An ultrasonic transducer receiving automatic shielding circuit

Abstract

The application discloses an automatic shielding circuit for an ultrasonic transducer receiver, which comprises a transmitting transducer, a clock generator, a flip-flop, a first analog switch and a receiving transducer connected in series; the normally open pin of the first analog switch is connected to the ground; the flip-flop outputs a high level to the first analog switch in a set time after the transmitting transducer transmits a signal; the common pin of the first analog switch is connected to the normally open pin, and the receiving transducer is grounded and forms a signal shield; the clock generator is used for controlling the time when the receiving transducer forms the signal shield; when the flip-flop outputs a low level, the common pin of the first analog switch is connected to the normally closed pin, and the receiving transducer normally receives a signal. The application can effectively reduce the influence of noise and other interference signals on the measurement result and improve the measurement accuracy of the ultrasonic gas meter.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ultrasonic circuit, in particular to an automatic shielding circuit for ultrasonic transducer receiving. BACKGROUND

[0002] The ultrasonic gas meter is an instrument for gas measurement by using ultrasonic technology. Its working principle is to emit and receive ultrasonic waves by a pair of ultrasonic transducers installed upstream and downstream of the gas flow, and to measure the gas flow rate in the pipeline by using the time difference of ultrasonic signal propagation in the gas medium along the flow and counter-flow directions, and then to calculate the instantaneous flow rate and cumulative gas consumption in the pipeline.

[0003] The prior art ultrasonic gas meter mainly uses threshold method or correlation method for flow measurement. Both methods rely on the emission transducer to emit ultrasonic signals and the receiving transducer to capture the reflected signals to calculate the flow.

[0004] However, this technical solution has certain technical defects: when the emission transducer excites signals, the receiving transducer is easily affected by noise and other interference signals due to weak signals. These interferences may come from environmental noise, electromagnetic interference, equipment vibration or circuit transient response, etc. Due to the existence of interference signals, the receiving transducer cannot accurately capture the reflected effective signals in the initial stage of signal excitation, resulting in inaccurate measurement results. SUMMARY

[0005] In view of the above defects of the prior art, the present application provides an automatic shielding circuit for ultrasonic excitation and receiving, which can effectively reduce the influence of noise and other interference signals on the measurement results and improve the measurement accuracy of the ultrasonic gas meter.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present application is:

[0007] An automatic shielding circuit for ultrasonic transducer receiving, comprising an emission transducer, a clock generator, a flip-flop, a first analog switch and a receiving transducer connected in series; the normally open pin of the first analog switch is connected to ground; the flip-flop outputs high level to the first analog switch within a set time after the emission transducer emits signals, the common pin of the first analog switch is connected to the normally open pin, and the receiving transducer is thus grounded and forms a signal shield; the clock generator is used to control the time for the receiving transducer to form a signal shield; when the flip-flop outputs low level, the common pin of the first analog switch is connected to the normally closed pin, and the receiving transducer normally receives signals.

[0008] In ultrasonic flow metering, the reason that the shielding is no longer disturbed by signals such as noise after a period of time is mainly related to the characteristics of the ultrasonic signal and the design of the shielding circuit. After the ultrasonic transducer transmits a signal, it needs a certain time for the signal to propagate to the measured medium (such as gas) and then reflect back. During this period, the receiving transducer is shielded to avoid receiving the strong signal generated during transmission and possible noise. In addition, the ultrasonic signal gradually attenuates during propagation in the medium, and after a period of shielding, the strong signal generated during transmission and noise have been attenuated to a low enough level that does not interfere with the receiving transducer.

[0009] The transmitting transducer normally excites a signal, and the receiving transducer receives the signal after the excitation signal is finished. The flip-flop and the first analog switch are located in the circuit between the excitation signal and the receiving signal. The purpose is to automatically capture the excitation signal and keep the receiving transducer grounded for a set time, thereby shielding the interference signal. The clock generator is used to control the flip-flop to output a high level and the time of the high level, such as when the clock generator generates an excitation pulse and the rising edge of the first pulse arrives, the flip-flop outputs a high level to the first analog switch until the last pulse of the clock generator ends. The high level of the flip-flop will control the first analog switch, so that the common pin and the normally open pin of the first analog switch are connected. Since the normally open pin is grounded, the receiving transducer will be grounded at this time, shielding external signals, and thus shielding noise signals. When the flip-flop outputs a low level to the first analog switch, the common pin and the normally closed pin of the first analog switch are connected, and at this time the receiving transducer is not connected to any impedance, normally receiving signals.

