Switching devices or contacts are widely used in various electrical or radio engineering devices. To increase the operational properties of the equipment, to extend the service life and increase the reliability of the connections, special sealed magnetically controlled contacts called reed relays are used.
The devices consist of a core made of soft magnetic material, to which contacts are connected through insulating gaskets. When a current is passed through a coil, a magnetic field appears in the core, which acts on the contacts and causes them to close. After stopping the supply of electric current through the coil, the contacts open.
Despite the use of various devices, today the reed relay is in many cases out of competition due to its ease of use, dry contact properties, galvanic isolation from batteries. It is still used in a variety of devices and circuits.
A reed relay is simply indispensable if it is necessary to ensure the durability and high reliability of the switching elements.
Reed switches are part of various sensors, position switches and
electromagnetic relays.
According to the functional features, reed switches are divided into switching, closing and opening ones. According to the design technological parameters of the device, they are divided into two categories: with mercury and dry contacts. The latter variety is practically no different from ordinary contacts. Mercury elements have a drop of mercury inside the glass sealed enclosure. This is necessary to wet the contacts during operation, which allows to improve the quality of the connection by reducing the transitional connection, and also helps to get rid of the rattling of the contacts.
The reed switch emits vibration or bounce when the contacts open or close. This results in a single response to multiple switching of the signal and a significant increase in response time. When these devices work in digital circuits, measures are taken to suppress side effects using triggers or RC chains.
In modern microcontroller boards, the bounce that creates a reed relay and other contacts is suppressed using software methods. However, this generally reduces the system performance.
Any reed switches in their design are presented in the form of a glass bottle, in the middle of which there are contacts. These elements are made as magnetic cores, which are welded at the ends to the cylinder. The outer ends of the core are needed to connect the device to an external circuit.
The most common are reed switches, the contact group of which works for short circuit. In such devices, each contact is made of an elastic ferromagnetic wire, flattened to a rectangular shape. To reduce the transition resistance and to increase the corrosion resistance, the contact surfaces are coated with gold, rhodium, palladium or silver and their alloys.