Magnetostrictive output signals compared: eight interfaces and their trade-offs

A magnetostrictive displacement sensor turns magnet position into an electrical signal for the controller. Germanjet electrical outputs are these types: 4-20 mA current, 0-10 V voltage, SSI, Start-Stop, CANopen, Profibus DP, EtherCAT and PROFINET. The interface does not change measuring capability. It changes how the data travel: how many cores, noise immunity, whether diagnostics ride along, and how many axes share one cable. The tables below compare advantages and disadvantages. Look at the controller ports first, then stroke and mounting.

Eight outputs on one table

Output	Type codes	Advantages	Disadvantages	Fits
4-20 mA current	161 / 184 / 185 / 191 / 121	Broken wire is not zero; long cable stays stable; almost every PLC has an analogue input	Resolution capped by the PLC A/D; one pair per axis; no status word	Single axis, retrofit, analogue channels only
0-10 V voltage	160 / 180 / 190 / 120	Simple wiring; older machines often have a voltage input	Broken wire looks like zero; more sensitive to noise and earth potential	Legacy voltage inputs
SSI	162 / 192	Digital and noise-tolerant; bit length and Gray code are configurable	Still point-to-point; longer cables force a lower baud	Motion cards, single-axis digital loops
Start-Stop	183 / 193	Very small interface; timing sits in the controller	Needs a fast timer; speed-of-sound drift is compensated on the PLC	Controllers with a native timer port
CANopen	194	Several axes on one twisted pair; EMCY can report a fault unsolicited	Less bandwidth than industrial Ethernet; 120 Ω at both ends	Mobile hydraulics, native CAN
Profibus DP	195	A Siemens installed backbone can keep its cable; mature GSD	Master–slave polling; rarely chosen for a new line	S7-300 / 400 retrofit
EtherCAT	197 / 198	Short cycles; DC can align multi-axis samples	Needs an EtherCAT master; IN/OUT order is mandatory	Fast multi-axis sync
PROFINET	199PROFINET	The on-board PN port is the controller; IRT	An RJ45 is not automatically a real-time master	New S7-1200 / 1500 lines

How type codes map to series: 160 / 161 / 162, 180–185, 190–199. Product matrix: analogue vs digital.

4-20 mA current

Series 16 uses 161; Series 19 often 191; Series 18 uses 184 / 185 (reversed span). Series 12 current is 121 (16-bit D/A).

Advantages

• Live zero: a broken wire is not “position at zero”.
• Voltage drop on a long cable does not change the current.
• Almost every PLC has an analogue input, so retrofit cost stays low.

Disadvantages

• Resolution is capped by the PLC A/D. Extra bits on the sensor do not lift that ceiling.
• One pair per axis; cabinet wiring grows quickly with axis count.
• No status word; faults other than a broken loop need a separate check.

The coarse analogue-versus-fieldbus split is in 4-20 mA or fieldbus. PLC stuck at zero: analogue reading at zero.

0-10 V voltage

Series 16 uses 160; Series 19 uses 190; Series 18 uses 180. Series 12 code 120 is listed as infinite resolution (limited by the controller A/D).

Advantages

• Wiring is simpler than a current loop.
• A stock of older machines only has a voltage input.

Disadvantages

• A broken wire and a true zero cannot be told apart.
• More sensitive to noise, earth potential and contact resistance; current is more stable on a long run.

Prefer current when the controller can take it.

SSI

Point-to-point digital: RS-422 clock and data. 162 is Series 16 in-cylinder; 192 is Series 19. The electrical figures are the same set; the mechanics are not. See 162 vs 192.

Advantages

• Digital transmission, clearly more noise-tolerant than analogue.
• Bit length and binary / Gray code are configurable; motion cards often already have the port.
• Still one cable per axis, lighter to configure than a fieldbus.

Disadvantages

• No multi-drop; cables and ports scale with axes.
• Longer cables force a lower baud — distance and rate trade off.

How to drop the clock after a longer cable: SSI length versus rate.

Start-Stop

Series 18 uses 183; Series 19 uses 193. See Start-Stop.

Advantages

• A very small interface: the sensor only issues start and stop pulses.
• Timing sits in the controller, so the electronics head does less work.

Disadvantages

• The controller needs a fast enough timer.
• Speed of sound drifts with temperature; compensation belongs on the PLC.

CANopen (194)

The physical layer is a CAN differential pair, not RS-485. 194 is CANopen; position objects follow DSP406. Detail: 194. Versus Profibus: CANopen vs Profibus.

Advantages

• Mobile and hydraulic controllers often have a native CAN port.
• Several axes share one twisted pair.
• EMCY can report a fault without waiting to be polled.

Disadvantages

• Less bandwidth than industrial Ethernet; cycles are not as short as EtherCAT.
• Baud versus length is a hard trade-off; 120 Ω is required at both ends.

Profibus DP (195)

The physical layer is RS-485. Detail: 195.

Advantages

• A Siemens S7-300 / 400 backbone can keep its cable.
• GSD configuration is mature; standard diagnostic telegrams are easy to read on site.

Disadvantages

• Master–slave polling; no EtherCAT-style distributed clock.
• New projects rarely choose it on purpose — it mainly keeps an old master alive.

EtherCAT (197 / 198)

197 is a dual-port daisy chain; 198 is a single M12 when space is tight. Detail: 197, 198. Versus PROFINET: PROFINET vs EtherCAT.

Advantages

• Processing-on-the-fly; cycle time follows data volume, which suits short multi-axis cycles.
• DC can align sample instants across axes.
• Slaves forward frames, so the sensor segment usually needs no extra switch.

Disadvantages

• You need an EtherCAT master. 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.

PROFINET (199)

Detail: 199PROFINET.

Advantages

• The on-board PN port on S7-1200 / 1500 is the controller, so a new line joins cleanly.
• Switches are allowed, which keeps cabinet wiring and later extra stations more flexible than a pure daisy chain.
• IRT can align multi-axis samples; diagnostics and device names fit Siemens plants.

Disadvantages

• An RJ45 on the CPU is not a PROFINET real-time master. Many ports are only for program download.
• A non-Siemens controller needs a separate master, which is not always cheaper than EtherCAT on a master you already have.

The four-bus table is comparing the whole fieldbus range.

How to choose

• Analogue input, single axis or retrofit → prefer 4-20 mA; use 0-10 V only if that is the only input.
• Motion card already has SSI, still one axis, need digital noise immunity → SSI.
• The controller times the pulses itself and the interface must stay small → Start-Stop.
• Mobile machine, hydraulic controller with CAN → 194.
• Siemens S7-300 / 400 installed backbone → 195.
• Fast multi-axis sync and an EtherCAT master already present → 197 / 198.
• New Siemens S7-1200 / 1500 line → 199.

Whatever port the controller has, that is the output the sensor should use. Fix the output type before stroke and mounting.