Reliability & Maintenance Center Safety

Safety PLCs Pay Off

Jane Alexander | November 15, 2018

As do-it-all devices, safety PLCs reduce risks and protect plant personnel and equipment without the complexity and bulkiness of standard PLC systems.

Safety programmable logic controllers (PLCs) can help build a better safety environment while also decreasing operating costs.

In short, according to Ted Cowie of Motion Industries, Birmingham, AL (, these devices protect workers and equipment. Cowie provided the following details on how safety PLCs deliver value in plants.


Standard PLCs provide functionality and reliability for controlling timing, fault diagnosis, sequencing, and switching for motors, pumps, valves, and other industrial devices.

Many plants also depend on standard PLCs configured in pairs to control machine processes and comply with regulatory standards. With additional input/output ports monitoring safety-system output signals, a second, redundant PLC safely shuts down equipment if the first PLC fails. This requires custom software and additional engineering to overcome the limitations of a standard PLC. Safety PLCs offer an alternative to that type of complex—and bulky—system.


The safety and reliability standards that govern manufacturing and industrial processes mitigate risk through safety integrity levels (SIL). With the SIL in mind, design teams developed a single device—called a safety PLC—that detects a failure and initiates a safe shutdown within seconds.

Safety PLCs detect unsafe conditions in a single machine, multiple machines, or across an enterprise. As a result, the units can monitor the quality of products manufactured across assembly lines or check on the operation of equipment in the plant. For example, safety PLCs monitor the load torque, speed, position, and the load movement of industrial hoists in real time.

Much of this occurs through the capability of a safety PLC to handle structured, high-level programming, allowing you and your team to adapt to different needs. Rather than rewiring your system, your team can add programming that ensures the safety of new operations.


Today, the specifications for safety-control systems encompass software, hardware, and operating systems. If your processes have grown beyond one or two E-stops, it may be time to evaluate the costs and benefits of safety-PLC technology. EP

Is Cost an Issue?

Safety PLCs combine standard PLC control functions with safety controls. Every safety PLC meets rigorous international standards and undergoes certification processes for design, hardware testing, software testing, and risk reduction. Those processes and tests ensure access to critical data and verify that safety PLCs execute instructions in the correct order.

Certainly, safety PLCs have higher initial costs and require programming. However, safety PLCs save costs in field wiring while providing the flexibility and scalability needed to monitor robotics, controls, or material-handling systems across the enterprise. Troubleshooting costs are reduced through the capability of a safety PLC to display the status of connected devices.

Ted Cowie is vice president, Sales, Safety & Industrial Products for Birmingham, AL-based Motion Industries. For more information, visit and/or The Safety Specialist at




Jane Alexander

Jane Alexander

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