level instrument

7/31/2019 Level Instrument

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INC - 02


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ITEM PAGE

Overview 6 Equipment Drawing 8

The Methods of Level Measurement 11

Glass Level Gauge 12

- Transparent Glass Level Gauge 14- Bicolor Glass Level Gauge 16- Reflex Glass Level Gauge 19

Magnetic Level Gauge 23 Bubble Type 25 Capacitance Type 27

D.P. Type 29

Diaphragm Type 31 Float Type 32

Displacer Type 33

Paddle Type 35


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ITEM PAGE Vibration Type (Tuning Fork) 37

- Condition Unit For Vibration Type (Tuning Fork) 39

- Drawing of Vibration Type (Tuning Fork) 41

Radio Active Type 42

NON-CONTACT TYPE

- Ultrasonic Type 44

- Radar Type 45

Tank Gauging System ( T.G.S. ) 50

How To Selection 52

Comparison Table 54

References 55


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The surface of a liquid is the interface between the liquid and someother medium, usually gas or vapor or sometimes, another liquid.The engine oil and gas tank gauges of automobiles are shiny examplesof liquid level measurement devices. The measurement and control ofliquid level is essential in a process plant, where a wide variety of

liquids are handled in both batch and continuous processes. Theaccurate measurement of level is important for environmentalprotection (for example, tank over flow to drains), plant safety,product quality, and inventory control.Almost all liquid level devices measure according to the position orheight of the liquid above a zero or lowest point, or the hydrostatic(or head) pressure.


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Measuring Principle:One principle of hydraulics isthat, liquids that are

contained in interconnectedspaces find a common level, ifthere is enough liquid. This

principle applies to the sight(or gauge) glass.

A sight glass is a device that isconnected to a tank in such away that the liquid level in thetank can be seen through the

glass.


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They are very common in the process industry.Sight glasses are usually installed with shutoff valves anda drain valve, mainly for maintenance purposes, repair andreplacement.

Application:Liquid

GR
http://glass/mrq-Level%20Gauge.pdfhttp://glass/B-06-09-(600dpi).pdf


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This instrument consists of a metal body,machined to have an internal chamber andone or more front windows (on each side ofthe gauge).On each window a special high resistance

plate transparent glass is applied withsealing joint and metal cover plate hold bybolts and nuts.

SPR
http://glass/SPR-transparent.pdf


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Fluid level indication is the result of thedifferent transparency property of the two

media (i.e. liquid and air or vapor).

In some case (i.e. for water / steam) thebest reading is obtained by conveyingupwards on the surface of separation

(liquid/steam or vapor interface), a sourceof light, located on the back of the gauge,the rays of which are totally reflected downto the observer.


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When in operation, bicolor level gauge showsto the observer port holes lighted green inthe water zone and port holes lighted red inthe steam zone. In case of long glass gauge,

the window appears part green and part red.This result is obtained exploiting thefollowing optical principle:different colors (in this case: red and

green) have a different index of refraction

when passing obliquely through differentmedia (in this case: glass, water and steam).


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For the purpose, the gauge body has atrapezoid section with glasses placed onthe non parallel faces. An illuminatorwith special red and a green filters is

fitted on the gauge at the opposite sidewith respect to the observer. Thisspecial illuminator conveys light throughthe filters obliquely to the back glassesof the level gauge.

Said filters allow crossing only to redand green rays.Such colored rays reach, through the


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back glass, the media inside level body.When the gauge contains steam, greenrays are considerably deviated and

prevented from emerging by the observer

side; then only red light, whose rays aresmoothly deviated by steam, passesthrough the whole internal hole, reachingthe observer. Conversely when rays findwater, red rays are considerably deviated

and lost inside the internal part of levelgauge, green rays can reach the frontglass and seen by the observer.


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This instrument consists of a metal body,machined to have an internal chamber andone or more front windows (on one side

only of the gauge).On each window a special high resistanceplate reflex glass is fitted with sealingjoint and metal cover plates hold by boltsand nuts.

SPR
http://glass/SPR-reflex.pdf


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Reflex level gauges working principle isbased on the light refraction andreflection laws. Reflex level gauges use

glasses having the face fitted towards the

chamber shaped to have prismatic grooveswith section angle of 90. When inoperation, the chamber is

filled with liquid in the lower zone and gases or vapors in the upperzone; the liquid level is distinguished by different brightness of the

glass in the liquid and in the gas/vapor zone. The reflex level gaugesdo not need a specific illumination: the day environmental light isenough. Only during the night an artificial light must be provided.


