Different Techniques for Level Measurments

1. DIFFERENT TECHNIQUES OF
LEVEL MEASURMENTS
Prem Baboo
Sr. Manager (Prod)
National Fertilizers Ltd. India
F.I.E., Institution of Engineers (India)
Technical Advisor & an Expert for
www.ureaknowhow.com

2. CONTENTS
1.INTRODUCTION .
2.PHYSICAL TECHNIQUE .
3.PRESSURE TECHNIQUE .
4.BUOYANCY TECHNIQUE .
5.CAPACITANCE TECHNIQUE .
6.RADAR TECHNIQUE .
7.CONDUCTIVITY TECHNIQUE
8.ULTRASONIC TECHNIQUE .
9.POWER SONIC TECHNIQUE .
10.RADIATION TECHNIQUE .

3. INTRODUCTION .
• What is a level ?
• WHY IT IS MEASURED ?
• WHY ITS MEASUREMENT IS IMPORTANT

4. LEVEL
THE LEVEL MAY BE EXPRESSED IN TERM OF PRESSURE EXERTED
OVER A DATUM LEVEL OR IN TERM OF THE LENGTH OF THE
LIQUID COLUMN.
WHY IT IS MEASURED ?
TO ENSURE THAT RIGHT AMOUNT OF LIQUID/SOLID ARE ADDED TO
THE VESSEL AT RIGHT TIME AND FOR SAFE OPERATION.
WHY ITS MEASUREMENT IS IMPORTANT ?
LEVEL MEASUREMENT IS ONE OF THE IMPORTANT PARAMETER IN ANY
PROCESS INDUSTRY LIKE OUR FERTILIZER PLANT.THE LEVEL HAS A
SIGNIFICANT EFFECT ON PROCESS QUALITY, CONTROLLABILITY ,
PROCESS STABILITY AND OPTIMISATION . HENCE PRECISE, ACCURATE
AND RELIABLE LEVEL MEASUREMENT IS NECESSARY . A WIDE VARIETY
OF LEVEL MEASURE MENT TECHNIQUES ARE AVAILABLE TO MEET THE
DIVERSE LEVEL REQUIREMENTS OF THE PROCESS INDUSTRY EVOLVED
OVER THE YEARS.

5. PHYSICAL TECHNIQUE
A.
DIRECT METHOD.
B.
INDIRECT METHOD.

6. GLASSES
DRAIN
LEVEL GAUGE
I/S
VALVES
DRAIN VALVE
CHECK VALVE
CHECK VALVE
TECNOMATIC (I) PR. LTD.

7. CHECK VALVE.
Level gauges have auto shut off ball check valves
generally. In the event of glass failure or gasket
burst, pressure difference between vessel and
gauge causes ball check to close entry of process
fluid in to the gauge chamber, Thus reducing
spillover of valuable process fluid. The extended tip
of trim prevents ball to shut off gauge during
startup.

8. SOME SAFETY HINTS
• Assembling and disassembling of gauge glass must
be done with the help of “ TORQUE WRENCH” and
in the sequence as shown in figure.
• The glass should not be in contact with any metal
surface. Temperature differences at points of contact
will set up high loading and may break glass.
• In steam service-glasses should be protected by mica
shields to reduce steam erosion and retighten gauge
after attains process temperature.
• While taking in line 1st
isolation valve should be crack
open & care must be taken to slowly warm up the
gauge glass and anyone should not be in front of level
gauge.

9. LEVEL GAUGE
ASSEMBLING &
DISASSEMBLING
SEQUENCE

10. TRANSPARENT GLASS
MODULE
• Material : Borosilicate Glass

11. GASKET
• Material :Asbestos (High Temp & Press).
• Teflon optional.
• Thickness : 1~ 2 mm Approx.

12. MICA
• It is provided to protect the Glass
from heat

13. INDIRECT METHOD
1.MAGNETIC LG:=
WHEN LOCAL LEVEL INDICATION IS REQUIRED ON CORROSIVE &
TOXIC / DANGERS MATERIAL .THE USE OF GLASS OR GASKETS AND
THREADED CONNECTIONS IS NOT DESIRABLE FOR SUCH
APPLICATIONS MAGN ETIC LEVEL GAUGES ARE USED.A FLOAT WITH
PERMANENT MAGNET INSIDE A SEALED CHAMBER AND INDICATOR
WAFERS ARE ATTRACTS TOWARDS MAGNET WHICH ARE IN GLASS
TUBE OUT SIDE THE CHAMBER,AS LEVEL GOES UP AND DOWN IN
THE VESSEL.
2.FLOAT ACTUATED LG:-
IT IS EMPLOYED IN OPEN VESSELS .THE FLOAT RESTS ON THE
SURFACE OF LIQUID,SUPPORTEDLY BY BUOY- ANT FORCE.THE
FLOAT IS CONNECTED TO A LIGHT WE- IGHT CABLE,THE OTHER END
OF WHICH IS CONNECTED TO A COUNTER WEIGHT. COUNTER WT
ALSO ACTS AS INDICATOR AND MOVES AGAINST A VERTICAL
SCALE.

14. MAGNETIC
LEVEL GAUGE

15. FLOAT
ACTUATED
LEVEL
GAUGE

19. PRESSURE TECHNIQUCE .
1.
STATIC PRESSURE ACTUATED
MECHANISMS .
2.
DIFFERENTIAL PRESSURE
ACTUATED MECHANISMS .

20. 1.STATIC PRESSURE ACTUATED
MECHANISMS .
Pressure is defined as the force per unit
area
WHERE THE LIQUID IS REQUIRED IN AN
OPEN TANK,THE PRESSURE DUE TO
LIQUID MAY BE FOUND BY USING WITH A
PG/LT CALIBRATED IN TERMS OF
LEVEL,DIRECTLY MOUNTED AT 2” OR 3”
ABOVE THE BOTTOM OF TANK.

