Relay Definition, History, Symbol, Material and How it Work

Sort History of Relay

The relay has a long history dating back to the early days of electrical engineering. The first relays were developed in the 1830s by Joseph Henry, an American scientist and inventor. Henry's relays were used to amplify weak telegraph signals, allowing them to travel long distances over telegraph wires.

The modern form of the relay was invented in the 1870s by Joseph Swan, a British physicist and chemist. Swan's relay used an electromagnet to open and close a set of contacts, allowing it to control the flow of electrical current through a circuit.

Relays became widely used in the early 20th century as the demand for electrical power and automation increased. They were used in a wide range of applications, including telephone systems, electrical power distribution, and industrial automation.

Over time, the design and construction of relays improved, with new materials and technologies being used to make them smaller, more reliable, and more efficient. Solid-state relays, which use semiconductors instead of electromagnets to control the flow of current, were developed in the 1960s and have become increasingly popular in modern automation systems.

Today, relays are still widely used in automation systems, electrical control circuits, and other applications where the control of electrical power is required. They are an essential component in many industrial and commercial systems, helping to ensure safe and reliable operation.

Relay Definition in Automation System

Mualtry - In automation systems, a relay is an electrical component used to switch a high voltage or current circuit on or off using a low voltage control signal. Relays are commonly used in automation systems to control the operation of various devices, such as motors, pumps, valves, and lights.

A relay works by using an electromagnet to open or close a set of contacts, which are used to switch the high voltage or current circuit on or off. When a low voltage control signal is applied to the relay, it energizes the electromagnet, which pulls the contacts together or releases them, depending on the type of relay.

Relays can be controlled by various types of devices, such as switches, sensors, programmable logic controllers (PLCs), and other automation systems. They are often used in conjunction with other electrical components, such as contactors, fuses, and circuit breakers, to provide reliable and safe operation of automation systems.

Relays come in various types and configurations, depending on the specific application and requirements. Some of the common types of relays used in automation systems include electromagnetic relays, solid-state relays, thermal relays, and time-delay relays. Each type of relay has its own advantages and disadvantages, and the selection of the appropriate type depends on the specific application and requirements.

How Relay Work ?

A relay is an electrical device that works by using an electromagnet to open or close a set of contacts. Here is a simplified explanation of how a relay works:

When a low voltage control signal is applied to the relay, it energizes the electromagnet, which generates a magnetic field. This magnetic field pulls a metal armature towards the electromagnet, which in turn opens or closes a set of contacts.

The contacts are usually made of metal and are designed to carry high voltage or current. When the contacts are closed, current can flow through the circuit, allowing the device being controlled by the relay to operate. When the contacts are open, current is interrupted, which turns off the device.

The electromagnet in the relay works like a switch, turning the device being controlled by the relay on or off. The low voltage control signal used to energize the electromagnet is often provided by a switch, sensor, or other control device in the automation system.

The design of the relay and the specific materials used to construct it can impact its performance and durability. Factors such as the strength of the electromagnet, the type of contacts, and the environmental conditions in which the relay is used can all affect the reliability and effectiveness of the relay.

Type of Relay

There are various types of relays used in automation systems. Here are some of the most common relay types:

1. Electromagnetic relays: These relays use an electromagnet to open or close a set of contacts. They are commonly used in industrial control systems and power distribution applications.
2. Solid-state relays: These relays use solid-state components, such as transistors, instead of mechanical contacts to switch a circuit on or off. They are often used in applications that require faster switching times and higher reliability.
3. Thermal relays: These relays use a bimetallic strip or other temperature-sensitive element to open or close a set of contacts based on the temperature of the circuit. They are often used in applications that require overload protection.
4. Reed relays: These relays use a small, magnetically-activated switch to open or close a set of contacts. They are often used in low-power applications, such as in telecommunications and medical devices.
5. Time-delay relays: These relays provide a time delay before opening or closing the contacts. They are often used in applications that require a delay, such as in motor starting or lighting control.
6. Polarized relays: These relays have a permanent magnet that maintains the polarity of the contacts. They are often used in applications that require a stable, unchanging polarity, such as in telecommunications and audio equipment.

These are just some of the many types of relays used in automation systems, and the selection of the appropriate type depends on the specific application and requirements.

Relay Symbol

The symbol for a relay in electrical diagrams and schematics typically consists of a rectangle with an angled corner, which represents the housing or casing of the relay. Inside the rectangle, there are two parallel lines that represent the two sets of contacts, which are typically designated as normally open (NO) or normally closed (NC). The electromagnet is represented by a coil-shaped symbol, often located on one side of the rectangle. The low voltage control signal is typically shown as a dashed line entering the relay symbol.

Here is an example of a relay symbol:

In this example, the angled corner of the rectangle is on the upper left side, and the coil symbol is on the right side. The contacts are represented by the lines in the middle, with the normally open (NO) contacts above and the normally closed (NC) contacts below. The dashed line entering the symbol represents the low voltage control signal.