Ultrasonic transducer receiving automatic shielding circuit

Abstract

An ultrasonic transducer receiving automatic shielding circuit comprises a transmitting transducer and further comprises a clock generator, a trigger, a first analog switch and a receiving transducer which are sequentially connected in series. A normally open pin of the first analog switch is grounded; the trigger outputs a high level to the first analog switch within a set time after the transmitting transducer transmits a signal, the common pin of the first analog switch is connected with the normally open pin, and the receiving transducer is grounded and forms signal shielding; the clock generator is used for controlling the signal shielding forming time of the receiving transducer; when the trigger outputs a low level, the common pin and the normally closed pin of the first analog switch are connected, and the receiving transducer normally receives a signal. According to the invention, the influence of noise and other interference signals on the metering result can be effectively reduced, and the metering precision of the ultrasonic gas meter is improved.

Description

Technical Field

[0001] The invention relates to the field of ultrasonic circuits, and in particular to an ultrasonic transducer receiving automatic shielding circuit. Background Art

[0002] An ultrasonic gas meter is an instrument that uses ultrasonic technology to measure gas. Its working principle is to transmit and receive ultrasonic waves through a pair of ultrasonic transducers installed upstream and downstream of the gas flow, and use the propagation time difference of the ultrasonic signal in the gas medium along the downstream and upstream directions to measure the gas flow rate in the pipeline, and then calculate the instantaneous flow rate of the gas in the pipeline and the cumulative gas consumption.

[0003] The existing ultrasonic gas meter mainly uses the threshold method or the correlation method to measure the flow rate. Both methods rely on the transmitting transducer to transmit the ultrasonic signal and the receiving transducer to capture the reflected signal to calculate the flow rate.

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

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

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: An ultrasonic transducer receiving automatic shielding circuit comprises a transmitting transducer, and also comprises a clock generator, a trigger, a first analog switch and a receiving transducer connected in series in sequence; the normally open pin of the first analog switch is grounded; within a set time after the transmitting transducer transmits a signal, the trigger outputs a high level to the first analog switch, the common pin of the first analog switch is connected to the normally open pin, and the receiving transducer is therefore grounded and forms a signal shield; the clock generator is used to control the time when the receiving transducer forms a signal shield; when the trigger outputs a low level, the common pin of the first analog switch is connected to the normally closed pin, and the receiving transducer receives the signal normally.

[0007] In ultrasonic flow measurement, the reason why the signal is no longer disturbed by noise after being shielded for a period of time is mainly related to the characteristics of ultrasonic signals and the design of shielding circuits. After the ultrasonic transducer transmits the signal, it takes a certain amount of time for the signal to propagate to the measured medium (such as gas) and then reflect back. During this period of time, the receiving transducer is shielded to avoid receiving the strong signal generated during transmission and the noise that may accompany it. In addition, the ultrasonic signal will gradually attenuate when propagating in the medium. After being shielded for a period of time, the strong signal and noise generated during transmission have been attenuated to a sufficiently low level and will not interfere with the receiving transducer.

[0008] The transmitting transducer normally excites the signal, and the receiving transducer receives the signal after the excitation signal is sent. The trigger and the first analog switch are located in the circuit between the excitation signal and the receiving signal, with the purpose of automatically capturing the excitation signal and keeping the receiving transducer grounded within the set time to shield the interference signal. The clock generator is used to control the trigger to transmit a high level and the time of transmitting the high level. For example, when the clock generator has an excitation pulse and the rising edge of the first pulse arrives, the trigger outputs a high level to the first analog switch until the last pulse of the clock generator ends. The high level of the trigger will control the first analog switch, so that the common pin of the first analog switch is connected to the normally open pin. Since the normally open pin is grounded, the receiving transducer will be grounded at this time, shielding the external signal, and also shielding the noise signal. When the trigger outputs a low level to the first analog switch, the common pin of the first analog switch is connected to the normally closed pin. At this time, the receiving transducer is not connected to any impedance and receives the signal normally.

[0009] In summary, the present invention can automatically start the shielding mechanism after the transmitting transducer sends a signal. After a precisely set time delay, the receiving transducer will automatically release the shielding state, allowing the receiving transducer to start capturing and processing signals, protecting the receiving transducer from interference, and significantly reducing the negative impact of noise and interference on the metering results, thereby greatly improving the metering accuracy of the ultrasonic gas meter. This technical solution realizes automatic control without manual intervention or reliance on complex control logic, simplifies the operation process, and ensures precise control of the shielding time.