[0010] In summary, the present application can automatically start the shielding mechanism after the transmitting transducer transmits a signal, and after a precisely set time delay, the receiving transducer will automatically unshield, allowing the receiving transducer to start capturing and processing signals, protecting the receiving transducer from interference, significantly reducing the negative impact of noise and interference on the measurement results, and greatly improving the measurement accuracy of ultrasonic gas meters. The technical solution realizes automatic control without the need for manual intervention or reliance on complex control logic, simplifies the operation process, and also ensures accurate control of the shielding time.

[0011] As a preferred embodiment, it further comprises a transducer one and a transducer two, and the two transducers are commonly connected with a control circuit, and the control circuit is used to select one of the transducers as the transmitting transducer and the other as the receiving transducer.

[0012] Through the control circuit, the system can flexibly select transducer one or transducer two as the transmitting transducer as needed, and the other naturally becomes the receiving transducer.

[0013] As a preferred, the control circuit comprises a second analog switch and a third analog switch; the second analog switch and the third analog switch are jointly connected with a signal generator, the signal generator generates a signal to the second analog switch and the third analog switch, and the second analog switch and the third analog switch select specific transmitting transducer and receiving transducer.

[0014] When the signal of the signal generator is 0, the second analog switch and the third analog switch select transducer two as the receiving transducer and transducer one as the transmitting transducer, at this time, the exciting pulse of the clock generator drives transducer one to send ultrasonic wave signal, and transducer two receives the ultrasonic wave signal and converts it into voltage signal. Similarly, when the signal of the signal generator is 1, the second analog switch and the third analog switch select transducer one as the receiving transducer and transducer two as the transmitting transducer, and when the exciting pulse of the clock generator drives transducer two to send ultrasonic wave signal, transducer one receives the ultrasonic wave signal and converts it into voltage signal.

[0015] As a preferred, the external resistance and capacitance connection pin of the flip-flop is connected with a power supply, and a third capacitor is connected between the power supply and the ground, for stabilizing the power supply of the flip-flop.

[0016] The third capacitor connected between the power supply and the ground is used to stabilize the power supply or reference voltage of the flip-flop, reduce the influence of power supply noise on the working of the flip-flop, and ensure that the flip-flop can reliably respond to the pulse signal of the clock generator.

[0017] As a preferred, the external capacitance connection pin of the flip-flop is connected with a fifth capacitor, which is used to form an RC delay circuit with the second resistance on the external resistance and capacitance connection pin of the flip-flop, to control the delay time of the high level output of the flip-flop.

[0018] The RC delay circuit is used to control the delay time of the high level output of the flip-flop, for example, when the exciting pulse appears at the clock generator end, when the falling edge of the first pulse comes, the output end of the flip-flop will output high level, and this signal will maintain high level for about 50us after the last pulse signal of the clock generator comes.

[0019] As a preferred, it further comprises an operational amplifier connected with the receiving transducer, for amplifying the signal received by the receiving transducer and transmitting it to the rear-end microcontroller unit.

[0020] The operational amplifier is used to amplify the ultrasonic wave signal received by the receiving transducer (transducer one or transducer two). Since the received signal is usually very weak, it needs to be amplified so that the microcontroller unit can effectively process and analyze it. The amplified signal output is transmitted to the rear-end microcontroller unit (MCU).

[0021] As a preferred, the inverting input of the operational amplifier is connected with the output through a capacitor six and a resistor four, and the capacitor six and the resistor four are connected in parallel to form an RC network, which is used to stabilize the working point of the operational amplifier and filter high-frequency noise.

[0022] By connecting an RC network between the inverting input and the output of the operational amplifier, the working point of the amplifier can be stabilized, reducing the drift of the working point caused by external interference or power fluctuations, thereby improving the stability and reliability of the amplifier. The working point refers to the static working state of the operational amplifier when it does not receive the transducer signal input. This state includes the output voltage of the operational amplifier and the static current through the operational amplifier. Stabilizing the working point means that the operational amplifier can work at a predetermined, stable voltage and current level, which is crucial to ensure the accuracy and reliability of signal processing. At the same time, high-frequency noise can be effectively filtered out, because the capacitor six can block the transmission of high-frequency noise to the inverting input, and the resistor four provides a low-impedance path for high-frequency noise to the ground, thereby reducing the impact of high-frequency noise on the amplified signal.

