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  2. Relay - Wikipedia

    en.wikipedia.org/wiki/Relay

    A relay allows circuits to be switched by electrical equipment: for example, a timer circuit with a relay could switch power at a preset time. For many years relays were the standard method of controlling industrial electronic systems. A number of relays could be used together to carry out complex functions (relay logic). The principle of relay ...

  3. Protective relay - Wikipedia

    en.wikipedia.org/wiki/Protective_relay

    A variant application of the attraction principle is the plunger-type or solenoid operator. A reed relay is another example of the attraction principle. "Moving coil" meters use a loop of wire turns in a stationary magnet, similar to a galvanometer but with a contact lever instead of a pointer. These can be made with very high sensitivity.

  4. Numerical relay - Wikipedia

    en.wikipedia.org/wiki/Numerical_relay

    Digital/numerical relays provide a front panel display, or display on a terminal through a communication interface. This is used to display relay settings and real-time current/voltage values, etc. More complex digital relays will have metering and communication protocol ports, allowing the relay to become an element in a SCADA system.

  5. Solid-state relay - Wikipedia

    en.wikipedia.org/wiki/Solid-state_relay

    A solid state relay (SSR) is an electronic switching device that switches on or off when an external voltage (AC or DC) is applied across its control terminals. They serve the same function as an electromechanical relay , but solid-state electronics contain no moving parts and have a longer operational lifetime.

  6. Output signal switching device - Wikipedia

    en.wikipedia.org/wiki/Output_Signal_Switching_Device

    External Device Monitor (EDM). The device issuing the OSSD signals may have an EDM input. The EDM is used to verify that the controlled device (safety relay) did indeed open when the OSSD signals were dropped. The safety relay has normally closed contacts, which close when the relay is de-energized, thereby turning on the EDM input.

  7. Relay logic - Wikipedia

    en.wikipedia.org/wiki/Relay_logic

    Example Ladder Logic Diagram. The schematic diagrams for relay logic circuits are often called line diagrams, because the inputs and outputs are essentially drawn in a series of lines. A relay logic circuit is an electrical network consisting of lines, or rungs, in which each line or rung must have continuity to enable the output device. A ...

  8. Mercury relay - Wikipedia

    en.wikipedia.org/wiki/Mercury_relay

    Normally closed mercury relay, with coil around top of tube and adjustable angle. A mercury relay (mercury displacement relay, mercury contactor) is a relay that uses mercury as the switching element. They are used as high-current switches or contactors, where contact erosion from constant cycling would be a problem for conventional relay contacts.

  9. Static relay - Wikipedia

    en.wikipedia.org/wiki/Static_relay

    In electrical systems, a static relay is a type of relay, an electrically operated switch, that has no moving parts. [1] Static relays are contrasted with electromechanical relays, which use moving parts to create a switching action. Both types of relay control electrical circuits through a switch that is open or closed depending upon an ...