[0010] Preferably, it further comprises transducer 1 and transducer 2, wherein the two transducers are commonly connected to a control circuit, and the control circuit is used to select one of the transducers as the transmitting transducer and the other transducer as the receiving transducer.

[0011] Through the control circuit, the system can flexibly select transducer one or transducer two as the transmitting transducer according to needs, and the other naturally becomes the receiving transducer.

[0012] Preferably, the control circuit includes a second analog switch and a third analog switch; the second analog switch and the third analog switch are commonly connected to 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 the specific transmitting transducer and the receiving transducer.

[0013] When the signal of the signal generator is 0, the second analog switch and the third analog switch select transducer 2 as the receiving transducer and transducer 1 as the transmitting transducer. At this time, the excitation pulse of the clock generator drives transducer 1 to send an ultrasonic signal, and transducer 2 receives the ultrasonic signal and converts it into a voltage signal. Similarly, when the signal of the signal generator is 1, the second analog switch and the third analog switch select transducer 1 as the receiving transducer and transducer 2 as the transmitting transducer. When the excitation pulse of the clock generator drives transducer 2 to send an ultrasonic signal, transducer 1 receives the ultrasonic signal and converts it into a voltage signal.

[0014] Preferably, a power supply is connected to the external resistor and capacitor connection pins of the trigger, and a capacitor three is connected between the power supply and the ground to stabilize the power supply of the trigger.

[0015] Capacitor three is connected between the power supply and the ground to stabilize the power supply or reference voltage of the trigger, reduce the influence of power supply noise on the operation of the trigger, and ensure that the trigger can reliably respond to the pulse signal of the clock generator.

[0016] Preferably, the external capacitor connection pin of the trigger is connected to capacitor five, which is used to form an RC delay circuit with the external resistor of the trigger and resistor two on the capacitor connection pin to control the delay time of the trigger outputting a high level.

[0017] The RC delay circuit is used to control the delay time of the trigger outputting a high level. For example, when an excitation pulse appears at the clock generator end, when the falling edge of the first pulse arrives, the trigger output end will output a high level. This signal will remain at a high level for about 50us after the last pulse signal of the clock generator arrives.

[0018] Preferably, it further comprises an operational amplifier connected to the receiving transducer, for amplifying the signal received by the receiving transducer and transmitting the amplified signal to a back-end microcontroller unit.

[0019] The operational amplifier is used to amplify the ultrasonic signal received by the receiving transducer (transducer 1 or transducer 2). Since the received signal is usually very weak, it needs to be amplified so that the microcontroller unit can process and analyze it effectively. The amplified signal output is passed to the back-end microcontroller unit (MCU).

[0020] Preferably, a capacitor six and a resistor four are connected between the inverting input terminal and the output terminal of the operational amplifier, and the capacitor six and the resistor four are connected in parallel to form an RC network for stabilizing the operating point of the operational amplifier and filtering out high-frequency noise.

[0021] By connecting an RC network in parallel between the inverting input and output of the operational amplifier, the operating point of the amplifier can be stabilized, and the operating point drift caused by external interference or power supply fluctuations can be reduced, thereby improving the stability and reliability of the amplifier. The operating point refers to the static working state of the operational amplifier when it does not receive a transducer signal input. This state includes the output voltage of the operational amplifier and the static current passing through the operational amplifier. A stable operating point means that the operational amplifier can operate at a predetermined, stable voltage and current level, which is essential to ensure the accuracy and reliability of signal processing. At the same time, high-frequency noise can be effectively filtered out, because capacitor six can block the high-frequency noise from being transmitted to the inverting input, and resistor four provides a low-impedance path to the ground for the high-frequency noise, thereby reducing the impact of high-frequency noise on the amplified signal.

[0022] Preferably, a capacitor nine is connected between the receiving transducer and the operational amplifier to isolate the DC component and allow the AC signal to pass through.

[0023] By isolating the DC component through 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. Capacitor nine allows the AC signal to pass while blocking the DC component, ensuring that the operational amplifier amplifies the valid AC signal, thereby improving the integrity and accuracy of the signal. At the same time, capacitor nine can prevent excessive voltage or current from damaging the operational amplifier, especially when there is a voltage spike that may occur between the receiving transducer and the operational amplifier.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention shields the receiving transducer immediately after the transmitting transducer excites the signal, so as to avoid the strong signal and the accompanying noise received at the initial stage of the signal excitation. The present invention does not require manual operation or reliance on complex control logic, reduces the complexity of the operation, and can accurately control the shielding time, thereby ensuring effective shielding of interference signals, thereby improving the accuracy and reliability of flow measurement.

