Direct Measurement Indirect Measurement Types of Level Measurement Level Gauge Float Dis-placer Differential Pressure Capacitance Ultrasonic Radar Nuclear Level Switch

1. Level
measurement
BY WEJDAN ABDALRHMAN

2. Level measurement:
 Vertical measurement :of process fluid taken
from the surface, or interface, to a fixed
reference point.
 Reference point :is normally the bottom of
the vessel holding the
substance.

3. Level Measurement Continuous:
 Continuously indicates the changing level of
process fluid.
 Required when it is necessary to observe the
position of fluid/interface continuously, e.g.
using mechanical device (glass gauge).

4. Point-to-Point measurement:
 Some processes require only that the level of
a substance be maintain between two points
(e.g. high and low level).
 Such system activates control devices only
when predetermined levels are
reached.

5. Direct Measurement:
 Involves straightforward approach.
 Actual level of process fluid is obtained directly.
- float
- dip stick
-glass gauges
 ADVANTAGE: Simple & economical, less / no
maintenance.
 DISADVANTAGE: Inadaptable to output signal
transmission for remote indication / control by itself

6. Indirect measurement:
 Involves conversion the measurement of other
physical quantity into level quantity.
-radar
-nuclear
-ultrasonic
-capacitance
-differential pressure
 ADVANTAGE: Adaptable to output signal transmission
for remote indication / control.
 DISADVANTAGE: Accuracy is affected by changes in
temperature of the process fluid.

7. Types of Level Measurement:
 Level Gauge
 Float
 Displacer
 Differential Pressure
 Capacitance
 Ultrasonic
 Radar
 Nuclear
 Level Switch

8. Level Gauge:
 Common technique for direct level measurement
 Used for several reasons:-
- economical.
- easy of maintenance.
- applicable to wide range of fluid
 Categorized into 3 groups:
 Flat ( glass gauge)
 Tubular (glass gauge) {Reflex- Transparent }
 Magnetic( glass gauge)

9. Float:
An object of lower density than the
process liquid is placed in the vessel,
causing it to float on the surface.
 Float rises and falls with the level.
Position of the float is sensed outside the
vessel to indicate level measurement.

10. Displacer:
 Working Principle :Based on Archimedes’ Principle
“ a body immersed in a liquid will be buoyed by a force
equal to the weight of the liquid displaced.”
 Volume of the displacer = V= (3.14xd2 / 4)xL
 Change in liquid level produce change in displacer
weight

11. Displacer( Mounting Configuration)
 Internal
Top-Mounted
Side-Mounted
 External
Top-Bottom
Side-Bottom
Side-Top
Side-Side

12. Advantages / Applications:
 Continuous level measurement.
 Applicable to non-viscous & clean liquids.
 High-accuracy, provided that liquid density is
constant.
 Wide range of measurement span, but cost
increases relatively.
 Liquid-liquid interface.

13. Disadvantages / Limitations:
 Inapplicable to solid.
 For coating media, the moving parts may be seized.
 Affected by density changes of process liquid
application.
 Leaking is possible (through torque tube).

14. Differential Pressure:
 Based on the principle that hydrostatic pressure varies
with changes in level.
 The principle of this measurement is that the
hydrostatic head, H exerted by a liquid is equal to the
specific gravity of that liquid, GL multiplied by the
height of the liquid, x.
H = (GL)(x)
 Where H = hydrostatic head in inches or meters of water, as applicable
x = height of liquid in inches, as applicable
GL = specific gravity of liquid

15. Differential Pressure:
H = (GL)(x)

16. Capacitance:
 As level changes, capacitance in the sensor
circuit also changes. Bridge misbalance occurs
- between probe and process media
(conductive applications).
- between probe and vessel wall
(insulating applications).
 This change is detected by the level switch's
internal circuitry - translated into a change in
the relay state of level switch.

17. Advantages / Applications:
 Capable of operating at extreme temperature
& pressure.
 No moving part.
 Usually only a single tank penetration is
required.

18. Disadvantages / Limitations:
Problems for media with varying
dielectric.
 Unsuitable to process media that
can coat the sensing element that
can reduce its reliability & accuracy.
- NOTE: even acids and caustics that don’t appear to coat
the sensing element
are so conductive that the thin film they leave can cause
serious error in
measurement.

19. Ultrasonic:
 Works on the principle of sending a sound
wave from a peizo-electric transducer to the
contents of the vessel.
- Measures the time taken for the reflected sound
wave (echo) to return to transducer.
- Successful measurement depends on reflection
from process material in a straight line back to
transducer.

20. Advantages / Applications:
 Unaffected by product density, conductivity /
dielectric constant.
 No moving part; device is non-contact with
process media.
 Single top vessel entry; leakage is less
probable.

21. Disadvantages / Limitations:
 Return signal may be affected by
- powders / particles.
- heavy vapour.
- surface turbulance.
- ambience noise.
 Inapplicable to vacuum & very-high-pressure
applications.

22. Radar:
 Microwave signal emission will burst towards
the process media.
 This burst is reflected by the surface and
detected by sensor.
 Level is inferred from the time of flight
(transmission to reception) of the microwave
signal.
 Microwave "echoes" are evaluated by sampling
and building up historical profile of the echoes.

23. Radar Types:
This design is suitable for
buffer & process tanks
This design is suitable for
requirement of high chemical
compatibility
Guided Type Regular Type

24. Guided-Type Working Principle:

25. Guided-Type VS Regular-Type:
Guided-Type Regular-Type
 Waveguide makes the signal less
vulnerable to distortion.
 Cannot be used if agitator is
present inside the vessel.
 Total non-contact solution for level
measurement.
 Agitator has little effect on the signal.

26. Advantages / Applications:
 Applicable to liquids & slurries application.
 Unaffected by
- extreme pressure / temperature.
- surface turbulence / agitation.
- steam / vapor / condensation.
- dense foam / dust / encrustation.
 No moving part.
 Single top vessel entry; leakage is less probable.
Low maintenance & easy installation

27. Disadvantages / Limitations:
 Inapplicable for interface-interface
measurement.
 Vapor effect can weaken the radar signal,
thus reducing its accuracy.

28. Nuclear
 Radioisotopes used for level measurement emit energy at a
fairly constant rate but in random bursts.
 Gamma radiation is generally used.
 Short wavelength and higher energy of gamma radiation
penetrates the vessel wall and process media.
 A detector on the other side of the vessel measures the
radiation field strength and infers the level in the vessel.
 Different radioisotopes are used, based on the penetrating
power needed to "see" the process within the vessel.

29. Advantages / Applications:
 Used when all other measurement types are
unsuccessful
 high pressure & temperature.
 toxic & corrosive media.
 Completely non-invasive; non-contact with process
media / atmosphere.

30. Disadvantages / Limitations:
 Expensive:
-maintenance
- periodic survey
- disposal is usually handled by licensed, external
authorities.

31. Level switch:
 Level switch is one type of level instrument that
performs.
 point level measurement.
 Level switch is used to indicate high or low level
alarm.
 A level switch is usually installed on the vessel as
addition to
 continuous-type level devices (for safeguarding
requirement).

32. Level switch:
- There are many types of level switches available:
 Float Switch
 Displacer Switch
 Thermal Switch
 Conductivity Switch
Measuring electrode

33. Advantages / Applications:
 Cost-effective: Economical method for point
level measurement.
 Compact: Easy mounting in small spaces.
 No moving parts: No wear and tear.

34. Disadvantages / Limitations:
 Level is not measured continuously.
 Intrusive-type: There is direct-contact with
process fluid.
 Its function as level alarm indicator can be
taken over by PLC.