How does a timing relay work?

How timing relay works — Answered:

Timer relay working principle:

Timing relays are divided into two classifications: the on-delay relay, and the off-delay relay. *The on-delay relay is sometimes referred to as a DOE or “Delay On Energize.” Off-delay relays are sometimes referred to as DODE or “Delay On De-energize.

Timing relays are similar to other relays in that they too use a coil to control the operation of contacts. The primary difference between a control relay and a timing relay is that the contacts of the timing relay delay changing their position when the coil is energized or de-energized.

In the diagram shown above, when the start button is pressed, both the control relay and the timing relay coils are energized. The control relay contacts react immediately and are used to provide seal-in for this circuit. Ten seconds after the TR coil is energized, the TR contacts on rung 3 will close. The symbol used for the TR contacts in rung 3 indicates that the contacts are NOTC, or normally open, timed closed.

Power off time delay relay circuit:

The operation of an off-delay timer is the opposite of the operation of an on-delay timer. The diagram shown here is typical of the circuit used to control a sump pump.

When the float switch in rung 1 closes, the TR contacts on rung 4 will immediately close, energizing coil M1. When the float switch opens, the timing period begins.

This example shows the TR contacts on rung 4 opening 15 seconds after the float switch opens. The symbol used for the TR contacts on rung 4 is NOTO, or normally open timed open.

It is important to note that some off-delay timing relays will operate by energizing and de-energizing of the coil. This is typical of both dashpot and pneumatic timers. Others such as the one shown here employ the use of a trigger switch, such as the float switch. In this case voltage to the coil is constant. The operation of the timing function is controlled by the operation of the trigger. This is typical of electronic timing relays.

Hopefully, this extra knowledge will help you better understand how to test a time delay relay. Learn more with the distance learning Motor Controls Course.