The document provides an extensive overview of liquid level measurement methods, including both direct and indirect techniques, critical for monitoring fluids in various industrial applications. It discusses specific devices like hook-type level indicators, sight glasses, and float-type sensors, as well as electrical methods such as capacitive and resistive levels. Additionally, it outlines the advantages and disadvantages of each method and their respective applications in different fields, including refineries, power stations, and chemical plants.

1. Presented by:-
1. Shreyas S. Muley

2. Contents
1. Introduction
2. Need for level measurement
3. Selection of Level Measurement Devices
4. Methods of Liquid Level Measurement
i. Direct Method
ii. Indirect Method
5. Direct methods
i. Hook type level indicator
ii. Sight glass
iii. Float type
6. Indirect methods
i. Hydrostatic Pressure type
ii. Electrical methods
iii. Ultrasonic level sensor
7. Electrical methods
i. Capacitive liquid level sensor

3.  Most industrial process use liquids such as water, chemical and fuels.
 These materials are stored in container ready for on demand use.
 It is very important to know the level and remaining volumes of these materials.
Introduction

4. Measurement of Liquid/solid Level:-
 Liquid level refers to the position or height of a liquid surface above a datum
line.
 Level measurements are made to a certain quantity of the liquid held with in a
container
 Level offers both the pressure and rate of flow in and out of the container and
as such its measurement and control is an important function in a variety of
processes.

5. Need for Level Measurement
Level measurement is important to monitor as well as
measure quantitatively the liquid content in
 Pressure Vessels, Reservoirs, Tanks.
 The liquid column height in open channel streams
 Level in fuel tanks of aircrafts

6. Selection of Level Measurement Devices
 Which substances need to be measured, for example, liquid, slurry, solid, interface, granular, or
powder.
 Specify whether the level sensor can be inserted into the tank or kept outside.
 Decide upon the suitability of continuous level or point sensor for the given application.
 Specify whether the substance being measured is electrically conductive or not.
 State the type of output required i.e. analog, relay or digital display.
 Indicate the required temperature and pressure ranges depending upon the application.
 Specify the required level measurement range.
 Identify whether turbulence, foam or vapour arises at the surface of the liquid or not.
 Make out whether material under consideration coats or builds up on surfaces.

7. The task of liquid level measurement may be accomplished by following methods:-
1. Direct methods
2. Indirect methods
 Direct method use the varying level of the liquid as a mean of obtaining the measurement
and the indirect method use a variable that changes with the liquid level to accurate the
measuring mechanism
Methods of Liquid Level Measurement

8. 1.Direct methods
This is the simplest method of measuring liquid level. In this method, the level of liquid is
measured directly by means of the following level indicators:
1) Hook-type Level Indicator
2) Sight Glass
3) Float-type

9. Hook-type Level Indicator
When the level of liquid in an open tank is measured directly on a scale (the scale may be in the liquid or
outside it), it is sometimes difficult to read the level accurately because of parallax error. In this case a hook
type of level indicator is used.

10. Construction:
Hook-type level indicator consists of a wire of corrosion resisting alloy (such as
stainless steel) about ¼ in (0.063 mm) diameter. Bent into U-Shane with one arm
longer than the other as shown in Fig. The shorter arm is pointed with a °60 tater.
While the longer one is attached to a slider having a Vernier scale. Which moves over
the main scale and indicates the level.
Working:
In hook-type level indicator, the hook is pushed below the surface of liquid whose
level is to be measured and gradually raised until the point is just about to break
through the surface. It is then clamped, and the level is read on the scale. This
principle is further utilized in the measuring point manometer in which the measuring
point consists of a steel point fixed with the point upwards underneath the water
surface.

11. Sight Glass
A sight glass (also called a gauge glass) is another method of liquid level measurement. It is
used for the continuous indication of liquid level within, tank or vessel.
Fig. basic dig of sight glass level indicator

12. Construction and working:
 A sight glass instrument consists of a graduated tube of toughened glass which is
connected to the interior of the tank at the bottom in which the water level is
required.
 Figure shows a simple sight glass for an open tank in which the liquid level in the
sight glass matches the level of liquid in the tank, As the Ievel of liquid in the tank
rises and falls, the level in the sight glass also rises and falls accordingly.
 Thus, by measuring the level in the sight glass, the level of liquid in the tank is
measured. In sight glass, it is not necessary to use the same liquid as in the tank.
Any other desired liquid also can be used

