A displacer level switch is a type of level switch that works by displacement. Displacer switches have a variety of variations, including a special kind of switch for use with containers that have surface wave action. This kind of switch is ideal for use in sumps, tanks, and containers where there is a smaller variation in liquid level. This design uses a spring to activate the switch rather than a float actuator. These switches are also idea for use with liquids that also contain solid particles.
The displacer level switch works on the buoyancy principle. The displacer is suspended from a spring. When the liquid covers the displacer sensor, the attractor moves up into the switch station magnet. This causes the magnet to pull into the sealing tube, which activates the output switch. When the liquid uncovers the displacer, the attractor is moved out of the magnetic field. This causes the output switch to turn off.
This system is ideal because it is controlled more by the weight of the liquid rather than the movement. In many cases, a float-actuated system can give inaccurate readings because simple movements in the liquid can cause the actuator to signal the switch to turn on or off at the wrong time. The spring system based on the weight that the liquid has on the spring is more resistant to faulty readings. This makes it ideal for use in moving water and containers that may also have solid particles, such as a sump tank. In general, a spring activated displacer switch is a little more expensive than a float-activated switch, but the higher level of accuracy makes it worth the higher cost in many industries.