A multi-frequency ultrasonic liquid level measuring device and method for non-metallic containers

Abstract

The application relates to the technical field of measuring equipment, and discloses a non-metal container multi-frequency ultrasonic liquid level measuring device and method, which comprises a controller, a multi-frequency ultrasonic excitation module, an ultrasonic transducer, a return signal processing and collecting module, a host and a display module; the controller is used for generating different frequency pulse width modulation control signals and transmitting the control signals to the multi-frequency ultrasonic excitation module; the multi-frequency ultrasonic excitation module is used for exciting high-voltage pulse signals of different frequencies and transmitting the high-voltage pulse signals to the ultrasonic transducer; the return signal processing and collecting module is used for amplifying and filtering return signals and transmitting the return signals to the host after the return signals are converted into digital signals; the host is used for extracting the transit time of the return signals, calculating a liquid level result according to the digital signals, the transit time and the geometric characteristics of the non-metal container, and transmitting the liquid level result to the display; and the display is used for displaying the liquid level result. The application has low liquid level measurement accuracy and high reliability.

Description

Technical Field

[0001] This invention relates to the field of measuring equipment technology, and specifically discloses a multi-frequency ultrasonic liquid level measuring device and method for non-metallic containers.

[0002] Background Introduction

[0003] In recent years, with the continuous development of electronic technology and automation, liquid level measurement and control technology has greatly improved. Industries such as food and beverage, pharmaceuticals, and aerospace all rely heavily on liquid level measurement, making its importance increasingly apparent. However, current non-invasive ultrasonic measurement methods mainly rely on the impedance method, which utilizes the energy of ultrasonic waves reflected at solid-liquid and solid-gas interfaces to indirectly measure liquid level. This method has advantages such as simple structure and non-contact operation. However, it also has some limitations. Firstly, when measuring liquid levels in containers with non-metallic walls, the energy difference between reflected waves at solid-liquid and solid-gas interfaces is small, leading to lower accuracy. Secondly, this method requires frequent up-and-down probe movement during measurement, and variations in the coupling degree between the probe and the container wall during the measurement process can reduce the reliability of the liquid level measurement. To address these problems, it is essential to research and design a novel multi-frequency ultrasonic liquid level measurement device and method for non-metallic containers to overcome the existing issues in liquid level measurement. Summary of the Invention

[0004] To overcome the problems of low accuracy and reduced reliability in existing liquid level measurement technologies that require frequent probe movement, this invention proposes a multi-frequency ultrasonic liquid level measurement device and method for non-metallic containers.

[0005] This invention provides a multi-frequency ultrasonic liquid level measuring device for non-metallic containers, comprising a controller, a multi-frequency ultrasonic excitation module, an ultrasonic transducer, an echo signal processing and acquisition module, a host computer, and a display module.

[0006] The controller is connected to the multi-frequency ultrasonic excitation module. The controller is used to generate control signals with different frequency pulse width modulations and transmit the control signals to the multi-frequency ultrasonic excitation module.

[0007] The multi-frequency ultrasonic excitation module is connected to the ultrasonic transducer. The multi-frequency ultrasonic excitation module is used to excite high-voltage pulse signals of different frequencies according to the control signal and transmit the high-voltage pulse signals of different frequencies to the ultrasonic transducer.

[0008] The ultrasonic transducer includes a low-frequency transmitting probe, a low-frequency receiving probe, an intermediate-frequency transmitting probe, an intermediate-frequency receiving probe, a high-frequency transmitting probe, and a high-frequency receiving probe, all of which are adjustable in angle to the sidewall of the non-metallic container and can be mounted on it. The low-frequency, intermediate-frequency, and high-frequency transmitting probes are all mounted at the same height on the first sidewall of the non-metallic container, and each probe is used to transmit ultrasonic waves according to the high-voltage pulse signal. The low-frequency, intermediate-frequency, and high-frequency receiving probes are all mounted at an angle adjustable to the first sidewall relative to the non-metallic container. On the third side wall symmetrical about the central axis of the container, the low-frequency receiving probe and the low-frequency transmitting probe are symmetrical about the central axis of the non-metallic container, the intermediate-frequency receiving probe and the intermediate-frequency transmitting probe are symmetrical about the central axis of the non-metallic container, and the high-frequency receiving probe and the high-frequency transmitting probe are symmetrical about the central axis of the non-metallic container. The low-frequency receiving probe, the intermediate-frequency receiving probe and the high-frequency receiving probe are all used to receive echoes. The output terminals of the low-frequency receiving probe, the intermediate-frequency receiving probe and the high-frequency receiving probe are all connected to the input terminal of the echo signal processing and acquisition module, and transmit the echoes to the echo signal processing and acquisition module.

[0009] The echo signal processing and acquisition module is connected to the host computer. The echo signal processing and acquisition module is used to amplify and filter the echo signal, and convert the echo signal into a digital signal and transmit it to the host computer.

[0010] The host computer is used to extract the transit time of the echo signal, and calculate the liquid level based on the digital signal, transit time, and geometric features of the non-metallic container to obtain the liquid level result, and transmit the liquid level result to the display.

[0011] The display is used to show the liquid level result.

[0012] According to some embodiments of the present invention, a multi-frequency ultrasonic liquid level measuring device for non-metallic containers is provided, wherein the multi-frequency ultrasonic excitation module includes a driving chip, a field-effect transistor, and a pulse transformer connected in sequence.

[0013] The input terminal of the driver chip is connected to the controller. The driver chip and the field-effect transistor are used to convert the control signal into a switching signal and transmit the switching signal to the pulse transformer.

[0014] The output terminal of the pulse transformer is connected to the input terminals of the low-frequency transmitting probe, the intermediate-frequency transmitting probe, and the high-frequency transmitting probe, respectively. The pulse transformer is used to generate high-voltage pulse signals of different frequencies according to the switching signal, and transmit the high-voltage pulse signals to one of the low-frequency transmitting probe, the intermediate-frequency transmitting probe, or the high-frequency transmitting probe.

[0015] According to some embodiments of the present invention, a multi-frequency ultrasonic liquid level measuring device for non-metallic containers has the following characteristics: the low-frequency transmitting probe has a transmitting frequency of 0.5 MHz, the medium-frequency transmitting probe has a transmitting frequency of 1 MHz, and the high-frequency transmitting probe has a transmitting frequency of 2 MHz.

