Ultrasonic flow sensor and thermal energy sensor with non-invasive identification of no flow and improved accuracy - Patents.com

Abstract

An ultrasonic flow sensor (1) is disclosed that is configured to measure the flow rate (Q) of a fluid (26) flowing through a tubular structure (2). The flow sensor (1) comprises: a first detector (34) arranged to transmit and receive ultrasonic waves (6, 8) using at least one ultrasonic transducer (4, 4'); and a temperature (T f a temperature sensor (14) arranged and configured to detect the surrounding temperature (ambient temperature) (T s ), and a data processor (10) configured to receive data detected by the at least one ultrasonic transducer (4, 4') and the temperature sensor (12, 14). The flow sensor (1) comprises: a temperature sensor (12) arranged and configured to detect a temperature (T f ), - determine whether the change in the predicted speed of sound (c) corresponds to the change in the calculated speed of sound based on the time of flight (t, t1, t2) - based on the following criteria: A) the change in the predicted speed of sound (c) corresponds to the change in the calculated speed of sound based on the time of flight (t, t1, t2), and B) the temperature difference (ΔT sf ) is less than a predetermined level that is preset at a fixed level between 0.01 and 0.5°C, the no-flow state in which no fluid is flowing is identified.

Description

[Technical field]

[0001] The present invention relates generally to ultrasonic flow sensors, and more particularly to clamp-on ultrasonic flow sensors. The present invention further relates to a thermal energy meter using an ultrasonic flow sensor, and to a clamp-on ultrasonic thermal energy meter. [Background technology]

[0002] Flow measurement is widely used for industry, construction, and power systems. Flow can be detected using various types of flow sensors. Flow sensors in the prior art include mechanical flow sensors and ultrasonic flow sensors. Ultrasonic flow sensors are mainly used in two versions: the so-called delta time-of-flight for measurements in pure fluids (water, gas, manufacturing liquids, etc.) and the Doppler effect for measuring fluids containing many particles (slurries, liquids with bubbles, etc.).

[0003] There are known limitations in prior art ultrasonic flow velocities that limit the use of the technique. One of these limitations is the difficulty in detecting no flow (fluid stagnation in a pipe), which is required to detect sensor offset.

[0004] Although prior art ultrasonic flow sensors are typically reliable and accurate, it would be advantageous to improve the measurement accuracy. Additionally, it would be advantageous to provide an ultrasonic calorimeter with improved accuracy. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to provide a method and an ultrasonic flow sensor that can provide detection with no flow. It is also an object of the present invention to provide a method and an ultrasonic flow sensor that can provide a higher accuracy than the solutions known in the prior art. It is also an object of the present invention to provide an ultrasonic thermal energy meter that has a higher accuracy than known ultrasonic thermal energy meters. [Means for solving the problem]

[0006] The object of the present invention can be achieved by an ultrasonic flow sensor as defined in claim 1 and by a method as defined in claim 19. Preferred embodiments are defined in the dependent claims, explained in the following description and illustrated in the accompanying drawings.

[0007] The flow sensor according to the present invention is an ultrasonic flow sensor configured to measure the flow rate of a fluid through a tubular structure, the flow sensor comprising: a first detector arranged to transmit and receive ultrasonic waves using at least one ultrasonic transducer; - a temperature sensor arranged and configured to detect a temperature of the fluid; - a temperature sensor arranged and configured to detect a surrounding temperature (ambient temperature); a data processor configured to receive data detected by the at least one ultrasonic transducer and the temperature sensor; This flow sensor: - determining the time-of-flight of an ultrasonic wave and calculating the change in the speed of sound based on this time-of-flight; - Calculate the expected change in sound speed as a function of the temperature of the detected fluid; -to determine whether the predicted change in sound speed corresponds to a change in sound speed calculated based on time-of-flight; - Based on the following criteria: A) the predicted change in sound speed corresponds to the calculated change in sound speed based on time-of-flight; and B) The temperature difference between the surroundings and the fluid falls below a predetermined level, which is fixed at a level between 0.01 and 0.5°C. When the above condition is satisfied, the no-flow state where no fluid flows is identified. It is composed.

[0008] This allows for detection at no flow, thereby allowing the offset of the flow sensor to be identified.

[0009] The tubular structure may be a pipe or another structure through which a fluid flows. 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.

[0010] 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.

[0011] The data processor may be a microprocessor.

[0012] In an embodiment, the no-flow condition is used to calibrate the ultrasonic flow measurement calculations of the flow sensor to ensure stable and accurate ultrasonic flow measurements of the flow sensor.

[0013] In an embodiment, the ultrasonic flow sensor is configured to calculate a correction value for the change in fluid density based on the change in the calculated sound speed based on the time of flight if the expected sound speed does not correspond to the change in the calculated sound speed based on the time of flight, thereby providing an ultrasonic flow sensor that can provide higher accuracy than solutions known in the prior art.

[0014] In an embodiment, the ultrasonic flow sensor is configured to calculate a correction value for the specific heat capacity of the fluid based on a correction value for density if the expected change in sound speed does not correspond to the change in sound speed calculated based on the time of flight, thereby providing an ultrasonic flow sensor that can provide higher accuracy than solutions known in the prior art.

[0015] In an embodiment, the ultrasonic flow sensor is configured to calculate a correction value for the flow rate of the fluid based on the change in the speed of sound calculated based on the time of flight if the expected change in the speed of sound does not correspond to the change in the speed of sound calculated based on the time of flight, thereby providing an ultrasonic flow sensor that can provide higher accuracy than solutions known in the prior art.

[0016] In an embodiment, the first detection unit is configured to detect a flow rate above a predetermined low flow level, representing a low flow rate measurable using the first detection unit. The flow sensor comprises a second detection unit, which: a first temperature sensor arranged and configured to detect an ambient temperature; 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 surroundings and the fluid. The temperature difference is 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, in which the flow sensor can detect a flow rate depending on the temperature difference. The one or more measurements made in the flow calibration area are used to determine one or more parameters needed to determine how the flow rate depends on the temperature difference in the flow calibration area and in a flow area below the flow calibration area.

[0017] 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, and in particular is able to detect flow rates below low flow levels.

[0018] In an embodiment, the second detection unit is configured to estimate the flow rate below the low flow level based on a single measurement and predetermined data including the density and specific heat capacity of the fluid.

[0019] In one embodiment, the second detection unit is configured to estimate the flow rate below the low flow level based on two single measurements.

[0020] This allows the two measurements to be used to adjust the curve representing the relationship between flow rate and temperature difference.

[0021] This can be done because the curve has a known shape (which follows the relationship defined by equations (1) and (6) as shown in and described with reference to FIG. 8).

[0022] In an embodiment, the second detection unit is configured to estimate the flow rate below the low flow level based on two or more measurements made at the flow calibration area.

[0023] In an embodiment, the flow sensor periodically or continuously: - to perform one or more measurements in the flow calibration area, and - configured to update further parameters necessary to determine how the flow rate depends on the temperature difference in the flow rate calibration area and in the flow rate area below the flow rate calibration area.