[0023] As a preferred, the receiving transducer is connected with the operational amplifier through a capacitor nine, which is used to isolate the DC component and allow the AC signal to pass through.

[0024] By isolating the DC component through the capacitor nine, the DC bias and noise in the circuit can be reduced, and the signal-to-noise ratio of the signal can be improved. The capacitor nine allows the AC signal to pass through while blocking the DC component, ensuring that the operational amplifier amplifies the effective AC signal, thereby improving the integrity and accuracy of the signal. At the same time, the capacitor nine can prevent excessive voltage or current from damaging the operational amplifier, especially when voltage spikes may occur between the receiving transducer and the operational amplifier.

[0025] Compared with the prior art, the beneficial effects of the present application are reflected in:

[0026] 1. The present application shields the receiving transducer immediately after the transmitting transducer excites the signal to avoid the strong signal and accompanying noise received in the initial stage of signal excitation. The present application does not require manual operation or rely on complex control logic, reducing the complexity of operation, and can accurately control the shielding time, thereby ensuring effective shielding of interference signals, thereby improving the accuracy and reliability of flow measurement.

[0027] 2. By controlling the circuit, not only provides a high degree of configurability, allowing the system to adjust according to specific application scenarios or needs, but also allows the system to adapt to different operating conditions and environments, because different transducers may have better adaptability to different media or conditions. In addition, if a transducer fails or performance declines, the system can switch to another transducer through the control circuit, thereby ensuring continuous operation of the system and continuous data acquisition.

[0028] 3. The power supply or reference voltage of the flip-flop is stabilized by connecting a capacitor three between the power supply and the ground, so as to reduce the influence of the power supply noise on the operation of the flip-flop and ensure that the flip-flop can reliably respond to the pulse signal of the clock generator.

[0029] 4. The received weak signal is amplified by the operational amplifier, so as to ensure that the signal will not lose information in the process of being transmitted to the MCU due to the weak signal, and help to reduce the influence of noise and interference, thereby improving the quality of the signal and enabling the MCU to more accurately analyze the signal. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a circuit diagram of the embodiment.

[0031] Wherein:

[0032] CLK, clock generator; U1, second analog switch; U2, third analog switch; U3, flip-flop; U4, first analog switch; operational amplifier U5, HNQ1, transducer one; HNQ2, transducer two; TSEN, signal generator; C3, capacitor three; C5, capacitor five; C6, capacitor six; C9, capacitor nine; C10, capacitor ten; R2, resistor two; R4, resistor four; R5, resistor five; R6, resistor six; R7, resistor seven; R8, resistor eight. DETAILED DESCRIPTION

[0033] In order to make the technical means, creative features, purposes and effects of the invention easy to understand, the invention will be further described in combination with specific drawings. However, the invention is not limited to the following embodiments.

[0034] It should be understood that the structure, proportion, size, etc. shown in the drawings attached to the present specification are only used to cooperate with the content disclosed in the specification, so as to be understood and read by those skilled in the art, and do not have technical substantive significance, and any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the invention, should still fall within the scope of the technical content disclosed by the invention.

[0035] Embodiment 1:

[0036] As Figure 1The automatic shielding circuit of an ultrasonic transducer receiver comprises a transmitting transducer, a clock generator CLK, a flip-flop U3, a first analog switch U4 and a receiving transducer connected in series. The normally open pin of the first analog switch U4 is connected to ground. The flip-flop U3 outputs high level to the first analog switch U4 within a set time after the transmitting transducer transmits a signal. The common pin of the first analog switch U4 is connected to the normally open pin, so that the receiving transducer is grounded and signal shielding is formed. The clock generator CLK is used to control the time of signal shielding formed by the receiving transducer. When the flip-flop U3 outputs low level, the common pin of the first analog switch U4 is connected to the normally closed pin, and the receiving transducer normally receives signals.

[0037] In ultrasonic flow measurement, the reason that the receiving transducer is not interfered by noise signals after a period of shielding is mainly related to the characteristics of ultrasonic signals and the design of shielding circuit. After the transmitting transducer transmits a signal, it needs a certain time for the signal to propagate to the measured medium (such as gas or water) and then to the receiving transducer. During the period before the transmitted ultrasonic signal reaches the receiving transducer, the receiving transducer is shielded from signals, so that the strong signal generated during transmission and possible noise can be avoided. In addition, the ultrasonic signal gradually attenuates during propagation in the medium. After a period of shielding, the strong signal generated during transmission and noise have been attenuated to a low enough level, which will not interfere with the receiving transducer.

