An online zero drift correction method for ultrasonic water meter

Abstract

The present invention provides an online zero drift correction method for an ultrasonic water meter, and belongs to the technical field of water meter error correction. A new U-shaped ultrasonic water meter structure with an inlet valve and an outlet valve is proposed. The zero drift calibration signal is sent through a host computer platform according to a certain time period. After the ultrasonic water meter receives the calibration signal, the zero drift calibration process is started in real time, which is convenient and quick. During the measurement process, in order to create a static water measurable environment, the switch of the two valves and the calculation of the uplink and downlink time are used to fully eliminate the influence of pipeline bubbles and the like on the zero drift measurement. The present invention realizes systematic measurement of zero drift problems caused by transducer aging and surface contamination through simple structural design and algorithm, realizes online periodic measurement of zero drift values ​​and compensation, fully solves the problem of decreased measurement performance and accuracy of ultrasonic water meters after running for a period of time, and can further improve the metering accuracy during the long-term operation of the water meter.

Description

Technical Field

[0001] The invention belongs to the technical field of water meter error correction, and in particular relates to an online zero drift correction method for an ultrasonic water meter. Background Art

[0002] During the application of ultrasonic water meters, due to the structural characteristics of the transducer, the device is prone to aging. At the same time, due to the water quality and the adhesion characteristics of the transducer surface, the surface will be contaminated, and a certain degree of zero drift will often occur. After the zero drift occurs, the metering characteristics will often change to a certain extent, and the metering results will have certain errors. At this time, the user and the unit to which the water meter belongs cannot grasp the current state of the water meter zero drift in time, which brings a great degree of trouble to the accurate water metering. At present, the zero drift value of the water meter is generally corrected during the process of the water meter leaving the factory. However, the disadvantage of this method is that the correction value at this time is often a compensation for the temperature drift, and does not take into account the zero drift caused by the aging of the transducer and surface contamination. At this time, the ultrasonic water meter has been shipped and installed on the pipeline. The installation environment of the water meter cannot be estimated, and the size of the zero drift cannot be accurately obtained and compensated through prediction. Another method is to arrange personnel to conduct on-site testing and calibration for each water meter on a regular basis. However, this method requires a lot of manpower and time, and it is difficult to avoid human errors in the process of large-scale calibration and testing. At the same time, since the site is not a standard test environment, the measured values ​​are often difficult to achieve the expected metering effect, so it is difficult to achieve accurate compensation for zero drift.

[0003] At present, the zero drift processing technology for ultrasonic water meters generally focuses on the links before the water meter leaves the factory, mainly focusing on filtering interference, smoothing fluctuations and other operations. When the zero drift is caused by the disturbance of the uplink and downlink time, it can be achieved through the sliding average filter algorithm and the Kalman filter algorithm. However, the zero drift is often related to the degree of transducer contamination and the degree of aging of the transducer. The prediction and calibration scheme before leaving the factory often cannot reflect the actual acquisition environment and errors. At present, there are few studies on online zero drift processing technology for ultrasonic water meters. Among them, CN202211503187 discloses "A method for reducing the zero drift of ultrasonic water meters", which mainly achieves the purpose of reducing the zero drift of ultrasonic water meters by online self-adjusting the working frequency. However, this method can only qualitatively reduce the value of zero drift caused by frequency drift for the zero drift problem caused by the impedance characteristics of the transducer, and cannot quantitatively test the value of zero drift and accurately compensate for it. In addition, CN201510942062.9 discloses "An ultrasonic water meter with automatic correction of zero drift and its correction" which adds a zero flow auxiliary correction transducer group, and uses the time difference measured by the measuring transducer group and the auxiliary transducer group for correction through a signal processing and display device. However, this method adds a transducer group, which is more complicated to implement. At the same time, an auxiliary transducer is used to measure the zero drift value and use the value as the zero drift of the measuring transducer group. This approach cannot reflect the impact of the thickness change caused by dirt adhering to the surface of the measuring transducer group and long-term grinding by sand and gravel in the water on the zero drift data, and can only partially reflect the changes in the precision timing chip due to time drift. Summary of the invention