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Liquid Zone:

This zone appears quite dark whenthe gauge is in operation andlighted as above said.


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Gas/Vapor Zone:This zone appears almost silverbright to the observer.

As for the liquid zone, the lightrays reach the glass/gas-vaporinterface with an angle around 45.

Since this angle is greater than glass/gas-vapor critical angle, the rays

are not refracted , but totally reflected making 90

turn, thus reachingthe nearest glass/gas-vapor interface again with angle of 45. For samereason they will be reflected and turned by 90 towards the observer,to whom the zone will appear silver bright.


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Measuring Principle:

Its principal based on magnetic property.A float containing a magnetic is placed

inside a sealed chamber, the float is freeto move and rises and falls with liquidlevel. Outside of chamber, there is smallsteel wafer which are free to rotate180. They are painted with two different

color, usually one side green and over sideis red.


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As the float moves, its magnetcauses the wafer to rotate, so thelevel surface will be indicated bythe one of wafer side.

Application:

Liquid

I G

R D
http://magnetic/DATA%20SHEET-LEVEL%20GAUGE.pdfhttp://magnetic/MRQ-MAGNETIC-LEVEL%20GAUGE.pdfhttp://magnetic/General%20Cataluge(Magnetic%20Level%20Gauges).pdfhttp://magnetic/IMAGE.pdf


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Measuring Principle:If an open-ended tube is submergedin the liquid, a constant air flow isinjected into it, and its pressure is

regulated at a value slightly greaterthan maximum head of the liquid inthe tank, air pressure in the systemwill be equal due to the hydrostatichead of the tank liquid at any level

because any excessive pressure willbubble air out at the bottom of thetube.


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This system is also called a purgesystem because air or some other gas(such as nitrogen), is continuouslybubbling from the bottom of pipe

keeping the liquid out. It is very wellsuited to measuring the level ofcorrosive liquids, viscous liquids, orliquids that contain entertained solids.

Application:

Liquid


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Measuring Principle:A metal ( and insulated ) probe in asilo or tank and the tank or silo wall

itself act as the two plates of acapacitor. The capacitance of thiscapacitor depends on the mediumbetween the probe and the wall.When only air is present, i.e. the tankor silo is empty, the capacitance ofthe capacitor is low.


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However, the capacitance willincrease when part of the probe iscovered with the product. Thechange of capacitance is convertedthrough an amplifier into a relayaction or an analogue output signal.

Application:

Liquid , Granular Solids.

I G

SPR
http://capacitance/SPR-capacitance.pdfhttp://capacitance/TI161FEN.PDFhttp://capacitance/image.pdf


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In this method the principle is based on the measurement of thehydrostatic pressure produced by a column of liquid of a given

height. The pressure is calculated using formula :

P = h. .g in which :

P = pressure h = height of the liquid column

G = acceleration due to gravity ( constant at a certain place )= relative density

SPECIFIC GRAVITY


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From this formula it can be seenthat if the specific gravity of themedium does not vary, the onlyvariable in the formula will be the

heighth.The pressure measured willtherefore be directlyproportional to height h, thelevel of the liquid in the tank.

Application:

Liquid I G

R DSPR
http://dp/SPR-d.p.pdfhttp://dp/Data%20Sheet-Pressure%20&%20Diff.%20Pressure.pdfhttp://dp/Press-P%20&%20DP%20Transmitter.pdfhttp://dp/TI256PEN.PDFhttp://dp/image.pdf


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I G


Detects the force exerted

by the process materialagainst the diaphragm

Application:

liquid , solid in silos.

Strain Gauge
http://diaphragm/TI256PEN.PDFhttp://diaphragm/image.pdf


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A floater with different shape (ballfloat, cylindrical float) move up and

down due to level moving. The roundfloat, which contains a small magnetand move upwards a tube. In the tubeone or more reed relays are placed.The reed relays will switch as the

(magnetic) float passes by.Application:

Liquid I G
http://float/1003_kfg_e.pdfhttp://float/image.pdf


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1.Magnetically coupled switch

2.Torque tube

3.Flexible disc

4.Spring balanced


Its operation is based on

Archimedes principle which statesthat the force produced by asubmerged body which is equal tothe weight of the fluid


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it displaces.Also , the interfacemeasurement could be done by thismethod.

