Method of measuring water temperature in instrumentation

Abstract

A measuring method for measuring water temperature in a meter (1), comprising the following steps: · causing a transmitter transducer (3a) of the meter (1) to emit an ultrasonic measurement signal (8), and collecting an electrical measurement signal (Sm) generated by a receiver transducer (3b) of the meter (1); · measuring the speed of the ultrasonic measurement signal and the level of the electrical measurement signal (Sm) in water; · using the level of the electrical measurement signal to determine whether the water temperature is less than or greater than an inflection point temperature corresponding to an inflection point; · estimating the water temperature based on the speed of the ultrasonic measurement signal by using a first formula when the water temperature is less than the inflection point temperature, and by using a second formula when the water temperature is greater than the inflection point temperature.

Description

Technical Field

[0001] The present invention relates to the field of meters for measuring water consumption, and in particular to hot water meters and thermal energy meters. Background Art

[0002] Ultrasonic water meters usually include a pipe through which water flows and two piezoelectric transducers, including an upstream transducer and a downstream transducer. The transducers are placed at the end of a path defined in the pipe, and the length of the path is precisely known. The upstream transducer transmits an ultrasonic measurement signal, which propagates along the path from upstream to downstream and is received by the downstream transducer. The downstream transducer transmits an ultrasonic measurement signal, which propagates along the path from downstream to upstream and is received by the upstream transducer. The average velocity of the water is estimated based on the difference between the travel times, and the flow rate of the water is calculated based on its average velocity.

[0003] It is advantageous to be able to measure water temperature in meters, especially with hot water meters and thermal energy meters (TEMs), which can handle water at temperatures up to 130°C.

[0004] Specifically, both the water distributor and the customer want to have access to this information. When this information is available, the measured value of the water temperature will be displayed on the LCD screen of the meter and transmitted to the water distributor via a wireless link.

[0005] refer to Figure 1 It is known that for a given water flow rate, for example 6 liters per hour (L / h), the metering error associated with the flow rate (curve C1) depends on the water temperature. Therefore, it is very important to know the water temperature accurately in order to be able to make appropriate corrections to the flow rate measurement and thus ensure that the measurement performance complies with the OIML R 49 standard, which requires a measurement accuracy within ±5%.

[0006] Therefore, it is quite routine to install temperature probes in hot water meters or heat energy meters.

[0007] It should be observed that when measuring thermal energy, two temperature probes are usually used in a customer's facility: one probe is located at the facility entrance (located in the meter) and the other probe is located at the facility outlet.

[0008] The presence of a probe in a meter naturally increases the cost of the meter and reduces its reliability. Summary of the invention

[0009] The object of the invention is to reduce the cost and to improve the reliability of a water meter without reducing the accuracy of the measurements it makes.

[0010] To achieve this object, a measuring method for measuring water temperature is provided, which method is at least partially performed in a meter and comprises the following steps:

[0011] causing a transmitter transducer of the meter to emit an ultrasonic measurement signal and acquiring an electrical measurement signal generated by a receiver transducer of the meter when the ultrasonic measurement signal is received after having traveled along a path of defined length in the water;

[0012] · measuring the velocity of the ultrasonic measurement signal in water;

[0013] Measure the level of electrical measurement signals;

[0014] using the level of the electrical measurement signal to determine whether the water temperature is less than or greater than an inflection point temperature corresponding to an inflection point in a curve that plots the speed of sound in water as a function of water temperature;

[0015] The water temperature is estimated from the speed of the ultrasonic measurement signal by using the first formula when the water temperature is less than the inflection point temperature and by using the second formula when the water temperature is greater than the inflection point temperature.

[0016] The measuring method of the invention therefore makes it possible to estimate the water temperature from the speed of the ultrasonic measurement signal.

[0017] Unfortunately, a curve plotting the speed of sound in water as a function of water temperature exhibits an inflection point at the inflection temperature, in such a way that the same speed of sound can correspond to two different water temperatures.

