Anti-interference ultrasonic flowmeter

Abstract

The invention discloses an anti-interference ultrasonic flowmeter, relates to the technical field of ultrasonic measurement, and solves the technical problems that an existing ultrasonic flowmeter is easily interfered by the environment, so that the ultrasonic signal quality is poor, and the measurement precision is not high. The ultrasonic flowmeter comprises an ultrasonic transducer, and a de-noising circuit, an integrating circuit, a signal mixing circuit and a main controller which are sequentially connected with a receiving input end of the ultrasonic transducer, the noise elimination circuit is used for eliminating noise in the ultrasonic echo signal; the integrating circuit is used for repeatedly measuring the first echo signal for multiple times so as to offset noise in the first echo signal; the signal mixing circuit is used for eliminating amplitude and phase interference caused by the local oscillator clock signal in the second echo signal; the main controller is used for receiving the third echo signal and calculating the flow of the fluid to be measured according to the third echo signal. The ultrasonic flowmeter is used for improving the quality of ultrasonic signals and improving the measurement precision of the ultrasonic flowmeter.

Description

Technical Field

[0001] The invention relates to the technical field of ultrasonic measurement, and in particular to an anti-interference ultrasonic flowmeter. Background Art

[0002] Ultrasonic flowmeter is an instrument that uses the propagation characteristics of ultrasonic waves in fluids to measure the flow of carriers. Due to the advantages of ultrasonic flowmeters such as high measurement accuracy, large range ratio, and no pressure loss, they are widely used in the field of measuring the flow of liquids such as water and oil. Ultrasonic flowmeters usually consist of two or more ultrasonic transducers, which are installed at different positions in the pipeline to send and receive ultrasonic signals to each other. By measuring the transmission time of ultrasonic waves in the downstream and upstream directions of the medium, the flow velocity of the fluid can be calculated, and then the flow rate can be obtained. However, ultrasonic flowmeters are affected by many factors in actual applications, and are particularly susceptible to interference from the external environment. For example, in a water environment, they will be interfered by water noise and external electromagnetic noise, which will make the ultrasonic signal quality poor, resulting in a certain error in the transit time of the ultrasonic signal and low measurement accuracy.

[0003] In the process of implementing the present invention, the inventors found that there are at least the following problems in the prior art:

[0004] Existing ultrasonic flow meters are easily affected by environmental interference, resulting in poor ultrasonic signal quality and low measurement accuracy. Summary of the invention

[0005] The purpose of the present invention is to provide an anti-interference ultrasonic flowmeter to solve the technical problem that the ultrasonic flowmeter in the prior art is easily interfered by the environment, resulting in poor ultrasonic signal quality and low measurement accuracy. The preferred technical solution among the many technical solutions provided by the present invention can produce many technical effects as described below.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides an anti-interference ultrasonic flowmeter, comprising an ultrasonic transducer, a noise elimination circuit, an integration circuit, a signal mixing circuit and a main controller which are sequentially connected to a receiving input end of the ultrasonic transducer; the ultrasonic transducer is used to transmit an ultrasonic signal and receive an ultrasonic echo signal; the noise elimination circuit is used to eliminate noise in the ultrasonic echo signal to obtain a first echo signal; the integration circuit is used to repeatedly measure the first echo signal multiple times to offset the noise in the first echo signal to obtain a second echo signal; the signal mixing circuit is used to eliminate interference in amplitude and phase caused by a local oscillator clock signal in the second echo signal to obtain a third echo signal; the main controller is used to receive the third echo signal and calculate the flow rate of the fluid to be measured according to the third echo signal.

[0008] Optionally, the noise reduction circuit includes a first low-noise amplifier, a second low-noise amplifier, a narrowband filter, a band-stop filter and a subtractor; after the ultrasonic echo signal is input into the first low-noise amplifier and the second low-noise amplifier for amplification processing respectively, it is filtered through the narrowband filter and the band-stop filter respectively to obtain a first filtered signal and a second filtered signal, and the first filtered signal and the second filtered signal are input into the subtractor for denoising to eliminate the noise in the ultrasonic echo signal and obtain the first echo signal.