[0004] In view of the above problems, the present invention provides an online zero drift correction method for an ultrasonic water meter, which is based on a U-shaped pipe integrally arranged with an ultrasonic water meter body, wherein the bottom horizontal pipe section of the U-shaped pipe is arranged horizontally, and an ultrasonic transducer is built in, and valves are respectively added to the upper parts of the two vertical ends of the U-shaped pipe, which are an inlet valve and an outlet valve; the ultrasonic transducer and the valve are both switched on and off by a built-in control chip of the ultrasonic water meter body, and the ultrasonic water meter body is connected to an Internet of Things platform terminal through a communication module;

[0005] The correction method comprises the following steps:

[0006] Get the actual compensation value of the time and the initialization process And zero drift error , the time and is the sum of the ultrasonic up-propagation time and the ultrasonic down-propagation time;

[0007] S1, after receiving the calibration instruction, close the inlet valve first, wait for a certain time to allow the bubbles to be discharged in time, and then close the outlet valve to make the interior in a static water state;

[0008] S2, obtaining the temperature information of the still water in the pipe section and obtaining the corresponding sound velocity data;

[0009] S3, combined with the compensation value of time and , using the sound velocity data and the flow path length parameters of the ultrasonic water meter, the theoretical values ​​of the upward propagation time and the downward propagation time are calculated. ;

[0010] S4, start the ultrasonic transducer, and the received ultrasonic signal is filtered and amplified, and then the uplink time is obtained by the time counting method. and downlink time , calculate the uplink time and downlink time Measurement of time and ;

[0011] S5, based on and , calculate the difference Δsum, if its absolute value is less than the threshold, enter S6, if its value is greater than the threshold, enter S1 process and retest;

[0012] S6, calculate the new zero drift value , replace the zero drift error obtained by initialization before ;

[0013]

[0014] At this time and It is consistent with the actual measurement of S4;

[0015] S7, based on the new zero drift value , calculate the true cumulative flow.

[0016] Preferably, the time and compensation value of the initialization process are obtained , the specific process is:

[0017] Obtain the length L of the sound channel, and use a thermometer to measure the temperature at the time of initialization. Calculate the speed of sound at this time by using a table lookup method or an approximate analytical formula for the relationship between ultrasound and temperature. The approximate analytical formula is:

[0018] C=1468+3.68(T-10)-0.0279(T-10)²

[0019] At this time, C is the solved sound speed, in meters per second, and T is the temperature measured during initialization, in degrees Celsius;

[0020] The uplink propagation time at initialization is measured by the timing chip and downlink propagation time The actual value of , sum the two, the summation formula is:

[0021]

[0022] Time and compensation value The calculation formula is:

[0023]

[0024] So as to obtain the compensation value of time during initialization .

[0025] Preferably, in S2, the temperature information of the still water in the pipe section is obtained by using a temperature sensor arranged in the bottom transverse pipe section, and the sound velocity information is obtained by looking up the table according to the temperature information and the sound velocity table in pure water;

[0026] Or according to the formula of the speed of ultrasound in pure water and temperature, the speed of ultrasound at this time can be calculated using the approximate analytical formula of the relationship between ultrasound and temperature. .

[0027] Preferably, the calculation process of S3 is:

[0028] = + ≈2* +

[0029] At this time, L represents the length of the ultrasonic flow meter sound channel; is the current propagation speed of ultrasound in water; is the velocity of water flowing in the pipe.

[0030] Preferably, the threshold in S5 is 100 ps.

[0031] Preferably, the specific process of S7 is:

[0032] Calculate the velocity of water flowing in a pipe Correction value:

[0033]

[0034] in, To recalculate the new zero drift value in a still water environment, L is the length of the ultrasonic propagation channel. The length of the ultrasonic upward and downward propagation channels is the same. is the current propagation speed of ultrasound in water;

[0035] Then calculate the volume instantaneous flow rate Correction value:

[0036]

[0037] K is the flow coefficient, which is used to correct the instantaneous flow error and is generally given by the actual flow test of the calibration device. is the diameter of the pipe.

