A major component behind the efficient functioning of today’s process control systems is the programmable logic controller, or PLC. Uniquely suited to withstand tough industrial environments, PLCs serve to reliably automate many manufacturing systems, such as assembly lines or industrial equipment.

However, in certain applications, such as those involving machinery that poses a risk of operator injury, an additional layer of protection is required. That is where the safety PLC comes into play. This blog will discuss the general purpose of the safety PLC and its capabilities as well as its advantages over the standard PLC.

What is a Safety PLC?


Understanding Safety PLCs

A safety PLC is still capable of supporting all the key manufacturing applications that a standard PLC does. Its biggest difference, however, is that it also integrates safety functions that allow it to control key safety systems as well. The key objectives of safety PLCs are:

  • Do not fail
  • If failure is unavoidable, fail only in only the safest and most predictable way possible

The safety PLC meets these objectives by incorporating multiple redundant microprocessors. These built-in redundancy layers are a key capability because it means safety PLCs can eliminate the need for safety relays that are often used to create redundancy in the standard PLC. Safety PLC platforms include several standard diagnostic systems which enable them to continuously monitor inputs and outputs, searching for any potentially unsafe conditions. If these monitoring mechanisms detect an internal failure, a safe shutdown is initiated.

At its highest safety integrity level, a safety PLC is capable of detecting over 99% of potential system failures. This makes them suitable for use in applications that could cause harm to the employees, operators, environment, business, and equipment, including applications and installations that need to meet IEC 61511 and IEC 61508.

Safety PLCs vs Standard PLCs

Although similar to the standard PLC, a set of rigorous international standards must be met to be considered a safety PLC. The key to implementing PLC safety systems is to incorporate the best of PLC capabilities and integrate a safety controller into a single system.

The main benefit of standard PLCs is that they are simple to wire, easy to use, and do not require experienced technicians for troubleshooting purposes. This will generally make them more affordable; however, they typically have no way of detecting wiring errors on input/output (I/O), such as channel mismatches, ground faults, and short circuits. Different output types can lead to additional instability, and problems may tend to increase with an increase in the number of relay types. Delays in communication between components can lead to difficulties in diagnosis, which can be catastrophic in certain industrial applications.

Cost should never be the primary motivator when it comes to ensuring the safety of personnel, the business, the environment, and the community. Even though there are some additional costs associated with purchasing and maintaining safety PLCs because of their rigorous adherence to safety standards, the peace of mind, security, and benefits of these controllers definitely outweigh any cost concerns:

  • Safety PLCs offer networking of input-output devices and diagnostics via human-machine interfaces. This can help to alleviate some installation costs.
  • Robust diagnostics or information tracking capabilities are easily integrated and provide flexibility in many safety-essential applications.
  • Financial and human resources can be minimized in field wiring, as safety PLCs serve to eliminate the need for safety relays.
  • A safety PLC system is easy to modify as it only requires basic programming updates, without installing additional relays or necessitating any wiring changes.

Safety PLCs from Turner Integrated Systems

At Turner Integrated Systems, we are capable of designing safety PLCs for a wide range of applications that require extra protection. Located in Rochester, New York, we have in-depth experience in many PLC categories, and we custom-design systems to meet specific safety and operational requirements for each project. Contact us today for more information about our safety PLCs.

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