21. PRESSURE CONVERSION TABLE
atm bar Kg/cm2 lb/in2 mmwc In of
H2O
kPa
atm 1.0133 1.0332 14.70 760.0 407.14 101.3
3
bar 0.9869 1.0197 14.504 750.0 401.81 100.0
Kg/cm2 0.9678 0.9807 14.22 735.5 394.05 98.07
lb/in2 0.0680 0.0689 0.0703 51.7 27.69 6.89
mmwc 1.316 X
10(-3)
1.333 X
10(-3)
1.360 X
10(-3)
1.934X
10(-2)
0.536 0.133
In of
H2O
2.456 X
10(-3)
2.489 X
10(-3)
2.538 X
10(-3)
3.611 X
10(-2)
1.867 0.249
kPa 9.869 X
10(-3)
1X10(-2 1.020 X
10(-2)
0.145 7.5 4.018

22. STATIC PR.METHOD
LOCAL
LOCAL INDICATORPG
PRESSURE= h (SG)
WHERE, h IS HEAD.
SG IS SPECFIC GRAVITY.

23. STATIC PR.METHOD
REMOTE
SUPPLY / OUT-PUT FOR
REMOTE
LT
PRESSURE= h (SG)
WHERE, h IS HEAD.
SG IS SPECFIC GRAVITY.
+
-

24. STATIC PRESSURE ACTUATED MECHANISMS .
AIR SUPPLYAFR
PURGE TUBE
ROTA-
METER
FEED
BACK
PRES
24VDC
& O/P
WIRES
PT

25. PG
PURGE
TUBE
AIR
SUPPLY

26. STATIC PR.PURGE METHOD.
WITH A PURGING GAS/AIR BLOWN
THROUGH THE STAND PIPE WHICH GOES
DOWN ALL MOST TO THE BOTTOM OF THE
TANK ABOUT 2” OR 3” ABOVE THE
SEDIMENTS,THE PRESSURE IN THE STAND
PIPE WILL BUILD UP UNTILL IT IS EQUAL
TO THAT DUE TO THE LIQUID ABOVE THE
LEVEL OF THE BOTTOM TIP OF THE PIPE.
THE PRESSURE IN THE BUBBLER PIPE IS
SLIGHTLY GREATER THAN THE HEAD
OVER THE BUBBLER PIPE.

27. 2.DP. ACTUATED
MECHANISMS
DIFFERENTIAL PRESSURE
METHOD ARE USED FOR
LEVEL MEASUREMENT BY
USING D.P. CELLS .

28. STRAIN BASED D.P. CELLS
•
Figure 3-4: Strain-Gage Based Pressure Cell

29. CAPACITANCE BASED D.P.
CELL
•
Figure 3-5: Capacitance-Based Pressure Cell

31. DIAPHRAM
• P1
• P2

32. DIAGPHRAGM
This is a widely used elastic element as a pressure
transducer. As used in gauge diaphragm ,are thin
piece of material which will move when force is
applied to one or the other or both side .the motion of
diaphragm can be transmitted by the suitable linkage
to make it indicating device. There are two classes of
diaphragm depending upon physical characteristics ,
and those made from materials which are having no
spring characteristic. The diaphragm depending on
another spring are called slack diaphragm.

33. CAPSULE
The capsule pressure gauge is nothing but it is
combined two diaphragm back to back The
efficiency and accuracy is than flat ,corrugate
dished type spring diaphragm. The large
deflection is produced by cascading
arrangement of capsules. The linkage and
pointer mechanism is same as flat, corrugated
and dished type diaphragm.

34. BELLOWS
• The basic advantage of using bellows other
diaphragm or or bourdon is that it developes
larger force to operate linkage in mechanical
gauge or mechanical transducer.It can be used
for gauge,absolute and differential pressure
measurements.The materials used for
fabricating bellows are stainless steel,
brass,phosphor bronze,monel.

35. BELLOW
• Link Accessory
• Pressure

37. LIQUID HAVE CONDENSIBLE VAPOURS
SUPPLY / OUT-PUT FOR
REMOTE
CONDENSATE POT SLIGHTLY
HIGH THAN IMPULSE CONNECTION
LP
HP
LT
-
+

38. BY USE OF DPT
MOST OF THE LIQUID UNDER PRESS,HAVE
CONDENSIBLE VAPOURS , SO TO PREVENT IN-
ACCURACIES DUE TO CONDENSATE IN
IMPULSE LINE CONNECTING THE D.P.CELL TO
THE TOP OF THE TANK. A CONDENSING POT IS
USED , IT IS HIGH PRESSURE SIDE OF D.P.CELL
TO A CONSTANT LIQUID HEAD+ VAPOUR
PRESSURE & LOWER PRESS.SIDE TO THE
VARIABLE HEAD + VAPOUR PRESS. NOW
D.P.CELL MEASURES THE DIFF, PRESS IN
TERMS OF LEVE OF THE VESSEL .

39. SUPPLY / OUT-PUT FOR
REMOTE
+ -
LP
HP
LIQUID HAVE NON-CONDENSIBLE
VAPOURS
X
X

40. DP OF A STEAM DRUM

41. DP OF A STEAM DRUM
DP
=H1(SG1)+H2(SG2)-H3(SG3)
DP
=0.03H1+0.76H2-0.99H3

42. CRYOGENIC MATERIAL
WHEN PROCESS MATERIAL IS LIQUID LIKE NITROGEN THE VESSEL
IS USUALLY SURROUNDED BY THERMALLY INSULATED &
EVACUATED COLD BOX. HERE THE LP SIDE OF DIRECT ACTING DP
CELL IS CONNECTED TO VAPOUR SPACE ABOVE THE LIQUID
NITROGEN. AS LIQUID NITROGEN APPROACHES THE HP SIDE OF DP
CELL WHICH IS AT AMBIENT TEMP. OUTSIDE THE COLD BOX ,ITS
TEMP. REACHES THE BOILING POINT OF NITROGEN. IT WILL BOIL &
FROM THAT POINT ON THE CONNECTING LINE WILL BE FILLED WITH
NITROGEN VAPOUR . THIS CAN CAUSE NOISE IN THE LEVEL
MEASURE MENT TO PROTECT AGAINST THIS, THE LIQUID PORTION
OF THE CONNECTING LINE SHOULD BE SLOPED BACK TOWARDS
THE TANK & CROSS SECTION OF THE LINE BE LARGE ( ABOUT INCH
IN Dia) TO MNIMIZE THE TURBULENCE CAUSED BY THE
SIMULTANEOUS BOILING & RECONDENSING OCCURING AT THE
LIQUID VAPOUR INTERFACE.