[0038] Finally calculate the cumulative flow Correction value:

[0039]

[0040] in, is the integration time constant, which divides the time equally according to the detection frequency. The frequency unit is times / second.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention proposes a novel U-shaped ultrasonic water meter structure with an inlet valve and an outlet valve, which can be used to switch the valve by issuing instructions through a host computer, thereby realizing the correction method of the present invention; the host computer platform sends a zero drift calibration signal according to a certain time period, and the ultrasonic water meter can start the zero drift calibration process in real time after receiving the calibration signal through a wireless network, which is convenient and quick.

[0043] The present invention achieves systematic measurement of zero drift problems caused by transducer aging and surface contamination through simple structural design and algorithms, and achieves online periodic measurement of zero drift values ​​and compensation, which fully solves the problem of decreased measurement performance and accuracy of ultrasonic water meters after running for a period of time, and can further improve the metering accuracy during long-term operation of water meters. During the measurement process, in order to create a static water measurable environment, the switching of two valves and the calculation of uplink and downlink time are used to fully eliminate the influence of pipeline bubbles on zero drift measurement, further expanding the application scenarios and environments of this patent. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the structure of the new ultrasonic water meter of the present invention.

[0045] Figure 2 Schematic diagram of the overall process of the correction method of the present invention.

[0046] Among them: 1. Ultrasonic water meter body; 2. U-shaped pipe; 3. Ultrasonic transducer; 4. Inlet valve; 5. Outlet valve. DETAILED DESCRIPTION

[0047] Ultrasonic water meter is a new type of water meter. Due to its wide range ratio, accurate measurement, small starting flow rate and small pressure loss, the design, production and debugging technology are becoming more and more mature. It has been widely used in various water metering occasions and is a good choice for upgrading traditional mechanical water meters. During operation, the ultrasonic water meter mainly relies on the ultrasonic transducer installed on the water meter pipeline to apply a pulse drive of a certain frequency and amplitude in a certain order, and then processes the signal received by the ultrasonic probe, and calculates the flow rate based on the time difference between the uplink and downlink calculated by the data. The measurement principle is as follows:

[0048] The time calculation formula for uplink propagation is:

[0049] (1)

[0050] The time calculation formula for downlink propagation is:

[0051] (2)

[0052] The calculation formula for the ultrasonic uplink and downlink propagation time difference is:

[0053] (3)

[0054] By transforming formula (3), we can get:

[0055] (4)

[0056] Volume instantaneous flow calculation formula:

[0057] (5)

[0058] Cumulative flow calculation formula:

[0059] (6)

[0060] In the formula, , : Ultrasonic uplink and downlink propagation time;

[0061] : The current propagation speed of ultrasound in water;

[0062] : The flow rate of water in the pipe;

[0063] : The instantaneous volume flow rate of water in a closed pipe;

[0064] D: Inner diameter of ultrasonic water meter measuring tube;

[0065] : The propagation time difference between uplink and downlink of ultrasonic wave;

[0066] : The cumulative flow of water in the closed pipe;

[0067] : measurement time;

[0068] : Compensation value of time and is determined during initialization.

[0069] Due to the time difference between uplink and downlink In the process of metering, due to the temperature characteristics of the transducer, the metering characteristics of the time metering chip and the processing characteristics of the pipe section, it is often inevitable to produce zero drift errors. When the flow rate is 0, the time difference between the uplink and downlink is not strictly 0, but a certain smaller value. If this value is not corrected and eliminated, it will often affect the range ratio and accuracy of the flow test. Especially in the process of small flow testing, the zero drift value of the time difference is a physical quantity that cannot be ignored. Therefore, in the design process of water meters with higher accuracy levels and large range ratios, the zero drift is generally corrected to a certain extent before leaving the factory to form a zero drift correction function.

