Thursday, February 24, 2011

From PLC to PAC based Computer System





Renowned for their reliability and robustness, the programmable logic controllers (PLCs) that have been used traditionally in factory automation have been evolving with the microprocessor control systems development. Originally oriented around the ladder logic that imitated the wiring of physical timers and relays, PLCs that have incorporated the computer control also need a way of handling more complex control tasks that can not be defined in the ladder logic. Tasks involving floating point arithmetic and PID control loops, for instance, require higher levels of processing and programming.

It has evolved into the programmable automation control (PAC) as more computing power has been added to the PLC, a computer based system, which is multi functional and can simultaneously monitor and control digital, analog and serial I/O signals from multiple sources. PACs, in contrast to their PLC ancestors, handles multiple domains like motion, logic, drives and process control on a single platform, which means they also use a single development environment with richer programming resources, a single data base and the ability to use open architectures for interfaces, networking and languages. The strength source for a PAC is its processing the power and its multiplicity of I/O capabilities. Most PAC manufacturers offer a huge of I/O variety modules for all kinds of special requirements. The I/O signals are then translated by the software. These capabilities are integrated in a rugged, industrial package.

Of course all this makes increasing demands on the processors, network silicon and chipset, including the Intel Celeron M and the low power Intel Core 2 Duo processors that integrate processor cores, PCI Express, USB 2.0, UARTs, SATA and Gigabit Ethernet. This enables the controller systems development with a scalable range of price and capabilities points but which share industry standards in terms of hardware compatibility, ease of the modularity and development.



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