Whats the Difference? Safety Relays vs Safety PLCs.

SAFETY RELAYS and Safety PLCs

An introduction to Relays and Plcs

In industrial workplaces, safety relays and safety PLCs are crucial for preventing accidents and ensuring employee safety. Safety relays manage safety-critical inputs and outputs, like emergency stop buttons, to stop machinery when hazards are detected. These devices are vital in industries such as manufacturing and automotive. Safety systems, including controllers, relays, and sensors, protect workers and machinery by monitoring safety functions and ensuring compliance with standards. The samos® PRO, with its intuitive samos® PLAN 6 software, and MOSAIC safety controllers, known for their expandable and modular design, are key solutions for managing multiple safety functions and enhancing safety control systems.

Key differences and features

The primary difference between a safety relay and a safety PLC lies in their complexity and functionality. Safety relays are simpler, electromechanical devices designed for specific safety functions, such as emergency stops or guard monitoring, and are well-suited for straightforward, single or two-step safety applications. In contrast, safety PLCs are more advanced and programmable, capable of handling complex safety tasks by using redundant microprocessors, which eliminate the need for multiple safety relays. Safety PLCs are ideal for applications requiring integrated and flexible safety solutions across multiple machines or processes.

Safety Relays

Safety PLCs

Functionality | Simple devices for opening/closing circuits

Complexity | Suitable for basic control tasks

Programming | No programming required

Scalability | Limited scalability; each relay performs a specific function

Diagnostics | Minimal diagnostics, typically visual indicators

Applications | Used for simple on/off control, e.g., lighting or motor starting

Costs | Generally, less expensive

Additional Features

Safety Relays (DOLD vs Wieland vs ReeR)

At Venus, we offer a range of different safety relays from DOLD, Wieland and ReeR. The DOLD UG6970 is a multifunctional safety module suitable for emergency stops, safety gates, and light curtains, complying with PL e and SIL 3 standards, and featuring adjustable safety functions with LED diagnostics. The Wieland SNV 4063KL-A is an emergency stop relay with time delay capabilities, designed for controlled stops with SIL certification, offering force-guided contacts and adjustable time ranges. The ReeR SR ONE is a safety relay with integrated muting functions, ideal for devices needing manual or automatic start/restart with EDM feedback, meeting SIL 3 and PL e standards, and providing LED status indicators. Other types of safety relay include time-delay relays, speed-monitoring relays, standstill monitoring and timer relays, PCB relays and relay expansion modules. Also available are type-specific control relays, like the safety edge relay, light curtains relay, or two-hand control relay. Each relay addresses specific safety needs, enhancing control in industrial applications.

DOLD

Wieland

ReeR

UF

UG

BH

SNA

SNE

SNO

SNS

SNT

SNV

SNZ

3 NO Contacts

4 NO Contacts

2 NO Contacts

3 NO Contacts

AD SR0

AD SRE

AD SRT

SR E4

SR ONE

SR SELECT

SR T

SR X

Featured Products

Our Product Range

Both safety relays and safety PLCs play essential roles in maintaining safe and efficient industrial operations. While safety relays provide reliable and straightforward solutions for specific safety tasks, safety PLCs offer flexibility and advanced control for complex safety requirements. Together, they form a comprehensive safety framework that protects workers, machinery, and the environment, ensuring compliance with safety standards and enhancing overall operational efficiency. As industries continue to evolve, the integration of these safety technologies will remain crucial in fostering safe and productive workplaces. Click the products below to view the offered products at Venus!

Click to view our Safety Relay product Range

Click to view our Safety PLC product Range

What does the PLC or Relay receive? – Safety Input Device Range

The effectiveness of any safety system, regardless of choice of PLC or relay, begins with its ability to detect hazards and trigger appropriate protective responses. As such, safety input products form the foundation of a reliable safety architecture. Selecting the correct components to match specific hazards is essential for maintaining workplace safety.

Venus Automation offers a wide range of safety input devices to suit varied industrial applications. Detection solutions include the safety light curtain range, available for body protection, hand protection, and finger protection. Options supporting long range sensing and outdoor environments are available, along with muting light curtain models designed for automated processes. Supporting components such as photo cells, connection boxes, and muting accessories are also supplied. Additional detection options include multi beam systems and advanced laser scanner technologies.

To detect presence or motion at close range, proximity sensors are available, including non-contact switches, with magnetic or RFID coding technologies. Enclosures come in plastic, metal, or stainless steel variants for application-specific durability.

Mechanical safety detection is supported by products such as safety edge and mounting systems, contact mats, and bumpers with relevant edge accessories. These are ideal for perimeter and surface-triggered protection zones. For advanced zone control, trapped key systems and blocking devices ensure process integrity.

Manual control inputs are also critical in many safety scenarios. Venus Automation provides safety enabling switches, limit switch options, foot pedal switches, control pads, and standard control components.

Together, these input systems interface with the machine’s transmission system, ensuring rapid response to unsafe conditions. Combined with suitable outputs and logic control, they serve as the first line of defence in safeguarding personnel and equipment.

Conclusion

Choosing between a safety relay and a safety PLC depends on the complexity of the application and safety requirements. For straightforward, single-function safety measures like emergency stop monitoring, safety relays offer a simple and cost-effective solution. However, when managing multiple safety functions across interconnected machinery, programmable safety controllers such as the samos® PRO or MOSAIC safety controller provide greater flexibility, scalability, and diagnostics.

While traditional relays are reliable, industries increasingly lean towards integrated safety PLCs for their ability to streamline complex safety processes and reduce wiring. Both solutions play an essential role in industrial safety, ensuring compliance with stringent regulations and protecting workers and equipment. Selecting the right system involves balancing cost, expandability, and ease of implementation. Whether opting for modular safety relays or advanced programmable logic controllers, implementing a well-designed safety system is crucial to fostering a safe and efficient workplace.