[0070] In order to better solve the zero drift compensation problem of the water meter during operation, the present invention proposes a new ultrasonic water meter structure and provides a specific installation method to reduce the occurrence of bubble retention. The mechanical structure of the ultrasonic water meter is as follows: Figure 1 As shown, it includes a U-shaped pipe 2 integrally arranged with the ultrasonic water meter body 1. In terms of installation requirements, the horizontal pipe section of the U-shaped pipe must be located at the bottom of the vertical position to ensure that the horizontal pipe section can still be filled with water after the water supply is cut off. The bottom horizontal pipe section of the U-shaped pipe 2 is arranged horizontally and has an ultrasonic transducer 3 built in. Two valves are added at both ends of the U-shaped pipe 2, namely an inlet valve 4 and an outlet valve 5. As shown in the figure, the ultrasonic transducer and the valve are both switched on and off by the built-in control chip of the ultrasonic water meter body.

[0071] The ultrasonic water meter has a wireless module integrated inside the main body, which can communicate with the IoT platform through a wireless communication interface. In order to calibrate the ultrasonic water meter, the IoT platform can issue instructions regularly or irregularly to perform individual zero drift correction on the ultrasonic water meter.

[0072] The overall correction method of the present invention is as follows Figure 2 First, obtain the actual compensation value of time and And zero drift error , the time and are the sum of the ultrasonic up-propagation time and the ultrasonic down-propagation time; and include the following process

[0073] S1, after receiving the calibration instruction, close the inlet valve first, wait for a certain time to allow the bubbles to be discharged in time, and then close the outlet valve to make the interior in a static water state;

[0074] S2, obtaining the temperature information of the still water in the pipe section and obtaining the corresponding sound velocity data;

[0075] S3, combined with the compensation value of time and , using the sound velocity data and the flow path length parameters of the ultrasonic water meter, the theoretical values ​​of the upward propagation time and the downward propagation time are calculated. ;

[0076] S4, start the ultrasonic transducer, and the received ultrasonic signal is filtered and amplified, and then the uplink time is obtained by the time counting method. and downlink time , calculate the uplink time and downlink time Measurement of time and ;

[0077] S5, based on and , calculate the difference Δsum, if its absolute value is less than the threshold, enter S6, if its value is greater than the threshold, enter S1 process and retest;

[0078] S6, calculate the new zero drift value , replace the zero drift error obtained by initialization before ;

[0079]

[0080] At this time and It is consistent with the actual measurement of S4;

[0081] S7, based on the new zero drift value , calculate the true cumulative flow.

[0082] 1. Initialization process time and Calculation of compensation value

[0083] The initialization process requires obtaining the time and compensation value , which is used for subsequent compensation calculations. Obtain the length L of the sound channel, and use a thermometer to measure the temperature at the time of initialization. Calculate the speed of sound at this time by using a table lookup method or an approximate analytical formula for the relationship between ultrasound and temperature. The approximate analytical formula is:

[0084] C=1468+3.68(T-10)-0.0279(T-10)²

[0085] At this time, C is the solved sound speed, in meters per second, and T is the temperature measured during initialization, in degrees Celsius;

[0086] The uplink propagation time at initialization is measured by the timing chip and downlink propagation time The actual value of , sum the two, the summation formula is:

[0087]

[0088] Time and compensation value The calculation formula is:

[0089]

[0090] So as to obtain the compensation value of time during initialization .

[0091] 2. Remote valve closing

[0092] After receiving the zero drift calibration command from the remote network, the valve closing action is started. First, the inlet valve is closed, and then the outlet valve is closed after waiting for 5 seconds so that the bubbles can be removed in time. At this time, the entire pipe section is in a closed state and the interior is in a static water state.

[0093] 3. Obtain sound speed data

[0094] The temperature information of the still water in the pipe section is obtained by using the temperature sensor installed in the bottom horizontal pipe section for temperature collection. The temperature sensor can preferably use thermocouples and thermal resistors. The temperature information of the still water in the pipe section is obtained by using the temperature change characteristics of thermocouples and thermal resistors. The sound velocity information is obtained by looking up the table based on the temperature information and the sound velocity table in pure water.