[0024] This makes it possible to provide reliable flow measurements and to regularly adjust the parameters due to changing environmental conditions (e.g. increased ventilation, etc.) The flow sensor is configured to automatically perform the required number of measurements in the flow calibration area, and to calculate and update further parameters needed to determine how the flow rate depends on the temperature difference in the flow calibration area and in the flow area below the flow calibration area.

[0025] In one embodiment, the term "regularly or continuously" should be understood to mean once per second in an attempt to provide one or more measurements in the flow calibration area.

[0026] In one embodiment, the term "regularly or continuously" should be understood to mean once every 5 seconds in an attempt to provide one or more measurements in the flow calibration area.

[0027] In one embodiment, the term "regularly or continuously" should be understood to mean once every 10 seconds in an attempt to provide one or more measurements in the flow calibration area.

[0028] In one embodiment, the term "regularly or continuously" should be understood to mean once every 30 seconds in an attempt to provide one or more measurements in the flow calibration area.

[0029] In one embodiment, the term "regularly or continuously" should be understood to mean once per minute in an attempt to provide one or more measurements at the flow calibration area.

[0030] In one embodiment, the term "regularly or continuously" should be understood to mean once every two minutes in an attempt to provide one or more measurements in the flow calibration area.

[0031] In one embodiment, the term "regularly or continuously" should be understood to mean once every five minutes in an attempt to provide one or more measurements in the flow calibration area.

[0032] In one embodiment, the term "regularly or continuously" should be understood to mean once every 15 minutes in an attempt to provide one or more measurements in the flow calibration area.

[0033] In one embodiment, the term "regularly or continuously" should be understood to mean once every 30 minutes in an attempt to provide one or more measurements in the flow calibration area.

[0034] In one embodiment, the term "regularly or continuously" should be understood to mean once per hour in an attempt to provide one or more measurements in the flow calibration area.

[0035] In the embodiment, the flow rate (Q) and the temperature difference (ΔT sf ) is defined by the following formula:

[0036]

number

[0037]

number

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

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

[0040] In an embodiment, the (second) temperature sensor is arranged and configured to detect the temperature of the fluid by measuring the temperature on the outside of the tubular structure. This makes it possible to provide the flow sensor as a clamp-on flow sensor that can be attached to the outside of a tubular structure (such as a pipe). Thus, it is not necessary to bring the second temperature sensor into direct contact with the fluid.

[0041] In an embodiment, the data processor and the (second) temperature sensor are located inside the housing, providing a simple, easy to install and robust flow sensor.

[0042] In an embodiment, the (first) temperature sensor is located within the housing, which allows all components of the flow sensor to be provided within a single housing.

[0043] In an embodiment, the (first) temperature sensor is arranged outside the housing, which makes it possible to take into account the propagation of heat by convection.

[0044] In an embodiment, the second detection unit comprises an intermediate temperature sensor arranged and configured to detect an intermediate temperature at an internal location of the housing, which is assumed to have a temperature between the ambient temperature and the temperature of the fluid, thereby making it possible to provide additional information and thus an improved estimation of the flow rate in the low flow rate range.

[0045] 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.

[0046] 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.

[0047] In one embodiment, the flow sensor is configured to automatically calculate the distance L that the transmitted and received ultrasound travels through the fluid based on the detected speed of sound c. This allows the flow rate through a pipe to be measured without knowing the exact pipe dimensions, and allows accurate measurements to be made even if deposits build up on the inner surface of the pipe over time.

[0048] A thermal energy meter according to the present invention comprises a flow sensor according to the present invention.

[0049] In an embodiment, the second detection unit is integrated into the first detection unit.In an embodiment, the second detection unit and the first detection unit are provided as separate units.

[0050] In one embodiment, the second detection unit is communicatively connected to a storage device or external device containing information about how flow rate depends on temperature difference, and the data processor is configured to access and use this information so as to determine the flow rate based on the temperature difference.

[0051] The method according to the invention is a method for measuring the flow rate of a fluid through a tubular structure by means of an ultrasonic flow sensor comprising a first detection unit comprising: - at least one ultrasonic transducer is provided, arranged to transmit and receive ultrasonic waves by using at least one ultrasonic transducer, the ultrasonic flow sensor comprising a temperature sensor arranged and configured to detect a temperature of the fluid; The method comprises the steps of: - determining the time-of-flight of the ultrasound; - calculating the change in speed of sound based on time of flight; - calculating the expected change in sound speed as a function of the temperature of the detected fluid; - determining whether the predicted change in sound speed corresponds to a change in sound speed calculated based on time-of-flight; -The following criteria: A) the predicted change in sound speed corresponds to the calculated change in sound speed based on time-of-flight; and B) The temperature difference between the surroundings and the fluid falls below a predetermined level, which is fixed at a level between 0.01 and 0.5°C. and identifying a no-flow state, in which there is no flow of fluid, when the first and second thresholds are satisfied.

[0052] This makes it possible to provide detection at no flow rate. In this way, an offset can be identified.

[0053] In an embodiment, the no-flow condition is used to calibrate the ultrasonic flow measurement calculations of the flow sensor to ensure stable and accurate ultrasonic flow measurements of the flow sensor.

[0054] In one embodiment, the ultrasonic flow sensor is configured to calculate a correction for fluid density changes based on the calculated change in sound speed based on time of flight when the expected sound speed does not correspond to the calculated change in sound speed based on time of flight, which can improve the accuracy of the flow measurement.

[0055] This allows a correction value for the fluid density to be determined to provide a more accurate measurement.

[0056] In an embodiment, the method includes calculating a correction value for the specific heat capacity of the fluid based on a correction value for the density if the expected change in sound speed does not correspond to the change in sound speed calculated based on the time of flight, thereby making it possible to provide measurements with improved accuracy.

[0057] In one embodiment, the method includes calculating a correction value for the flow rate of the fluid based on the calculated change in sound speed based on the time of flight if the expected change in sound speed does not correspond to the change in sound speed calculated based on the time of flight, thereby improving the accuracy of the flow rate measurement.

[0058] In an embodiment, the first detection unit is configured to detect a flow rate above a predetermined low flow level, representing the lowest flow rate that can be measured using the first detection unit, and the method comprises: detecting a second detection unit; - To detect the surrounding temperature (ambient temperature) by means of a temperature sensor; - detecting the temperature of the fluid by a temperature sensor arranged and configured to detect the temperature of the fluid; - for estimating a flow rate below a low flow level based on a temperature difference between the surroundings and the fluid by a temperature sensor, The method comprises the steps of: a) performing one or more measurements by a first detection unit in a flow calibration area, in which the flow sensor is capable of detecting a flow rate depending on a temperature difference; b) applying one or more measurements made at the flow calibration area to determine one or more parameters required to determine how the flow rate depends on the temperature difference at the flow calibration area and at a flow area below the flow calibration area; and c) estimating a flow rate below the low flow level based on one or more measurements made at the flow calibration area.