[0016] According to some embodiments of the present invention, a multi-frequency ultrasonic liquid level measuring device for a non-metallic container is provided, wherein a low-frequency transmitting probe, a medium-frequency transmitting probe, and a high-frequency transmitting probe are installed at equal intervals on a first side wall of the non-metallic container, and a low-frequency receiving probe, a medium-frequency receiving probe, and a high-frequency receiving probe are installed at equal intervals on a third side wall of the non-metallic container.

[0017] According to some embodiments of the present invention, a multi-frequency ultrasonic liquid level measuring device for non-metallic containers is provided, wherein the spacing between the low-frequency transmitting probe, the intermediate-frequency transmitting probe and the high-frequency transmitting probe is one-quarter of the width of the first sidewall, and the spacing between the low-frequency receiving probe, the intermediate-frequency receiving probe and the high-frequency receiving probe is one-quarter of the width of the third sidewall.

[0018] According to some embodiments of the present invention, a multi-frequency ultrasonic liquid level measuring device for non-metallic containers is provided, wherein the low-frequency transmitting probe, low-frequency receiving probe, intermediate-frequency transmitting probe, intermediate-frequency receiving probe, high-frequency transmitting probe, and high-frequency receiving probe are all provided with angle adjustment knobs. The angle adjustment knobs are used to adjust the angle of the low-frequency transmitting probe, low-frequency receiving probe, intermediate-frequency transmitting probe, intermediate-frequency receiving probe, high-frequency transmitting probe, or high-frequency receiving probe. The angle adjustment range of the low-frequency transmitting probe, low-frequency receiving probe, intermediate-frequency transmitting probe, intermediate-frequency receiving probe, high-frequency transmitting probe, and high-frequency receiving probe is 0°-60°.

[0019] The input ends of the low-frequency transmitting probe, the intermediate-frequency transmitting probe, and the high-frequency transmitting probe are all equipped with transmitting probe BNC interfaces, which are used to connect to the multi-frequency ultrasonic excitation module. The output ends of the low-frequency receiving probe, the intermediate-frequency receiving probe, and the high-frequency receiving probe are all equipped with receiving probe BNC interfaces, which are used to connect to the echo signal processing and acquisition module.

[0020] The low-frequency transmitting probe, low-frequency receiving probe, intermediate-frequency transmitting probe, intermediate-frequency receiving probe, high-frequency transmitting probe, and high-frequency receiving probe are all equipped with piezoelectric crystals.

[0021] According to some embodiments of the present invention, a multi-frequency ultrasonic liquid level measuring device for non-metallic containers is provided, wherein the echo signal processing and acquisition module includes a multi-channel amplifier circuit module, a multi-channel bandpass filter circuit module, and an AD acquisition circuit module connected in sequence.

[0022] The input terminal of the multi-channel amplifier circuit module is connected to the BNC interface of the receiving probe of the low-frequency receiving probe, the intermediate-frequency receiving probe and the high-frequency receiving probe respectively. The multi-channel amplifier circuit module is used to amplify the received echo to obtain an amplified echo and transmit the amplified echo to the multi-channel bandpass filter circuit module.

[0023] The multi-channel bandpass filter circuit module is used to filter the amplified echo to obtain an amplified echo filtered signal, and transmit the amplified echo filtered signal to the AD acquisition circuit module.

[0024] The output of the AD acquisition circuit module is connected to the host computer. The AD acquisition circuit module converts the amplified echo-filtered signal into a digital signal and transmits the digital signal to the host computer. The sampling frequency of the AD acquisition circuit module is 65MHz, which is more than ten times the frequency of the ultrasonic signal.

[0025] According to some embodiments of the present invention, a multi-frequency ultrasonic liquid level measuring device for non-metallic containers, wherein the host computer calculates the liquid level result based on the digital signal, transit time, and geometric characteristics of the non-metallic container, including:

[0026] The distance the ultrasonic wave travels from its entry into the liquid to its contact with the liquid surface is determined based on the geometric characteristics of the non-metallic container. As shown in formula (1):

[0027]

[0028] Where b represents the distance between the inner surface of the first sidewall and the inner surface of the third sidewall of the non-metallic container, and β represents the incident angle of the ultrasonic wave propagating from the first sidewall into the liquid.

[0029] The distance the ultrasound travels in a liquid from its entry to its contact with the liquid surface is determined based on the transit time. As shown in formula (2):

[0030]

[0031] Where c1 represents the propagation speed of ultrasound in the first sidewall, c2 represents the propagation speed of ultrasound in the liquid, t represents the transit time, L1 represents one of the following: the length between the piezoelectric crystal of the low-frequency transmitter and the probe surface of the low-frequency transmitter, the length between the piezoelectric crystal of the medium-frequency transmitter and the probe surface of the medium-frequency transmitter, or the length between the piezoelectric crystal of the high-frequency transmitter and the probe surface of the high-frequency transmitter; L2 represents the thickness of the first sidewall; and α represents the incident angle of the ultrasound propagation into the first sidewall.

[0032] According to Snell's Law Combining formulas (1) and (2), the liquid level result is obtained as shown in formula (3):

[0033]

[0034] Where H represents the liquid level result, and h1 represents the height of the low-frequency, medium-frequency, and high-frequency transmitting probes from the inner surface of the bottom of the non-metallic container.

[0035] A method for multi-frequency ultrasonic liquid level measurement of non-metallic containers, using the aforementioned multi-frequency ultrasonic liquid level measurement device for non-metallic containers to detect liquid level, includes the following steps:

[0036] S1. The low-frequency transmitting probe, the intermediate-frequency transmitting probe, and the high-frequency transmitting probe are installed at the same height on the first side wall of the non-metallic container. The low-frequency receiving probe, the intermediate-frequency receiving probe, and the high-frequency receiving probe are all installed on the third side wall, which is symmetrical to the first side wall about the central axis of the non-metallic container. The low-frequency receiving probe is symmetrical to the low-frequency transmitting probe about the central axis of the non-metallic container, the intermediate-frequency receiving probe is symmetrical to the intermediate-frequency transmitting probe about the central axis of the non-metallic container, and the high-frequency receiving probe is symmetrical to the high-frequency transmitting probe about the central axis of the non-metallic container. The low-frequency transmitting probe, the intermediate-frequency transmitting probe, and the high-frequency transmitting probe are installed at equal intervals on the first side wall of the non-metallic container, and the low-frequency receiving probe, the intermediate-frequency receiving probe, and the high-frequency receiving probe are installed at equal intervals on the third side wall of the non-metallic container.

