Hardwired Safety Relays or Safety PLCs

Choosing the right safety system for your industrial environment can make a significant difference in protecting your workers and equipment. The decision between Hardwired Safety Relays and Safety PLCs is vital at the project design stage. With both options offering distinct advantages, understanding their differences will help you choose the best solution for your specific needs.

Understanding Hardwired Safety Relays

Hardwired safety relays are traditional devices specifically designed to monitor safety circuits. They work on a straightforward principle: when a safety device, such as an emergency stop button, is activated, the relay immediately interrupts the power to the machinery. This quick action prevents potential hazards, ensuring worker safety.

These relays are known for their durability and ease of installation. Their typical low cost ranges, make them an economic option for smaller operations or industries with less complex safety needs. They require minimal programming—often just basic wiring—which is appealing to facilities looking for a quick safety solution.

However, it’s essential to note that hardwired safety relays come with limitations on flexibility. Once these systems are installed, making changes or upgrades can be labour-intensive, requiring significant rewiring. For example, a company may find that it needs additional safety features as operations grow; retrofitting a hardwired relay system can cost thousands in labor alone.

Exploring Safety PLCs

On the other hand, safety PLCs (also known as Fail-Safe CPUs) provide a more sophisticated option for safety management. They combine standard PLC capabilities with advanced safety features, allowing for the management of more complex safety applications.

Safety PLCs can handle multiple safety functions at once and can be programmed to adapt to various scenarios. For instance, in the example in the figure below it is used to monitor Emergency Stops, and Light Curtains simultaneously, adjusting their response according to specific thresholds. This flexibility becomes invaluable for larger operations or fast-paced environments, where safety requirements often change.

While safety PLCs typically have a higher initial cost on paper—they can save time and resources, including electrical labour for wiring. Their capability to integrate with other systems, along with real-time monitoring and data analytics, enhances overall safety management. In addition the diagnostics are a game changer (when done properly) for troubleshooting machine wiring and faults.

Safety PLCs also offer different SIL/PL ratings according to the application and configuration with safety components. In the case of the example below SIL3/PLe rating was achieved with a cost-effective S7-1200FC CPU, without the need of a Safety Partner CPU.

Key Differences Between Hardwired Safety Relays and Safety PLCs

1. Complexity: Hardwired safety relays are simpler and easier to install; safety PLCs offer advanced programming capabilities for more complex needs.

2. Cost: While hardwired safety relays are generally more affordable upfront, safety PLCs may provide better long-term value due to their flexibility and adaptability.

   
   

3. Maintenance: Modifying hardwired systems can be challenging; safety PLCs can be updated easily through software changes, simplifying maintenance, also offering tamper-resistant features to avoid significant employee injury or fatality.

   
   

4. Functionality: Safety PLCs can manage multiple safety functions and integrate seamlessly with other systems, while hardwired relays handle specific tasks only. Not to mention the ability to integrate complex motion components and operate seamlessly together, ie. 1500TF PLCs, or L8xES PLCs

   
   

   

   Example of Machine Safety with Light Curtain, Emergency Stop, and HMI Safety Status

Choosing the Best Fit for Your Needs

Deciding between hardwired safety relays and safety PLCs ultimately hinges on the unique requirements of your operation. If your facility is smaller with relatively simple safety needs, hardwired safety relays may be the best fit. Their ease of use, reliability, and lower initial cost make them attractive for many manufacturers.

However, if your operations are more complex or subject to frequent changes in safety requirements, investing in a safety PLC could yield significant benefits. The advanced features, enhanced safety management, and long-term viability of safety PLCs makes it a well-worth investment.

Evaluating your specific needs against the strengths and limitations of each option will lead you to the right choice.

Prioritizing Safety in Your Operations

In summary, both hardwired safety relays and safety PLCs are effective solutions for industrial safety management. By grasping the differences and evaluating your unique operational demands, you can confidently select the appropriate system. Remember, whether your choice leans toward the simplicity of hardwired relays or the advanced features of safety PLCs, prioritizing safety in your setup remains the most important goal.

Reach out to us to evaluate your Machine Safety requirements, and any Machine Safety upgrades.