44. BY USE OF DPT (PURGE)
FOR HIGH VISCOSIVE, SUSPENDED
PARTICLES & SLURRIES LIQUIDS
PURGE TYPE DIFFERENTIAL
PRESSURE TRANSMITTER ARE USED
PURGE MEDIA MAY BE WATER OR
GAS / AIR .

45. PURGE IS AIR OR GAS
PURGE ROTAMETER
DIFF,PRESS TRANSMETER
LP SIDE
HP SIDE
A-FIG
DPT
x
x
x x
x x
x
x x
DRAIN VALVE

46. PURGE IS WATER
PURGE ROTAMETER
DIFF,PRESS TRANSMETER
HP SIDE
LP SIDE
B-FIG
DPT
x
x
x x
x x
x
x x
DRAIN VALVE

47. BUOYANCY TECHNIQUCE
1.
FLOAT TYPE LEVEL TROL.
2.
FLOAT TYPE LEVEL INDICATOR.
3.
FLOAT TYPE LEVEL SWITCH.

48. 1.FLOAT TYPE LT.
FLOATS ARE MOTION BALANCE DEVICES
THAT MOVE UP & DOWN WITH LIQUID
LEVEL ,DUE TO WEIGHT VARIATION OF
FLOATS IN ACCORDANCE WITH BUOYANT
FORCE ACTING ON FLOATS & WEIGHT
VARIATION OF FLOATS IS EQUAL TO FLUID
DISPLACED.

49. PRINCIPLE
• ARCHIMEDES PRINCIPLE STATED THAT ,WHEN AN
OBJECT IS WHOLLY OR PARTIALLY IMMERSED IN
A FLUID, IT EXPERIENCES A BUOYANT FORCE (OR
UPTHRUST) WHICH IS EQUAL TO WEIGHT OF FLUID
DISPLACED BY THE OBJECT.
• THE TENDENCY OF A BODY TO FLOAT OR TO RISE
WHEN SUB- MERGED IN FLUID IS CALLED
,BUOYANCY.
• 100 CUBIC INCH DISPLACER WILL GENERATE A
BUOYANT FORCE OF 3.6 POUND.

50. FLOAT CHAMBER
0% LEVEL
100% LEVEL
DRAIN VALVE
LEVEL
TROL

51. WORKING
NOW WHEN THERE IS NO LIQUID IN THE FLOAT
CHAMBER,THE ENTIRED WEIGHT OF FLOAT
ATTACHED TO THE TORQUE ARM CAUSES A
TURING MOMENT ON TORQUE TUBE EQUAL TO
TORSIONAL STRESS SET UP IN THE TORQUE ROD
IT IS ZERO SIGNAL TO THE TRANSDUCER
ATTACHED AT OTHER END OF TORQUE ROD. FILL
UP THE LIQUID/WATER UPTO 100%. ANGULAR
DISPLACEMENT TO OTHER END OF TORQUE ROD
IS PROPORTIONAL TO LOSS OF THE WEIGHT OF
FLOAT AND IS AMPLIFIED BY TRANSDUCER.
NOTE:- SEE SG OF LIQUID IF CALIBRATE BY WATER

52. DENSITY
MATERIAL DENSITY(g/cm3)
ICE 0.92
WATER 1
GLYCERINE 1.26
IRON 7.8
MERCURY 13.6
GOLD 19.3
AMMONIA 0.587
UREA 1.15
CONDENSATE 0.83

53. DISPLACERS
• For 1.st and 2.nd series standard displacers are
made of AISI 316 stainless steel.
• For 3.rd and 4.th series displacers are made of solid
Aluminum 99.5%.
• Special Teflon displacers are available for all rating
and for temperature below 150 Deg C.
• Level range: 14”, 32”, 48”,60”,72”,84”,96” and
120”.On request all sizes.
• For displacer SG limits are defined.

54. FEATURE OF LEVEL TROL
• LT ARE MORE ACURATE & RELIABLE
FOR CLEAN LIQUID OF CONSTANT
DENSITY &TEMPERATURE.
• BY FLOAT CHAMBER,IT IS CALIBRATE /
REPAIR WITHOUT DISTURBING
PROCESS.
• FLOAT LENGTH AVAILABLE ARE 14”,
32”,48”,60” AND EVEN UPTO 60 feet.

55. LIMITATION OF LT
• LT IS NOT SUITED FOR SLURRY, SLUDGE
SERVICES BECAUSE COATING OF
DISPLACER CHANGE ITS VOLUME &
THEREFORE ITS BUOYANT FORCE.
• CHANGE IN DENSITY / TEMP OF PROCESS
MATRIAL CAUSE ERROR.
• COSTLY AS COMPARED.

56. WHY DENSITY CAUSE AN
ERROR ?
WEIGHT = MASS *ACCELERATION DUE TO GRAVITY.
Ie, 1 NEWTON = 1 kg * 9.8 m/s.sq.
MASS = VOLUME * DENSITY.
SO,
WEIGHT =
VOLUME * DENSITY * ACCELERATION. DUE TO GRAVITY

57. 2.FLOAT TYPE LEVE
INDICATOR.

