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 the peripheral devices. Conventional coupling relays are unsuitable for this purpose, as they can interrupt the safety chain and prevent a safe shutdown in the event of a hazard. This issue is resolved by using safe coupling relays.

Safe coupling relays are redundantly constructed and self-monitoring, enabling the standard-compliant coupling of safety-related signals up to the highest safety requirements according to SIL 3 and PL e. This ensures that the safety function is maintained even if a fault occurs within the relay.

Typical applications of safe coupling relays include:

• Galvanic isolation of digital 24V signals to 230V
• Safe coupling of sensor signals, such as pressure switches, to the control system
• Contact amplification for control units with limited output power
• Filtering of test pulses sent by safety controllers

In contrast, non-safe coupling relays do not offer monitoring or redundancy, which can interrupt the safety chain. They are primarily used in applications where no safety-related shutdown is required.

Technical features of safe coupling relays:

• Usable up to SIL 3 / PL e according to EN ISO 13849-1 and IEC 61508
• Redundant design with force-guided contacts
• Self-monitoring for fault detection
• Galvanic isolation of control and load circuits
• Filtering of test pulses for signal processing
• Robust design for use in safety-critical applications

By using safe coupling relays, the safety chain remains intact, and safety-related control signals are transmitted to peripheral devices in compliance with standards. They are used in the process industry, machine control systems, and plants where the highest safety requirements are essential.