[0025] 2. Through the control circuit, it not only provides a high degree of configurability, allowing the system to be adjusted according to specific application scenarios or requirements, 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 its performance degrades, the system can switch to another transducer through the control circuit, thereby ensuring the continuous operation of the system and continuous data collection.

[0026] 3. By connecting capacitor 3 between the power supply and the ground, the power supply or reference voltage of the trigger is stabilized, the influence of power supply noise on the operation of the trigger is reduced, and the trigger is ensured to reliably respond to the pulse signal of the clock generator.

[0027] 4. Amplify the weak signal received by the operational amplifier to ensure that the signal will not be lost due to the signal being too weak during transmission to the MCU, and help reduce the impact of noise and interference, thereby improving the signal quality and enabling the MCU to more accurately analyze the signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a circuit diagram of an embodiment.

[0029] in: CLK, clock generator; U1, second analog switch; U2, third analog switch; U3, trigger; U4, first analog switch; operational amplifier U5; HNQ1, transducer 1; HNQ2, transducer 2; TSEN, signal generator; C3, capacitor 3; C5, capacitor 5; C6, capacitor 6; C9, capacitor 9; C10, capacitor 10; R2, resistor 2; R4, resistor 4. R5, resistor 5; R6, resistor 6; R7, resistor 7; R8, resistor 8. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, objectives and effects of the invention easier to understand, the invention is further described with reference to specific diagrams. However, the invention is not limited to the following implementation cases.

[0031] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

[0032] Embodiment 1: like Figure 1An ultrasonic transducer receiving automatic shielding circuit shown includes a transmitting transducer, and also includes a clock generator CLK, a trigger U3, a first analog switch U4 and a receiving transducer connected in series in sequence; the normally open pin of the first analog switch U4 is grounded; within a set time after the transmitting transducer transmits a signal, the trigger U3 outputs a high level to the first analog switch U4, and the common pin of the first analog switch U4 is connected to the normally open pin, so the receiving transducer is grounded and a signal shield is formed; the clock generator CLK is used to control the time for the receiving transducer to form a signal shield; when the trigger 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 receives the signal normally.

[0033] In ultrasonic flow measurement, the reason why the signal is no longer disturbed by noise after a period of shielding is mainly related to the characteristics of ultrasonic signals and the design of shielding circuits. After the ultrasonic transducer transmits the signal, it takes a certain amount of time for the signal to propagate to the measured medium (such as gas, water), and then transmit to the receiving transducer. During the period before the transmitted ultrasonic signal reaches the receiving transducer, shielding the receiving transducer signal can avoid receiving the strong signal generated during the transmission and the noise that may be accompanied. In addition, the ultrasonic signal will gradually attenuate when propagating in the medium. After a period of shielding, the strong signal and noise generated during the transmission have been attenuated to a sufficiently low level and will not interfere with the receiving transducer.

[0034] The transmitting transducer normally excites the signal, and the receiving transducer receives the signal after the excitation signal is sent. The trigger 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 within the set time, so as to shield the interference signal. The clock generator CLK is used to control the trigger U3 to transmit a high level and the time of transmitting a high level. For example, when the clock generator CLK has an excitation pulse and the rising edge of the first pulse arrives, the trigger U3 outputs a high level to the first analog switch U4 until the last pulse of the clock generator CLK ends. The high level of the trigger 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 grounded, the receiving transducer will be grounded at this time, shielding the external signal, and also shielding the noise signal. When the trigger U3 outputs a low level to the first analog switch U4, the common pin of the first analog switch U4 is connected to the normally closed pin. At this time, the receiving transducer is not connected to any impedance and receives the signal normally.

[0035] Specifically, Figure 1As shown, it also includes transducer 1 HNQ1 and transducer 2 HNQ2, the second analog switch U1 and the third analog switch U2 are connected to a signal generator TSEN, the signal generator TSEN generates a signal 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 a specific transmitting transducer and a receiving transducer from the two transducers. In this embodiment, the first analog switch U4, the second analog switch U1 and the third analog switch U2 all select a bidirectional single-pole double-throw analog switch of model TS5A9411, and its working principle and structure are the prior art.