[0009] Optionally, the integration circuit includes an operational amplifier U4, a resistor R19, a capacitor C17, a resistor R18, and a capacitor C16; the positive input terminal of the operational amplifier U4 is connected to the noise cancellation circuit through the resistor R18, and the positive input terminal of the operational amplifier U4 is grounded through the capacitor C16, the reverse input terminal is grounded through the resistor R19, and the output terminal is connected to the signal mixing circuit; the capacitor C17 is connected in parallel between the reverse input terminal and the output terminal of the operational amplifier U4.

[0010] Optionally, the signal mixing circuit mixes the second echo signal and a local oscillator signal of the second echo signal by means of switch mixing to obtain a third echo signal.

[0011] Optionally, the signal mixing circuit includes a first analog switch, a second analog switch, a first inverter and a second inverter; the second echo signal and the local oscillator signal are both input into the first analog switch, and are connected to the second analog switch through the first inverter and the second inverter respectively; the output ends of the first inverter and the second inverter are both connected to the main controller.

[0012] Optionally, when the local oscillator signal is at a positive level, the first analog switch is turned on, the second analog switch is turned off, and the signal mixing circuit outputs a positive second echo signal; when the local oscillator signal is at a negative level, the first analog switch is turned off, the second analog switch is closed, and the signal mixing circuit outputs a negative second echo signal; the positive second echo signal and the negative second echo signal are mixed to obtain the third echo signal.

[0013] Optionally, the signal mixing circuit is also provided with a clock chip for detecting whether the obtained third echo signal is abnormal; and judging whether the third echo signal is abnormal by using the measurement clock signal MAIN_CLK sent by the clock chip to the first analog switch and the reference clock signal REF_CLK sent to the second analog switch.

[0014] Optionally, the measurement clock signal MAIN_CLK sent by the clock chip to the first analog switch and the reference clock signal REF_CLK sent to the second analog switch are used to determine whether the third echo signal is abnormal, including: the clock chip outputs the measurement clock signal MAIN_CLK and does not output the reference clock signal REF_CLK, and the first flow rate is calculated according to the difference between the measurement clock signal MAIN_CLK and the reference clock signal REF_CLK at this time; the clock chip does not output the measurement clock signal MAIN_CLK, but outputs the reference clock signal signal REF_CLK, and calculate the second flow rate according to the difference between the measurement clock signal MAIN_CLK and the reference clock signal REF_CLK at this time; determine whether the absolute value of the difference between the first flow rate and the second flow rate is greater than a preset error threshold; if the absolute value of the difference between the first flow rate and the second flow rate is greater than the error threshold, determine that the third echo signal detected this time is abnormal, and re-detect; if the absolute value of the difference between the first flow rate and the second flow rate is not greater than the preset error threshold, determine that the third echo signal detected this time is normal, and obtain the third echo signal.

[0015] Optionally, a low-pass filter circuit and an emitter follower circuit are also arranged between the signal mixing circuit and the main controller; the low-pass filter circuit is used to receive the third echo signal and filter out the higher harmonics in the third echo signal; the emitter follower circuit is used to receive the filtered third echo signal and increase the input impedance of the third echo signal.

[0016] Optionally, a frequency selective amplifier circuit is further provided between the integration circuit and the signal mixing circuit; the frequency selective amplifier circuit is used to amplify the second echo signal within the frequency band range and suppress the second echo signal outside the frequency band range.

[0017] Implementing one of the above technical solutions of the present invention has the following advantages or beneficial effects:

[0018] The present invention can remove most of the noise of the ultrasonic echo signal received by the ultrasonic transducer by setting a noise elimination circuit, thereby improving the signal-to-noise ratio of the ultrasonic echo signal; further, an integration circuit is provided, and multiple measurements are performed according to the repeatability and randomness of the signal, and the signals are accumulated in phase. The noise cancels each other due to its randomness, thereby achieving further noise reduction of the signal; at the same time, a signal mixing circuit is also provided, which can eliminate the interference of the amplitude and phase brought by the local oscillation clock signal, and further improve the signal quality; through the multiple denoising of the noise elimination circuit, the integration circuit and the signal mixing circuit, a large part of the noise in the ultrasonic echo signal can be removed, the quality of the ultrasonic signal can be improved, and the measurement accuracy of the ultrasonic flowmeter can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. It is obvious that the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0020] Figure 1 is a structural block diagram of an anti-interference ultrasonic flowmeter according to an embodiment of the present invention;

