Reed relay is an electronic device which contains a reed switch, a coil that creates a magnetic field, a diode for managing the back EMF generated from the coil. It is a package encapsulated with different connection terminals. Reed relay is a device which makes use of low resistance metallic switch path.

Basic Overview of Reed Relay and its Working

Reed Switch

This switch is made up of two metallic blades. This is made up of ferromagnetic material which is sealed with glass material. This seal is called a hermetic seal which helps to prevent the contaminants from entering the critical area called the contact area. Mostly the reed switch is in open contact in normal state.

The presence of a magnetic field that is applied along the axis of the reed blades intensifies the magnetic field. The reed blades are, and this increases the magnetic field further. The open contact makes the reed blades to attract each other, and this deflects the blades. With the creation of the magnetic field, the blades touch each other and this result in electrical contact.

The reed switch does not contain any movable parts except the blade. This is because the switch does not include any pivot points which helps in movement. The switch area or the contact area is sealed hermetically by using a glass envelope and filling it with inert gas. You can also make use of a vacuum to fill the glass envelope. Sealing the contact area offers a long mechanical life.

The reed switch design is of variable size. The deflection of blades does not take place in case of longer switches. Deflections take place quickly in case of short reeds this because the short reeds are made up of thinner material. This creates a great impact on the contact area and its rating. With small reed switches, small relays can be constructed. It is better to make use of larger switches as it is mechanically robust with great contact area. This improves the signal carrying capability.

The contact area of the switch is made of several plating materials like rhodium, ruthenium, iridium which belong to the rare platinum group. These are wear resistant, hard and possess greater resistance stability. This is the reason for its long life and extended operation time. Tungsten is the preferred material in high voltage conditions due to its high melting point and resistance. The contacts of the reed switch can also be coated with other materials like electroplating and vacuum deposition.

Generating Magnetic Field

A reed relay operates with the help of the magnetic field created which closes the reed switch contacts. In reed relays the magnetic field is built with the help of the coil. The current is passed in between the coil. The axial magnetic field is generated by the coil which closes the reed contacts.

Different levels of the magnetic field should be generated to close the contacts of various types of reed switches.
The above is the basic overview of reed relay and its working.

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