Level Measurement.pptx

7/27/2019 Level Measurement.pptx

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PROCESS

INSTRUMENTATION

A Presentation

on

Level measurement


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Presented to:

Madhusudhan Sir

Presented By:

Nitish.G.R


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LEVELMEASUREMENT

Level measurement is defined as the determination

of position of an interface between the two media.

These media may be solids, fluids or thecombination of solid and fluid.

Many methods are available for the measurement

of level with its own advantages and disadvantages


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IMPORTANCEOFLEVELMEASUREMENT

The measurement of level is of great importance in

the industrial field, particularly when control is also

necessary.

Most of the industrial process require the amount of

material in a tank or closed vessels.

In many situations it is not possible to view theinterior of equipments directly.


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LEVEL MEASURING SENSORS

Level measuring sensors detect the level of

substances that flow, including liquids, slurries,

granular materials, and powders.

The substance whose level to be measured can be

Inside a container or in its natural form (e.g. a river or a

lake).

In open tank or closed tank


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CLASSIFICATIONOF LEVEL MEASURING

SYSTEMS

Liquid or Solid Level Measurement

Point or Continuous Level Measurement *

Electromechanical or Electromagnetic LevelMeasurement

Contacting or Non-Contacting Level Measurement


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GENERAL CONSIDERATIONSIN LEVEL

MEASURING SENSOR SELECTION

Density and viscosity

Chemical composition

Ambient temperature Process temperature

Process pressure

Regulated environment

Process agitation


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POINT/SWITCH LEVEL MEASUREMENT AND

DETECTION SYSTEMS

Point level measurement sensors are used to mark

a single discrete liquid heighta preset level

condition.

They are:

Floats

Displacers

Conductivity Probes

Vibrating fork Resonance


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FLOATS


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A float operated liquid level control operates on the

basic buoyancy principle, which states, "a body

(float) immersed in a liquid is buoyed upward by a

force equal to the weight of the

displaced liquid". As a result, floats ride on the

liquid surface partially submerged and move the

same distance the liquid level moves.


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ADVANTAGESAND DISADVANTAGES:

The Advantages of this method are that it is

relatively simple, suitable for various products, and

very accurate.

The Disadvantages are that it requires a certain

amount of mechanical equipment, especially in

pressure vessels.


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DISPLACERS


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DISPLACERS

Displacer level sensors are force balance devices

in accordance with Archimedes' principle which

states thatthe buoyant force acting on an object

equals the weight of the fluid displaced.


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The obvious Advantage of this method is that the

absolute level does not change.

The Disadvantages are that it is dependent on

relative density and requires a significant amount of

mechanical equipment. Cost of installation for

displacers is high and many refineries are now

replacing them due to the inaccuracies experienced

under process density changes especially on

interface duties.


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CONDUCTIVITYPROBES

The principle for this form of level measurement is

that the presence of a product will cause a change

in the resistance between two conductors.


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The Advantages of this method are simple,

inexpensive and suitable for dual or multiple point

control.

The Disadvantages are probe cannot become

contaminated with grease or other deposits and has

limited suitability for products of varying

conductivity.


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VIBRATING FORKS RESONANCE

Frequency changes which shift tuning fork Piezo

crystal which oscillates forks and Solution causes a

reduction in resonant frequency Second crystal

detects.


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Advantages:

No moving parts, thus no maintenance.

Can be mounted in any position.

Small and can be mounted in a 1-in or smallermounting boss.

Disadvantages:

They are prone to material buildup between thetines.

Build up material can cause inaccurate reading.


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CONTINUOUS LEVEL MEASUREMENTAND

DETECTION SYSTEMS

Continuous level sensors are more sophisticated

and can provide level monitoring of an entire

system.

They include;

Radar Systems

Ultrasonic Systems

RTD

Magnetostrictive


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RADAR


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It is a Continuous level measurement system

Extremely short microwave impulses with low

emitted power in the 6.3 GHz frequency range areemitted by the antenna system to the measured

product, reflected by the product surface and

received again by the antenna system.

Guided wave radar is used to measure the level of

bulk solids and powders.

Micro-pulses at the speed of light are transmitted

and reach the material surface and reflect back to

the GWR.

Time is calculated and it is converted into level of

the solid surface.


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ADVANTAGES:

Response is instantaneous.

Reading is not affected by the dust.

Accuracy is very high.

It is used to measure the level up to 115 feet. Can be used for high temperature and high

pressure.

Installation is very easy.


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DISADVANTAGES:

Purchasing cost is high.

Pulses can be damaged by the large particles.

Not used for sanitary applications.


