CN111609901A

CN111609901A - High-precision short-distance ultrasonic liquid level measuring device

Info

Publication number: CN111609901A
Application number: CN202010445756.2A
Authority: CN
Inventors: 薛萍; 邢健文; 王宏民
Original assignee: Harbin University of Science and Technology
Current assignee: Harbin University of Science and Technology
Priority date: 2020-05-24
Filing date: 2020-05-24
Publication date: 2020-09-01
Anticipated expiration: 2040-05-24
Also published as: CN111609901B

Abstract

The invention discloses a high-precision short-distance ultrasonic liquid level measuring device, and belongs to the technical field of measuring instruments. The invention aims to solve the problem that a liquid level measuring device in the prior art has large measuring error. The ultrasonic wave detection device comprises a main controller, an ultrasonic wave transmitting and receiving device, a waveguide tube and a floating plate, wherein the waveguide tube is a hollow cylindrical structure with openings at the upper end and the lower end; the invention improves the liquid level measurement precision and solves the problem of large measurement error of the liquid level measurement device in the prior art.

Description

High-precision short-distance ultrasonic liquid level measuring device

Technical Field

The invention relates to the technical field of measuring instruments, in particular to a high-precision short-distance ultrasonic liquid level measuring device which is used for high-precision measurement of short-distance liquid levels.

Background

The frequency of sound wave which can be heard by human ears is 20Hz-20kHz, and the ultrasonic wave is sound wave which exceeds the hearing limit of human ears, namely mechanical wave with the frequency exceeding 20 kHz. The ultrasonic wave has the characteristics of good permeability, strong directivity and short wavelength, and is widely used for distance measurement, speed measurement, stone breaking, sterilization and disinfection and the like. The ultrasonic wave is utilized to carry out distance measurement, the method is rapid and convenient, the calculation is simple, the real-time control is easy to realize, and the measurement precision can meet the requirement, so the ultrasonic wave is widely applied in the field of distance measurement.

By utilizing the characteristic that the ultrasonic waves are transmitted when meeting the change of a medium in the transmission process, most of the existing ultrasonic liquid level measuring devices adopt a non-contact mode, namely, an ultrasonic probe has a certain interval with the liquid level and does not directly contact with the liquid level to be measured. The small-range liquid level measuring device disclosed in the Chinese patent CN201410734794 and the float reflection type ultrasonic liquid level sensor disclosed in the Chinese patent CN209148097U both adopt a method that an ultrasonic transducer or a guide rod directly contacts with liquid. However, if this method is used in the case that the liquid to be measured is acid-base, the ultrasonic transducer and the guide rod may be corroded by direct contact with the liquid, which may cause an influence. The requirement of GB/T11828 water level measuring instrument is that the accuracy is within the measuring range, the maximum allowable error of the ultrasonic water level meter is not more than +/-3 cm based on the measured result of still water. The dead zone of the existing ultrasonic liquid level meter is usually 30cm-50cm, and the short-distance measurement of 30cm cannot be realized; the existing non-contact ultrasonic liquid level meter is accurate when measuring static liquid level, but the error is large under the condition of dynamic fluctuation, and the reason is that echo spurious reflection can be caused under the fluctuation condition, so that the receiving device can not accurately receive echo signals, interference can be caused to the measuring result, and the error is increased.

Disclosure of Invention

In order to solve the problems, the invention provides a high-precision short-distance ultrasonic liquid level measuring device, which solves the problems that the dead zone of the liquid level measuring device in the prior art is too large and the measurement is inaccurate when the liquid level is not stable.

The utility model provides a high accuracy short distance ultrasonic wave level measurement device, includes main control unit, ultrasonic emission receiving arrangement, wave guide and kickboard, the wave guide is the open hollow tubular structure in upper and lower both ends, and the lower extreme of the vertical installation of wave guide and wave guide stretches into in treating the survey liquid level, and the kickboard floats on the liquid level in the wave guide, and ultrasonic emission receiving arrangement installs in the kickboard top.