[0095] In addition, the speed of sound data at this time can be calculated based on the corresponding formula of ultrasound speed and temperature in pure water using the approximate analytical formula of the relationship between ultrasound and temperature. .

[0096] 4. Calculation of theoretical values ​​of uplink and downlink propagation time

[0097] After obtaining the sound velocity data, the theoretical values ​​of the upstream propagation time and the downstream propagation time are calculated using the flow path length parameters of the ultrasonic water meter. The calculation formula is:

[0098]

[0099] = + ≈2* +

[0100] At this time, L represents the length of the ultrasonic flow meter sound channel, and Represents the compensation value of time, which is a constant value, mainly related to the amplitude of the ultrasonic signal and the design length of the circuit, and has been calibrated in advance through initialization measurement in the factory design of the ultrasonic flowmeter.

[0101] 5. Calculation of measured values ​​of uplink and downlink propagation time

[0102] In the ultrasonic water meter, the single-chip microcomputer is used to send out the flow test start signal. At this time, the flow metering chip transmits the ultrasonic transducer drive pulse signal. The order of the transducer pair transmission can be determined according to the actual situation. At this time, one of the transducers is used as the transmitting unit and the other transducer is used as the receiving unit. After completing the sending and receiving actions, the transmission and receiving order is exchanged. After the received ultrasonic signal passes through the filtering link and the amplification link, the uplink time and downlink time are obtained through the time counting method. At this time, the uplink time can be calculated and downlink time Measurement of time and .

[0103] 6. Measurement and calibration environment assessment

[0104] When performing online zero drift correction on an ultrasonic water meter, it is necessary to ensure that the entire calibration environment is in a hydrostatic and closed state, and that no bubbles exist inside the flow channels for ultrasonic transmission and reception.

[0105] According to the empirical value, when the pipe is full, record the measured value sum(T) of the uplink and downlink propagation time and the theoretical value of the uplink and downlink propagation time , and find the difference between these two physical quantities, Δsum=sum(T)- , where the value calculated by Δsum may be positive or negative. The value for comparison here should be the absolute value of the calculated value. The absolute value of Δsum should be guaranteed to be less than 100ps. At this time, it can be guaranteed that the entire test pipe section is in a state of no bubbles or full pipe state. If the difference value is greater than 100ps, it means that there are bubbles in the pipe section or it is in a half-pipe or empty pipe state. At this time, it is not suitable to perform zero drift calibration. It is necessary to abandon the calibration operation and wait until the calibration conditions are met before testing again.

[0106] 7. Correction of zero drift value

[0107] The goal of the online zero drift correction process of ultrasonic water meters is to obtain a zero drift calibration value, which is a time value that needs to be applied for compensation in subsequent flow calculations. The calculation formula for the new zero drift value is: ,here is the downlink propagation time, When performing zero drift compensation calibration, first use the time difference in static water state. It is used to replace the previously calculated zero drift error and is included in the original storage calibration time difference position inside the memory chip to compensate for the flow error.

[0108] 8. Correction of flow error

[0109] The cumulative flow calculated by the ultrasonic water meter is the most important data for the ultrasonic water meter, which directly determines the grade and range of the ultrasonic water meter. If the flow correction is not performed at the minimum flow Q1, it will often result in a large measurement error. Therefore, when the cumulative flow in the time range T0 is calculated according to formulas (4)-(6), the cumulative flow needs to be corrected. During the calculation process, formula 4 is modified to , formula (5) and formula (6) remain unchanged, and the calculated result can be used as the corrected true cumulative flow.

[0110] The present invention is further described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0111] During the initialization process, the time and compensation values ​​are first calibrated through measurement.

[0112] If the temperature measured by the thermocouple is 10℃, the speed of sound can be calculated by the formula: C=1468+3.68(T-10)-0.0279(T-10)²; the speed of sound is 1468m / S. Select a DN15 metal copper pipe section from a manufacturer, and the length of the sound channel can be obtained from the manual provided by the manufacturer as 82.8mm.