[0021] Figure 2 is a structural block diagram of a noise cancellation circuit according to an embodiment of the present invention;

[0022] Figure 3 is a structural block diagram of a phase subtractor according to an embodiment of the present invention;

[0023] Figure 4 is a circuit diagram of a first low noise amplifier and a second low noise amplifier according to an embodiment of the present invention;

[0024] Figure 5 is a circuit diagram of a narrowband filter according to an embodiment of the present invention;

[0025] Figure 6 is a circuit diagram of a band-stop filter according to an embodiment of the present invention;

[0026] Figure 7 is a circuit diagram of an integration circuit according to an embodiment of the present invention;

[0027] Figure 8 is a structural block diagram of a signal mixing circuit according to an embodiment of the present invention;

[0028] Fig. 9 is a circuit diagram of a first analog switch and a second analog switch according to an embodiment of the present invention;

[0029] Fig.10 4 is a circuit diagram of a clock chip according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention clearer, the various exemplary embodiments to be described below will refer to the corresponding drawings, which constitute a part of the exemplary embodiments, wherein various exemplary embodiments that may be used to implement the present invention are described. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation methods described in the following exemplary embodiments do not represent all implementation methods consistent with the present disclosure. It should be understood that they are only examples of processes, methods, devices, etc. that are consistent with some aspects of the present disclosure as detailed in the attached claims, and other embodiments may also be used, or the embodiments listed herein may be modified in structure and function without departing from the scope and essence of the present invention.

[0031] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", etc. indicate the orientation or positional relationship based on the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the elements referred to must have a specific orientation, be constructed and operated in a specific orientation. The terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. The term "multiple" means two or more. The terms "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, an integral connection, a mechanical connection, an electrical connection, a communication connection, a direct connection, an indirect connection through an intermediate medium, and can be the internal connection of two elements or the interaction relationship between two elements. The term "and / or" includes any and all combinations of one or more related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0032] In order to illustrate the technical solution of the present invention, a specific embodiment is used below for description, and only the parts related to the embodiment of the present invention are shown.

[0033] Embodiment 1:

[0034] like Figure 1As shown, the present invention provides an anti-interference ultrasonic flowmeter, including an ultrasonic transducer, a noise elimination circuit, an integration circuit, a signal mixing circuit and a main controller connected to the receiving input end of the ultrasonic transducer in sequence; the ultrasonic transducer is used to transmit ultrasonic signals and receive ultrasonic echo signals; at least two ultrasonic transducers are provided, one is set as a transmitting transducer, and the other is correspondingly set as a receiving transducer, and the two can alternately transmit and receive ultrasonic signals and ultrasonic echo signals along the flow direction of the medium and the reverse direction of the flow of the medium; after the ultrasonic transducer receives the ultrasonic echo signal, it sends it to the noise elimination circuit through the receiving input end. The noise elimination circuit is used to eliminate the noise in the ultrasonic echo signal to obtain a first echo signal; the integration circuit is used to repeatedly measure the first echo signal multiple times to offset the noise in the first echo signal to obtain a second echo signal; the signal mixing circuit is used to eliminate the interference of amplitude and phase caused by the local oscillation clock signal in the second echo signal to obtain a third echo signal; the main controller is used to receive the third echo signal and calculate the flow rate of the fluid to be measured according to the third echo signal.

