An Introduction to Time Relays


Time relays are often referred to as timers – a relay is simply a switch that is electrically operated by a control. Today, most timers are either electromechanical or electronic, operating digitally. But both types of control are designed to switch electrical devices on or off. They do this using timing diagrams, which make use of their time interval – days, minutes and so on.

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Time Delay and Exact Switching

The timer can switch equipment off or on after a set delay, or interval, such as a number of hours after it was last activated. That’s what’s happening when the integrated timer in a TV displays a message asking whether it’s OK to shut down the TV, or the light switch in the hallway of a block of flats switches itself off a couple of minutes after being activated.

Alternatively, the timer can operate the switch on and off at precise times in the day, as a central heating timer does. The central heating control is electromechanical – the time clock slowly rotates, driven by a motor, and the switches are mechanically triggered when the clock arrives at the set time, usually by a circuit being completed.

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However, even in domestic use, many timers are now purely electronic. The timing is carried out by semiconductors, and the on and off functions by electronic switches. There are no mechanical moving parts. The 555 timer chip is perhaps one of the most widely used electrical control components ever produced to control on/off switches.

Combining Timing with Other Controls

Timers lend themselves to applications where timing is combined with another function. A common combination is a timer with a sensor. One of the most useful simple electrical control components from is a light sensor which senses that it is dark and sends a message to the timer relay to switch on an electric light.

Although there are different modes for timing relays, depending on whether they are used for exact time switch-on and switch-off functions or for delay switching, sophisticated controls can be built up from simple components by combining different timing relay operations and other equipment such as sensors.

However, there are now large numbers of relays that will implement a function such as a time delay before a switch-off that can be bought off the shelf for easy installation.

Written by Alex

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