Furthermore, a plurality of uniformly arranged counterweight bodies are arranged at the lower end of the floating plate, and the density of the counterweight bodies is greater than that of the liquid to be measured.

Further, the counterweight body is hung below the floating plate through a connecting line.

Further, the weight body is installed at the edge of the floating plate and the center of the floating plate.

Furthermore, the exterior of the counterweight body is provided with an anticorrosion shell.

Furthermore, the ultrasonic transmitting and receiving device comprises an ultrasonic transmitting circuit and an ultrasonic receiving circuit, and the main controller is respectively connected with the ultrasonic transmitting circuit and the ultrasonic receiving circuit.

Further, ultrasonic emission circuit includes ultrasonic emission probe and parallel connection's first receiving circuit and second receiving circuit, and first receiving circuit is the same with second receiving circuit's structure, first receiving circuit includes first resistance, electric capacity with higher speed, triode, pull-down resistance and a plurality of parallelly connected collecting electrode resistance, main control unit is connected to first resistance one end, and the base of triode is connected to the first resistance other end, electric capacity with higher speed connects in first resistance both ends, and the base and the projecting pole of triode are connected respectively to the both ends of pull-down resistance, the collecting electrode of triode is connected to collecting electrode resistance one end, and the other end is connected power.

Further, the ultrasonic receiving circuit comprises an ultrasonic receiving probe and a receiving circuit, and the receiving circuit comprises a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a first capacitor, a sixth capacitor, a potentiometer and a comparison amplifier; the ultrasonic receiving probe is connected with a power supply through a second resistor, one end of a first capacitor is connected between the ultrasonic receiving probe and the second resistor, the other end of the first capacitor is connected between the third resistor and the potentiometer, the other end of the potentiometer is grounded through a fourth resistor, the sliding end of the potentiometer is connected with the inverting input end of a comparison amplifier, the non-inverting input end of the comparison amplifier is connected between the fifth resistor and the sixth resistor, and the output end of the comparison amplifier is connected with an RC filter circuit consisting of an eighth resistor and a sixth capacitor.

Furthermore, the second capacitor and the third capacitor are connected in parallel to form a first filter circuit, the fourth capacitor and the fifth capacitor are connected in parallel to form a second filter circuit, the first filter circuit is connected with the third resistor, and the second filter circuit is connected with the fifth resistor.

Further, the output end of the comparison amplifier is connected with a seventh resistor.

As mentioned above, the high-precision short-distance ultrasonic liquid level measuring device provided by the invention has the following effects:

this application has adopted waveguide and kickboard complex structure, and when the liquid level takes place undulant, the waveguide cooperates with its inside kickboard, greatly reduced the fluctuation range of kickboard, furthest has kept the balance of kickboard and ultrasonic emission receiving arrangement position, has improved measurement accuracy.

This application adopts the underneath heavy object that is furnished with of float, prevents that the float shake from making the device more reliable and more stable, and current device only is applicable to pure liquid moreover, and the material that this device adopted is polytetrafluoroethylene, applicable in the measuring environment of corrosive liquids such as acidity.

The liquid level measuring device is suitable for measuring the short-distance liquid level within the distance range of 2cm-10cm, and the measuring precision can reach 1 mm.

Drawings

FIG. 1 is a schematic view of the overall structure of a high-precision short-distance ultrasonic liquid level measuring device according to an embodiment of the present invention;

FIG. 2 is a top view of the float plate and counterweight according to one embodiment of the present invention;

FIG. 3 is a schematic diagram of an ultrasonic transmitter circuit in accordance with an embodiment of the present invention;

FIG. 4 is a schematic diagram of an ultrasonic receiving circuit according to an embodiment of the present invention;

FIG. 5 is a waveform diagram illustrating the processing result of echo signals according to an embodiment of the present invention;

FIG. 6 is a graph of ultrasonic echo amplitude attenuation for an embodiment of the present invention;

FIG. 7 is a waveform of an ultrasonic echo shaped by a comparator according to an embodiment of the present invention;

FIG. 8 is an ultrasonic echo amplitude attenuation diagram and a relationship between a transmission waveform and an echo after pulse width compensation, FIG. 8a is an ultrasonic echo amplitude attenuation diagram, and FIG. 8b is a relationship between a transmission wave and an echo;

FIG. 9 is a flow chart of liquid level measurement according to an embodiment of the present invention.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.

