PLC (Programmable Logic Controller) programming involves writing instructions or a set of codes to control the operations of machines or industrial processes. Here are the basic steps involved in PLC programming
Programmable Logic Controllers (PLCs) are an essential part of modern industrial automation systems. These devices are used to control and monitor a wide variety of industrial processes and machines. PLCs are programmed using specialized software that is designed to make the process of creating and editing programs as simple and straightforward as possible.
In this article, we will introduce you to the basics of PLC programming. We will discuss the programming software used to create PLC programs, the ladder diagram programming language, basic logic functions, the mnemonic code used in programming, and CX-Programmer, a popular programming software used in the industry.
Basic PLC Programming Concepts
Before we dive into the programming, let's first understand some basic concepts of PLC programming:
Inputs and Outputs - PLCs are designed to handle multiple inputs and outputs. Inputs can be sensors, switches, and other devices that detect changes in the process. Outputs can be motors, solenoids, and other devices that are controlled by the PLC.
Timers and Counters - PLCs have built-in timers and counters that can be used to control the duration of a process or count the number of operations.
Programming Languages - As mentioned earlier, PLC programming is written in ladder logic. Other programming languages such as function block diagram (FBD) and structured text (ST) can also be used.
Programming Steps - PLC programming involves the following steps:
- Understanding the process to be controlled
- Creating a program flowchart
- Translating the flowchart into ladder logic
- Testing the program
- Uploading the program to the PLC
Basic PLC Programming Instructions
PLC programming uses a set of instructions to control the inputs and outputs. Let's take a look at some basic instructions:
- AND - This instruction is used to check if two inputs are true.
- OR - This instruction is used to check if either of two inputs is true.
- NOT - This instruction is used to check if an input is false.
- Timer - This instruction is used to control the duration of a process.
- Counter - This instruction is used to count the number of operations.
- Set/Reset - These instructions are used to turn an output on or off.
- Compare - This instruction is used to compare two values.
Basic PLC Programming Example
Let's consider an example of a conveyor system that needs to be controlled by a PLC. The conveyor system has a start button, stop button, and a proximity sensor that detects the presence of an object on the conveyor. The PLC is programmed to start the conveyor when the start button is pressed, stop the conveyor when the stop button is pressed, and stop the conveyor when an object is detected by the proximity sensor.
The program flowchart for this process would look like this:
- If the start button is pressed, turn on the conveyor.
- If the stop button is pressed, turn off the conveyor.
- If an object is detected by the proximity sensor, turn off the conveyor.
Programming Software:
The programming software used to create and edit PLC programs is specifically designed to make the process as easy as possible. This software provides a graphical user interface that allows the programmer to create and edit programs using a range of different programming languages. Most programming software also includes a range of built-in debugging tools that can help the programmer to identify and fix errors in their code.
Ladder Diagram:
Ladder Diagram is a graphical programming language that is widely used in the industry. This programming language is based on a set of logic functions that are combined to create a visual representation of the control system. The ladder diagram is made up of rungs, which represent a single logic function or a combination of logic functions.
Basic Logic Functions:
Logic functions are the building blocks of PLC programming. These functions are used to perform logical operations on input signals to produce output signals. Some of the basic logic functions used in PLC programming include AND, OR, NOT, and XOR.
AND Function: The AND function is used to combine two or more input signals. The output signal of an AND function is true only when all input signals are true.
OR Function: The OR function is used to combine two or more input signals. The output signal of an OR function is true when any of the input signals are true.
NOT Function: The NOT function is used to invert the logical state of an input signal. The output signal of a NOT function is true when the input signal is false and vice versa.
XOR Function: The XOR function is used to combine two input signals. The output signal of an XOR function is true when the two input signals are different.
Mnemonic Code:
Mnemonic code is a programming language that uses a set of abbreviations and symbols to represent logic functions. This programming language is used to create more complex programs that cannot be easily created using ladder diagram. Some of the common abbreviations used in mnemonic code include LD (Load), AN (And), OR (Or), and NOT.
CX-Programmer:
CX-Programmer is a popular programming software used in the industry. This software provides a range of tools and features that make the process of creating and editing PLC programs as simple as possible. Some of the key features of CX-Programmer include a graphical user interface, support for a range of programming languages, built-in debugging tools, and support for a wide range of PLC models.
Conclusion:
PLC programming is an essential part of modern industrial automation systems. The programming software used to create PLC programs is specifically designed to make the process as easy as possible. The ladder diagram programming language is widely used in the industry, and basic logic functions such as AND, OR, NOT, and XOR are used to perform logical operations on input signals to produce output signals. Mnemonic code is used to create more complex programs, and CX-Programmer is a popular programming software used in the industry.