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