[0035] The present invention can remove most of the noise of the ultrasonic echo signal received by the ultrasonic transducer by setting a noise elimination circuit, thereby improving the signal-to-noise ratio of the ultrasonic echo signal; further, an integration circuit is provided, and multiple measurements are performed according to the repeatability and randomness of the signal, and the signals are accumulated in phase. The noise cancels each other due to its randomness, thereby achieving further noise reduction of the signal; at the same time, a signal mixing circuit is also provided, which can eliminate the interference of the amplitude and phase brought by the local oscillation clock signal, and further improve the signal quality; through the multiple denoising of the noise elimination circuit, the integration circuit and the signal mixing circuit, a large part of the noise in the ultrasonic echo signal can be removed, the quality of the ultrasonic signal can be improved, and the measurement accuracy of the ultrasonic flowmeter can be improved.

[0036] As an alternative implementation, Figure 2 As shown, the noise reduction circuit includes a first low noise amplifier, a second low noise amplifier, a narrowband filter, a band stop filter and a phase subtractor; the output end of the first low noise amplifier is connected to the input end of the narrowband filter, the output end of the second low noise amplifier is connected to the input end of the band stop filter, and the output end of the narrowband filter and the output end of the band stop filter are respectively connected to the input end of the phase subtractor; the ultrasonic echo signal is input into the first low noise amplifier and the second low noise amplifier for amplification processing respectively, and then filtered by the narrowband filter and the band stop filter respectively to obtain a first filtered signal and a second filtered signal, and the first filtered signal and the second filtered signal are input into the phase subtractor for denoising to eliminate the noise in the ultrasonic echo signal and obtain the first echo signal.

[0037] Specifically, Figure 3As shown, the phase subtractor includes a resistor R1, a resistor R2, a resistor R3 and an operational amplifier U1, the first signal V1 is input into the positive input terminal of the operational amplifier U1 through the resistor R1, the second signal V2 is input into the reverse input terminal of the operational amplifier U1 through the resistor R2, and the resistor R3 is connected in parallel between the reverse input terminal and the output terminal of the operational amplifier, wherein the first signal V1 is an ultrasonic echo signal filtered by a narrowband filter, and the second signal V2 is an ultrasonic echo signal filtered by a band-stop filter. The working principle of the noise elimination circuit is as follows: the received ultrasonic echo signal is f0+△f, wherein f0 is the measured signal, and △f is the noise signal. After the ultrasonic echo signal is input into the first low-noise amplifier and the second low-noise amplifier for amplification, the signal becomes A*(f0+△f), wherein A is the amplification multiple, one way is filtered by the narrowband filter to obtain the first signal V1=A*f0+A*△f, and the other way is filtered by the band-stop filter to obtain the second signal V2=A*△f. The two signals are input into the positive input and negative input of the operational amplifier U3 respectively, and are set in the phase subtractor, R3 = H*R2, then the output of the phase subtractor V0 = (H+1)*S2-H*S1 = (H+1)*A*f0+A*△f. Therefore, the signal-to-noise ratio when the noise elimination circuit is not used is The signal-to-noise ratio after using the noise elimination circuit is Therefore, within the range allowed by the bandwidth of the phase subtractor, the higher the multiple of R3 / R2, the higher the signal-to-noise ratio of the signal after noise cancellation by the noise cancellation circuit, so that most of the noise in the ultrasonic echo signal can be effectively removed by the noise cancellation circuit.

[0038] like Figure 4 As shown, the first low noise amplifier and the second low noise amplifier both use a low noise instrumentation amplifier of model INA827 / AD8236, which has low noise and high precision and can reduce the interference of ultrasonic echo signals during amplification. Figure 5 As shown, the narrowband filter includes an operational amplifier U3, a capacitor C10, a capacitor C11, a resistor R11, a resistor R12, a resistor R13 and a resistor R14; the amplified ultrasonic echo signal is sequentially input to the positive input terminal of the operational amplifier U3 through the resistor R11 and the capacitor C10, the positive input terminal of the operational amplifier U3 is also grounded through the resistor R12, the reverse input terminal is grounded through the resistor R14, and the output terminal is connected to the subtractor; the resistor R13 is connected in parallel between the output terminal and the positive input terminal of the operational amplifier U3; the model of the operational amplifier U3 is ADA4891-1ARJZ-R7, which has the characteristics of high speed and stability. The narrowband filter can suppress unnecessary signals in the ultrasonic echo signal. Figure 6As shown, the band-stop filter includes an operational amplifier U2, a resistor R5, a resistor R4, a resistor R6, a resistor R7, a capacitor C5, a capacitor C6 and a capacitor C7; the amplified ultrasonic echo signal is sequentially input into the positive input end of the operational amplifier U2 through the resistor R4 and the resistor R5; the reverse input end of the operational amplifier U2 is grounded through the resistor R7, and the output end is connected to the phase subtractor. The resistor R4 and the resistor R5 are grounded through the capacitor C7; the capacitor C5 and the capacitor C6 are connected in parallel at both ends of the resistor R4 and the resistor R5, and the capacitor C5 and the capacitor C6 are connected in series. One end of the resistor R6 is connected to the output end of the operational amplifier U2, and the other end is connected between the capacitor C5 and the capacitor C6. The model of the operational amplifier U2 is ADA4891, which has the characteristics of high precision and small error. The band-stop filter can filter out the signals in the unnecessary frequency range in the ultrasonic echo signal, thereby eliminating the noise and interference signals in the frequency range.