[0059] This makes it possible to detect lower flow rates than with the prior art.

[0060] In an embodiment, the method includes performing two or more flow measurements in a flow calibration area.

[0061] In an embodiment, the method comprises regularly or continuously: - taking one or more measurements at a flow calibration area; and - updating further parameters needed to determine how the flow rate depends on the temperature difference in the flow rate calibration area and in the flow rate area below the flow rate calibration area; Includes.

[0062] In one embodiment, the flow rate (Q) and the temperature difference (ΔT sf ) is defined by the following formula:

[0063]

number

[0064]

number

[0065] In an embodiment, the temperature of the fluid is measured by a temperature sensor located on the outside of the tubular structure.

[0066] In an embodiment, the method includes detecting an intermediate temperature by an intermediate temperature sensor disposed at an interior position of a housing, the housing housing containing a temperature sensor for detecting a temperature of the fluid and the intermediate temperature sensor, the intermediate temperature being expected to have a value between the ambient temperature and the temperature of the fluid.

[0067] In an embodiment, the method includes the step of measuring the density and / or estimated inhomogeneity of the fluid prior to measuring the flow rate.

[0068] This allows for improved flow measurement and allows for the density and / or inhomogeneity of the fluid to be taken into account.

[0069] In one embodiment, the method includes a step of calculating a correction value for the specific heat capacity of the fluid if the detected value of the sound speed c does not correspond to the expected sound speed c as a function of the temperature of the detected fluid. This allows the flow sensor to be applied to provide a thermal energy meter with improved accuracy. Using the correction value for the specific heat capacity of the fluid ensures that the thermal energy meter delivers the most accurate measurement.

[0070] 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.

[0071] In one embodiment, the method includes automatically calculating the distance L traveled through the fluid by the transmitted and received ultrasound waves based on the detected values ​​of the speed of sound c (and optionally the measured time of flight). This makes it possible to measure the flow rate in a pipe without knowing the exact pipe dimensions. Accurate measurements can be made even if deposits are introduced on the inner surface of the pipe over time.

[0072] As a method for measuring the thermal energy of a fluid, the method according to the invention is applied to detect the flow rate of the fluid.

[0073] 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 liquid containing water. In one embodiment, the fluid is a gas.

[0074] The 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.

[0075] The first sensing unit may be a useful displacement meter, which 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.

[0076] The first detection unit may be configured as an ultrasonic flow sensor. In one embodiment, the first detection unit comprises one or more ultrasonic transducers. In one embodiment, the first detection unit comprises one or more ultrasonic transmitters and one or more ultrasonic receivers.

[0077] The data processor may be a microprocessor.

[0078] In one embodiment, the second detection unit includes a storage device containing information on how the flow rate depends on the temperature difference, and the data processor is configured to access and use this information to determine the flow rate based on the temperature difference. In a flow rate range below a low flow rate level, the second detection unit can determine the flow rate based on the temperature difference value. This can be achieved when the relationship between the flow rate and the temperature difference is known and stored in the storage device.

[0079] The predicted sound speed depends on the temperature of the detected fluid and can be calculated using a relationship between a given sound speed as a function of the temperature of the fluid. By way of example, if the fluid is pure water, the relationship between the predicted sound speed as a function of the temperature of the detected fluid is defined as illustrated in FIG.

[0080] If the fluid is different from pure water (e.g., water containing salt, sugar, or other substances), a different predetermined relationship between the predicted speed of sound as a function of the detected fluid temperature can be used.

[0081] The expected sound speed can be compared to the detected sound speed value by simply detecting and comparing the sound speed, which can be performed using the following equation (16): (16)

[0082]

number

[0083] A correction value for density and flow rate is calculated if the detected sound speed value does not correspond to the expected sound speed. The density correction value can be calculated using the following equation (18): (18)

[0084]

number

[0085] In one embodiment, the flow sensor is configured to calculate a correction value for the specific heat capacity of the fluid if the detected value of the sound speed c does not correspond to the expected sound speed c as a function of the temperature of the detected fluid. This allows the flow sensor to be applied to provide a thermal energy meter with improved accuracy. Using the correction value for the specific heat capacity of the fluid ensures that the thermal energy meter delivers the most accurate measurement.

[0086] In one embodiment, the fluid is a liquid, hi one embodiment, a water-containing liquid, hi one embodiment, the fluid is a gas.

[0087] In one embodiment, the method comprises the steps of: - storing information about how the flow rate depends on the temperature difference; using this information to determine a flow rate based on the temperature difference.

[0088] This allows the stored information to be used to provide flow rate estimates in a simple and reliable manner. The information can be stored on an external device. In one embodiment, the information is stored on a web-based service.

[0089] In one embodiment, the method comprises the steps of: - storing information about how the flow rate depends on the temperature difference in a second detection unit; using this information to determine a flow rate based on the temperature difference.

[0090] This allows the stored information to be used to provide an estimate of flow rate in a simple and reliable manner.

[0091] In one embodiment, the method is performed by a flow sensor with a data processor, the data processor and the second temperature sensor being disposed inside the housing.

[0092] In one embodiment, the method is performed with a flow sensor, where a first temperature sensor is disposed within the housing.

[0093] In one embodiment, the method is performed with a flow sensor, where the first temperature sensor is disposed outside the housing.

[0094] In one embodiment, the method comprises the steps of: - carrying out one or more measurements on a sample of the fluid; - applying one or more measurements to calculate the density of the fluid and / or the estimated fluid inhomogeneity prior to measuring the fluid.

[0095] In one embodiment, the estimated fluid heterogeneity corresponds to the content of one or more substrates in the fluid, which may be one of the following additional substances: sugar, salt, ethylene, glycol, glycerol, propylene glycol.

[0096] The present invention will be more fully understood from the detailed description given hereinafter. The accompanying drawings are given by way of example only and do not limit the invention. [Brief description of the drawings]

[0097] [Figure 1A] 1 is a graph showing the temperature difference between the surroundings and the fluid flowing through the pipe as a function of the flow rate of the fluid through the pipe. [Figure 1B] 1B is a graph showing the low flow rate portion of the graph shown in FIG. 1A. [Figure 2A] 1 is a schematic diagram of a clamp-on flow sensor according to the present invention; [Figure 2B] FIG. 2 is a schematic diagram of another clamp-on flow sensor according to the present invention. [Figure 3A] 1 is a schematic diagram of a flow sensor according to the present invention; [Figure 3B] 2 is a schematic diagram of another flow sensor according to the present invention; [Figure 4A] FIG. 1 is a schematic diagram of a clamp-on flow sensor according to the present invention mounted on the outside of a pipe. [Figure 4B] 2 is a schematic diagram of another flow sensor according to the present invention; [Figure 5A] 1 is a schematic diagram of a flow sensor according to the present invention; [Figure 5B] 2 is a schematic diagram of another flow sensor according to the present invention; [Figure 6A] 1 is a schematic diagram of a flow sensor according to the present invention; [Figure 6B] 2 is a schematic diagram of another flow sensor according to the present invention; [Figure 7] 1 is a graph showing the speed of sound in water as a function of water temperature. [Figure 8] 1 is a graph showing flow rate as a function of temperature differential. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0098] Referring now in detail to the figures intended to illustrate preferred embodiments of the invention, the temperature difference ΔT between the surroundings and the fluid flowing through the pipe as a function of the flow rate Q of the fluid through the pipe is sf A graph 28 representing is illustrated in FIG. 1A.

