user manual

IRU-2xx4/3xx4 Rev. A2, 11/08
4
Automation Products Group, Inc.
APG...Providing tailored solutions for measurement applications
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UNDERSTANDING ULTRASONICS
Ultrasonic sensors measure distance by using a transducer to send out ultra-
sonic bursts. Each burst contains a series of pulsed sound waves. The ultra-
sonic burst emits in the shape of a cone, reflects off the detected target, and is
received by the transducer. The time required for this burst to travel to and from
the target is measured and converted into a distance measurement by the sensor.
Ultrasonic sensing is affected by several factors including the target’s surface,
size, angle and the distance from the sensor. Environmental conditions such as
temperature, humidity, gases, and pressure may also affect the measurement.
APG sensors automatically compensate for most of these varied environments.
The following considerations will help ensure the best possible sensing condi-
tions.
SURFACE
The ideal target surface is hard and smooth. This surface will reflect a greater
amount of signal than a soft, rough surface. A weak echo, which is the result of
a small or soft object, will reduce the operating distance of the sensor and
decrease its accuracy.
DISTANCE
The shorter the distance from the sensor to an object, the stronger the returning
echo will be. Therefore, as the distance increases, the object requires better
reflective characteristics to return a sufficient echo.
SIZE
A large object will have more surface to reflect the signal than a small one. The
surface area recognized as the target is generally the portion closest to the
sensor.
ANGLE
The inclination of the objects’ surface facing the ultrasonic sensor affects the
reflectivity of the object. The portion perpendicular to the sensor returns the
echo. If the entire surface is at a great enough angle, the signal will be reflected
away from the sensor and no echo will be detected.