A relay is an automation component whose input size changes gradually. Once it reaches a predefined value, the output size changes suddenly. Relays can be electrical, mechanical, thermal, pneumatic, etc. They can be either DC or AC. Electromagnetic relays, based on their design, can be:
Electronic relays, depending on the control signal type, can be categorized as photo, thermal, sound, time, etc. They can be either contact or non-contact types. Key parameters of relays include: operating voltage or current, active coil resistance, contact type and quantity, maximum switching power or current, and activation/release times.
Finder relays, timer modules.