In brief
An ultrasonic sensor measures distances or detects objects by emitting sound pulses above the audible range and evaluating the travel time of the echo.
Contents
What is Ultrasonic sensor?
An ultrasonic sensor emits short sound pulses and receives the echo reflected by the object. From the travel time and the speed of sound, the electronics calculate the distance. Because the principle works independently of colour, transparency and surface gloss, the sensor is suitable for glass, films, liquids and bulk materials, for example for level measurement, roll diameter detection or presence detection. The method also works more reliably than many optical sensors in dusty or misty environments.
There are ultrasonic proximity sensors with a switching output, sensors with an analogue output for continuous distance measurement, and through-beam and retro-reflective systems. Key ratings are measuring range with a blind zone directly in front of the sensor, sound cone shape, resolution, output type (switching output, current or voltage, digital interface), response time, temperature compensation and degree of protection. Because the speed of sound depends on the air temperature, many sensors compensate for this effect internally. Several sensors next to each other can interfere with one another if they are not synchronised.
Measurement errors are caused by inclined or sound-absorbing surfaces, strong air movement, temperature fluctuations and deposits on the transducer face. After a replacement, switching points or measuring range usually have to be set again.
In practice: maintenance and procurement
For a replacement, the manufacturer part number, measuring range, output type, housing style, voltage, connector and degree of protection are needed. Document the set switching points or scaling before removal so that the replacement unit can be commissioned without lengthy trial and error.
Synonyms and abbreviations: ultrasonic proximity sensor · ultrasonic distance sensor · ultrasonic level sensor · ultrasonic transducer
Frequently asked questions
What is the blind zone of an ultrasonic sensor?
The blind zone is the area directly in front of the sensor in which no reliable measurement is possible, because the transducer first has to stop oscillating after transmitting. Objects in this zone are not detected or are detected incorrectly. When installing, the sensor must therefore be positioned so that the object is always outside this range.
When is an ultrasonic sensor better than a photoelectric sensor?
Ultrasonic sensors have the advantage with transparent or highly reflective objects, changing colours and in dusty or misty environments where optical sensors reach their limits. Photoelectric sensors, on the other hand, respond faster and have a narrower detection range, which is better for small objects or high cycle rates.
What information is needed to replace an ultrasonic sensor?
The manufacturer part number, measuring range, output type such as switching output, 4–20 mA or 0–10 V, housing style and thread size, supply voltage, connector type and degree of protection are needed. It should also be known which medium is being detected, as foam or soft surfaces influence the selection.