Please, someone tell me how positive displacement level detectors work.

 

I haven't heard the term applied to a level detector. It's usually applied to a Pump e.g. Gear or Progressive cavity type or Flowmeter, gear type. Anyway it's referring to the fluid being displaced by some form of solid object.

Roy

 

This covers a number of Instrument types but I would think you are referring to a level transmitter and you will see a typical one here:

http://www.masoneilan.com/internet/...ts/masoneilan/products/instruments/cu7000.pdf

Sandy

 

Magnetrol makes a displacer type level switch and displacer controllers...

See http://www.magnetrol.com/us/

 

So that's what you meant, "displacer type". The "positive" threw me off, it has no place in that context.

A displacer switch has a ceramic or stainless displacer suspended from a spring. When the displacer is immersed in fluid it gets lighter by the same weight as the fluid it displaces, the spring shortens and operates the switch. "A combination of Hooks Law and Archimedes Principle"

Roy