Time delay relays, or timer relays are used to prevent two events or processes from occurring simultaneously by providing a time delay between them. Getting the right timer relays for your specific applications depends on what your particular requirements are as well as your understanding of how the various timer relays function. There are various types of timer relays available on the market for different applications. Below is a look at how some common timer relays available on the market today function.

ON Delay Timer

Timing begins immediately when input voltage is applied. Once the time delay period elapses, relay contacts transfer to the energised state. The relay contacts will remain in that state until power is cut off. Upon removal of power, relay contacts switch to the unenergised state. If power is disconnected before the delay has completed, the output relays will be turned OFF and the delay time will be reset.

Some typical applications of ON delay timers include pedestrian push buttons used to change light signals in high traffic work places where safety is a concern, self-triggered security alarm systems and start motors of automatic cars.

Interval ON Timer

As soon as input power is applied, relay contacts transfer to the energised state and the timing period starts. Once the time delay period has ended, the relay contacts will switch to the unenergised state. At this point, power must be shut down so as to reset the time delay. If power supply is turned OFF before the time delay interval has elapsed, the contacts will de-energise and terminate the time delay. A good example of a typical application of Interval ON timers include amusement park rides where a person rides for a specific period when a specific amount of money is inserted.

OFF Delay Timer

Generally, there is a delay between the time the input relay turns OFF and the time the output relay turns OFF. Upon application of power to the relay terminals, the timer is ready to turn ON a trigger. Timing begins when the trigger is released, and after completion of the set time delay, the output relay is de-energised. Any disengagement of the trigger over the course of the time delay will reset the relay and the output will remain energised. Some typical applications of OFF delay timers include the operation of car ceiling lights and staircase lighting installations operated with momentary switches.