With each new feature, industrial controllers become more flexible and better able to manage the complex functions required to run modern equipment. The PLCs of the late 60s were the first step in a long line of advancements in controllers that include modern PLCs and PCs. Deciding between PLCs and PCs requires the evaluation of processing power, customization and durability.

Features to Consider

Processing power, ability to customize and durability are basic features that directly impact effective performance of industrial controllers. They determine how long it takes to move to the next action, how data from inputs are processed and whether the controller will hold up under use.

Processing Power

All controllers, even real-time controllers, experience latency or delays between the time of input and the generated output. This becomes more pronounced as the amount of data processed increases. Programming language and software can impact the latency range of a controller, as well. How much of a delay can your automation process handle before a controller is considered ineffective?

Customization

Customizations of industrial controllers to meet the specifications for a project fall into two general categories: hardware and software. Limitations to core characteristics such as memory, types of processors and power sources can be addressed with hardware modules or upgrades. Specialized or proprietary software to process data or provide users with a desired interface is another way to customize controllers. But, there are tradeoffs for each feature you modify. Be clear which customizations you need and which ones you want.

Durability

Many industrial environments include heat, moisture or vibration. A primary consideration for industrial controllers is whether they have the ruggedness to handle these kinds of environmental elements long-term. In what kind of environment will your controller need to be located?

Further, durability is more than having a physically robust unit. Modern industrial controllers often include networking abilities, which can expose your equipment to undesirable virtual elements such as viruses. Limiting who or what has access to your programming is just as important as minimizing the amount of dust or heat to which your controller is exposed.

What Do PLCs Have to Offer?

Early PLCs used Boolean logic, or ladder logic, to provide programming for relays. As a combination of relays opened or closed, the PLC was able to perform different functions. Modern PLCs have evolved with technology to be able to handle more complex programming than before. Some PLCs still use Boolean logic, but others use IEC 61131-3 standard languages, which allows for more complex programming.

Even with IEC 61131-3 standard languages, PLCs are limited in ways that PCs are not. To meet the memory and processor capacity of a PC, a PLC usually requires customization. Weigh manufacturer limits and available upgrades against your project’s requirements.

PLCs also support other types of customizations, such as adding I/O ports or adding and removing modules. Cost does increase significantly, however, as additional modules are included.

PLCs are known for their inherent ruggedness and durability. For instance, standard PLCs don’t have moving parts, which can be beneficial for locations with high vibration. PLCs also have not been as susceptible to virus attacks as PCs. Software to protect the controller from malicious programming changes or viruses is likely to become more important as networking requirements increase to accommodate the IoT within an industry setting.

Are PCs a Better Choice?

PCs benefit from some of the same technological advancements that have served to expand PLC functionality. Industrial PCs are viable options alongside, or in lieu of, PLCs in industrial control schemes.

PCs tend to have better memory and processors than PLCs, which means that less hardware customization may be needed upfront for a PC controller. Card slots allow for additional hardware upgrades for specific memory or processing requirements. PCs can be further customized using software. In addition, industrial PCs take advantage of standard programming languages which means that software packages for PCs can be added to perform advanced data processing or other functions.

Compared to the base PLC, PCs are not as inherently durable, but they can be modified. For example, customizations such as solid-state drives or fanless cooling options would be needed for the controller to handle vibration and dust, respectively. PCs also require security features not normally needed for PLCs, such as antivirus software.

Processing power, customization needs, and durability are important factors for industrial controllers. Whichever you choose, both PCs and PLCs should be customized to fit your project needs. Weigh each modification carefully against its tradeoffs and you will be well on your way to project success.

Sources:

  1. https://www.controleng.com/articles/fundamentals-of-real-time-processing-in-automation-and-control/
  2. https://www.controleng.com/articles/fundamentals-of-real-time-processing-in-automation-and-control-part-2/
  3. https://www.controleng.com/articles/inside-machines-pc-versus-plc-comparing-control-options/
  4. https://www.machinedesign.com/controllers/has-plc-met-its-match