PACs are used in process controlProgrammable automation controllers—PACs. You've been hearing a lot about them lately. But what are they really, how do they differ from the hardware you're using now, and why should you be interested?

Let's take that last question first: Why should you be interested in PACs?

The answer lies in the demands of today's industrial applications, where interfacing with signals from sensors and actuators is now just the starting point. Advanced control features, network connectivity, integration of remote and distributed subsystems, device interoperability, and enterprise-wide data integration are all requirements you may be called upon to meet.

If there's a simpler way to meet these requirements, you'd probably like to know about it. And today, PACs seem to be emerging as that simpler way.

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How are PACs different?

PACs differ from the hardware you're probably using now in several ways. In effect, PACs expand the capabilities of hardware you're using now by merging features of more traditional PLC , DCS, and RTU systems, plus adding some capabilities from PCs.

  • PLC. Traditional PLC (programmable logic controller) systems provided discrete-logic-based control of input/output (I/O) signals, using ladder logic programming.
  • DCS. DCS (Distributed control system) technology traditionally provided process control—batch control where product variations are made according to recipes, or continuous process control.

  • RTU. The traditional remote terminal unit (RTU—also called a remote telemetry unit) provided multiple communication options for monitoring remote assets, such as radio towers or pipelines.

  • PC. PC-based control traditionally linked an adapter card on a computer to I/O, with custom applications written for control and communication.

Compare features of PACs with those of traditional PLCs, DCSs, RTUs, and PCs. 

So, what is a PAC?

PACs are used for remote monitoring and data acquisition, discrete manufacturing, and process controlIt's generally agreed that industry 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.

ARC defines a PAC as having the following characteristics:
  • Operates using a single platform in multiple domains, including logic, motion, drives, and process control. Because a single PAC can do all types of control , monitoring, and data acquisition, system expansion and change are simplified.
  • Employs a single development platform using common tagging and a single database for development tasks across a range of disciplines. The same software is used for all development; this IDE (Integrated development environment) reduces development time.
  • Tightly integrates controller hardware and software. When hardware and software are designed together, systems are easier and faster to build. Some PAC manufacturers, such as Opto 22, include surprisingly capable software with a PAC purchase.
  • Is programmable using software tools capable of designing control programs to support a process that "flows" across several machines or units, integrating multiple domains into a single system.
  • Operates on open, modular architectures that mirror industry applications, from machine layouts in factories to unit operation in process plants. Since each installation is different, the system must be able to add or change modules easily.
  • Employs de-facto standards for network interfaces, languages, and protocols, allowing data exchange as part of networked multi-vendor systems.
  • Provides efficient processing and I/O scanning. A PAC's first duties are efficient monitoring, control, and data acquisition. Traditional continuous scanning, for example, is often less efficient than exception-based scanning performed only when control logic dictates.

Key Advantages of a PAC

PACs are used in industrial applicationsThese defining characteristics also describe the key advantages of using PACs in industrial applications:

  • A single controller with integrated software handles multiple functions across multiple domains.
  • Complex and changing requirements can be met with little additional cost.
  • Modular designs make expansion easier.
  • Networking and communication capabilities link disparate systems and provide more accurate and timely data.
  • Total system cost is lowered, because integrated hardware and software are less expensive, and because development and integration time is reduced.
  • Modular design improves cash flow.

In summary, PACs now provide the multi-function, multi-domain, multi-tasking, modular, standards-based and efficient control, networking, and communications processor most suited to today's industrial applications.

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