2. Mechanical Method of Level
Measurement
1) Dipstick Method
2) Sight glass Method
3) Bob and tape method
4) Hook gauge method
5) Float gauges
6) Indirect method of level measurement
3. Hydraulic methods of Level
Measurement
This method uses pressure measuring devices.
A. Open topped vessels:
Level of liquid can be measured at bottom by
transducer
Level of liquid(h) related to pressure(p) is given
by
h=p/density of liquid *accl due to gravity.
4. Hydraulic methods of Level
Measurement Cont…
B. Sealed vessel:
Differential pressure of top and bottom of
tank is measured
Transducer used is diaphragm
h=diff press measured by transducers/ (density
of liquid *accl due to gravity)
5. Hydraulic methods of Level
Measurement cont…
C. Bubbler unit:
Consists dip pipe reaching till bottom
Steady gas is flown through it
Bubbles emerge from the bottom of the vessel
Nitrogen or even air is used.
Pressure in the tube is equal to liquid pressure
at bottom.
7. Electrical Methods of level
measurement
• A. Resistive method:
Called as contact point method.
Uses mercury column as conductor
Various resistances are connected at different levels
of liquid.
When liquid level rises, mercury column also
increases
So corresponding resistances are short circuited
Resistances are chosen such that 1/R is a linear
function of liquid levels. So we get step wise
measurement
9. Electrical Methods of level
measurement Cont…
B. Inductive method:
Based on variable permeability method.
Consists of two coils (l1 & l2) wound on steel tube
consisting conducting liquid.
Coils are in series aided through resistor
arrangement is excited by ac system
Value of coil inductance is used for predetermined level
of liquid in tube.
When level off liquid changes permeability changes
and hence inductance and hence output voltages
11. Electrical Methods of level
measurement Cont…
C. Capacitance method
• The capacitance for the basic capacitor arrangement
shown in Figure 1 can be computed from the equation:
C = E (εA/d)
where:
C = capacitance in picofarads (pF)
E = a constant known as the absolute permittivity of free
space
ε = relative dielectric constant of the insulating material
A = effective area of the conductors
d = distance between the conductors
13. Nucleonic method of level
Measurement
• A nucleonic gauge consists of a suitable source
(or a number of sources) of alpha, beta, gamma,
neutron or X ray radiation arranged in a fixed
geometrical relationship with one or more
radiation detectors. Most of nucleonic gauges are
based on a few most common nuclear
techniques.
• Basic principle states that absorption of beta or
gamma rays varies with amount of thickness of
liquid between source and detector
• So it becomes a function of liquid level
15. Ultrasonic method
• ultrasonic level instruments operate on the basic
principle of using sound waves to determine fluid
level. The frequency range for ultrasonic methods
is ~20–200 kHz, and sonic types use a frequency
of 10 kHz.
• A top-of-tank mounted transducer directs waves
downward in bursts onto the surface of the
material whose level is to be measured. Echoes of
these waves return to the transducer, which
performs calculations to convert the distance of
wave travel into a measure of level in the tank.
