CN103499375A - High-precision ultrasonic level gauge measuring distance based on time delay method - Google Patents

Abstract

The invention discloses a high-precision ultrasonic level gauge measuring a distance based on a time delay method. The high-precision ultrasonic level gauge comprises a single-chip microcomputer controller, a keyboard module, a storage module, an alarming module, a displaying module, ultrasonic wave receiving and transmitting modules and a serial-port communication module. The keyboard module, the storage module, the alarming module, the displaying module, the ultrasonic wave receiving and transmitting modules and the serial-port communication module are respectively connected with the single-chip microcomputer controller. The serial-port communication module is further connected with a PC. The two ultrasonic wave receiving and transmitting modules are arranged above a liquid level. The distances between the two ultrasonic wave receiving and transmitting modules and the liquid level are different. According to the ultrasonic level gauge, measuring results of two ultrasonic probes at different levels are used for correcting the sound speed and eliminating time delay errors of hardware in a single-chip microcomputer. In addition, an arithmetic mean smoothing method is used for reducing errors generated by the unstable liquid level caused by external environment and thus, the liquid level can be accurately measured with ultrasonic waves.

Description

A high-precision ultrasonic liquid level gauge based on time-delay method for distance measurement

technical field

The present invention relates to a ranging device, in particular to a high-precision ultrasonic liquid level gauge based on time-delay method ranging. the

Background technique

Today, with the development of science and technology, with the rapid development and wide application of ultrasonic technology, ultrasonic has been widely used in daily life and industrial fields, such as radar detection, outdoor site distance measurement, measurement of reservoir water level, measurement of container depth, etc. . Liquid level measurement plays a very important role in industrial production. The quantity of liquid raw materials can be determined by measuring the liquid level in the container. Real-time measurement and monitoring of the liquid level in the container can ensure the continuity, reliability and reliability of industrial production. Safety provides a basis for material balance and production budget in the production process. At the same time, liquid level measurement is also closely related to our daily life. It is not only used for liquid measurement in various container pipes, but also for water level measurement in rivers, lakes, seas and reservoirs.

At present, whether it is the measurement of the water level of the reservoir, the measurement of the liquid level of the large oil tank, or the measurement of the liquid level of the small container or other liquid level measurements, the requirements for the measurement accuracy are getting higher and higher. For example, the capacity of large oil storage tanks used in the petrochemical sector is generally between 1,000 and 100,000m3, and a small liquid level measurement error will cause a large absolute error. Therefore, high-precision liquid level measurement plays an important role in daily life and industrial production.

来对声速进行校正。但是该方法只考虑了温度的影响而忽略了其他因素如湿度、压力等对超声波的传播速度的影响，而且温度测量也存在一定程度的误差，导致利用该方法的超声波液位仪的测量精度仍较低。而另一种采用自校准技术对声速补偿的方法是在系统中设置参考挡板，并使参考探头与挡板距离保持一定值，且此挡板不能挡住另一个探头到液面的超声波，超声波从参考探头发出，经参考挡板发射后回至探头而被接收，由于参考探头与挡板之间距离是精确已知的，因此利用参考探头能计算出在工作环境中的声速，这种方法可以补偿任何因素如温度、湿度和压力等引起的声速变化。但是在容器内安装挡板不仅增加了施工难度，而且挡板过小减弱了挡板反射的超声波，而挡板过大影响另一个探头到液面的超声波，因此挡板过小和过大都会对此类超声波液位计的正常工作产生一定的影响。本发明提出了一种新的自校准技术来对声速进行校正，从而实现超声波液位的精确测量。 The ultrasonic liquid level gauge can measure the height of the liquid level through a non-contact method, so the purpose of liquid level measurement can be achieved without touching the liquid level, especially suitable for metallurgy and chemical industries with strong corrosion, strong radiation, strong pollution and strong acid. Liquid level measurement under harsh conditions such as alkali. The propagation speed of ultrasonic waves in different media is different. Even in the same medium, the speed is affected by various factors, such as temperature, pressure, humidity, composition and viscosity. In order to improve the measurement accuracy of the ultrasonic liquid level gauge, it is necessary to try to obtain the accurate propagation speed of the ultrasonic wave in the working environment. In the traditional ultrasonic liquid level system, the sound velocity is mostly corrected by measuring the temperature, so as to improve the accuracy of liquid level measurement. Generally, after adding a temperature measurement module to the system to obtain the temperature T of the ultrasonic propagation environment, use the formula

