and the intermediate temperature sensor (16) to detect an intermediate temperature (T ｉ ), the method according to claim 17, wherein the intermediate temperature (T ｉ ) is expected to have a value between the ambient temperature (T ｓ ) and the temperature (T ｆ ) of the fluid (26).

23. The method according to claim 17, comprising the step of measuring an estimated value of the density and / or the non-uniformity of the fluid (26) before measuring the flow rate (Q).

24. The method - The step of determining the flight time (t, t １ , t ２ ) of the ultrasonic waves (6, 8); - calculating a change in the speed of sound based on the flight time (t, t １ , t ２ ); - calculating a change in the predicted speed of sound (c) as a function of the detected temperature (T ｆ ) of the fluid (26); - determining whether the change in the predicted speed of sound (c) matches the change in the speed of sound (c) calculated based on the flight time (t, t １ , t ２ ); comprises the method according to claim 17.

25. The method is such that when the predicted speed of sound (c) does not match the change in the speed of sound calculated based on the flight time (t, t １ , t ２ ), based on the change in the speed of sound calculated based on the flight time (t, t １ , t ２ ), the method includes a step of calculating a correction value for the change in the density (ρ) of the fluid (26), the method according to claim 24.

26. The method is such that when the change in the predicted speed of sound (c) does not match the change in the speed of sound calculated based on the flight time (t, t １ , t ２ ), a corrected value of the specific heat capacity (c ｐ ) of the fluid (26) is calculated based on the corrected value of the density (ρ), the method according to claim 24, which is configured to do so.

27. The method includes calculating a correction value for the flow rate (Q) of the fluid (26) based on a change in the speed of sound calculated based on the flight times (t, t １ , t ２ ) when the predicted change in the speed of sound (c) does not match the change in the speed of sound calculated based on the flight times (t, t １ , t ２ ), the method according to claim 24.

28. The method according to claim 17, which is carried out by using a clamp-on flow sensor (1) configured to measure the flow rate (Q) of the fluid (26) from the outside of the tubular structure (2).

29. The method is carried out using an ultrasonic flow sensor (1), and the first detection unit (34) comprises at least one ultrasonic transducer (4, 4') arranged to transmit ultrasonic waves (6) and at least one ultrasonic transducer (4, 4') arranged to receive ultrasonic waves (8). The method according to claim 17.

30. The method - calculating a change in the predicted speed of sound (c) as a function of the detected temperature (T ｆ ) of the fluid (26); - automatically calculating a distance (L) traveled by the transmitted ultrasonic wave (6) and the received ultrasonic wave (8) in the fluid (26) based on a detected value of the speed of sound (c); comprises the method according to claim 17.

31. The method according to claim 17, comprising the step of estimating the thermal energy with a heating system or a cooling system.

32. A thermal energy meter (5) comprising the sensor (1) according to claim 1.

Images