Zander Aachen SR3AD AC/DC 24V Safety switching device

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. In safety-critical control systems (e.g., emergency stop functions), signals must be transmitted safely without interrupting the safety chain. Conventional coupling relays are not suitable for this purpose, as they lack safety features and, therefore, cannot guarantee a safe shutdown of the machine or system in the event of a hazard.

Safe coupling relays solve this problem. These relays are redundantly constructed and feature self-monitoring mechanisms that enable a safe and standard-compliant coupling of safety-related signals. They are certified to the highest safety standards (up to SIL 3 according to IEC 61508 and PL e according to EN ISO 13849-1), ensuring that the safety function remains intact even if an internal relay failure occurs.

### Typical applications of safe coupling relays:

• Galvanic isolation of 24V digital signals to 230V to safely separate control and load circuits.
• Safe coupling of sensor signals (e.g., from pressure switches) to the control system, enabling 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 safe 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: Internal faults within the coupling relay are automatically detected and reported when the safety function is next requested.
• 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 signal types.

### 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:

• Increased safety: Ensures the safety function is maintained even in the event of an internal relay failure.
• Safety certification: Meets the highest safety standards (SIL 3 / PL e).
• Reliable transmission: Prevents interference and interruptions in the safety chain.
• Robust design: Suitable for harsh environments in the process industry, machine control, and industrial plants.

### Conclusion:
Safe coupling relays are an essential component of safety-critical control systems. They ensure that safety-related control signals are transmitted to peripheral devices in compliance 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.