Measurement Principle / Effective Use of Ultrasonic Sensor

Measurement Principle of Ultrasonic Sensor

Ultrasonic sensors transmit ultrasonic waves from its sensor head and again receives the ultrasonic waves reflected from an object. By measuring the length of time from the transmission to reception of the sonic wave, it detects the position of the object.

Roles of Temperature Sensor (FW-H10R)

The head sensor FW-H10R comes with a temperature sensor for temperature compensation. This is because the sound velocity in the atmosphere changes depending on temperature. The temperature sensor inside the sensor head senses the temperature and compensates for the changes of sound velocity.

Sound Velocity in the Atmosphere

The sound velocity in the atmosphere reaches 331.45 m/s when the temperature is 0°C. The sound velocity at different temperatures can be calculated with the following formula.

Where C: Sound velocity, T: Current temperature C＝331.45 m/s ＋ 0.607 m/s x T°C

Sound velocity increases by 0.607 m/s every time the temperature rises 1°C. Effective Use of Ultrasound Sensor Detection of Liquid Level Ultrasonic sensors are widely used for liquid level detection. However, in some cases, measurements may not be successful, such as when the surface of the liquid is rough or foamed up, or other objects on the liquid are wrongly detected. In such cases, please place a pipe on top of the sensor head as shown below. By detecting the liquid level inside the pipe, a wavy surface and entering of bubbles can be prevented.   Detection of Acid, Alkali, and Organic Solvent Level Although ultrasonic sensors are often used for liquid level detection, if it is used for acid, alkali, or organic solvents, the sensor head can become damaged. In such cases, please examine introducing the countermeasures introduced below. Countermeasure 1: In the Case of Hermetically-sealed Tank   Enclose the sensor head with the tube with the length shorter than the height of the insensible area and inject air from the back of the tube. By sealing the back of the tube, entry of volatile gas can be prevented because of the difference of air pressure. Countermeasure 2: In the Case of Open Top Tank   Purging air in front of the sensor head and pushing volatile gas away in the horizontal direction will prevent the sensor head from deteriorating. Countermeasure 3: In the Case that Air Purge is not Possible   Protect the exposed sensor head surface inside the tank by applying chemical resistant grease.