AKTU syllabus based Level measurement, Industrial Measuring Instruments

1. Level
Measurement
Industrial Measuring Instruments(AKTU)

2. Defination
 Level is defined as the filling height of
a liquid or bulk material.
 The liquid level is expressed in terms
of length of the liquid column or in
terms of the pressure the column
exerts over a datum level.

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

4. Methods of level
Measurement
Two methods are generally used
in industries for measuring liquid
level.
◦ Direct Method
◦ Indirect Method

5. Direct Method
This is the simplest method of
measuring liquid level where the level
is measured directly by means of the
following liquid level indicators
◦ Sight Glass Level Indicator
◦ Float Type Level Indicator

6. Types of Level Measurement
 Float type gauge
 Purge method
 Differential pressure method
 Conductive and capacitive method
 Electromechanical method

7. Sight Glass
A sight glass (also called as gauge glass) is
used for the continuous indication of liquid
level within a tank or vessel
◦ Construction:- 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 liquid level is required
◦ Working:- as the level of the 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.

8. Sight Glass

9. Float type gauge
 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.
 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.
 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

12. Indirect Measurement Methods
The indirect methods are further classified in to the
following groups.
(i)Hydrostatic and (ii)Electrical
The hydrostatic methods are categorized in to
 Pressure gauge method
 Purge system
The electrical methods have two subclasses
 Capacitance method
 Radiation method

13. Differential pressure method

15. Capacitive Type
This is an electrical method for
measuring and indicating liquid level in
industries
Types of Capacitive Methods
◦ Variable Area Method
◦ Capacitive Voltage Divider Method
◦ Variable Dielectric Constant Method

17. The operation is based upon the familiar equation of
a parallel plate capacitor given by
C = K A/D
Where , C = Capacitance , in farad
K = Dielectric Constant
A = Area of plate, in m²
D = Distance between two plates, in m
if A and D are constant, then the capacitance is
directly proportional to the dielectric constant, and
this principle is used in the capacitance level
indicators.

18. Ultrasonic Level
Measurement Ultrasonic waves detect an object in the same way as Radar does it. Ultrasonic
uses the sound waves, and Radar uses radio waves. When ultrasonic pulse signal
is targeted towards an object, it is reflected by the object and echo returns to the
sender. The time travelled by the ultrasonic pulse is calculated, and the distance
of the object is found.
 Bats use well known method to measure the distance while travelling.
 Ultrasonic level measurement principle is also used to find out fish positions in
ocean, locate submarines below water level, also the position of a scuba diver in
sea.
 An ultrasonic level transmitter is fixed at the top of a tank half filled with liquid.
 The reference level for all measurements is the bottom of the tank.
 Level to be detected is marked as “C”, and “B” is the distance of the ultrasonic
sensor from the liquid level.
 Ultrasonic pulse signals are transmitted from the transmitter, and it is reflected
back to the sensor.
 Travel time of the ultrasonic pulse from sensor to target and back is calculated.
Level “C” can be found by multiplying half of this time with the speed of sound in
air.
The measuring unit final result can be centimeters, feet, inches etc.
Level = Speed of sound in air x Time delay / 2

20. Electromechanical level
Measurement
 A sensing weight is let down on a measuring tape via a counter
wheel.
 Tensile force of the weight is reduced as it hits the product surface.
 This is recognized, the direction of rotation of the motor reversed
and the tape rewound.
 As the sensing weight moves downwards, the revolutions of the
wheel are counted using a non-contact method.
 Every count pulse corresponds to a defined length. The level is
obtained by subtracting this length from the overall length (tank
height).
 Old seafarers used a weight on a rope to test the depth to the
bottom of the sea.
 In industrial level measurement, the basic idea of sounding is still
utilized in the electromechanical level system.
 Where other measurement methods are limited, applications
involving bulk solids predominantly use electromechanical level
measurements.

22. Thank You