[0037] S2. The controller transmits a control signal to the multi-frequency ultrasonic excitation module, causing the multi-frequency ultrasonic excitation module to generate a 1MHz high-voltage pulse signal. The multi-frequency ultrasonic excitation module transmits the 1MHz high-voltage pulse signal to the intermediate frequency transmitting probe. The intermediate frequency transmitting probe emits 1MHz ultrasonic waves. The ultrasonic waves are refracted by the first sidewall of the non-metallic container and enter the liquid. They are then reflected by the liquid surface and refracted by the third sidewall of the non-metallic container before entering the intermediate frequency receiving probe.

[0038] S3. The echo signal processing and acquisition module amplifies and filters the echo signal, and converts the echo signal into a digital signal before transmitting it to the host.

[0039] S4. The host records the amplitude, transit time, transmission angle and installation height of the intermediate frequency (IF) receiving probe, and reception angle and installation height of the IF receiving probe. It determines whether the amplitude of the echo signal is at its maximum value. If it is not at its maximum value, it adjusts the transmission angle and installation height of the IF receiving probe and the reception angle and installation height of the IF receiving probe, and repeats steps S2-S4 until the amplitude of the received echo signal is at its maximum. When the amplitude of the echo signal is at its maximum value, it records the transmission angle and installation height of the IF receiving probe and the reception angle and installation height of the IF receiving probe at this time.

[0040] S5. The host computer calculates the liquid level based on the digital signal, transit time, and geometric characteristics of the non-metallic container to obtain a preliminary liquid level result;

[0041] S6. When the preliminary liquid level result is less than 0.5 times the height of the non-metallic container, the high-frequency transmitting probe and the high-frequency receiving probe are used for measurement. The high-frequency transmitting probe is adjusted to the transmitting angle and installation height recorded in step S4, and the high-frequency receiving probe is adjusted to the receiving angle and installation height recorded in step S4. The controller controls the high-frequency transmitting probe to emit 2MHz ultrasonic waves, and the liquid level is calculated using the method in step S5 to obtain the liquid level result. If the preliminary liquid level result is greater than 0.5 times the height of the non-metallic container, a low-frequency transmitting probe is used for measurement. The low-frequency transmitting probe is adjusted to the transmitting angle and installation height recorded in step S4, and the low-frequency receiving probe is adjusted to the receiving angle and installation height recorded in step S4. The controller controls the low-frequency transmitting probe to emit 0.5MHz ultrasonic waves, and the liquid level is calculated using the method in step S5 to obtain the liquid level result.

[0042] According to some embodiments of the present invention, a method for multi-frequency ultrasonic liquid level measurement of a non-metallic container, in step S5, the host computer calculates the liquid level result based on the digital signal, transit time, and geometric characteristics of the non-metallic container, including:

[0043] The distance the ultrasonic wave travels from its entry into the liquid to its contact with the liquid surface is determined based on the geometric characteristics of the non-metallic container. As shown in formula (1):

[0044]

[0045] Where b represents the distance between the inner surface of the first sidewall and the inner surface of the third sidewall of the non-metallic container, and β represents the incident angle of the ultrasonic wave propagating from the first sidewall into the liquid.

[0046] The distance the ultrasound travels in a liquid from its entry to its contact with the liquid surface is determined based on the transit time. As shown in formula (2):

[0047]

[0048] Where c1 represents the propagation speed of ultrasound in the first sidewall, c2 represents the propagation speed of ultrasound in the liquid, t represents the transit time, L1 represents one of the following: the length between the piezoelectric crystal of the low-frequency transmitter and the probe surface of the low-frequency transmitter, the length between the piezoelectric crystal of the medium-frequency transmitter and the probe surface of the medium-frequency transmitter, or the length between the piezoelectric crystal of the high-frequency transmitter and the probe surface of the high-frequency transmitter; L2 represents the thickness of the first sidewall; and α represents the incident angle of the ultrasound propagation into the first sidewall.

[0049] According to Snell's Law Combining formulas (1) and (2), the liquid level result is obtained as shown in formula (3):

[0050]

[0051] Where H represents the liquid level result, and h1 represents the height of the low-frequency, medium-frequency, and high-frequency transmitting probes from the inner surface of the bottom of the non-metallic container.

[0052] This invention discloses a multi-frequency ultrasonic liquid level measuring device and method for non-metallic containers. During liquid level measurement, multiple ultrasonic transmitting probes and ultrasonic receiving probes with different frequencies and adjustable angles are used. By selecting different frequency ultrasonic waves, the measurement range can be expanded while improving the accuracy of liquid level detection. In addition, this invention avoids the problem of low liquid level accuracy caused by frequent up-and-down movement of the probe and different coupling degrees between the probe and the container wall, which is a common issue in impedance method measurement, thus improving the reliability of detection. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the overall structure of a multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to an embodiment of the present invention.

[0054] Figure 2 This is a front view schematic diagram of the connection between the ultrasonic transducer and the non-metallic container in an embodiment of the present invention;

[0055] Figure 3 This is a top view schematic diagram of the connection between the ultrasonic transducer and the non-metallic container in an embodiment of the present invention;

[0056] Figure 4 This is a schematic flowchart of a multi-frequency ultrasonic liquid level measurement method for non-metallic containers according to an embodiment of the present invention.

[0057] Figure 5 This is a schematic diagram of the ultrasonic path during liquid level measurement in an embodiment of the present invention.

[0058] In the diagram: 1. Controller; 2. Multi-frequency ultrasonic excitation module; 3. Ultrasonic transducer; 3-1. Low-frequency transmitting probe; 3-2. Low-frequency receiving probe; 3-3. Medium-frequency transmitting probe; 3-4. Medium-frequency receiving probe; 3-5. High-frequency transmitting probe; 3-6. High-frequency receiving probe; 4. Echo signal processing and acquisition module; 5. Main unit; 6. Display module; 7. Non-metallic container; 7-1. First sidewall; 7-2. Third sidewall; 8. Angle adjustment knob; 9. Transmitting probe BNC interface; 10. Receiving probe BNC interface; 11. Liquid; 12. Piezoelectric crystal. Detailed Implementation

