Float switches

What float-based measuring systems are there for level monitoring?

With float-based measuring systems for level monitoring, a distinction is made between float switches, level sensors and bypass level indicators. Float switches are used for the point-based limit level detection of one or several levels. Because they are simple, universally applicable and exceptionally reliable, float switches have a very wide range of applications. Depending on accuracy requirements, level sensors are available with reed chains or magnetostrictive measuring systems. Bypass level indicators are mounted on the side of the tank and are often combined with a magnetic display for a visual level indication.

What does a float switch consist of?

The measurement technology for level is based on buoyancy of a hollow body, the so-called float. Due to its low density and buoyancy, the float is raised when the level of the liquid rises and lowered when the level of the liquid falls. A float-based measurement technology uses the movement generated by the level change to measure the level. Modern float switches have a very sophisticated design. In its simplest form, a float switch is made up of the following components:

• A hollow float body with an enclosed magnet
• A guide tube for guiding the float
• Adjusting collars to limit the movement of the float on the tube
• A reed contact located inside

How does a float switch work?

A reed contact, also known as a reed switch, involves contact leaves that are located inside the hermetically encapsulated glass body. These contact leaves move towards or away from each other due to a magnetic field. If a float switch is used with a reed switch with the switching function of normally open and a magnetic field is applied, the contact leaves move towards each other. Current can then flow through the contact of the leaves and a switching signal can be detected. If a float switch with the switching function normally closed is being used, the contact leaves move away from each other and the current circuit is interrupted as soon as a magnetic field is applied. A further option is the use of a change-over contact, where three contact leaves are used within the glass body. Three contact leaves allow one normally closed and one normally open switch to be used simultaneously in each operating state.

To generate the desired switching signal, i.e. to close or open the contact leaves, a magnetic field must be applied. Adjusting collars are used to limit the movement of the float body at the desired position and are fitted by the manufacturer. Thus, when the level rises to the defined level, the defined switching signal can follow.

How do I find a suitable float switch?

To find the right float switch for your application, you should define the following parameters:

• Number of switch contacts / switching outputs
• Position and function of every switching output
• Guide tube length
• Electrical connection (e.g. PVC cable outlet)
• Process connection
• Material (stainless steel, plastic, …).