Principle and Introduction of Ultrasonic Ranging Sensor

What is ultrasonic ranging sensor

Due to the strong directivity of ultrasonic waves, slow energy consumption, and long distances in the medium, ultrasonic waves are often used for distance measurement. For example, ultrasonic rangefinders and level measuring instruments can be realized by ultrasonic waves. ultrasonic distance sensor module is often quick, convenient, simple to calculate, easy to achieve real-time control, and can meet industrial practical requirements in terms of measurement accuracy, so it has also been widely used in the development of mobile robots.

In order for a mobile robot to automatically avoid obstacles and walk, it must be equipped with a distance measuring system so that it can obtain the distance information (distance and direction) from the obstacle in time. The three-direction (front, left, and right) ultrasonic distance measurement sensor is introduced is to provide a movement distance information for the robot to understand its front, left and right environment.

Principle of ultrasonic ranging sensor

1, ultrasonic generator

 In order to research and use ultrasonic waves, many ultrasonic generators have been designed and made. Generally speaking, ultrasonic generators can be divided into two categories: one is to generate ultrasonic waves electrically, and the other is to generate ultrasonic waves mechanically. Electrical methods include piezoelectric, magnetostrictive, and electric, etc.; mechanical methods include galton flute, liquid whistle, and air whistle. The frequency, power and characteristics of the ultrasonic waves they produce are different, so their uses are also different. At present, the piezoelectric ultrasonic distance sensor is more commonly used.

2, the principle of piezoelectric ultrasonic generator

Piezoelectric ultrasonic generator actually uses the resonance of piezoelectric crystal to work. The internal structure of the ultrasonic generator is shown in figure . It has two piezoelectric wafers and a resonance plate. When a pulse signal is applied to its two poles and the frequency is equal to the natural oscillation frequency of the piezoelectric wafer, the piezoelectric wafer will resonate and drive the resonance plate to vibrate to generate ultrasonic waves. On the contrary, if no voltage is applied between the two electrodes, when the resonance plate receives ultrasonic waves, it will press the piezoelectric chip to vibrate and convert the mechanical energy into electrical signals. Then it becomes an ultrasonic receiver.

3, the principle of ultrasonic ranging sensor

 The ultrasonic transmitter emits ultrasonic waves in a certain direction, and starts timing at the same time as the launch time. The ultrasonic waves propagate in the air and return immediately when encountering obstacles on the way. The ultrasonic receiver immediately stops timing when it receives the reflected waves. The propagation speed of ultrasonic waves in the air is 340m/s. According to the time t recorded by the timer, the distance (s) between the launch point and the obstacle can be calculated, namely: s=340t/2. This is the so-called time difference ranging method.

The principle of ultrasonic ranging sensor is to use the known propagation speed of ultrasonic waves in the air to measure the time when the sound wave encounters obstacles and reflect back after transmission, and calculate the actual distance from the transmitting point to the obstacle based on the time difference between transmission and reception. It can be seen that the principle of ultrasonic ranging is the same as that of radar.

In the formula, L is the measured distance length; C is the propagation speed of ultrasonic waves in the air; T is the time difference of the measuring distance propagation (T is half of the time value of transmission to reception).

Arduino ultrasonic distance sensors is mainly used for distance measurement in reversing reminders, construction sites, industrial sites, etc. Although the current distance measurement range can reach 100 meters, the accuracy of measurement can only reach the order of centimeters.

Due to the advantages of easy directional emission, good directionality, easy control of intensity, and no direct contact with the object being measured, ultrasonic waves are an ideal method for liquid height measurement. It is necessary to achieve millimeter-level measurement accuracy in precise liquid level measurement, but the current domestic ultrasonic ranging special integrated circuits are only centimeter-level measurement accuracy. By analyzing the causes of the ultrasonic ranging error, improving the measurement time difference to the microsecond level, and using the LM92 temperature sensor to compensate the sound wave propagation velocity, the high-precision ultrasonic range finder we designed can achieve millimeter-level measurement accuracy.