Ultrasonic Sensors

Ultrasonic sensors (also known as transceivers when they both send and receive, but more generally called transducers) work on a principle similar to radar or sonar, which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively.

 Active ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor, measuring the time interval between sending the signal and receiving the echo to determine the distance to an object. Passive ultrasonic sensors are basically microphones that detect ultrasonic noise that is present under certain conditions.

An ultrasonic sensor has two parts:

  • A transmitter that sends out a signal that humans cannot hear.
  • A receiver that receives the signal after it has bounced off nearby objects.

The sensor sends out its signal and determines how long the signal takes to come back.

  • If the object is very close to the sensor, the signal comes back quickly.
  • If the object is far away from the sensor, the signal takes longer to come back.
  • If objects are too far away from the sensor, the signal takes so long to come back (or is very weak when it comes back) that the receiver cannot detect it.


The sensor sends a message back to the computer brick telling it the time taken for the signal to return. Then the brick uses this info to compute how far away the object is.

How does an ultrasonic sensor work?

  • The ultrasonic sensor uses a pair of transducers. The sensor emits a sound pulse and measures the distance of the object depending on the time taken by the echo to return back to the other side.
  • Electrical energy is converted to sound to send the pulse, and then the sound received back is converted to electricity, which is what the brick understands.


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.

Configuration for detecting a liquid with a rough surface

  • 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.

  • Detection of Distance

Ultrasonic sensors are also used for distance detection in rear motion of automobiles and depth of many bores where measurement of distance is not easy by other means.



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