Banner U-GAGE ULTRA-BEAM Series - Manual (Page 2)

Ultrasonics are sound waves of frequencies above the range of human
hearing. Like all sound waves, ultrasonic waves (or "ultrasound") are
produced by a vibrating object. In ULTRA-BEAM sensors, the
vibrating object is called a transducer. It is constructed of thin, highly
flexible gold-plated plastic foil stretched over an aluminum backplate
which is held in place by a leaf spring. The transducer is part of an
electrical circuit, and vibrates when an AC voltage (of the desired
operating frequency of the transducer) is applied to it. This vibration
causes an audible "ticking" sound from the transducer. The sound is
normal: each "tick" is a string of 16 ultrasonic sensing pulses.
The AC voltage, which can be visualized as a sine wave, alternately
compresses and expands the transducer. This action compresses and
expands the air molecules in front of the sensor, sending "waves" of
ultrasonic sound outward from the transducer's face. In ULTRA-
BEAM sensors, the transducer is not constantly transmitting ultrasonic
sound, but instead is switched "on" and "off" at a regular rate. During
the "off" times (in between "ticks"), the transducer acts as a receiver and
listens for ultrasonic waves reflected from objects in its path.
A basic knowledge of how ultrasonic waves behave in air can be of help
in using ultrasonic sensors successfully:
(1) The intensity of ultrasonic sound decreases with the square of
the distance from the sound source. For example, if the intensity of
ultrasonic sound at a distance of 1' in front of the sensor is designated
as "1", then the intensity at 3 times that distance is (1/3)
2 , or 1/9th.
If the radiated sound hits an object and is reflected back to the
transducer, the object becomes the "source" for the waves on the return
trip, and the intensity of the waves is reduced again by the square of the
distance. The stronger the generated ultrasonic waves, the stronger
will be the returned waves. And, the more efficient the object is as a
reflector of ultrasonic waves, the stronger will be the returned waves.
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"923" series ULTRA-BEAMs
DISTANCE TO 2FT X 2FT TARGET--FEET
SENSING AXIS
1) The "sensing axis" is an imagi-
nary line originating at and per-
pendicular to the center of the
transducer.
2) Response pattern is drawn for
a 2 square foot smooth, solid sur-
face.
3) Symmetry of the pattern may
be assumed in all sensing planes.
4) The rounded portion of the
curve past the 20' point indicates
an area where sensing is unreli-
able. Effective range is from 20"
to 20' (0,5 to 6m).
FIGURE A: Response Pattern, "923" Series Sensors
Behavior of Ultrasonic Waves
How Ultrasonics are Generated
BASIC THEORY OF ULTRASOUND
(2) Ultrasonic waves are affected by the size, density, orientation,
shape, surface , and location of the object being sensed.
a) Size of the object: at a given distance in front of the sensor, a large
object reflects more ultrasonic energy than does a smaller, otherwise
identical object at the same position, and so is more easily sensed. The
recommended object size for "923" series sensors is 1 square foot of
reflective surface area presented to the sensor for each 10' of sensing
distance. This is an "average figure", and is influenced by other char-
acteristics of the object being sensed.
b) Density of the object: density is the mass of an object per unit of
volume. The more dense the object being sensed, the stronger is the
sound reflection, and the more reliably the object can be sensed. This
fact calls to mind experiences with audible sound in everyday life. For
example, a wall covered with hardboard paneling reflects sound more
efficiently than does a wall covered only by foam insulation panels. The
hardboard paneling is denser than the foam. Ultrasonics are affected
similarly. Note that water and other liquids (although they are certainly
not solid) are nonetheless denser than materials like foam. This makes
them better reflectors than foam. The table on the next page lists some
materials and their relative effectiveness as ultrasonic reflectors.
FIGURE B: "Sensing Window" Concept
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DISTANCE FROM SENSOR--FEET
20" = NEAR SENSING LIMIT OF SENSOR and
NEAR LIMIT OF SENSING WINDOW
20' = FAR SENSING LIMIT OF SENSOR and
FAR LIMIT OF SENSING WINDOW
SENSING WINDOW: depth adjustable from 12" to 18'4";
sensing window may be placed anywhere between NEAR
and FAR limits of sensor.
"QD" (Quick Disconnect) connectors are standard on ULTRA-BEAM
sensors. DC models use a 4-pin connector; AC models use a 5-pin
connector. Mating 12-foot SO-type cables must be ordered separately.
Three sensor models are available, based on operating (power supply)
voltage: model SU923QD for 18-30V dc, model SUA923QD for 105-
130V ac, and model SUB923QD for 210-260V ac (see specifications).
ULTRA-BEAM "923" series sensor housings are constructed of
tough, corrosion-proof molded Valox™ . Electronic circuitry is epoxy
encapsulated for shock and vibration resistance. The ultrasonic
transducer (protected by a stamped metal screen) will not be damaged
by temporary contact with moisture, but should be kept free of
condensation and contamination for optimum operation.
The Banner model SMB900 two-axis mounting bracket is ideal for use
with "923" series sensors.