What Is the Difference Between a Relay and a Switch?

Industrial automation is becoming a popular strategy for companies looking to reduce costs, increase productivity, and enhance the quality of their products. In order for an industrial automation system to work effectively, several intelligent devices must be employed. These devices typically have a sensory or modulatory function and must give feedback to external consoles, such as PCs. Two of these devices which are widely used but sometimes confused are relays and timers. In this blog, we will discuss the function and differences between these two devices.

A relay is a type of switch used to control a circuit by utilizing a low-power input signal. The basic form of these devices has long been used in applications ranging from telegraph circuits to early computers. Most relays work using electromagnetic properties. Specifically, they are designed with a wire coiled around an iron core, called a solenoid. These two components are surrounded by a yoke, which has a spring and moveable armature attached to it The armature is equipped with one or more contacts, which can make or break a circuit depending on its position. When an electric current is applied to the coil, the resulting magnetic field allows the armature to change location. For example, if no current is applied to the coil, the armature maintains a resting position, and there is no contact with an external circuit. However, when a current is applied to the coil, the armature will move and create a contact point with the adjacent circuit.

Timers also act as switches but are activated by a distinct mechanism with differing applications from a relay. While there are several classes of timers, they all work using similar principles. Specifically, these devices are triggered through a preset time variable and will alter the connection of a current when activated. In industrial automation, timers are generally split into three categories: automated timers, built-in timers, and motion timers. Automated timers are programmed either manually or with the use of an algorithm to control a group of devices. When implemented correctly, they improve energy efficiency by turning machines off during downtime. Built-in timers include machines or appliances with a timer function already embedded in them. A computer with a sleep timer is the most simple example of such a timer. Finally, motion timers are paired with motion sensors, the most common application being a light that automatically turns off after a certain period without detecting movement.

The biggest difference between a switch and a relay is the applications in which they are used. Relays are generally used to isolate circuits so that each one can be independently controlled. Additionally, they can be used to create logic pathways in which one relay can activate or inhibit the function of others. Timers, on the other hand, are used to control the operation of multiple devices at once. Additionally, relays are almost always considered active electronic components, meaning they require an external current to operate. Conversely, timers can be either active or passive depending on the design and application. Sometimes, timers are used to control the flow of electricity to a relay, in which case, the system is called a timer relay.


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