[0018] Fortunately, the level of the electrical measurement signal received by the receiver transducer varies almost linearly as a function of the water temperature. Therefore, the level of the electrical measurement signal is used to determine whether the water temperature is before or after the inflection point, making it possible to select the "correct" formula for accurately estimating the "correct" temperature corresponding to the measured speed of the ultrasonic measurement signal. Therefore, the water temperature is measured in a very accurate manner even for temperatures exceeding the inflection point temperature.

[0019] Therefore, the measured water temperature can be used to correct the water flow rate measurement, making its flow rate measurement very accurate even if there is no temperature probe in the water meter.

[0020] For hot water meters, it is therefore no longer necessary to provide said meters with a temperature probe.

[0021] When measuring thermal energy, the probe in the meter can be omitted and only one probe (located at the facility outlet) is required to make the measurement.

[0022] Therefore, water meters are cheaper and more reliable.

[0023] A measurement method as described above is also provided, comprising, in order to determine whether the water temperature is less than or greater than the inflection point temperature, a step of comparing the level of the electrical measurement signal with a predefined threshold value equal to a first reference level of the electrical measurement signal multiplied by a reference factor, the first reference level being previously measured during a phase of calibrating the instrument when the water temperature was equal to the first reference temperature, and the reference factor corresponding to a level variation of the electrical measurement signal that is expected based on the temperature difference between the first reference temperature and the inflection point temperature.

[0024] A measurement method as described above is also provided, wherein before the meter is put into use, a reference factor is calculated based on at least one second reference level of the electrical measurement signal measured when the water temperature is equal to a second reference temperature and based on a third reference level of the electrical measurement signal measured when the water temperature is equal to a third reference temperature.

[0025] There is also provided a measuring method as described above, wherein the second reference level and the third reference level are measured during a phase of calibrating the meter, and the reference factors are then meter specific.

[0026] There is also provided a measuring method as described above, wherein the second reference level and the third reference level are measured for a plurality of other meters similar to the meter, and the reference factor is common to the plurality of meters.

[0027] There is also provided a measuring method as described above, further comprising the steps of estimating the flow rate of water by using the velocity of the ultrasonic measurement signal, and correcting the flow rate of water by using the water temperature as estimated by the measuring method.

[0028] Also provided is a measuring method as described above, wherein the first formula and the second formula are derived from a first equation and a second equation of the speed of sound in water as a function of water temperature, respectively, and the first equation and the second equation are quadratic equations.

[0029] There is also provided a measurement method as described above, wherein the first equation is:

[0030] Vs=-0.0325×T 2 +4.4218×T+1403.9

[0031] And the second equation is:

[0032] Vs=-0.0101×T 2 +1.226×T+1518.8,

[0033] where Vs is the speed of sound in water, and where T is the water temperature.

[0034] There is also provided a measuring method as described above, wherein the level of the electrical measurement signal is equal to the mean of the amplitudes of a plurality of lobes, said lobes being located in the middle of a portion of the electrical measurement signal, wherein said electrical measurement signal exhibits a substantially constant amplitude.

[0035] There is also provided a measuring method as described above; wherein the inflection point temperature is within the range of 74°C ± 2°C.

[0036] There is also provided a meter comprising at least one transducer and a processor assembly, the meter being arranged to perform the above-mentioned measurement method.

[0037] There is also provided a meter as described above, which is a water meter.

[0038] There is also provided a meter as described above, which is a thermal energy meter.

[0039] There is also provided a computer program comprising instructions for causing a processor component of a meter as described above to perform the steps of the measurement method described above.

[0040] A computer-readable storage medium is also provided, which stores the above-mentioned computer program.

[0041] The present invention may be better understood in light of the following description of specific non-limiting implementations of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] With reference to the accompanying drawings, in which:

[0043] [ Figure 1 ] Figure 1 shows a graph including a metering error curve relating to the measurement of the flow rate of water as a function of the water temperature for a flow rate of 6 L / h;

[0044] [ Figure 2 ] Figure 2 An ultrasonic measuring device for a water meter implementing the present invention is shown;

[0045] [ Figure 3 ] Figure 3 showing a graph including a curve plotting the change in the speed of sound in water as a function of temperature;

[0046] [ Figure 4 ] Figure 4 A graph is shown including a curve drawn approximately before the inflection point at 74°C. Figure 3 The quadratic function of the curve;