[0038] The transmitting transducer normally excites a signal, and the receiving transducer receives the signal after the excitation signal is finished. The flip-flop U3 and the first analog switch U4 are located in the circuit between the excitation signal and the receiving signal. The purpose is to automatically capture the excitation signal and keep the receiving transducer grounded for a set time to shield the interference signal. The clock generator CLK is used to control the flip-flop U3 to output high level and the time of high level transmission. For example, when the clock generator CLK generates an excitation pulse and the rising edge of the first pulse arrives, the flip-flop U3 outputs high level to the first analog switch U4 until the last pulse of the clock generator CLK ends. The high level of the flip-flop U3 will control the first analog switch U4, so that the common pin of the first analog switch U4 is connected to the normally open pin. Since the normally open pin is connected to ground, the receiving transducer will be grounded at this time, shielding external signals and thus shielding noise signals. When the flip-flop U3 outputs low level to the first analog switch U4, the common pin of the first analog switch U4 is connected to the normally closed pin, and at this time the receiving transducer is not connected to any impedance, normally receiving signals.

[0039] Specifically, as shown in FIG. 1, the automatic shielding circuit of an ultrasonic transducer receiver comprises a transmitting transducer 1, a clock generator CLK, a flip-flop U3, a first analog switch U4 and a receiving transducer 2 connected in series. The normally open pin of the first analog switch U4 is connected to ground. The flip-flop U3 outputs high level to the first analog switch U4 within a set time after the transmitting transducer transmits a signal. The common pin of the first analog switch U4 is connected to the normally open pin, so that the receiving transducer is grounded and signal shielding is formed. The clock generator CLK is used to control the time of signal shielding formed by the receiving transducer. When the flip-flop U3 outputs low level, the common pin of the first analog switch U4 is connected to the normally closed pin, and the receiving transducer normally receives signals. Figure 1The transducer one HNQ1 and the transducer two HNQ2 are also included. The second analog switch U1 and the third analog switch U2 are commonly connected with a signal generator TSEN, which generates signals to the second analog switch U1 and the third analog switch U2. The second analog switch U1 and the third analog switch U2 select specific transmitting transducer and receiving transducer among the two transducers. In this embodiment, the first analog switch U4, the second analog switch U1 and the third analog switch U2 are all double-throw single-pole analog switches of TS5A9411 type, whose working principle and structure are prior art.

[0040] When the signal of the signal generator TSEN is 0, the pin 5 and the pin 4 of the second analog switch U1 and the pin 5 and the pin 4 of the third analog switch U2 are connected. The second analog switch U1 and the third analog switch U2 select the transducer two HNQ2 as the receiving transducer and the transducer one HNQ1 as the transmitting transducer. At this time, the excitation pulse of the clock generator CLK drives the transducer one HNQ1 to send the ultrasonic signal, and the transducer two HNQ2 receives the ultrasonic signal and converts it into a voltage signal. Similarly, when the signal of the signal generator TSEN is 1, the pin 5 and the pin 6 of the second analog switch U1 and the pin 5 and the pin 6 of the third analog switch U2 are connected. The second analog switch U1 and the third analog switch U2 select the transducer one HNQ1 as the receiving transducer and the transducer two HNQ2 as the transmitting transducer. When the excitation pulse of the clock generator CLK drives the transducer two HNQ2 to send the ultrasonic signal, the transducer one HNQ1 receives the ultrasonic signal and converts it into a voltage signal.

[0041] Through the control circuit, the system can flexibly select the transducer one HNQ1 or the transducer two HNQ2 as the transmitting transducer according to the needs, and the other one naturally becomes the receiving transducer. This method not only provides a high degree of configurability, allowing the system to adjust according to specific application scenarios or needs, but also allows the system to adapt to different operating conditions and environments, as different transducers may have better adaptability to different media or conditions. In addition, if one transducer fails or its performance decreases, the system can switch to the other transducer through the control circuit, thereby ensuring the continuous operation of the system and the continuous acquisition of data.