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ULTRASONICLEVELMEASUREMENT

Ultrasonic level measurement technique is used to

measure the level of solid without contacting the

solid.


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Ultrasonic level transmitter sends

sound waves into the vessel where

solid is placed and is reflected back

to the ultrasonic level transmitter.

Ultrasonic transmitters work on the principle of

sending a sound wave from a peizo electrictransducer to the contents of the vessel.

Software enhances the signal.

The device measures the length of time it takes for

the reflected sound wave to return to the

transducer.


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ADVANTAGES :

It is non-contact sensor.

It compensates the temperature changes automatically.

Can be used for temperature less than 3000F.

It can be used for less than 260 feet.

Response time is less.

Installation is easy.


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DISADVANTAGES:

It is used for pressure less than 40psi.

Reading is changed due to the change in the angle

of repose.

It is not suitable for light weight material due to the

absorbing of sound waves signal.

Heavy dust affects the performance.

Uneven shape of solids affects the performance.


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TIME-DOMAIN REFLECTOMETRY TDR

The principle of this technology is to launch an

extremely short microwave impulse on a

waveguide, which can be a cable or rod.

This waveguide, or probe,

contains the signal in a

close area around the

cable or rod.


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The Advantages of TDR level measurements are

disregard of the presence of vapors, steam, dust, gas

layers, buildup, temperature changes, pressure

changes, acoustic noise, changing density of the

material to be measured, changing dielectric constant ofthe material to be measured, and changing conductivity

of the material to be measured.

Some Disadvantages of this measuring system are that

it does come in contact with the process and is anintrusive form of measurement. The system is not

suitable for highly agitated liquids.


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MAGNETOSTRICTIVE

A magnetostrictive system consists of a

magnetostrictive wire in a probe and a donut-

shaped float containing a permanent magnet. The

float is the only moving part and travels up and

down the probe.


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Advantages are high accuracy and independence

from material characteristics such as conductivity

and dielectric constants.

Disadvantages are limitations to relatively clean

liquids and anything that would cause the float to

hang up on the probe.


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OTHERS METHODS FOR LEVEL

MEASUREMENT

Dip Stick

Weight and cable

Laser. Thru wave radar

Load cells.

Strain gauges


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DIPSTICK

Simple and cheap

Can be used with any wetmaterial and not affected by

density.

Can not be used withpressurized tanks

Visual indication only(electronic versions areavailable)


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WEIGHTANDCABLELEVELSENSOR


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WEIGHTANDCABLELEVELSENSOR

Weight and cable level sensors have been used for

many years to measure the level of the solids in

storage vessels.

The instrument lowers a weight on the cable and

touches the solid surface and rises to the sensor.

The distance it travels is measured and converted

into level of the solid.


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ADVANTAGES:

For high temperature system.

It is very easy to install.

Less cost.

It is not affected by the angle of repose. It can be used for dusty particles.

Not affected by the process condition.

It can be used to measure the level up to 150 feet.


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DISADVANTAGES:

Response time is high.

For dusty application regular maintenance is

required.

It is used for pressure less than 30psi.

Accuracy is moderate for greater than 30 feet.

It has moving parts so parts may wear and require

maintenance.


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LASERLEVELSYSTEM

It is used to measure the

level for very difficult

applications.

Laser is a narrow beam

that does not scatter on

reflection.

It is used for long ranges.


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ADVANTAGES:

No calibration is required.

It can measure level up to 250 feet.

Reading is not affected by the angle of repose. No effect of process conditions (temperature,

pressure).

Installation is easy.

Response is instantaneous. High accuracy.


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DISADVANTAGES:

Purchasing cost is very high.

It is not suitable for high dust application


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THRU-AIRRADARSENSOR


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It operates on the same principle of GWR (Guided

Wave radar) sensor. But it more desirable due to

following advantages over GWR.

It is non-intrusive.

It can operate at higher temperature and pressure

than guided wave radar level sensor.

It is used to measure the level up to 130feet.

Response is instantaneous than GWR


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DISADVANTAGES:

It is used for those type of materials having

dielectric constant greater than 1.8.

Cleaning is required for dusty applications.


Proper installation and set up is required.


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LOADCELLS


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Load cells operate on the principle that when loads

are applied on them than they change their

resistance, capacitance and inductance.

But mostly are designed to change their resistance.


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ADVANTAGES:

It is not intrusive system.

Can be used for extreme conditions.

Un-affected by the dust. It can be used for dangerous materials.

Highly accurate.

Ranges from 100 lbs to 1,000,000 lbs.


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DISADVANTAGES:


Calibration is required.

Require extra attention to get accuracy.


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THANKYOU

Documents

Level Measurement.pptx