[0047] [ Figure 5 ] Figure 5 A graph is shown including a curve drawn approximately after the inflection point at 74°C. Figure 3 The quadratic function of the curve;

[0048] [ Figure 6 ] Figure 6 shows a graph including a curve plotting an electrical measurement signal as a function of time;

[0049] [ Figure 7 ] Figure 7 shows a graph including a curve plotting the expected level of the electrical measurement signal as a function of water temperature;

[0050] [ Figure 8 ] Figure 8 The steps of the measuring method of the present invention are shown. DETAILED DESCRIPTION

[0051] refer to Figure 2 In this example, the invention is implemented in a hot water meter 1 for measuring the consumption of hot water supplied by a water distribution network to customer facilities.

[0052] The meter 1 comprises firstly a communication module which enables it to communicate with an information system (IS) of a network manager, possibly via a data concentrator, a gateway or indeed another meter (such as a regional smart meter). The communication module can perform any type of communication and for example communication via a cellular network of the 2G, 3G, 4G, Cat-M or NB-IoT type, communication using the Long Range (LoRa) protocol, radio communication using the Wize standard operating at a frequency of 169 megahertz (MHz), etc. At regular time intervals, the meter 1 uses the communication module to transmit to the IS the measurements that have been made.

[0053] The meter 1 also comprises a pipeline conveying the water flow supplied by the distribution network to the customer's facility, and an ultrasonic measuring device 2 .

[0054] The water in the pipe flows from upstream to downstream, as shown by arrow F.

[0055] The ultrasonic measuring device 2 comprises an upstream transducer 3a and a downstream transducer 3b. The upstream transducer 3a and the downstream transducer 3b are a pair. In this example, the upstream transducer 3a and the downstream transducer 3b are piezoelectric transducers.

[0056] The ultrasonic measuring device 2 further comprises a measuring module 4 connected to the upstream transducer 3a and the downstream transducer 3b.

[0057] The measurement module 4 comprises a processor module comprising instructions suitable for executing a program for performing the measurement method of the present invention. The program is stored in a memory connected to or incorporated into the processor component 5. As an example, the processor component 5 can be a processor, a digital signal processor (DSP), a microcontroller, or indeed a programmable logic circuit, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC).

[0058] The measurement module 4 also includes an analog-to-digital converter (ADC) 6 (possibly included in the processor assembly 5).

[0059] The processor assembly 5 controls both the upstream transducer 3a and the downstream transducer 3b.

[0060] Each of the upstream and downstream transducers 3a and 3b acts sequentially to perform the function of a transmitter transducer and the function of a receiver transducer.

[0061] exist Figure 2 In FIG. 1 , the upstream transducer 3a is shown as performing the function of a transmitter transducer, while the downstream transducer is shown as performing the function of a receiver transducer.

[0062] The processor assembly 5 generates an electrical excitation signal 7 and transmits the electrical excitation signal 7 to the transmitter transducer. The processor assembly 5 thus causes the transmitter transducer to transmit an ultrasonic measurement signal 8. The receiver transducer receives the ultrasonic measurement signal 9 after the ultrasonic measurement signal 8 has passed through the water along a path of defined length L.

[0063] In this example, the path of defined length L is the straight path between the upstream transducer 3a and the downstream transducer 3b. The defined length L is typically equal to 7 centimeters (cm). It should be observed that the distance L is accurately measured during a calibration phase performed at the factory before the meter 1 is put into service.

[0064] In this example, the electrical excitation signal 7 is a signal with a frequency of f us And the period is T us Square wave signal. Frequency f us It is typically in the range of 900 kilohertz (kHz) to 4 megahertz (MHz), and in this example is equal to 1 MHz.

[0065] When the transmitter transducer is the upstream transducer 3a, the ultrasonic measurement signal 8 therefore travels along a path of defined length L from upstream to downstream between the upstream transducer 3a and the downstream transducer 3b.

[0066] When the transmitter transducer is the downstream transducer 3b, the ultrasonic measurement signal 8 travels along a path of defined length L from downstream to upstream between the downstream transducer 3b and the upstream transducer 3a.

