Detection based on “Ultrasonic Waves”
What is an ultrasonic / level sensor?

This section provides a detailed look at ultrasonic sensors.

Outline and detection principle

As the name indicates, ultrasonic / level sensors measure distance by using ultrasonic waves.
The sensor head emits an ultrasonic wave and receives the wave reflected back from the target. ultrasonic / level sensors measure the distance to the target by measuring the time between the emission and reception.

Outline and detection principle

An optical sensor has a transmitter and receiver, whereas an ultrasonic / level sensor uses a single ultrasonic element for both emission and reception. In a reflective model ultrasonic / level sensor, a single oscillator emits and receives ultrasonic waves alternately. This enables miniaturisation of the sensor head.

Distance calculation

The distance can be calculated with the following formula:

Distance L = 1/2 × T × C

where L is the distance, T is the time between the emission and reception, and C is the sonic speed. (The value is multiplied by 1/2 because T is the time for go-and-return distance.)


The following list shows typical characteristics enabled by the detection system.

[Transparent object detectable]

Since ultrasonic waves can reflect off a glass or liquid surface and return to the sensor head, even transparent targets can be detected.

[Resistant to mist and dirt]

Detection is not affected by accumulation of dust or dirt.

[Complex shaped objects detectable]

Presence detection is stable even for targets such as mesh trays or springs.


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