Safe and non-safe coupling relays:

In the process industry, the safe transmission of safety-related signals from the controller to peripheral devices is crucial, especially for emergency stop functions or machine and personnel protection. Conventional coupling relays are unsuitable for this task, as they lack safety features and may interrupt the safety chain. This interruption could prevent the system from performing a safe shutdown in the event of a hazard.

To solve this issue, safe coupling relays are used. These relays are certified to the highest safety standards (up to SIL 3 according to IEC 61508 and PL e according to EN ISO 13849-1) and ensure that safety-related signals are transmitted to peripheral devices in compliance with the standards. Safe coupling relays are redundantly constructed and feature self-monitoring, which detects and reports faults within the relay. This ensures that the safety function remains intact even if an internal failure occurs.

### Typical applications of safe coupling relays:

• Galvanic isolation of 24V digital signals to 230V, ensuring the safe separation of control and load circuits.
• Safe coupling of sensor signals (e.g., pressure switches) to the control system, ensuring the secure connection of safety-related sensors to the control system.
• Contact amplification for control units with limited output power, allowing larger loads to be switched safely.
• Filtering of test pulses from safety controllers to prevent signal disruptions and ensure only valid signals are processed.

### Features of safe coupling relays:

• Redundant design: Safe coupling relays use force-guided contacts, ensuring that a contact failure does not lead to a loss of the safety function.
• Self-monitoring: The coupling relay detects internal faults independently and reports them so that the safety function remains intact.
• Compliance with safety standards: Safe coupling relays meet the highest safety requirements up to SIL 3 (IEC 61508) and PL e (EN ISO 13849-1).
• Galvanic isolation: Control and load circuits are galvanically isolated to prevent interference or overvoltage.
• Detection of test pulses: Safe coupling relays filter out test pulses from controllers to prevent them from triggering incorrect signals.
• Flexibility and versatility: They can be used in a wide range of applications and support both digital and analog signals.

### Differences between safe and non-safe coupling relays:
| Feature | Safe Coupling Relay | Non-Safe Coupling Relay |
|---------------------------- |-------------------------------------|-------------------------------------|
| Force-guided contacts | Yes | No |
| Redundancy | Yes | No |
| Self-monitoring | Yes | No |
| Certified up to SIL/PL | Up to SIL 3 / PL e | No safety certification |
| Galvanic isolation | Yes | Optional, not always available |
| Filtering of test pulses | Yes | No |

### Advantages of safe coupling relays:

• Highest safety standards: Certification up to SIL 3 and PL e ensures compliance with safety regulations.
• Increased fault tolerance: Relay faults do not lead to the loss of the safety function, as errors are detected through self-monitoring.
• Reliable signal transmission: Prevents interference and interruptions in the safety chain through galvanic isolation.
• Robust design: Suitable for use in process industries, machine control, and safety-critical plants.

### Conclusion:
Safe coupling relays are essential for safety-critical control systems. They ensure that safety-related control signals are transmitted to peripheral devices in accordance with standards. Thanks to force-guided contacts, self-monitoring, and certification up to SIL 3 / PL e, safe coupling relays guarantee that the safety function remains intact even if an internal fault occurs. In contrast, non-safe coupling relays provide no such guarantee and are only suitable for simple, non-safety-related applications.