Understanding Programmable Automation Controllers (PACs) in Industrial … Proportional-Integral-Derivative PLC Programmable Logic … are connected to I/O modules on an intermediate … For example, it is well understood that a typical control system must interface with signals from simple sensors and actuators, yet for many modern applications this is merely the starting point. Advanced control features, network connectivity, device interoperability, and enterprise data integration are all capabilities increasingly demanded in a …

Making a PLC More Like a PC Using a PLC to meet modern application requirements for network connectivity, device interoperability, and enterprise data integration presents other challenges. These types of tasks are usually more suited to the capabilities of a computer (PC). To provide these capabilities in a PLC-based application, additional processors, network gateways or converters, “middleware” software running on a separate PC, and special software for enterprise systems must often be integrated into the system. Making a PC More Like a PLC On the other hand, a PC packaged for industrial environments can provide many of the capabilities sought in modern applications, particularly those needed for networking and data communication. Similar to augmenting a PLC to accomplish PC-like tasks, however, an industrial PC that needs to perform PLC-like tasks, such as machine or process control, also requires expansion. For example, a PC may be using an operating system that is not optimized for high-performance and deterministic industrial applications. Additional I/O expansion cards or special extensions may need to be integrated into the PC’s operating system to provide the high-performance, deterministic or near-deterministic operation. Introducing the PAC Automation manufacturers have responded to the modern industrial application’s increased scope of requirements with industrial control devices that blend the advantages of PLC-style deterministic machine or process control with the flexible configuration and enterprise integration strengths of PC-based systems. Such a device has been termed a programmable automation controller, or PAC. While the idea of combining PLC and PC-based technologies for industrial control has been attempted previously, it has usually only been done through the “add-on” type of approach described earlier, where additional middleware, processors, or both are used in conjunction with one or more PLCs. A PAC, however, has advanced capabilities needed built into its design. For example, to perform functions like counting, latching, PID loop control, and data acquisition and delivery, a typical PLC-based control system requires additional, and often expensive, processing hardware. A PAC has these capabilities built in. A PAC is notable for its modular design and construction, as well as the use of open architectures to provide expandability and interconnection with other devices and business systems. In particular, PACs are marked both by efficient processing and I/O scanning, and by the variety of ways in which they can integrate with enterprise business systems. Characteristics of a PAC Most agree that industrial analyst ARC Advisory Group originated the term “PAC.” ARC coined the term for two reasons: to help automation hardware users better define their application needs, and to give automation hardware vendors a term to more clearly communicate the capabilities of their products. According to ARC, a programmable automation controller must fulfill the following requirements: Operate using a single platform in multiple domains, including logic, motion, drives, and process control. Employ a single development platform using common tagging and a single database for development tasks across a range of disciplines. Tightly integrate controller hardware and software. Be programmable using software tools that can design control programs to support a process that “flows” across several machines or units.

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