Selecting a Magnetostrictive Displacement Sensor: 4-20 mA Analog or CANopen Fieldbus?

When buying a magnetostrictive displacement sensor, the first question that cannot be avoided is: analog or fieldbus for the signal output? The two are not a matter of "whichever is more advanced is more suitable", but of your control system and operating conditions. The boundaries of each are set out below.

When analog output (4-20 mA / 0-10 V) is the right choice

Analog is the traditional but most robust approach. The sensor converts position into a standard current or voltage and feeds it directly into a PLC analog input module.

• Advantages: simple wiring; almost any PLC has analog inputs; a low commissioning threshold — a multimeter is enough to measure; low cost per point.
• Disadvantages: resolution is limited by the PLC's ADC bit depth (commonly 12–16 bit); one channel takes only one signal, so multi-axis machines need more cabling; long runs suffer voltage drop and temperature drift; immunity is only moderate, and running alongside power cables invites crosstalk.

Products such as the Series 191 analog suit single-axis machines, retrofits and cost-sensitive applications.

When fieldbus output (CANopen / Profibus / EtherCAT / PROFINET) is the right choice

The bus packs position data into digital telegrams and hangs multiple devices on a single communications cable.

• Advantages: digital transmission and high resolution (16 bit and above is readily achieved); one bus can carry dozens of axes, saving cable and cabinet space; built-in diagnostics (open circuit, overtravel, communications timeout); strong immunity — differential signalling copes with the shop-floor electromagnetic environment.
• Disadvantages: a matching bus master is required (the controller must support the protocol); commissioning needs familiarity with PDO/SDO or GSD files, so the threshold is higher; hardware cost per point is somewhat higher than analog.

Multi-axis synchronisation, servo closed loops and lines that need remote diagnostics almost always go to the bus — for example Series 194 CANopen and Series 197 EtherCAT.

How to choose: one table makes it clear

Practical constraints of protection rating and signal type

Whether analog or fieldbus, connector protection must keep up. The sensor body can achieve IP67 or even IP69K (for example the Series 13 mobile hydraulic type), but the protection rating of the plug and cable is often the weak link — on a bus in wet, oily environments you depend even more on a reliable M12 connector; do not let the interface hold the installation back.