In this article, we are going to discuss another PLC ladder logic example of a lighting control system using 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 a lighting control system using PLC. One should note that these are the basic examples of PLC ladder logic examples for PLC ladder logic practices.
Lighting Control System
In this example, we will see to turn the lights of a building, office, or home on and off using switches.
Problem Statement
Draw a ladder logic diagram to turn ON and OFF the lights of an office. Suppose there are 5 rooms on a floor of an office and each room has a switch.
Pressing Switch 1 turns ON the lamps L1, L2, L3, and L4, Pressing Switch 2 turns ON the lamps L5, L6, L7, and L8, Pressing Switch 3 turns ON the lamps L9, L10, L11, and L12, Pressing Switch 4 turns ON the lamps L13, and L14, Pressing Switch 5 turns ON the lamps L15, and L16, and pressing switch 6 will turn OFF all the lamps.
Write down a ladder logic program for the lighting control system.
List of Input and Output Tags
In this example, we have used 6 inputs and 16 outputs. Each input indicates a switch and each output indicates a lamp.
| Address | Description | Type |
| I0.0 | SWITCH 1 | INPUT |
| I0.1 | SWITCH 2 | INPUT |
| I0.2 | SWITCH 3 | INPUT |
| I0.3 | SWITCH 4 | INPUT |
| I0.4 | SWITCH 5 | INPUT |
| I0.5 | SWITCH 6 | INPUT |
| Q0.0 | LAMP 1 | OUTPUT |
| Q0.1 | LAMP 2 | OUTPUT |
| Q0.2 | LAMP 3 | OUTPUT |
| Q0.3 | LAMP 4 | OUTPUT |
| Q0.4 | LAMP 5 | OUTPUT |
| Q0.5 | LAMP 6 | OUTPUT |
| Q0.6 | LAMP 7 | OUTPUT |
| Q0.7 | LAMP 8 | OUTPUT |
| Q1.0 | LAMP 9 | OUTPUT |
| Q1.1 | LAMP 10 | OUTPUT |
| Q1.2 | LAMP 11 | OUTPUT |
| Q1.3 | LAMP 12 | OUTPUT |
| Q1.4 | LAMP 13 | OUTPUT |
| Q1.5 | LAMP 14 | OUTPUT |
| Q1.6 | LAMP 15 | OUTPUT |
| Q1.7 | LAMP 16 | OUTPUT |
Lighting Control System Ladder Logic Diagram
In this 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.
Switch 1 of the ladder logic diagram of lighting control is shown in the figure below.
Switch 1 (N.O) and Switch 6 (N.C) are connected in series, while the output lamps are connected in parallel with each other. When Switch 1 is pressed, it turns ON and the outputs i.e. Lamp 1, Lamp 2, Lamp 3, and Lamp 4 turn ON. If switch 6 is pressed, it will disconnect the supply as switch 6 is N.C. and hence, the output lamps will also turn OFF.
The ladder logic diagram for switch 2 and switch 3 is the same. The figure below shows the ladder logic diagram for switch 2.
Switch 2 (N.O) and Switch 6 (N.C) are connected in series, while the output lamps are connected in parallel with each other. When Switch 2 is pressed, it turns ON and the outputs i.e. Lamp 5, Lamp 6, Lamp 7, and Lamp 8 turn ON. If switch 6 is pressed, it will disconnect the supply as switch 6 is N.C. and hence, the output lamps will also turn OFF.
The ladder logic diagram for switch 2 and switch 3 is the same and is shown in the figure below.
Switch 4 (N.O) and Switch 6 (N.C) are connected in series, while the output lamps are connected in parallel with each other. When Switch 4 is pressed, it turns ON and the outputs i.e. Lamp 13, and Lamp 14 turn ON. If switch 6 is pressed, it will disconnect the supply as switch 6 is N.C. and hence, the output lamps will also turn OFF.
The full ladder logic program of the problem is shown below.
Download lighting control system plc program, plc programming examples, and solutions pdf.
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