releitä

Relays, or releitä in Finnish, are electrically operated switches that enable a low-power signal to control a higher-power circuit. A typical relay includes a coil, an armature, and a set of contacts. When current flows through the coil, the magnetic field attracts the armature, causing the contacts to open or close. Relays provide electrical isolation between the control circuit and the load circuit, and they can switch various types of loads, including AC and DC.

Types vary: electromechanical relays (EMR) with moving parts; solid-state relays (SSR) that use semiconductor switches; reed relays with sealed reed contacts; latching relays that hold their state after the coil is energized; automotive relays designed for vehicles.

Common contact configurations include SPST, SPDT, DPDT, and more, offering normally open and normally closed contacts. Key specifications include coil voltage and resistance, contact rating (current and voltage), contact arrangement, switching time, isolation voltage, and mechanical life. Coils are usually rated for low voltages (e.g., 3–24 V) and draw a small current relative to the load they control.

Relays are used in automation, control systems, telecommunications, and safety interlocks to interface digital logic with motors, heaters, pumps, or lighting. Solid-state relays offer fast switching, long life, and quiet operation but may have higher on-state leakage and heat losses. The concept has its roots in 19th-century telegraph technology and remains a foundational component in modern control systems, often complemented by relays in PLCs and relay-based logic.