Which PROFINET real-time class delivers the strictest determinism (cycle <= 31.25 us with jitter <= 1 us), making it suitable for motion-control applications?
C — IRT (Isochronous Real-Time)
IRT (Isochronous Real-Time) is correct because it uses precise time-slot scheduling with cycle times down to 31.25 us and jitter below 1 us, which is what motion control demands. NRT is wrong because it carries standard TCP/IP traffic with no timing guarantee and is intended for configuration, diagnostics and web HMIs. RT Class 1 is wrong because, although prioritised at Layer 2 (VLAN tag), its cycle is in the order of 10 ms with millisecond jitter, suitable for typical IO but not motion. TSN is wrong because, while it is the emerging IEEE 802.1 successor to IRT and enables OT/IT convergence, it is not the classical PROFINET class historically associated with the figures stated in the question.
If the spec sheet quotes cycle times in microseconds rather than milliseconds, you are almost certainly in IRT territory and you must verify that every switch on the path is IRT-certified.
- A.NRT (Non Real-Time)
- B.RT Class 1 (Real-Time)
- C.IRT (Isochronous Real-Time)✓
- D.TSN (Time-Sensitive Networking)
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