[0059] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0060] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. The terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0061] This embodiment provides a multi-frequency ultrasonic liquid level measuring device for non-metallic containers, such as... Figure 1 As shown, the system includes a controller 1, a multi-frequency ultrasonic excitation module 2, an ultrasonic transducer 3, an echo signal processing and acquisition module 4, a main unit 5, and a display module 6. The controller 1 is connected to the multi-frequency ultrasonic excitation module 2 and is used to generate control signals with different frequency pulse width modulations, and transmit these control signals to the multi-frequency ultrasonic excitation module 2. The multi-frequency ultrasonic excitation module 2 is connected to the ultrasonic transducer 3 and is used to excite high-voltage pulse signals of different frequencies according to the control signals, and transmit these high-voltage pulse signals of different frequencies to the ultrasonic transducer 3. Figure 2 and Figure 3As shown, the ultrasonic transducer 3 includes a low-frequency transmitting probe 3-1, a low-frequency receiving probe 3-2, an intermediate-frequency transmitting probe 3-3, an intermediate-frequency receiving probe 3-4, a high-frequency transmitting probe 3-5, and a high-frequency receiving probe 3-6, which can be mounted on the non-metallic container 7 and whose angle with the side wall of the non-metallic container 7 is adjustable. The low-frequency transmitting probe 3-1, intermediate-frequency transmitting probe 3-3, and high-frequency transmitting probe 3-5 are all mounted at the same height on the first side wall 7-1 of the non-metallic container 7, and are used to transmit ultrasonic waves according to a high-voltage pulse signal. The low-frequency receiving probe 3-2, intermediate-frequency receiving probe 3-4, and high-frequency receiving probe 3-6 are all mounted on a third side wall 7-2 that is symmetrical to the first side wall 7-1 about the central axis of the non-metallic container 7. The low-frequency receiving probe 3-2 is symmetrical to the low-frequency transmitting probe 3-1 about the central axis of the non-metallic container 7, and the intermediate-frequency receiving probe 3-4 is symmetrical to the first side wall 7-1 about the central axis of the non-metallic container 7. The intermediate frequency transmitting probe 3-3 is symmetrical about the central axis of the non-metallic container 7. The high frequency receiving probe 3-6 and the high frequency transmitting probe 3-5 are symmetrical about the central axis of the non-metallic container 7. The low frequency receiving probe 3-2, the intermediate frequency receiving probe 3-4, and the high frequency receiving probe 3-6 are all used to receive echoes. The output terminals of the low frequency receiving probe 3-2, the intermediate frequency receiving probe 3-4, and the high frequency receiving probe 3-6 are all connected to the input terminal of the echo signal processing and acquisition module 4, and transmit the echoes to the echo signal processing and acquisition module 4. The echo signal processing and acquisition module 4 is connected to the host 5. The echo signal processing and acquisition module 4 is used to amplify and filter the echo signals, and convert the echo signals into digital signals before transmitting them to the host 5. The host 5 is used to extract the transit time of the echo signals, and calculate the liquid level based on the digital signals, transit time, and geometric characteristics of the non-metallic container 7, and transmit the liquid level results to the display. The display is used to display the liquid level results.

[0062] In this preferred embodiment, the controller 1 is connected to the multi-frequency ultrasonic excitation module 2 via a board-to-board connector; the multi-frequency ultrasonic excitation module 2 is connected to the low-frequency transmitting probe 3-1, the medium-frequency transmitting probe 3-3, and the high-frequency transmitting probe 3-5 via cables; the low-frequency receiving probe 3-2, the medium-frequency receiving probe 3-4, and the high-frequency receiving probe 3-6 are all connected to the echo signal processing and acquisition module 4 via cables; and the echo signal processing and acquisition module 4 is connected to the host 5 via a cable. High-frequency ultrasound has good longitudinal resolution and high accuracy in liquid level measurement, but its attenuation is large. Low-frequency ultrasound has strong penetration and a large measurement range, but its accuracy is lower. Therefore, using multiple ultrasonic transmitting probes of different frequencies can improve measurement accuracy while expanding the measurement range.

[0063] The multi-frequency ultrasonic excitation module 2 may include a driver chip, a field-effect transistor, and a pulse transformer connected in sequence; the input terminal of the driver chip is connected to the controller 1, and the driver chip and the field-effect transistor are used to convert the control signal into a switching signal and transmit the switching signal to the pulse transformer; the output terminal of the pulse transformer is connected to the input terminals of the low-frequency transmitting probe 3-1, the intermediate-frequency transmitting probe 3-3, and the high-frequency transmitting probe 3-5 respectively; the pulse transformer is used to generate high-voltage pulse signals of different frequencies according to the switching signal and transmit the high-voltage pulse signals to one of the low-frequency transmitting probe 3-1, the intermediate-frequency transmitting probe 3-3, or the high-frequency transmitting probe 3-5.

[0064] In a preferred embodiment, the low-frequency transmitting probe 3-1 can transmit at a frequency of 0.5 MHz, the intermediate-frequency transmitting probe 3-3 at a frequency of 1 MHz, and the high-frequency transmitting probe 3-5 at a frequency of 2 MHz. The low-frequency transmitting probe 3-1, the intermediate-frequency transmitting probe 3-3, and the high-frequency transmitting probe 3-5 are installed at equal intervals on the first sidewall 7-1 of the non-metallic container 7, and the low-frequency receiving probe 3-2, the intermediate-frequency receiving probe 3-4, and the high-frequency receiving probe 3-6 are installed at equal intervals on the third sidewall 7-2 of the non-metallic container 7. Preferably, the spacing between the low-frequency transmitting probe 3-1, the intermediate-frequency transmitting probe 3-3, and the high-frequency transmitting probe 3-5 can be one-quarter of the width of the first sidewall 7-1, and the spacing between the low-frequency receiving probe 3-2, the intermediate-frequency receiving probe 3-4, and the high-frequency receiving probe 3-6 can be one-quarter of the width of the third sidewall 7-2.

[0065] The low-frequency transmitting probe 3-1, low-frequency receiving probe 3-2, intermediate-frequency transmitting probe 3-3, intermediate-frequency receiving probe 3-4, high-frequency transmitting probe 3-5, and high-frequency receiving probe 3-6 are all equipped with angle adjustment knobs 8. These knobs are used to adjust the angle of each probe. The angle adjustment range for all probes is 0°-60°. The input ends of the low-frequency transmitting probe 3-1, the intermediate-frequency transmitting probe 3-3, and the high-frequency transmitting probe 3-5 are all equipped with transmitting probe BNC interfaces 9, which are used to connect to the multi-frequency ultrasonic excitation module 2. The output ends of the low-frequency receiving probe 3-2, the intermediate-frequency receiving probe 3-4, and the high-frequency receiving probe 3-6 are all equipped with receiving probe BNC interfaces 10, which are used to connect to the echo signal processing and acquisition module 4. The low-frequency transmitting probe 3-1, the low-frequency receiving probe 3-2, the intermediate-frequency transmitting probe 3-3, the intermediate-frequency receiving probe 3-4, the high-frequency transmitting probe 3-5, and the high-frequency receiving probe 3-6 are all equipped with piezoelectric crystals 12.