It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.

The high-precision short-distance ultrasonic liquid level measuring device of the embodiment is shown in fig. 1 and comprises: including main control unit in shell 1, the shell 1, ultrasonic wave transmitting and receiving device 2 is installed to the shell lower extreme, and waveguide 3 is installed to the lower extreme of shell 1, waveguide 3 is the open hollow tubular structure in upper and lower both ends, and in the lower extreme of 3 vertical installations of waveguide and waveguide stretched into the liquid 6 that awaits measuring, measured liquid 6 dress was in container 5, floated floating plate 4 on the liquid level in waveguide 3, shown ultrasonic wave transmitting and receiving device 2 installs in floating plate 4 top, and the main control unit that this embodiment adopted includes the STC15 singlechip.

The distance between the axial edge of the floating plate 4 and the inner wall of the waveguide 3 ranges from 4mm to 7mm, the distance selected in the embodiment is 5mm, the floating plate can freely move up and down in the waveguide, the stability of the liquid level can be kept to the maximum extent, and the floating plate 4 selected in the embodiment is made of polytetrafluoroethylene. In this embodiment, the diameter of the ultrasonic probe is 1.3cm, the diameter of the inner wall of the waveguide is 6cm, and the length of the waveguide is 13 cm.

The ultrasonic transmitting and receiving device 2 is used for transmitting and receiving ultrasonic waves, the floating plate 4 always floats on the liquid level of the liquid 6 to be detected, the floating plate rises along with the rising of the liquid level of the liquid 6 to be detected, the floating plate 4 only vertically moves up and down along with the lowering of the liquid level of the liquid 6 to be detected, when the liquid level fluctuates, the upper surface of the floating plate 4 is always parallel to the surface of the ultrasonic transmitting and receiving device 2 due to the limitation of the waveguide tube 3, the ultrasonic waves are reflected at an angle of 90 degrees of the reflecting surface, and the situation that the reflected signals cannot return back on the original way is avoided.

Because the floating plate density is less, so appear the shake easily when the liquid level appears undulant, can bring the error for the measuring result in the ultrasonic wave liquid level measurement process, so, this embodiment floating plate lower extreme is equipped with a plurality of evenly arranged's counter weight bodies 7, counter weight body 7 density is greater than the density of the liquid 6 that awaits measuring, guarantees that floating plate 4 remains stable all the time on the liquid level in the measurement process, reduces the shake, guarantees that echo signal returns on the way.

Because the density of different measured liquids is different, need set up different counter weights, for the installation replacement is convenient, counter weights 7 hang through the connecting wire in 4 below strakes to in order to make the upper surface of strakes 4 keep the level, counter weights 7 are installed in the edge of strakes and the center department of strakes, as shown in fig. 2, the quantity of the counter weights 7 of this embodiment is 5, makes the center of strakes 4 move down, keeps stable can not shake at will.

Since part of the liquid to be measured is corrosive, the counterweight body 7 of the present embodiment has an anticorrosive case outside.

The ultrasonic transmitting and receiving device of the embodiment comprises an ultrasonic transmitting circuit and an ultrasonic receiving circuit, and the main controller is respectively connected with the ultrasonic transmitting circuit and the ultrasonic receiving circuit.

