ON/OFF PLC Output with Switch using S7-1200 PLC

Explanation:-

When Start switch (SW1) will be pressed then Output (Lamp 1) will be on and Output (Lamp 1) will be turned off if switch will be turned off.

Program:- Write the ladder Logic for Above application.
Input List:
Start Switch-I0.0

Output List:
Lamp 1 -Q0.0

ON/OFF PLC Output with Switch using S7-1200 PLC

Explanation:-

When Start switch (SW1) will be pressed then Output (Lamp 1) will be on and Output (Lamp 1) will be turned off if switch will be turned off.

Program:- Write the ladder Logic for Above application.
Input List:
Start Switch-I0.0

Output List:
Lamp 1 -Q0.0

Motor Start/Stop operation with trip indication lamp

Application:-There is one machine in the factory, we want to start/stop motor using push button g from the panel. Give motor ON lamp and motor trip lamp on the panel. When motor is running ON lamp should be ON and if motor trip due to some problem, trip lamp should be ON. Write the PLC program in LAD and FBD language.

Solution:-Here we will make PLC program in the PLC so operator can operate motor from the panel and get indication on the panel. And also we will take inputs signal and outputs for our application

Diagram:-

 

PLC Program:-Write the PLC program from above application using LAD diagram language.

PLC program explanation:-

As per our application we wrote PLC program. In this program we have considered following inputs and outputs for our application. We can use any make PLC for our application.

Inputs:-

Start Button:-I0.0

Stop Button:-I0.1

Trip Input:-I0.2

Outputs:-

Motor:-Q0.0

Motor On Lamp: Q0.1

Trip Lamp:-Q0.2

Network 1:-In this network we are starting and stopping motor by push button. By pressing Start (I0.0) motor can be started and by pressing stop PB (I0.1), motor (Q0.0) can be stopped.

Network 2:-In this network we wrote the logic for motor ON lamp or indication (Q0.1). SO when motor is running, Motor ON lamp is also ON.

Network 3:-For safety purpose we have considered here trip lamp (Q0.2). So when trip signal (I0.2) is ON, trip lamp is also ON.

3 Phase Motor Control using PLC Ladder Logic

3 Phase Motor Control using PLC

This is PLC Program for Forward and Reverse control for 3 Phase Asynchronous Motor.Lear how to write PLC logic for 3 phase motor control logic using PLC.

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Water filling and Discharging Process

Water filling and Discharging Process

Water filling and discharging process used in idustry.Write PLC logic for the filling and discharging process using ladder language.

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Water filling and Discharging Process

Water filling and Discharging Process

Water filling and discharging process used in idustry.Write PLC logic for the filling and discharging process using ladder language.

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Explain equal instruction using example

Explain equal instruction using example

Application:-Explain Equal instruction in the PLC. Write PLC program for explanation using ladder diagram language.

Components:-Programmable logic controller, HMI panel, wires, 24 VDC lamp, 24 VDC power source.

Diagram:-

Explanation:-

Consider a simple example for explanation of equal instruction in the PLC. Here we have taken simple HMI (Human Machine Interface) for display and programmable Logic Controller (PLC) for programming. Take two value set value 1 and set value 2 for example. Here if both the value in the set value 1 and set value 2 equal then lamp will be ON. So we need to use == instruction for above example.

Enter 50 value in the set value 1 box and enter 50 value in the set value 2 box so lamp should be ON and if someone enter 25 value in the set value 2 box, lamp should not be ON.

PLC program:-

Write the ladder program for above application using ladder diagram language. Here for ladder logic we can use any supported PLC system like S7-1200, S7-300, S7-1500 or any other PLC which can support this instruction. For PLC logic we need digital inputs and outputs.

For our application lamp is digital output. Two set values from the HMI are input words.

Digital Output:-

Lamp=Q0.0

M Memory:-

Set value 1:-MW10

Set Value 2:-MW12

PLC program Explanation:-

In network 1 we tow values are compared with comparison instruction. Set value 1 (MW) is compared with Value 2 (MW12).Hence if both values are equal, lamp (Q0.0) will be ON.

In comparator instruction, two operands are compared, we can set data time in comparator instruction.

Latching and unlatching Circuit.

PLC Program for Latching and Unlatching Circuit

Problem Description:

In many basic conveying or water-filling systems, the operator manually controls a water pump to fill a tank. This requires the operator to:

• Start the pump manually and wait while the tank fills.
• Monitor the tank level continuously.
• Stop the pump manually when the tank reaches the High-Level sensor.

This approach is inefficient and prone to human error.

 

Automation Requirement:

The system should:

• Allow the operator to start the pump manually with a push button.
• Keep the pump latched ON (i.e., running continuously) after the button is released.
• Automatically stop the pump when the tank reaches the High-Level (sensor).
• Prevent the pump from restarting until the operator initiates it again.

 

Example Scenario:

Let’s consider a manual water conveying system where:

• A START pushbutton is used to begin pumping.
• A High-Level float sensor detects when the tank is full.
• A STOP condition is automatically triggered when the tank reaches this level.

Problem Diagram

Problem Solution

In this application, we consider a storage tank that is filled using a water pump. The system is equipped with the following components:

• One high-level sensor to detect when the tank is full.
• A control panel with:
• A START push button (PB) to manually start the pump.
• A STOP push button (PB) to stop the pump manually if needed.

The operation is as follows:

• When the operator presses the START PB, the water pump is energized to begin filling the tank.
• The pump continues to run until the high-level sensor detects that the tank is full.
• Upon detecting the high level, the sensor sends a signal to automatically stop the pump.
• This sequence is implemented using SET and RESET (Latch/Unlatch) instructions in the PLC to maintain the pump state between operator actions and sensor inputs.

Although the actual system includes a manual discharge valve for emptying the tank, it is not included in the logic control for this program.

Note: This same logic can also be implemented using relays in conventional control panels.

 

Program

Here is PLC program for Latching and unlatched circuit for output.

 

Network 1

 

Network 2

List of Inputs and Outputs

Input

Signal Description	Address
START Push Button	I0.0
STOP Push Button	I0.1
High-Level Sensor	I0.2
Low-Level Sensor	I0.3

 

Output

Signal Description	Address
Water Pump	Q0.0

 

Program Description

For this application, we are using a Siemens S7-1200 PLC programmed with TIA Portal software. The same logic can also be implemented using conventional relay-based circuits.

This program demonstrates a latching and unlatching circuit, commonly used in fluid control applications.

Network 1: Latching Logic (SET Instruction)

The START push button (I0.0) is used to start the water pump (Q0.0).

When pressed, it activates the SET instruction, latching the pump output (Q0.0).

A normally open contact of the Low-Level sensor (I0.3) is placed in series with the START PB to ensure the pump only starts if the tank is not already full.

A normally open contact of the Water Pump output (Q0.0) is also included to maintain the latched condition once the START PB is released.

 

Network 2: Unlatching Logic (RESET Instruction)

The High-Level sensor (I0.2) is used to stop the pump automatically when the tank is full.

A normally open contact of I0.2 is used with the RESET instruction to unlatch the output (Q0.0).

For manual stopping, the STOP push button (I0.1) is connected in parallel with the High-Level sensor input, providing an alternative way to reset the pump.

Runtime Test Cases

Inputs Condition	Output	Physical Result
I0.0 = 1 & I0.3 = 1	Q0.0 = 1	Water Pump ON
I0.1 = 1	Q0.0 = 0	Water Pump OFF (Manually)
I0.2 = 1	Q0.0 = 0	Water Pump OFF (Auto-Stop)