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51-650 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. Mode 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.

Ultrasonic

transducer

Transmit

crystal

Receive

crystal

Figure 1

Ultrasonic Signal Transmission

Across Transducer Gap