Timer Relays

Timer Relay:-   

Time delay relays are simply control relays with a time delay built in. Their purpose is to control an event based on time, the difference between relays and time delay is when the output contact open and close; on a control relay, it happens when the voltage is applied and removed from the coil: at which the contact can open or close before or after some time delay.

more about relay timers

On Delay timers:-    Upon application of an input voltage on the relay coil the time delay (t) begins. At the end of the time delay (t) the output is energized. Input voltage must be removed to reset the time delay relay and de-energize the output.

In general On delay timers provide delay to turn ON an NO contact (turn off an NC contact).

   Here

 Trg: represents trigger pulse or generally called power-supply to the coil.

 Q: notifies when the switching of output contacts occur (i.e. NO connects  and NC disconnects)

Ta: Refers to time period for which the delay is to be provided or can be  said that it is the time for which the timer counts.

Off Delay timers:- Upon application of input voltage to the coil, the output is energized at the same time. Once the input voltage to the coil is removed the time delay(t) begins and the output is de-energized at the end of time delay(t). It thus clarifies that an Off delay timer provides additional time to the output. And keeps it in the ON state even after the input voltage to the coil is removed (but only for pre-set time delay).

Here;

 Trg: represents trigger pulse or generally called power-supply to the coil.

 Q: notifies when the switching of output contacts occur (i.e. NO connects  and NC disconnects)

 Ta: Refers to time period for which the delay is to be provided or can be  said that it is the time for which the timer counts.

 R: is the reset pulse

Links for further clarification

• Some questions on relay
• Application requirements for time delay relays
• PDF file Relays Timers and Terminal Blocks.pdf