[0066] The echo signal processing and acquisition module 4 may include a multi-channel amplifier circuit module, a multi-channel bandpass filter circuit module, and an AD acquisition circuit module connected in sequence. The input terminal of the multi-channel amplifier circuit module is connected to the BNC interface 10 of the receiving probes of the low-frequency receiving probe 3-2, the intermediate-frequency receiving probe 3-4, and the high-frequency receiving probe 3-6, respectively. The multi-channel amplifier circuit module is used to amplify the received echo to obtain an amplified echo and transmit the amplified echo to the multi-channel bandpass filter circuit module. The multi-channel bandpass filter circuit module is used to filter the amplified echo to obtain an amplified echo filter signal and transmit the amplified echo filter signal to the AD acquisition circuit module. The output terminal of the AD acquisition circuit module is connected to the host 5. The AD acquisition circuit module is used to convert the amplified echo filter signal into a digital signal and transmit the digital signal to the host 5. The sampling frequency of the AD acquisition circuit module can be 65MHz, which is more than ten times the frequency of the ultrasonic signal.

[0067] The host 5 calculates the liquid level based on the digital signal, transit time, and geometric characteristics of the non-metallic container 7, and obtains the following liquid level results:

[0068] The distance the ultrasonic wave travels from its entry into the liquid 11 to its contact with the surface of the liquid 11 is obtained based on the geometric characteristics of the non-metallic container 7. As shown in formula (1):

[0069]

[0070] Where b represents the distance between the inner surface of the first sidewall 7-1 and the inner surface of the third sidewall 7-2 of the non-metallic container 7, and β represents the incident angle of the ultrasonic wave propagating from the first sidewall 7-1 into the liquid 11.

[0071] The distance traveled by the ultrasonic wave in liquid 11 from its entry to its contact with the surface of liquid 11 is obtained based on the transit time. As shown in formula (2):

[0072]

[0073] Wherein, c1 represents the propagation speed of the ultrasonic wave in the first sidewall 7-1, c2 represents the propagation speed of the ultrasonic wave in the liquid 11, t represents the transit time, L1 represents one of the following: the length between the piezoelectric crystal 12 of the low-frequency transmitting probe 3-1 and the probe surface of the low-frequency transmitting probe 3-1, the length between the piezoelectric crystal 12 of the intermediate-frequency transmitting probe 3-3 and the probe surface of the intermediate-frequency transmitting probe 3-3, or the length between the piezoelectric crystal 12 of the high-frequency transmitting probe 3-5 and the probe surface of the high-frequency transmitting probe 3-5, L2 represents the thickness of the first sidewall 7-1, and α represents the incident angle of the ultrasonic wave propagating into the first sidewall 7-1.

[0074] According to Snell's Law Combining formulas (1) and (2), we obtain the liquid level result, as shown in formula (3):

[0075]

[0076] Where H represents the liquid level result, and h1 represents the height of the low-frequency transmitting probe 3-1, the medium-frequency transmitting probe 3-3, and the high-frequency transmitting probe 3-5 from the bottom inner surface of the non-metallic container 7.

[0077] In this implementation, the angle is calculated by combining the geometric characteristics of the non-metallic container 7, the transit time, and Snell's law to obtain the liquid level information. The mathematical method of calculating the angle avoids liquid level errors caused by angle readings and automates the calculation process.

[0078] This embodiment also provides a method for multi-frequency ultrasonic liquid level measurement of non-metallic containers, using the aforementioned multi-frequency ultrasonic liquid level measurement device for non-metallic containers to detect liquid flow rate, such as... Figure 4 As shown, it includes the following steps:

[0079] S1. Install all probes on the side wall of the non-metallic container 7, specifically including: installing the low-frequency transmitting probe 3-1, the intermediate-frequency transmitting probe 3-3, and the high-frequency transmitting probe 3-5 at the same height on the first side wall 7-1 of the non-metallic container 7; and installing the low-frequency receiving probe 3-2, the intermediate-frequency receiving probe 3-4, and the high-frequency receiving probe 3-6 on the third side wall 7-2, which is symmetrical to the first side wall 7-1 about the central axis of the non-metallic container 7, with the low-frequency receiving probe 3-2 and the low-frequency transmitting probe 3-1 about the central axis of the non-metallic container 7. The intermediate frequency receiving probe 3-4 and the intermediate frequency transmitting probe 3-3 are symmetrical about the central axis of the non-metallic container 7. The high frequency receiving probe 3-6 and the high frequency transmitting probe 3-5 are symmetrical about the central axis of the non-metallic container 7. The low frequency transmitting probe 3-1, the intermediate frequency transmitting probe 3-3 and the high frequency transmitting probe 3-5 are installed at equal intervals on the first side wall 7-1 of the non-metallic container 7. The low frequency receiving probe 3-2, the intermediate frequency receiving probe 3-4 and the high frequency receiving probe 3-6 are installed at equal intervals on the third side wall 7-2 of the non-metallic container 7.

[0080] S2. Controller 1 transmits a control signal to the multi-frequency ultrasonic excitation module 2, causing the multi-frequency ultrasonic excitation module 2 to generate a 1MHz high-voltage pulse signal. The multi-frequency ultrasonic excitation module 2 transmits the 1MHz high-voltage pulse signal to the intermediate frequency transmitting probe 3-3, and the intermediate frequency transmitting probe 3-3 emits 1MHz ultrasonic waves. Figure 5As shown, the ultrasonic wave enters the liquid 11 through the refraction of the first side wall 7-1 of the non-metallic container 7, and then enters the intermediate frequency receiving probe 3-4 through the reflection of the surface of the liquid 11 and the refraction of the third side wall 7-2 of the non-metallic container 7.

[0081] S3. The echo signal processing and acquisition module 4 amplifies and filters the echo signal, and converts the echo signal into a digital signal before transmitting it to the host 5;

[0082] S4. The host 5 records the amplitude, transit time, transmission angle and installation height of the intermediate frequency receiving probe 3-4, and reception angle and installation height of the intermediate frequency receiving probe 3-4. It determines whether the amplitude of the echo signal is at its maximum value. If it is not at its maximum value, it adjusts the transmission angle and installation height of the intermediate frequency receiving probe 3-4 and the reception angle and installation height of the intermediate frequency receiving probe 3-4, and repeats steps S2-S4 until the amplitude of the received echo signal is at its maximum. When the amplitude of the echo signal is at its maximum value, it records the transmission angle and installation height of the intermediate frequency receiving probe 3-4 and the reception angle and installation height of the intermediate frequency receiving probe 3-4 at this time.