[0099] Graph 28 (represented by a solid line) shows the flow rate at low flow levels Q A At low flow levels Q A represents the lowest flow rate that can be measured by the prior art flow sensor. However, at low flow levels Q A below which the graph 28 is extrapolated. This low region 30 is represented by the dotted oval.

[0100] FIG. 1B illustrates the low flow portion 30 in the graph 28 shown in FIG. 1A. Prior art flow sensors A Although the flow sensor and method according to the present invention cannot detect flow rates below this low flow level Q A A flow measurement below .mu.m can be provided.

[0101] Basic flow level Q B When the temperature difference ΔT exceeds sf is constant, so the flow rate Q is irrelevant.

[0102] Low flow level Q A and the basic flow level Q B In the flow rate calibration area B2, the temperature difference ΔT sf increases as a function of the flow rate Q. In this flow calibration region B2, a first measurement M1 of the flow sensor and a second measurement M2 of the flow sensor are represented.

[0103] How does the flow rate Q change the temperature difference ΔT in the flow rate calibration area B2 and the flow rate area B1 below the flow rate calibration area B2? sf It is possible to use one or more of the flow sensor measurements made in flow calibration area B2 to determine the parameters needed to determine how the flow rate depends on the flow rate.

[0104] Temperature difference ΔT as a function of flow rate Q sf is given by the following equation (1). (1)

[0105]

number

[0106] Thus, in the flow region B1 where the flow sensor cannot provide any measurement, the flow rate Q M3 It is possible to determine the flow rate Q M3 is the measured temperature difference ΔT detected by the flow sensor M3 Based on the above, it can be determined that the flow rate Q M3 is expressed by formula (1), or the detected temperature difference ΔT sf This can be determined by the following equation (2), which defines the flow rate Q as a function of: (2)

[0107]

number

[0108] The flow sensor and method according to the present invention detects the temperature difference ΔT between the surroundings and the fluid flowing through the pipe. sf By measuring the low flow level Q A This estimation is possible because one or more flow measurements M1, M2 made in flow calibration region B2 are used to determine the unknowns in equation (1) or equation (2). In this way, any flow rate Q in flow region B1 can be calculated using equation (2).

[0109] In Fig. 1B, it can be seen that the first flow rate Q1 is detected based on the measured first temperature difference ΔT1. Similarly, Fig. 1B shows that the first flow rate Q2 is detected based on the measured second temperature difference ΔT2.

[0110] Low flow level Q A is the measured temperature difference ΔT A Similarly, the basic flow level Q B is the measured higher temperature difference ΔT B Corresponds to.

[0111] The temperature difference can be detected using a temperature sensor, which is a sensor according to the invention, as shown and described with reference to Figures 2A, 2B, 3A, 3B and 4B.

[0112] In one embodiment, a flow sensor according to the present invention used to measure water at 20° C. in flow calibration area B2 is applied for measurement at point M2, which is 2 ml / s (i.e. 0.000002 m 3 / s) flow rate Q M2 , and a temperature difference of 10°C ΔT M2 Corresponds to.

[0113] Temperature difference between the surroundings and the fluid, ΔT sf The relationship between the flow rate Q and the pressure is given by equation (2): (2)

[0114]

number

[0115] [Table 1]

[0116] In another example, a 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 and the following values ​​can be calculated: Table 2

[0117] [Table 2]

[0118] 2A illustrates a schematic of a clamp-on flow sensor 1 according to the 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.

[0119] The flow sensor 1 comprises a first temperature sensor 12 arranged to detect the ambient temperature (temperature around 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 generator 4 and a second ultrasonic generator 4'. The wave generators are formed as piezoelectric transducers 4, 4' arranged and configured to generate ultrasonic waves, which 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 of 1 / 2L. The total travel distance is therefore L.

[0120] The piezoelectric transducers 4, 4' are operated as transducers to detect the flow rate Q through the pipe using acoustic waves 6, 8. In one embodiment, the flow sensor 1 comprises several piezoelectric transducers 4, 4' to make the flow rate Q in the pipe 2 less dependent on the cross section. The operating frequency depends on the application and can be in the 100-200 kHz frequency range for gases and in the higher MHz frequency range for liquids.

[0121] In one embodiment, the flow sensor 1 is a Doppler effect 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 the ultrasonic waves 6 and receiving the ultrasonic waves 8. In a Doppler effect 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 faster the liquid flows, the greater the frequency shift between the emitted and reflected waves.

[0122] 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 the other piezoelectric transducer 4' can be used to receive the reflected ultrasonic waves 8.

[0123] In one embodiment, the flow sensor 1 is a propagation-based flow sensor 1. In this embodiment, the flow sensor 1 applies two piezoelectric transducers, operating as both transmitter and receiver, arranged at an angle to the flow Q direction. The transmission of ultrasonic waves in a flowing medium generates 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 of the flow Q and in the opposite direction. The propagation-based measurement method is independent of the sound propagation speed and therefore of the medium. In this way, it is possible to measure different liquids or gases using the same setup.

[0124] The temperature sensors 12, 14 and the piezoelectric transducers 4, 4' are connected to a data processor 10. This allows the data processor 10 to process data from the temperature sensors 12, 14 and the piezoelectric transducers 4, 4' and thereby to detect the flow rate based on this data.

[0125] 2A, the second temperature sensor 14 is placed 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 usually correspond to or be very close to the temperature of the fluid 26 inside the pipe 2.

[0126] In the low flow region, 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. Indeed, 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 The flow rate is determined based on the above. (9)ΔT sf =|T s -T f | Here, T s is the surrounding 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.

[0127] Figure 2B illustrates a schematic of a clamp-on flow sensor 1 according to the 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. A 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 this structure. Both ultrasound waves 6, 8 are shown to travel a distance of 1 / 2L. The total travel distance is therefore L.

[0128] 3A illustrates a schematic 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 comprises a housing 20 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 liquid containing water) in the pipe 2.

[0129] The flow sensor 1 detects the surrounding temperature (e.g., 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 comprises a second temperature sensor 14 arranged to detect an intermediate temperature T i A third temperature sensor 16 is arranged to detect the intermediate temperature T i is the ambient temperature T s and the temperature T of fluid 26 f It was predicted that the value would be between .

[0130] 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 that are 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 and described with reference to Figures 2A and 2B.

[0131] 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 thus able to process data from the temperature sensors 12, 14 and the piezoelectric transducers 4, 4' and thereby detect the flow rate based on this data.

