WO2002035190A1

WO2002035190A1 - A method for measuring liquid level in large oil tanks with ultrasonic wave

Info

Publication number: WO2002035190A1
Application number: PCT/CN2000/000745
Authority: WO
Inventors: Zhi Lu; Sining Lu
Original assignee: Zhi Lu
Priority date: 2000-10-25
Filing date: 2000-12-29
Publication date: 2002-05-02
Also published as: AU2001223436A1; CN1350164A

Abstract

A method for measuring liquid level in large oil tanks with ultrasonic wave, characterized in that a microcomputer sends a transmitter an instruction to launch ultrasonic pulse signals toward the liquid level under essential explosion proof conditions until a receiver receives an echo signal, the intensities of the ultrasonic pulse signals are increased from low to high or decreased from high to low. Compared to the prior art, the ultrasonic wave measuring liquid device according to the invention is capable of measuring liquid level in large oil tanks, whose explosion-proof level is iaIICT6, its accuracy excels 0.2% of the true distance, achieving a blind zone less than 15cm, and improving the degree of intelligentization and automation, and it is convenient to operate the device. It has been proved that the method according to the invention is a unique one that can measure liquid level in large oil tanks. However, prior ultrasonic wave measuring devices cannot measure the liquid level in large oil tanks.

Description

Method for ultrasonically measuring liquid level of large oil tank

The present invention relates to a system for measuring distance using the reflection of ultrasonic waves, and particularly to a method for ultrasonically measuring the liquid level of a large oil tank. Background technique

Utilizing ultrasonic ranging or measuring the level are both a carrier wave, a square-modulated pulse wave, and a modulated pulse wave with a square envelope composed of the carrier wave and the square-modulated pulse wave. Amplifying, the transmitter transmits an ultrasonic pulse signal to the measured target. The reflected wave is reflected back from the measured target and received by the receiver. After amplification, detection, comparative shaping, data processing, the dynamic blind zone or gating window is given, the level is displayed, and the ultrasonic wave travels from the transmitter to the measured U mark once. The required cycle time determines the distance of the target. In order to accurately measure the distance, it is required that the resolution of the ultrasonic wave is high, and the accuracy of the cycle time measurement is high. In order to achieve long-distance measurement, the detection ability is required. At the same time, it is required to eliminate the interference of environmental noise and various false echoes in the tank.

In order to improve the comprehensive performance of the ultrasonic positioner, many improvement schemes have been proposed, and better performance positioners have been developed, such as the Canadian company Mill tronics, Germany's Enrerss + Hauser, and Vegason. From famous companies, their ultrasonic positioners have adopted the method of increasing the energy of transmitting ultrasonic signals, that is, increasing the pulse voltage and the pulse width of the excitation transmitter to obtain the strongest target echo. The negative effect is that many false echoes are generated in the material storage tank, such as the side wall echoes of the storage tank, the inherent structure echoes in the tank, and the multiple echoes caused by the different shapes of the tank top. Material positioning brings many difficulties, so many effective technical measures have been taken in software and hardware to solve the problem caused by false echoes. If any company marks these false echoes in empty tanks in advance and puts them Stored, and Miltronics first built a mathematical model using the exponential decay law of ultrasonic waves with the propagation distance. The regular echo signal is a true echo, otherwise it is a false echo. The above measures make the application of ultrasonic positioning technology The domain is constantly expanding.

As we all know, increasing the pulse voltage and the pulse width of the excitation transmitter is helpful for long-distance measurement. However, with the increase of the echo signal, the internal wall echo of the tank, the echo of the inherent structure, and the shape of the tank top False echoes such as reflected echoes and multiple echoes have also increased and become more complicated. Even if the problems of false echoes can be eliminated, the ultrasonic energy required by the oil tank must not exceed the limit of 19 micrometers that is intrinsically safe. For this special explosion-proof requirement of Joule, the above-mentioned method for enhancing the transmission of ultrasonic energy is not feasible, so no ultrasonic instrument capable of measuring the liquid level of large oil tanks has appeared. Disclosure of invention

The purpose of the present invention is to provide a method for ultrasonically measuring the liquid level of a large oil tank. The pulse signal wave emitted by the transmitter to the liquid surface is a micro-energy ultrasonic wave. The micro-energy ultrasonic wave can effectively avoid the interference of false echoes in the oil tank. The use of micro-energy ultrasonics below 19 microjoules can not only meet the requirements of safety and explosion protection of oil tanks, but also greatly simplify the structure of the instrument, reduce costs, and increase the degree of intelligence and automation.