[0083] S5. The host 5 calculates the liquid level based on the digital signal, transit time, and geometric characteristics of the non-metallic container 7 to obtain a preliminary liquid level result;

[0084] The host 5 calculates the liquid level based on the digital signal, transit time, and geometric characteristics of the non-metallic container 7, and obtains the following liquid level results:

[0085] The distance the ultrasonic wave travels from its entry into the liquid 11 to its contact with the surface of the liquid 11 is obtained based on the geometric characteristics of the non-metallic container 7. As shown in formula (1):

[0086]

[0087] Where b represents the distance between the inner surface of the first sidewall 7-1 and the inner surface of the third sidewall 7-2 of the non-metallic container 7, and β represents the incident angle of the ultrasonic wave propagating from the first sidewall 7-1 into the liquid 11.

[0088] The distance traveled by the ultrasonic wave in liquid 11 from its entry to its contact with the surface of liquid 11 is obtained based on the transit time. As shown in formula (2):

[0089]

[0090] Wherein, c1 represents the propagation speed of the ultrasonic wave in the first sidewall 7-1, c2 represents the propagation speed of the ultrasonic wave in the liquid 11, t represents the transit time, L1 represents one of the following: the length between the piezoelectric crystal 12 of the low-frequency transmitting probe 3-1 and the probe surface of the low-frequency transmitting probe 3-1, the length between the piezoelectric crystal 12 of the intermediate-frequency transmitting probe 3-3 and the probe surface of the intermediate-frequency transmitting probe 3-3, or the length between the piezoelectric crystal 12 of the high-frequency transmitting probe 3-5 and the probe surface of the high-frequency transmitting probe 3-5, L2 represents the thickness of the first sidewall 7-1, and α represents the incident angle of the ultrasonic wave propagating into the first sidewall 7-1.

[0091] According to Snell's Law Combining formulas (1) and (2), we obtain the liquid level result, as shown in formula (3):

[0092]

[0093] Where H represents the liquid level result, and h1 represents the height of the low-frequency transmitting probe 3-1, the medium-frequency transmitting probe 3-3, and the high-frequency transmitting probe 3-5 from the bottom inner surface of the non-metallic container 7.

[0094] S6. When the preliminary liquid level result is less than 0.5 times the height of the non-metallic container 7, a high-frequency transmitting probe 3-5 and a high-frequency receiving probe 3-6 are used for measurement. The high-frequency transmitting probe 3-5 is adjusted to the transmitting angle and installation height recorded in step S4, and the high-frequency receiving probe 3-6 is adjusted to the receiving angle and installation height recorded in step S4. The controller 1 controls the high-frequency transmitting probe 3-5 to emit 2MHz ultrasonic waves, and the liquid level is calculated using the method in step S5 to obtain the liquid level result. If the preliminary liquid level result is greater than 0.5 times the height of the non-metallic container 7, a low-frequency transmitting probe 3-1 is used for measurement. The low-frequency transmitting probe 3-1 is adjusted to the transmitting angle and installation height recorded in step S4, and the low-frequency receiving probe 3-2 is adjusted to the receiving angle and installation height recorded in step S4. The controller 1 controls the low-frequency transmitting probe 3-1 to emit 0.5MHz ultrasonic waves, and the liquid level is calculated using the method in step S5 to obtain the liquid level result.

[0095] This invention utilizes ultrasonic probes with adjustable angles at different frequencies. By selecting ultrasonic waves of different frequencies and using the container's geometric features and transit time to calculate the liquid level, it can improve measurement accuracy while maximizing the measurement range, thus providing a new method for ultrasonic liquid level detection.

[0096] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A multi-frequency ultrasonic liquid level measuring device for non-metallic containers, characterized in that, It includes a controller (1), a multi-frequency ultrasonic excitation module (2), an ultrasonic transducer (3), an echo signal processing and acquisition module (4), a host (5), and a display module (6); The controller (1) is connected to the multi-frequency ultrasonic excitation module (2). The controller (1) is used to generate control signals with different frequency pulse width modulation and transmit the control signals to the multi-frequency ultrasonic excitation module (2). The multi-frequency ultrasonic excitation module (2) is connected to the ultrasonic transducer (3). The multi-frequency ultrasonic excitation module (2) is used to generate high-voltage pulse signals of different frequencies according to the control signal and transmit the high-voltage pulse signals of different frequencies to the ultrasonic transducer (3). The ultrasonic transducer (3) includes a low-frequency transmitting probe (3-1), a low-frequency receiving probe (3-2), a medium-frequency transmitting probe (3-3), a medium-frequency receiving probe (3-4), a high-frequency transmitting probe (3-5), and a high-frequency receiving probe (3-6), which can be mounted on a non-metallic container (7) and whose angle with the side wall of the non-metallic container (7) is adjustable. The low-frequency transmitting probe (3-1), the medium-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) are all mounted at the same height on the first side wall (7-1) of the non-metallic container (7). The low-frequency transmitting probe (3-1), the medium-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) are all used to transmit ultrasonic waves according to the high-voltage pulse signal. The low-frequency receiving probe (3-2), the medium-frequency receiving probe (3-4), and the high-frequency receiving probe (3-6) are all mounted at the same height on the first side wall (7-1) of the non-metallic container (7). -1) On the third sidewall (7-2) symmetrical about the central axis of the non-metallic container (7), the low-frequency receiving probe (3-2) and the low-frequency transmitting probe (3-1) are symmetrical about the central axis of the non-metallic container (7), the intermediate-frequency receiving probe (3-4) and the intermediate-frequency transmitting probe (3-3) are symmetrical about the central axis of the non-metallic container (7), and the high-frequency receiving probe (3-6) and the high-frequency transmitting probe (3-5) are symmetrical about the central axis of the non-metallic container (7). The low-frequency receiving probe (3-2), the intermediate-frequency receiving probe (3-4) and the high-frequency receiving probe (3-6) are all used to receive echoes. The output ends of the low-frequency receiving probe (3-2), the intermediate-frequency receiving probe (3-4) and the high-frequency receiving probe (3-6) are all connected to the input end of the echo signal processing and acquisition module (4) and transmit the echoes to the echo signal processing and acquisition module (4). The echo signal processing and acquisition module (4) is connected to the host (5). The echo signal processing and acquisition module (4) is used to amplify and filter the echo signal, and convert the echo signal into a digital signal and transmit it to the host (5). The host (5) is used to extract the transit time of the echo signal, and to calculate the liquid level based on the digital signal, transit time and the geometric characteristics of the non-metallic container (7), and to transmit the liquid level result to the display. The display is used to show the liquid level result.

