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FLOW MEASUREMENT & MEASUREMENT OF LIQUID LEVEL - Coggle Diagram
FLOW MEASUREMENT & MEASUREMENT
OF LIQUID LEVEL
MEASUREMENT OF LIQUID LEVEL
To measure the quantity of liquid held in a container or vessel.
Liquid level affects both pressure and rate of flow in and out of
the container
therefore its measurement and control becomes important to a lot of processes in modern manufacturing plant
Classification
Direct method
Method which the actual liquid level is directly indicated by a
simple mechanical type of device
Dip-stick 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 (moving fluid)
Not possible for real
time observation
Sight Glass Method (Piezo-meter)
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 (clean & coloured liquids)
Drawbacks
Not suitable for dirty, viscous & corrosive liquids
Manually recording needed
Float Gauge Method
Determining the liquid level always follow the varying
liquid level.
The float usually used are hollow cylindrical ceramic float or disc shaped floats of synthetic
material
Working Principle
consists of
Float
Counter Weight
Keeps the chain/tape taut as the liquid rises or falls with any change in the liquid level
a flexible connection that may be a chain or a thin metallic perforated tape
The chain attached on a gear or sprocket wheel to which the point is attached
Any movement of this wheel would indicate on a suitably calibrated scale the level of liquid in the tank
A floating body, because of its buoyancy, would always follow the varying liquid level
Therefore, float-operated devices such as Float Gauge are capable of giving continuously, direct liquid level measurement.
The floats generally used are hollow metal spheres, cylindrical ceramic floats/disc shape floats or synthetic material.
The top of the float is usually made sloping so that any solid suspensions in the liquid do not settle on the float and change its weight
Advantages
direct liquid level
measurement
Capable of giving continuous
Drawbacks
Proper correction is required if there is a change in
the liquid density
Hook Gauge 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
Drawbacks
Manually operated and no automatic reading
Accuracy up to +- 0.1mm.
Working Principle
In this device, a vertical tubular rod is provided a vernier scale to
be clamped at a suitable height at the upper end and a U-shaped
hook at the lower end.
This rod moves in a guide bracket fixed to a rigid body at the
datum or reference level has a main graduated scale in it
The movable rod is brought downwards so that the hook is
pushed below the surface of the liquid
It is then gradually raised until the top of the hook breaks through
the surface of the liquid
1 more item...
In a large tank/reservoir, a small change in level would mean
large metric changes.
For such applications, a simple hook gage
is quite suitable
Indirect method.
Ultrasonic Level Sensors
Used for non-contact level sensing of highly viscous
liquids, as well as bulk solids
Widely used in water treatment applications for pump control and open channel flow measurement
In this technique, liquid level variations are quite accurately determined by
detecting the total time taken by the wave to travel to the liquid and then back to the receiver
The longer these times travel, the farther away is
the liquid surface
Sound waves are directed towards the free surface
of the liquid from an ultrasound transmitter
waves get reflected from the surface of the
liquid and are received by the receiver
Hydrostatic Pressure Level Measurement Device
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