Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
IEC 62411: Real-time Ethernet PROFINET IO – Decentralised Periphery for Industrial Automation
IEC PAS 62411 | First Edition 2005 | IEC 61158 Type 10
1. Introduction to PROFINET IO
IEC PAS 62411 defines PROFINET IO, a real-time Ethernet protocol for decentralised periphery in industrial automation. It provides a framework for communication between IO controllers (PLCs) and IO devices (sensors, actuators, drives) over standard Ethernet infrastructure.
PROFINET IO supports RT (Real-Time) for standard cyclic I/O and IRT (Isochronous Real-Time) for deterministic motion control with synchronised clock distribution.
RT achieves 250 µs cycle times for standard I/O; IRT achieves 31.25 µs with jitter below 1 µs for demanding motion control.
2. System Architecture
2.1 Device Roles
IO Controller (PLC) executes the automation program. IO Device is a distributed field device providing process data. IO Supervisor is an engineering station for commissioning and diagnostics.
2.2 Slot Model
| Element | Description |
|---|---|
| Application Process Interface (API) | Logical grouping of application objects |
| Slot | Physical or logical module |
| Subslot | Individual data channel within a slot |
The slot/subslot model enables flexible device configuration and plug-and-play behaviour.
3. Real-Time Communication
3.1 RT and IRT
RT uses IEEE 802.1Q VLAN tagging for prioritisation. IRT adds precision time synchronisation per IEEE 1588/IEC 61588 with dedicated time slots.
3.2 Time Synchronisation
IRT uses hierarchical clock synchronisation with line delay measurements to calculate precise timing offsets for each device.
| Parameter | Description |
|---|---|
| Line Delay Measurement | Propagation delay between adjacent devices |
| Green Interval | IRT scheduled communication slot |
| Red Interval | RT and standard Ethernet slot |
4. Engineering Design Insights
IRT green/red interval separation allows mixed operation of motion control and IT traffic. DCP simplifies network setup with automatic address assignment. MRP supports ring topologies with rapid failover.
IRT requires specialised switches with schedule-driven forwarding and transparent clocking. Standard switches introduce variable latency unsuitable for IRT.
5. Frequently Asked Questions
Q: Difference between RT and IRT?
A: RT uses 802.1Q priority; IRT adds deterministic scheduling and synchronised clocks.
A: RT uses 802.1Q priority; IRT adds deterministic scheduling and synchronised clocks.
Q: Can PROFINET share switches with standard Ethernet?
A: RT can via VLAN; IRT requires specialised switches.
A: RT can via VLAN; IRT requires specialised switches.
Q: How are devices addressed?
A: By device name (not IP). DCP maps names to IP addresses during startup.
A: By device name (not IP). DCP maps names to IP addresses during startup.
Q: What diagnostics are available?
A: Channel-specific error reporting, alarm handling, and logbook mechanism.
A: Channel-specific error reporting, alarm handling, and logbook mechanism.
