EN 50325-5:2010

Background and Context

EN 50325-5:2010 is the European Standard that defines how CANopen networks can be used in functional safety applications. Published by CENELEC in July 2010 and reconfirmed in May 2023, it carries the formal title Industrial Communications Subsystem Based on ISO 11898 (CAN) for Controller-Device Interfaces — Part 5: Functional Safety Communication Based on EN 50325-4 and is widely known simply as CANopen Safety.

The standard sits atop EN 50325-4 (CANopen), which is itself built on the ISO 11898 CAN physical and data link layer. Rather than replacing CANopen, EN 50325-5 extends it — adding a Safety Communication Layer (SCL) that enables CANopen networks to carry safety-relevant data with the integrity required by the EN 61508 series for functional safety of electrical, electronic, and programmable electronic systems.

Why CANopen Safety Was Needed

By the mid-2000s, fieldbus technology had become widely adopted in industrial automation — but standard CANopen (EN 50325-4) was designed for general-purpose control communications, not for safety-critical data exchange. A standard CAN message offers no guarantee that corruption will be detected, no protection against message loss or duplication, and no mechanism to identify silent device failure. In applications where a communication fault could cause injury or loss of life — a robot arm that fails to stop, a crane that drops its load, a safety light curtain that fails to respond — this is unacceptable.

EN 50325-5 addresses this gap by layering a dedicated safety protocol on top of existing CANopen infrastructure. The approach is intentionally conservative: the standard treats the underlying CAN/CANopen transport as an untrusted "black pipe" and implements all safety measures within the application layer itself, rather than relying on the transport to guarantee integrity. This white channel approach means EN 50325-5 can coexist with non-safety CANopen traffic on the same network, and no replacement of existing CANopen hardware is required.

Scope and Application Areas

EN 50325-5 applies to any EN 50325-4-based network that needs to provide safety-related communication between devices in accordance with EN 61508. It supports applications across a broad range of industries:

• Manufacturing and machinery — safety PLCs, safety-rated drives and servo systems, robot safety circuits
• Mobile machinery — agricultural equipment, construction machinery, cranes
• Medical devices — operating theatre equipment, patient-handling systems
• Process control — safety instrumented systems (SIS) in line with EN 61511

The standard defines requirements at the communication layer only. It does not cover safety-related configuration and commissioning procedures (which are application- and system-specific), nor does it address electrical safety, intrinsic safety for explosive atmospheres, or cybersecurity.

Relationship to Other Standards

EN 50325-5 is part of a broader functional safety and fieldbus standards ecosystem. The foundational safety requirements come from the EN 61508 series, which defines Safety Integrity Levels (SIL 1 through SIL 4) and the systematic requirements safety systems must meet. General principles for safety fieldbus communication are established in EN 61784-3, which provides common rules applicable across all functional safety fieldbus profiles; EN 50325-5 is the CANopen-specific profile within that framework.

In machinery contexts, EN 50325-5 interfaces with EN 62061 (functional safety for machinery, SIL-based), EN ISO 13849-1 (safety-related parts of control systems, Performance Level-based), EN 61800-5-2 (safety functions for drives), and EN 61131-6 (safety for PLCs). In process industries, EN 61511 applies alongside EN 61508. The standard also references EN 61326-3-1 and EN 61326-3-2 for EMC immunity requirements — an important consideration given that CAN networks in industrial environments are routinely exposed to electrical noise.

Core Technical Concepts

The primary safety mechanism defined by EN 50325-5 is the SR Data Object (SRDO) — a safety-wrapped extension of the standard CANopen Process Data Object (PDO). Key design elements include:

• Dual-message transmission: Each SRDO is sent as a pair of CAN messages — the data message and an inverted copy — providing an automatic cross-check at the receiver.
• CRC integrity: A CRC is computed over the safety-relevant data and configuration parameters, including node addresses and COB-IDs.
• Safeguard Cycle Time (SCT): A watchdog mechanism that ensures messages arrive within the expected time window.
• SR Validation Time (SRVT): Governs how long a receiver waits before validating the SRDO pair.
• Global Failsafe Command (GFC): A broadcast message that instructs all SR devices on the network to enter their safe state simultaneously, enabling a coordinated network-wide response to a detected fault.

The SCL management section of the standard covers SR network initialization, boot-up sequencing, and device configuration, ensuring that safety-related devices enter operational mode only after their configuration has been verified as consistent and correct.

SIL Claims and Implementation Considerations

A critical point the standard makes explicit: implementing EN 50325-5 in a device does not automatically make that device a safety device. The SIL claim of a complete system depends on how the services and protocols are implemented across both the devices and the system as a whole — including application software, hardware design, and overall safety lifecycle management. Implementers must demonstrate compliance with the broader EN 61508 series requirements beyond what the communication profile alone provides.

When properly implemented, the standard supports up to SIL 2 at the communication layer. The informative Annex A provides four example SR communication models — point-to-point, one-to-many, many-to-one, and broadcast architectures — to help system designers structure their safety networks.

Getting this right requires deep expertise in both the CANopen protocol stack and the EN 61508 functional safety requirements. For development teams building products on CANopen, starting with a proven, standards-compliant protocol stack significantly reduces development time and the risk of subtle protocol errors that could undermine a SIL claim. Simma Software's CANopen stack is designed for embedded systems and provides a solid foundation for both standard and safety-related CANopen development.

Conclusion

EN 50325-5:2010 fills an important niche: it gives engineers a standardized, proven path to leverage the widespread CANopen ecosystem for functional safety applications — without requiring a separate, dedicated safety bus. By defining a well-specified safety communication layer that sits cleanly on top of standard CANopen, the standard enables mixed safety and non-safety traffic on the same network, simplifies system architecture, and provides a clear route to SIL certification.

For anyone designing safety-rated machinery, mobile equipment, or process control systems that already use — or are considering — CANopen, understanding EN 50325-5 is essential groundwork. Implementing it successfully requires both a thorough understanding of the standard and a reliable protocol stack to build on. Simma Software brings decades of CAN expertise to this challenge. Their CANopen software stack gives development teams a proven starting point, whether they are building standard CANopen devices or targeting the safety communication profile defined in EN 50325-5.