U

ltrasound technology was developed during

WWII under the acronym SONAR (SOund

Navigation And Ranging). First applied to

process control in the 1960s, ultrasonic level measure-

ment continues to play a significant role in liquid level

measurement to this day.

Ultrasonic instruments are made

for both contact and non-contact

(or through-air) level sensing. This

of contact ultrasonic products that

provide single and dual point liq-

uid level measurement in

virtually every process industry.

Continuous-Wave and

Pulsed-Signal Sensing

Ultrasonic contact level sensing

is achieved by either continuous-

wave or pulsed-signal technology.

Our Model 910 continuous-wave

switch uses two piezoelectric

crystals positioned opposite each

other across the transducer gap.

The transmit crystal generates an acoustical signal

which the receive crystal converts into an electrical

signal. When liquid is present in the transducer gap,

the amplifier becomes as oscillator causing a relay

circuit in the electronics to indicate a wet gap

condition. When liquid vacates the gap, the amplifier

returns to an idle state.

Pulsed-signal Models 940/941 and 961/962 feature

a digital electronic amplifier

which produces a powerful

pulse of ultrasonic energy five

to ten times stronger than most

continuous wave units. This

pulsed-signal technology will

provide more accurate measure-

ment in conditions of aeration,

suspended solids, turbulence,

and highly viscous liquids.

Thetransmitcrystalofpulse-

signalunitsgeneratespulsesof

high-frequencyultrasonic

energyonlymillisecondsin

duration.Inbetweeneachpulse

thereceivecrystal“listens”forthe

transmission.Ifliquidispresent

inthegapthereceivecrystal

detectsthepulseandreportsa

wetgapconditiontotheelectronics.Whenthegapisfilled

withair,thereceivecrystalcannotdetectthepulse,and

reportsadrygapcondition.

2

Contact Ultrasonic Level Sensing

Contact ultrasonic level switches

use ceramic discs called piezo-

electric crystals to transmit and

receive ultrasonic energy. A

transmit crystal (T) is positioned

on one side of a transducer gap

and a receive crystal (R) is posi-

tioned on the opposite side. Tip-

sensitive style gaps—the only

style used on Echotel

the end of the transducer.

Challenging process conditions such as

suspended solids or aeration are best

managed with pulsed-signal technology.

Models 961/962 switches further minimize

the effects of mild turbulence or splashing

with adjustable time delays.

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