to correct for the speed of sound. However, this method only considers the influence of temperature and ignores the influence of other factors such as humidity, pressure, etc. lower. Another way to use self-calibration technology to compensate the sound velocity is to set a reference baffle in the system, and keep the distance between the reference probe and the baffle at a certain value, and this baffle cannot block the ultrasonic wave from another probe to the liquid surface. It is emitted from the reference probe, transmitted by the reference baffle and returned to the probe to be received. Since the distance between the reference probe and the baffle is accurately known, the sound velocity in the working environment can be calculated by using the reference probe. This method It can compensate the change of sound velocity caused by any factors such as temperature, humidity and pressure. However, installing a baffle in the container not only increases the difficulty of construction, but too small a baffle weakens the ultrasonic waves reflected by the baffle, and too large a baffle affects the ultrasonic waves from another probe to the liquid surface, so too small and too large a baffle will cause problems It has a certain impact on the normal operation of this type of ultrasonic liquid level gauge. The invention proposes a new self-calibration technology to correct the sound velocity, so as to realize the accurate measurement of the ultrasonic liquid level.

Contents of the invention

In order to solve the above problems, the present invention discloses a high-precision ultrasonic liquid level gauge based on time-delay method for distance measurement.

In order to achieve the above object, the present invention provides the following technical solutions: a high-precision ultrasonic liquid level gauge based on time-delay method distance measurement, including a single-chip controller, a keyboard module, a storage module, an alarm module, a display module, an ultrasonic transceiver module, a serial port Communication module, described keyboard module, storage module, alarm module, display module, ultrasonic transceiver module, serial port communication module are connected with described single-chip controller respectively, and serial port communication module is also connected with PC, and described ultrasonic transceiver There are two modules, and the two ultrasonic transceiver modules are arranged above the liquid surface, and the heights of the two ultrasonic transceiver modules from the liquid surface are different.

As an improvement of the present invention, the model of the single-chip microcomputer controller adopted is STC89C52.

As an improvement of the present invention, the model used for the ultrasonic transceiver module is HC-SR04.

As an improvement of the present invention, the memory module adopts memory AT24C02.

As an improvement of the present invention, the display module includes a 1602LCD display screen.

As an improvement of the present invention, the alarm module is mainly composed of a buzzer, a triode and a resistor.

Beneficial effects of the present invention:

The ultrasonic liquid level gauge designed in the present invention does not need to add a temperature measuring unit or install a baffle, and can compensate for any factors such as temperature, humidity and pressure. Problems affecting level measurement. The ultrasonic liquid level gauge uses the measurement results of two ultrasonic probes arranged at different heights to correct the sound velocity and eliminate the hardware delay error inside the single-chip microcomputer, and uses the arithmetic mean filtering method to reduce the liquid level caused by the external environment. The error generated, so as to realize the accurate measurement of ultrasonic liquid level. This system can realize the storage of measurement data to facilitate subsequent tabulation and measurement curve drawing. The alarm circuit can provide effective early warning around the clock, and a serial communication module is designed so that the operator can monitor the liquid level gauge through a PC. Remote monitoring brings great convenience to the operator's outdoor measurement work.

Description of drawings

Fig. 1 is a system structure block diagram of the present invention;

Fig. 2 is a system schematic diagram of the present invention;

Fig. 3 is the circuit diagram of the single-chip microcomputer controller of the present invention;

Fig. 4 is the ultrasonic transceiver module circuit diagram of the present invention;

Fig. 5 is a memory module circuit diagram;

Figure 6 is a circuit diagram of the display module;

Fig. 7 is a serial port communication module circuit diagram;

Fig. 8 is a keyboard module circuit diagram;

Figure 9 is a circuit diagram of the alarm circuit.

Detailed ways

The technical solutions provided by the present invention will be described in detail below in conjunction with specific examples. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

As shown in Figure 1, it is a structural block diagram of a high-precision ultrasonic liquid level gauge based on the time-delay method for distance measurement of the present invention, including a single-chip controller, a keyboard module, a storage module, an alarm module, a display module, an ultrasonic transceiver module, and serial communication Module, described keyboard module, memory module, alarm module, display module, ultrasonic transceiver module, serial port communication module are connected with described single-chip controller respectively, and serial port communication module is also connected with PC, and described ultrasonic transceiver module Two ultrasonic transceiver modules are provided, and the two ultrasonic transceiver modules are arranged above the liquid surface, and the heights of the two ultrasonic transceiver modules from the liquid surface are different.

