PLC or PAC: What to consider when choosing a controller for your industrial application

It is such a fast-moving world that even the most common automation technologies evolve in response to industry-specific needs. As a result, there are several key factors to consider when evaluating future controller purchases.

The programmable logic controller (PLC) and its more advanced cousin, the programmable automation controller (PAC), have long been the leading technologies for automated process control in continuous processing and discrete manufacturing production applications.

But even these technologies are changing in light of new industry demands for greater connectivity, flexibility and data sharing. The lines between a PLC and a PAC have definitely blurred since PACs were first described in the early 2000s. Originally, PLCs replaced hard-wired relay systems and ladder logic was used to represent in software what engineers used to see in physical design.

With tightly integrated hardware and software and a single development platform and database, PACs offered easier development in multiple domains, including logic, drives and process control. For larger systems that include many channels of analogue I/O and/or a variety of control functions and communication needs, the PAC architecture is often preferred.

Clearly, PLCs and PACs will continue to have a place in the industry for many years to come, but new automation applications will require controllers to have additional features and capabilities. These new requirements include data processing at the edge, the ability to interface directly with enterprise and cloud software, information technology (IT) compatibility and, most importantly, cyber security.

IT compatibility and security used to be an afterthought in the controller purchasing process, but digital transformation initiatives now make them essential. In addition, controllers must support applications and programming languages that enable data processing at the edge and direct interaction with business systems. Modern controllers must be first-class citizens in business networks as well as control systems.

Open and modular architecture

The more open architecture of a PAC generally means that it is based on standards that make it compatible with other systems in addition to those from the same vendor. It can be programmable using any of the IEC 61131-3 industrial control programming languages, for example, provide support for OPC and common industrial protocols such as Modbus, and offer free integration kits for other systems.

A modular design means that system changes and expansion can be easier with the PAC architecture, which is based on distributed, independent and cooperative components, rather than relying on a central controller. In a factory, processes can be changed and new production lines can be added and controlled by a PAC without significantly reprogramming or overloading a central controller. The PAC can also integrate with existing processes and other controllers as needed.

So, CLP or PAC?

The choice of a controller for a specific application depends on several considerations. First, what are the functional requirements today and what can be expected in the future? Direct machine control, especially high-speed discrete control or motion control with few expected changes, may indicate that a PLC works best. A more complex application, especially if it is expected to expand or change, might argue for a PAC.

If you are interested in learning more about how to choose a controller according to your industrial application, we invite you to learn more about the following considerations for application of servo drives, motion controllers and PLCs, as well as the differences between PLC vs. DCS.

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