AME Unit 9 Q10 – Answer

Nov 2020

Here’s an example of a floatation device that produces an output signal for remotely controlling the liquid level in a tank, along with a sketch:

Device: Magnetic Float Level Switch with Integrated Transmitter

Sketch:

  1. Tank: Depicts the storage tank containing the liquid being monitored.
  2. Float: A hollow, buoyant cylinder (shown in red) floats atop the liquid surface.
  3. Guide Rod: A vertical rod attached to the tank’s top guides the float movement vertically.
  4. Magnet: A permanent magnet is mounted inside the float, facing downwards.
  5. Reed Switch: One or more reed switches (magnetically sensitive switches) are positioned alongside the guide rod at predetermined levels within the tank.
  6. Wiring: Each reed switch connects to a dedicated wire running to the control unit.

Operation:

  • As the liquid level rises, the float moves up along the guide rod.
  • The magnet inside the float triggers the reed switch positioned at the corresponding level as it passes by.
  • The activated reed switch completes the circuit for its associated wire, sending an electrical signal to the control unit.
  • The control unit interprets the signal based on which reed switch was activated, indicating the liquid level reaching that specific point.
  • Depending on the system configuration, the control unit can then activate pumps, valves, or other devices to maintain the desired liquid level in the tank.

Benefits:

  • Non-invasive: No contact with the liquid, minimizing contamination or maintenance needs.
  • Reliable: Simple and robust design with minimal moving parts.
  • Customizable: Multiple reed switches can be used to create multi-level control.

Limitations:

  • Accuracy: Limited to discrete level readings at the positions of the reed switches.
  • Sensitivity: May not be suitable for highly precise level control requirements.

Alternative Options:

  • Float Switch with Mechanical Lever: Instead of reed switches, the lever attached to the float can directly activate switches or valves mechanically.
  • Hydrostatic Pressure Transmitter: Measures the pressure exerted by the liquid column, providing a continuous and more accurate level reading.

Choosing the right type of floatation device depends on factors like desired level control precision, system complexity, and cost considerations.