Level Switches

Table of Contents

What are Level Switches?

A level switch is a way to detect the level of a liquid, powder or granulated materials in a container. There are few different types of level switches but they all serve the same purpose. When the conducting liquid reaches a certain height in the tank, a circuit is changed or completed and will output a signal or alert to the liquid level. You can have a high-level or low-level switch [1].Level switches are used in a large variety of applications such as oil tanks, washing machines, and wells [2].

Types of Level Switches

There are three main types of float switches you can use, depending on the application.

• One type of level switches is a float switch. The switch floats on top of the liquid and responds to the level moving up or down with an internal sensor in the switch. This sensor can complete a circuit to form an alert for the surface level of the tank
• The second type of level switches is a capacitance switch. This works by having a probe hanging from a certain height into the tank, forming a two plate capacitor with the wall of the tank and the probe. When the level reaches the probe, a the capacitance changes between the probe and the wall due to the differing dielectric constant for the liquid compared to air. This triggers a change in the circuit for an alert to the changing level of liquid.

• The last type of level switch is a vibrating switch. This works by utilizing 2 hanging vibrating prongs, and when the liquid reaches the prongs, their frequency changes. A device picks up this change and sends an alert [3].

  Figure 1: A basic float switch [4]	Figure 2: A capacitance level transmitter [5]	Figure 3: A couple of different sizes of vibrating fork level sensors [6]

Applications for Level Switches

Design Parameters for Level Switches

Switch Type

• Electromechanical Switch-These switches have mechanical contacts and can handle a much wider range of voltage and current. These are not affected by dirt or magnetic fields and can withstand up to 1000°C. These switches cost more, and do not last as long.
• Solid-State Switch-These switches do not having moving parts in the assembly. These are able to respond much faster than an electromechanical switch.

Electrical Configuration

• Normally Open (NO)-These circuits become closed when a "contact" is made (when the level reaches the specified height).
• Normally Closed (NC)-These circuits are closed and current runs, until the correct level is reached in the tank.