[0132] The third temperature sensor 16 located provides a temperature measurement that can be applied to provide the flow sensor 1 with an improved estimate of the flow rate below low flow levels. The improved estimate is based on the difference between two temperatures: - Difference ΔT between the surroundings and the fluid 26 sf : (10)ΔT sf =|T s -T f | and - temperature difference ΔT between an intermediate point in the housing 20 and the fluid 26 i f: (11)ΔT i f=|T i -T f | This can be achieved by using:

[0133] The thermal energy meter 5 comprises an external temperature sensor 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 amount of heat (thermal energy) consumed. 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.

[0134] Fig. 3B illustrates a schematic of another 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 placed on the outer surface of the housing 20. The thermal energy meter 5 comprises a temperature sensor 17 mounted on the outer surface of the supply 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 amount of heat (thermal energy) consumed.

[0135] 4A illustrates a schematic of a clamp-on flow sensor 1 according to the present invention. The flow sensor 1 is attached to the outside of a pipe 2. The flow sensor 1 comprises a housing 20 having a contact structure that matches the outer shape of the pipe 2. A thermal connection structure (e.g. a metal layer) is attached to the contact structure. The thermal connection structure thereby reduces the thermal resistance, thereby providing an improved and efficient heat transfer between the pipe 2 and a temperature sensor (not shown) of the flow sensor 2.

[0136] In one embodiment, the thermal connection structure is a metal foil coated with thermal adhesive on each side. Such a thermal connection structure can provide a permanent attachment and reduces thermal resistance by filling micro air voids at the joint. In one embodiment, the thermal connection structure is a thermally conductive aluminum tape. The thermal connection structure is a thermally conductive double-sided structural adhesive aluminum tape.

[0137] 4B is a schematic diagram of a flow sensor 2 according to the present invention. The flow sensor 2 comprises a mechanical flow detection unit 24, which is placed inside the pipe 3 and is therefore submerged in the fluid 26.

[0138] The flow sensor 1 is a useful displacement meter that requires the fluid to be directed to a mechanical displacement component of the 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 may be detected by using a direct connection to the data processor 10 or by 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 flow 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.

[0139] The flow sensor 1 comprises a first temperature sensor 12 arranged and configured to detect a surrounding temperature (e.g., ambient temperature). The flow sensor 1 comprises a second temperature sensor 14 arranged and configured to detect a temperature of the fluid 26 inside the pipe 3. The second temperature sensor 14 rests against an outer portion of the wall of the pipe 3. However, in another embodiment, the second temperature sensor 14 may be located inside the pipe 3. In another embodiment, the second temperature sensor 14 may be integrated into the wall of the pipe 3.

[0140] The flow sensor 1 comprises a pipe 3 provided with a first flange 18 and a second flange 18'. These flanges 18, 18' are mechanically connected to corresponding flanges 19, 19' of the two pipes 2, 2'. In one embodiment, the flanges 18, 18' are replaced with similar mounting structures designed to mount the flow sensor 1 to the pipes 2, 2'.

[0141] In one embodiment, the distal portions of the pipes 2, 2' are provided with male threads, while the distal portion of the flow sensor 3 is provided with corresponding female threads, allowing the pipe 3 to be screwed onto the pipes 2, 2'.

[0142] In one embodiment, the distal portions of the pipes 2, 2' are provided with female threads, while the distal portion of the pipe 3 of the flow sensor 3 is provided with corresponding male threads, allowing the pipe 3 to be screwed onto the pipes 2, 2'.

[0143] Figure 5A is a schematic diagram of a flow sensor 1 according to the invention. The flow sensor 1 essentially corresponds to the one shown in Figure 3A.

[0144] Figure 5B is a schematic diagram of a flow sensor 1 according to the invention. The flow sensor 1 essentially corresponds to the one shown in Figure 3B.

[0145] 5A and 5B, however, the housing 20 comprises a portion that rests against the pipe 2, while the second temperature sensor 14 as well as the piezoelectric transducers 4, 4' extend through said portion of the housing 20 for direct connection to an outer portion of the pipe 2 when the flow sensor 1 is mounted on the pipe 2. It is possible to apply a fastening structure, such as a cable tie or a hose clamp, for fastening the flow sensor to the pipe 2.

[0146] 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.

[0147] The flow sensor 1 according to the present invention takes advantage of the fact that the fluid 26 will most likely transfer heat between the physical zones through which it flows, and that these physical zones will have different temperatures. By detecting the temperature difference between these zones, it is possible to provide a surrogate measurement for the flow rate.

[0148] Therefore, the flow sensor 1 and method according to the present invention is able to detect flow rates in the low flow range, where prior art flow sensors are unable to detect any flow rate.

[0149] Furthermore, the flow sensor 1 and method according to the present invention may provide an overall improved (more accurate) flow detection by utilizing the temperature differences between the above-mentioned zones.

[0150] The amount of heat transfer from a fluid to its surroundings, q (corresponding to E / t), is defined by the following equation (12): (12)q = UAΔT sf Here, ΔT sf 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.

[0151] The heat transfer coefficient U is defined by the following equation (13). (13) U = k / s where k is the thermal conductivity of the material through which the heat transfer occurs, and s is the thickness of the material through which the heat transfer occurs.

[0152] The working principle of the Doppler effect flow sensor 1 is shown in FIG. 6A and will be generally described with reference thereto. The Doppler effect flow sensor is affected by changes in the speed of sound in the fluid 26. Therefore, the Doppler effect flow sensor is sensitive to changes in density and temperature in the fluid 26. Therefore, many Doppler effect flow sensors in the prior art are not suitable for highly accurate measurement applications. However, the present invention is capable of detecting the temperature and speed of sound in the fluid 26 and compensating for temperature and fluid (density) changes, thus providing improved accuracy. Similarly, the present invention is capable of detecting the density of the fluid 26 (through taking measurements of a sample of the fluid 26) and compensating for temperature and / or fluid (density) changes to further improve the accuracy of the flow sensor 1.

[0153] The Doppler effect flow sensor 1 is a time-of-flight ultrasonic flow sensor, which measures the time it takes for sound to travel between a transmitter 4 and a receiver 4'. In a typical setup, such as the one illustrated in Figure 6A, two transducers (transmitter / receiver) 4, 4' are placed on either side of a pipe 2 in which the flow rate Q is to be measured. The transmitters 4, 4' transmit pulsatile ultrasound 6 at a given frequency from one side to the other. The average fluid velocity V is proportional to the difference in frequencies.

[0154] Therefore, the fluid velocity V can be expressed as: (14)

[0155]

number

[0156] The flow rate Q is determined by the fluid velocity V and the cross-sectional area A of pipe 2. pipe It can be calculated as the product between: (15)q=VA pipe

[0157] At the same time, the speed of sound c is given by the following equation (16): (16)

[0158]

number

[0159] The flow sensor 1 shown in Figure 6A comprises a first temperature sensor 12 arranged to detect the ambient temperature (the temperature around 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 thereby able to process the data and calculate the flow rate Q based on the data from the temperature sensors 12, 14 and the two transducers 4, 4'.

