Programmable Logic Controllers (PLCs) are widely used in industrial automation to control machinery and processes. PLCs have evolved to meet the increasing demand for safety and reliability in industrial settings. Safety PLCs are specially designed to provide safety functions in addition to standard control functions.

While both Standard and Safety PLCs serve the same purpose of automating machine processes, they differ in terms of their design, functionality, and application. Standard PLCs are suitable for applications where safety is not a critical issue, while Safety PLCs are designed to meet the stringent safety requirements of mission-critical or safety-related applications.

Understanding the differences between Standard and Safety PLCs is essential for selecting the appropriate type of PLC for your application. In this article, we will explore the key differences between Standard and Safety PLCs, their advantages and disadvantages, and when to use each type of PLC.

What are Safety PLCs?

Safety PLCs, or safety programmable logic controllers, are specialized types of PLCs designed to ensure the safety of people, machines, and processes in industrial environments. They are used in applications where safety is critical, such as in chemical plants, oil refineries, and power plants.

Safety PLCs are designed to meet specific safety standards, such as IEC 61508 and IEC 61511, and are certified by third-party organizations to ensure their reliability and safety. They are equipped with safety-related input and output modules that are designed to detect and respond to safety-related events, such as emergency stops, light curtains, and safety gates.

Unlike standard PLCs, safety PLCs are designed to be fail-safe, meaning that they are designed to fail in a safe manner in the event of a fault or failure. They are also designed to be redundant, meaning that they have multiple processors and input/output modules that can take over in the event of a failure.

What are Standard PLCs?

Standard Programmable Logic Controllers (PLCs) are industrial computers that are used to control and automate various processes in manufacturing, transportation, energy, and other industries. They are designed to receive inputs from sensors and other devices, process the data using logic and algorithms, and provide outputs to actuators and other devices to control the process.

Standard PLCs are capable of performing a wide range of functions, such as:

• Monitoring and controlling temperature, pressure, flow, and other process variables
• Controlling motors, pumps, valves, and other mechanical devices
• Implementing logic and arithmetic operations
• Communicating with other devices and systems

Standard PLCs are typically programmed using ladder logic, which is a graphical programming language that represents the logic of the control system in a ladder-like fashion. They are also equipped with various communication protocols and interfaces, such as Ethernet, RS-232, and USB, which allow them to communicate with other devices and systems.

Standard PLCs are widely used in various industries due to their flexibility, reliability, and ease of use. They can be programmed and configured to meet the specific needs of different applications, and can be easily integrated with other devices and systems.

Differences between Safety and Standard PLCs

While both safety and standard PLCs are designed to automate machine processes, functions, and production lines, there are key differences between them that can affect the safety and efficiency of your operation. Here are some of the main differences:

Another key difference between safety and standard PLCs is that safety PLCs are designed to react quickly to potentially dangerous situations. They have faster response times and can shut down a machine or process in milliseconds to prevent harm to people or damage to equipment. Standard PLCs, on the other hand, are designed for general automation purposes and may not react as quickly to potentially dangerous situations.

In summary, safety PLCs are designed specifically for safety applications and have built-in safety functions, redundancy in their hardware, and meet specific safety standards. Standard PLCs, on the other hand, are designed for general automation purposes and do not typically have built-in safety functions or redundancy in their hardware.

When to Use Safety PLCs

Safety PLCs are designed to provide an extra layer of protection for workers and equipment in hazardous environments. They are ideal for applications where a failure in the control system could lead to serious injury or death. Here are a few examples of situations where safety PLCs are commonly used:

• Machine guarding: Safety PLCs can be used to monitor safety interlocks and other safety devices on machinery, ensuring that they are functioning properly and preventing unauthorized access to hazardous areas.
• Emergency stop systems: Safety PLCs can be used to monitor emergency stop buttons and other safety devices, ensuring that they are functioning properly and can be activated quickly in the event of an emergency.
• Process safety: Safety PLCs can be used to monitor critical process parameters, such as temperature, pressure, and flow rate, and take corrective action if necessary to prevent equipment damage or process failures.
• High-risk industries: Safety PLCs are commonly used in industries such as oil and gas, chemical manufacturing, and nuclear power generation, where the consequences of a control system failure can be catastrophic.

It is important to note that safety PLCs are not always necessary for every safety application. In some cases, standard PLCs or safety relays may be sufficient to meet the required safety standards. The decision to use safety PLCs should be based on a thorough risk assessment and analysis of the specific application.

When to Use Standard PLCs

Standard PLCs are designed for general-purpose automation applications. They are ideal for controlling simple processes that do not require advanced safety features. These systems are commonly used in industries such as automotive, food and beverage, packaging, and material handling. Here are some situations where standard PLCs are a good choice:

• When the automation process does not involve hazardous machinery or materials
• When the process does not require advanced safety features such as emergency stop, light curtains, or safety interlocks
• When the system does not require SIL (Safety Integrity Level) certification
• When the cost of the system is a primary concern

Standard PLCs are also a good choice for applications that require high-speed processing and real-time control. These systems can handle complex logic and arithmetic operations quickly and efficiently. Additionally, standard PLCs are typically easier to program and maintain than safety PLCs, making them a good choice for smaller projects or applications that do not require advanced safety features.

However, it is important to note that standard PLCs should not be used in applications where safety is a critical concern. In these situations, safety PLCs should be used instead.

Conclusion

Choosing between a standard PLC and a safety PLC depends on the specific application and the level of safety required. In general, safety PLCs are more expensive and complex than standard PLCs, but they offer a higher level of safety and reliability.

Standard PLCs are suitable for many applications that do not require a high level of safety or where the risks are low. They are also more affordable and easier to program and maintain than safety PLCs.

However, safety PLCs are essential for applications where the risks are high, such as in the chemical, oil and gas, and nuclear industries. They provide a higher level of safety and reliability, and they are designed to meet the requirements of safety standards and regulations.

When choosing between a standard and safety PLC, it is essential to consider the specific requirements of the application, the level of safety required, and the budget. It is also important to work with a qualified engineer or system integrator who has experience in designing and implementing safety systems.