[0042] Specifically, as Figure 1As shown in the embodiment, the trigger U3 is a dual-path retriggerable monostable multivibrator of SN74LV123 type. The external resistance and capacitance connection pin (R / CEXT) of the trigger U3 is connected with a power supply, and a capacitor C3 is connected between the power supply and the ground, for stabilizing the power supply of the trigger U3. A capacitor C3 is connected between the power supply and the ground, for stabilizing the power supply or reference voltage of the trigger U3, reducing the influence of the power supply noise on the operation of the trigger U3, and ensuring that the trigger U3 can reliably respond to the pulse signal of the clock generator CLK. In the circuit of the embodiment, a capacitor is connected between the power supply and the ground of a plurality of elements, for stabilizing the power supply. The power supply and the ground of the second analog switch U1, the third analog switch U2, the trigger U3, the first analog switch U4, and the operational amplifier U5 are all connected with capacitors.

[0043] The external capacitance connection pin (CEXT) of the trigger U3 is connected with a capacitor C5, for forming an RC delay circuit with the resistance R2 on the R / CEXT pin of the trigger U3, to control the delay time of the high level output of the trigger U3. When the falling edge of the first pulse of the clock generator CLK arrives, the Q pin of the trigger U3 will output a high level 1, at this time, the pin 5 and the pin 6 of the first analog switch U4 are connected, because the pin 5 of the first analog switch U4 is connected to the pin 5 of the third analog switch U2 at this time, which is equivalent to shorting the output signal of the receiving transducer to the ground, the Q pin of the trigger U3 will maintain a high level 1 until the last falling edge of the clock generator CLK, and will maintain the delay time TW after that, the value of TW can be determined by the values of the resistance R2 and the capacitor C5. For example, when the trigger pulse appears at the clock generator CLK, when the falling edge of the first pulse arrives, the output end of the trigger U3 will output a high level, and this signal will maintain a high level for about 50us after the last pulse signal of the clock generator CLK arrives. The delay time is determined by the values of the capacitor C5 and the resistance R2.

[0044] The clock generator CLK signal controls the trigger U3, and then controls the connection of the pin 5 and the pin 6 of the first analog switch U4 chip to the ground through the Q pin of the trigger U3 being 1, the pin 5 of the first analog switch U4 only has a connection with the pin 5 of the third analog switch U2 at this time, at this time, the third analog switch U2 is always connected to the receiving transducer, and the second analog switch U1 is connected to the transmitting transducer, which can be controlled by the signal of the TSEN. The distance between the ultrasonic signal from the transmitting transducer to the receiving transducer is fixed, and the time is also basically fixed, so by selecting appropriate R2 and C5, the signal emitted by the transmitting transducer can not reach the receiving transducer, and the pin 5 of the third analog switch U2 is directly connected to the ground, thereby avoiding interference from external signals.

[0045] Specifically, asFigure 1 As shown, it also contains an operational amplifier U5 connected with the receiving transducer, used to amplify the signal received by the receiving transducer and transmit to the back-end microcontroller unit. Operational amplifier U5 is used to amplify the ultrasonic signal received by the receiving transducer. Since the received signal is usually very weak, it needs to be amplified in order to facilitate the microcontroller unit for effective processing and analysis. The amplified signal output is transmitted to the back-end microcontroller unit (MCU). MCU is the control center of the circuit, responsible for processing signals and performing related calculations and control tasks. By amplifying the received weak signal through operational amplifier U5, it ensures that the signal will not lose information during transmission to the MCU due to the signal being too weak, and helps to reduce the impact of noise and interference, thereby improving the quality of the signal, so that the MCU can more accurately analyze the signal.

[0046] Specifically, the inverting input of operational amplifier U5 is connected with the output of the capacitor six C6 and resistor four R4, and capacitor six C6 and resistor four R4 are connected in parallel to form an RC network, which is used to stabilize the operating point of operational amplifier U5 and filter out high-frequency noise. By connecting an RC network between the inverting input and output of operational amplifier U5, the operating point of the amplifier can be stabilized, reducing the operating point drift caused by external interference or power supply fluctuations, thereby improving the stability and reliability of the amplifier. The operating point refers to the static operating state of operational amplifier U5 when there is no receiving transducer signal input. This state includes the output voltage of the operational amplifier and the static current passing through the operational amplifier. Stabilizing the operating point means that the operational amplifier can work at a predetermined, stable voltage and current level, which is crucial for ensuring the accuracy and reliability of signal processing. At the same time, it can effectively filter out high-frequency noise, because capacitor six C6 can block high-frequency noise from passing to the inverting input, while resistor four R4 provides a low-impedance path for high-frequency noise to ground, thereby reducing the impact of high-frequency noise on the amplified signal.

