PLC Ladder Logic Examples – Example 1

In this article, we are going to discuss another PLC ladder logic example of the output control system. To understand this concept, we have taken the example of lamps that will be controlled with the use of different switches and push-buttons.

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 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

In this ladder logic example, we will see how to draw a ladder logic diagram to control the different outputs of a system.

Problem Statement

Draw a ladder logic diagram to control the output as per the given logic. Make use of start and stop pushbuttons, 6 switches to turn on and off the 9 lamps.

Take a start and stop push button to turn on and off the system. Use switch 1 to turn ON Lamps L1, L2, L3, use switch 2 to turn ON Lamps L4, L5, L6, use switch 3 to turn ON Lamps L7, L8, L9.

Now next switches are used to turn OFF the lamps. Pressing Switch 4 will turn OFF lamps L1, L5, L9. Pressing Switch 5 will turn OFF lamps L3, L4, L8. Pressing Switch 6 will turn OFF lamps L2, L6, L7.

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 8 inputs, 9 outputs, and a memory. Among 8 inputs, 2 are push buttons, and the rest switch.

Address	Description	Type
I0.0	START PUSH BUTTON	INPUT
I0.1	STOP PUSH BUTTON	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
I0.7	SWITCH 6	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
Q0.4	LAMP L5	OUTPUT
Q0.5	LAMP L6	OUTPUT
Q0.6	LAMP L7	OUTPUT
Q0.7	LAMP L8	OUTPUT
Q1.0	LAMP L9	OUTPUT

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.

For a better explanation, we have divided the program into 4 networks. The function of each network is discussed below.

Network 1

It is the cycle Start and Stop network. Push Button (PB) is used for starting and stopping purposes.

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) and is stopped by pressing STOP PB(I0.1).

Network 2

Network 2 shows control of lamps L1, L2, and L3 with the help of different switches.

When switch 1 is pressed I0.2 turns ON resulting in turning ON the lamps L1, L2, and L3. Now if we press switch 4, the lamp L1 will turn OFF. Similarly, pressing switches 6 and 5 will turn OFF the lamps L2 and L3 respectively.

Network3

Network 3 shows control of lamps L4, L5, and L6 with the help of different switches.

When switch 2 is pressed I0.3 turns ON resulting in turning ON the lamps L4, L5, and L6. Now if we press switch 5, the lamp L4 will turn OFF. Similarly, pressing switches 4 and 6 will turn OFF the lamps L5 and L6 respectively.

Network 4

Network 4 shows control of lamps L7, L8, and L9 with the help of different switches.

When switch 1 is pressed I0.2 turns ON resulting in turning ON the lamps L1, L2, and L3. Now if we press switch 4, the lamp L1 will turn OFF. Similarly, pressing switches 6 and 5 will turn OFF the lamps L2 and L3 respectively.

Networks 2,3, and 4 can be combined to form a single network. The same is shown in the figure below.

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