2. The multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to claim 1, characterized in that, The multi-frequency ultrasonic excitation module (2) includes a driver chip, a field-effect transistor, and a pulse transformer connected in sequence; The input terminal of the driver chip is connected to the controller (1). The driver chip and the field-effect transistor are used to convert the control signal into a switching signal and transmit the switching signal to the pulse transformer. The output terminal of the pulse transformer is connected to the input terminals of the low-frequency transmitting probe (3-1), the intermediate-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5), respectively. The pulse transformer is used to generate high-voltage pulse signals of different frequencies according to the switching signal, and transmit the high-voltage pulse signals to one of the low-frequency transmitting probe (3-1), the intermediate-frequency transmitting probe (3-3), or the high-frequency transmitting probe (3-5).

3. The multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to claim 1, characterized in that, The low-frequency transmitting probe (3-1) has a transmitting frequency of 0.5MHz, the medium-frequency transmitting probe (3-3) has a transmitting frequency of 1MHz, and the high-frequency transmitting probe (3-5) has a transmitting frequency of 2MHz.

4. The multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to claim 1, characterized in that, The low-frequency transmitting probe (3-1), the intermediate-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) are installed at equal intervals on the first side wall (7-1) of the non-metallic container (7), and the low-frequency receiving probe (3-2), the intermediate-frequency receiving probe (3-4), and the high-frequency receiving probe (3-6) are installed at equal intervals on the third side wall (7-2) of the non-metallic container (7).

5. The multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to claim 1, characterized in that, The spacing between the low-frequency transmitting probe (3-1), the intermediate-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) is one-quarter of the width of the first sidewall (7-1), and the spacing between the low-frequency receiving probe (3-2), the intermediate-frequency receiving probe (3-4), and the high-frequency receiving probe (3-6) is one-quarter of the width of the third sidewall (7-2).

6. The multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to claim 1, characterized in that, The low-frequency transmitting probe (3-1), low-frequency receiving probe (3-2), intermediate-frequency transmitting probe (3-3), intermediate-frequency receiving probe (3-4), high-frequency transmitting probe (3-5), and high-frequency receiving probe (3-6) are all equipped with an angle adjustment knob (8). The angle adjustment knob (8) is used to adjust the angle of the low-frequency transmitting probe (3-1), low-frequency receiving probe (3-2), intermediate-frequency transmitting probe (3-3), intermediate-frequency receiving probe (3-4), high-frequency transmitting probe (3-5), or high-frequency receiving probe (3-6). The angle adjustment range of the low-frequency transmitting probe (3-1), low-frequency receiving probe (3-2), intermediate-frequency transmitting probe (3-3), intermediate-frequency receiving probe (3-4), high-frequency transmitting probe (3-5), and high-frequency receiving probe (3-6) is 0°-60°. The input ends of the low-frequency transmitting probe (3-1), the medium-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) are all provided with transmitting probe BNC interfaces (9), which are used to connect to the multi-frequency ultrasonic excitation module (2). The output ends of the low-frequency receiving probe (3-2), the medium-frequency receiving probe (3-4), and the high-frequency receiving probe (3-6) are all provided with receiving probe BNC interfaces (10), which are used to connect to the echo signal processing and acquisition module (4). The low-frequency transmitting probe (3-1), low-frequency receiving probe (3-2), intermediate-frequency transmitting probe (3-3), intermediate-frequency receiving probe (3-4), high-frequency transmitting probe (3-5), and high-frequency receiving probe (3-6) are all equipped with piezoelectric crystals (12).

7. A multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to claim 6, characterized in that, The echo signal processing and acquisition module (4) includes a multi-channel amplifier circuit module, a multi-channel bandpass filter circuit module and an AD acquisition circuit module connected in sequence; The input terminal of the multi-channel amplifier circuit module is connected to the BNC interface (10) of the receiving probes of the low-frequency receiving probe (3-2), the intermediate-frequency receiving probe (3-4), and the high-frequency receiving probe (3-6), respectively. The multi-channel amplifier circuit module is used to amplify the received echo to obtain an amplified echo and transmit the amplified echo to the multi-channel bandpass filter circuit module. The multi-channel bandpass filter circuit module is used to filter the amplified echo to obtain an amplified echo filtered signal, and transmit the amplified echo filtered signal to the AD acquisition circuit module. The output terminal of the AD acquisition circuit module is connected to the host (5). The AD acquisition circuit module is used to convert the amplified echo filter signal into a digital signal and transmit the digital signal to the host (5). The sampling frequency of the AD acquisition circuit module is 65MHz.

8. A multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to claim 6, characterized in that, The host (5) calculates the liquid level based on the digital signal, transit time, and geometric characteristics of the non-metallic container (7) to obtain the following liquid level results: The distance the ultrasonic wave travels from entering the liquid (11) to contacting the surface of the liquid (11) is obtained based on the geometric characteristics of the non-metallic container (7). As shown in formula (1): Where b represents the distance between the inner surface of the first sidewall (7-1) and the inner surface of the third sidewall (7-2) of the non-metallic container (7), and β represents the incident angle of the ultrasonic wave propagating from the first sidewall (7-1) into the liquid (11). The distance traveled by the ultrasonic wave in the liquid (11) from its entry to its contact with the surface of the liquid (11) is obtained based on the transit time. As shown in formula (2): Where c1 represents the propagation speed of ultrasound in the first sidewall (7-1), c2 represents the propagation speed of ultrasound in the liquid (11), t represents the transit time, L1 represents one of the following: the length between the piezoelectric crystal (12) of the low-frequency transmitting probe (3-1) and the probe surface of the low-frequency transmitting probe (3-1), the length between the piezoelectric crystal (12) of the medium-frequency transmitting probe (3-3) and the probe surface of the medium-frequency transmitting probe (3-3), or the length between the piezoelectric crystal (12) of the high-frequency transmitting probe (3-5) and the probe surface of the high-frequency transmitting probe (3-5), L2 represents the thickness of the first sidewall (7-1), and α represents the incident angle of ultrasound propagation into the first sidewall (7-1). According to Snell's Law Combining formulas (1) and (2), the liquid level result is obtained as shown in formula (3): Where H represents the liquid level result, and h1 represents the height of the low-frequency transmitting probe (3-1), the medium-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) from the bottom inner surface of the non-metallic container (7).

