In this article, we will discuss the on-delay timer working. In on delay timer, the timer changes its contacts after reaching the preset time(On delay time).
As its name suggests the timer contacts changeovers after some delay. It means the timer does not change over its contacts until the preset time is reached.
The on-delay timer is used in the star-delta starter. The motor first connects in star and then after a lapse of on delay time the delta contactor picks up.
On Delay Timer Working
The on-delay relay timer changeovers the state of its contacts by controlling the energization of the timer. The time for which the on-delay timer is set or programmed is called the preset time. The Preset time can be set from milliseconds to hours and even days, depending on the applications. However, in industrial control and automation, it is set to seconds and minutes.
When the timer receives the power supply, the timer starts counting the time from zero to pre-set value. The duration of time from the energization of the timer to the pre-set time is the accumulated time of the timer.
When the accumulated time reaches the value of pre-set value, i,e. when the accumulated time equals the pre-set time, the timer changes its contacts. The timer’s close contacts open and open contacts close.
When the timer’s power supply is removed, the accumulated time reduces to zero, and the contacts return to their original state.
Timing Diagram of On delay Timer
The timing diagram of on delay timer is shown below.
When the timer is powered at the point ‘A’, it does not change its contacts instantly. It changes its contacts after a lapse of delay time. The on-delay time lapse at point ‘B’ and the timer changes its contacts from NO to NC and vice versa.