APG IRU-9400 user manual - Manual (Page 5)

Rev. B1, 3/10 IRU Series
5
Automation Products Group, Inc.
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• Understanding Ultrasonics
Ultrasonic sensors use a transducer to transmit bursts of ultrasonic sound
waves. Each burst contains a series of pulsed sound waves that emit in the
shape of a cone, reflect off the target, and are detected by the sensor. The time
required for the sound waves to travel to and from the target is converted into
a distance measurement by the sensor. Ultrasonic sensing is affected by several
factors including the target surface, distance, size, and angle. The following
considerations will help ensure the best possible target conditions.
Surface
The ideal target surface is hard and smooth. This type of surface will reflect a
greater amount of signal than a soft or uneven surface. Sound wave absorbent
materials, such as granules and powders, will reduce the operating range of the
sensor and decrease measurement accuracy.
Distance
Sound wave attenuation increases as the distance traveled increases. Therefore,
targets at longer ranges require better reflective characteristics than targets that
are closer to the sensor.
Size
A large object will have a greater surface area to reflect the signal than a smaller
one. Therefore, a large target will be detected at a greater distance than a small
target. The surface area recognized as the target will generally be the portion
closest to the sensor.