Float switches are among the most widely used devices for liquid level detection in industrial applications. Understanding their working principles helps in selecting and applying them correctly.

Basic Working Principle

A float switch operates on a simple yet effective principle: a float containing a permanent magnet moves with the liquid level. When the float reaches a predetermined position, the magnetic field actuates a reed switch located in the switch housing or stem.

Key Components

Float: Contains a permanent magnet, designed to float on the liquid surface
Reed Switch: Hermetically sealed electrical switch activated by magnetic field
Stem/Housing: Guides float movement and protects electrical components
Process Connection: Mounts the switch to the tank

Switch Configurations

Float switches are available in different electrical configurations:

Normally Open (NO): Circuit closes when liquid reaches switch point
Normally Closed (NC): Circuit opens when liquid reaches switch point
SPDT (Single Pole Double Throw): Provides both NO and NC contacts
DPDT (Double Pole Double Throw): Two independent switch circuits

Mounting Configurations

Different mounting options suit various tank configurations:

Top Mount: Installed through tank top, float hangs down
Side Mount: Installed through tank wall, float moves vertically along stem
Bottom Mount: Installed at tank bottom, float rises with liquid level

Advantages

Simple and reliable mechanical operation
No external power required for basic versions
Cost-effective solution
Wide range of materials for different media
Easy installation and maintenance

Applications

Float switches are used in:

Water tanks and reservoirs
Fuel and oil storage
Chemical processing
Food and beverage industry
Marine applications
HVAC systems