Programmable Logic Controller (PLC) and Ladder Diagram
In this tutorial you will learn all the concepts of PLC, Ladder logic programs, How it works, why we need PLC, Why we use them and History of PLC in the field of Automation. So let’s talk about the Programmable Logic Controllers (PLC’s). The first question is what is a PLC?
Programmable Logic Controllers are probably sounded an awful lot like a computer yes it is. It basically specializes computer that made for industrial and other commercial applications. The basic difference between a normal computer or Microcontroller and PLC is that the PLC has more INPUT and OUTPUT capability. It can directly read voltages, switch inputs, digital inputs and also directly controls the output.
So, first of all, we learn what exactly mean of the Programmable Logic Controller.
Programmable Logic controller
What is the meaning of controller..? What is the importance of controller? When we say that the system is controlled the exact meaning of this is that we controlled the different parameters of a system. For example, if we
are controlling the vehicle either we control it by steering or by breaks or something else. If the speed is increased and we want to stop the vehicle what will we do, we remove the feet from the accelerator or press the breaks ultimately we add or remove something in the system. So controller controls different parameters which are ultimately affecting the system performance.
Now why it is called as a logical controller. In previous we see controller controls different parameters but the parameters with a certain logic. For example we have a controller for elevator If you are on the 3rd floor and calls a lift after getting in and pressing the button of ground floor and at the same time in 4th floor someone press the call button what exactly elevator perform first on that time..? does it go up and pick them first or does it come down to the ground floor first. To manage all that the logics will be used so called a Programmable logic controller.
PLC is basically a controller that you can program. So it’s the controller that works under the certain logic and that logic can be changed or can be altered by using a programming.
Why Use PLC in Automation
Where is the need of Automation? If you have 2 cars and have a chance to automate 1 car. Among of both cars, 1 is used only one time to travel between “A” to “B” area and second car travel daily from “A” to “B” area. Which of them car you are going to automate obviously the second car which needs daily working the same things. So PLC’s also used in Automation to do same things billions or trillions of time a day which is impossible for a human being or if it’s possible so humans actually can’t do same work again and again but the robots can they will not get tired. Another example for automation is picked and place robots that pick and placed things again and again. So automation is used for repetitive actions occurs and for automation PLC’s are highly recommended.
How PLC Works
General plc structure. In the middle, there is the main brain of PLC the controller. On the left side Inputs. Inputs have transistor and sensors. Depends on what is your requirement whether you want to monitor the flow and control it or you want to monitor the flow and control it or you want to monitor the Temperature and control it. Based upon that where ever the parameters you need to monitor that particular sensors are going to work as an input and all sensors coupled to PLC. Now this PLC on the other side is connected to the Output. Output has actuators. Now second Input in which PLC parameters process is based on some logic. Logic will be provided to PLC through the programming and there is special programming software for PLC programmings which will discuss later. After the process of plc for both inputs, we have actuators at the output side of Solenoid valve, servo motors, stepper motors etc. Between the Input, PLC, and Output there is insulator which is used for the safety of microprocessor of the PLC.
Programming (Ladder logic diagram)
Ladder diagram programming there are many other software for PLC programming. we used “WPL soft”. PLC is similar to the microcontroller and it is also connected to the computer. The logic that you want to perform the task you have to make in a program called ladder diagram and transfer it to PLC and PLC execute the program and come across some logic and then those logic controls the output.
First of all, we will see what are the components of ladder diagram
Ladder diagram consists of two vertical lines called power relay. It can also have horizontal lines. The program starts from the input power relay and ends at output power relay. In ladder diagram, all the inputs are represented as switches. There are two type of switches
- Normally open.
- Normally closed.
Normally open means it is in a normal condition like normal electrical buttons. For example, you have to ON fan and you turned the button ON then the electricity passed through it but at normal condition, before turning On the switch the fan is OFF.
In Normally Closed switch condition the electrical contact is made and the current flowing through it. But if you click to turn ON it. It will be going to turn off originally. At the output, there will be relay or Coil. Why we call it a ladder diagram the simple answer is its programming looks like a ladder so it is called as a ladder diagram.
This was the basic introduction to the Programmable Logic Controller (PLC) and Ladder logic.
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