[0160] The operating principle of the Doppler effect flow sensor 1 for measuring the flow rate in a fluid containing particles 32 is shown in and will be briefly described with reference to FIG. 6B.

[0161] The fluid velocity V can be calculated using the following equation (17): (18)

[0162]

number

[0163] The flow rate Q is determined by the fluid velocity V and the cross-sectional area A of pipe 2. pipe It can be calculated as the product between: (15) Q = VA pipe

[0164] Equations 15 and 16 can also be used when calculating flow rates using the flow sensors shown in Figures 2A, 2B, 3A, and 3B.

[0165] Figure 7 is a graph representing the speed of sound in water c as a function of the water's temperature T. However, similar graphs can be made for other fluids. In the following, water simply represents a considered fluid and water can be replaced by another liquid.

[0166] When the dimensions of a tubular structure (such as a pipe) through which a flow rate Q of water flows are unknown, an estimation of the distance L that sound travels in water is necessary. This problem applies in particular to ultrasonic clamp-on sensors. Over time, deposits can be brought to the inner surface of the pipe. This will gradually reduce the distance L. The present invention accordingly enables the estimation of the distance L under such circumstances.

[0167] By determining the speed of sound in water, c, it is possible to estimate the distance L, thereby improving the accuracy of the detected water velocity V and flow rate Q. Thus, the change in the speed of sound in water, c, is highly relevant.

[0168] When the speed of sound c is found, it is possible to calculate the distance L that sound travels in water.

[0169] The speed of sound, c, is given by the following equation (12): (18)c=√K / ρ where K is the bulk modulus and ρ is the density.

[0170] Since 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 (such as glycol) in the water.

[0171] When the tilt angle α is known, the average water velocity V in the pipe (measured by delta time of flight) can be found using the following equation (19): (19)

[0172]

number

[0173] When the speed of sound c is known, L can be calculated or estimated (since t1 and t2 are measured) using the following equation (16): (16)

[0174]

number

[0175] Thus, the flow rate Q is determined by the average water velocity V and the cross-sectional area A of the pipe 2. pipe It can be calculated as the product between: (15) Q = VA pipe

[0176] Using the measured fluid temperature T and the measured time of flight, the density ρ and speed of sound c can be determined by using equation (18).

[0177] When the flow sensor is calibrated in pure water at a temperature T2 of 26° C., FIG. 7 shows that the sound speed c (at T2) is 1500 m / s. When a lower temperature T1 of 21.5° C. is detected, the sound speed c (at T1) is 1485 m / s. Thus, by calibrating the flow sensor using a fluid (e.g., a liquid such as water) at known temperature T and density ρ, a simple temperature measurement is sufficient to detect the sound speed c by using equation (18). (18)c=√K / ρ

[0178] The specific heat capacity of a fluid (eg, water) depends on the content of additional substances (eg, sugar, salt, ethylene glycol, glycerol, or propylene glycol).

[0179] When the sound speed c is known, it is possible to calculate the specific heat capacity of a fluid (e.g. water) with additional substances based on the density of the detected fluid, which can make the thermal energy meter with the flow sensor according to the present invention more accurate.

[0180] It may be advantageous to measure the content of additional substances (e.g. sugar, salt, ethylene glycol, glycerol, or propylene glycol) so that the flow sensor can be calibrated based on these measurements.

[0181] [Example 1] If 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 speed of sound c (at T2) is 1500 m / s.

[0182] When the speed of sound c (1500 m / s) is known, L can be calculated using the following equation (16) (since t1 and t2 are detected by the flow sensor): (16)

[0183]

number

[0184] When the flow sensor is used at a later time, the predicted sound speed c at the same temperature T2 of 26°C will be 1500 m / s. However, if the detected sound speed c calculated using Eq. (16) and the known L is 1485 m / s, the decrease in sound speed is approximately 1%. This can be caused by the change in density ρ of water. Assuming the bulk modulus K is constant, Eq. (18) results in an increase in density ρ of approximately 2% (using Eq. 18).

[0185] If the flow sensor is used in a thermal energy meter, it is possible to correct the heat capacity of a particular water based on the detected water density. It can then be concluded that the content of the additional substance (e.g. sugar, salt, ethylene glycol, glycerol, or propylene glycol) has increased. In this way, it is possible to improve the accuracy of the thermal energy meter. This is true because the content of the additional substance (e.g. sugar, salt, ethylene glycol, glycerol, or propylene glycol) can change over time. If the flow sensor is configured to automatically detect changes in the fluid density, the thermal energy meter can be used in the flow sensor, allowing for high accuracy even if the content of the additional substance changes over time.

[0186] FIG. 8 shows a flow rate Q detected by the flow sensor according to the present invention, as a function of a temperature difference ΔT sf Illustrate a graph showing the relationship between

[0187] Low flow level Q A represents the lowest flow rate that can be measured by the prior art flow sensor. Prior art flow sensors are sensitive to low flow levels Q A and the flow sensor and method according to the present invention cannot detect flow rates below this low flow level Q A A flow measurement below .mu.m can be provided.

[0188] Basic flow level Q B above the temperature difference ΔT sf is constant and therefore independent of the flow rate Q.

[0189] Low flow level Q A and the basic flow level Q B In the flow rate calibration area B2, the temperature difference ΔT sf increases as a function of the flow rate Q. In this flow calibration region B2, a first flow sensor measurement M1 and a second flow sensor measurement M2 are represented.

[0190] The measurements M1 and M2 of these flow sensors show how the flow rate Q is proportional to the temperature difference ΔT in the flow calibration region B2 and in the flow region B1 below the flow calibration region B2. sf A flow calibration is performed in the flow calibration area B2 to determine the parameters that are needed to determine the dependence of the flow rate Q and the temperature difference ΔT. sf The relationship between is given by equation (2): (2)

[0191]

number

[0192] Temperature difference ΔT1, ΔT M3 It is possible to measure ΔT and ΔT2 and calculate the flow rate Q using equation (2). [Explanation of symbols]

[0193] 1 Flow Sensor 2, 2', 3 pipes 4, 4' Ultrasonic transducer (piezoelectric transducer) 5. Heat Energy Meter 6. Ultrasonic vibration waves 8 Reflected ultrasonic vibration waves 10 Data processors (microprocessors) 12 Temperature Sensor 14 Temperature Sensor 16 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 rate calibration area c p Specific Heat Capacity k Thermal conductivity U heat transfer coefficient A surface area W Volume t Time of Flight t' Time of Flight to Compensate for Temperature Δt Delta Time of Flight t1, t2 time of flight dt1, dt2 temperature difference dt A , dt B temperature difference dt M1 , dt M2 temperature difference dt M3 temperature difference s 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 fluid velocity α angle L distance

Claims

1. An ultrasonic flow sensor (1) configured to measure the flow rate (Q) of a fluid (26) flowing through a tubular structure (2), A first detection unit (34) arranged to transmit and receive ultrasonic waves (6, 8) by using at least one ultrasonic transducer (4, 4'); A temperature sensor (14) arranged and configured to detect the temperature (T ｆ of the fluid (26). The temperature around (ambient temperature) (T ｓ ), a temperature sensor (12) arranged and configured to detect A data processor (10) configured to receive data detected by at least one of the ultrasonic transducers (4, 4') and the temperature sensors (12, 14), wherein the flow sensor (1) Determine the time of flight (t, t １ , t ２ ) of the ultrasonic waves (6, 8), and calculate the change in the speed of sound based on the time of flight (t, t １ , t ２ ). As a function of the temperature (T ｆ ) of the detected fluid (26), calculate the predicted change in the speed of sound (c), Whether the predicted change in the speed of sound (c) corresponds to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ). is configured to identify a no-flow state where there is no flow rate of the fluid (26) when the following criteria, namely, A) The change in the predicted speed of sound (c) corresponds to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ), and B) The temperature difference (ΔT ｓｆ ) between the surroundings and the fluid (26) falls below a predetermined level preset at a fixed level between 0.01 and 0.5 °C, are satisfied. A flow sensor (1), characterized in that it is configured in this way.