[0039] As an alternative implementation, Figure 7 As shown, the integration circuit includes an operational amplifier U4, a resistor R19, a capacitor C17, a resistor R18, and a capacitor C16; the positive input end of the operational amplifier U4 is connected to the noise elimination circuit through the resistor R18, and the positive input end of the operational amplifier U4 is grounded through the capacitor C16, the reverse input end is grounded through the resistor R19, and the output end is connected to the signal mixing circuit; the capacitor C17 is connected in parallel between the reverse input end and the output end of the operational amplifier U4. The model of the operational amplifier U3 is also ADA4891-1ARJZ-R7, which can ensure the test stability of the integration circuit. The resistor R18 and the capacitor C16 constitute a low-pass filter, which can filter the input first echo signal, and the resistor R19, the capacitor C17 and the operational amplifier U4 constitute an integration detection circuit for repeatedly measuring the signal. The integration circuit can repeatedly measure the first echo signal according to the repeatability of the signal and the randomness of the noise, so that the signals are accumulated in phase, and the noise cancels each other due to its randomness, thereby achieving secondary noise reduction.

[0040] As an optional implementation, the signal mixing circuit mixes the second echo signal and the local oscillator signal of the second echo signal by means of switch mixing to obtain a third echo signal. Usually, mixing is implemented by using nonlinear components or dedicated multipliers, but this mixing method will cause the amplitude and phase information of the local oscillator signal to be introduced into the output signal, which will interfere with the output signal, and both nonlinear components and dedicated multipliers will generate a lot of interference and distortion, including interference noise, parasitic channel interference, cross-modulation distortion, and mutual modulation distortion, which will have an adverse effect on the performance of the receiver. Therefore, the signal mixing circuit of this embodiment adopts a switch mixing method, which can effectively suppress the interference caused by the above factors.

[0041] Specifically, Figure 8As shown, the signal mixing circuit includes a first analog switch K1, a second analog switch K2, a first inverter D1 and a second inverter D2; the second echo signal V3 and the local oscillator signal V4 are both input into the first analog switch K1, and are connected to the first analog switch K2 through the first inverter D1 and the second inverter D2 respectively; the output ends of the first inverter D1 and the second inverter D2 are both connected to the main controller. When the local oscillator signal is at a positive level, the first analog switch K1 is turned on, the first analog switch K2 is turned off, and the signal mixing circuit outputs a positive second echo signal; when the local oscillator signal is at a negative level, the first analog switch K1 is turned off, the first analog switch K2 is closed, and the signal mixing circuit outputs a negative second echo signal; the positive second echo signal and the negative second echo signal are mixed to obtain a third echo signal. As shown Fig. 9 As shown, the models of the first analog switch K1 and the first analog switch K2 are both SN74LV4051ADR, which is an 8-way multiplexing chip. All ports support operation with mixed mode voltage, which can ensure the accuracy of signal mixing.

