How OEMs should choose between PLCs/PACs and industrial PCs

“A machine builder might choose a PC-based solution if an application calls for heavy data-handling/interaction, large amounts of data retention and/or interactions with other systems, such as subsystems or higher-level systems,” says Terrance Brinkley, director of Michigan operations, senior electrical engineer, Patti Engineering, a system integrator headquartered in Auburn Hills, Michigan.

“A machine builder might choose a PLC/PAC-based solution due to the reliability and durability This solution generally has product availability and a life expectancy for 10+ years, which can support the long-term modifications,” he indicates.

"The two primary reasons for selecting a PC-based control platform for long-term specification are the ability to make the best hardware choice for your application separately from the software, and many software options are hardware-agnostic,” explains Ted Thayer, principal product specialist for control systems, Phoenix Contact USA. “A programmer can choose the most applicable programming and runtime software to use for the application.”

Given that both the hardware and software can be chosen separately, the system will be easier to adapt to changes over the long term, notes Thayer. “Should hardware or software be discontinued, become hard to obtain, or a better option eventually presents itself, it will be easier to just change the necessary component without having to start from scratch,” he says.

“Both options have pros and cons to consider,” notes Danny Weiss, senior product manager, Newark. “The application is a key factor in deciding PC-based or PLC/PAC equipment. Machine builders should consider buying an industrial PC that incorporates long-term available components and choose from new product families to benefit from the longest possible product life. PLCs/PACs are more stable and have less down time. They allow engineers to develop, modify and expand the functionality of control systems through software, rather than hardware changes to the system, thus increasing longevity of the product.”

Choosing a PLC- or PC-based control system comes down to a few key decision points, offers Thomas Kuckhoff, product manager—controllers and industrial PCs, Omron Automation Americas. Those considerations include:

• Machine certifications—"PLCs are notoriously long lived, industrially hardened to survive different factory conditions,” says Kuckhoff. “For machines which require specific certifications, a PLC control system which remains constant is needed. Driven by Moore’s Law, PC hardware is constantly evolving. Not only does this affect spare-part availability, but it can affect machine certification, as well. While PCs do reap the benefit of hardware independence, updating hardware can require recertification and all the costs that entails.”

• Integration into downstream customer facility—"Globally open industrial protocols allow for a lot of inter-manufacturer communication,” notes Kuckhoff. “While both PLCs and IPCs can communicate on globally open industrial protocols, it is the scale and speed of the communication, which can drive machine builders into a specific control-based unit. Understanding the customer’s network can help guide machine builders to set up for a smooth machine run-off at the customer’s site.”

• Integration into digitalization network—"Gathering plant floor data, transporting the data to a central location and visualizing the data is becoming a bigger driver for manufacturing facilities when it comes to machine selection,” says Kuckhoff. “The amount of data being collected from the plant floor, the devices which are collecting the data and the rate of which the visualization of the data is required are often key parameters, which help guide a machine builder into a specific control-based unit. Of course, being able to provide more data, without added cost, then becomes a competitive advantage for machine builders.”

• Control security—“PC-based systems need constant and periodic operating-system security patches to protect against potential cyber vulnerabilities as PC-based systems commonly use Windows or Linux as the operating system and are thus susceptible to Windows- and Linux-based exploits,” warns Kuckhoff. “Even though vulnerabilities can also be found in PLCs, they are significantly less common than PCs. In addition, PC-based patches can affect current programs and processes running on the system, causing additional and sometimes significant downtime, whereas PLC platforms can have backward-compatibility, eliminating this risk.”