[0067] Ultrasonic measurement signal 8 is transmitted by the transmitter transducer ( Figure 2 The upstream transducer 3a) in the E The ultrasonic measurement signal 9 is transmitted by the receiver transducer ( Figure 2 The downstream transducer 3b) in the E Level N R take over.

[0068] The ADC 6 of the measuring module 4 digitizes the electrical measuring signal generated by the receiver transducer when receiving the ultrasonic measuring signal 9 and it generates a measuring sample. us =1 MHz, the sampling frequency is usually 4 MHz in order to comply with the Shannon criterion. The processor assembly 5 acquires the digitized electrical measurement signal.

[0069] When the transmitter transducer is the upstream transducer 3a, the processor assembly 5 uses the electrical measurement signal to measure the travel time taken by the ultrasonic measurement signal 8 along a path of defined length from upstream to downstream.

[0070] In practice, the processor assembly 5 measures the global transmission time T from the upstream transducer 3a to the downstream transducer 3b AB .

[0071] The global transmission time T AB So that:

[0072] T AB =TA A +ToF AB +TR B ,in:

[0073] ·TA A is the on-time of the upstream transducer 3a;

[0074] ToFAB corresponds to the flight time taken by the ultrasound measurement signal 8 to travel along a path of defined length between the upstream transducer 3a and the downstream transducer 3b;

[0075] ·TR B is the reception time of the downstream transducer 3b.

[0076] Similarly, when the transmitter transducer is the downstream transducer 3b, the processor assembly 5 measures the global transmission time T BA , which makes:

[0077] T BA =TA B +ToF BA +TR A ,in:

[0078] ·TA B is the on-time of the downstream transducer 3b;

[0079] ToF BA corresponds to the flight time taken by the ultrasonic measurement signal 8 to travel along a path of defined length between the downstream transducer 3 b and the upstream transducer 3 a;

[0080] ·TR A is the reception time of the upstream transducer 3a.

[0081] Assumptions:

[0082] TA A =TA B TR A =TR B (paired transducers), the following formula is obtained:

[0083] ΔT=T BA -T AB =ToF BA -ToF AB =DToF,

[0084] Where DToF is differential time of flight.

[0085] However, DToF is proportional to the average speed of the water, so the processor module 5 can then calculate the average speed of the water by using DToF. The average speed is signed, and it can be positive, negative or zero.

[0086] The processor assembly 5 then deduce the flow rate of the water flowing in the pipe of the meter 1 from the average velocity of the water.

[0087] Thus, the electrical measurement signal is used to generate a measurement of the water flow rate. However, as described below, in the measurement method of the present invention, the electrical measurement signal is also used to determine whether the water temperature is less than or greater than the inflection point temperature. The inflection point temperature corresponds to the inflection point in a curve that plots the speed of sound in water as a function of water temperature.

[0088] In this example, the inflection point temperature is equal to 74°C.

[0089] In the measuring method of the invention, the water temperature is estimated from the measurement of the velocity of the ultrasonic measuring signal in the water.

[0090] In order to estimate the velocity of the water, the processor assembly 5 therefore starts by measuring the velocity of the ultrasound measurement signal in the water, ie the speed of sound in the water.

[0091] The sum of the flight times is proportional to the distance L between the upstream transducer 3a and the downstream transducer 3b, and inversely proportional to the speed of sound in water.

[0092] The processor assembly 5 therefore infers the speed of sound in water from the sum of the flight times.

[0093] The processor assembly 5 then estimates the water temperature based on the speed of sound in the water.

[0094] Figure 3 The curve C2 of FIG. 1 shows how the speed of sound in water varies with the water temperature, which varies in the range of 0.1°C to 100°C in the figure. As mentioned above, the curve C2 exhibits an inflection point at about 74°C: the curve rises to 74°C and decreases above 74°C. Because at this inflection point, the same speed of sound in water can correspond to two different water temperature values. Therefore, as an example, for the same speed of sound in water of 1542 meters per second (m / s), the water temperature may be equal to 50°C, or equal to 100°C. Curve C2 can be approximated by two quadratic function curves. Curve C3 (such as Figure 4 Curve C4 (as shown in Figure 5 ) corresponds to water with a temperature above 74°C.

