How Reed Switch Sensors Work and Their Structure

A typical reed switch sensor has the form of a small tube with a diameter of a few millimeters and a length of two to three centimeters. There are wires leading out of both ends of the tube for connecting the element to an electrical circuit. Inside the reed switch, there are two ferromagnetic blades positioned in such a way that they remain open in the absence of an external magnetic field, and no current flows through the element. However, if such a field appears, whether it comes from a permanent magnet or an electromagnet, an attractive force occurs between the blades. Sufficient magnetic field strength causes magnetization of the blades, eventually bringing them closer together, closing the circuit. When the magnetic field ceases to exist, the blades return to their original positions. The presented diagram describes the operation of typical reed switches, but there are more types available on the market, differing in construction, parameters, and applications. Designers often opt for reed switches with three terminals, known as COM. When choosing to use reed switches, it is important to remember that due to their construction, they are not suitable for heavy loads. Excessive current could cause an electric arc to form and damage the delicate ends of the blades, resulting in irreversible damage to the component.