4 Level Measurement

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4. Level Measurement

,

Lutfi Al-Sharif


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pst c s.

Float S stems. Pressure Measuring devices.

. Ultrasonic systems.

Radar (microwave) methods.

. Other methods (laser, heated wire).


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e o s o eve easuremen


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Metal bar itched with markings.

.

Is only an approximate method.

Only suitable for shallow tanks.

devices.

Another simple device is the sight glass-tube.


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Simple, cheap and widely used.

- .

Float and arm system with potentiometer

s use n cars or ue measurement. An th r t m i th fl t n t

gauge.

s cons s s o a ape wrappe on a s aconnected to a float.


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As the fluid level changes, the float move

u and down and hence rotates the shaft. The rotation of the shaft is recorded and

. More complicated system but give better

accuracy.


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By measuring the pressure at the bottom

of the vessel/tank the level can bededuced.

Open topped vessel.

Sealed vessel.

l r ni .

In the bubbler unit, the flow of gas isa us e un u es s ar o appear.


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The level of the fluid can be arrived at by

dividin the ressure b the roduct ofand the density.

affect the accuracy of the result.


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Hydrostatic Devices


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The bubbler has an advantage over the

other two methods in that it does not sufferfrom the maintenance problem of leaks at

tappings.


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By placing two parallel plates inside the

li uid and measurin the ca acitancebetween them, the level of the liquid can

.

The capacitance depends on the area ofthe plates, the distance between them and

the ermittivit of the li uid. The change in level changes the effective

capacitor.


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Capacitive LevelSensing


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Capacitive LevelSensing


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If the liquid is non-conducting, then the

lates do not need to be insulated. However, where the liquid is conductive

. Liquids with high permittivity will provide

good sensitivity.


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Ultrasonic devices are used to send and

receive the reflected ultrasonic si nal fromthe fluid level.

. The speed of sound in the fluid depends

on temperature.

compensate for the change inempera ure.


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Frequency ranges from 40 kHz to 400

kHz. The speed of ultrasound also depends on

,dioxide concentration.


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UltrasonicDevice


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UltrasonicDevice


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Still very expensive method.

(closed tanks, turbulence, and obstacles,

.

They rely on receiving a reflected signalwith a phase difference to the signal

Unaffected by temperature and pressurevar a ons as oppose o .


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The tank filled with fluid is radiated at one

end and the out ut detected at the otherend.

rays depends on the amount of the fluid inthe tank.

-invasive.


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Vibrating level sensor.

elements.

aser et o s.


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Contact devices are less reliable that

contact-less devices. Methods that are less subject to variations

. .,microwave).

4 Level Measurement

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