How do float switches and liquid level sensors work?

Float switches and other liquid level sensors are devices with the purpose of opening or closing a circuit as the level of a liquid rises or falls.

They are most commonly used to control or measure the flow of liquid in or out of the vessel, as with sump pumps or fuel level gauges, liquid level sensors can be found in a variety of different forms being used for countless different applications.

Most switches are normally ‘closed’, meaning the two wires coming from the top of the switch complete a circuit when the float is at its low point, resting on its bottom clip (for example, when the tank is dry).

To complete a circuit, float switches utilise a magnetic reed switch. The reed switch consists of two contacts sealed in a glass tube. When a magnet comes close to the two contacts, they become attracted to each other and touch, allowing current to pass through. When the magnet moves away, the contacts demagnetize and separate-breaking the circuit-.

Types of Float Switches:

  • Vertical Reed Float Switches
  • Horizontal Float Switches
  • Ultrasonic Liquid Level Sensors
  • Optical Liquid Level Sensors
  • Hydrostatic Liquid Level Sensors
  • Vertical Reed Float Switches

Properly used float switches have the potential to deliver millions of on/off cycles, for years of dependable operation.

Failures are typically due to overloading, regularly caused by spiking voltage.