[0042] Specifically, the working principle of the signal mixing circuit is as follows: the input second echo signal V3 and its local oscillator signal V4 are: Then take the square wave signal V with the same frequency as the local oscillator signal V4 ’ 4 is:

[0043] V ’ 4 can be expanded into Fourier series to obtain:

[0044]

[0045] Obviously, V'4 is a collection of multiple harmonics with ω2 as the fundamental wave, so V3 and V ’ 4 mixing, and then taking the fundamental wave to obtain V3 and V ’ 4 mixing result, V3 and V ’ The mixing of 4 is:

[0046]

[0047] Then, after filtering out the sum frequency and difference frequency high-order harmonics through a low-pass filter circuit, formula (1) can be obtained:

[0048]

[0049] It can be seen from formula (1) that the final result after mixing is a signal whose amplitude and phase are only related to the input signal, and whose frequency is the difference between the input signal and the local oscillator signal. Obviously, mixing in this way can preserve the original information of the signal to the greatest extent while minimizing the influence of the local oscillator signal.

[0050] The input second echo signal is divided into two paths, which are input to the first analog switch K1 and the first analog switch K2K2 respectively. The conduction of the analog switch is affected by the signal V ’ 4(V ’ 4 is a square wave signal with the same frequency as the local oscillator signal V4). When the local oscillator signal is at a positive level (i.e., the square wave signal V ’ 4 is a positive level), the first analog switch K1 is turned on, the first analog switch K2 is turned off, and the signal mixing circuit outputs a positive second echo signal V3; when the local oscillator signal is a negative level (i.e., the square wave signal V ’ 4 is a negative level), the first analog switch K1 is turned off, the first analog switch K2 is closed, and the signal mixing circuit outputs a negative second echo signal of -V3; the positive second echo signal and the negative second echo signal are mixed to obtain a third echo signal. Obviously, the obtained third echo signal is consistent with the result of formula (1). Thus, signal mixing is realized. In this way, the output signal amplitude and phase only depend on the input second echo signal V3, and are not related to the square wave signal V ’ 4. This removes the interference of the amplitude and phase information of the local oscillator signal, further improving the accuracy of the ultrasonic echo signal.

[0051] The output result after mixing contains high-order harmonics. Therefore, this embodiment also sets a low-pass filter circuit to filter V3 and V ’ 4 is mixed and processed to obtain a third echo signal. A low-pass filter circuit and an emitter follower circuit are also arranged between the signal mixing circuit and the main controller; the low-pass filter circuit is used to receive the third echo signal and filter out the higher harmonics in the third echo signal; the emitter follower circuit is used to receive the filtered third echo signal and increase the input impedance of the third echo signal. Adding an emitter follower circuit at the ADC acquisition interface of the main controller can reduce signal interference. The higher input impedance can effectively reduce the current flow in the circuit, thereby reducing interference between signals; it can improve the signal-to-noise ratio. By reducing the noise current, the high input impedance can improve the signal-to-noise ratio, making the signal transmission between the signal source and the circuit clearer; it can also reduce errors. The high input impedance can reduce the offset voltage and current, thereby reducing the error in the measurement process.

[0052] like Fig.10 As shown, the signal mixing circuit is further provided with a clock chip for detecting whether the obtained third echo signal is abnormal; the CLK0 pin of the clock chip is connected to the pin 11 of the first analog switch K1, and the CLK0 pin is connected to the pin 10 of the first analog switch K2. Whether the third echo signal is abnormal is determined by the measurement clock signal MAIN_CLK sent by the clock chip to the first analog switch K1 and the reference clock signal REF_CLK sent to the first analog switch K2.

