Relæer

Reläer are electrically operated switches that enable a low-power control signal to switch a higher-power circuit. They provide electrical isolation between the control side and the load side, and they can be used to invert, amplify, or interface signals in automation and signaling systems.

A typical relä consists of a coil, an armature, a set of contacts, and a housing. When the coil is energized, the magnetic field draws the armature, changing the state of the contacts; when the coil is de-energized, a return spring returns the armature to its resting position. This results in opening or closing of the load circuit.

Reläer come in several types: electromechanical relays (EMR) with moving contacts, solid-state relays (SSR) that use electronic switches, reed relays with a sealed reed switch, and latching relays that retain their state after a pulse. They are available in various contact arrangements (SPST, SPDT, DPDT, and multi-pole variants) and coil voltages (commonly 5–24 V DC, sometimes AC coils). Contact materials such as silver alloys (AgNi, AgCdO) are chosen for durability and low contact resistance. Relay ratings include coil power and load current/voltage, along with isolation voltage and mechanical life.

Solid-state relays offer fast switching and no moving parts but may have leakage currents and higher on-state voltage drop. Electromechanical relays can handle higher surge currents and provide tactile isolation, at the expense of wear and slower operation. Reed relays use a hermetically sealed contact in a small package and are suited for signal applications; latching relays require a second pulse to reset.

Reläer are used in industrial automation, automotive electrical systems, telecommunications, and control logic. Selection considers coil voltage, contact rating, switching speed, environmental conditions, and required isolation. Standards from UL, IEC, and others govern safety and reliability.