Tuesday, March 1, 2011

PACs for the Future of Control

With a number of vendors producing Programmable Automation Controllers (PACs) that combine the functionality of a PC and reliability of a PLC, PACs currently are increasingly being incorporated into control systems.

For the last decade a passionate debate has raged about the PLCs (programmable logic controllers) advantages and disadvantages compared to PC-based control. As the technological differences between PLC and PC wane, with PLCs using commercial off the shelf (COTS) hardware and PC systems incorporating real-time operating systems, a new class of controllers, the PAC is emerging. PAC, a new acronym created by ARC (Automation Research Corporation), stands for Programmable Automation Controller and is used to describe an industrial controller new generation of that combine the functionality of a PLC and a PC. The PAC acronym is being used both by PC control companies to describe their industrial control platforms and by traditional PLC vendors to describe their high end systems.

PLCs have evolved to incorporate communication over networks, analog I/O, and new programming standards such as IEC 61131-3 during the three decades following their introduction. Engineers create 80 percent industrial applications with a few analog I/O points, digital I/O, and simple programming techniques. Experts from ARC, the online PLC training source PLCS.net and VDC (Venture Development Corporation), estimate that:
• 77% of PLCs are used in small applications (less than 128 I/O)
• 72%of PLC I/O is digital
• 80%of PLC application challenges are solved with a set of 20 ladder-logic instructions.

Due to 80 percent of industrial applications are solved by traditional tools, there is strong demand for simple low-cost PLCs. This has spurred the low-cost micro PLCs growth with digital I/O that use ladder logic. It has also created a controller technology discontinuity, where 80 percent of applications require simple, low cost controllers and 20 percent relentlessly push the traditional control systems capabilities. The applications that drop within the 20 percent are built by engineers who require higher loop rates, more analog capabilities, advanced control algorithms, and better integration with the enterprise network.

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