13. Ranges
 The standard practice is not to go for a glass tube of more than 900 mm length
 Two or more sight level gauges are provided at different levels if the height of the tank is
more than 900 mm
 This gauge is made to withstand pressures of 350 psi of steam pressure at 252ºC or 1000 psi
of liquid pressures
Advantages
 Direct reading is possible.
 Special designs are available for use up to 316ºC and 1000 psi.
 Glass less designs are available in numerous materials for corrosion resistance

14. Disadvantages
1.Readings are noted where the tank is located which is not always convenient.
2. Since sight glasses are located on the outside the tanks, the liquid in the sight glass may freeze in
cold weather even though the liquid inside the tank does not, and thus, it may cause error in the
reading.
3. Heavy, viscous liquids or liquids containing material which fall out of solution and clog the tube
cannot be measured satisfactorily by a sight glass.
4. Overlapping gauges needed for long level spans.
5. Accuracy and readability depend on cleanliness of glass and fluid

15. Materials
 Simple glass or plastic material is used up to 30kg/cm² pressure and 200ºc
temperature
 A reflex type design where the tube is metal casting with a thick glass material
is used up to 36kg/cm² pressure and 550ºc temperature
Applications
 Refineries
 Off-shore
 Oil and gas
 Power stations
 Chemical plants
 Thermofluid oil installations
 Refrigerating plants
 Cyrogenic service
Fig. sight glass level
indicator

16. Fig. oil refinery
Fig. level measurement in
power station
Fig. oil and gas
measurement Fig. chemical industry

17. Float-type
• In this the float rests on the surface of liquid and follows the changing level of
liquid.
• The movement of the float is transmitted to a pointer through a suitable
mechanism which indicates the level on a calibrated scale
Fig. basic diagram of float type level indicator

18. Construction
• It consists of a float made of stainless steel or copper or phosphor bronze with
nickel plating to avoid rusting which rests over the surface of the liquid
• The float movement is transmitted to the pointer by a stainless steel or
phosphor bronze flexible cable wound around a pulley, and the pointer indicates
liquid level
Fig. float type level indicator with
scale

19. Types of floats
• The design of float is very important hence floats of
the following shapes are used
• Hollow metal spheres
• Cylindrical shaped float
• Disc shaped floats
Fig. Hollow metal spheres
Fig. Cylindrical shaped float
Fig. Disc shaped floats

20. Working
• When the liquid level rises or falls a buoyant force equal to weight of the displaced liquid is available
• It pushes the float up or down.
• The float movement is transmitted to a pointer through a suitable mechanism
• It indicates the level on a calibrated scale

21. Advantages
 Economical
 Reliable designs
 It is possible to read the liquid levels in tanks below ground level
 Operated at large temperature ranges
Disadvantages
 Limited to moderate pressures.
 Prone to corrosion if liquids and materials are not compatible.
 Does not work properly if placed in a slurry or liquid solution with surface particles.
 Buildup of material on the float causes changes in weight displacement.
 Can only be used with non-freezing fluids.

22. Applications
 Fire Water Towers
 Sump Pits
 Fuel Tanks
 Coolant Tanks
 Low Water Conditions
 Heater Protection
 Leak Detection
 Overfill Warning
 Spill Prevention
Fig. water heater
Fig. Water towers

23. Fig. overfill warning
Fig. in vehicle fuel system

24. Fig. coolant tanks

25. INDIRECT METHODS:
Indirect methods liquid level measurements converts the changes in liquid level
into some other form such as resistive, capacitive or inductive beyond force,
hydrostatic pressure … Etc. and measures them. Thus the change occurred in these
parameters gives the measures of liquid level.
Different types of indirect method are as follows:-
1. Hydrostatic pressure type
2. Electrical methods
3. Ultrasonic level sensor

26. Electrical methods
In an electrical method, the liquid level position is measured by converting the level
position into an electrical signal
Electrical methods are divided into two types:-
1. Capacitive
2. Resistive

27. Capacitance level sensors are used for wide variety of
solids, aqueous and organic liquids, and slurries. The
technique is frequently referred as RF as radio frequency
signals applied to the capacitance circuit. The sensors can
be designed to sense material with dielectric constants as
low as 1.1 (coke and fly ash) and as high as 88 (water) or
more. Sludges and slurries such as dehydrated cake and
sewage slurry (dielectric constant approx. 50) and liquid
chemicals such as quicklime (dielectric constant approx.
90) can also be sensed. Dual-probe capacitance level
sensors can also be used to sense the interface between
two immiscible liquids with substantially different dielectric
constants.
Since capacitance level sensors are electronic devices,
phase modulation and the use of higher frequencies
makes the sensor suitable for applications in which
dielectric constants are similar.
CAPACITIVE LIQUID LEVEL SENSOR:
Fig. basic dig of CPLL sensor

