A reed relay consists of a reed switch (dry reed switch) and a durable magnet or an actuating coil. It is a switching element formed by sealing two magnetic and conductive reeds in parallel in a glass tube filled with lather.

How it works: If a permanent magnet is placed near a reed switch, or a coil is wound around the switch and current is passed through it, the two reeds will become magnetized by the magnetic field. Because the two reeds' proximal ends have different magnetic properties and are attracted to each other, they touch, connecting the controlled circuit. If the permanent magnet is removed, or the current flowing into the coil is cut off, the magnetic field disappears, and the reeds, relying on their own elastic force, break away from the contact, disconnecting the controlled circuit. Reed switches come in various sizes, ranging from miniature to small, ranging from the size of a grain of rice to large, similar to a pencil.

The actuating coil of a reed relay can be placed outside the reed switch, using the internal magnetic field of the coil to drive the reed switch. It can also be placed around the reed switch, using the external magnetic field of the coil to drive the reed switch (an iron core can be placed at the base of the coil to increase the driving force).

The characteristics of this relay are:

(1) The contacts are isolated from the atmosphere and the tube is filled with inert gas, thus preventing corrosion from external organic vapor and contacts, and greatly reducing the oxidation or carbonization of contacts caused by sparks;

(2) The reed is light and short, with a high natural frequency. The contact on-off action time is usually only 1 to 3 ms, which is 3 to 10 times faster than that of ordinary electromagnetic relays.

(3) Small size and light weight;

(4) The disadvantage is that the switch capacity is small, the contact resistance is large and it is easy to vibrate.

In addition to forming a reed relay with the coil, the reed switch can also be used very conveniently in conjunction with a permanent magnet. The permanent magnet can approach the reed switch from any direction to make it move. I will not go into details here.