What are the classifications of relays?

Update:23-04-2021
1. According to the working principle or structural characteristics of the relay:
1) Electromagnetic relay: an electrical relay that uses the suction force generated between the electromagnet core and the armature by the current in the input circuit to work.
2) Solid state relay: refers to a relay whose input and output are isolated with electronic components performing their functions without mechanical moving parts.
3) Temperature relay: A relay that acts when the outside temperature reaches a given value.
4) Reed relay: It is a relay that uses the reed action sealed in the tube and has the dual functions of the electric contact reed and the armature magnetic circuit to open, close or switch the circuit.
5) Time relay: When the input signal is added or removed, the output part needs to be delayed or time-limited before closing or disconnecting the controlled circuit relay until the specified time.
6) High-frequency relay: It is used to switch high-frequency and radio-frequency circuits with minimal loss.
7) Polarized relay: a relay that has a combined action of a polarized magnetic field and a control current through the magnetic field generated by the control coil. The operating direction of the relay depends on the direction of the current flowing in the control coil.
8) Other types of relays: such as optical relays, acoustic relays, thermal relays, instrumentation relays, Hall effect relays, differential relays, etc.
2. Classified according to the dimensions of the relay:
1) Miniature relays: relays with the longest side dimension not greater than 10 mm.
2) Ultra-small miniature relays: relays whose longest side dimension is greater than 10 mm but not greater than 25 mm.
3) Small miniature relays: relays whose longest side dimension is greater than 25 mm but not greater than 50 mm.
Note: For sealed or enclosed relays, the external dimensions are the maximum dimensions of the relay body in three mutually perpendicular directions, excluding the dimensions of mounting parts, terminals, crimping, crimping, flanging and sealing solder joints.
3. According to the load of the relay, it is divided into:
1) Micro-power relay: When the open circuit voltage of the contact is 28V DC, the (resistive) relay is 0.1A, 0.2A.
2) Weak power relay: When the open circuit voltage of the contact is 28V DC, the (resistive) relay is 0.A, 1A.
3) Medium power relay: When the open circuit voltage of the contact is 28V DC, the (resistive) relay is 2A, 5A.
4) High-power relay: When the open circuit voltage of the contact is 28V DC, (resistive) is a relay of 10A, 15A, 20A, 25A, 40A...
4. Classified according to the protection characteristics of relays:
1) Sealed relay: The contact and the coil are sealed in the cover by welding or other methods, and the relay is isolated from the surrounding medium, and its leakage rate is low.
2) Enclosed relay: a relay whose contacts and coils are sealed (unsealed) with a cover.
3) Open-type relays: relays that do not need a protective cover to protect electric shocks and coils.
The most commonly used relays in electronic production are electromagnetic relays and reed relays.