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Ultrasonic Sensors Knowledge (Part 2): Influences on the Sound Beam

Ultrasonic sensor sound beam
With the ULTRA-PROG-IR software, disruptive objects can also be suppressed using specific programming of blind zones without modifying the beam. The object can no longer be detected in this blind zone

Reliable object detection by an ultrasonic sensor is in large part determined by the correct configuration of the sound beam. The recognition behavior of the sound beam is also referred to as the response curve. This curve shows the distance at which a particular object can be reliably detected.

The response curve depends on the reflective properties of the object. Objects with a large surface area and optimum orientation are more easily recognized than small, round objects, or objects with poor reflective properties. Pepperl+Fuchs knows about the importance of this fact, and adds sound beam diagrams for various objects, e.g. a standard 100 x 100 mm plate or 25 mm rod to its ultrasonic sensors’ datasheets. The beam width can be adjusted on many models, focusing the ultrasonic sensor precisely on the target object.

Object shape and surface

A major reason to use ultrasonic sensors is their ability to recognize most materials and surfaces. Color is of no consequence and they can detect solids, liquids, or powders. Surface properties also have no effect on detection reliability. It does not matter if the surface is rough, smooth, high gloss, transparent, dirty, wet, or dry – a high-quality ultrasonic sensor delivers precise results.

The best reflection can be reached when level, smooth surfaces are positioned at right angles to the sensor surfaces. If the angle to the surface object is not 90°, the returning sound can be deflected away from the transducer, and it will no longer be detectable. Large angle deviations are possible when recording rough or uneven surfaces. The amplitude of the reflected ultrasonic signal must be high enough to allow reliable measurement. Similarly, high levels of dust and humidity reduce the acoustic energy and can reduce the maximum range of the ultrasonic sensor.

Temperature and humidity

The range of ultrasonic signals is also influenced by the relative humidity and temperature of the ambient air. Generally speaking, the sensing range decreases with increasing temperature and increasing humidity. This reduction is not linear and differs from sensor to sensor.

Dust, rain, and snow

Heavy dust, rain, or snow reduces acoustic energy and can diminish the beam or reduce the maximum range of ultrasonic sensors. Light dust and dirt deposits on the transducer surface will not influence measurement. Accumulation of water, snow, and ice must be prevented with proper installation (i.e. protective enclosures).

Sound beam modification with software

Ultrasonic sensors with adjustable sound beams allow customization of the sensing threshold. The sensing range can be adjusted to suit the object being detected via programming software or a Teach-In function. Pepperl+Fuchs’ ultrasonic sensors are programmed using the ULTRA3000, SONPROG, PACTware (IO-LINK), or ULTRA-PROG-IR software.

They enable precise control of the overall acoustic beam width. This means that the beam can be reduced in both length (axial sound beam) and width (lateral sound beam). Lateral and axial sound beam width can also be adjusted independently. This allows disruptive or reflective objects within the sensing range to be suppressed. Reducing the sound beam size allows disruptive objects or attachments on machines or in tanks to be suppressed.

Now available: Technology Guide Ultrasonic Sensors