The specific content of the present invention is described in detail below:

A method for ultrasonically measuring the liquid level of a large oil tank, which comprises generating a carrier wave, a square modulation pulse wave, a modulated wave with a square envelope formed by the carrier wave and a square modulation pulse wave, and amplifying a pulse signal transmitted by the transmitter to the target. The wave is reflected back from the measured object. After amplification, detection, comparative shaping, data processing, a dynamic blind zone or gating window is given, and the level display is characterized by: under intrinsically safe and explosion-proof conditions, the microcomputer makes the transmitter face the liquid surface. The intensity of the transmitted ultrasonic pulse signal increases from weak to strong, or decreases from strong to weak until the receiver receives the liquid level echo signal; the intensity of the ultrasonic pulse signal transmitted by the transmitter changes It is realized by the microcomputer automatically changing the excitation voltage pulse width of the transmitter, and the voltage pulse width changes with the change of the liquid level; the intensity of the ultrasonic pulse signal emitted by the transmitter is automatically changed by the microcomputer. The pulse amplitude is realized, and the voltage pulse amplitude is changed with the change of the liquid level; the transmitter Transmitting an ultrasonic pulse signal whose intensity The degree change is realized by the microcomputer automatically and simultaneously changing the width and amplitude of the excitation voltage pulse of the transmitter, and the width and amplitude of the voltage pulse change with the change of the liquid level. The tube of the drawings is to be explained

Figure 1 is a schematic diagram of the oil level target search process of the method;

Figure 2 is a schematic circuit diagram of a device for implementing the method of the present invention;

FIG. 3 is a program operation diagram of the method of the present invention. Nie Jia way of implementing the present invention

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, so as to further understand other advantages and features of the present invention.

According to the exponential attenuation of the ultrasonic sound pressure with the propagation distance, its calculation formula is

Where h is the ultrasonic transmission distance;

P. Is the sound pressure value at the distance h = lm;

P is the sound pressure value at a distance h from the sound source;

a is the sound absorption coefficient of the shield.

The transmitter F transmits a micro-energy ultrasonic wave to the measured target receiver F ', and the micro-energy ultrasonic wave decays exponentially with the propagation distance in the medium, as shown in FIG. 1, where A, B, and C respectively represent ultrasonic waves of different energy. In the case of attenuation with distance in the medium, where A and B indicate that the ultrasonic energy is attenuated before reaching the receiver in the medium, there is no target echo, and C has an echo and is received by the receiver. The dashed lines Pa, Pb, and Pc in the figure represent the attenuation changes of the above-mentioned ultrasonic sound intensities of different energies with the propagation distance.