9. A method for multi-frequency ultrasonic liquid level measurement in non-metallic containers, characterized in that, Using the multi-frequency ultrasonic liquid level measuring device for non-metallic containers according to any one of claims 1-8 to detect liquid level includes the following steps: S1. Install the low-frequency transmitting probe (3-1), the intermediate-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) at the same height on the first sidewall (7-1) of the non-metallic container (7). Install the low-frequency receiving probe (3-2), the intermediate-frequency receiving probe (3-4), and the high-frequency receiving probe (3-6) on the third sidewall (7-2) which is symmetrical to the first sidewall (7-1) about the central axis of the non-metallic container (7). The low-frequency receiving probe (3-2) is symmetrical to the low-frequency transmitting probe (3-1) about the central axis of the non-metallic container (7). The intermediate-frequency receiving probe (3-4) is symmetrical to the low-frequency transmitting probe (3-1) about the central axis of the non-metallic container (7). The low-frequency transmitting probe (3-1), the intermediate-frequency transmitting probe (3-3), and the high-frequency receiving probe (3-6) are symmetrical about the central axis of the non-metallic container (7). The low-frequency transmitting probe (3-1), the intermediate-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) are installed at equal intervals on the first side wall (7-1) of the non-metallic container (7). The low-frequency receiving probe (3-2), the intermediate-frequency receiving probe (3-4), and the high-frequency receiving probe (3-6) are installed at equal intervals on the third side wall (7-2) of the non-metallic container (7). S2. The controller (1) transmits a control signal to the multi-frequency ultrasonic excitation module (2) so that the multi-frequency ultrasonic excitation module (2) generates a 1MHz high-voltage pulse signal. The multi-frequency ultrasonic excitation module (2) transmits the 1MHz high-voltage pulse signal to the intermediate frequency transmitting probe (3-3). The intermediate frequency transmitting probe (3-3) emits 1MHz ultrasonic waves. The ultrasonic waves are refracted by the first sidewall (7-1) of the non-metallic container (7) and enter the liquid (11). Then, after reflection from the surface of the liquid (11) and refraction by the third sidewall (7-2) of the non-metallic container (7), they enter the intermediate frequency receiving probe (3-4). S3. Echo signal processing and acquisition module (4) amplifies and filters the echo signal, and converts the echo signal into a digital signal and transmits it to the host (5); S4. The host (5) records the amplitude, transit time, transmission angle and installation height of the intermediate frequency receiving probe (3-4) and the receiving angle and installation height of the intermediate frequency receiving probe (3-4), and determines whether the amplitude of the echo signal is the maximum value. If it is not the maximum value, the host adjusts the transmission angle and installation height of the intermediate frequency receiving probe (3-4) and the receiving angle and installation height of the intermediate frequency receiving probe (3-4), and repeats steps S2-S4 until the amplitude of the received echo signal is the maximum. When the amplitude of the echo signal is the maximum value, the host records the transmission angle and installation height of the intermediate frequency receiving probe (3-4) and the receiving angle and installation height of the intermediate frequency receiving probe (3-4) at this time. S5. The host (5) calculates the liquid level based on the digital signal, transit time, and geometric characteristics of the non-metallic container (7) to obtain a preliminary liquid level result; S6. When the preliminary liquid level result is less than 0.5 times the height of the non-metallic container (7), the high-frequency transmitting probe (3-5) and the high-frequency receiving probe (3-6) are used for measurement. The high-frequency transmitting probe (3-5) is adjusted to the transmitting angle and installation height recorded in step S4, and the high-frequency receiving probe (3-6) is adjusted to the receiving angle and installation height recorded in step S4. The controller (1) controls the high-frequency transmitting probe (3-5) to emit 2MHz ultrasonic waves, and the liquid level is calculated using the method in step S5. The liquid level result is obtained. If the preliminary liquid level result is greater than 0.5 times the height of the non-metallic container (7), a low-frequency transmitting probe (3-1) is used for measurement. The low-frequency transmitting probe (3-1) is adjusted to the transmitting angle and installation height recorded in step S4, and the low-frequency receiving probe (3-2) is adjusted to the receiving angle and installation height recorded in step S4. The controller (1) controls the low-frequency transmitting probe (3-1) to emit 0.5MHz ultrasonic waves. The liquid level is calculated by the method in step S5 to obtain the liquid level result.

10. A method for multi-frequency ultrasonic liquid level measurement in non-metallic containers according to claim 9, characterized in that, In step S5, the host (5) calculates the liquid level based on the digital signal, transit time, and geometric characteristics of the non-metallic container (7) to obtain the liquid level result, including: The distance the ultrasonic wave travels from entering the liquid (11) to contacting the surface of the liquid (11) is obtained based on the geometric characteristics of the non-metallic container (7). As shown in formula (1): Where b represents the distance between the inner surface of the first sidewall (7-1) and the inner surface of the third sidewall (7-2) of the non-metallic container (7), and β represents the incident angle of the ultrasonic wave propagating from the first sidewall (7-1) into the liquid (11). The distance traveled by the ultrasonic wave in the liquid (11) from its entry to its contact with the surface of the liquid (11) is obtained based on the transit time. As shown in formula (2): Where c1 represents the propagation speed of ultrasound in the first sidewall (7-1), c2 represents the propagation speed of ultrasound in the liquid (11), t represents the transit time, L1 represents one of the following: the length between the piezoelectric crystal (12) of the low-frequency transmitting probe (3-1) and the probe surface of the low-frequency transmitting probe (3-1), the length between the piezoelectric crystal (12) of the medium-frequency transmitting probe (3-3) and the probe surface of the medium-frequency transmitting probe (3-3), or the length between the piezoelectric crystal (12) of the high-frequency transmitting probe (3-5) and the probe surface of the high-frequency transmitting probe (3-5), L2 represents the thickness of the first sidewall (7-1), and α represents the incident angle of ultrasound propagation into the first sidewall (7-1). According to Snell's Law Combining formulas (1) and (2), the liquid level result is obtained as shown in formula (3): Where H represents the liquid level result, and h1 represents the height of the low-frequency transmitting probe (3-1), the medium-frequency transmitting probe (3-3), and the high-frequency transmitting probe (3-5) from the bottom inner surface of the non-metallic container (7).

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