A Relay separates a high voltage circuit from a low power circuit and allows a microprocessor to control heavy electrical loads. Relays reduce costs by simplifying wiring and reducing engineering time.
A relay consists of an iron core delimited with the control coil, load contacts and control switch. When energized the coil produces magnetic field that makes the upper contact arm attract the lower one and close the circuit.
A Relay is an electromechanical device that allows a relatively small electric signal to switch a much larger electric signal. It has a coil circuit and a contact (or contact) circuit that are electrically isolated from one another.
The relay has a heavy-duty frame that holds and supports the mechanical parts inside. These include an electromagnet, a fixed set of switch contacts, a movable armature and a spring.
When the coil is energized the magnetic field produced around it attracts the armature, pulling it down onto the fixed switch contacts. The contacts close and complete the high current circuit between the coil terminals. The armature is then returned to its ‘at rest’ position by the tension of the spring.
To determine the condition of a relay’s contacts, you can connect a multimeter to its entrance and exit pins to see if they have continuity. If the contacts are ‘normally open’ or ‘normally closed’ you can use this information to determine whether the coil is functioning properly.
A relay is used to switch high current loads where the switching capacity of the in-line switch or existing circuit exceeds. Usually relays are configured with one central pole which is hinged or pivoted such that when the coil is fed with voltage (i.e. energised) it is pulled downwards by the electromagnetic action of the coil and joins with one of the side terminals of the relay known as the N/C contact.
When the coil is switched off the hinged armature is pushed back into its at rest position by a spring and disconnects the N/C contact. This completes a low current circuit between the two contact terminals and the relay is said to be de-energized.
The large reverse EMF that’s generated by the de-energized relay coil trying to discharge through the driver transistor causes instant damage so a flyback diode is always connected across the relay coil. Alternatively a suitably rated resistor can be used to perform the same function.
There are many types of relay module configurations. Relay modules come in different sizes and have a host of features that can make them suitable for a wide variety of applications.
One common type of relay is the Single-Pole, Single-Throw (SPST) configuration. This has two terminals that can be connected or disconnected and is usually used to control one device, such as a light.
Another common type is the Double-Pole, Double-Throw (DPDT) configuration. This has two poles that can be controlled and is often used for devices such as motors.
Other configurations include the Change-Over (CO) and Transfer contacts, which provide a “break before make” functionality. Also, there are ratchet and latching relays that are found in some electrical switches, such as low voltage breaker solid state trip units. These have settings and time current curves just like the standard relays. They may be labeled differently by the manufacturer.
Relays provide a means of controlling multiple circuits by one signal. Their use reduces noise in low voltage applications and prevents arcing in high voltage applications. Relays can be used in a variety of ways, with different configurations having specific features.
Relay has few mechanical parts like Electromagnet, movable armature, spring support/stand or yoke, contacts and a Coil, all arranged in a logical manner to perform their function. Its Plastic case can be separated to see all these internal components, their design and functionality.
When the coil is de-energized, it loses its magnetic property and the armature returns to its initial position. This is aided by a force which is approximately half the strength of the magnetic force, provided by spring or gravity. The movable armature makes or breaks (depending upon the construction) a connection with the contact(s). Change-over, or double-throw (DT), contacts control two circuits. Single-break (SB) contacts break a circuit in one place, while double-break (DB) contacts break the circuit in two places. 중계