7

MEASUREMENT

RANGE

CALCULATIONS

SURFACE AGITATION: Surface agitation or waves can degrade

the performance. Moderate agitation results in only slight degrada-

tion of performance. The worst case is when the surface is a good

reflector, but in the wrong direction. (Refer to sensor alignment.)

VAPOR AND STEAM: Vapors in the air space, above the process,

become apparent, and cause problems when the liquid process

temperature is well above the temperature of the airspace. The

greater the difference, the more expected vapor problems. The

problems result from condensation or layering in the sound path,

both of which attenuate the sound signal, degrading performance.

Avoid steam if possible.

To avoid these problems, ensure that the vessel is insulated so that

vapors are less likely to condense. If a vent is used, be sure that the

vent, which is where condensation will form, is well away from

the sensor.

BEAM SPREAD INTERFERENCE: It is strongly recommended

that nothing be allowed within the sensor’s beam, except the liquid

which is being monitored. Often, the signal from the liquid will be

strong, compared to the signal from other sources, such as, ladder

rungs filling process material, support struts, etc. For that

reason,some applications may provide satisfactory results, even

with than 60 interference. Interference from agitator blades is only

an intermittent interference that usually has little effect on perfor-

mance.

It is recommended there be no interference within the 6° half angle

of the sensor beam. If interference is unavoidable, make the inter-

ference as far as possible from the sensor so that the real signal at

the longest distance is stronger than the interference signal.

SENSOR ALIGNMENT: Optimum performance is obtained when

the sensor is perfectly aligned. If the process is not perpendicular to

the sound beam, the sound will not reflect properly back to the

sensor. The effect is significant.

FOAM: Even small thicknesses of foam can attenuate the ultra-

sound and render the system inoperative. If possible, moving the

sensor to an area in the tank where there is less foam, will improve

the performance. Thick, heavy density foams can sometimes pro-

duce a reflection from the top of the foam. The multipliers shown

at right are general guidelines. For further assistance consult

the factory.

DUST: Dust attenuates the sound and results in poor performance.

Even barely perceptible haze in the air can cause significant

attenuation.

AIR MOVEMENT: The movement of air, as possible in an open top

vessel, can create a layer from which the sound will reflect. This will

be most noticeable in applications where vapors or steam tend to

form.

AMBIENT TEMPERATURE: The ambient temperature can have a

significant effect on the sound and on the sensor’s capability to

transmit and receive sound. The most noticeable effect on the

sensor is at the temperature extremes.

PRESSURE: Sound requires air molecules to be able to travel.

Sound will not travel in a vacuum. Likewise, higher pressures will

allow the sound to continue without decay, which can cause prob-

lems with multiple echoes.

Smooth, glass-like surface . . . . . . . . . .1.0

Slight agitation, choppiness . . . . . . . . .0.9

Heavy agitation . . . . . . . . . . . . . . . . . . .0.8

Slight vortex

. . . . . . . . . . . . . . . . . . . .0.7

Multiply all values together in the application column

Choose a range value from the Maximum Range Table

Maximum allowable measurement range for this application

No condensation . . . . . . . . . . . . . . . . . .1.0

Little condensation . . . . . . . . . . . . . . . .0.9

Much condensation/ foggy

appearance . . . . . . . . . . . . . . . . . . . . . .0.8

No interference within 3.5°

half beam angle . . . . . . . . . . . . . . . . . . .1.0

Agitator at speed less than 60 RPM . . .1.0

Agitator at speed greater than

60 RPM . . . . . . . . . . . . . . .Consult factory

Interference outside 4°, far from

sensor (in bottom third of range) . . . . . .0.8

Interference outside 4°, near to

sensor (in top third of range) . . . . . . . . .0.5

No foam . . . . . . . . . . . . . . . . . . . . . . . .1.0

Light froth, less than 0.25" thick . . . . . .0.8

Light foam, less than 0.5" thick . . . . . .0.5

Light foam, more than 1" thick . . . . . . .0.1

No dust . . . . . . . . . . . . . . . . . . . . . . . . .1.0

Haze, barely perceptible . . . . . . . . . . . .0.7

Slight dust . . . . . . . . . . . . . . . . . . . . . . .0.4

Heavy dust . . . . . . . . . . . . . . . . . . . . . .0.1

No air movement . . . . . . . . . . . . . . . . .1.0

Open vessel, but sensor below rim . . .0.8

Open air movement in sound path . . . .0.7

-20° to +140° F (-29° to +50° C) . . . . . .1.0

-40° to -20° F (-40° to +29° C) . . . . . . . .0.9

+140° to +160° F (+50° to +70° C) . . . .0.9

-10° to +50 psig (0.689 to +3.45 bar) . .1.0

Pressures outside

above rating . . . . . . . . . . . .Consult factory

Beam perpendicular to liquid surface . .1.0

Beam 4° off from perpendicular . . . . . .0.5

x

PERFORMANCE

OPERATING PARAMETER

CONDITION

MULTIPLIER

APPLICATION