1 Introduction

Measurement plays a vital role in the entire human society. Without accurate measurement, fairness and reasonableness cannot be reflected. Flow measurement is a key concern of the instrument and meter manufacturing industry. As one of the components of measurement science, it has an inseparable relationship with people's daily life, industrial production, and measurement science research. The realization of accurate flow measurement plays an important role in ensuring product quality, improving production efficiency, and promoting the development of science and technology. Especially in today's era when energy resources are extremely scarce and energy demand is increasing, the role of flow measurement in the national economy is becoming more and more obvious. With the rapid development of DSP (Digital Signal Processor), IC (Integrated circuit) and embedded technologies, fluid flow measurement technology is also developing in the direction of intelligence, convenience and diversity. With the improvement of process technology, microprocessors The more and more powerful functions of the digital signal processing technology and high-speed digital control chip are becoming more and more mature, so that the ultrasonic technology has been very good application in the flow measurement.

2. Application of ultrasonic and ultrasonic technology

2.1 Introduction to Ultrasound

Sound waves are the propagation form of the mechanical vibration state (or energy) of an object. The so-called vibration refers to the form of reciprocating motion of the mass point of a substance near its equilibrium position. For example, after a drum head is struck, it vibrates up and down. This state of vibration propagates in all directions through the air medium, which is called a sound wave. Scientists call the number of vibrations per second the frequency of sound, and the unit is hertz (Hz). The frequency of sound waves that human ears can hear is 20Hz～20000Hz. When the vibration frequency of sound waves is less than 20Hz or greater than 20KHz, the human ears can't hear them. Therefore, this sound wave with a frequency higher than 20000 Hz is called ultrasound. It has good directionality, strong penetrating ability, easy to obtain concentrated sound energy, and spreads far in water. From the end of the 19th century to the beginning of the 20th century, after the piezoelectric effect and the inverse piezoelectric effect were discovered in physics, people solved The use of electronics technology to generate ultrasound has quickly opened the historical chapter of the development and promotion of ultrasound technology. For more than a century, ultrasound has been widely used in various fields such as science and technology, social production and life. With the continuous development of science and technology, ultrasonic technology has been seen everywhere in people's daily lives, such as household ultrasonic water meters and ultrasonic heat meters used for heating measurement in the north.

2.2 Application of ultrasonic technology

Ultrasonic technology is one of the general technologies based on physics, electronics, machinery and materials. It is completed through the physical process of ultrasonic generation, propagation and reception. Using ultrasonic cavitation, it can be used to clean many objects that are difficult to clean manually. By increasing the pressure of the ultrasonic wave propagating in the liquid, it generates a great force, which pulls the liquid into cavities and forms countless small and dense bubbles. As the pressure increases, the bubbles burst to produce a huge shock wave , Will hit the dirt on the surface of the cleaning object to achieve the purpose of cleaning the object. In addition, due to ultrasonic

2.2 Application of ultrasonic technology

Ultrasonic technology is one of the general technologies based on physics, electronics, machinery and materials. It is completed through the physical process of ultrasonic generation, propagation and reception. Using ultrasonic cavitation, it can be used to clean many objects that are difficult to clean manually. By increasing the pressure of the ultrasonic wave propagating in the liquid, it generates a great force, which pulls the liquid into cavities and forms countless small and dense bubbles. As the pressure increases, the bubbles burst to produce a huge shock wave , Will hit the dirt on the surface of the cleaning object to achieve the purpose of cleaning the object,In addition, because ultrasound has a strong effect of penetrating solids, this cavitation can also clean the inner surface of objects immersed in the liquid under the action of ultrasound to a certain extent. Ultrasound technology has been widely used in medical examinations, such as B-ultrasound technology commonly found in various hospitals. B-ultrasound uses an ultrasonic probe to transmit a set of ultrasonic waves to a specific position of the human body, scans in a certain direction, and then can judge the distance and nature of the organ according to the delay time and strength of the echo. Computer processing forms a visible B-ultrasound image, which can inspect the internal organs invisible to the naked eye. Ultrasonic technology can also be used to measure distance, such as sonar technology and reversing radar. The reversing radar uses the known propagation speed of ultrasonic waves in the air to measure the time it takes for the ultrasonic waves to reflect off obstacles after transmission, and calculate the actual distance between the transmitting point and the obstacle according to the time difference between transmission and reception, and to remind when the vehicle is reversing. Effect. Similarly, sonar technology is used underwater to determine the location of fish and obstacles in the water.

3. The principle of ultrasonic flow measurement

When the ultrasonic signal propagates in the fluid, it carries the flow velocity information of the fluid. By detecting the ultrasonic signal passing through the fluid, the flow velocity of the fluid can be detected and converted into a flow rate. This topic uses the time difference method in the ultrasonic flow measurement method to measure the flow, and uses the reflection method to install the ultrasonic transducer on the same side of the measurement pipeline. The principle structure diagram of the flow measurement of the ultrasonic flowmeter is shown in Figure 1.1. The transducers 1 and 2 are installed on the same side of the pipeline upstream and downstream. When the flow is detected, under the action of the control circuit: The reflector A and reflector B reflect the ultrasonic signal to the transducer 2. At the same time, the high-precision time measuring unit records the propagation time T of the ultrasonic wave from the upstream transducer 1 to the downstream transducer 2; the transducer 2 receives it The upstream ultrasonic signal also emits the ultrasonic signal. The signal is reflected by the mirror B and the mirror A to the transducer 1. Similarly, the high-precision time measurement unit records the propagation time T from the downstream transducer 2 to the upstream transducer 1. Inversely, due to the influence of water flow speed, Tcis and T inverse are not equal, there is a time difference △T, and finally the flow rate is calculated by △T.