As shown in fig. 3, the ultrasonic transmitting circuit of this embodiment adopts a triode switch circuit, because the ultrasonic transducer needs an alternating excitation signal to drive, and in order to have a sufficient driving voltage, two triode switch circuits are selected, which can generate an excitation signal and also have an amplification function to generate a sufficient driving voltage, and as shown in the figure, the ultrasonic transmitting circuit includes an ultrasonic transmitting probe S1, and a first receiving circuit a and a second receiving circuit B connected in parallel, the first receiving circuit a and the second receiving circuit B have the same structure and the same function of the corresponding components, the first receiving circuit a includes a first resistor R1, an accelerating capacitor C1, a triode Q, a pull-down resistor R2, and parallel collector resistors R3, R4, R5, R6, and R7, and parallel collector resistors R3, R4, R5, R6, and R7 which can increase power, the circuit is characterized in that one end of a first resistor R1 is connected with a main controller, the other end of the first resistor R1 is connected with a base electrode of a triode Q, an accelerating capacitor C1 is connected in parallel with two ends of a first resistor R1, two ends of a pull-down resistor R2 are respectively connected with the base electrode and an emitter electrode of the triode Q, one end of a collector resistor is connected with a collector electrode of the triode Q, the other end of the collector resistor is connected with a power supply, correspondingly, a second receiving circuit B comprises a resistor R1 ', an accelerating capacitor C1', a triode Q ', a pull-down resistor R2', collector resistors R3 ', R4', R5 ', R6' and R7 'which are connected in parallel, two ends of the resistor R1 and the resistor R1' and two pin necklaces of the main controller, firstly, a command is sent to a single chip microcomputer 15 through a serial port, the STC15 sends a frequency of 300kHz and a duty ratio of 1 to two ends of: 1. the ultrasonic wave measuring device comprises 10 square waves with half period difference in period, the number of the square waves is used for driving a transmitting probe S1, the higher the frequency of the adopted ultrasonic wave is, the shorter the wavelength is, the smaller the spread angle of the sound beam is, the more concentrated the energy is, the better the directivity and discrimination are, the higher the frequency is, the larger the sound wave attenuation is, the short-distance measurement can be carried out, the problem that the ultrasonic wave with the frequency of 40khz in the prior art cannot meet the measurement of the short-distance condition is solved, the short-distance liquid level measurement with the measuring distance range of 2cm-10cm is realized, and the measuring precision can reach 1 mm; the ultrasonic transmitting circuit is powered by 12V voltage, and the amplification effect of the triode is adopted, so that square waves with the amplitude of 15V alternation can be generated at the two ends of the ultrasonic transmitting probe S1, and the ultrasonic transmitting probe S1 is better driven, and ultrasonic waves are generated.

As shown in fig. 4, the ultrasonic receiving circuit of the present embodiment includes an ultrasonic receiving probe S2 and a receiving circuit, where the receiving circuit includes a second resistor R8, a third resistor R9, a fourth resistor R10, a fifth resistor R11, a sixth resistor R12, a seventh resistor R13, an eighth resistor R14, a first capacitor C2, a second capacitor C3, a third capacitor C4, a fourth capacitor C5, a fifth capacitor C6, a sixth capacitor C7, a potentiometer R and a comparison amplifier U; the third resistor R9, the potentiometer R and the fourth resistor R10 are sequentially connected in series, the fifth resistor R11 and the sixth resistor R12 are connected in series, one end of the ultrasonic receiving probe S2 is connected with a power supply through the second resistor R8, one end of the first capacitor C2 is connected between the ultrasonic receiving probe S2 and the second resistor R8, the other end of the first capacitor C2 is connected between the third resistor R9 and the potentiometer R, the other end of the potentiometer R is grounded through the fourth resistor R10, the inverting input end of the potentiometer R is connected with the inverting input end of the comparison amplifier U, the non-inverting input end of the comparison amplifier U is connected between the fifth resistor R11 and the sixth resistor R12, the output end of the comparison amplifier U is connected with an RC filter circuit composed of the eighth resistor R14 and the sixth resistor C7, the amplified signal is shaped, filtered and output to the sliding amplifier, and the output end of the comparison amplifier is connected with the seventh resistor R13; the amplitude of the signal received by the ultrasonic receiving probe S2 is too small, the main controller cannot identify and process the signal, the signal received by the ultrasonic receiving probe S2 is coupled to one end of the potentiometer R through the first capacitor C2, the amplitude of the positive input end of the comparison amplifier U is 2.5V, noise can be filtered, and only useful signals can be amplified; the output end of the comparison amplifier U is an OC gate output, and a seventh resistor R13 is required to be added to the output end to serve as a pull-up resistor; the whole circuit is powered by a 5V power supply. The ultrasonic receiving probe S2 receives the echo signal, the echo signal passes through the receiving part, the capacitor C2 couples the small signal to the filtering part, the small signal passes through the filtering capacitor and then is sent to the amplifying comparator part, the useful signal is extracted after the small signal passes through the comparator, the small signal is rectified through the RC filtering circuit, the signal is kept stable, the same judgment standard can be kept when the small signal returns to the main controller, and the error is reduced.

