Latching Cercuit (Controlling The motor by pressing Start Stop Button)

Latching Circuit for Motor Control – Ladder Logic Application

Objective

To control a motor using momentary Start and Stop pushbuttons. Once the motor is turned ON using the Start button, it should remain energized (latched) even after the Start button is released. The motor should turn OFF only when the Stop button is pressed.

 

Working Principle

• Start Button (I0.0):
  A normally open (N.O.) push-button. When pressed, it energizes the motor.
• Latching Logic:
  The motor output coil (Q0.0) is fed back into the same rung to maintain the ON state, creating a memory or latching loop.
• Stop Button (I0.1):
  A normally closed (N.C.) push-button. When pressed, it breaks the circuit and stops the motor by de-energizing Q0.0.

Ladder Logic Program

 Explanation

• Rung 1 energizes the motor output Q0.0 when all conditions below are true:
• The Start button (I0.0) is pressed.
• The Stop button (I0.1) is NOT pressed (i.e., remains closed).
• The motor output (Q0.0) is used in a parallel branch to maintain the circuit (latching).
• The latching branch ensures that once Q0.0 turns ON, it holds the rung logic true even if the Start button is released.
• Pressing the Stop button opens its normally closed contact, breaking the circuit and turning OFF Q0.0, thereby stopping the motor.

 

 

AND & OR Gate Opertion in Ladder language

AND & OR Gate Operation Using Ladder Logic

🎯 Objective:

Control two lamps using four switches through:

• AND Gate logic (series connection)
• OR Gate logic (parallel connection)

📘 Application Description

We have four input switches and two output lamps. Two control scenarios are implemented:

✅ Task 1 – AND Gate Logic (Series Connection)

• Inputs: SW1 (I0.0), SW2 (I0.1)
• Output: Lamp 1 (Q0.0)
• Logic: Lamp 1 turns ON only if both SW1 and SW2 are turned ON.
• Equivalent to: Q0.0 = I0.0 AND I0.1

✅ Task 2 – OR Gate Logic (Parallel Connection)

• Inputs: SW3 (I0.2), SW4 (I0.3)
• Output: Lamp 2 (Q0.1)
• Logic: Lamp 2 turns ON if either SW3 or SW4 is ON.
• Equivalent to: Q0.1 = I0.2 OR I0.3

🧠 Input/Output Assignment

Device	Address
SW1	I0.0
SW2	I0.1
SW3	I0.2
SW4	I0.3
Lamp 1	Q0.0
Lamp 2	Q0.1

 

Network 1 :-The first rung connects SW1 and SW2 in series—mimicking an AND gate.

https://plcscadaacademy.blogspot.com/

Network 2 :- The second rung connects SW3 and SW4 in parallel—mimicking an OR gate.

https://plcscadaacademy.blogspot.com/