Profibus vs Profinet comparison
Profibus, introduced in 1989, and Profinet, introduced in 2003, represent two generations of industrial communication promoted by Profibus & Profinet International. While Profibus relies on classic serial fieldbuses, Profinet moves the same ecosystem to industrial Ethernet, adding real-time determinism and IP scalability. The comparison highlights that Profinet achieves cycle times below 31.25 µs in synchronized motion applications, compared to the typical millisecond of Profibus DP.
Comparison table of characteristics
Section titled “Comparison table of characteristics”| Characteristic | Profibus | Profinet |
|---|---|---|
| Year introduced | 1989 | 2003 |
| Transmission medium | Twisted pair RS-485, fiber optic, MBP | Ethernet (twisted pair, fiber optic, wireless) |
| Supported topology | Line, tree, star (with repeaters) | Star, tree, ring, line |
| Maximum speed | 12 Mbit/s | 1 Gbit/s (copper) / 10 Gbit/s (fiber) |
| Maximum distance per segment | 1200 m / 3937 ft at 9.6 kbit/s; 100 m / 328 ft at 12 Mbit/s | 100 m / 328 ft (copper); up to 100 km / 62 mi (fiber) |
| Maximum number of nodes | 126 per network (with repeaters) | Unlimited (depends on Ethernet infrastructure) |
| Typical cycle time | ≥1 ms | ≤1 ms (RT); < 31.25 µs (IRT) |
| Medium access protocol | Token passing between masters, slave polling | Profinet IO (provider/consumer) over Ethernet with IT |
| IEC standard | IEC 61158 Type 3 | IEC 61158 Type 10 |
Network architecture and topology
Section titled “Network architecture and topology”Profibus segments a network into up to 126 stations via a trunk line governed by token passing, while Profinet organizes controllers (IO‑Controller) and field devices (IO‑Device) over a fully switched Ethernet topology with no theoretical station limit. In Profibus, adding repeaters allows extending branches but maintains a master‑slave hierarchy; Profinet in Conformance Class B requires certification of switches, guaranteeing ring topologies with media redundancy without cyclic interruption. Application profiles inherited from Profibus are integrated into Profinet via representatives (IO‑Proxy), facilitating coexistence of both worlds without re-engineering the control loop.
Transmission media and distances
Section titled “Transmission media and distances”The maximum distance per segment in Profibus DP is 1200 m / 3937 ft at 9.6 kbit/s and decreases to 100 m / 328 ft at 12 Mbit/s, while Profinet over copper Ethernet is limited to 100 m / 328 ft per link, but can reach 100 km / 62 mi with single-mode fiber. Profibus PA uses MBP (Manchester Bus Powered) over the same physical pair, limiting speed to 31.25 kbit/s and distance to 1900 m / 6234 ft, whereas Profinet over fiber or WLAN does not inherit that restriction. Robustness against noise in Profibus is improved by cable shielding and active terminators; Profinet transfers that robustness by using shielded Ethernet cables and managed switches that allow network diagnostics via SNMP in CC‑B.
Speeds and real-time performance
Section titled “Speeds and real-time performance”Profibus DP reaches a fixed speed of up to 12 Mbit/s, sufficient for 1 ms cycles in sequential control, while Profinet in CC‑C offers 100 Mbit/s with IRT (Isochronous Real Time), achieving phase synchronization with jitter below 1 µs and cycles of 31.25 µs, ideal for multi-axis motion control. In CC‑D, Profinet relies on Time‑Sensitive Networking (TSN) over Gigabit Ethernet to guarantee bandwidth even in converged networks with IT and OT traffic. Profibus latency is deterministic but dependent on network size; Profinet separates cyclic data from acyclic data at Ethernet layer 2, keeping jitter bounded regardless of the number of devices.
Number of supported devices
Section titled “Number of supported devices”Profibus allows up to 126 stations per physical network, while Profinet is scalable to thousands of devices, since each IO‑Device occupies an IP address within an Ethernet subnet and subnets are interconnected via layer‑2 switches. In process applications, Profibus PA is usually limited to 32 devices per segment, whereas Profinet in a ring topology can chain up to 50 IO‑Devices without a repeater, expandable with additional switches. Integrating Profibus devices through a proxy in Profinet does not reduce the total number of Profibus nodes in the original segment, but allows unifying management of the entire installation in a single IP protocol.
Typical applications
Section titled “Typical applications”Profibus is used in more than 50 million installed nodes in process and factory automation, standing out in environments with long distances and explosive atmospheres (Profinet did not exist when many chemical plants were designed). Profinet exceeds 50 million devices in high-speed synchronized motion control, robotics, and production systems that converge with corporate IT. Profinet conformance classes (CC‑A to CC‑D) cover everything from smart buildings to fully integrated factories with transparent redundancy, while Profibus remains the most common choice for modernizing existing installations without changing the RS‑485 field wiring.
References
Section titled “References”- automationdirect.com: https://www.automationdirect.com/adc/home/home