Method of Level Measurement

• Mechanical• Hydraulic• Pneumatic• Electrical• Nucleonic• Ultrasonic

Mechanical Method of Level Measurement

1) Dipstick Method2) Sight glass Method3) Bob and tape method 4) Hook gauge method5) Float gauges6) Indirect method of level measurement

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.

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)

Hydraulic methods of Level Measurement cont…

C. Bubbler unit:Consists dip pipe reaching till bottomSteady gas is flown through itBubbles emerge from the bottom of the vesselNitrogen or even air is used.Pressure in the tube is equal to liquid pressure

at bottom.

Pneumatic Method of level measurement

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

Electrical Methods of level measurement Cont…

• A. Resistive method:

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

Electrical Methods of level measurement Cont…

B. Inductive method:

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

spaceε = relative dielectric constant of the insulating materialA = effective area of the conductorsd = distance between the conductors

Electrical Methods of level measurement Cont…

C. Capacitance method

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

Nucleonic method of level Measurement

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.

Ultrasonic method