To implement the method of the present invention, a circuit diagram of a device as shown in FIG. 1 may be adopted. The device includes a microcomputer minimum unit 1 including a frequency divider ι, a transmission control unit 2, a transmission amplification unit 3, and a transformer. Transmitter T, transmitter and receiver F, receiving amplifier 4, detector 5, comparison shaper 6, display unit, the central controller IC1 sends the mode number in the program memory ROM to the frequency divider as the transmission instruction IC2, the mode number contains the setting parameters of the modulation wave that stimulates the transmitter's pulse signal from narrow to wide and then decreases from wide to narrow, and the transmission pulse frequency and operating instructions that match the transmitter, frequency division When the IC2 receives the instruction, its OUT1 port immediately gives a modulated negative pulse signal according to the pulse width set by the program. The negative pulse signal becomes a positive pulse modulation signal after being inverted by the NAND gate 22, and is sent in two ways at the same time. One is sent to input terminal 5 of AND gate 27 and 1 to 27 via level shifter 25, and the other is sent to the GATE0 port of frequency divider IC2 to turn on the carrier signal. The OUT0 port of frequency divider IC2 is pressed. The carrier pulse signal is sent by the on-time controlled by the pulse width of the modulation signal. This signal is sent to pin 6 of AND gate 26 via level shifter 23 and sent to AND via NAND gate 21 and level shifter 24 via the other path. Foot 2 of door 27, when with When one of the pins 6 of 26 or 27 of the AND gate 27 is at a high potential, the corresponding AND gate is turned on. Because the carrier pulse signal changes periodically, the AND gates 26 and 27 are also periodically connected accordingly. And the output pins 4 and 3 output positive pulse signals respectively, and the pulse signals are sent to the corresponding input gates of the two FET amplifiers 31 or 32 in the amplifying unit 3 to excite the corresponding amplifiers, The two amplifiers alternately amplify the signal according to the period of the carrier pulse signal, and cut off the operation according to the width of the modulated pulse signal. The emission control unit 2 and the amplifying unit 3 combine the carrier wave and the square modulation pulse wave into a modulated envelope with a square envelope The transformer T excites the transmitter F to transmit ultrasonic waves. The two ends of the primary winding of the transformer T are respectively connected to the drains of two field effect tubes 31 and 32. The center taps of the primary winding of the transformer T are respectively connected to one end of the resistor R and the capacitor C. The other end of R is connected to DC power source + Vcc, the other end of capacitor C is grounded, one end of the secondary winding of transformer T is connected to the ground ends of transmitter and receiver F, and the other end is connected to the transmitter And a signal terminal F is connected to the receiver, the electrical excitation signal from a pulse width varying between 1 μ s to 512 μ s, the pulse width is automatically changed by the microcomputer, and therefore the emitted energy is automatically changed. The signal end is connected to the input end of the receiving amplifier 4. When the receiver receives an echo signal, the signal is sent to the INTO interrupt port of the central controller IC1 through the amplifier 4, the detector 5 and the comparison shaper 6, and the central controller IC1 records the interruption time, The distance is calculated according to the time required for ultrasonic round-trip, and a dynamic blind zone or gating window is given according to the measured distance. The dynamic blind zone or gating window is used to prevent false echo interference. When the liquid level echo signal causes the central controller IC1 to be interrupted, the central controller IC1 sends the signal data to the data storage RAM and performs data processing at the same time. The processed data is sent to the display H through P16 port for display. Divider IC1 uses 8032 and frequency divider IC2 uses 8253. IC1 is connected to ROM, RAM, and frequency divider IC2 in a conventional manner.

The safe energy of different levels of intrinsically safe (intrinsically safe) instruments must be less than the minimum ignition energy of the corresponding level, see the table below:

Example:

5m 处的进的 A method of ultrasonically measuring the liquid level of large oil tanks, applied to the monitoring of the liquid level in large oil storage tanks, storage tank capacity of 5000m ³ , vaulted storage tank, on the top cover of the tank wall 1. 5m 的进optical aperture disposed ultrasonic transmitter - receiver from the transmitter to the tank bottom is 14.42 meters, 22.7 meters in diameter can bottom, transmitter - receiver implicitly diameter of 260, a height of 200mm, the operating frequency is ^24.2 KC, the voltage pulse of the excitation transmitter is 250Vp-p. It has passed the inspection of the national explosion-proof inspection department and has passed the ia II CT6 level explosion-proof certificate, which is the highest explosion-proof certificate in the intrinsically safe type. In order to automatically compensate for the change in sound velocity caused by temperature, a multi-point temperature sensor composed of DS1820 protected by a nylon sleeve is used. The sensor is arranged in an oil tank. The ultrasonic transmitter is connected to the transmitter with a 50m 5-core cable. The transmitter contains a control transmitting, receiving and data processing unit, etc. The transmitter has a communication interface RS485 and is connected to the host installed in the central control room via the IKm communication cable. The transmitter and the host implement bidirectional communication. Communication, the host computer is equipped with programmable operation keys to achieve a variety of analog and digital display of the liquid level, such as high oil level «, oil storage volume, weight, oil temperature and achieve abnormal oil level ^ = Gen alarm and control The relay interface for oil pump opening and closing, the host has 4-20mA analog output and communication interface with industrial computer or PC. The transmitter has obtained the national explosion-proof certificate level (ΠΙΒΤ5, which can be used for the explosion-proof type explosion-proof level certificate of zone II, and the explosion-proof certificate level of the multi-point temperature sensor is iaIIBT6. When performing liquid level measurement, turn on the power The instrument enters initialization, and then starts to search for the liquid level target. In this process, the transmitter sequentially transmits ultrasonic pulse signals according to the program mode number, and the corresponding pulse widths are 1με, 5μ≤, 10με, 20 s, 30 μs ..., ΠΟμε, At this time, the liquid level target was searched. The displayed liquid level height was 2.474m, the distance from the liquid level to the transmitter was 11.946m, and the temperature was 24.5 ° C. After that, the instrument entered the formal measurement operation procedure. The transmitter transmitted ultrasonic waves with a pulse width of 120 s. The signal and continuous measurement, the instrument shows that the level height is 2.474, 2.475, 2.476, 2.474 ······.

