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An introduction to electrical control components

Electrical components are utilised to power a series of events which control the functioning of a control panel. While some are manually operated such as light switches and can be simple to comprehend, others are electrically triggered such as control relays.

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There are simple electrical control components such as relays, which carry out a single function, and advanced components such as programmable logic controllers (PLC), which carry out multiple functions.

Control relays

These are an important component in electronic devices. In essence, a control relay is a component that opens or closes a switch to allow an electric current to flow through a conducting coil. They typically control the flow of power in circuits and are used in motors, power supply systems and transistors.

At a very basic level, a control relay, like those found at, contains an electrical coil in addition to a spring with both stationary and moveable electrical contacts.

One method of operation for this type of relay is that when an electric current flows through the coil, the magnetic field pulls shut the device’s switch. When the current stops flowing, the switch opens again.

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Timing relays

These are the next most basic control components that are electrically activated, according to Essentially, they are just control relays that have timers built in to them, to control the time at which their moveable contacts change position. They can act as a type of shock absorber which stops immediate, full motion when the current is switched on or off.

There are four basic types of time-delay relay contacts:

-Normally open, timed-closed contact.
-Normally open, timed-open contact.
-Normally closed, timed-open contact.
-Normally closed, timed-closed contact.

Timing relays are used in industrial control logic circuits. Examples include:

-Flashing light control
-Engine auto start control
-Furnace safety purge control
-Conveyor belt sequence delay

Programmable Logic Controller (PLC)

These are made up of a number of different components, such as timers and relays, that come together in one unit and they can be individually programmed.

Advantages of using a PLC:

-Price. A PLC is often cheaper than using a number of individual component parts.
-Size. A PLC is often smaller than many individual components combined together.
-Flexibility. You can reprogram a PLC more easily than having to rewire a number of individual control components.


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