58. 3.FLOAT TYPE LEVEL SWITCH.

59. 3.FLOAT TYPE LEVEL SWITCH.

60. TYPICAL L/S APPLICATION

61. RADAR TECHNIQUE .
• HISTORY :FIRST TIME(1925),A.TAYLOR &
LEO YOUNG OF U.S.NAVY USED RADAR TO
MEASURE THE HEIGHT OF EARTH’S
IONOSPHERE.
• 1934,THEY USED FOR NAVY SHIPS.
• 1935,ENGLAND USED IT TO DETECT
AIRCRAFT.
• IT USED AS LEVEL GAUGE IN 1976.

62. PRINCIPLE.
THE PRINCIPLE OF WORKING
RADAR TYPE LEVEL TRANS
MITTER IS BASED UPON THE
TECHNOLOGY TDR (TIME
DOMAIN REFLECTOMETRY).
RADAR STAND FOR ?

63. RADAR
RA-STANDS FOR RADIO.
D-STANDSFOR DETECTION.
A- STANDS FOR AND.
R-STANDS FOR RANGING.

65. COMPONENTS.
1. RADAR SENSORS CONSIST OF TRANSMITT-
ER,AN ANTENNA,A RECEIVER WITH SIGNAL
PROCESSOR. TRANSMITTER IS MOUNTED ON
TOP OF VESSEL.
2. ITS SOLID STATE OSCILLATOR SENDS OUT AN
ELECTROMAGNETIC WAVES (USING A SELECTED
CARRIER FREQUENCY AND WAVE- FORM) AIMED
DOWN AT THE SURFACE OF THE PROCESS
FLUID IN VESSEL. THE FREQUENCY USED IS
TYPICALLY 10 GHz.

66. WORKING.
THE ANTENNA IS OF TWO TYPES PARABOLIC
DISH AND HORN TYPE.THE SIGNAL RADIATED
TOWARDS THE SURFACE OF THE PROCESS
LIQUID.A PORTION IS REFLECTED BACK TO
THE ANTENNA,WHERE IT IS COLLECTED &
ROUTED TO THE RECEIVER.HERE, A
MICROPROCESSOR CALCULATES THE TIME
OF FLIGHT AND HENCE THE LEVEL OF
PROCESS LIQUID.

67. TIME OF FLIGHT
TIME OF FLIGHT .
RADAR
PULSE
PULSE SEQUENCE
TIME FOR RECEIVER

68. TIME OF FLIGHT
• THE TIME OF FLIGHT IS THE PERIOD
BETWEEN THE TRANSMISSION OF
RADAR PULSE AND THE RECEPTION
OF THE RETURN ECHO. IT IS
DETERMINED BY THE RADAR
DETECTOR,WHICH IS
SIMULTANEOUSLY EXPOSED TO SENT
AND REFLECTED SIGNAL. DETECTOR
O/P IS BASED ON THE DIFFERENCE.

69. FOR EXAMPLE
• IF THE IMPULSES ARE EMITTED BY
ANTENA SYSTEM AS IMPULSE
PACKETS WITH PULSE DURATION OF
1/n SECOND AND IMPULSE BREAKS
OF 278 ns, THIS CORRESPONDS TO A
PULSE FREQUENCY OF 3.6 MHz.

70. t
t
TIME TRANSFORMATION

71. THE LEVEL.
THE DEPTH OF VAPOUR SPACE IS AS
WHERE “T” IS TIME OF FLIGHT
AND “C” IS SPEED OF RADAR
SIGNAL & EQUAL TO VELOCITY
OF LIGHT.
THE LEVEL IS L = E-d
‘d’= T/2c

73. THE RADAR SIGNALS REACT TO TWO
ELECTRICAL PRIMARY QUANTITIES:-
1. THE ELECTRICAL CONDUCTIVITY OF THE SUBSTANCE.
2. THE DIELECTRIC OF THE SUBSTANCE.
ALL PRODUCTS , WHICH ARE ELECTRICALLY
CONDUCTIVE OR HAVE A DIELECTRIC CONSTANT
GREATER THAN 1.5 ,HAVE SUFFICENT GOOD REFLECTION
CHARACTERISTICS FOR RELIABLE & ACCURATE RADAR
LEVEL MEASUREMENT.

74. DESIGN
• THE LARGER THE ANTENNA’S Dia,GREATER THE SIGNAL
STRENGTH.
• THE DRAWBACK OF SMALL ANTENNA INCLUDE HIGHER
BEAM SPREADING & THE CORRESPONDING INCREASED
THE CHANCE OF REFLECTION FROM OBSTACLE WITH IN
THE TANK & ON +VE SIDE,THERE IS A GREATER CHANCE
THAT THE EMITTED BEAM WILL BE REFLECTED BACK TO
DETECTOR,ALIGNMENT OF SENSOR IS NOT CRITICAL.
• CONTACT & NON-CONTACT ALSO AVAILABLE

77. FEATURES OF GWR ( LT )
• LEVEL IS NOT AFFECTED BY MEDIA VARIABLES SUCH AS
PRESSURE,DENSITY,PH,VISCOSITY.
• EASY BENCH CONFIGURATION-NO NEED FOR LEVEL
SIMULATION.
• TWO WIRE,INTRINSICALLY SAFE LOOP POWERED
• 360 DEGREE ROTATABLE HOUSING CAN BE DIS-
MANTLED WITHOUT DEPRESSURING THE VESSEL VIA
QUICK CONNECT / DISCONNECT PROBE COUPLING,SO
ON LINE MAINTANCE IS POSSIBLE.
• HART DIGITAL COMMUNICATION.
• PROBE DESIGN UPTO 400 DEG–C / 350 KG/CM2
• SATURATED STEAM APPLICATION UP TO 110 KG/CM2 &
320 DEG-C.
• CRYOGENIC APPLICATION UPTO -150 DEG –C
• ACCURACY UP TO 0.01% OF THE SPAN.