[0095] Curve C3 is defined between 0°C and 74°C by the following first equation:

[0096] Vs=-0.0325×T 2 +4.4218×T+1403.9,

[0097] where Vs is the speed of sound in water, and where T is the water temperature.

[0098] Curve C4 is defined between 74°C and 100°C by the following second equation:

[0099] Vs=-0.0101×T 2 +1.226×T+1518.8.

[0100] In order to determine which equation should be used in order to find the "correct" temperature corresponding to the estimated speed of sound in the water, and thus eliminate the uncertainty associated with the fact that two different temperatures (one above 74° C. and the other below 74° C.) may correspond exactly to the same speed of sound, the processor assembly 5 measures the level of the electrical measurement signal, and then determines from the level of the electrical measurement signal whether the water temperature is less than or greater than 74° C. Specifically, the level of the electrical measurement signal may produce a relatively inaccurate estimate of the water temperature, but may be sufficient to determine whether the water temperature is less than or greater than 74° C., and thus determine whether the first equation or the second equation should be used to accurately estimate the water temperature.

[0101] Figure 6An electrical measurement signal Sm is shown. The electrical measurement signal Sm comprises a first portion 10 and a second portion 11. In the first portion 10, the amplitude of the electrical measurement signal Sm increases significantly and then decreases. In the second portion 11, the amplitude of the electrical measurement signal Sm is relatively constant.

[0102] In this example, the amplitude of the electrical measurement signal Sm is greater in the first portion 10 due to the fact that the excitation frequency of the transmitter transducer does not correspond exactly to its resonance frequency. Of course, it is possible to choose an excitation frequency equal to the resonance frequency of the transmitter transducer.

[0103] In this example, the level of the electrical measurement signal Sm used is the level of a "plateau" 12 in the second portion 11 of the electrical measurement signal Sm. More precisely, in this example, the level of the electrical measurement signal Sm is equal to the mean of the amplitudes of a plurality of lobes (e.g. ten lobes) located in the middle of a portion of the electrical measurement signal Sm in which the electrical measurement signal Sm exhibits a substantially constant amplitude (i.e. in the middle of the second portion 11).

[0104] It has been found that the level of the electrical measurement signal decreases linearly with increasing temperature. Figure 7 As shown in , the linear curve C5 gives the level of the electrical measurement signal of the electric meter 1 as a function of the water temperature.

[0105] In order to determine whether the water temperature is less than or greater than 74° C., the processor assembly 5 compares the level of the electrical measurement signal with the expected level for water at a temperature equal to 74° C. The expected level for a temperature of 74° C. is determined by knowing the first reference level of the electrical measurement signal previously measured during a phase of calibration of the meter 1 at water at a temperature equal to the first reference temperature, and by using a reference factor. The reference factor is a percentage corresponding to the change in level of the electrical measurement signal that is expected according to the difference between the first reference temperature and 74° C.

[0106] The processor assembly 5 compares the level of the electrical measurement signal Sm with a predefined threshold value, which is equal to a first reference level of the electrical measurement signal multiplied by a reference factor.

[0107] As an example, the first reference temperature is equal to 20°C.

[0108] Before the meter is put into use, a reference factor is calculated based on at least one second reference level of the electrical measurement signal measured when the water temperature is equal to the second reference temperature and based on a third reference level of the electrical measurement signal measured when the water temperature is equal to the third reference level.

[0109] The second reference level, the third reference level and the reference factor may be measured during a phase of calibrating the meter 1. Thus, during said calibration phase, the level of the electrical measurement signal is measured in the meter 1 when the water has a temperature equal to the second reference temperature in order to obtain the second reference level, and subsequently when the water has a temperature equal to the third reference temperature in order to obtain the third reference level. The reference factor obtained varies from meter 1 to meter 1. Naturally, in this case it is advantageous that the second reference temperature (or indeed the third reference temperature) is equal to the first reference temperature, and therefore the second reference level (or indeed the third reference level) is equal to the first reference level, since two measurement points are then sufficient to define the reference factor and the first reference level used in operation.

