Magnetostrictive Displacement Sensor on Industrial Ethernet: PROFINET vs EtherCAT

PROFINET is controller and device, EtherCAT is master and slave; the first question is which master the PLC already carries. For position feedback on industrial Ethernet, Germanjet includes two types: 199PROFINET and 197 / 198 EtherCAT. The roles differ: PROFINET is controller and device; EtherCAT is master and slave. The first test is still whether the PLC has that master. See which fieldbus does my PLC support.

PROFINET (199) — advantages

• The on-board PN port on Siemens S7-1200 / S7-1500 is the controller, so a new line is cheap to join.
• Switches are allowed, which keeps cabinet wiring and later extra stations more flexible than a pure daisy chain.
• IRT can align multi-axis sample times on Siemens motion or hydraulic synchronisation.
• Diagnostics, device names and topology detection help when a unit is swapped.
• Configuration uses GSDML, the same habit as TIA Portal.

PROFINET — disadvantages

• An RJ45 on the CPU is not a PROFINET real-time master. Many ports are only for program download and ordinary TCP.
• A non-Siemens controller needs a master card or licence; that is not always cheaper than choosing EtherCAT on a master you already have.
• In IRT the topology is locked; a cable change must be reflected in the project.
• The shortest scan is usually longer than EtherCAT processing-on-the-fly — enough for most cylinder loops, but check the master on very short motion cycles.

Configuration and device names: 199PROFINET explained, IRT and device names.

EtherCAT (197 / 198) — advantages

• The Ethernet frame walks the slaves and is read/written on the fly; cycle time follows data volume, not “one frame per station”.
• DC distributed clocks align sample instants across axes, cleaner than a polling bus.
• Slaves forward frames, so the sensor segment usually does not need its own switch.
• No terminating resistor; leave the last slave OUT open.
• 198 is a single M12 — one less port when nodes are dense.

EtherCAT — disadvantages

• You need an EtherCAT master (motion controller, IPC master, or a licensed soft PLC). A Siemens on-board PN port is not an EtherCAT master.
• IN → OUT order is mandatory; a reversal shows up as a wrong sequence or a stuck Init.
• A bus cycle shorter than the sensor update rate only rereads the same position. Update rate follows stroke; see refresh rate and control cycle.
• Connectors are often M12 D-coded; do not mix with analogue A-coded or SSI D70. See matching the connector.

Slave and DC: 197, 198, DC and jitter.

Side by side

An RJ45 on the CPU is not automatically a PROFINET real-time master or an EtherCAT master; confirm it before ordering 199 or 197. Four-bus table: comparing the whole fieldbus range. Output types: output signals compared.