1. Method of Level Measurement
Mechanical
Hydraulic
Pneumatic
Electrical
Nucleonic
Ultrasonic

2. Mechanical Method of Level Measurement
Dipstick Method
Sight glass Method
Bob and tape method
Hook gauge method
Float gauges
Indirect method of level measurement

3. Hydraulic methods of Level Measurement
This method uses pressure measuring devices.
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.

6. Pneumatic Method of level measurement

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

8. Electrical Methods of level measurement Cont…
A. Resistive method:

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

10. Electrical Methods of level measurement Cont…
B. Inductive method:

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

12. Electrical Methods of level measurement Cont…
C. Capacitance method

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

14. Nucleonic method of level Measurement

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.

16. Ultrasonic method