Programmable Logic Controller (PLC), also termed an industrial computer, plays a major role in industrial automation. PLCs have robust construction and exceptional features like simple-to-use hardware, dependable controlling capabilities, programming ease, counters and timers, sequential control, and PID controllers. This makes PLCs special-purpose computers in industries and other control-platform areas. Let us discuss various types and applications of PLC systems.
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Introduction to PLC Systems
PLCs have been developed to replace conventional control panels that function based on electromagnetic logic relays, which depend on the timers in control platforms that have been deployed in the industries.
PLCs can continuously monitor the inputs from sensors and generate the needed output decisions to run the actuators based on the system. Each PLC system requires three modules: CPU, power supply, and one or multiple I/O modules.
Types Of PLC
PLCs are built as either modular or single units. A compact or integrated PLC is made with multiple modules inside one case. Therefore, the manufacturer and not the user decides its I/O features. Some integrated PLCs permit the connection of added I/Os, which makes them more modular.
- Modular PLCs
Modular PLCs are made with multiple elements that are connected to a common bus or rack with extendable input/output features. Each modular PLC has CPU, power supply, and other I/O modules that are connected in one rack. They may have been built by one or several makers.
Modular PLCs are available in various sizes with different I/O connectivity, computing functions, power supply, etc. Modular PLCs are classified into large, medium, and small types based on the number of I/O functions and the program memory size.
- Small PLCs
A small PLC is a robust and compact unit placed or mounted next to the equipment that needs to be managed. It is used to replace hard-wired timers, counters, and relay logic. The expandability of this PLC’s I/O module is restricted to one or two modules. Small PLCs utilize relay ladder language or logic instruction list as coding language.
- Medium-Sized PLCs
Medium-sized PLCs are being used in sectors that permit multiple plug-in modules that are placed on the system’s backplane. Hundreds of I/O points are offered by including added I/O cards. Apart from that, this PLC provides communication module features.
- Large PLCs
Large PLCs are leveraged in applications that require complex process management functions. These PLCs have much higher capacities than the medium type when it comes to communication modules, I/O points, coding languages, memory, and other factors. Large PLCs are utilized in distributed control platforms, big plants, and SCADA systems.
Applications of PLCs
PLCs are commonly used in process control applications in industries. These devices can perform control operations, measure the number of boxes, operate the conveyor belt, and other tasks.
In a PLC, sensor outputs like the position sensor are linked to the input module. Further, the output modules control a motor. On activation of the sensors, the PLC’s CPU scans the inputs and processes them correspondingly as per the program. It then generates the needed outputs to run the motor and control the conveyor.
The combination of SCADA and PLC control system is commonly leveraged in power utility platforms like distribution and transmission systems, and industrial automation. PLCs are also used for programmable sequential switching applications. You need to select the right type of PLC for your application needs by considering each type’s features and suitability for the task.
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