78. LIMITATION
• REFLECTIVE PROPERTIES OF PROCESS MATERIAL
AFFECT RETURNED RADAR SIGNAL STRENGTH SO IF
DUST PARTICLE SIZE INCREASES,OR IF THE FOAM &
DUST GETS THICK,IT WILL NO LONGER DETECT THE
LIQUID LEVEL. INSTEAD THE DUST OR FOAM LEVEL WILL
BE MEASURED.
• INTERNAL PIPING,DEPOSITS ON THE ANTENNA,MULTIPLE
REFLECTIONS OR REFLECTION FROM THE WALL CAN
ALL INTERFERE WITH THE PROPER OPERATION OF A
RADAR SENSOR.
• CANNOT BE USED IF LIQUID SURFACE NOT FLAT.

79. CAPACITANCE TECHNIQUE .
• A CAPACITOR CONSISTS OF TWO CONDUCTORS
PLATES SEPARATED BY AN INSULATOR CALLED
AS DIELECTRIC CONSTANT.
• THE WORD CAPACITANCE IS DERIVED FROM THE
WORD CAPACITY.THE CAPACITY MEANS HOW
MUCH QUANTITY CAN BE STORED / PLACED IN
THE VESSEL,TANK . IN CASE OF THE
CONDUCTOR WE ARE TAKING ABOUT HOW
MUCH CHARGE CAN BE STORED/PLACED.
• IF WE GIVE THE +“Q” UNIT OF CHARGE TO THE
CONDUCTOR, ITS POTENTIAL”V” WILL RISE.
ACTUAL RISE OF THE POTENTIAL DUE TO THIS
CHARGE WILL BE DEPEND ON THE SIZE OF THE
CONDUCTOR AND ITS POSITION RELATIVE TO
ANY NEGHBOURING CONDUCTOR.

80. Q = CV OR C = Q / V
*CAPACITY = CHARGE / POTENTIAL
THE CAPACITANCE UNIT IS THE FARAD,DEFINED AS
THE POTENTIAL CREATED WHEN ONE VOLT.BATTERY
IS CONCETED TO A CAPACITOR CAUSES THE STORAGE
OF ONE COULOMB OF ELECTRIC ENERGY.
+ -
PLATES
DISTANCE=D
DIELETRIC (AIR)
VOLTS

82. FACTORS EFFECTING THE CAPACITY OF THE
CONDENCER ARE AS:-
1.AREA OF THE PLATES.
2.DISTANCE BETWEEN THE PLATES.
CAPACITY OF THE CONDENCER(C) IS DIRECTLY PROPORTIONAL
TO THE AREA 0F THE PLATE AND INVERSELY PROPORTIONAL
TO THE DISTANCE BETWEEN THE PLATES.
C = K A / D
WHERE “C” IS THE CAPACITANCE (FARAD)
“A” IS AREA OF THE PLATES( METRE Sq )
“K” IS THE DIELECTRIC CONSTANT .
“D” IS THE DISTANCE BETWEEN THE PLATES(METRE)
CONSEQUENTLY;# THE LARGER THE AREA OF THE PLATES AND
THE CLOSER THE PLATES , THE HIGHER THE CAPACITANCE.
# THE HIGHER THE DIELECTRIC CONSTANT, THE HIGHER THE
CAPACITANCE.

83. WORKING
IN LEVEL MEASUREMENT,AREA OF THE PLATE
( ELECTRODE ) AND DISTANCE BETWEEN ELECTRODES IS
FIXED AND REMAINS CONSTANT.
HENCE FROM ABOVE DISCUSSION CAPACITANCE IS
DIRECTLY PROPORTINAL TO THE DIELECTRIC CONSTANT
OF THE MATERIAL BETWEEN THE PLATES AND VARIES
WITH RESPECT TO CHANGE IN LEVEL. THE BEST LEVEL
MEASUREMENT ARE OBTAINED WHEN THE CHANGE IN
CAPACITANCE ARE HIGH, MEANS CHANGE BY 0% AND
100% LEVEL.

85. PHYSICAL CAP. PROBE
Dead length

86. MEASUREMENT IS MADE BY APPLY AN RF ( BY
THE ELECTRONIC CIRCUIT ) BETWEEN THE
CONDUCTIVE PROBE AND VESSEL WALL .THE RF
SIGNAL RESULTS IN A CURRENT FLOW THROUGH
THE DIELECTRIC PROCESS MATERIAL IN THE TANK
FROM THE PROBE TO THE VESSEL WALL.WHEN
THE LEVEL IN THE TANK DROPS & THE PROBE IS
EXPOSED TO THE VAPOUR / AIR,THE DIELECTRIC
CONSTANT OF VAPOUR / AIR IS LESS AS COMPAR-
ED TO THE PROCESS LIQUID.THIS CAUSE A DROP
IN CAPACITANCE READING & DROPS IN CURRENT
FLOW.THE CHANGE IS DETECTED BY THE
ELECTRONIC CIRCUITRY AND TRANSLATED IN TO
A SCALED ANALOG SIGNAL 4-20mA

87. 24VDC,4-20mA
LOOP POWERED
FOAM CAUSE ERROR
DIELECTRIC STBILITY
CRITICAL
MEDIA
LEVEL
MEDIA
BUILDUP

89. NOW DITANCE BETWEEN TWO CAPACITANCE
PLATES ABOVE WATER SURFACE(CHAMBER &
PROBE) IS LARGE,SO “CA” IS SMALL.
CONVERSELY ,THE DISTANCE BETWEEN
PLATES BELOW WATER SURFACE( PROBE &
WATER) IS SMALL AND THEREFORE,THE “CB”
WILL BE LARGER COMPARED WITH “CA”.THE
NET RESULT IS THAT ANY RISE IN THE WATER
LEVEL WILL CAUSE AN INCREASE IN
CAPACITANCE THAT CAN BE MEASURED IN
TERMS OF LEVEL.

