Detailed explanation of ultrasonic sensor ranging method

    In daily production and life, ultrasonic ranging sensors are mainly used in car reversing radar, robot automatic obstacle avoidance walking, construction sites, and some industrial sites such as liquid level, well depth, pipeline length and other occasions that require automatic non-contact ranging. There are currently two commonly used ultrasonic ranging solutions. One is an ultrasonic ranging system based on a single-chip microcomputer or an embedded device, and the other is an ultrasonic ranging system based on a CPLD (Complex Programmable Logic Device). To understand the related application design of ultrasonic ranging sensors, we must first understand the working principle of ultrasonic sensor ranging.

Working principle of ultrasonic sensor ranging

Ultrasonic sensors are sensors that convert ultrasonic signals into other energy signals (usually electrical signals). Ultrasonic waves refer to mechanical shock waves generated in elastic media with a frequency greater than 20 kHz. They have strong directivity, slow energy consumption, and relatively long propagation distances. Therefore, they are often used for non-contact distance measurement. Due to the great penetration of ultrasonic waves on liquids and solids, especially in solids that are opaque to sunlight. Ultrasonic waves encountering impurities or interfaces will produce significant reflections and form reflections into echoes, and touching moving objects can produce the Doppler effect. Therefore, ultrasonic ranging has a better adaptability to the environment. In addition, ultrasonic measurement can get a good compromise in real time, accuracy and price.

At present, there are many methods of ultrasonic ranging: such as round-trip time detection method, phase detection method, acoustic wave amplitude detection method. The principle is that the ultrasonic sensor emits ultrasonic waves of a certain frequency, propagates through the air medium, and then reflects back after reaching the measurement target or obstacle. After reflection, the ultrasonic receiver receives the pulse. The distance is related. Test the transmission time to find the distance. For example:

Assuming that s is the distance between the measured object and the rangefinder, the measured time is t / s, and the ultrasonic propagation velocity is represented by v / m · s-1, then there is a relationship (1)

s=vt／2 (1)

In the case of high accuracy requirements, it is necessary to consider the influence of temperature on the ultrasonic propagation speed, and correct the ultrasonic propagation speed according to equation (2) to reduce errors.

v = 331.4 + 0.607T (2)

In the formula, T is the actual temperature unit is ℃, v is the unit of ultrasonic wave propagation velocity in the medium is m / s.

The principle of ultrasonic distance measurement is to transmit ultrasonic waves in a certain direction through the ultrasonic transmitter, and start timing at the same time as the transmission time.When the ultrasonic waves propagate in the air, they will return immediately when they encounter obstacles. . The ultrasonic ranging sensor uses the principle of ultrasonic echo ranging and uses precise time difference measurement technology to detect the distance between the sensor and the target. It uses a small angle and small blind area ultrasonic sensor, which has accurate measurement, no contact, waterproof and anti-proof. Corrosion, low cost and other advantages. The common method of ultrasonic ranging sensors is that one radiating head corresponds to one receiving head, and multiple transmitting heads correspond to one receiving head. Based on the characteristics of simple, easy to operate and no damage based on ultrasonic ranging, it is necessary to measure the time of ultrasonic round trip , You can find the distance. This is how the ultrasonic ranging sensor works.