2. The no-flow state is used to calibrate the ultrasonic flow measurement calculation of the flow sensor (1) in order to ensure stable and accurate ultrasonic flow measurement of the flow sensor (1). The flow sensor (1) according to claim 1.

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

4. If the expected change in the speed of sound (c) does not correspond to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ), the flow rate sensor (1) according to claim 3, configured to calculate a correction value of a specific heat capacity (c ｐ ) in the fluid (26) based on a correction value of the density (ρ).

5. If the predicted change in the speed of sound (c) does not correspond to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ), the flow rate sensor (1) according to claim 3, which is configured to calculate a correction value for the change in the flow rate (Q) of the fluid (26) based on the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ).

6. The first detection unit (34) detects a flow rate (Q) that exceeds a predetermined low flow rate level (Q Ａ ), which represents a low flow rate (Q Ａ ) that can be measured using the first detection unit (34). The flow rate sensor (1) includes a second detection unit (36), and the second detection unit (36) is The ambient temperature (ambient temperature) (T ｓ ) and a first temperature sensor (12) arranged and configured to detect Comprising a data processor (10) connected to the temperature sensors (12, 14), The second detection unit (36) estimates a flow rate (Q) below the low flow rate level (Q) based on a temperature difference (ΔT) between the surroundings and the fluid (26). ｓｆ ), and is configured to estimate a flow rate (Q) below the low flow rate level (Q) based on the temperature difference (ΔT). Ａ ), where the temperature difference (ΔT) is measured by the first temperature sensor (12) and the second temperature sensor (14). The second detection unit (36) is configured to estimate a flow rate (Q) below the low flow rate level (Q) based on one or more measurements (M, M) made in the flow rate calibration region (B). ｓｆ ), where in the flow rate calibration region (B), the flow rate sensor (1) can detect the flow rate (Q) depending on the temperature difference (ΔT). The one or more measurements (M, M) made in the flow rate calibration region (B) are used to determine one or more parameters required to determine how the flow rate (Q) depends on the temperature difference (ΔT) in the flow rate calibration region (B) and in the flow rate region (B) below the flow rate calibration region (B). The flow rate sensor (1) according to claim 1. ２ ), and is configured to estimate a flow rate (Q) below the low flow rate level (Q) based on one or more measurements (M, M) made in the flow rate calibration region (B). １ , M ２ ), where in the flow rate calibration region (B), the flow rate sensor (1) can detect the flow rate (Q) depending on the temperature difference (ΔT). The one or more measurements (M, M) made in the flow rate calibration region (B) are used to determine one or more parameters required to determine how the flow rate (Q) depends on the temperature difference (ΔT) in the flow rate calibration region (B) and in the flow rate region (B) below the flow rate calibration region (B). The flow rate sensor (1) according to claim 1. Ａ ), and is configured to estimate a flow rate (Q) below the low flow rate level (Q) based on one or more measurements (M, M) made in the flow rate calibration region (B). ２ ), where in the flow rate calibration region (B), the flow rate sensor (1) can detect the flow rate (Q) depending on the temperature difference (ΔT). The one or more measurements (M, M) made in the flow rate calibration region (B) are used to determine one or more parameters required to determine how the flow rate (Q) depends on the temperature difference (ΔT) in the flow rate calibration region (B) and in the flow rate region (B) below the flow rate calibration region (B). The flow rate sensor (1) according to claim 1. ｓｆ ), and is configured to estimate a flow rate (Q) below the low flow rate level (Q) based on one or more measurements (M, M) made in the flow rate calibration region (B). ２ ), where in the flow rate calibration region (B), the flow rate sensor (1) can detect the flow rate (Q) depending on the temperature difference (ΔT). The one or more measurements (M, M) made in the flow rate calibration region (B) are used to determine one or more parameters required to determine how the flow rate (Q) depends on the temperature difference (ΔT) in the flow rate calibration region (B) and in the flow rate region (B) below the flow rate calibration region (B). The flow rate sensor (1) according to claim 1. １ , M ２ ), and is configured to estimate a flow rate (Q) below the low flow rate level (Q) based on one or more measurements (M, M) made in the flow rate calibration region (B). ２ ), where in the flow rate calibration region (B), the flow rate sensor (1) can detect the flow rate (Q) depending on the temperature difference (ΔT). The one or more measurements (M, M) made in the flow rate calibration region (B) are used to determine one or more parameters required to determine how the flow rate (Q) depends on the temperature difference (ΔT) in the flow rate calibration region (B) and in the flow rate region (B) below the flow rate calibration region (B). The flow rate sensor (1) according to claim 1. ２ ), and is configured to estimate a flow rate (Q) below the low flow rate level (Q) based on one or more measurements (M, M) made in the flow rate calibration region (B). １ ), where in the flow rate calibration region (B), the flow rate sensor (1) can detect the flow rate (Q) depending on the temperature difference (ΔT). The one or more measurements (M, M) made in the flow rate calibration region (B) are used to determine one or more parameters required to determine how the flow rate (Q) depends on the temperature difference (ΔT) in the flow rate calibration region (B) and in the flow rate region (B) below the flow rate calibration region (B). The flow rate sensor (1) according to claim 1. ｓｆ ), where in the flow rate calibration region (B), the flow rate sensor (1) can detect the flow rate (Q) depending on the temperature difference (ΔT). The one or more measurements (M, M) made in the flow rate calibration region (B) are used to determine one or more parameters required to determine how the flow rate (Q) depends on the temperature difference (ΔT) in the flow rate calibration region (B) and in the flow rate region (B) below the flow rate calibration region (B). The flow rate sensor (1) according to claim 1.

7. The second detection unit (36) performs a single measurement (M １ , M ２ ), and is configured to estimate a flow rate (Q) below the low level (Q Ａ ) based on predetermined data including the density (ρ) and the specific heat capacity (Cp) of the fluid (26). The flow rate sensor (1) according to claim 6.