Fig. 3 is the circuit diagram of single-chip controller of the present invention, selects the STC89C52 single-chip microcomputer of low power consumption in the single-chip microcomputer, it is a kind of low power consumption, high performance and 8 CMOS microprocessors with 8KB programmable Flash memory in the system, It has the advantages of fast speed, high reliability, low power consumption and low price. The single-chip microcomputer STC89C52 controls the ultrasonic transceiver circuit to transmit ultrasonic signals, and receives the echo signals transmitted by the ultrasonic module, and performs sound velocity correction and hardware delay error compensation to realize the measurement of the liquid level, and is also responsible for controlling the keyboard circuit, storage circuit, alarm circuit, LCD display circuit and serial port communication circuit, etc. The main control module circuit of the single-chip microcomputer is shown in Figure 3, mainly including the clock circuit and reset circuit of the single-chip microcomputer. When the microcontroller is powered on, the oscillator will always work and generate a continuous oscillation clock. The reset circuit has two functions of power-on automatic reset and manual reset. When the crystal oscillator is working, the RST pin will continue to be high for 2 machine cycles to reset the microcontroller.

的位置上。HC-SR04一体化超声波模块是集发送、接收、放大和解调为一体的超声波收发器。通过单片机内部定时器给出一个10us以上的脉冲触发信号给HC-SR04的TRIG引脚，则该模块内部循环发出8个40kHz 周期电平，并自动检测是否有信号返回。当检测到信号返回时，该模块把接收信号经过放大和解调后通过该模块的ECHO引脚送到单片机的IO口。 Fig. 4 is the circuit diagram of the ultrasonic transceiver module of the present invention. In order to improve the accuracy of the liquid level measurement value, the ultrasonic transceiver module adopts two integrated ultrasonic modules HC-SR04, which are respectively installed at heights with a difference of

position. HC-SR04 integrated ultrasonic module is an ultrasonic transceiver integrating sending, receiving, amplification and demodulation. A pulse trigger signal of more than 10us is given to the TRIG pin of HC-SR04 through the internal timer of the single-chip microcomputer, and then the module internally sends out 8 40kHz cycle levels, and automatically detects whether there is a signal return. When the return signal is detected, the module sends the received signal to the IO port of the microcontroller through the ECHO pin of the module after amplification and demodulation.

Figure 5 is the circuit diagram of the storage module. In order to realize the real-time recording of the measured value of the liquid level, a serial EEPROM memory AT24C02 is added to this system, and the measured value of the liquid level at different times is stored in the memory, so that the user can check the corresponding information and data analysis. At the same time, in order to reduce the influence of the error caused by the insufficient stability of the liquid level, the single-chip microcomputer can take the average value every N of the measurement data of the same liquid level saved by the storage circuit. Obviously, the storage circuit can realize this function more conveniently.

Figure 6 is the circuit diagram of the display module. The display module circuit uses a 1602LCD display screen. When the system is just powered on or reset, the display screen displays "Ultrasonic level measuring system". When the alarm height is set through an external interrupt, the display screen displays "Set Alarm". When the liquid level is measured, it will display "Height" and display the liquid level height in the current environment. When the liquid level exceeds the alarm height and the buzzer alarms, the display will display "Warning!". When the serial port transmits data, the display will display "Sending".

Figure 7 is a circuit diagram of the serial port communication module. This system has the function of remote communication between the single-chip microcomputer and the PC, and the operator can perform remote monitoring and operation. The single-chip microcomputer transmits the liquid level measurement data to the PC through the serial port, and saves it in the PC, which can be further analyzed and printed. Because the levels provided by the single-chip microcomputer and the computer are different, the single-chip microcomputer provides the TTL level, while the computer provides the TS232 level, and the MAX232 chip is required to convert the two to achieve communication.

Figure 8 is the circuit diagram of the keyboard module. The keyboard circuit is mainly responsible for setting the warning level alarm height and viewing the stored data. Independent keyboards are used. One end of each keyboard is connected to the IO port of the microcontroller, and the other end is grounded.

Figure 9 is the circuit diagram of the alarm circuit. The alarm circuit is mainly composed of a buzzer, a triode and a resistor. When the liquid level reaches the warning height, the P3.5 port of the single chip microcomputer outputs a high level, drives the buzzer to issue an alarm, and reminds the user to pay attention The height of the liquid level.