[0036] When the signal of the signal generator TSEN is 0, the pins 5 and 4 of the second analog switch U1 and the pins 5 and 4 of the third analog switch U2 are connected, and the second analog switch U1 and the third analog switch U2 select the transducer 2 HNQ2 as the receiving transducer and the transducer 1 HNQ1 as the transmitting transducer. At this time, the excitation pulse of the clock generator CLK drives the transducer 1 HNQ1 to send an ultrasonic signal, and the transducer 2 HNQ2 receives the ultrasonic signal and converts it into a voltage signal. Similarly, when the signal of the signal generator TSEN is 1, the pins 5 and 6 of the second analog switch U1 and the pins 5 and 6 of the third analog switch U2 are connected, and the second analog switch U1 and the third analog switch U2 select the transducer 1 HNQ1 as the receiving transducer and the transducer 2 HNQ2 as the transmitting transducer. When the excitation pulse of the clock generator CLK drives the transducer 2 HNQ2 to send an ultrasonic signal, the transducer 1 HNQ1 receives the ultrasonic signal and converts it into a voltage signal.

[0037] Through the control circuit, the system can flexibly select transducer 1 HNQ1 or transducer 2 HNQ2 as the transmitting transducer as needed, and the other naturally becomes the receiving transducer. This approach not only provides a high degree of configurability, allowing the system to be adjusted 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 one transducer fails or its performance degrades, the system can switch to another transducer through the control circuit, thereby ensuring the continuous operation of the system and continuous data acquisition.

[0038] Specifically, Figure 1As shown, in this embodiment, the trigger U3 selects a dual-channel retriggerable monostable multivibrator of model SN74LV123. A power supply is connected to the external resistor and capacitor connection pin (R / CEXT) of the trigger U3, and a capacitor C3 is connected between the power supply and the ground to stabilize the power supply of the trigger U3. A capacitor C3 is connected between the power supply and the ground to stabilize the power supply or reference voltage of the trigger U3, reduce the influence of the power supply noise on the operation of the trigger U3, and ensure that the trigger U3 can reliably respond to the pulse signal of the clock generator CLK. In the circuit of this embodiment, capacitors are connected between the power supply and the ground of multiple components to stabilize the power supply. Capacitors are connected between 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.

[0039] The external capacitor connection pin (CEXT) of the trigger U3 is connected with a capacitor C5, which is used to form an RC delay circuit with the resistor R2 on the R / CEXT pin of the trigger U3 to control the delay time of the trigger U3 outputting a high level. When the falling edge pulse of the clock generator CLK arrives, when the falling edge of the first pulse of the trigger U3 arrives, the Q pin of the trigger U3 will output a high level 1. At this time, the pin 5 and pin 6 of the first analog switch U4 are connected, because at this time the pin 5 of the first analog switch U4 is connected to the pin 5 of the third analog switch U2, which is equivalent to the output signal of the receiving transducer being shorted 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 also maintain a delay time of TW thereafter. The TW value can be determined by the value of the resistor R2 and the capacitor C5. For example, when an excitation pulse appears at the clock generator CLK end, 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 remain at a high level for about 50us after the arrival of the last pulse signal of the clock generator CLK. The delay time is determined by the values ​​of capacitor C5 and resistor R2.

[0040] The clock generator CLK signal controls the trigger U3, and then controls the pins 5 and 6 of the first analog switch U4 chip to be connected and grounded when the Q pin of the trigger U3 is 1. The pin 5 of the first analog switch U4 is only connected to the pin 5 of the third analog switch U2. 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. This can be controlled by controlling the signal of TSEN. The distance between the ultrasonic signal from the transmitting transducer to the receiving transducer is fixed, and the time is basically fixed. Therefore, by selecting appropriate R2 and C5, the pin 5 of the third analog switch U2 can be grounded before the signal sent by the transmitting transducer reaches the receiving transducer, thereby avoiding interference from external signals.

[0041] Specifically, Figure 1 As shown, it also includes an operational amplifier U5 connected to the receiving transducer, which is used to amplify the signal received by the receiving transducer and transmit it to the back-end microcontroller unit. The 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 so that the microcontroller unit can effectively process and analyze it. The amplified signal output is transmitted to the back-end microcontroller unit (MCU). The MCU is the control center of the circuit, responsible for processing signals and performing related calculations and control tasks. The weak signal received is amplified by the operational amplifier U5 to ensure that the signal will not lose information during the transmission to the MCU due to the signal being too weak, and it helps to reduce the impact of noise and interference, thereby improving the quality of the signal, so that the MCU can more accurately parse the signal.