28. Working Principle
The principle of capacitive level measurement is based on change of capacitance. An insulated electrode acts as
one plate of capacitor and the tank wall (or reference electrode in a non-metallic vessel) acts as the other plate. The
capacitance depends on the fluid level. An empty tank has a lower capacitance while a filled tank has a higher
capacitance.
A simple capacitor consists of two electrode plate separated by a small thickness of an insulator such as
solid, liquid, gas, or vacuum. This insulator is also called as dielectric.
Fig. principle dig

29. Therefore, it is seen from the above relation that if A and D are constant, then the capacitance of a capacitor is
directly proportional to the dielectric constant, and this principle is utilized in the capacitance level indicator.
Where:
C = capacitance in picofarads (pF)
E = a constant known as the absolute permittivity of free space
K = relative dielectric constant of the insulating material
A = effective area of the conductors
d = distance between the conductors
This change in capacitance can be measured using AC bridge.
It is given by following equation:-
C = E (K A/d)

30. Measurement:
 Measurement is made by applying an RF signal between the conductive probe and the vessel wall.
The RF signal results in a very low 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 dielectric constant drops causing a drop in the capacitance
reading and a minute drop in current flow
 This change is detected by the level switch's internal circuitry and translated into a change in the relay
state of the level switch in case of point level detection.
 In the case of continuous level detectors, the output is not a relay state, but a scaled analog signal.
Level Measurement can be divided into three categories:
· Measurement of non-conductive material
· Measurement of conductive material
· Non-contact measurement

31. Non-conducting material:
For measuring level of non conducting liquids, bare probe arrangement is used as liquid resistance is
sufficiently high to make it dielectric. Since the electrode and tank are fixed in place, the distance (d) is
constant, capacitance is directly proportional to the level of the material acting as dielectric.
Conducting Material:
In conducting liquids, the probe plates are insulated using thin coating of glass or plastic to avoid short circuiting. The
conductive material acts as the ground plate of the capacitor.
Proximity measurements (Non-contact type measurements):
In Proximity level measurement is the area of the capacitance plates is fixed, but distance between plates varies.
Proximity level measurement does not produce a linear output and are used when the level varies by several inches.

32. While supplying liquid

33. While discharging liquid

34. Advantages of Capacitive level measurement:
1. Relatively inexpensive
2. Versatile
3. Reliable
4. Requires minimal maintenance
5. Contains no moving parts
6. Easy to install and can be adapted easily for different size of vessels
7. Good range of measurement, from few cm to about 100 m
8. Rugged
9. Simple to use
10. Easy to clean
11. Can be designed for high temperature and pressure applications

35. Disadvantages
1. Performance is severely affected by dirt and other contaminants as they change the dielectric constant
2. Changes in temperature affects the sensitivity
3. Measured fluids must have proper dielectric strength
4. Recalibration is required if measured materials changes in composition or moisture content
5. Probe length and mounting must suit the tank

36. Applications:
Capacitance Level Probes are used for measuring level of :-
1. Liquids
2. Powered and granular solids
3. Liquid metals at very high temperature
4. Liquefied gases at very low temperature
5. Corrosive materials like hydrofluoric acid
6. Very high pressure industrial processes.

37. Fig. measuring water level
Fig. fuel system

38. Fig. measurement of fuel level in automotive fuel tanks

39. Values of Dielectric Constants

40. Methods of mounting

41. References
1. nritech.edu.in/eLearning/MECH-4-1/IV-I-MECH-AE-I&CS-Unit-4.pdf
2. https://instrumentationtools.com/category/level-measurement/
3. http://coep.vlab.co.in/?sub=33&brch=91&sim=449&cnt=1
4. https://www.omega.com/literature/transactions/volume4/T9904-13-RF-CAP.html
5. https://www.slideshare.net/SrinivasaRao110/level-measurement-71235678?qid=ebf4391d-
28aa-40eb-94c9-b74233351adf&v=&b=&from_search=5
6. https://auto.howstuffworks.com/fuel-gauge1.html
7. https://www.liquidlevel.com/typical-applications/