PLC Ladder Logic Examples – Example 4

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 with the use of different switches.

A switch is a device used to make or break the connection in an electric circuit. We use switches in our daily life. A common example of a switch is the on/off button in our homes and offices.

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

PLC Ladder Logic Example 4

In this ladder logic example, we will see how to draw a ladder logic diagram to control the lamp outputs of a system. Lamps are just a representation of output, one can take different parameters like motors, pumps as an output.

Problem Statement

Draw a ladder logic diagram to control the lamp output as per the given logic. Make use of only switches, don’t use push buttons.

• Take START switch to start the system.
• Turning ON switch 1 turns lamps L1 and L2 ON.
• Turning ON switch 2 turns lamps L3 and L4 ON.
• Turning ON switch 3 turns lamps L1 and L3 OFF.
• Turning ON switch 4 turns lamps L2 and L4 OFF.
• Turning ON switch 5 turns ON all lamps.
• Turning ON switch 6 turns OFF all lamps.

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 7 inputs, 4 outputs, and a memory.

Address	Description	Type
I0.0	START SWITCH	INPUT
I0.1	STOP SWITCH / SWITCH 6	INPUT
I0.2	SWITCH 1	INPUT
I0.3	SWITCH 2	INPUT
I0.4	SWITCH 3	INPUT
I0.5	SWITCH 4	INPUT
I0.6	SWITCH 5	INPUT
M0.0	SYSTEM MEMORY	MEMORY
Q0.0	LAMP L1	OUTPUT
Q0.1	LAMP L2	OUTPUT
Q0.2	LAMP L3	OUTPUT
Q0.3	LAMP L4	OUTPUT

Ladder Logic Diagram of Example 4

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.

Though it is a simple program, we have divided it into two networks. Please note that dividing the program into two networks doesn’t affect the program. In the Siemens TIA portal, you can divide the program into n number of networks for simplicity and better understanding of the program.

Network 1

It is the cycle Start and Stop network. This network has two switches i.e. start switch and stop switch and they are connected in series. The output gives a system memory that will be used in network 2.

Start switch (I0.0) is N.O and stop switch (I0.1) is N.C.

Network 2

Switch 1 (N.O) is connected in series to the output lamps L1 and L2. Similarly, switch 2 (N.O) is connected in series to the output lamps L3 and L4.

For lamp L1, switch 3 (N.C) and switch 5 (N.O) are connected in parallel. Similarly, for lamp L2, switch 4 (N.C) and switch 5 (N.O) are connected in parallel.

For lamp L3, switch 3 (N.C) and switch 5 (N.O) are connected in parallel. Similarly, for lamp L4, switch 4 (N.C) and switch 5 (N.O) are connected in parallel.

Working of Network 2

• When switch 1 is turned ON, lamps L1 and L2 turn ON. Similarly, when switch 2 is turned ON, lamps L3 and L4 turn ON.
• When switch 3 is turned ON, switch 3 (N.C) in the network becomes (N.O) and this will turn OFF lamps L1 and L3.
• When switch 4 is turned ON, switch 4 (N.C) in the network becomes (N.O) and this will turn OFF lamps L2 and L4.
• When switch 5 is turned ON, all the outputs i.e lamps L1, L2, L3, and L4 will turn ON.