A relay is a switch that controls circuits electromechanically. It can perform many switching operations and is available in a wide variety of configurations, poles, and throws. Its basic function is to switch one circuit on or off by powering a different circuit with a low-power signal. Relays have a wide range of applications in everyday use, from controlling the headlights in a car to sending data over long distance telephone lines.
Relays have a variety of mechanical parts, including an iron core, control coil, movable armature, and contact sets. The most important component that influences dependability is the contact, which must be able to interrupt currents without causing excessive mechanical stress and friction. The type of current to be interrupted, size and frequency of interruption, and voltage of operation determine the selection of the appropriate contact material.
The mechanical elements of a relay are designed to allow it to operate over a wide range of conditions with minimal damage or wear. The design must also be capable of handling the load to which it will be subjected. For example, a relay used in a motor starter must be able to withstand the high vibration and shock loads that are common in these applications.
Inside the relay, the iron core is surrounded by a control coil. When the relay’s coil circuit is energized by a low-power signal, it creates a magnetic field that attracts and moves the movable armature. The movement of the armature opens or closes a set of contacts (depending upon the construction of the relay).
Most relays have two pins for DC supply, named the coil and common terminals. The common terminal functions as the output, while the other, called a normally open (NO) and normally closed (NC) terminal, connects to the device to be controlled. The NO and NC contacts are connected by force, often a spring, to the armature, so that when the relay is de-energized they will return to their normal positions.
While there are many different types of relays, they all share the same general architecture. A relay consists of an iron core, a coil of copper wire wound around it, and a movable armature with contact points. The armature is held by a metal yoke that is attached to the base of the coil, and the yoke is seated in a bearing.
The relay’s coil circuit and internal switching contacts have separate electrical ratings. The coil is usually rated for the amount of current that it can carry continuously, while the switching contacts are rated for their voltage and ampere rating. 중계