[0113] Put the pipe section into still water and seal both ends. If the metering chip reads that the uplink propagation time is 66981.16ns and the downlink propagation time is 66981.14ns, the sum of the uplink and downlink propagation time is sum=66981.16ns+66981.14ns=133962.3ns.

[0114] At this time, according to the formula get Convert to ns value

[0115] =133962.3-2*0.0828*10 9 / 1468=21155.76ns, store the calculated time and compensation value into the storage unit.

[0116] The host computer platform sends a zero drift calibration signal at a certain time period, and the ultrasonic water meter starts the zero drift calibration process after receiving the calibration signal through the wireless network.

[0117] After starting the zero drift calibration process, the first step of the ultrasonic water meter is to close the valve to create a static water environment. The order of closing the valve is to close the inlet valve first, and then wait for 5 seconds before closing the outlet valve, so that the bubbles can be removed in time.

[0118] After the valve is closed, the temperature acquisition phase begins. At this time, the water temperature in the pipe is 15.9°C, which is obtained through the thermal resistor. The sound velocity at this time is 1469.0m / s, which is obtained through the table lookup. The theoretical values ​​of the upward propagation time and the downward propagation time are calculated using the flow channel length parameters of the ultrasonic water meter.

[0119] for:

[0120] =2* + =2*0.0828*10 9 / 1469+21155.76=133885.508ns

[0121] After starting the test, the time measurement chip can be easily read. At this time, the temperature of the static water pipe section is first measured by the temperature sensor of the ultrasonic water meter, and the theoretical value of the time and the time in the upward and downward directions are calculated according to the flow path length parameters in the pipeline. After that, the flow measurement operation is started, and the driving square wave pulse signal is sent in sequence through the installed transducer, and the signal receiving process is started. According to the output results of the time chip, the accurate time of the ultrasonic pulse upward and the accurate time of the downward are obtained. The output of the time chip can generally be set to the average of the arrival time of 20 consecutive upward pulses and downward pulses. It is used to reduce the error caused by signal fluctuations.

[0122] Get the uplink propagation time and the downlink propagation time. If the uplink propagation time collected at this time is 66942.73 and the downlink propagation time is 66942.74, the uplink time is obtained according to the formula and downlink time The measured value of time and sum(T) = + The size is 133885.47, according to:

[0123] Δsum = sum(T) -

[0124] The calculated difference is 0.038ns=38ps. The absolute value of Δsum is less than 100ps, which means that the entire test pipe section is free of bubbles or full. It can be determined that the entire pipe environment is suitable for zero drift calibration.

[0125] Once it is determined that the pipeline environment meets the zero drift test requirements, the time difference in the uplink and downlink directions is calculated through the output results of the time chip. If the uplink propagation time is 66942.73 and the downlink propagation time is 66942.74, the time difference is 0.1ns.

[0126] As well as formula (5) and formula (6), if the test time is taken as one second, the flow rate that needs to be compensated can be calculated according to the pre-set proportional coefficient K.

[0127] The flow rate that needs to be compensated is written into a fixed storage area inside the memory chip. In subsequent flow calculations, this value is used to correct the final calculated flow rate.

[0128] If the water in the pipeline cannot meet the full pipe condition or there are a certain number of bubbles, the valve closing operation will be started and recalibration will be performed after the conditions are met next time.

[0129] During the valve closing process, a certain sequence is also used. The setting here is to open the outlet valve first and then the inlet valve. At this time, the entire pipeline can resume normal water supply. After that, the final result of the calibration at this time can be informed to the upper computer through the communication signal interface, so as to plan and prepare for the specific time of the next zero drift calibration.

