How A Relay Works


Motion Control
July/August 1999


How do Relays work?

by Arnold Offner

Blue Arrow Introduction
White Arrow Input Voltages
White Arrow Relay Contacts
White Arrow Activating Relays
White Arrow Solid State Relays


Relays have two forms: electromechanical and solid-state. The former consists of a coil that causes mechanical movement of a contact set, while the latter has no moving parts. Both can interface to different control systems and, depending on the application, are used to either isolate sensing, counting or high frequency signals or to create a link between the same or differing voltage levels.


Not every control signal has the same voltage potential, yet systems from different manufacturers must share or communicate with one another. Using a relay allows digital (ON/OFF) signal transmission between different control components. Basically, relays are electrical switches that control electrical circuits by opening or closing contacts in other circuits. Manually, one could operate a switch every 300 milliseconds; however, relays have response times ranging from about 5 to 20 milliseconds, far faster than the human hand.
Blue ArrowInput Voltages


Arnold Offner is the interface product marketing manager at Phoenix Contact, Inc. Contact him at P.O. Box 4100, Harrisburg, PA 17111-0100; tel: (800) 888-7388;



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