PLC (Programmable Logic Controller) is a key component in industrial automation systems. It is a device that is used to control and monitor machinery and processes in manufacturing plants, power stations, and other industrial facilities. A PLC technician is responsible for designing, programming, and maintaining the PLC systems. As a professional in this field, it is important to have a deep understanding of the basic working modes of PLC and the scanning process. In this article, we will explore these two aspects in detail.
The Two Basic Working Modes of PLC
There are two basic working modes of PLC – the Programming mode and the Run mode. These modes determine the overall functionality of the PLC system and are crucial for its proper operation.
Programming Mode
The Programming mode is used for creating, editing, and downloading the PLC program. In this mode, the technician uses a programming device, such as a laptop or a handheld programmer, to connect to the PLC and perform the necessary programming tasks. It is important to note that the PLC cannot process any input or output signals in this mode. Therefore, it is crucial to switch to the Run mode for the PLC to operate.
Run Mode
The Run mode is the operating mode of the PLC. In this mode, the PLC executes the program that has been created in the Programming mode. The PLC continuously scans the inputs and outputs and updates the program output according to the logic programmed. The Run mode is vital for the proper functioning of the PLC as it allows the PLC to control the industrial processes based on the programmed logic.
The Scanning Process
The scanning process is an essential part of the Run mode and is responsible for the PLC's overall operation. The scanning process involves three main steps – Input Scan, Program Scan, and Output Scan.
Input Scan
In the Input Scan step, the PLC reads the status of input devices connected to it. These input devices can be sensors, switches, or other devices that provide information about the process or machinery. The PLC continuously monitors these inputs and updates the input status in the memory.
Program Scan
In the Program Scan step, the PLC executes the program logic that has been created in the Programming mode. The PLC reads the input status from the memory and compares it with the programmed logic. Based on this comparison, the PLC determines the status of the output devices.
Output Scan
In the Output Scan step, the PLC updates the status of the output devices connected to it. These output devices can be motors, valves, or other devices that control the process or machinery. The PLC updates the output status based on the logic programmed in the previous step and sends the signals to the output devices.
The scanning process is continuous, and all three steps are completed within a fraction of a second. This quick scanning process allows the PLC to respond to changes in the inputs and control the outputs in real-time, making it an efficient and reliable control system.
In Conclusion
As a PLC professional technician, having a thorough understanding of the two basic working modes of PLC and the scanning process is crucial for maintaining and troubleshooting industrial automation systems. The Programming mode is used for creating and editing the PLC program, while the Run mode is responsible for executing the program and controlling the processes. The scanning process is the backbone of the PLC's operation, and its continuous and quick performance ensures the smooth functioning of the industrial processes. With the ever-increasing use of PLCs in industrial automation, it is essential for technicians to have a deep understanding of its working modes and scanning process to ensure optimal performance and efficiency of the systems.