Programmable Logic Control (PLC) is an industrial computer with special built-in operating system that is specially developed and adapted to control manufacturing process. PLC is commonly used in automobile industry, but it can also be used for various other industries such as robotic, amusement rides and other purposes in factory assembly lines. To put it short, PLC is a very important computerized equipment used in manufacturing processes which require high level of control, precision and reliability. PLC can come in various sizes and shapes. It will depend on for what purpose and industry the computer is used. Some comes in small pocket size with fix input and output points (also often called brick PLC), while some others, which is used in automotive industries are large. One of the best things about using PLC is the fact that it is modular. It means the input and output devices can easily be mixed and matched to adapt with the needs of the manufacturing process.
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A Brief History of PLC
Before PLC was found, electromechanical and industry manufacturing process took advantage of relay logic systems. It consists of plenty of relays, cam timers, loop controllers and many other processes. It was pretty effective but it was also very time consuming and expensive. To solve this, PLC was developed to replace the old relay logic systems. The first ever PLC was developed in 1969 by Modicon for General Motor’s automotive manufacturing needs. The inventor’s name was Dick Morley and the PLC itself was named model 084. Model 084 really changed how automotive industry worked. Thanks to the new controllers, rewiring and using additional hardware is not necessary anymore. Furthermore, since PLC can work faster with less hardware, manufacturing process becomes more cost and space efficient. Four years after Model 084, Model 184 was introduced. The world’s first commercially successful PLC was developed by Michael Greenberg. After several decades, automobile industry is still the biggest user of PLC technology.
How It Works PLC
PLC consists of three components—the power supply, CPU and input and output section. All three components play important role but it is the input and output section that keeps the control functioning. Once a digital or analog input is activated, the user defined logic is processed and written into output values, the PLC will keep running. The system is designed to work in such a rigorous environment so it will keep working for years without requiring too many human interventions.
Input and Output Devices PLC
Input and output devices are some of the most important components in Programmable Logic Control. What type of input and output devices a PLC has will vary, depend on what the machine needs and also the tasks that are assigned to the input and output sections. But mostly, here are some of the most common input and output devices found in a PLC.
Input PLC
- Switches (pressure switches, temperature switches, vacuum switches, etc.) - Sensors (photoelectric sensors, proximity sensors, condition sensors, etc.) ·
Output PLC
- Actuators - Alarms - Printer - Fan - Valves - Motor Starters.