Electromechanical relays are switching relays that utilize mechanical action to close a circuit and create a path between a power source and a load. They have a number of advantages and disadvantages when compared to solid state relays. Solid state devices will tend to fail short circuit, whereas electromechanical relays will tend to fail as either an open or a short circuit depending on the type selected. Either failure mode may be an advantage or disadvantage depending upon the application.Advantages of electromechanical relays over their electronic counterparts include: no leakage current, very low series impedance (low power dissipation, no heat sink requirement), extreme temperature ranges supported, no low voltage droop effects when off, higher tolerance to ESD and high voltage spikes. Disadvantages include: moving part failure, overload causing contact damage due to arcing, wetting current requirements and contact arcing causing radio frequency interference (RFI). Electromechanical relays usually have a shorter lifespan than solid-state alternatives, but also offer the distinct advantage of extremely high isolation to the control circuit. The operation of the relay is typically controlled by a solenoid. Near this coil is a ferromagnetic element on a control arm that opens or short circuits the relay connections. When there is no current flowing through the solenoid, the control arm remains in its default position. When a control signal is present the solenoid is energized and the relay is in its on state. This could be short of open circuit off depending on the relay type. Solenoid produce voltage spikes when suddenly switched. For this reasons electromechanical relays need diode protection that clamps this spike to the ground. 더 읽기 읽기 안 함