39 Timer Circuits Overview

So far all the circuits we have been looking at have all used instantaneous contacts. Both motor starters and control relays have contacts that change their state as soon as the coil is energized.

If a circuit requires some sort of delay in timing action, perhaps for sequence control or safety purposes, then timing relays can be used to provide this function. For example, a conveyor belt system might have several motors installed in it. Starting each motor at the same time could induce a very large inrush current on the system. One way to minimize the effects of these inrush currents is to stagger the starting of the motors with on-delay timers.

If this same conveyor belt system was designed so that each segment fed onto the next and at the end of the work day each conveyor segment had to be cleared, using off-delay timers would allow the circuit to be arranged so that after pressing a single stop button, each of the motors continued to run for a limited time until all product was cleared off them.

Timers can also be used to provide both plugging and anti-plugging for certain circuits. Indeed the range of application for timers is nearly limitless.