The working principle of the present invention is as follows:

The single-chip microcomputer is the core control part of the whole system, which is responsible for controlling the peripheral circuits and calculating the output. First, the single-chip microcomputer transmits the signal to two ultrasonic probes placed at different heights to transmit ultrasonic signals through the transmitting circuit. The ultrasonic signals of the two probes meet the liquid surface and reflect back, and are received by their respective transducers and converted into electrical signals. After amplification, filtering, shaping and other processing, it is transmitted to the single-chip microcomputer. Since the height difference between the two probes is known accurately, the echo delay measurement results of two ultrasonic probes installed in different positions can be used in the single-chip microcomputer. Calculate the sound velocity in the working environment at that time, and can eliminate the hardware delay error inside the single-chip microcomputer. After the sound velocity correction and hardware delay error compensation, the liquid level can be calculated by the single-chip microcomputer using the delay measurement result of a certain probe, and then Through the display circuit, if the liquid level reaches the warning height, it can automatically alarm, and can also realize the remote communication function with the PC through the communication interface, so as to realize the remote monitoring of the liquid level. The storage module can save the liquid level measurement values at different times, which is convenient for users to consult and record and analyze relevant data. The keyboard module is mainly responsible for setting the warning height of the liquid level and viewing the stored data.

，为了保证两个探头能够独立进行超声的发射和接收，而互不干扰各自工作，则要求两个探头在横向上也要相距一段距离。在工作时，两个探头同时发射超声波并独立接收各自的回波信号，假设测量得到探头1从发射超声波到接收到回波所经历的时间为t ₁，探头2从发射超声波到接收到回波所经历的时间为t ₂。由于硬件电路处理存在一定延时的，这是因为在使用时延法测距时，需要使用单片机的外部中断来检测回波信号，中断响应需要一定处理时间，而在进入中断子程序后还要执行若干条指令，因此单片机内部的硬件延时也是不可忽略的，即回波时延测量值t ₁和t ₂中包含了硬件延时误差，由于两个探头的时延测量方法相同，因此在两者测量过程中的硬件延时误差也可近似认为相同，假设硬件延时误差为Δt以及在系统工作时的声速为c，那么根据时延测距原理，探头1到液面的垂直距离为 The principle of sound velocity correction and hardware delay error compensation proposed by Fang Ming: As shown in Figure 2, probe 1 and probe 2 are respectively installed at two positions with different heights, and the height difference between the two probes is

, in order to ensure that the two probes can independently transmit and receive ultrasound without interfering with each other's work, it is required that the two probes should also be separated by a certain distance in the lateral direction. When working, the two probes transmit ultrasonic waves at the same time and receive their own echo signals independently. Assume that the measured time from probe 1 to receive echo is t ₁ , and probe 2 from transmit ultrasonic to receive echo The elapsed time is t ₂ . Because there is a certain delay in the processing of the hardware circuit, this is because when using the delay method to measure distance, the external interrupt of the single-chip microcomputer needs to be used to detect the echo signal, and the interrupt response needs a certain processing time, and after entering the interrupt subroutine Execute several instructions, so the hardware delay inside the microcontroller cannot be ignored, that is, the echo delay measurement values t ₁ and t ₂ contain hardware delay errors. Since the delay measurement methods of the two probes are the same, the The hardware delay error in the two measurement processes can also be considered to be approximately the same. Assuming that the hardware delay error is Δt and the sound velocity is c when the system is working, then according to the principle of delay ranging, the vertical distance from probe 1 to the liquid surface for

                                  (1)

(1)

The vertical distance from probe 2 to the liquid surface is

(2)

Subtracting formula (2) and formula (1), we can get:

                          (3)

(3)

、t ₁和t ₂是已知的，因此可以求得声速c为 Since in formula (3)

, t ₁ and t ₂ are known, so the speed of sound c can be obtained as

                                        (4)

(4)

是精确已知的，而时延测量值t ₂ 和 t ₁  本来是包含了单片机内部的硬件延时误差的，但两者相减后，硬件延时误差Δt能够相互抵消，因此根据公式（4）计算得到的声速c是非常精确的。 In formula (4), the height difference of the two probes

is known accurately, and the delay measurement values t ₂ and t ₁ originally included the hardware delay error inside the microcontroller, but after subtracting the two, the hardware delay error Δt can cancel each other out, so according to the formula ( 4) The calculated sound velocity c is very accurate.