[0047] Specifically, as shown in the figure, Figure 1As shown, the receiving transducer is connected with the operational amplifier U5 through the capacitor nine C9, which is used to isolate the direct current component and allow the alternating current signal to pass. By isolating the direct current component through the capacitor nine C9, the direct current bias and noise in the circuit can be reduced, and the signal-to-noise ratio of the signal can be improved. The capacitor nine C9 allows the alternating current signal to pass while blocking the direct current component, ensuring that the operational amplifier U5 amplifies the effective alternating current signal, thereby improving the integrity and accuracy of the signal. At the same time, the capacitor nine C9 can prevent excessive voltage or current from damaging the operational amplifier U5, especially when voltage spikes may occur between the receiving transducer and the operational amplifier. In order to keep the signal after amplification at a direct current component level, it is convenient for the subsequent circuit to process, the positive input terminal of the operational amplifier U5 is connected with the series of resistance six R6 and resistance seven R7, and the series is connected with the power supply. The pin 2 of the operational amplifier U5 is connected with the capacitor ten C10 between the resistance seven R7. The resistance R6 is connected with the resistance eight R8 between the ground. The positive input terminal of the operational amplifier U5 is connected with the resistance five R5, the capacitor nine C9 between the ground.

Claims

1. An ultrasonic transducer receive automatic shielding circuit, characterized by, The control circuit is used for selecting one of the transducers as a transmitting transducer and the other as a receiving transducer; the control circuit comprises a second analog switch (U1) and a third analog switch (U2); the second analog switch (U1) and the third analog switch (U2) are connected with a signal generator (TSEN) in common, the signal generator (TSEN) generates signals to the second analog switch (U1) and the third analog switch (U2), and the second analog switch (U1) and the third analog switch (U2) select the specific transmitting transducer and the receiving transducer; the shielding circuit further comprises a clock generator (CLK), a flip-flop (U3) and a first analog switch (U4) connected in series, and the flip-flop (U3) and the first analog switch (U4) are located in the circuit between the excitation signal and the receiving signal; the normally open pin of the first analog switch (U4) is connected to the ground; the flip-flop (U3) outputs a high level to the first analog switch (U4) within a set time after the transmitting transducer transmits a signal, the common pin of the first analog switch (U4) is connected to the normally open pin and the ground, and the common pin of the first analog switch (U4) is only connected to the common pin of the third analog switch (U2); at this time, the third analog switch (U2) is always connected to the receiving transducer, the receiving transducer is thus grounded and forms a signal shielding; the clock generator (CLK) is used for controlling the time of the receiving transducer forming the signal shielding; when the flip-flop (U3) outputs a low level, the common pin of the first analog switch (U4) is connected to the normally closed pin, and the receiving transducer normally receives signals.

2. The ultrasonic transducer receive automatic shielding circuit of claim 1, wherein, The external resistance and capacitor connection pin of the flip-flop (U3) is connected with a power supply, and a capacitor three (C3) is connected between the power supply and the ground, for stabilizing the power supply of the flip-flop (U3).

3. The ultrasonic transducer receive automatic shielding circuit of claim 2, wherein, The external capacitor connection pin of the flip-flop (U3) is connected with a capacitor five (C5), for forming an RC delay circuit with the resistance two (R2) on the external resistance and capacitor connection pin of the flip-flop (U3), to control the delay time of the flip-flop (U3) outputting a high level.

4. The ultrasonic transducer receive automatic shielding circuit of claim 1, wherein, An operational amplifier (U5) connected with the receiving transducer is further included, for amplifying the signal received by the receiving transducer and transmitting to a back-end microcontroller unit.

5. The ultrasonic transducer receive automatic shielding circuit of claim 4, wherein, The inverting input end and the output end of the operational amplifier (U5) are connected with a capacitor six (C6) and a resistance four (R4), and the capacitor six (C6) and the resistance four (R4) are connected in parallel to form an RC network, for stabilizing the working point of the operational amplifier (U5) and filtering high-frequency noise.

6. The ultrasonic transducer receive automatic shielding circuit of claim 5, wherein, A capacitor nine (C9) is connected between the receiving transducer and the operational amplifier (U5), for isolating direct current components and allowing alternating current signals to pass.

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