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A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis.
A PLC can be either an unlisted or listed company on the stock exchanges. In the United Kingdom, a public limited company usually must include the words "public limited company" or the abbreviation "PLC" or "plc" at the end and as part of the legal company name.
Siemens SIMATIC S7-300 PLC CPU with three I/O modules attached. As with other programmable logic controllers, SIMATIC devices are intended to separate the control of a machine from the machine's direct operation, in a more lightweight and versatile manner than controls hard-wired for a specific machine. Early SIMATIC devices were transistor ...
A feedback control loop is directly controlled by the RTU or PLC, but the SCADA software monitors the overall performance of the loop. For example, a PLC may control the flow of cooling water through part of an industrial process to a set point level, but the SCADA system software will allow operators to change the set points for the flow.
The term usually describes environments containing industrial control systems (ICS), such as supervisory control and data acquisition (SCADA) systems, distributed control system (DCS), remote terminal units (RTU) and programmable logic controllers (PLC), as well as dedicated networks and organization units.
This allows SCADA system engineers to perform both the design and implementation of a program to be executed on an RTU or PLC. A programmable automation controller (PAC) is a compact controller that combines the features and capabilities of a PC-based control system with that of a typical PLC. PACs are deployed in SCADA systems to provide RTU ...
Public Limited Company (PLC): a public company limited by shares; Limited by Guarantee (Ltd./Gte.): a company limited by guarantee (non-profit company) Unlimited (ULtd.): A company with a share capital, similar to its limited company (Ltd., or PLC.) counterparts, but where the liability of the members or shareholders is not limited
A simplified PAL device. The programmable elements (shown as a fuse) connect both the true and complemented inputs to the AND gates. These AND gates, also known as product terms, are ORed together to form a sum-of-products logic array.