Safe and Non-Safe Coupling Relays – Standard-Compliant Signal Transmission for Maximum Safety

In process industries, the safe transmission of signals is essential, especially when safety-critical signals, such as the output signals of a safety controller, must be connected to the periphery. Simple coupling relays are not suitable for this purpose as they can interrupt the safety chain, making a safe shutdown in the event of a hazard no longer possible.

Safe Coupling Relays – Functionality and Advantages
Safe coupling relays solve this problem through a redundant and self-monitoring design. These relays are designed to detect failures, such as contact welding, and ensure a safe shutdown. This allows them to enable the standard-compliant coupling of safety-critical signals up to the highest safety requirements according to SIL 3 / PL e.

Typical applications of safe coupling relays:

• Galvanic Isolation: Coupling digital 24V signals to 230V to avoid interference.
• Safe Coupling of Sensor Signals: Connecting safety-critical signals (e.g., from pressure monitors) to the controller.
• Contact Reinforcement: Reinforcement of controller outputs with limited output power.
• Test Pulse Filtering: Filtering of test pulses emitted by safety controllers to ensure proper detection of shutdown conditions.

Differences between safe and non-safe coupling relays
| Feature | Safe Coupling Relays | Non-Safe Coupling Relays |
|-----------------------|-----------------------------------|--------------------------------------|
| Purpose | Ensure the safety chain | Normal signal transmission |
| Self-Monitoring | Yes, with fault detection | No |
| Redundancy | Redundant switching contacts | Single contacts |
| Safety Requirement | Up to SIL 3 / PL e | None |
| Application Areas | Safety-critical applications | General control signals |

Why use safe coupling relays?

• Safety Function: They ensure that safety-critical signals are correctly and reliably transmitted in the event of an emergency.
• Standards Compliance: Meets the safety category requirements up to SIL 3 (according to IEC 61508) and PL e (according to EN ISO 13849-1).
• Fault Detection: With self-monitoring, failures such as contact welding or line faults are detected immediately.
• Flexibility: Safe coupling relays enable the connection of 24V control signals to 230V loads, making them ideal for industrial automation.

Safe coupling relays are an essential component of modern safety concepts. They not only provide the advantage of standard-compliant signal transmission but also offer improved diagnostics and fault security. Rely on safe coupling relays for maximum process safety.