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51-650 Model 961/962 Echotel SIL Safety Manual
1.0
Introduction
1.1
Product Description
Echotel
®
Model 961 and 962 ultrasonic level switches
utilize pulsed signal technology to detect high, low, or dual
point level in a broad range of liquid media applications.
Model 961 is a single-point level switch. Model 962 is a
dual-point switch used as a level controller or to control
pumps in an auto-fill or auto-empty mode.
Both Model 961 and 962 switches are suitable for use in
Safety Integrity Level (SIL) 2 loops.
1.2
Theory of Operation
Model 961/962 switches utilize ultrasonic energy to detect
the presence or absence of liquid in a single or dual point
transducer. Ultrasonic contact level technology uses high-
frequency sound waves that are easily transmitted across a
transducer gap (see Figure 1) in the presence of a liquid
media, but are attenuated when the gap is dry.
Model 961/962 switches use an ultrasonic frequency of
2 MHz to perform this liquid level measurement in a wide
variety of process media and application conditions.
The transducer uses a pair of piezoelectric crystals that are
encapsulated in epoxy at the tip of the transducer. The crys-
tals are made of a ceramic material that vibrates at a given
frequency when subjected to an applied voltage. The trans-
mit crystal converts the applied voltage from the electronics
into an ultrasonic signal. When liquid is present in the gap,
the receive crystal senses the ultrasonic signal from the
transmit crystal and converts 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.
1.2.1 Transducer Design
Magnetrol’s advanced transducer design performs in difficult
process conditions. Model 961 has a tip-sensitive transducer
with an arched gap increasing its performance in aerated or
foamy liquids. Model 962 has a tip-sensitive lower gap and
flow-through upper gap permitting separations of 125 inches
(318 cm).
Ultrasonic
transducer
Transmit
crystal
Receive
crystal
Figure 1
Ultrasonic Signal Transmission
Across Transducer Gap