90. AS A LEVEL SWITCH
CAPACITANCE DEVICES ARE ALSO MOSTLY USED FOR
ON-OFF SERVICES AS LEVEL SWITCHES, FOR SUCH
FUNCTION CAPACITANCE PROBES ARE MOUNTED IN
HORIZONTIAL POSITION SO THAT LARGE PLATE AREA IS
EFFECTIVELY USED. SUCH LEVEL SWITCHES ARE USED IN
ON-OFF CONTROL TO A PUMP OR LOW & HIGH ALARM.
CHANGE IN CAPACITANCE,”C”=(K2- K1)*A / D
WHERE K1,IS DIELECTRIC CONSTANT OF VAPOUR/AIR AND
K2,IS DIELECTRIC CONSTANT OF PROCESS MATERIAL.
“D”IS THE DISTANCE BETWEEN PLATES.

91. LEVEL SWITCH

92. USED IN
UREA
STORAGE

96. APPLICATION OF CAPACITANCE LEVEL SENSORS

97. FEATURES OF CAP. (LG);
1. ONLY ONE PROBE IS USED AS COMPARED TO
HYDRASTEP.
2. COST WISE CHEAP THAN OTHER ie RADAR ETC.
3. USED IN LARGE SIZE / DIAMETERS VESSEL , BY USING
STILLING WELL.
4.TWO WIRE INTRINSICALLY SAFE LOOP POWERED
LEVEL TRANSMITTER WITH 24VDC SUPPLY & 4-20mA
5. USED FOR SOLIDS BY FLEXIBLE PROBES.
6.EASY TO CALIBRATE & REPAIR IF PROBE CHAMBER IS
USED AND REPEATABILITY IS 1.0%.
7. ELECTRONIC CARD ASSEMBLY CAN BE MOUNTED AT
A DISTANCE 100 ft.
8. 8.A HIGH SENSITIVE DESIGN (0.5pF) ALSO AVAILABLE &
RESPONSE TIME IS 100 ms.

98. DIELECTRIC CONSTANT VALUES FOR

100. PROBE DESIGN
THE MOST COMMON PROBE DESIGN IS STAIN-
ESS STEAL ROD OF ¼” OR ½” DIA, SUITABLE
FOR NON-CONDUCTIVE/NON-CORROSIVE
MATERIAL.THE PROBE IS INSULATED FROM
HOUSING & BIN WALL BY AN LOW DIELECTRIC
INSULATOR,SUCH AS NYLON OR RYTON.THESE
POLYMERS HAVE MAX. OPERATING TEMP 175-
350 DEGREE-C. CERAMIC CAN BE USED FOR
HIGHER TEMP APPLICATION OR IF ABRASION
RESISTANCE IS REQUIRED. FOR APPLICATION
WHERE THE PROCESS MATERIAL IS CONDUCTIE
& CORROSIVE,THE PROBE MUST BE COATED
WITH TEFLON,KYNAR & POLYETHYLENE.

101. LIMITATION
• DIELECTRIC CONSTANT CHANGE WITH TEMPERATURE ABOUT
0.1% PER DEGREE – C .
• INSTALLATION IS IMPOSSIBLE IF VESSEL IS AGITATE.
• CHEMICAL CHANGES OF THE MEASURED MATERIAL EFFECT THE
DIELECTRIC CONSTANT SO THE LEVEL.
• IN SOLID MEASUREMENT VARIATION IN PARTICLES SIZE EFFECT
THE DIELECTRIC CONSTANT SO THE LEVEL .
• PRODUCT COATING ON THE PROBE MAY EFFECT ACCURATE
LEVEL MEASUREMENT .
• THE MINIMUM DIFFERENTIAL CAPACITANCE REQURIRED FOR
LEVEL MEASUREMENT SHOULD BE HIGH AS 10 pf
• INSULATION HAS BROKEN DOWN ie AGE FACTOR AND DUE THE
EFFECT OF TEMPERATURE.

102. ULTRASONIC TECHNIQUE .
HISTORY.
THE ORIGIN OF ULTRASONIC LEVEL
INST,GOES BACK TO ECHOMETERS USED
IN MEASURING THE DEPTH OF WELL BY
FIRING A BLANK SHELL AND TIMING THE
RETURN OF ECHO.

103. PRINCIPLE
THESE OPERATE ON THE
PRINCIPLE OF SONAR
DETECTOR.
SONAR STAND FOR ?

104. SONAR.
• SO-STANDS FOR SOUND.
• N-STANDS FOR NAVIGATION.
• A- STANDS FOR AND.
• R-STANDS FOR RANGING.

105. THE VELOCITY OF ULTRASONIC VARIES
WITH BOTH THE SUBSTANCE
THROUGH WHICH IT TRAVEL & WITH
THE TEMP,OF SUBSTANCE.SO,THE
SPEED OF SOUND IS TO BE USED IN
LEVEL MEASURING, THE SUBSTANCE
THROUGH WHICH IT TRAVEL MUST BE
WELL KNOWN & TEMP- VARIATION
MUST BE MEASURE & COMPENSATED.

106. TYPES OF ULTRASONIC
A
RETURNED ECHO TIMING.
B
SIGNAL ABSORPTION.

107. RETURNED ECHO TIMING.
SENSOR ASSEMBLY
SENSOR ASSEMBLY

108. SIGNAL ABSORPTION
SENSOR
ASSEMBLY

109. WORKING
THE ULTRASONIC LEVEL SENSOR
ASSEMBLY CONSIST OF SEPARATE TX &
RECEIVER ELEMENTS.A SINGLE
TRANSDUCER IS CYCLED ON & OFF AT
REGULAR INTERVALS TO LISTEN FOR
RELECTED ECHO.

