E C H O T E L
®
N O N - C O N TA C T U LT R A S O U N D
Non-Contact Ultrasonic Level Measurement
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on-contact ultrasonic level technology is a
proven method for accurate liquid level meas-
urement. Process control instruments utilizing
this technology sense and measure liquid level, volume,
or open channel flow without making physical contact
with the liquid itself. This offers distinct advantages
over many contact technologies in applications where
corrosive media, suspended solids, changing media
characteristics, or coating media are present.
Measuring with Ultrasound
Two components make
up a typical non-contact
Ultrasound 101:
ultrasonic measurement
The Basics
device: the transmitter, or
electronics; and the trans-
ducer, or sensor. A piezo-
electric crystal within the
transducer converts electrical
signals generated by the
transmitter into a series of
ultrasonic pulses. Under
ideal conditions, these pulses
are transmitted through free
air at the speed of sound
until they come into contact
with the liquid surface
where they are reflected
back to the transducer. The
transmitter’s electronics then
measures the pulse’s round-
trip time and digitally
processes the information to
indicate liquid level. A trans-
mitter programmed with a
vessel’s geometry can calcu-
late the liquid volume of a
vessel. A transmitter pro-
grammed to convert the
level reading into units of volume per time can meas-
ure the liquid flow rate in an open channel.
Assuring Signal Integrity
In the real world of process management, an ultra-
sonic signal launched into free air is vulnerable to
distortion from many sources. Unless safeguards are
taken by mechanical means or advanced
signal processing, non-contact measurement
can be greatly compromised.
The most obvious form of inter-
ference are the physical structures
inside of a vessel—pipes, ladders, struts,
agitator blades, or irregular tank geometry. All of these
can fall within the path of the ultrasonic beam to com-
promise the signal.
The greater the distance from the transducer, the
wider the beam spreads,
thereby increasing the like-
lihood that a “false target”
will enter the beam’s path.
At 2 feet from the trans-
ducer, a typical ultrasonic
beam may be less than 6
inches in diameter; but at
35 feet from the transducer
The
Transmitter
houses
the electronics for signal
the conical shaped beam
processing and control
will expand to a diameter
outputs. Depending on
of 7 feet.
the model, transmitters
Magnetrol’s 335, 355,
can be mounted either
344 and 345 transmitters
integrally or remotely.
have a False Target
The
Transducer
is
Rejection feature which
located inside the
filters out obstructions that
vessel. It transmits and
may lie within the path of
receives the ultrasonic
the beam. By entering the
signals.
locations of the obstruc-
tions into the transmitter’s
false target memory, the
user can program out the
erroneous targets.
As an additional
measure to assure instru-
ment integrity, Magnetrol
transmitters feature a self-
diagnostics capability which continuously checks all
relays, outputs and the overall function of the trans-
ducer and electronics.
Ambient temperature can also have a significant
effect on the accuracy of a non-contact ultrasonic
transmitter. As temperature decreases, air becomes
2
more dense, resulting in slower sound velocity. Since
measurement is directly dependent on sound speed, it is
necessary to compensate for temperature changes. All
Magnetrol’s transducers include a temperature compensa-
tion circuit which continuously monitors the temperature
at the sensor and compensates for variations over the full
temperature range of the transducer.
Ultrasonic non-contact devices are typically rated for
a maximum range in ideal conditions. But process condi-
tions can impact the maximum range of measurement.
These conditions include surface agitation, vapors and
steam, foam and air movement. A derating multiplier can
be computed to yield a new maximum range for optimum
performance. A lower frequency transducer, such as the
38 kHz model, provides increased power with a longer
wavelength to increase measurement range and improve
performance where steam, vapors or turbulence may be
present.
Technology Advantages and Limitations
The advantages of non-contact sensing are:
•
No contact with corrosive, contaminating liquids.
•
Accurate to within 0.25% of measured span.
•
Continuous and multiple-point sensing available.
•
No moving parts for reduced maintenance.
•
Not affected by changes in liquid properties such as
specific gravity, dielectric shifts, pH, etc.
•
Intrinsically safe, non-incendive and explosion proof
instruments are available.
Conditions limiting ultrasound’s effectiveness include:
•
Surface foam that absorbs the ultrasonic signal.
• Vapors that significantly alter the speed of sound.
•
Operating pressures exceeding 50 psig (3.45 bar).
•
Temperatures exceeding +200° F (+93° C).
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Real World Applications
Echotel non-contact ultrasonic transmitters have been
engineered to meet the process requirements of major
industries including: Oil & Gas, Chemicals, Food &
Beverage, Power Generation, Pulp and Paper, Water
& Wastewater, Pharmaceutical, and Petrochemical.