The calibration results of the device implementing this method: the maximum range is 28m, the dead zone is 0.15m, and the accuracy is two thousandths of the measured distance.

The program operation diagram adopted by the method of the present invention is shown in Fig. 3, where P1-P5 are the search target process and P6-P12 are the process of measuring the oil tank level. In the process of searching for the target, the software program is divided into several energy modes and numbered according to the strength of the transmitted pulse signal. After completing the initialization of P1, the microcomputer sequentially orders the transmitter to transmit ultrasonic waves to the liquid surface and counts P2 in sequence, and the receiver sequentially Receive liquid level echo P3, determine P4 by echo signal detection output, the microcomputer calculates the liquid level distance P5 when there is detection output, and returns to P2 if there is no detection output; according to the measured distance and the corresponding transmitted signal pulse width The official measurement of P6 is started. The transmitter transmits ultrasonic waves to the liquid surface and counts P7, receives the echo signal P8, and judges the detection output P9. When there is an output, the computer calculates the distance P10 and displays Pll, and returns when the set measurement period T is reached. To P7, if there is no detection output, return to P2.

The present invention has been described in detail above with reference to preferred embodiments, but those skilled in the art can understand that the present invention is not limited to the above embodiments, and people can make many changes and modifications based on this without departing from the scope of the claims. Spirit and scope.

Claims

Compared with the prior art, the present invention has the following outstanding advantages:

1. The method of the present invention emits ultrasonic signals with very weak energy. The main lobe of the beam is very narrow and the side lobe is extremely small. It will not generate echoes on the side wall of the tank in the side of the lobe, and it will not cause much noise. Secondary reflection echoes, so the echoes measured according to the running procedure during the search of the target can only be true liquid level echoes. Because the micro-energy ultrasonic wave does not produce false echoes, the true liquid level echoes are clearly displayed, so the threshold value of the comparative shaper can be set very low, which is less than 2% of the traditional technology. The low threshold value can not only be measured. The time when the echo arrives is closer to the true value, improving the measurement accuracy, and the lower the threshold is, the greater the detection distance is. Only low-energy ultrasound can obtain a low threshold. The measurement accuracy of the method of the present invention is always better than the measured distance of 0. 2%, while the traditional method when the measurement distance is full range (F, S), the measurement accuracy is 0.25%, as the actual measurement distance decreases, its measurement accuracy decreases.

2. During the whole measurement process, the microcomputer automatically provides the best ultrasonic energy suitable for the measured distance, and this energy changes with the change of the liquid level.

3. The method of the present invention can reduce the dead zone by 50%. The reason is that the emission pulse signal generated by weak energy has very little tailing and the threshold value of the shaper is very low.

4. The application of micro-energy ultrasonic technology provides a new development space for the advancement of ultrasonic measurement technology.

PC CWO 02/35190 PCT / CN00 / 00745 "Claim

1. A method for ultrasonically measuring the level of a large oil tank, comprising generating a carrier wave, a square modulated pulse wave, a modulated wave with a square envelope formed by the carrier wave and a square modulated pulse wave, amplifying, The pulse signal wave is reflected back from the measured target, and is amplified, detected, compared with the shape, and processed with data. The corresponding dynamic blind zone, or the gating window, and the level display are characterized by the following features: The intensity of the ultrasonic pulse signal transmitted from the transmitter to the liquid surface is sequentially increased from weak to strong, or decreased from strong to weak until the receiver receives the liquid level echo signal.

2. The method according to claim 1,

It is characterized in that the intensity change of the ultrasonic pulse signal emitted by the transmitter is realized by the microcomputer automatically changing the excitation voltage pulse width of the transmitter, and the voltage pulse width changes with the change of the liquid level.

3. The method according to claim 1,

It is characterized in that the intensity change of the ultrasonic pulse signal emitted by the transmitter is realized by the microcomputer automatically changing the excitation voltage pulse amplitude of the transmitter, and the voltage pulse amplitude changes with the change of the liquid level.

4. The method according to claim 1,

It is characterized in that: the intensity change of the ultrasonic pulse signal emitted by the transmitter is realized by the microcomputer automatically and simultaneously changing the width and amplitude of the excitation voltage pulse of the transmitter, and the width and amplitude of the voltage pulse change with the change of the liquid level .