[0053] Specifically, to determine whether the third echo signal is abnormal by using the measurement clock signal MAIN_CLK sent by the clock chip to the first analog switch K1 and the reference clock signal REF_CLK sent to the first analog switch K2, the following steps are included: S1. The clock chip outputs the measurement clock signal MAIN_CLK and does not output the reference clock signal REF_CLK. Calculate the first flow rate according to the difference between the measurement clock signal MAIN_CLK and the reference clock signal REF_CLK at this time; S2. The clock chip does not output the measurement clock signal MAIN_CLK and outputs the reference clock signal REF_CLK. Calculate the second flow rate according to the difference between the measurement clock signal MAIN_CLK and the reference clock signal REF_CLK at this time; S3. Determine whether the absolute value of the difference between the first flow rate and the second flow rate is greater than the preset error threshold; S4. If the absolute value of the difference between the first flow rate and the second flow rate is greater than the preset error threshold, it is determined that the third echo signal detected this time is abnormal and re-detection is required; S5. If the absolute value of the difference between the first flow rate and the second flow rate is not greater than the preset error threshold, it is determined that the detection this time is normal and the third echo signal is obtained. Whenever a third echo signal passes through the signal mixing circuit, the clock chip sends the measurement clock signal MAIN_CLK and the reference clock signal REF_CLK to the first analog switch K1 and the first analog switch K2. For example, set the measurement clock signal MAIN_CLK to 1 MHz, the reference clock signal REF_CLK to 900 KHz, the signal SIG_IN (i.e., the above-mentioned second echo signal and its local oscillator signal) input to the two analog switches to be 1 MHz + δf, where δf is the frequency offset measured from the received data, and the error threshold is a; during the detection, first receive the measurement clock signal MAIN_CLK and do not receive the reference clock signal REF_CLK, then calculate the signal F(SIG_OUT) output by the analog switch as F(SIG_OUT) = F(MAIN_CLK) - F(REF_CLK) = δf1, and then calculate the first flow rate V1 according to the value of δf1; then receive the reference clock signal REF_CLK and do not receive the measurement clock signal MAIN_CLK, then calculate the signal SIG_OUT output by the analog switch as: F(SIG_OUT) = F(MAIN_CLK) - F(REF_CLK) = 100 KHz + δf2, and then calculate the second flow rate V2 according to the value of δf2. If |V1 - V2| < a, it means that the flow rate measured this time is normal and the third ultrasonic echo signal passing through is not abnormal and can pass normally; if |V1 - V2| > a, it means that the flow rate measured this time is abnormal, there may be a large error in the third ultrasonic echo signal, and the third echo signal passing through this time is not used and re-measurement is required. By setting the clock chip to detect the two clock signals of the analog switch, the accuracy and stability of the ultrasonic echo signal are improved.

[0054] A frequency-selective amplifier circuit is also provided between the integration circuit and the signal mixing circuit; the frequency-selective amplifier circuit is used to amplify the second echo signal within the frequency band and suppress the second echo signal outside the frequency band. The frequency-selective amplifier circuit is an RC series-parallel frequency-selective amplifier circuit constructed by an operational amplifier, and the upper sideband and lower sideband of the selected frequency can be determined by f=1 / 2πRC. The function of the frequency-selective amplifier module is to amplify the signal within the required frequency band and suppress the signal outside the frequency band, thereby improving the signal-to-noise ratio of the useful signal.

[0055] The embodiment is only a specific example and does not represent only one implementation mode of the present invention.

[0056] The above description is only the preferred embodiment of the present invention. It is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the protection scope of the present invention.

Claims

1. An anti-interference ultrasonic flow meter, characterized in that: It includes an ultrasonic transducer, a noise elimination circuit, an integration circuit, a signal mixing circuit and a main controller which are sequentially connected to the receiving input end of the ultrasonic transducer; The ultrasonic transducer is used to transmit ultrasonic signals and receive ultrasonic echo signals; The noise elimination circuit is used to eliminate the noise in the ultrasonic echo signal to obtain a first echo signal; The integration circuit is used to repeatedly measure the first echo signal for multiple times to offset the noise in the first echo signal and obtain a second echo signal; The signal mixing circuit is used to eliminate the interference of amplitude and phase caused by the local oscillator clock signal in the second echo signal, so as to obtain a third echo signal; The main controller is used to receive the third echo signal and calculate the flow rate of the fluid to be measured according to the third echo signal.

2. The anti-interference ultrasonic flowmeter according to claim 1, characterized in that: The noise reduction circuit includes a first low-noise amplifier, a second low-noise amplifier, a narrowband filter, a band-stop filter and a subtractor; after the ultrasonic echo signal is input into the first low-noise amplifier and the second low-noise amplifier for amplification processing respectively, it is filtered through the narrowband filter and the band-stop filter respectively to obtain a first filtered signal and a second filtered signal, and the first filtered signal and the second filtered signal are input into the subtractor for denoising to eliminate the noise in the ultrasonic echo signal and obtain the first echo signal.

