A magnetic reed switch is a simple electromechanical device used to control or sense the presence of a magnetic field. It consists of two thin, ferromagnetic, and flexible metal reeds (usually made of nickel-iron) inside a hermetically sealed glass tube. The reeds are coated with a non-conductive material and positioned parallel to each other, but with a small gap between them.
The working principle of a magnetic reed switch is based on the behavior of these reeds in the presence of a magnetic field. When no external magnetic field is applied, the reeds remain separate due to their natural spring-like tension. This open position creates a gap between them, and the switch is in the "off" or "open" state.
However, when an external magnetic field is brought close to the reed switch, the ferromagnetic reeds become magnetized and attract each other. The magnetic force overcomes their spring tension, causing the reeds to snap together and make contact. This action closes the gap and completes the electrical circuit, turning the switch into the "on" or "closed" state.
The magnetic field required to trigger the switch depends on the specific reed switch's sensitivity and the strength of the magnetic field. Reed switches come in various sensitivity ratings to suit different applications.
One of the advantages of a magnetic reed switch is its simplicity and reliability. It has no mechanical parts other than the reeds themselves, leading to minimal wear and tear over time. As a result, reed switches often have a long operational life.
Magnetic reed switches are commonly used in various applications, including security systems, door and window sensors, flow sensors, automotive sensors, and proximity sensors. They are particularly useful in situations where a non-contact switch is required, or when a sealed switch is necessary to protect against harsh environments like dust, moisture, or corrosive substances.