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CHAPTER 6 FLOW MEASUREMENT & MEASUREMENT OF LIQUID LEVEL - Coggle…
CHAPTER 6
FLOW MEASUREMENT & MEASUREMENT OF LIQUID LEVEL
MEASUREMENT OF LIQUID LEVEL
To measure the quantity of liquid held in a container or vessel.
a. Direct method.
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.
Sight Glass Method (Piezo-meter)
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 (clean & coloured 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.
Float Gauge Method.
Method?
Determining the liquid level that always follow the varying liquid level. The float usually used are hollow metal spheres, cylindrical ceramic float or disc shaped floats of synthetic material
• Advantages of float gauges are sufficiently accurate when properly calibrated after installation.
b. Indirect method.
Ultrasonic level sensors
Used for non-contact level sensing of highly viscous liquids, as well as bulk solids.
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. (time travel technique)
Requires high degree of experience and skill to operate since the actual instrument is expensive.
Automatic level control using ultrasonic sensor to minimize operator involvement
To provide automatic control, thus, machines, electronics or computer replace the operations of the human.
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.
Hydrostatic Pressure Level Measurement Device
The hydrostatic pressure created by a liquid is directly related to the height of the liquid column (p = pgh).
The rise and fall of the liquid level causes a corresponding increase or decrease in the pressure p which is directly proportional to the liquid level h.
The dial or scale of the pressure gauge is calibrated in the units of level measurement
