Voltage relays switch current between circuits using an electrical or pneumatic signal. They are used in various applications, including home appliances and testing equipment. Electromechanical and solid state relays are the two main types, with solid state relays being more durable and efficient. Relays are classified by their load capacity and can be used for on/off control or logic applications.
Voltage relays are electrical devices whose primary function is to switch current from one circuit to another. Using a relay allows you to control a large amount of current with a small amount of current. The relay is activated remotely using an electrical signal. In some applications, the remote signal may be pneumatic.
Voltage relays can be found in a wide variety of applications. One of the most common and oldest uses is in the switching offices of the telephone and telegraph industry. They are also used extensively in automated test equipment and are found in most major home appliances and electronics, including computers.
In a typical relay, there is a lever that makes a connection with a contact. When the lever and the contact touch, the circuit is said to be closed. When the two components do not touch, the circuit is considered open. When the relay is actuated, the lever is moved from its current position to the other position, from open to closed or vice versa. This action is to transmit power from one circuit to another circuit.
One of the basic uses of these relays is for simple on/off control. An example of this would be a refrigeration system driving a compressor. When the compressor turns on, a surge of electrical current is required to initially turn it on. The relay is used to redirect, or relay, current to the compressor circuit at the appropriate time.
Voltage relays are also used in logic applications. This feature is especially popular in equipment used for testing. The voltage relay provides the ability to move current from one point to another in a defined logical sequence.
The two broadly defined categories of relays are electromechanical and solid state. There are a variety of different styles and types under each classification. Electromechanical relays contain moving mechanical parts. The action of the relay is activated by current flowing through a coil of wire, which creates a magnetic field to operate the relay. Magnetic force is used to move the contact lever, causing an open circuit to close or a closed circuit to open.
Solid state voltage relays use light from light emitting diodes to achieve relay activation. The lack of moving parts makes them more durable than electromechanical types. Also, solid state relays typically have faster reaction times, which makes them more efficient.
Another attribute relays are characterized by is the amount of load, or current, they can handle. In most cases, relays are classified as low voltage relays or high voltage relays. In general, high voltage relays operate at voltages above 5,000 volts. There are, however, applications where a high voltage relay with a lower power rating is used.
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