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Latching and Unlatching Circuit Using Ladder Logic

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By Prathima

 What is PLC

A Programmable Logic Controller, or PLC, is a Micro controller Based Device  used for industrial automation. These controllers can make  automatic  for a specific process, machinery, Home Automation  or even an entire production line. Latching is used in plc as well as hardware circuit to make the circuit in continuously on condition.

 Latching Circuit in PLC

Generally Latching is a circuit used to keep the output continuously in on Condition. Latching is only applicable for the push button or switches which has spring act.
When you are using hardware circuit you can use relay or contactors, these two components is used to make load in on condition. In Below concepts we can understand the concepts of latching and unlatching circuit by using switches
  Case1: When you are using Toggle switch, latching is not required. Check in below circuit.
In this case toggle switch is used to on the motor, when switch is on motor gets on, toggle switch doesn’t have any spring action so when you activate the switch motor or load gets activated.
Case2: When we use push button it has spring action. It will on when you press the switch and it will  off when u release the push button. It will not on continuously.
 When we are using push button to on or off the heavy loads we need to use latching. Latching can be made by using Electromagnetic relay or contactors.
     Here we taken two Changeover Relay to make the circuit on continuously 
The above circuit showing that relay is acting as latching(Holding Circuit). When p.b is activated  relay get activated and motor gets activated continuously. In this case motor will  not off.

Latching and Unlatching Circuit.

Latching is nothing but load is in activated condition, Unlatching defines deactivation. In this circuit we taken two push button. i.e start and stop, Electromagnetic Relay is used for latching.
When  switch is pressed motor gets activated immediately and when stop p.b is on load will get deactivate.

accordance with  a stored program and generates outputs to control machine and process.


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