Detailed explanation of ultrasonic sensor ranging measurement method

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

Working principle of ultrasonic sensor

Ultrasonic sensors are sensors that convert ultrasonic signals into other energy signals (usually electrical signals). Ultrasound refers to the mechanical shock wave generated in elastic media with a frequency greater than 20 kHz. It has the characteristics of strong directivity, slow energy consumption, and relatively long propagation distance, so it is often used for non-contact ranging. Because the ultrasonic wave has a great ability to penetrate liquids and solids, especially in solids that are opaque to sunlight. When the ultrasonic wave hits the impurity or the interface, it will produce a significant reflection to form an echo, and it can produce a doppler effect when it hits a moving object. , So ultrasonic ranging has better adaptability to the environment.

At present, there are many methods of ultrasonic module distance sensor: such as round-trip time detection method, phase detection method, and acoustic wave amplitude detection method. The principle of the ultrasonic sensor emits a certain frequency of ultrasonic waves, propagated by air medium, and reflects back after reaching the measurement target or obstacle. After reflection, the ultrasonic receiver receives the pulse. The time it takes is the round-trip time. The round-trip time is related to the propagation of ultrasonic waves. The distance of the journey is related. The test transmission time can get the distance. For example: Assuming is the distance between the measured object and the rangefinder, the measured time is t/s, and the ultrasonic propagation velocity is expressed by v/m·s-1, then there is a relational expression (1)s=vt／2 (1) 

In the case of high accuracy requirements, the influence of temperature on the ultrasonic propagation velocity needs to be considered, and the ultrasonic propagation velocity should be corrected according to formula (2) to reduce the error.

v=331.4+0.607T (2) In the formula, T is the actual temperature in ℃, and v is the propagation speed of ultrasonic in the medium in m/s.

Working principle of ultrasonic ranging  sensor

The principle of ultrasonic ranging is to transmit ultrasonic waves in a certain direction through an ultrasonic transmitter, and start timing at the same time as the launch time. When the ultrasonic waves propagate in the air, they will return immediately when they encounter obstacles. The ultrasonic receiver immediately stops timing when the reflected wave is received. . The ultrasonic distance measuring sensor adopts the principle of ultrasonic echo distance measurement and uses precise time difference measurement technology to detect the distance between the sensor and the target. It adopts a small angle and small blind area ultrasonic sensor, which has accurate measurement, no contact, waterproof, and corrosion, low cost and other advantages. The commonly used method of ultrasonic ranging sensor is that one radiation head corresponds to one receiving head, and multiple transmitting heads correspond to one receiving head. Based on the simple, easy-to-operate and non-damage characteristics of ultrasonic distance measurement, the ultrasonic round-trip time must be measured. , You can get the distance. This is the working principle of the ultrasonic ranging sensor.

Ultrasonic distance measurement sensor module, ultrasonic distance measurement sensor module has two optional transmission modes, namely free running mode: when there is power, the sensor itself sends trigger and burst signals (for basic applications); external trigger mode: external system (controller or processor circuit) control trigger signal for advanced applications, these two modes are suitable for various purposes, in addition, the sensor also involves two input power sources, one is low voltage (5V) suitable for processor circuits and the other The high voltage (12V) is suitable for the controller to measure the distance to obstacles of 3.5m (at 5V), 5m (at 12V), and use UART communication to send data, the resolution is within 5mm. On the other hand, in various occasions, users can choose different setting modes according to their own environment, such as free-running/UART trigger/external trigger setting, etc. At the same time, they can also decide whether to use ring buffer and output according to the test UART communication baud rate setting. The signal has a high-performance ASIC chip to ensure stable transmission and sensitive reception. Therefore, the communication between the sensor and the PC uses the'interface board' (RS232, power regulator) to display the data and use the monitoring program on the PC (super terminal is available) to change the actual .The receiving ultrasonic real-time amplification uses UART (ASCII, mm) output distance to convert the detection signal into a TTL-level rectangular signal (square wave) according to real-time.