PLC Steps – Your Guide to Industrial Automation

Timer Functions – TON, TOF, and TP

In this chapter, we will explore the three basic timer types used in TIA Portal programming: TON (On-Delay Timer), TOF (Off-Delay Timer), and TP (Pulse Timer). We will provide practical examples demonstrating their typical applications.

TON – On-Delay Timer

Function

Delays the activation of an output by a specified time after the input signal turns TRUE.

Example 1: Activate an Alarm 1 Second After Signal Arrival

• Objective: When the input signal becomes TRUE, the alarm output will turn ON after a 1-second delay.

SCL / Ladder Implementation

Create a new Function Block (FB) and prepare the structure. Use Ladder or SCL, not both

Call the FB to OB1 and map Input and Output

TOF – Off-Delay Timer

Function

Keeps the output ON for a specified time after the input signal turns FALSE.

Example 2: Keep Motor ON if Input is Lost for Less Than 1 Second

• Objective: Motor stays ON while the input signal is TRUE. If the input drops FALSE, the motor remains ON for 1 second before turning OFF.

SCL / Ladder Implementation

Create a new Function Block (FB) and prepare the structure

Call the FB to OB1 and map Input and Output

TP – Pulse Timer

Function

Generates a fixed-length pulse on the output when the input signal goes TRUE.

Example 3: Generate a 500 ms Pulse When Input is Activated

• Objective: When the input signal changes from FALSE to TRUE, output a 500 ms pulse.

SCL / Ladder Implementation

Create a new Function Block (FB) and prepare the structure

Call the FB to OB1 and map Input and Output.

Summury

Timer	Description	Typical Use Case
TON	Delays output ON after input TRUE	Delay alarms, soft start signals
TOF	Delays output OFF after input FALSE	Motor run-on timers, signal hold
TP	Generates fixed-length pulse	Pulse outputs, triggers, alarms

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