[0110] As an example, the second reference temperature is equal to 20°C and the third reference temperature is equal to 50°C.

[0111] Alternatively, the linear curve C5 may be obtained from measurements made on a large number of instruments similar to the meter 1. As an example, the "similar" instruments may be instruments having the same part number (P / N) as the meter 1. The "large number" of instruments enables a linear curve to be defined that represents the expected level of the electrical measurement signal and that is relevant to all instruments similar to the meter 1. In this case, the second reference level and the third reference level are measured for a plurality of other instruments similar to the meter 1, and the reference factors used are common to the plurality of instruments.

[0112] For example, the following might apply to meter 1:

[0113] N(74℃)=0.7×N(20℃),

[0114] Wherein N(74°C) is the expected level of the electrical measurement signal of water at a temperature equal to 74°C, wherein N(20°C) is the first reference level (i.e. the level of the electrical measurement signal measured at the first reference temperature during the calibration phase, specifically equal to 20°C), and 0.7 is the reference factor.

[0115] The reference factor is equal to 0.7, which means that in operation, for the meter 1 , the expected level of the electrical measurement signal at 74° C. is equal to 0.7 times the level at 20° C. (first reference level).

[0116] Thus, in operation and in order to determine whether the water temperature is less than or greater than 74° C., the processor assembly 5 compares the level of the electrical measurement signal with a predefined threshold value, which in this example is equal to:

[0117] 0.7×N(20℃).

[0118] Based on the comparison, the processor component 5 derives whether the water temperature is less than or greater than 74°C: if the level of the electrical measurement signal is greater than a predefined threshold, the processor component infers that the water temperature is less than 74°C, and if the level of the electrical measurement signal is less than the predefined threshold, the processor component 5 infers that the water temperature is greater than 74°C.

[0119] The processor assembly 5 then generates an accurate estimate of the water temperature based on the speed of the ultrasonic measurement signal by applying one or the other of the equations for the change in speed of sound. If the water temperature is less than 74°C, the processor assembly 5 uses a first formula derived from the first equation above, and if the water temperature is greater than 74°C, a second formula derived from the second equation is used.

[0120] It should be observed that both the first and second equations are for the curve ( Figure 3 The quadratic approximation of the curve C2) is itself part of a fifth order function curve. The use of a formula derived from a quadratic curve is very advantageous in terms of the computational resources required by the processor assembly 5 to execute the invention.

[0121] The processor assembly 5 then corrects the measurement of the water flow rate according to the estimated water temperature.

[0122] Figure 8 The main steps performed to estimate the water temperature in operation are summarized in.

[0123] The processor assembly 5 starts by measuring the level of the electrical measurement signal (step E1 ).

[0124] The processor assembly 5 then compares the level of the electrical measurement signal Sm with a predefined threshold value equal to a first reference level of the electrical measurement signal multiplied by a reference factor (step E2 ).

[0125] If the level of the electrical measurement signal is strictly greater than the predefined threshold, the processor assembly 5 infers that the water temperature is strictly less than 74° C. and selects the first formula (step E3). If the measured level of the electrical measurement signal is less than or equal to the predefined threshold, the processor assembly 5 infers that the water temperature is greater than or equal to 74° C. and selects the second formula (step E4).

[0126] The processor assembly 5 then accurately calculates the water temperature by using the selected formula (step E5 ).

[0127] Naturally, the invention is not limited to the embodiments described but covers any variant coming within the ambit of the invention as defined by the claims.

[0128] The number of transducers in an ultrasonic measuring device is not necessarily equal to two. As an example, only one transducer may be provided, which transmits an ultrasonic measuring signal, which is reflected by a reflective element incorporated into the pipe and collected by said transducer. A single transducer successively performs the function of a transmitter transducer and the function of a receiver transducer for the same ultrasonic measuring signal.

[0129] In the above description of the invention, all steps of the measurement method are performed in the processor component of the meter. However, the measurement method may be performed in multiple components, or indeed may be performed at least partially outside the meter. For example, the water temperature may be estimated and the flow rate corrected in another meter, a data concentrator, or a server remote from the meter.