The second capacitor C3 and the third capacitor C4 are connected in parallel to form a first filter circuit, the fourth capacitor C5 and the fifth capacitor C6 are connected in parallel to form a second filter circuit, the interference of a power supply to signals is large due to the fact that the frequency of 300kHz signals is high, the power supply needs to be additionally provided with a filter capacitor, the interference of power supply noise is reduced, the first filter circuit is connected with the third resistor R9, and the second filter circuit is connected with the fifth resistor R11.

The ultrasonic transmitting probe S1 and the ultrasonic receiving probe S2 are one probe, and when the ultrasonic transmitting probe S1 transmits ultrasonic waves, the ultrasonic transmitting probe S3578 and the ultrasonic receiving probe S2 are switched.

The control output end of the main controller is connected with the output ends of the triode switch circuit and the ultrasonic receiving circuit of the ultrasonic transmitting circuit and used for storing the set threshold voltage; sending a control command to the ultrasonic transmitting circuit, receiving a return signal received by the ultrasonic receiving circuit, processing the return signal to obtain distance information, timing by using a clock inside the main controller, and shaping the echo signal as shown in fig. 5, wherein a channel CH1 is the processed echo signal, and a channel CH2 is the transmitting signal; the processed signals are more stable, the main controller of the embodiment adopts falling edge triggering and stops timing, and after shaping of the echo signal processing circuit, the falling edge of each echo can be ensured to be more stable, the triggering standards of the main controller can be the same, and errors are reduced.

The working process of the liquid level measuring device in the embodiment is as follows:

the ultrasonic transmitting probe transmits ten ultrasonic waves with the frequency of 300kHz to the obstacle, and the wavelength can be obtained to be 1.15mm according to a frequency and wavelength formula of lambda-uT, wherein lambda is the wavelength, u is the wave velocity, and T is the period, and the frequency meets the requirement;

the timing is started by delaying a period of time to avoid the interference of the aftershock signal, the delay time is determined by the image of the transmitted signal, and the delay time is at least 33 microseconds as a group of ten pulses are transmitted each time, the timing is started from the transmission of the first pulse, and the period is 3.3 microseconds each time;

the ultrasonic ranging device transmits ultrasonic waves to a target obstacle, then converts the ultrasonic waves into a receiving mode, receives a returned signal, receives the returned signal, amplifies the signal through the amplifier and sends the amplified signal to the main controller;

the main control unit receives the signal after amplification, stop timing, handle data, obtain distance information, but when ultrasonic signal returns, along with the increase of distance, received signal width can reduce gradually, after the comparator plastic, can cause the leading edge to move backward, and the leading edge moves backward means that ultrasonic echo measurement time delay is back, when losing a signal, will cause the error of 1.1mm at most, so the main control unit of this embodiment adopts the echo compensation method to compensate echo signal, the compensation mode is:

where T is the period of the transmitted 300kHz ultrasonic family, T₁In order to measure the pulse width of the echo, v is the propagation speed of the ultrasonic wave, S is the distance from the liquid level to be measured to the ultrasonic transducer, and t is the transit time, the method can compensate the backward moving front edge and reduce the error generated by the waveform front edge delay.

