PLC Ladder Logic Examples – Timers Example

We have discussed many PLC ladder logic examples on our blog and in this article, we are going to see another example. To understand this concept, we have taken the example of lamps that will be controlled by making use of timers.

PLC timers are internal PLC instructions that are used to delay input and output signals in the PLC program.

In this article, we are going to see how to draw a ladder logic diagram for controlling the lamp outputs using PLC timers. One should note that these are the basic examples of PLC ladder logic examples for PLC ladder logic practices.

PLC Ladder Logic Example – Using Timers

In this ladder logic example, we will see how to draw a ladder logic diagram to control the lamp outputs of a system using on-delay timers.

Problem Statement

Draw a ladder logic diagram to control the lamp output as per the given logic. Make use of On-Delay timers for this problem.

• Start the system using the start push button.
• Timer T1 receives an impulse from system memory to give output (lamp L1) after 2 seconds.
• Similarly, L2 turns ON after 4 seconds after receiving an impulse.
• Similarly, L3 turns ON after 6 seconds after receiving an impulse.
• Similarly, L4 turns ON after 8 seconds after receiving an impulse.
• In the end, all lamps turn off after 10 seconds after receiving an impulse.

Write down a ladder logic diagram for the above problem statement.

List of Input and Output Tags

In this PLC ladder logic example, we have used one input, 5 T-ON timers, and 4 lamps.

Address	Description	Type
I0.0	START PUSH BUTTON	INPUT
M0.0	CYCLE ON/OFF MEMORY	MEMORY
M0.1	STOP MEMORY	MEMORY
Q0.0	LAMP L1	OUTPUT
Q0.1	LAMP L2	OUTPUT
Q0.2	LAMP L3	OUTPUT
Q0.3	LAMP L4	OUTPUT
DB1	T-ON TIMER 2 SECONDS	TIMER
DB2	T-ON TIMER 4 SECONDS	TIMER
DB3	T-ON TIMER 6 SECONDS	TIMER
DB4	T-ON TIMER 8 SECONDS	TIMER
DB5	T-ON TIMER 10 SECONDS	TIMER

Ladder Logic Diagram

In this PLC ladder logic example, we have used Siemens S7-1500 PLC and Siemens TIA portal for programming a ladder logic diagram. The PLC we selected has a work memory of 250 kB, 24 V DC power supply with 24V DC 32 digital inputs, 16 digital outputs, 4 analog inputs, and 2 analog outputs on board.

The problem can be solved using 2 approaches.

1. Draw a ladder logic diagram by taking timers in parallel that receive an impulse from the push button.
2. Draw a ladder logic diagram by taking timers in series. The first-timer receives an impulse from the push button. This timer will give an impulse to the next timer in series after its predefined time.

Ladder Logic Example of Timer – Approach 1

To read the program well, we have divided the program into two networks.

Network 1

It is the cycle Start and Stop network. Start Push Button (PB) is used to start the cycle.

A Normally Closed (NC) input is taken for Stopping the cycle. A Normally Open (NO) input is taken to start the cycle. A memory (M0.0) is taken that will be used in further networks. This memory is latched to the Start PB.

The cycle is started by pressing START PB (I0.0).

Network 2

It is the main program network that contains 5 timers and 4 output lamps. All the timers are connected in parallel to each other. All the timers receive an impulse from the start push button at the same time.

Working of Network 2

• Timer DB1 receives an impulse from the start push button. T-ON timer will run for 2 seconds and it will turn on the lamp L1.
• Timer DB2 receives an impulse from the start push button. T-ON timer will run for 4 seconds and it will turn on the lamp L2.

• Timer DB3 receives an impulse from the start push button. T-ON timer will run for 6 seconds and it will turn on the lamp L3.
• Timer DB4 receives an impulse from the start push button. T-ON timer will run for 8 seconds and it will turn on the lamp L4.
• Timer DB5 receives an impulse from the start push button. T-ON timer will run for 10 seconds and it will turn off all the lamps.

Ladder Logic Example of Timer – Approach 2

In approach 2, network 1 is the same as that in approach 1. Only the change is in network 2.

In this approach, all the timers are connected in series with each other. Each timer has given a preset value of 2 seconds. Unlike approach 1, an impulse from the start push button is received only by timer DB1.

Working of Network 2

• Timer DB1 receives an impulse from the start push button. T-ON timer will run for 2 seconds. This gives an impulse for the next timer DB2 and it will turn on the lamp L1.
• Timer DB2 receives an impulse from the timer DB1. T-ON timer will run for 2 seconds. This gives an impulse for the next timer DB3 and it will turn on the lamp L2.
• Timer DB3 receives an impulse from the timer DB2. T-ON timer will run for 2 seconds. This gives an impulse for the next timer DB4 and it will turn on the lamp L3.
• Timer DB4 receives an impulse from the timer DB3. T-ON timer will run for 2 seconds. This gives an impulse for the next timer DB5 and it will turn on the lamp L4.
• Timer DB5 receives an impulse from the timer DB4. T-ON timer will run for 2 seconds and run the output of stop memory. This results in the stoppage of all the lamps.