Each expansion and powerful programming tools
PACs offer extensive built-in functionality, and they have a modular design that simplifies system changes and expansion, making it easy to add up to thousands of I/O points. By contrast, a typical PLC is designed to control much smaller systems, with high I/O counts often impractical, due to performance degradation.
Multiple PAC programming languages offer flexibility and easy scalability for larger systems. In particular, most PACs offer tag-based naming conventions. This means programming system changes in a PAC doesn't involve the complex re-engineering to make such changes in an average PLC.
With a PAC, a single tag-name database is shared across all development tools, thus requiring only one software package for programming. Each tag can consist of a descriptive English syntax name and can be assigned to specific functions before being tied to a particular I/O or memory address. This means variable names no longer must function as both a name and a description. Where previously names consisted of numbers or arcane expressions such as "bits(3).5," easy-to-understand terms such as "Tank 1 High Level" can be used instead.
Built-in capabilities reduce costs
Overall, PACs provide greater flexibility in programming, larger memory capacity, better interoperability, and more features and functions than a PLC -- all at less cost than a DCS. A PAC is also easier to implement than a DCS and more scalable for lower I/O count applications.
With an I/O capacity in the hundreds of thousands, extensive built-in memory, and powerful processing capability, a single PAC can be used to monitor and control large systems encompassing several areas of a plant or an entire facility.
In addition to monitoring and controlling large areas of a plant, a PAC reduces costs by simplifying the communication of data between the plant floor and higher-level computing applications and systems. The built-in communication capabilities of a PAC often negate the need to invest in middleware, extra gateways, and components, because the standard protocols and networking ports in a PAC make it easy to communicate with SQL databases, ERP systems, asset management systems, and enterprise-wide historians.