For an environment with high precision requirement, the influence of temperature on the transmission speed of the ultrasonic wave needs to be considered, and the transmission speed of the ultrasonic wave needs to be compensated for by v being 331.5+0.607C so as to reduce the error, wherein C is the actual temperature and is the unit of centigrade, and v is the actual propagation speed of the ultrasonic wave and is the unit of m/s.

The specific compensation principle is shown in fig. 6-8, the ultrasonic ranging adopts a group wave transmission mode, that is, about 10 complete waveforms are transmitted at a time and then enter an echo receiving mode, a receiving circuit part is generally provided with a comparator and an amplifier, the amplitude of an ultrasonic echo is reduced along with the increase of the distance, and an ultrasonic echo signal attenuation graph and a waveform shaped by the comparator are shown in fig. 6-7. As can be seen from the figure, as the distance increases, the width of the received pulse narrows and the leading edge moves backward, causing time measurement errors. The waveform after shaping is composed of a plurality of ultrasonic wave periods, the forward edge backward movement means that 300kHz ultrasonic waves are adopted in the design after the ultrasonic echo measurement time delay, and 1.1mm of error is caused by losing one ultrasonic wave period, so that the error of time measurement needs to be reduced by taking measures.

Fig. 8 is a schematic diagram of the echo pulse width compensation method, in which the dotted line indicates the period of the transmitted ultrasonic wave and the solid line indicates the echo width. The diagram shows the phase relationship of the transmit wave and the echo front. T is₁The measured echo pulse width; Δ t is the lag time; it can be seen that the method can compensate the pulse width of the echo, and the farther the distance is, the narrower the pulse width of the echo is, the more the time lag is, the larger the compensation amount is.

After echo compensation, the obtained compensated signal is measured by adopting a cross-correlation method detection method to obtain accurate transit time, and the longer the measurement distance is, the weaker the echo energy is, so that the echo compensation method provided by the application enables the obtained echo waveform to be more accurate, and further the calculated transit time is more accurate.

The cross-correlation method is one of the most basic and effective methods for measuring the transit time, and has strong noise suppression capability. The measurement principle of the cross-correlation method is that if the signal sent by the ultrasonic wave is x (t) and the received ultrasonic wave signal is y (t), the cross-correlation function M of the two signals is_xy(T) may be prepared from

And (6) obtaining. After the cross-correlation operation is performed by the above formula, the time T corresponding to the peak point of the cross-correlation function can be obtained, so that the accurate transit time T can be obtained.

Aiming at the problem that the distance measurement distance of the device is short, a threshold value with the distance measurement distance of 2cm-10cm needs to be set before measurement, the threshold value is set to remove noise and extract useful signals, and in the embodiment, the adopted amplitude threshold value is 45 dB; in actual measurement, in order to better distinguish a valid signal from an interference signal, the amplitude of the threshold is determined by experimental debugging, so that a corresponding accurate threshold value at a specific distance is measured, and then the obtained signal is compensated.

The signal after echo compensation is processed to shape the signal into a sine signal, that is, the ultrasonic signal after compensation is optimized to obtain an ideal signal, then the signal is input y (T), the ultrasonic signal which is initially transmitted is x (T), and the cross-correlation function is obtained by a formula to obtain the transit time. Aiming at the characteristic of short measuring distance of the device, the transit time passes through M_xyAnd (T) is obtained, wherein x is (T) y (T), the convolution is carried out, and then the cross-correlation signal is calculated by using a fast Fourier algorithm, so that the calculation efficiency is improved, and the measurement accuracy is also improved.

The obtained transit time is the time difference between the detection of the emitted ultrasonic wave and the reception of the echo, so that the distance between the target object and the ultrasonic emission probe is calculated.

