Zander Aachen SR3AD AC/DC 24V Safety switching device

Safe and non-safe coupling relays:

In the process industry, safety-related signals, such as the output signals of a safety controller, must be reliably transmitted to peripheral devices. Conventional coupling relays are unsuitable for this task, as they can interrupt the safety chain, making it impossible to ensure a safe shutdown in the event of a hazard.

This issue is resolved by using safe coupling relays. These relays are redundantly constructed and feature self-monitoring capabilities. This allows for the standard-compliant coupling of safety-related signals in accordance with the highest safety standards up to SIL 3 / PL e. Even in the event of an internal relay fault, the safety function is maintained.

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 such as pressure switches to the control system, ensuring the reliable transmission of safety-related signals.
• Contact amplification for control units with limited output power, enabling the control of larger loads safely.
• Filtering of test pulses sent by safety controllers, preventing signal disruptions and ensuring error-free signal processing.

### Features of safe coupling relays:

• Redundancy and force-guided contacts: The use of force-guided relays ensures that the safety chain remains intact even if one component of the relay fails.
• Self-monitoring: The coupling relay can detect internal faults on its own and report them, allowing the system to respond appropriately the next time the safety function is requested.
• Safety requirements: Safe coupling relays meet the highest safety standards up to SIL 3 (IEC 61508) and PL e (EN ISO 13849-1).
• Galvanic isolation: Control and load circuits are electrically separated to prevent interference or overvoltage.
• Flexibility: Supports various signal types (digital 24V to 230V, OSSD signals, etc.).

### 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 | Not specified |
| Galvanic isolation | Yes | Optional, not always available |
| Filtering of test pulses | Yes | No |

Conclusion:

While non-safe coupling relays are sufficient for standard applications, safe coupling relays are essential for safety-critical processes. They ensure that safety-related control signals are transmitted to peripheral devices in accordance with the standards, and they guarantee that the safety function is maintained at all times – even if a fault occurs within the coupling relay.