110. FREQUENCY RANGE
FREQUENCY RANGE OF ULTRASONIC
IS 20~45 KHz FOR LEVEL GAUGES
(SLIGHTLY HIGH THAN AUDIBLE
SOUND WHICH IS 9~10 KHz) ARE
GENRATED BY ELECTROSTATIC &
PIEZOELECTRIC TRANSDUCERS.

111. AN ELECTROSTATIC TRANSDUCERS
IS MADE UP OF THIN ,FLEXIBLE GOLD PLATED PLASTIC FOIL ,
STRECHED OVERAN ALLUMINIUM BACK PLATE & HELD UP IN
PLACE BY LEAF SPRING ( USED FOR CLEAN ENVIRONMENT ).
PIEZOELECTRICTRANSDUCERS
UTILISE CERAMIC OR POLYMER CRYSTAL VIBRATED AT THEIR
NATURAL FREQUENCY. THEASE ARE MORE RUGGED.

112. FEATURES OF ULTRASONIC
LEVEL GAUGE
• SELF CALI BRATION FEATURE .
• ACCURACY IS WITH IN 5mm UPTO 30 ft .
• EASY BENCH CONFIGURATION-NO NEED FOR
LEVEL SIMULATION.
• TWO WIRE,INTRINSICALLY SAFE LOOP POWERED
• 360 DEGREE ROTATABLE HOUSING CAN BE DIS-
MANTLED WITHOUT DEPRESSURING THE VESSEL
VIA QUICK CONNECT / DISCONNECT PROBE
COUPLING,SO ON LINE MAINTANCE IS POSSIBLE.
• HART DIGITAL COMMUNICATION.
• BETTER FOR DIRTY / FOAM OR LARGE GRAIN SIZE.

113. CALIBRATION
TARGET

114. LIMITATION
• TEMP OF PROCESS MATERIAL AFFECT
ULTRASONIC SIGNAL ,SO THE
LEVEL(COMPENSATION IS REQD.)
• AFFECTED BY COMPOSITION OF THE
VAPOUR SPACE.
• RESPONSE TIME IS LESS THAN RADAR.
• ACCURACY IS LIMTED UPTO 30 ft.

115. SOUND’S VELOCITY.
MEDIA TEMP VELOCITY
AIR 0 DEG-C 332 m/s
AIR 20 DEG-C 344 m/s
AIR 100 DEG-C 392 m/s
WATER 20 DEG-C 1498 m/s
SEA-WATER 20 DEG-C 1543 m/s
HYDROGEN 0 DEG-C 1284 m/s

116. CONDUCTIVITY TECHNIQUE

122. HYDRASTEP SYSTEM
• THE HYDRASTEP SYSTEM HAVE BEEN DESIGNED AS
ELECTRONIC ALTERNATIVES TO CONVENTIAL VISUAL
WATER GAUGES ON BOILERS,GIIVING MORE RELIABLE &
SAFER WATER LEVEL. THE SYSTEM IS BASED ON
SIGNIFICANT DIFFERENCE IN RESISTIVITES OF WATER &
STEAM OVER THE RANGE 100 DEG-C TO 560 DEG-C .
• THE CELL CONSTANT IS DETERMINED BY THE LENGTH
& DIAMETER OF ELECTRODE TIP & WATER COLUMN
BORE.
• BY CHOSING THE CELL CONSTANT IN WATER LESS
THAN 100 K ohms & GREATER THAN 10 M ohms.

123. Hyderastep Electrode

124. POWER SONIC TECHNIQUE

127. RADIATION TECHNIQUE;
• IT IS BASED ON THE PROPERTIES OF GAMMA
RAYS, THAT THEY COULD PASS THROUGH A
SEEMINGLY SOLID, IMPENETRABLE MASS OF
MATTER & GAMMA RAYS LOST SOME OF THEIR
INTENSITY.
• GAMMA RAYS WERE AFFECTED BY THE
SPECIFIC GRAVITY ,TOTAL THICKNESS OF
OBJECT & BY DISTANC BETWEEN GAMMA RAYS
SOURCE & DETECTOR.

128. BASED ON PHYSICAL LAW OF ATTENUATION OF
NUCLEAR RADIATION AS IT PASSES THROUGH
MATTER. THE ABSORBTION OF GAMMA RADIATION
FOLLOWS AN EXPONENTIAL LAW.
I=I0e-μρd
A BEAM OF RAYS WITH THE ORIGINAL INTENSITY I0
IS WEAKENED AS IT PASSES THROUGH MATTER
HAVING THICKNESS “d” AND DENSITY “ρ”,
THE MASS WEAKENING CO-EF μ DEPENDS
ON THE TYPE OF RADIATION SOURCE USED.

133. SOURCE;
COBALT-60 HAVE ENERGY LEVEL
=1.33 MeV.
CESIUM-137 HAVE ENERGY LEVEL
=0.56 MeV.

134. ROD SOURCEROD SOURCE
• TYPE
CONSTRUCTED AS ROD.
• LENGTH
1040MM IN ONE PART AND INACTIVE PART AT THE
BOTTOM 800 MM.
• MATERIAL
COBALT 60
• RANGE
35 mCurie

135. SHIELDINGSHIELDING
THE SHEILDING CONSISTS OF A LEAD CYLINDERTHE SHEILDING CONSISTS OF A LEAD CYLINDER
WITH A RADIATION EXIT SLOT, THE CYLINDER ISWITH A RADIATION EXIT SLOT, THE CYLINDER IS
WELDED IN TO A STEEL TUBE THAT IS SHIELDEDWELDED IN TO A STEEL TUBE THAT IS SHIELDED
WITH A STEEL COVER. THE CYLINDER ISWITH A STEEL COVER. THE CYLINDER IS
MOUNTED IN SUCH A STRUCTURAL FRAMEMOUNTED IN SUCH A STRUCTURAL FRAME
THAT BY TURNING IT THRO’ 90 DEG ADDITIONALTHAT BY TURNING IT THRO’ 90 DEG ADDITIONAL
SHIELDING IS PROVIDED FOR EFFECTIVESHIELDING IS PROVIDED FOR EFFECTIVE
RADIATION BEAM BY THE STRUCTURAL FRAMERADIATION BEAM BY THE STRUCTURAL FRAME

