Level Measurement

Displacer Type Level measurement – Leveltrol

Principle of Level trol:

Working of level trol is based on the Archemedesprinciple which states that the resulting fluid pressure on the body acts vertically upward through the body’s center of gravity when a body is immersed in a liquid and is equal to the weight of the fluid that the body displaces.

The body hereafter will be called a displacer. The rise in level and the reduction in weight of the displacer are directly proportional.

Construction of Displacer

The spring balance is not a convenient level indication method and will be replaced by the “Torque tube” torsion spring.

This unique mechanism is used by almost all manufacturers of displacement type level measuring instruments to convert the displacer’s vertical movement into a rotating movement in the instrument for indication or transmission. Two main functions of the torque tube

The design of the torque tube varies from manufacturer to manufacturer

Working of displacer level measurement:

In operation, when the displacer hangs freely in the air and the displacer’s full weight acts on the torque arm, this will result in a torque on the length of the torque tube fixed at one end.

The torque tube will twist and the torque tube rod will twist as well when it twists. The torque tube acts as a spring here.

The twist on the torque tube will be reduced and the torque tube rod will rotate accordingly as the displacer loses its weight due to an increase in level.

This rotation is proportional to the displacer’s weight, which is also proportional to the level increase.

The following needs to be considered when selecting the torque tube material:

  • Capability of the material to resist corrosion.
  • Elastic properties of the material over a wide range of temperatures.
  • The nature of the fluid being handled.


Instrumentation Engineer

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