Demystifying IO-Link Safety: A Guide to Safety Blocks and Their Capabilities

Comparing “IO-Link” and “Safety” to “IO-Link Safety”

Many I/O blocks have “IO-Link” and “Safety,” which can create confusion about the specific safety features they offer. Here’s a quick overview of safety-labeled blocks and how they relate to IO-Link Safety.

Safety network blocks

These blocks have I/O ports where Pin 4 and Pin 2 are OSSD signals (safety ports). OSSD, or output switching signal devices, send 24-volt signals over two wires to verify safe operation. If either signal drops to 0 volts (apart from brief safety-check pulses), it’s interpreted as a safety event triggering the machine to enter a safe state. Safety network blocks are designed for standard (non-networked) safety devices and communicate directly back to a safety controller using protocols like CIP Safety or PROFIsafe. These blocks typically monitor between 8 to 16 standard safety devices, which have no built-in intelligence.

Safety network blocks with IO-Link

Blocks in this category typically feature a mix of I/O ports ranging from standard I/O to standard IO-Link communication. They also include ports where Pin 4 and Pin 2 are OSSD signals (safety ports). These blocks communicate via safety protocols and have limited ports for connecting standard (non-networked) safety devices. They offer some versatility, allowing you to connect standard sensors, IO-Link devices, and safety devices. However, you may be short on the specific type of port you need, leading to additional blocks to meet safety or IO-Link requirements. The safety devices themselves have no built-in intelligence.

Safety over IO-Link blocks

In this system architecture, standard IO-Link Masters communicate with Safety PLCs/Controllers using standard protocols like EtherNet/IP and PROFINET. Safety over IO-Link devices, currently limited to only Safety over IO-Link hubs, are connected to the IO-Link ports of these masters. The Safety PLCs/Controllers use safety protocols like PROFIsafe to communicate with the IO-Link Master, which then bridges the connection to the Safety over the IO-Link hub via the “black channel” Using the IO-Link communication channel. The ports on these safety over IO-Link hubs use Pin 4 and Pin 2 as OSSD signals (safety ports), allowing for the connection of standard (non-networked) safety devices. This system served as a “gap filler” while IO-Link Safety was in development, enabling both standard IO-Link devices and Safety over IO-Link hubs to connect to any port, adding versatility to applications and showcasing the early advantages of IO-Link. However, the safety devices still have no built-in intelligence.

IO-Link Safety

IO-Link Safety introduces a safety communication layer to the IO-Link system. Unlike Safety over IO-Link, this safety layer applies to both the IO-Link Master and IO-Link Safety devices. In a network using CIP Safety or PROFIsafe, the safety communication protocol takes priority over standard EtherNet/IP or PRIFONET data when both coexist on the same network. The same principle applies to IO-Link Safety: both standard and safety IO-Link protocols can run over the same physical cable between the IO-Link Master ports and IO-Link Safety devices, with IO-Link Safety having the highest priority. For more details on the IO-Link Safety protocol, you can visit the IO-Link Consortium's website at io-link.com.

In this architecture, IO-Link Safety Masters communicate with Safety PLCs/Controllers using safety protocols like CIP Safety and PROFIsafe. The Masters ports can use Pin 4 and Pin 2 as OSSD signals (safety ports), so standard (non-network) to connect standard (non-networked) safety devices. Pin 4 also supports both standard IO-Link and IO-Link Safety communication for standard IO-Link devices and IO-Link Safety devices, respectively. This setup provides the most versatile safety solution available, as IO-Link Safety Masters can accommodate standard safety devices, standard IO-Link devices, and IO-Link Safety devices. Intelligence is not built into IO-Link Safety devices.

Benefits of IO-Link Safety

• IO-Link Safety devices are fieldbus-neutral: simply choose an IO-Link Safety Master that matches the protocol of the Safety PLCs/Controllers.

• IO-Link Safety Master port flexibility: you can connect standard (non-network) safety devices, standard IO-Link devices, and IO-Link Safety devices.

• Parameter storage: parameters for both standard IO-Link and IO-Link Safety can be stored, making device replacement easier.

• Smart data from IO-Link Safety devices: access more information, such as internal temperature, humidity, cycle count, power usage, diagnostics, and more.

• Simplified wiring: IO-Link Safety devices can connect to the IO-Link Master port using standard 3- to 4-conductor cables.

• IIoT integration: IO-Link Safety provides better visibility to higher-level systems like SCADA, enabling safety device-level monitoring.

I'm excited to see how quickly IO-Link Safety will be adopted, especially given the rapid growth of IO-Link in recent years. The future looks promising with advancements like IO-Link Wireless, IO-Link Safety, IO-Link Wireless, and eventually, Single-Pair Ethernet (SPE). With all these new capabilities, what application won't IO-Link be able to support?