136. SCINTILLATION COUNTERSCINTILLATION COUNTER
THE RADIATION
DETECTOR CONSISTS
OF A SCINTILLATION
COUNTER WITH HIGH
SPECIFIC SENSITIVITY
TO GAMMA RADIATION

137. THE NaI CRYSTAL CONVERTS THE GAMMA QUANTATHE NaI CRYSTAL CONVERTS THE GAMMA QUANTA
EMITTED BY THE RADIO ACTIVE SOURCE IN TO LIGHTEMITTED BY THE RADIO ACTIVE SOURCE IN TO LIGHT
FLASHES,THE QUANTITY OF WHICH IS PROPORTIONALFLASHES,THE QUANTITY OF WHICH IS PROPORTIONAL
TO THE INCIDENT RADIATION INTENSITY.THE CRYSTALTO THE INCIDENT RADIATION INTENSITY.THE CRYSTAL
IS OPTICALLY COUPLED WITH A PHOTOMULTIPLIER INIS OPTICALLY COUPLED WITH A PHOTOMULTIPLIER IN
WHOSE PHOTOSENSITIVE LAYER THE LIGHT FLASHESWHOSE PHOTOSENSITIVE LAYER THE LIGHT FLASHES
RELEASE ELECTRONS.RELEASE ELECTRONS.
AN HV SUPPLY APPLIED TO THIS LAYER ACCELARATESAN HV SUPPLY APPLIED TO THIS LAYER ACCELARATES
THE ELECTRONS TOWARDS THE ANODE WHERE THEYTHE ELECTRONS TOWARDS THE ANODE WHERE THEY
RELEASE FURTHER ELECTRONS AS THEY IMPINGE ON ARELEASE FURTHER ELECTRONS AS THEY IMPINGE ON A
DYNODE SYSTEM. THUS HIGH AMPLITUDE PULSES AREDYNODE SYSTEM. THUS HIGH AMPLITUDE PULSES ARE
PRODUCED AND SUBSIQUENTLY CONVERTED IN TOPRODUCED AND SUBSIQUENTLY CONVERTED IN TO
STANDARD PULSES OF APPROX. 10V BY A SERIESSTANDARD PULSES OF APPROX. 10V BY A SERIES
AMPLIFIER.AMPLIFIER.

138. THE GAUGETHE GAUGE
THE LEVEL GAUGE LB-323 IS A MICROPROCESSORTHE LEVEL GAUGE LB-323 IS A MICROPROCESSOR
CONTROLLED SYSTEM THAT ALSO SUPPLIES THECONTROLLED SYSTEM THAT ALSO SUPPLIES THE
OPERATING & CONTROL VOLTAGE TOOPERATING & CONTROL VOLTAGE TO
SCINTILLATION COUNTER.THE STANDARD PULSESSCINTILLATION COUNTER.THE STANDARD PULSES
SUPPLIED BY THE DETECTOR IS PROCESSED BYSUPPLIED BY THE DETECTOR IS PROCESSED BY
THIS SYSTEM AND CALCULATES THE AVERAGETHIS SYSTEM AND CALCULATES THE AVERAGE
COUNT RATE AND COMPUTES FINAL RESULTS ONCOUNT RATE AND COMPUTES FINAL RESULTS ON
THE BASIS OF PRE PROGRAMMED PARAMETERS.THE BASIS OF PRE PROGRAMMED PARAMETERS.
IT GIVES AN OUTPUT OF 4-20 mA .IT GIVES AN OUTPUT OF 4-20 mA .

139. 10 75
COMPUTE
MEASURE
CODE
ENTER
LOCKED
PROBE FAILED
I
O
POWER
SWITCH
CODE DISPLAY LVEL DISPLAY
FRONT PANEL OF LB-323

141. THE HALF LIFE OF COBALT-60(USED AT ¾-LT-2)
IS 5.3 YEARS.THIS MEANS THAT,IN 5.3 YEARS,THE
ACTIVITY OF A 100 milliCurieCOBALT-60 SOURCE
WILL REDUCED TO 50 (mCi) milliCurie .
ONE mCi IS DEFINED AS THE RATE OF
ACTIVITY OF ONE milligram OF RADIUM 226.
WHEN USED FOR LEVEL MEASUREMENT
THE CONTINUOUS LOSS OF SOURCE STRENGTH
REQUIRE NOT ONLY CONTINUOUS COMPENSAT
-ION BUT EVENTUALLY,THE SOURCE MUST BE
REPLACED. THIS MEANS NOT ONLY THE EXPENSE
OF PURCHASING ANEW SOURCE , BUT ALSO THE
COST OF DISPOSING OF OLD ONE.

142. FEATURES
• Non contact, continuous level measurement
• independent of pressure, temperature and chemical
properties of the product
• use of rod sources enables linearization of measuring
signal even at the beginning of the measuring range
• adaptable for all shapes of vessel (cylindrical, conical, etc)
• simple to calibrate (only one measuring point is needed)
• source design for output signal proportional to product
level or volume
• measuring range of several meters possible (more than 10
m)
• automatic decay compensation
• minimal source activity through the use of scintillation
counters
• indication in % level or millimeters

143. RADIATION EXPOSURE LIMITS
• UP TO 0.2 Sv
• Up to 1.0 Sv
• Up to 2.0 Sv
• More than 6 Sv
• No Effect evident
• Slight changes of blood structures but
no serious damage is likely to occur
• Radiation hangover, vomiting, serious
illness possible, good chances of
recuperation
• No chance of survival
• The above limits are for the whole
body exposure to radiation for a short
time , but permanent exposure to
radiation will cause much damage due
to regenerative capacity of living
organism.