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measurement of liquid level - Coggle Diagram
measurement of liquid level
To measure the quantity of liquid held in a container or vessel.
classification
direct
dip-stick method
Method
Determining the liquid level by dipping a graduated rod in a
liquid.
Application?
Level of oil in car engine.
Level of oil in petrol station
Advantages
Economic
Drawbacks
Not accurate
Method which the actual liquid level is directly indicated by a
simple mechanical type of device.
Sight Glass Method
Method
Determining the liquid level by a graduated glass tube mounted on the side of the liquid containing vessel for providing a visual indication of the liquid level
advantages
Simple & direct
drawbacks
Not suitable for dirty, viscous & corrosive liquids.
Hook Gauge Method
Method
Determining the liquid level in a large tank for accurate measure of a very small changes. A small change in a large tank would mean large volumetric changes.
Advantages
Accuracy up to +- 0.1mm.
Drawbacks
Manually operated and no automatic reading
Float Gauge Method
Method
determining the liquid level that always follow the varying liquid level. the float usually used are hollow metal spheres, cylindriacl ceramic float or disc shaped floats of synthetic material
Advantages:
Capable of giving continuous, direct liquid level
measurement
Drawbacks
Proper correction is required if there is a change in
the liquid density.
indirect
Ultrasonic level sensors
Used for non-contact level sensing of highly viscous
liquids, as well as bulk solids
They are also widely used in water treatment applications for pump control and open channel flow measurement.
Sound waves are directed towards the free surface of the liquid from an ultrasound transmitter.
These waves get reflected from the surface of the liquid and are received by the receiver.
Hydrostatic Pressure
•The hydrostatic pressure created by a liquid is directly related to the height of the liquid column (p = pgh).
a pressure gauge is installed at the bottom or on the side of the tank containing the liquid.
These gauges function smoothly when the liquids are clean and non-corrosive. For corrosive liquids with solid suspensions, diaphragm seals between the fluid and the pressure gauge are generally employed
The dial or scale of the pressure gauge is calibrated in the units
of level measurement
Automatic Level Control
The controller performs the function of the human in
evaluating the measurement and providing the output
signals, u and v, to change the valve setting via an actuator connected to the valve by mechanical linkage.
When automatic control is applied to systems, which are
designed to regulate the value of some variable to a set point,
it is called process control.
Liquid level affects both pressure and rate of flow in and out of the container and therefore its measurement and control becomes important to a lot of processes in modern manufacturing plant.