[0042] Specifically, a capacitor six C6 and a resistor four R4 are connected between the inverting input terminal and the output terminal of the operational amplifier U5, and the capacitor six C6 and the resistor four R4 are connected in parallel to form an RC network for stabilizing the operating point of the operational amplifier U5 and filtering out high-frequency noise. By connecting the RC network in parallel between the inverting input terminal and the output terminal of the operational amplifier U5, the operating point of the amplifier can be stabilized, and the operating point drift caused by external interference or power supply fluctuations can be reduced, thereby improving the stability and reliability of the amplifier. The operating point refers to the static operating state of the operational amplifier U5 when no transducer signal input is received. This state includes the output voltage of the operational amplifier and the static current passing through the operational amplifier. A stable operating point means that the operational amplifier can operate 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 C6 can block the high-frequency noise from being transmitted to the inverting input terminal, and the resistor four R4 provides a low-impedance path to the ground for the high-frequency noise, thereby reducing the impact of high-frequency noise on the amplified signal.

[0043] Specifically, Figure 1As shown, a capacitor C9 is connected between the receiving transducer and the operational amplifier U5 to isolate the DC component and allow the AC signal to pass. The DC component is isolated by the capacitor C9, which can reduce the DC bias and noise in the circuit and improve the signal-to-noise ratio. The capacitor C9 allows the AC signal to pass while blocking the DC component, ensuring that the operational amplifier U5 amplifies the effective AC signal, thereby improving the integrity and accuracy of the signal. At the same time, the capacitor C9 can prevent excessive voltage or current from damaging the operational amplifier U5, especially when the voltage spike may occur between the receiving transducer and the operational amplifier. In order to keep the signal after amplification at the level of a DC component and facilitate subsequent circuit processing, the non-inverting input terminal of the operational amplifier U5 is connected with a series resistor R6 and a resistor R7, and the power supply is connected after the series connection. A capacitor C10 is connected between the pin 2 of the operational amplifier U5 and the resistor R7. A resistor R8 is connected between the resistor R6 and the ground. A resistor R5 and a capacitor C9 are connected between the non-inverting input terminal of the operational amplifier U5 and the ground.

Claims

1. An ultrasonic transducer receiving automatic shielding circuit, comprising a transmitting transducer, characterized in that: The invention also comprises a clock generator (CLK), a trigger (U3), a first analog switch (U4) and a receiving transducer which are connected in series in sequence; the normally open pin of the first analog switch (U4) is grounded; within a set time after the transmitting transducer transmits a signal, the trigger (U3) outputs a high level to the first analog switch (U4), the common pin of the first analog switch (U4) is connected to the normally open pin, and the receiving transducer is therefore grounded and a signal shield is formed; the clock generator (CLK) is used to control the time when the receiving transducer forms a signal shield; when the trigger (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 receives the signal normally.

2. The ultrasonic transducer receiving automatic shielding circuit according to claim 1, characterized in that: It also includes transducer 1 (HNQ1) and transducer 2 (HNQ2), the two transducers are commonly connected to a control circuit, and the control circuit is used to select one of the transducers as the transmitting transducer and the other transducer as the receiving transducer.

3. The ultrasonic transducer receiving automatic shielding circuit according to claim 2, characterized in that: 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 commonly connected to a signal generator (TSEN), the signal generator (TSEN) generates a signal 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.

4. The ultrasonic transducer receiving automatic shielding circuit according to claim 1, characterized in that: The external resistor and capacitor connection pins of the trigger (U3) are connected to a power supply, and a capacitor three (C3) is connected between the power supply and the ground to stabilize the power supply of the trigger (U3).

5. The ultrasonic transducer receiving automatic shielding circuit according to claim 4, characterized in that: The external capacitor connection pin of the trigger (U3) is connected to a capacitor five (C5), which is used to form an RC delay circuit with the external resistor of the trigger (U3) and the resistor two (R2) on the capacitor connection pin, so as to control the delay time of the trigger (U3) outputting a high level.

6. The ultrasonic transducer receiving automatic shielding circuit according to claim 1, characterized in that: It also includes an operational amplifier (U5) connected to the receiving transducer, which is used to amplify the signal received by the receiving transducer and transmit it to the back-end microcontroller unit.

7. The ultrasonic transducer receiving automatic shielding circuit according to claim 6, characterized in that: A capacitor six (C6) and a resistor four (R4) are connected between the inverting input terminal and the output terminal of the operational amplifier (U5), and the capacitor six (C6) and the resistor four (R4) are connected in parallel to form an RC network for stabilizing the operating point of the operational amplifier (U5) and filtering out high-frequency noise.

8. The ultrasonic transducer receiving automatic shielding circuit according to claim 7, characterized in that: A capacitor nine (C9) is connected between the receiving transducer and the operational amplifier (U5) for isolating a DC component and allowing an AC signal to pass through.

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