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Wednesday, March 14, 2012

Different level measuring systems : A Comparison






ADVANTAGES/DISADVANTAGES OF LEVEL MEASURING SYSTEMS:

Here below is a table showing the comparison of different level measuring systems I have posted before. The table gives the advantages and disadvantages of different methods along with the principle they use.


PRINCIPLE

SYSTEM

CHARACTERISTICS

ADVANTAGE

DISADVANTAGE








SIGHT

DIPSTICK

Simple, cheap, instant

Need to remove to read

SIGHT GLASS

Cheap, fairly foolproof, pressure up to 700 Mpa and 300oC

Need to careful handling, brittle.


TAPE/FLOAT

Cheap, can be used with corrosive liquids, but opening for tape.

Low pressure/ atmospheric only.
Can Stick.

POTENTIOMETER FLOAT

Voltage output as above

Stiction

MAGNETIC

As above

Stiction



DISPLACERS

SPRING BALANCE

Can be used for interfaces, limited range.

Expensive

TORQUE  TUBE

Most displacer transmitters use this, accurate but limited range.

Limited range.



PRESSURE

PRESSURE GAUGE

Cheap, open and closed tank.

Not available readily in low range in H2O.

BUBBLER METHOD

Can be used for slurries, or corrosive mixtures.

Requires air supply.

WEIGHT

LOAD CELLS

Accurate non-contact method.

Need frequent recalibration.


ELECTRICAL

CONDUCTIVITY

Rugged, requires little maintenance.

Limited to conductive liquids.

RESISTANCE

Rugged, requires little maintenance.

First few inches not accurate.

CAPACITIVE

Rugged and accurate.

Tank must be metal if only probe is used.

ULTRASONIC

ECHO TYPE

Non-contact

High pressurize wont work, expensive.

RADIATION

ABSORPTION

Non-intrusive.

Expensive, not accurate, hazardous source.

THERMAL

THERMISTOR

New method, cost reasonable.

On/Off only


Article Source: Level Measurement by N. Asyiddin  

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Basics of Instrumentation & Control


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Pressure


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Flow


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Level


To view more posts on LEVEL : CLICK HERE

Temperature


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Analytical Instrumentation


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