level measuring instruments, level measuring techniques, types of level measurements , direct and indirect level measurements.

1. Topic Level Measurement
Instruments
Presented to: Mr. Fahad Ali
Presented by: Mr. Rizwan
Mr. Tayyab

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Contents:
DIRECT LEVEL MEASUREMENT
1) Gauge glass
2) Floats
i. Ball float
ii. Magnetic type
iii. Chain type
INDIRECT LIQUID LEVEL MEASUREMENT
1) Pressure Level Detectors
i. Differential pressure type
ii. Bubbler tube
2) Electrical Methods
i. Capacitance level detectors
ii. Conductivity level detectors
3) Radiation Level Detectors
i. Radar/Microwave
ii. Ultrasonic
iii. Nuclear

3. DIRECT LEVEL MEASUREMENT
• Introduction:
The sensing and control of level or height of
materials in container or vessel is necessary in
many process industries and require proper
instrumentation techniques to be devised.
The level measurement dependent on factors like
density, temperature etc.
The most commonly used techniques are Gauge
Glass and Floats.
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1. Gauge Glass
This is the most simple direct method of level
measurement.
A transparent tube is attached vertically
adjacent to the vessel.
A scale is attached with the tube to give the
measurement of the liquid level.
The tube can be made of glass or plastic
depending on the process fluids temperature
and pressure.
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2. Floats:
Floats are based on the buoyancy principle, placed on
the surface or interface between two phases they are
motion balanced devices that move with the changing
level.
We have different types of floats.
1. Ball float
2. Magnetic type
3. Chain type
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1. Ball float:
• As the name indicates this type consists of a
float shaped like a ball.
• Hollow sphere of metal is most commonly
used.
• Material should have density less than the
density of liquid to allow it to float on the
liquid surface.
• It has a pulley like arrangement having a lever
attached to a rotary shaft.
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2. Magnetic type:
Float of magnetic material and coupling float to
actuate and read level on a scale.
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3. Chain type:
It is almost similar to ball type, the difference
is only that the weight of the float and
keeping chain have constant tension.
It is a direct measuring instrument.
The level is indicated by movement of the
counterweight over a reading scale.

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INDIRECT LIQUID LEVEL MEASUREMENT
Indirect level measurement involves converting measurements of
some other quantity in terms of height.
1) Pressure Level Detectors
i. Differential pressure type :
The pressure exerted by column of liquid in a vessel also known as hydrostatic
head is utilized to indicate the level of liquid in the vessel.
The weight or pressure of liquid in a vessel is directly proportional to its
height/level and density.

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Cont….
The differential pressure is created by taking higher pressure at
the bottom of the tank and lower pressure or atmospheric
pressure as reference.
When the vessel is not open to atmosphere or in a pressurized
vessel the lower pressure is also taken from the vessel usually at
the top.
The pressure sensors utilized for level measurement can be any of
the available for the pressure measurement.

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ii. Bubbler tube
This instrument essentially consists of a tube with its open end
inserted near the bottom of the tank.
Inert gas or clean air is forced out of the tube. As the gas flows
down to the tube’s outlet, the pressure in the tube rises until it
overcomes the hydrostatic pressure produced by the liquid level at
the outlet.
That pressure equals the process fluid’s density multiplied by its
depth from the end of the tube to the surface and is monitored by
a pressure transducer connected to the tube.

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Diagram:

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2) Electrical Methods
i. Capacitance level detectors
• In which an inner electrode and an outer
electrode which act as the plates of the
capacitor.
• Process fluid act as dielectric medium.
• As the liquid level rises, the capacitance is
changed because the dielectric medium
between the plates changes its level. Thus
capacitance is proportional to level
measurement.
ii. Conductivity level detectors
• It is a simple low cost instrument used for
point detection level measurement.
• An electric circuit is setup using electrode
probes inserted in the system.
• When the probes are immersed in the water
the conductive fluid completes the circuit on
contact with the probes and hence the
current is indicative that set level point is
achieved.

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Diagrams:
• Capacitance level detectors • Conductivity level detectors

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3) Radiation Level Detectors
Materials radiate and absorb energy waves or radiation.
This property has non-contact level detectors.
The working principle is same for all; a radiation source
directs radiations towards the process vessel.
A sensor or detector receives back the reflected/transmitted
radiation. Travel time or time of flight is calculated and is
measure of the level in the vessel.

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Diagram of Ultrasonic and Radiation level
detector:

17. FR Thank You.
M. Rizwan Jamil 2015-BT-CHEM-20
rizwanrss357@gmail.com
03016089774