Editing Relay (section)

=== Machine tool relay ===

A machine tool relay is a type standardized for industrial control of [[machine tool]]s, transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally open to normally closed status, easily replaceable coils, and a [[Design|form factor]] that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the [[programmable logic controller]] (PLC) mostly displaced the machine tool relay from sequential control applications.

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 logic is based on relays which energize and de-energize associated contacts.  Relay logic is the predecessor of [[ladder logic]], which is commonly used in [[programmable logic controller]]s.