Application:

Liquid

I G

R D

INTERFACESPR
http://displacement/SPR-displacer.pdfhttp://displacement/DATA%20SHEET-DISPLACER.pdfhttp://displacement/MRQ-LEVEL%20DISPLACER.pdfhttp://displacement/general%20catalogue_.pdfhttp://displacement/Image.pdf


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Measuring Principle:The moment of inertia of a rotatingpaddle changes depending on whetherthe paddle is in air or in contact witha product.A paddle mounted on a shaftprojecting into the silo is driven by asmall synchronous motor through areduction gear. When the vane

encounters resistance from theproduct, the rotating drive systemsupported on bearings will move.

I G
http://paddle/pls200_fi01_part4_en.pdfhttp://paddle/image.pdf


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Two micro switches positioned to

detectthis movement will changeover. When the product no longer

exerts a resistance against thepaddle, the drive mechanism willreturn to its original position and onecontact will restart the motor, whilethe other will indicate the change in

level.Application:

Solid


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Measuring Principle:The damping of a vibrating fork bychanges in mass will cause afrequency shift in the vibrating

element. The system consists of atwo tines mounted on a membranewith a natural resonance ofapproximately 120Hz (tuning fork

principle).

Two piezoelectric crystals are mounted on the membrane. Oneof these crystals is driven by a 120Hz oscillator, causing thesystem to resonate when the tines are not covered by the

product.


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Due to this free vibrating the other crystal givesa signal with the same frequency. When the

product produces a damping effect on thesystem, the second crystal will no longer product

the resonance signal and the amplifier will switch.Because relatively little energy is needed todampen the resonance frequency, a tuning forklevel switch (Soliphant) is capable of detectinglevels in products with very low relative density,

i.e. 20kg/m3.

Application:SolidGRD
http://vibrating/data%20sheet-level%20switch%20-tunning%20fork.pdfhttp://vibrating/Mrq-level%20switch%20-tunning%20fork.pdfhttp://vibrating/TI249FEN.pdf


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G

Signal transmission:The intrinsically safe signal input ofthe limit switch is galvanically isolatedfrom the power supply and signal

output.The condition unit powers the tuningfork measuring sensors with a two-wire DC loop and receives a frequencywhich signals whether or not the limit

has been reached. The power supply issuperimposed with the current pulses(PFM signals) from the measuringtransmitter.
http://vibrating/TI203FEN.pdf


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The pulse width is approximately 200s and a current strength ofapproximately 10 mA.

Signal evaluation:The condition unit evaluates thefrequency and switches the outputrelay for the level alarm. The relayswitching state is displayed by a yellow

LED on the front panel of thecondition unit.


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0

90

270

180

30

315

225

150


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Measuring Principle:There is one source for sending ray. UsuallyALPHA,BETA and GAMMA are used as aray. The other hand, one point of detector

receive rays directly from source (withoutany change) and another points will receiverays that some of them are absorbed bymaterial. The different between twoamount is proportional with level of surface.

Application:

Liquid , SolidI
http://radioactive/image.pdf


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Measuring Principle:Short ultrasonic pulses in the rangeof 35KHz up to 70KHz are emittedto the product surface and then

reflected received by thetransducer. The time from emissionto respection of the signalsdepends on the level in the vessel.

Application:Liquid , Solid I G

R

d=c*t/2c: speed of light

L=E-d D
http://ultrasonic/DATA%20SHEET-ULTRASONIC.pdfhttp://ultrasonic/MRQ-LEVEL-ULTRA%20SONIC.pdfhttp://ultrasonic/TI365FEN.PDFhttp://ultrasonic/image.pdf


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Measuring Principle:Radar use electromagnetic waves typically in the K-band or X-band (6~28 GHz).

Tow basic principles of operation exist for continuous level radar

transmitters and gauges.


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1.Frequency modulatedcarrier wave (FMCW) :

The time of flight of thereflected single is

measured by controllingthe sensor oscillator sothat it sends out a linearfrequency sweep at a fixedbandwidth and sweep time.


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2. PULSE :The sensor transmits a pulse of microwave energy andreceives a return signal from the material level surface.

The transit time of signal is calculated and used to determine

the distance to the level surface.