和分别为探头1和探头2从发射超声波到接收到从已知的固定位置反射的回波所经历的时间，那么根据式（4）可以计算此时超声波的传播速度

，由于在此场合中探头1和探头2分别离固定位置的距离和

也是已知的，因此液位计的固定硬件延时误差

为 The liquid level measurement value is not only related to the sound velocity, but also related to the time delay measurement value. Therefore, in order to obtain a high-precision liquid level measurement value, it is necessary to eliminate the hardware delay error Δt in the time delay measurement value, which can be obtained by the following method Correct this inherent hardware delay error: the two probes in this ultrasonic level gauge can be used to measure a known fixed position, assuming

and are respectively the time elapsed by probe 1 and probe 2 from transmitting the ultrasonic wave to receiving the echo reflected from a known fixed position, then the propagation velocity of the ultrasonic wave at this time can be calculated according to formula (4)

, because the distances between probe 1 and probe 2 from the fixed position in this case are and

is also known, so the fixed hardware delay error of the level gauge

for

                                  （5）

(5)

，就能消除延时误差，再结合由式（4）计算的声速c就可以得到高精度的液位测量值，则容器内液位H的计算公式为 In the actual measurement, the delay measurement value t ₁ of the probe 1 is subtracted from the inherent delay error of the hardware

, the delay error can be eliminated, combined with the sound velocity c calculated by formula (4), a high-precision liquid level measurement value can be obtained, then the calculation formula of the liquid level H in the container is

                               (6)

(6)

为超声波换能器探头1到液面底部的距离。 In the formula,

is the distance from the ultrasonic transducer probe 1 to the bottom of the liquid surface.

In the actual measurement process, especially outdoor measurement, it is difficult to ensure that the liquid level reaches a completely static state due to weather conditions. When the liquid level fluctuates up and down, the measurement result will fluctuate around a certain value. If the measurement is only performed once, the random interference is too large. Therefore, this liquid level gauge further improves the accuracy by means of digital average filtering. Carry out N times of measurement and calculate the average value, and take the average value as the final effective measurement value.

The ultrasonic liquid level gauge designed in the present invention does not need to add a temperature measuring unit or install a baffle, and can compensate for any factors such as temperature, humidity and pressure. Problems affecting level measurement. The ultrasonic liquid level gauge uses the measurement results of two ultrasonic probes arranged at different heights to correct the sound velocity and eliminate the hardware delay error inside the single-chip microcomputer, and uses the arithmetic mean filtering method to reduce the liquid level caused by the external environment. The error generated, so as to realize the accurate measurement of ultrasonic liquid level. This system can realize the storage of measurement data to facilitate subsequent tabulation and measurement curve drawing. The alarm circuit can provide effective early warning around the clock, and a serial communication module is designed so that the operator can monitor the liquid level gauge through a PC. Remote monitoring brings great convenience to the operator's outdoor measurement work.

The technical means disclosed in the solutions of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims (6)

1. the high-precision ultrasonic liquid level gauge based on time delay method range finding, it is characterized in that: comprise singlechip controller, Keysheet module, memory module, alarm module, display module, ultrasonic transceiver module, serial communication modular, described Keysheet module, memory module, alarm module, display module, ultrasonic transceiver module, serial communication modular is connected with described singlechip controller respectively, serial communication modular also is connected with PC, described ultrasonic transceiver module is provided with two, described two ultrasonic transceiver modules are arranged on the top of liquid level, and two ultrasonic transceiver modules are not identical apart from the height of liquid level.

2. a kind of high-precision ultrasonic liquid level gauge based on time delay method range finding according to claim 1, it is characterized in that: the model that described singlechip controller adopts is STC89C52.

3. a kind of high-precision ultrasonic liquid level gauge based on time delay method range finding according to claim 1, it is characterized in that: the model that described ultrasonic transceiver module adopts is HC-SR04.

4. a kind of high-precision ultrasonic liquid level gauge based on the range finding of time delay method according to claim 1, is characterized in that: described memory module employing storer AT24C02.

5. a kind of high-precision ultrasonic liquid level gauge based on time delay method range finding according to claim 1, it is characterized in that: described display module comprises the 1602LCD display screen.

6. a kind of high-precision ultrasonic liquid level gauge based on time delay method range finding according to claim 1, it is characterized in that: described alarm module mainly consists of hummer, triode and resistance.

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