Page 648 - Sensors and Systems - North American Catalog
Basic HTML Version
Ultrasonic Sensors
3
Ultrasonic Sensors,
Thru-Beam Sensors,
cylindrical
3
.2
Ultrasonic Sensors,
Diffuse Mode Sensors,
cylindrical
3
.1
Ultrasonic Sensors,
Thru-Beam Sensors,
rectangular types
3
.2
Ultrasonic Sensors,
Diffuse Mode Sensors,
rectangular types
3
.1
3
.3
3
.3
Ultraschallsensoren,
Ultrasonic Sensor Accessories
3
.4
Ultrasonic Sensors,
Speciality Models,
cylindrical
Ultrasonic Sensors,
Speciality Models,
rectangular types
646
Germany: +49 621 776-4411
Refer to General Notes Relating to Product Information
Pepperl+Fuchs Group
USA: +1 330 486 0001
Singapore: +65 6779 9091
Copyright Pepperl+Fuchs
Ultrasonic Sensors
Introduction
Fundamentals of Ultrasonic Detection
Operating principles and technology of ultrasonic
sensors
Sound with a frequency over 16kHz is inaudible to the human ear. This is
referred to as ultrasound. Ultrasonics travel at 344 m/s through the air - the
same as audible sound. By evaluating the speed of sound and its runtime,
the distance of an object can be measured precisely.
Ultrasonic sensors are ideal for consistent object detection, even in harsh
and problematic conditions. Objects made from different materials and with
different shapes, colors, or consistencies are reliably detected.
Pepperl+Fuchs ultrasonic sensors operate with a piezoelectric transducer
as the sound transmitter and receiver. A patented process is used to
decouple the ultrasonics to the air - an acoustically thin medium.
Ultrasonic sensors are available with switching and/or analog outputs.
Depending on the model, different output functions are available.
Transducer
Decoupling
layer
Integral skin foam
Piezoceramic
Deadband/unuseable area
The deadband is the unusable area that defines the minimum distance
for target detection. The transducer transmits a series of sonic pulses and
converts the echo pulse into a voltage. The integrated controller computes
the distance from the echo time and the velocity of sound. The transmitted
pulse duration ∆t and the decay time of the sonic transducer result in an
unusable area where the ultrasonic sensor cannot detect an object.
Attenuation
time
Echo propagation time 2
τ
Emitter pulse
Echo
U
t
0
t
1
∆
t
t
Sensing range
The active area of the ultrasonic sensor is known as the sensing range, s
d
,
and is limited by the shortest and longest operating distance. The longest
operating distance is included in the model number.
The ultrasonic sensor detects objects within its sensing range, regardless
of whether these objects approach the sensor axially or move through the
beam angle laterally.
actual
switching distance
switching distance 2
or
upper limit
switching distance 1
or
lower limit
minimum
switching
distance
object
unusable
area
sensing range s d
switching interval
or
measuring interval
maximum
switching
distance
aperture angle
S
Response curves
The following figure shows the detection areas for two typical objects. The
specified object is detected within this area.
0
200
400
600
900
1000
400
300
200
100
0
-100
-200
-300
-400
X
Y
Characteristic response curve
Distance X [mm]
DistanceY [mm]
flat surface 100 mm x 100 mm
round bar, Ø 25 mm
wide sound lobe
narrow sound lobe
The upper part of the diagram illustrates the response characteristic on a
standard flat plate measuring 100 mm x 100 mm, the lower part using a rod
with a diameter of 25 mm as the object. Many sensors include a feature for
setting the sound beam width. Both sound beam shapes are shown in the
diagram.
The information in the type designation relates to a normal flat plate
measuring 100 mm x 100 mm. This plate must be perpendicular to the
propagation direction of the ultrasonic signal. The sound is reflected away
from upright objects and the echo does not reach the sensor.
