What is Ultrasonic Sensor?

Ultrasonic sensors are mainly used for liquid level measurement, but can also be used to measure solids or detect obstructions. However, few people know the operating principle of ultrasonic sensors as well as the applications of ultrasonic sensors in industry.

1. What is Ultrasonic Sensor?

Ultrasound is a term that refers to a form of sound with a frequency much higher than that which the human ear can hear because the human ear can hear the threshold of 20000 Hz. Frequency lower than the frequency that the human ear can hear is often called infrasound, usually infrasound falls around 20Hz.

Ultrasonic waves can propagate in many different mediums such as air, liquid, solid, etc. In the same medium, the higher the frequency, the shorter the wavelength of the sound. . Because of that short wavelength, the resolution of ultrasonic waves hitting the object is enough to achieve accuracy as high as a few millimeters.

Therefore, ultrasonic sensors are widely used in medicine or industry to measure the distance of liquids, ultrasonic cleaning, ultrasonic welding machines, ultrasonic material insertion…

The industry uses ultrasonic sensors for distance measurement, obstacle detection, water level measurement, solid level measurement… with 4-20mA analog output signal transmitted to PLC or controllers.

2. Working principle of Ultrasonic Sensor

The ultrasonic sensor works on the principle of give and take, i.e. the sensor itself will emit waves continuously at the speed of ultrasonic waves. When this wavelength encounters an obstacle, it will respond to this wavelength, the ultrasonic sensor will receive this feedback wavelength and analyze the time of light emission and wave reception to know the distance from the obstacle to the sensor. It is because of this that we know the distance from the sensor to the liquid or solid level accurately.

As the figure describes how the ultrasonic sensor works, the sensor will continuously emit waves from the sensor head. The sound waves will meet the liquid and bounce back. The broadcast and reception times are converted by the sensor into a 4-20mA or 0-10V analog signal.

3. Structure of the Ultrasonic Sensor

An ultrasonic sensor consists of a part that can emit ultrasonic waves by a small power transducer capable of emitting a signal. Ultrasonic transducers have many different forms, divided into straight transducers (longitudinal waves) and transverse transducers (transverse waves), surface wave transducers, dual transducers (1 signal generator – 1 signal receiver, etc.) Depending on the purpose of use, people choose the most suitable ultrasonic sensor probe, all of which have the same ultrasonic sensor structure as follows:

+ Generator: Vibrates with a vibrator (usually made of ceramic material with a diameter of about 15 mm) to create ultrasonic waves and propagate into the air.

+ Receiver: When the vibrator receives the ultrasonic wave, it generates a corresponding mechanical vibration according to the ultrasonic wave and converts it into electrical energy at the output of the receiver.

+ Control: Controls the ultrasonic transmission of the transmitter using an integrated circuit and evaluates whether the receiver receives the signal (ultrasonic waves) and the size of the received signal.

+ Power supply: The ultrasonic sensor is usually powered by an external DC power supply with a voltage of PCB ± 10% or 24 V ± 10% and is supplied to the sensor via an internal voltage regulator circuit.