Similarly, a parallel set of instructions will perform a logical OR. Just as a series of relay contacts perform a logical AND function, not allowing current to pass unless all the contacts are closed, so a series of 'examine if on' instructions will energize its output storage bit if all the input bits are on. Discrete inputs are given a unique address, and a PLC instruction can test if the input state is on or off. The most basic function of a programmable controller is to emulate the functions of electro-mechanical relays. Desktop logic applications find use in less critical situations, such as laboratory automation and use in small facilities where the application is less demanding and critical. Operating systems such as Windows do not lend themselves to deterministic logic execution, with the result that the controller may not always respond to changes of input status with the consistency in timing expected from PLCs. Desktop computer controllers have not been generally accepted in heavy industry because the desktop computers run on less stable operating systems than PLCs, and because the desktop computer hardware is typically not designed to the same levels of tolerance to temperature, humidity, vibration, and longevity as the processors used in PLCs. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications.

The data handling, storage, processing power, and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. Industry-standard Ethernet communications are used for I/O, controllers, and supervisory interface to operator and maintenance stations and third-party systems.The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems, and networking. GE’s DCS solutions feature high-speed, networked I/O for simplex, dual, and triple redundant systems. The Mark VIe DCS consists of intelligent controllers, I/O modules, secure cloud connectivity solutions, advanced analytics software, and apps to provide real-time process optimization and control with minimal disruption to deployed applications. GE’s DCS enables users to improve operational efficiency, optimize production, and unlock new revenue opportunities by leveraging advanced data analytics. Leverage high performance plant control logic combined with comprehensive fail-safe protection, self-testing, and fault reporting to help reduce costs, and improve safety.

Enhance operation of key subsystems by reacting instantly to changing load demands and continually maintaining ideal conditions at every stage of the water/steam cycle. GE’s Integrated Plant Control DCS (Distributed Control System) is a solution for managing complex plant processes in an efficient, consistent, and secure way.

Engineering control systems plc pdf