Skip to content
Why do PLC need safety circuits?

Why do PLC need safety circuits?


In the industrial world, Programmable Logic Controllers (PLCs) play a vital role in automating processes and controlling machinery. They are widely used in various industries, from manufacturing to energy production. While PLCs offer numerous benefits in terms of efficiency and productivity, it is crucial to ensure the safety of both workers and equipment. This is where safety circuits come into play.

The Importance of Safety in Industrial Settings

Industrial environments can be hazardous, with machines and systems that pose risks to operators and nearby personnel. Accidents can result in injuries, damage to equipment, and even loss of life. Therefore, it is paramount to implement safety measures to mitigate these risks. PLC safety circuits provide an additional layer of protection by monitoring and controlling various safety-related aspects.

Functions of Safety Circuits in PLCs

Safety circuits integrated into PLC systems serve several critical functions. They are designed to detect potentially dangerous situations and initiate appropriate actions to prevent accidents. These functions may include:

  1. Emergency stop: Safety circuits enable emergency stop buttons or switches to immediately halt all machine operations when pressed. This instantaneous response can prevent injuries or further damage.
  2. Safe access: By incorporating safety devices like interlocks, light curtains, and safety gates, PLC safety circuits ensure that access to hazardous areas is restricted. These devices send signals to the PLC, which can then control the machine’s operation accordingly.
  3. Safety monitoring: Safety circuits constantly monitor critical parameters such as temperature, pressure, voltage, and current. If any values exceed predefined safe limits, the circuit triggers appropriate actions, such as shutting down the machine or activating alarms.
  4. Guarding against unexpected movements: PLCs can detect movements or deviations from expected patterns using sensors. Safety circuits can then respond by stopping or slowing down the machine to prevent accidents.

The Role of Safety Standards

To ensure the effectiveness and reliability of safety circuits, they need to comply with industry-specific safety standards. The application of these standards guarantees that the implemented safety measures are adequate and meet the required safety levels. Some widely recognized safety standards in the UK include the Machinery Directive (2006/42/EC) and the Control of Substances Hazardous to Health Regulations (COSHH).

“Implementing safety circuits in PLC systems is not just a legal requirement; it is essential for safeguarding people and assets in industrial settings.” – Industrial Safety Expert

Benefits of Safety Circuits in PLCs

The integration of safety circuits into PLC systems offers several benefits, including:

  • Employee safety: Safety circuits protect workers from hazardous situations, reducing the risk of workplace accidents and injuries.
  • Equipment protection: By monitoring critical parameters, safety circuits can prevent equipment damage caused by excessive temperatures, pressure, or voltage.
  • Compliance with regulations: Implementing safety circuits ensures adherence to safety regulations and standards, avoiding potential legal and financial liabilities.
  • Increased productivity: By minimizing downtime due to accidents, safety circuits contribute to uninterrupted production and increased overall efficiency.

What is a safety controller in PLC?


A safety controller is an essential component of a Programmable Logic Controller (PLC) system. It is responsible for monitoring and managing safety-related functions within the PLC, ensuring the protection of personnel and equipment.

The Importance of Safety Circuits in PLCs

Safety circuits are crucial in PLC systems as they provide an additional layer of protection for operators, preventing accidents and potential hazards. These circuits monitor critical safety parameters, such as emergency stops, machine guards, and safety interlocks.

The Role of a Safety Controller

The safety controller acts as the brain of the safety circuit, continuously monitoring inputs and controlling outputs to ensure a safe operating environment. It receives signals from various safety devices and initiates appropriate actions, such as stopping a machine when a safety breach is detected.

Features and Functions

Safety controllers come with a variety of features to suit different industrial applications. Some common functions include:

  1. Safety input monitoring: The safety controller constantly checks inputs from safety devices, such as light curtains or emergency stop buttons, for any abnormalities.
  2. Logic processing: It performs logical operations to determine the appropriate response based on the input signals received.
  3. Safe output control: Upon detecting a safety breach, the safety controller sends signals to activate safety mechanisms, such as stopping the machinery or initiating an alarm.
  4. Diagnostic capabilities: Many safety controllers offer diagnostic tools to troubleshoot any issues within the safety circuit and ensure proper functionality.

Benefits of Using a Safety Controller

Utilizing a safety controller in a PLC system offers several advantages, including:

Enhanced safety: By continuously monitoring safety parameters, a safety controller significantly reduces the risk of accidents and injuries in industrial environments.

Flexibility: Safety controllers can be easily integrated into existing PLC systems, allowing for seamless implementation and customization of safety protocols.

Compliance: Incorporating a safety controller ensures compliance with industry standards and regulations, providing peace of mind to both operators and regulatory authorities.

What are the fundamental and significant differences between PLC vs Safety PLC?


In the world of industrial automation, Programmable Logic Controllers (PLCs) play a vital role in controlling and monitoring various processes. However, when it comes to safety critical applications, a specialized version called Safety PLCs are employed. Safety PLCs are designed to meet stringent safety requirements and provide additional features to ensure safe operation.


While both PLCs and Safety PLCs share common functionalities such as input/output control and data processing, Safety PLCs go beyond these basic functions. They are equipped with advanced safety features like built-in safety functions, redundant system architecture, and fault diagnostics.


Safety PLCs are engineered to provide higher levels of reliability compared to standard PLCs. This is achieved through redundancy in hardware components and software algorithms, allowing for fault tolerance and minimizing the risk of system failure.

Standards and Certifications

Safety PLCs must comply with specific safety standards and certifications to ensure their suitability for safety-critical applications. These standards often include SIL (Safety Integrity Level) ratings, which define the level of reliability and performance required for the system.


The programming languages used for PLCs and Safety PLCs are generally the same. However, Safety PLCs may offer additional safety-oriented programming languages, such as function block diagrams or structured text, which enable the implementation of complex safety logic.


PLCs are widely used in various industrial sectors for process automation and control. Safety PLCs, on the other hand, find their applications in critical environments where human safety is paramount, such as in manufacturing plants, power generation facilities, or transportation systems.

Benefits of Safety PLCs

  1. Safety PLCs offer enhanced safety features and functions to minimize the risk of accidents and protect human lives.
  2. They provide diagnostic capabilities for early fault detection and troubleshooting.
  3. With their redundant architecture, Safety PLCs ensure continuous operation even in the event of a hardware failure.
  4. Safety PLCs are compatible with various safety devices and systems, enabling seamless integration into existing safety infrastructures.

In summary

While PLCs serve as the backbone of automation systems, Safety PLCs cater specifically to safety-critical applications, offering advanced safety features, high reliability, and compliance with specific safety standards. Employing Safety PLCs ensures that industrial processes are adequately protected, giving peace of mind to operators and minimizing the risk of accidents.


In conclusion, a safety controller is a vital component of a PLC system as it provides an added layer of protection and ensures the safe operation of machinery. By continuously monitoring safety parameters and controlling safety mechanisms, a safety controller plays a crucial role in preventing accidents and maintaining a secure working environment.

0 0 votes
Article Rating
Notify of
Inline Feedbacks
View all comments
Would love your thoughts, please comment.x