SNAP-PAC Systems

Systems 22 was founded in March 1993 to promote Opto 22 automation products to the Australian market. For more than 30 years, Opto 22 has been developing quality hardware and software solutions for thousands of automation applications around the globe. Opto 22 was one of the first companies to recognize and implement solutions involving personal computers. Today Opto 22 is meeting complex industrial automation and information technology challenges by providing solutions for companies who use commercial computer technology. In Australia, Systems 22 has supplied Opto 22 for applications as diverse as I/O for the Sydney Harbour Tunnel and Solid State Relays in petrol pumps.

Programmable 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.

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 (Distributed Control System) , and RTU systems, plus adding some capabilities from personal computers (PC (personal computer)).

PLC. Traditional programmable logic controller (PLC (programmable logic controller) ) systems provided discrete-logic-based control of input/output (I/O) signals, using ladder logic programming.

DCS. Distributed control system (DCS) 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.

It'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:

Operate 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.
Employ 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 integrate 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.
Be 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.
Operate 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.
Employ de-facto standards for network interfaces, languages, and protocols, allowing data exchange as part of networked multi-vendor systems.
Provide 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.