[0130] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0131] Although the above describes the specific implementation methods of the present invention, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. An online zero drift correction method for an ultrasonic water meter, characterized in that: Based on a U-shaped pipe integrally arranged with the ultrasonic water meter body, the bottom horizontal pipe section of the U-shaped pipe is arranged horizontally, and an ultrasonic transducer is built in. Valves are added to the upper parts of the two vertical ends of the U-shaped pipe, which are an inlet valve and an outlet valve respectively; the ultrasonic transducer and the valve are both switched on and off by a built-in control chip of the ultrasonic water meter body, and the ultrasonic water meter body is connected to the Internet of Things platform terminal through a communication module; The calibration method The process includes: Get the actual compensation value of the time and the initialization process And zero drift error , the time and is the sum of the ultrasonic up-propagation time and the ultrasonic down-propagation time; S1, after receiving the calibration instruction, close the inlet valve first, wait for a certain time to allow the bubbles to be discharged in time, and then close the outlet valve to make the interior in a static water state; S2, obtaining the temperature information of the still water in the pipe section and obtaining the corresponding sound velocity data; S3, combined with the compensation value of time and , using the sound velocity data and the flow path length parameters of the ultrasonic water meter, the theoretical values ​​of the upward propagation time and the downward propagation time are calculated. ; S4, start the ultrasonic transducer, and the received ultrasonic signal is filtered and amplified, and then the uplink time is obtained by the time counting method. and downlink time , calculate the uplink time and downlink time Measurement of time and ; S5, based on and , calculate the difference Δsum, if its absolute value is less than the threshold, enter S6, if its value is greater than the threshold, enter S1 process and retest; S6, calculate the new zero drift value , replace the zero drift error obtained by initialization before ; At this time and It is consistent with the actual measurement of S4; S7, based on the new zero drift value , calculate the true cumulative flow.

2. The method for online zero drift correction of an ultrasonic water meter as claimed in claim 1, characterized in that: The time and compensation value of the initialization process are obtained , the specific process is: Obtain the length L of the sound channel, and use a thermometer to measure the temperature at the time of initialization. Calculate the speed of sound at this time by using a table lookup method or an approximate analytical formula for the relationship between ultrasound and temperature. The approximate analytical formula is: C=1468+3.68(T-10)-0.0279(T-10)² At this time, C is the solved sound speed, in meters per second, and T is the temperature measured during initialization, in degrees Celsius; The uplink propagation time at initialization is measured by the timing chip and downlink propagation time The actual value of , sum the two, the summation formula is: Time and compensation value The calculation formula is: So as to obtain the compensation value of time during initialization .

3. The method for online zero drift correction of an ultrasonic water meter as claimed in claim 1, characterized in that: In S2, the temperature information of the still water in the pipe section is obtained by using a temperature sensor arranged in the bottom transverse pipe section, and the sound velocity information is obtained by looking up the table according to the temperature information and the sound velocity table in pure water; Or according to the formula of the speed of ultrasound in pure water and temperature, the speed of ultrasound at this time can be calculated using the approximate analytical formula of the relationship between ultrasound and temperature. .

4. The method for online zero drift correction of an ultrasonic water meter according to claim 1, characterized in that: The calculation process of S3 is: = + ≈2* + At this time, L represents the length of the ultrasonic flow meter sound channel; is the current propagation speed of ultrasound in water; is the velocity of water flowing in the pipe.

5. The method for online zero drift correction of an ultrasonic water meter as claimed in claim 1, characterized in that: The threshold value in S5 is 100 ps.

6. The method for online zero drift correction of an ultrasonic water meter as claimed in claim 1, characterized in that: The specific process of S7 is as follows: Calculate the velocity of water flowing in a pipe Correction value: in, To recalculate the new zero drift value in a still water environment, L is the length of the ultrasonic propagation channel. The length of the ultrasonic upward and downward propagation channels is the same. is the current propagation speed of ultrasound in water; Then calculate the volume instantaneous flow rate Correction value: K is the flow coefficient, which is used to correct the instantaneous flow error and is given by the actual flow test of the calibration device. is the diameter of the pipe; Finally calculate the cumulative flow Correction value: in, is the integration time constant, which divides the time equally according to the detection frequency. The frequency unit is times / second.

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