How a TON (Timer on Delay) instruction works in PLC?

In PLC programming, Timer instructions are utilized to delay signals by a set length of time.

After Bit instructions, Timers are considered to be the most essential PLC programming concepts to understand.

TON (Timer on Delay) instruction Parameters

The TON instruction has 2 input and 2 output parameters.

IN Input

The IN Input parameter is utilized to initiate the timer. When this variable becomes True, the timer starts timing.

PT (Preset Time)

The PT (Preset Time) input parameter defines the timer’s top limit. When the timer has been running for this amount of time, it has elapsed and stopped timing.

Q Output

The Q output parameter specifies whether the timer has expired. It returns True if the timer has been running for PT (Preset Time) & False otherwise.

ET (Elapsed Time)

The ET (Elapsed Time) output parameter represents how long the timer has been operating. When IN is True, this value increases with each scan; when IN is False, it resets.

A timing diagram makes it easier to comprehend how the TON instruction behaves. The timing diagram below illustrates how a timer acts over time and when certain events occur.

Function of TON Instruction

At t0, the IN Input parameter changes to True, & the timer starts timing. Since then, the value of the ET output parameter has increased with each scan.

At t0 + PT, the ET value is equal to the PT input parameter. The timer has elapsed, & the output parameter Q is now True. Also, once the timer has ended, the ET value stops developing.

At t1, the IN parameter is set to False, & the ET value is reset to zero. As the ET value no longer equal the PT value, the output Q is False.

At t2, the IN parameter returns to True, and the ET value rises until t3, when the IN parameter becomes False. Because the ET value did not equal the PT value, the output parameter Q fails to turn into True.

Utilizing these parameters, TON instruction works in PLC.