8. The second detection unit (36) is based on two or more measurements (M ２ ), M １ ), made in the flow calibration region (B ２ ), and is configured to estimate a flow rate (Q) below the low flow rate level (Q Ａ ). The flow sensor (1) according to claim 6.

9. Regularly or continuously, Flow correction area (B ２ ) perform one or more measurements (M １ , M ２ ), and How the flow rate (Q) is in the flow rate calibration region (B ２ ), and the flow rate region (B ２ ) below the flow rate calibration region (B １ ), to update further parameters required to determine whether it depends on the temperature difference (ΔT ｓｆ ), the flow sensor (1) according to claim 6, which is configured as such.

10. The dependence between the flow rate (Q) and the temperature difference (ΔT ｓｆ ) is defined by the following mathematical formula, 【Number 1】 or 【Number 2】 Here, C １ is a constant, and ΔT Ｂ is the temperature difference corresponding to the basic flow rate level, the flow rate sensor (1) according to claim 6.

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

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

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

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

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

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

17. Based on the detected value of the speed of sound (c), the ultrasonic wave (6) transmitted and the ultrasonic wave (8) received are configured to automatically calculate the distance (L) traveled by the fluid (26). The flow sensor (1) according to claim 1.

18. A heat energy meter (5) comprising the flow sensor (1) according to claim 1.

19. A method for measuring the flow rate (Q) of a fluid (26) flowing through a tubular structure (2) by means of an ultrasonic flow sensor (1), comprising a first detection unit (34), wherein in the first detection unit (34), At least one ultrasonic transducer (4, 4'), arranged to transmit and receive ultrasonic waves (6, 8) by using at least one of said ultrasonic transducers (4, 4'), said ultrasonic flow sensor (1) having a temperature sensor (14) arranged and configured to detect the temperature (T ｆ ) of the fluid (26), is provided with at least one ultrasonic transducer (4, 4'). wherein the method Step of determining the time of flight (t, t １ , t ２ ) of the ultrasonic waves (6, 8) and The step of calculating the change in the speed of sound based on the time of flight (t, t １ , t ２ ); Calculating a change in a predicted speed of sound (c) as a function of the temperature (T ｆ ) of the detected fluid (26); Step of determining whether the change in the predicted speed of sound (c) corresponds to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ); the following criteria A) The change in the predicted speed of sound (c) corresponds to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ), and B) The temperature difference (ΔT ｓｆ ) between the surroundings and the fluid (26) falls below a predetermined level set in advance at a fixed level between 0.01 and 0.5 °C. when satisfied, identifying a no-flow state in which the fluid (26) has no flow rate, the method comprising.

20. The method according to claim 19, wherein the no-flow state is used to calibrate the ultrasonic flow measurement calculation of the flow sensor (1) in order to ensure a stable and accurate ultrasonic flow measurement of the flow sensor (1).

21. If the predicted speed of sound (c) does not correspond to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ), the method according to claim 19, comprising the step of calculating a correction value for the change in the density (ρ) of the fluid (26) based on the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ).

22. If the expected change in the speed of sound (c) does not correspond to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ), the method according to claim 19, comprising the step of calculating a corrected value of a specific heat capacity (c ｐ ) in the fluid (26) based on a corrected value of the density (ρ).

23. If the predicted change in the speed of sound (c) does not correspond to the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ), calculating a correction value of the flow rate (Q) of the fluid (26) based on the change in the speed of sound calculated based on the time of flight (t, t １ , t ２ ), the method according to claim 19, comprising the step of.

24. The first detection unit (34) detects a flow rate (Q) that exceeds a predetermined low flow rate level (Q Ａ ), which represents the lowest flow rate (Q Ａ ) that can be measured using the first detection unit (34). The method includes using a second detection unit (36). The temperature sensor (12) detects the surrounding temperature (ambient temperature) (T ｓ ) for detection purposes. The temperature (T of the fluid (26) ｆ ) is detected by a temperature sensor (14) arranged and configured to detect the temperature (T of the fluid (26) ｆ ), for detecting the temperature (T of the fluid (26). Based on the temperature difference (ΔT ｓｆ ) measured by the temperature sensors (12, 14) between the surroundings and the fluid (26), to estimate a flow rate (Q Ａ ) that is below the low flow rate level (Q ), comprising the step of applying to wherein the method a) In the flow rate calibration region (B ２ ), a step of performing one or more measurements (M １ , M ２ ) by the first detection unit (34), wherein in the flow rate calibration region (B ２ ), the flow rate sensor (1) can detect the flow rate (Q) depending on the temperature difference (ΔT ｓｆ ); and the step of performing b) How the flow rate (Q) is determined by the temperature difference in the flow rate calibration region (B ２ ), and the flow rate region (B ２ ) below the flow rate calibration region (B １ ), to determine one or more parameters required for determining whether it depends on the temperature difference in the flow rate region (B ２ ), applying one or more of the measurements (M １ , M ２ ) made in the flow rate calibration region (B ); c) based on one or more of said measurements (M ２ １ ２ ) made in said flow correction region (B), estimating a flow rate (Q) below said low flow rate level (Q Ａ ); the method of claim 19, comprising:​​​​​​​​

25. The step of performing flow rate measurement two or more times in the flow rate correction region (B ２ ) is included, and the method according to claim 24.

26. regularly or continuously, Flow correction area (B ２ ) performing said measurement (M １ , M ２ ) one or more times; How the flow rate (Q) is in the flow rate calibration region (B ２ ), and the flow rate region (B ２ ) below the flow rate calibration region (B １ ), to determine whether it depends on the temperature difference (ΔT ｓｆ ), and updating a further parameter required for this, the method according to claim 24, comprising.

27. The dependence between the flow rate (Q) and the temperature difference (ΔT ｓｆ ) is defined by the following mathematical formula, [Number 3] or, [Number 4] Here, C １ is a constant, and ΔT Ｂ is the temperature difference corresponding to the basic flow rate level, the method according to claim 24.

28. The temperature (T ｆ ) of the fluid (26) is measured by a temperature sensor arranged outside the tubular structure (2), the method according to claim 19.

29. A step of detecting an intermediate temperature (T ｉ ) by an intermediate temperature sensor (16) disposed at an inner position of a housing (20), wherein the housing (20) houses the temperature sensor (14) used for detecting the temperature (T ｆ ) of a fluid (26) and the intermediate temperature sensor (16), and the intermediate temperature (T ｉ ) is assumed to have a value between the ambient temperature (T ｓ ) and the temperature (T ｆ ) of the fluid (26). The method according to claim 19, comprising the detecting step.

30. The method according to claim 19, comprising the step of measuring the density and / or the estimated inhomogeneity of the fluid (26) before measuring the flow rate (Q).

31. The method according to claim 19, implemented 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).

32. The method according to claim 19, comprising the step of automatically calculating the distance (L) traveled by the transmitted ultrasonic wave (6) and the received ultrasonic wave (8) through the fluid (26) based on the detected value of the speed of sound (c).

33. A method for measuring the thermal energy of a fluid (26), applying the method according to claim 19 to detect the flow rate (Q) of the fluid.

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