Reed Switches are almost ubiquitously present in popular electronic devices. The switch operates in the presence of a magnetic field. It was first invented by Bell Laboratories in 1936. Actually, a reed switch contains two metal rods sealed inside a glass rod. In a typical switch, these metals rods are separated until a magnetic field is applied that force the metal rods to come in contact with each other. When in contact, these metal rods pave the way for the electric current to flow through the metal inducing an electric charge.
Where these Switches are used?
Reed switches are miniature devices, which are easily integrated into laptops, cell phones, and home security systems. Have you ever thought how is it possible for the laptop to switch off automatically whenever you close the lid? Similarly, most cell phones will turn off on flipping. These devices use a small version of reed switch that activates when it comes in contact with a magnet. Think of a reed switch as a draw bridge that has two gates. Whenever the switch is closed, the two gates are in contact allowing the traffic to pass. In our case, the traffic is the electric current. As soon as the two doors are separated, the flow of the current is halted. The entire purpose of a reed switch is to activate or de-activate an electric circuit.
Practical Use
Interestingly, these circuits can also be triggered the other way around. For example, we may want an alarm to activate when the two circuits are not in contact. If you have security alarm installed inside a house that is internally connected to a door or a window frame, then opening a door will disconnect the two metal frames triggering an emergency alarm. Likewise, a bank safe has a magnet attached to the frame that comes in contact with the door when it is close. As soon as the door opens, the magnet and the door panel will separate generating an electronic response. If required, a security guard sitting at a remote station can detect such an electric response on a computer screen.
What is Special about Reed Switches?
The two reed metal bars inside the glass rod are made up of magnetic material that acts more like a spring. Just as a spring recoils, the two metal rods are also extremely elastic. The protective casing around the reed switch is not made up of basic material. Instead, it is a special glass that is hard enough to protect the two metals from atmospheric corrosion. Therefore, these reed switches are routinely used in hazardous environments where normal glass will break up during explosive conditions. The special glass is an infrared-absorbing glass that can concentrate a heat source inside the sealing zone of the tube.