Ultrasonic signals are like
audible sound waves, except the frequencies
are much higher. Our ultrasonic transducers
have piezoelectric crystals which resonate
to a desired frequency and convert electric
energy into acoustic energy and vice versa.
The illustration below shows how sound waves
are reflected from a target back to the transducer.
An output signal is produced to perform some
kind of indicating or control function. A
minimum distance from the sensor is required
to provide a time delay so that the "echoes"
can be interpreted. Variables which can affect
the operation of ultrasonic sensing include:
target surface angle, reflective surface roughness
or changes in temperature or humidity. The
targets can have any kind of reflective form
- even round objects.
Advantages of Ultrasonic Sensors
When used for sensing functions,
the ultrasonic method has unique advantages
over conventional sensors:
- Discrete distances to moving
objects can be detected and measured.
- Less affected by target materials and surfaces,
and not affected by color.
- Can detect small objects over long operating
- Resistance to external disturbances such
as vibration, infrared radiation, ambient
noise, and EMI radiation.
Two Ultrasonic Sensor Types
The following diagrams summarize
the distinctions between proximity and ranging
An object passing anywhere within
the preset range will be detected and generate
an output signal. The detect point is independent
of target size, material, or degree of reflectivity.
Precise distance(s) of an object
moving to and from the sensor are measured
via time intervals between transmitted and
reflected bursts of ultrasonic sound. The
example shows a target detected at six inches
from sensor and moving to 10 inches. The distance
change is continuously calculated and outputted.