The ultrasonic wave that this application adopted is that the frequency is 300kHz, what current ultrasonic ranging device generally adopted is that the frequency is 40 kHz's ultrasonic wave, the ultrasonic wave wavelength of this frequency is longer, can't measure the short distance, so adopt high-frequency ultrasonic wave, 40kHz ultrasonic ranging device has the not high problem of measurement accuracy moreover, so select to adopt the frequency to be 300 kHz's ultrasonic wave, because the application of new material, new technology, can make the very height of measuring accuracy by a wide margin, and the range of application is also very expanded greatly moreover.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. The utility model provides a high accuracy short distance ultrasonic wave liquid level measurement device which characterized in that: including main control unit, ultrasonic wave emission receiving arrangement, wave guide and kickboard, the wave guide is the open hollow tubular structure in upper and lower both ends, and the vertical installation of wave guide and the lower extreme of wave guide stretch into in the liquid level of waiting to survey, and the kickboard floats on the liquid level in the wave guide, and ultrasonic wave emission receiving arrangement installs in the kickboard top.

2. A high precision short range ultrasonic level measuring device according to claim 1, wherein: the lower end of the floating plate is provided with a plurality of evenly distributed counterweight bodies, and the density of the counterweight bodies is greater than that of the liquid to be measured.

3. A high precision short range ultrasonic level measuring device according to claim 2, wherein: the counterweight body is suspended below the floating plate through a connecting line.

4. A high precision short range ultrasonic level measuring device according to claim 2, wherein: the counterweight body is arranged at the edge of the floating plate and the center of the floating plate.

5. A high precision short range ultrasonic level measuring device according to claim 2, wherein: and an anti-corrosion shell is arranged outside the counterweight body.

6. A high precision short range ultrasonic level measuring device according to claim 1, wherein: the ultrasonic transmitting and receiving device comprises an ultrasonic transmitting circuit and an ultrasonic receiving circuit, and the main controller is respectively connected with the ultrasonic transmitting circuit and the ultrasonic receiving circuit.

7. A high precision short range ultrasonic level measuring device according to claim 6, wherein: ultrasonic emission circuit includes ultrasonic emission probe and parallel connection's first receiving circuit and second receiving circuit, and first receiving circuit is the same with second receiving circuit's structure, first receiving circuit includes first resistance, electric capacity with higher speed, triode, pull-down resistance and a plurality of parallelly connected collecting electrode resistance, main control unit is connected to first resistance one end, and the base of triode is connected to the first resistance other end, electric capacity with higher speed connects in first resistance both ends, and the base and the projecting pole of triode are connected respectively to the both ends of pull-down resistance, the collecting electrode of triode is connected to collecting electrode resistance one end, other end connecting source.

8. A high precision short range ultrasonic level measuring device according to claim 6, wherein: the ultrasonic receiving circuit comprises an ultrasonic receiving probe and a receiving circuit, and the receiving circuit comprises a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a first capacitor, a sixth capacitor, a potentiometer and a comparison amplifier; the ultrasonic receiving probe is connected with a power supply through a second resistor, one end of a first capacitor is connected between the ultrasonic receiving probe and the second resistor, the other end of the first capacitor is connected between the third resistor and the potentiometer, the other end of the potentiometer is grounded through a fourth resistor, the sliding end of the potentiometer is connected with the inverting input end of a comparison amplifier, the non-inverting input end of the comparison amplifier is connected between the fifth resistor and the sixth resistor, and the output end of the comparison amplifier is connected with an RC filter circuit consisting of an eighth resistor and a sixth capacitor.

9. A high precision short range ultrasonic level measuring device according to claim 8, wherein: the second capacitor and the third capacitor are connected in parallel to form a first filter circuit, the fourth capacitor and the fifth capacitor are connected in parallel to form a second filter circuit, the first filter circuit is connected with the third resistor, and the second filter circuit is connected with the fifth resistor.

10. A high precision short range ultrasonic level measuring device according to claim 8, wherein: and the output end of the comparison amplifier is connected with a seventh resistor.