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Term Description
Solenoid An electrical coil equipped with a magnetic core. Energizing the coil moves the core. Removing the current lets the solenoid core return to its normal position. Solenoids move levers, open valves, and so on.
Source (Electrical) The ability to provide current flow.
SPDT Single-Pole Double-Throw - A three-terminal switch or relay in which one central terminal connects to either one of the other two terminals. This type of switch can alternately connect a signal to one of two devices.
SPST Single-Pole Single-Throw - A two-terminal switch or relay that can open or close one circuit.
SSR Solid State Relay - A solid state circuit that employs devices such as opto-couplers, transistors, and triacs to perform the function of a mechanical relay. See: Relay.
Supply Current The total current that a circuit requires from a power supply.
Suppression Diode A reverse-biased diode placed across a relay or solenoid coil. When the coil loses power, the diode provides a short circuit that quickly dissipates energy stored in the coil.
Surge Current A high charging current that flows into a power supply filter capacitor or similar circuit as the power is first turned on. Similar to inrush current.
Surge Suppressor A circuit that limits the effects of power surges. Devices such as metal-oxide varistors (MOVs), zener diodes, and fuses provide this function.
Switch An electronic or mechanical device that can connect one signal to a series of connections. Switches ideally have zero impedance when closed and infinite impedance when open.
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