Basic PLC Exercise on Heater and Cooler for Students

Basic PLC exercise on heater and cooler based on the low-level and high-level temperature sensors for students.

Note: Before proceeding further with this PLC programming example please consider that this program is for education to learn ladder logic.

Heater and Cooler PLC Exercise

Problem Statement:

Design a PLC ladder logic for the following application.

We are using one toggle switch and two Sensors to control the Heater and Cooler.

If the Low-Temperature Sensor gets activated (temperature is below 25 degrees), a heater should run for 45 seconds.

If the High-Temperature Sensor gets activated ( Temperature is above 30 degrees), a cooler should run for 45 seconds.

Ladder Logic Videos

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This video explains the mentioned PLC problem statement with detailed steps.

Inputs and Outputs

Digital Inputs:

Start Button: I0.0

Low Temperature Sensor: I0.1

High Temperature Sensor: I0.2

Digital Outputs:

Heater: Q0.0

Cooler: Q0.1

PLC Program

Program Description

We have used Normally Open Contact for the Start Button(I0.0), Low-Temperature Sensor (I0.1), and High-Temperature Sensor (Q0.2).

In Rung 0:

1. Normally Open Contact is used for Start Button (I0.0) and Low Temperature Sensor (I0.1) to turn ON the output Heater (Q0.0).
2. Timer-type TP is used to Turn ON the output Heater (Q0.0) for a limited time.

In Rung 1:

1. Normally Open Contact is used for the Start Button (I0.0) and High Temperature Sensor (I0.2) to turn ON the output Cooler (Q0.1).
2. Timer-type TP is used to Turn ON the output Cooler (Q0.1) for a limited time.

Program Simulation Results

We simulated our PLC program and analyze the results.

Rung 0:

When the Start Button (I0.0) is turned ON and the Low-Temperature sensor (I0.1) gets activated, the signal will flow through the Start Button (I0.0) and Low-Temperature Sensor (I0.1) as Normally Open Contact is used for the Start Button (I0.0) and Low-Temperature Sensor (I0.1).

The output Heater (Q0.0) turns ON for 45 seconds because Timer Function Block type TP is used to turn ON the output Heater (Q0.0) for a limited time and the time is set to 45 seconds. After 45 seconds, the output Heater (Q0.0) will turn OFF.

Rung 1:

When the Start Button (I0.0) is turned ON and the High-Temperature sensor (I0.2) gets activated, the signal will flow through the Start Button (I0.0) and High-Temperature Sensor (I0.2) as Normally Open Contact is used for the Start Button (I0.0) and High-Temperature Sensor (I0.2).

The output Cooler (Q0.1) turns ON for 45 seconds because Timer Function Block type TP is used to turn ON the output Cooler (Q0.1) for a limited time and the time is set to 45 seconds. After 45 seconds, the output Cooler (Q0.1)  will turn OFF.

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