Application:Liquid , Solid

I G

R D

INTERFACESPR
http://radar/SPR-radar.pdfhttp://radar/TI358FEN.PDFhttp://radar/DATA%20SHEET-RADAR.pdfhttp://radar/Mrq-level-%20radar.pdfhttp://radar/TI358FEN.PDF


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I G


The most important application of radar is tank gauging systemsome pressure transmitter and multi-stage temperature

transmitter are applied and all of outputs enters in to oneprocessing module or one computer equipped with manufacture'ssoftware for calculate a real level measurement and then itstransmitted to central control room.
http://radar/TGS/interface.pdfhttp://radar/TGS/image.pdf


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Item Description Type Gauge Switch Transm. Interface Non- ContactType

1 Bubble P P2 Capacitance P P P3 Conductive P4 Displacement P P5 Diffrential Pressure P P6 Float P P P7 Glass P8 Magnetic P9 Paddle P10 Radiation P P P11 Radar P P12 Ultrasonic P P13 Vibrating P14 Weighing P P


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- ENDRESS + HAUSER LEVEL HANDBOOK

- http://www.cesare-bonetti.it

- ANDREW, W.G. APPLIED INSTRUMENTATION IN THE PROCESS

INDUSTRIES, 2ND EDITION, GULF PUBLISHING COMPANY, 1979.

- LIPTAK, B.G. PROCESS MEASUREMENT & ANALYSIS,

4TH EDITION, CRC PRESS, 1995.


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http://picture/workshop.pdfhttp://picture/site.pdfhttp://picture/miscellaneous.pdf


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SG = LIQUID/ WATER AT STANDARD CONDITIONS

SG = GAS/ AIR AT STANDARD CONDITIONS

T = 60 OF , 15.6 OC

P = 14.696 PSI , 101.325 KPa


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The operating principle of strain gauges is more than 100 years old, and was discovered whenLord Kelvin reported that metallic conductors subjected to mechanical strain exhibited acorresponding change in electrical resistant. These units are called unbounded wire gaugesbecause the wire elements are mounted on a mechanical frame whose parts can move in relationto each other, causing a change in wire tension as load changes. Therefore, the change inelectrical resistance is a measure of strain.


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Strain gauge transducers can be built by usingunbounded wire elements that are stretchedbetween a fixed and a moving

point on an elastic pressure sensor.

These devices are sensitive, but fragile andvibration sensitive.


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A wire filament is attached to a test specimen by plasticcement and the strain in the wire is measured in terms ofits resistance. Constantan, nichrome, platinum or Karma-type alloy wires, foils, or semiconductor materials can bepermanently bonded to the strained surface. Such straingauge designs are inherently unstable due to temperature

sensitivity, and hysterics caused by thermo elasticstrain.


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The diffused semiconductor strain gauge, which consists of resistance elements diffused

into a single silicon chip. The silicon wafer acts as the sensor diaphragm, reducing both

the size and the cost of the sensor. The silicon wafer is more reliable than the metal

Diaphragms because after being strained it returns to its original shape due to its

excellent elasticity.

The sensitivity of semiconductor-type strain gauges is 100- fold greater than that of wirestrain gauges. The thickness of the wafer determines

the pressure range of the sensor.

Standard units are available from 0-1 to 0-250 PSIG,

but they are most often used on instrument air service

ranges of 3 to 15 PSIG. These sensors are small,

inexpensive, accurate, and repeatable, and theyprovide a wide pressure range and a strong output

signal level. Their limitations include sensitivity to ambient temperature variations, which

can be compensated for in the intelligent transmitter designs.


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A further improvement is the thin film

strain gauge that eliminates the need for adhesive

bonding . The gauge is produced by first

depositing an electrical insulation

(typically a ceramic) onto the stressed

metal surface, and then depositing the straingage onto this insulation layer. Because the

thin film gage is molecularly bonded to the specimen, the installation is much more stable

and the stressed force detector can be a metallic diaphragm or beam with a deposited

layer of ceramic insulation.


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Interface level control is maintaining the level between two immiscible liquidshaving different specific gravities. Occasionally there is need in a process to controlsuch an interface in a vessel. The displacement level method is used for suchapplications. It becomes obvious that the difference in specific gravity of two fluidsdetermines the change in force as the interface level changes through the floatrange.


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One of the unique capabilities of RF levelmeasuring instrumentation is to indicate and/orcontrol an interface between two immiscibleliquids, each having a different dielectric constant.Oil/water interface measurement is a commonapplication of this type. It is important to note that

a vertically-mounted electrode must be fullysubmerged at all times to provide correct interfacedetection. If it isnt, the electrode will be exposedto two interfaces; the first being between air or agas and the upper phase material, and the second

being between the low and high dielectric constant liquids. The zero is calibrated when theprobe is completely submerged in the low dielectric constant liquid. The 100% point is

established using the span adjustment when the entire electrode is submerged in the highdielectric constant liquid. In the oil/water example, as the interface rises on the electrode,a greater percentage of it is submerged in the higher dielectric constant liquid. This causesan increase in the capacitance generated and a corresponding increase in the outputsignal.

level instrument

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