940-111E-004 Datasheet, PDF (3/8 Pages) Magnetrol International, Inc. – Echotel® Model 940/941

1.0 Introduction
1.1 Description
Echotel Model 940 & 941 Ultrasonic Level Switches are
compact integral units that utilize pulsed signal technology
to perform high or low level measurement in a wide variety
of liquid applications. These switches feature pulsed
electronics that are encapsulated at the top of the process
fitting and a 316 stainless steel tip-sensitive transducer.
Model 940 features a 1 amp SPDT relay output while
the 941 has a current shift output.
Customer
provided
conduit
1.2
Ultrasonic
transducer
Transmit
crystal
Receive
crystal
Figure 1
Ultrasonic signal transmission
across transducer gap
Principle of Operation
Echotel 940 & 941 level switches utilize ultrasonic energy
to detect the presence or absence of liquid in a tip sensitive
transducer gap. The principle of contact ultrasonic tech-
nology is that high frequency sound waves are easily trans-
mitted across a transducer gap in the presence of liquid,
but are attenuated when the gap is dry (see Figure 1).
The Model 940 & 941 use this ultrasonic technology to
perform liquid level measurement in a wide variety of
process media and application conditions.
A pair of piezoelectric crystals are encapsulated in epoxy at
the tip of the transducer. The crystals are made of a ceramic
material that vibrates at a given frequency when subjected
to an applied voltage. The transmit crystal converts the
applied voltage from the electronics into an ultrasonic signal.
When liquid is present in the gap, the receive crystal is
able to sense the ultrasonic signal from the transmit crystal
and convert it back to an electrical signal. This signal is
sent to the electronics to indicate the presence of liquid in
the transducer gap. When there is no liquid present, the
ultrasonic signal is attenuated and is not detected by the
receive crystal.
1.3 Getting Started
Model 940 & 941 are extremely compact level switches
with electronics completely potted in an extension piece
directly above the stainless steel transducer. The
18" (457 mm) long 18 AWG flying lead wires are typically
terminated either inside conduit or a customer supplied
junction box. No special tools are required to perform
installation.
51-647 Echotel Model 940 & 941 Ultrasonic Level Switches
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