[0130] The present invention can be implemented in a water meter or a heat meter. The water can be fresh water or salt water.

[0131] The considered inflection point temperature does not necessarily have to be exactly equal to 74°C, but may be equal to about 74°C, for example, it may be in the range of 74°C±2°C.

Claims

1. A measuring method for measuring water temperature, the method being at least partially performed in a meter (1) and comprising the following steps: causing the transmitter transducer (3a) of the meter (1) to emit an ultrasonic measurement signal (8) and acquiring an electrical measurement signal (Sm) generated by the receiver transducer (3b) of the meter (1) when the ultrasonic measurement signal is received after having traveled along a path of defined length (L) in the water; characterized in that the method comprises the following steps: measuring the velocity of the ultrasonic measurement signal in the water; measuring the level of the electrical measurement signal (Sm); using the level of the electrical measurement signal to determine whether the temperature of the water is less than or greater than an inflection point temperature corresponding to an inflection point in a curve that plots the speed of sound in water as a function of the temperature of the water; The temperature of the water is estimated from the velocity of the ultrasonic measurement signal by using a first formula if the temperature of the water is less than the inflection point temperature, and by using a second formula if the temperature of the water is greater than the inflection point temperature.

2. The measuring method according to claim 1, characterized in that: The invention comprises the step of comparing the level of the electrical measurement signal with a predefined threshold value equal to a first reference level of the electrical measurement signal multiplied by a reference factor, in order to determine whether the temperature of the water is less than or greater than the inflection point temperature, the first reference level being previously measured during a phase of calibrating the meter (1) when the temperature of the water was equal to the first reference temperature, and the reference factor corresponding to a variation of the level of the electrical measurement signal that is to be expected from the temperature difference between the first reference temperature and the inflection point temperature.

3. The measuring method according to claim 2, characterized in that: Before the meter (1) is put into use, the reference factor is calculated based on at least one second reference level of the electrical measurement signal measured when the temperature of the water is equal to the second reference temperature and a third reference level of the electrical measurement signal measured when the temperature of the water is equal to the third reference temperature.

4. The measuring method according to claim 3, characterized in that: The second reference level and the third reference level are measured during a phase of calibrating the meter (1), and the reference factors are then specific to the meter (1).

5. The measuring method according to claim 3, characterized in that: The second reference level and the third reference level are measured for a plurality of other meters, and the reference factor is common to the plurality of meters.

6. A measuring method according to any preceding claim, characterised in that Also included are the steps of estimating the flow rate of the water by using the velocity of the ultrasonic measurement signal, and correcting the flow rate of the water by using the temperature of the water as estimated by the measurement method.

7. The measuring method according to any one of claims 1 to 5, characterized in that: The first formula and the second formula are derived from a first equation and a second equation for the speed of sound in water that varies with the temperature of the water, respectively, and the first equation and the second equation are quadratic equations.

8. The measuring method according to claim 7, characterized in that: The first equation is: Vs=0.0325×T 2 +4.4218×T+1403.9 And the second equation is: Vs=0.0101×T 2 +1.226×T+1518.8, where Vs is the speed of sound in the water, and where T is the temperature of the water.

9. The measuring method according to any one of claims 1 to 5, characterized in that: The level of the electrical measurement signal is equal to the mean of the amplitudes of a plurality of lobes located in the middle of a portion (11) of the electrical measurement signal (Sm) exhibiting a substantially constant amplitude.

10. The measuring method according to any one of claims 1 to 5, characterized in that: The inflection point temperature is within the range of 74°C ± 2°C.

11. An instrument comprising at least one transducer (3a, 3b) and a processor assembly (5), the instrument being arranged to perform a measurement method as claimed in any preceding claim.

12. The meter according to claim 11, characterized in that The meter is a water meter.

13. The meter according to claim 11, characterized in that The instrument is a heat meter.

14. A computer-readable storage medium storing a computer program comprising instructions for causing a processor component (5) of a meter (1) according to any one of claims 11 to 13 to execute the steps of a measurement method according to any one of claims 1 to 10.

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