Safety PLC vs Standard PLC: What’s the Difference?

There are lots of differences between a safety PLC and a normal PLC. The safety PLC provides efficient solutions to machines and systems. It integrates multiple safety sensors. It is very compact and saves space in the automation cabinet. Besides, the optional extension modules allow you to adapt the number of inputs and outputs flexibly to your specific applications. By using a safety PLC you can be able to configure and commission everything quickly and easily. They have different functions and applications. But before comparing these two devices let’s look at the definition of the safety PLC

What is a Safety PLC?

The safety PLC is a special type of PLC that protects people, machines and processes, the environment, and investments. It is an ideal choice for the safety circuits of the wind turbine, crane, material handling, hoist, robot, and other factory and process applications.

It reduces wiring time by enabling safety networks to monitor and/or control all of the devices on a single safety network.

The safety PLC provides efficient solutions to machines and systems. It integrates multiple safety sensors. It is very compact and saves space in the automation cabinet. Besides, the optional extension modules allow you to adapt the number of inputs and outputs flexibly to your specific applications. By using a safety PLC you can be able to configure and commission everything quickly and easily.

The purpose of the safety PLC is to integrate functional safety functions into control systems. There is no need for separate cables for the safety circuits. It has the duty of executing the safety application program and exchanging safety-related control information with the safe slave modules assigned to it.

Additionally, designing safety systems around standard controllers requires additional engineering time, I/O hardware, and wiring to support the safety portion of the application. Also, special software is required to run the application.

Safety PLC vs Standard PLC

1. The idea of connecting machine safety control directly to the PLC still may cause concern for some people. When you consider the history of the PLC in the industry this is a very understandable emotion. However, today’s safety PLC is quite different than the PLC used for automation control. Standard duty PLCs have evolved to be a highly reliable tool in the industry today; however, they are still based on single linear processing of single monitored inputs. This means that any point of failure can cause an unknown failure mode and that is intolerable for protecting personnel from injuries caused by machines in motion. Any system will someday fail it is understandable that the standard duty PLC cannot be relied upon when it comes to the safety of employees working around the machine. Therefore, the standard duty PLC must have additional system components to be able to protect the operator and machine even when there are hardware or software faults present. Now, this layer of special safety components that were once only allowed in the hardwired safety relays has been successfully integrated into the PLC to create a true hybrid that brings safety protection layers and automation control together. Safety PLCs now use control reliable design and layers of protection to meet the high levels of reliability required by the current standards.
2. Safety PLCs are suited for applications at SIL 2 and SIL 3 where they can be certified for use in most common safety applications.
3. The redundancy and self-checking features of safety PLCs come with a price tag. Safety PLCs cost approximately 25% to 30% more than their standard PLCs.
4. Another important thing to note is that safety PLCs are still a relatively new product with new technology. Engineers and technicians are not familiar with the newer technology so additional training may be necessary for safety PLCs.
5. You can easily recognize a safety PLC from its body. Safety PLCs have a yellow body. (Or a yellow line is available on its body)
6. Normal PLC has wide application areas. In industrial environments, you can see lots of PLCs. But safety PLC can be used in only safety applications.

Some examples of safety PLC applications are:

– Material handling (Distribution centers, airports, harbors, etc. )

• AGVs (Automated Guided Vehicles)
• Cranes
• Hoists, etc.

– Robot applications

• Robot cells (B&W, press, laser cutting, etc.)

– Winder applications (Metals, Pulp&Paper, etc.)

– Various process automation applications

• Hydrogen tank stations
• Boilers
• Burner Management Systems, etc.

In conclusion, the safety PLC is a specialized type of PLC that is designed to provide reliable and efficient solutions to machines and systems. It integrates multiple safety sensors, is very compact and saves space in the automation cabinet. The safety PLC is an ideal choice for the safety circuits of machines and processes, protecting people, the environment and investments. While the standard PLC has evolved to be a highly reliable tool in the industry, it is still based on single linear processing of single monitored inputs, making it unsuitable for safety applications. Safety PLCs have successfully integrated the safety protection layers and automation control making them suitable for applications at SIL 2 and SIL 3. However, safety PLCs come with a higher price tag and require additional training for engineers and technicians. Overall, safety PLCs are a relatively new product with new technology that provides a reliable and efficient solution for safety applications.

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