Chemical Feed Tanks
Clarifier Level
Influent/Effluent Flow
Fuel Oil Storage
Condensate Storage
Open Atmosphere Sumps
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NON-CONTACT ULTRASOUND
300/301
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Advanced Electronics
For Liquid Level,
Volume or Open
Channel Flow
Available as an integral or remote mounted unit,
this versatile and powerful ultrasonic transmitter
is easy to install and quick to calibrate.
Isolated 4–20 mA output with an active/passive mode for
loop power or device power. RS-485 with Modbus protocol
allows bi-directional communication with DCS or PLC. Two
or four 10 amp SPDT gold flash relays for a wide variety of
alarm and control schemes.
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Explosion-Proof Transmitter and Transducer
The Model 300/301 has Explosion-Proof FM and CSA
agency approvals for both the transducer and the trans-
mitter: Class
I
, Division 1, Groups B, C, and D.
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Model 300/301
A 16-button keypad and
two-line, 16-character
LCD display is inside
the explosion-proof
housing
Model 300/301 Transmitter Specifications
Power Supply
Fast, Password-Protected Calibration
Unique QuickCal
™
calibration feature allows complete system
calibration in 90 seconds. A password protection feature also
prevents unwanted tampering with the configuration data.
Transducer Specifications
Frequency
Beam Angle
Max Range/Span
Dead Zone
Process Temp
Process Pressure
Cable Length
38 kHz
Conical 12°
30 feet (9.1 m) / 28.5 feet (8.7 m)
18 inches (460 mm) minimum
-40° to +163° F (-40° to +73° C)
Atmospheric to 50 psig (3.45 bar)
500 feet maximum
120 VAC ±10%, 50-60 Hz
240 VAC ±10%, 50-60 Hz
24 VDC ±20%
Power Consumption
Analog Output Signal
12 watts maximum
1,000
Ω
loop resistance
Active Mode 4–20 mA (isolated); maximum of
Passive Mode 4–20 mA (isolated); loop resist-
ance dependent on power supply
(32 volt max) 1,000
Ω
@ 24 volts
Applications
Digital Output
Relays
Fail-safe
Ambient Temperature
Electronics
Display
Keypad
Response Time
Accuracy
RS-485 with Modbus
10 amp SPDT resistive (0, 2 or 4)
User selectable for analog and
relay outputs
-40° to +160° F (-40° to +71° C)
Two-line, 32 character LCD
16-button (inside housing)
2 seconds, typical
±0.25% of calibrated span
• Viscous Fluids
• Acids, Caustics
• Water & Wastewater
• Chemicals
• Pulp & Paper
• Power Generation
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NON-CONTACT ULTRASOUND
335
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For Liquid Level,
Volume or Open
Channel Flow
With flexible software, advanced signal processing
and a powerful transducer, the Model 335 offers
outstanding measurement performance and value.
Hinged, Dual Compartments
The LCD module compartment houses the
user interface and the lower compartment
houses the wiring terminals. A screw
release allows the LCD compartment
to swing completely clear of the
wiring module.
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View of LCD
Plug-In Display Module
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335 Electronics
Advanced digital signal processing provides
optimum performance in a variety of process
conditions.
Echotel 335 Transmitter Specifications
Power Supply
Output Signal
Fault Detection
Relay
Fail-safe
Ambient Temperature
Display
Keypad
LED Status Indication
Compensation
Accuracy
Enclosure
Protection
4–20 mA (isolated); 600
Ω
load
85 to 255 VAC
LED, and 3.6 or 22 mA
One, 3-amp SPDT
Software selectable
-22° to +140° F (-30° to +60° C)
Removable six-digit LCD module
with dual function bar graph
4-button menu-driven data entry
Echo strength, power, relay LED’s
Auto temperature compensation
over transducer operating range
±0.2% of measured distance,
plus 0.05% of the range
Dual compartment cast aluminum
NEMA 6 (IP 67)
Transducer Specifications
Frequency
Beam Angle
Max Range
Dead Zone
Process Temp
Process Pressure
Material
Protection
Applications
50 kHz
Conical 7°
26 feet (8 m)
14 inches (350 mm)
-22° to +195° F (-30° to +90° C)
Atmospheric to 44 psig (3 bar)
Polypropylene
NEMA 6P (IP68)
Configurable 3 amp SPDT relay,
• Sump, Well, & Tank Level
• Open Channel Flow
• Water & Wastewater Treatment
• Chemical Storage Tanks
• Food & Beverage Containers
• Pulp & Paper Vessels
5
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The module offers easy set-up and config-
uration of all process parameters via four
push buttons. The custom graphics LCD
displays six-characters and a bar graph of
signal strength or tank level. The module can
be removed to configure other 335 units.
module through
housing cover
window
Enlarged view
of LCD module
in working unit
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LCD module
removed
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