3. The anti-interference ultrasonic flowmeter according to claim 1, characterized in that: The integration circuit includes an operational amplifier U4, a resistor R19, a capacitor C17, a resistor R18, and a capacitor C16; the positive input terminal of the operational amplifier U4 is connected to the noise elimination circuit through the resistor R18, and the positive input terminal of the operational amplifier U4 is grounded through the capacitor C16, the reverse input terminal is grounded through the resistor R19, and the output terminal is connected to the signal mixing circuit; the capacitor C17 is connected in parallel between the reverse input terminal and the output terminal of the operational amplifier U4.

4. The anti-interference ultrasonic flowmeter according to claim 1, characterized in that: The signal mixing circuit mixes the second echo signal and the local oscillator signal of the second echo signal by means of switch mixing to obtain a third echo signal.

5. The anti-interference ultrasonic flowmeter according to claim 4, characterized in that: The signal mixing circuit includes a first analog switch, a second analog switch, a first inverter and a second inverter; the second echo signal and the local oscillator signal are both input into the first analog switch and are connected to the second analog switch through the first inverter and the second inverter respectively; the output ends of the first inverter and the second inverter are both connected to the main controller.

6. The anti-interference ultrasonic flowmeter according to claim 5, characterized in that: When the local oscillator signal is at a positive level, the first analog switch is turned on, the second analog switch is turned off, and the signal mixing circuit outputs a positive second echo signal; when the local oscillator signal is at a negative level, the first analog switch is turned off, the second analog switch is closed, and the signal mixing circuit outputs a negative second echo signal; the positive second echo signal and the negative second echo signal are mixed to obtain the third echo signal.

7. The anti-interference ultrasonic flowmeter according to claim 6, characterized in that: The signal mixing circuit is also provided with a clock chip for detecting whether the obtained third echo signal is abnormal; the measurement clock signal MAIN_CLK sent by the clock chip to the first analog switch and the reference clock signal REF_CLK sent to the second analog switch are used to determine whether the third echo signal is abnormal.

8. The anti-interference ultrasonic flowmeter according to claim 7, characterized in that: The method of judging whether the third echo signal is abnormal based on the measurement clock signal MAIN_CLK sent by the clock chip to the first analog switch and the reference clock signal REF_CLK sent to the second analog switch comprises: The clock chip outputs the measurement clock signal MAIN_CLK and does not output the reference clock signal REF_CLK, and the first flow rate is calculated according to the difference between the measurement clock signal MAIN_CLK and the reference clock signal REF_CLK; The clock chip does not output the measurement clock signal MAIN_CLK, but outputs the reference clock signal REF_CLK, and calculates the second flow rate according to the difference between the measurement clock signal MAIN_CLK and the reference clock signal REF_CLK; Determining whether an absolute value of a difference between the first flow rate and the second flow rate is greater than a preset error threshold; If the absolute value of the difference between the first flow velocity and the second flow velocity is greater than the error threshold, it is determined that the third echo signal detected this time is abnormal and re-detection is performed; If the absolute value of the difference between the first flow velocity and the second flow velocity is not greater than a preset error threshold, it is determined that the third echo signal detected this time is normal, and the third echo signal is acquired.

9. The anti-interference ultrasonic flowmeter according to claim 1, characterized in that: A low-pass filter circuit and an emitter follower circuit are also arranged between the signal mixing circuit and the main controller; the low-pass filter circuit is used to receive the third echo signal and filter out the higher harmonics in the third echo signal; the emitter follower circuit is used to receive the filtered third echo signal and increase the input impedance of the third echo signal.

10. The anti-interference ultrasonic flowmeter according to claim 1, characterized in that: A frequency-selective amplifier circuit is also provided between the integration circuit and the signal mixing circuit; the frequency-selective amplifier circuit is used to amplify the second echo signal within the frequency band and suppress the second echo signal outside the frequency band.

Images