LEVEL MEASUREMENTS Flashcards
the height or depth of a liquid in a particular level
LEVEL
determination of the position of an existing interface bet. two media
Measurement of Level
probably the first of the process variable to be measured and controlled
Liquid Level
Reasons for Level Measurement
- Safety
- Economy
- Monitoring
importance of monitoring of level in bulk storage tanks
- Plant efficiency may be assessed and optimized
- Stock records may be kept
- Cost may be correctly allocated
In the OIL and GAS industries, level measurement is necessary to achieve the ff. objectives
- Compute the tank inventories of hydrocarbon liquid and utility liquid
- Protect Equipment such as columns, compressors, turbines and pumps from damage
- Protect operating and maintenance personnel against injury resulting from hydrocarbon, corrosive or toxic spillage
- Protect the environment from the release of objectionable liquids into the rivers and seas
- Control phase separation processes and product loading operations
Methods of level mesurements
- Direct method
2. Indirect method
Direct methods of level measurement
- Dip sticks and Lead Lines
- Sight Glass
- Chain or Float Gauge
simple, almost straightforward and economical
Direct Method
types of sight glass
- Magnetic
- Reflex
- Transparent
- Bi-color
it provides a continuous visual indication of liquid level in a process vessel or a small tank and more convenient than dip stick, dip rod and manual gauging tapes
Sight Glass
used in corrosive or hazardous chemical
Magnetic sight glass
Used in pressurized vessel (condenser, evaporator)
Reflex sight glass
most common in process wave, it can be changed (viscous and uncolored fluid)
Transparent sight glass
used in high pressure boiler steam drum, steam boiler
Bi-color sight glass
uses the principle of buoyant element that floats on the surface of the liquid and changes position as the liquid level varies
Chain or Float Gauge
connected by a chain or flexible cable and the rotating member of the pulley is in turn connected to and indicating device w/ measurement graduation
Float
depend on the material having a physical property which can be measured and related to level
Indirect or Inferred Methods
Indirect methods
- Buoyancy
- Hydrostatic head
- Sonar or ultrasonic
- Microwave
- Conductance
- Capacitance
- Radiation
- Weight
- Resistance
- Micro-impulse
the force produced by a submerged body which is equal to the weight of the fluid it displaces
Buoyancy
the force or weight produced by the height of the liquid
Hydrostatic head
materials to be measured reflect or afflect in a detectable manner high frequency sound signals generated at appropriate locations near the measured material
Sonar or ultrasonic
similar to ultrasonic but uses microwave instead of ultrasonic beam
Microwave
at desired points of level detection, the material to be measured ( or ceases to conduct) electricity between two fixed locations or between a probe and vessel wall
Conductance
the material to be measured serves as a variable dielectric bet. two fixed capacitor plates.
Capacitance
the material measured absorbs radiant energy
Radiation
the force due to weight can be related very closely to level when it’s density is constant
Weight
pressure of the measured material squeezes two narrowly separated conductor together; reducing overall circuit resistance in an amount proportional to level
Resistance
“time of flight”, electrical impulses launch and travels back in frequency directly proportional to the level of the liquid
Micro-Impulse
the force produced when a body is submerged into a liquid with a constany density is equal to the fluid displaced
Archimedes Principle
a special type of spring that acts in an upward direction in opposition to the weight of the displacer
(Twist Force)
Torque Tube
this method relies on the pressure of the measured liquid head to provide level indication
Hydrostatic Head or Differential Method
One of the oldest and simplest methods of level measurement is called the ________________
Air bubbler, air purge or dip tube
provide the bubbles
Totameter
empty space that remains
Ulage
Yung may laman
Fillage
the air pressure is nearly linear to the water pressure and therefore water depth
Bubbler Systems
used when contact is not desirable
sonar or ultrasonic device (normally referred to as “radar”)
measuring liquid level in vessel by bouncing a travelling wave off the surface of the liquid
Echo Based Level Measuring Device
designed for continuous, non-contact level measurement of liquids, pastes and slurries.
Microwave (Radar)
travel in speed of light of 2.9979x10^8 m/s in perfect vacuum
Radiowaves
operate on the principle of electrical conductivity
conductivity level switches
the property of a circuit that stores electrons and thus opposes a change in voltage in the circuit
Capacitance
an electrical component that consists of two conductors separated by a dielectric or insulator
Capacitor
Capacitance value is determined by:
- area of the conductors (plates)
- distance between the plates
- dielectric constant of the insulator between the plates
the material in the vessel which will determine the capacitance value when it rises and falls
Dielectric
advantages of capacitance level devices
- they contain no moving parts
- simple and rugged design is possible
- design for corrosive application is possible
- easy to clean
- sanitary design is available for food processing industry
- extreme temperature and pressure requirements are possible by careful design
- can be designed for explosion proof service
Limitations of Capacitance level devices
- measurement is subject to error caused by temperature changes affecting the dielectric constant of the material to be measured
- coating of the probe by conductive material causes error in measurement
- usually empirical calibration techniques are used
- in solids measurement, variations in particle size affect the dielectric constant
variations in particle size
- alpha particles
- beta particles
were first used in instrumentation and related industries in the early 1950’s
Nuclear Radiation
can be used for either point or continuous applications
Nuclear Radiation Measurement
In point measurement, there are two basic components:
- radiation source
2. detector with associated amplifier
the detector is usually a ________________ with a solid-state amplifier and associated power supplies
Geiger-Mueller tube
it use a weighing machine attached to the tank to weigh the liquid
Weight Method
A device that has gained performance in level applications consist of a tape type resistance-sensing element (called “METRITAPE)
used when feasible
Resistance Devices
