Checking a Magnetostrictive Displacement Sensor with a Multimeter: 5 Steps to Locate the Fault

To tell a magnetostrictive displacement sensor good from bad, five multimeter steps localise the fault to supply, output, lamps, insulation or install. When a field sensor "has no signal", the first move is not necessarily to remove it and send it for repair. With a multimeter, the five steps below can quickly decide whether the problem is the sensor body, or the supply, wiring, position magnet or installation. Decide correctly, then decide whether to return it to the factory or handle it on site — time and money saved.

Step 1: measure the supply voltage

First confirm that the sensor supply is normal. Most electronics heads work at +24 V (20.4–28.8 V); Series 13 also accepts +12 V. Reverse polarity −30 V and over-voltage 36 V are protection limits; isolation is typically 500 Vdc; voltage-output load ≥5 kΩ. Set the multimeter to DC voltage and measure across the supply terminals: voltage is 0 → check the power supply and wiring; voltage is normal → go to the next step. Many "no output" cases are simply a broken supply or a loose wire.

Step 2: measure the output signal

With the supply normal, measure the signal output. Analog (0-10 V / 4-20 mA): move the position magnet slowly along the rod and watch whether the output voltage/current changes linearly with position. If 4-20 mA does not move smoothly as the magnet slides, the signal path is at fault, not the cylinder. If the voltage is constant or jumps, the signal path has a problem. Fieldbus types (SSI/CANopen/EtherCAT and others): analog voltage cannot be measured directly; focus on the fieldbus terminating resistor, address and shield earthing (see fieldbus data-loss troubleshooting).

Step 3: look at the LED diagnostic lamps

Germanjet sensors have built-in LED diagnostics: green on, red off = normal; both lamps on = magnet not detected (including leaving the valid stroke / over-range). Full lamp table: electronics-head LEDs. When both lamps are on, first move to mid-stroke: if the lamps recover it was over-range; if they stay dual-on, check a fallen / reversed magnet or the air gap.

Step 4: measure insulation resistance

With the multimeter resistance range (or a megohmmeter) measure insulation of the signal cores to earth (the housing). Insulation that is too low (for example tens of kΩ or below) indicates internal water ingress or damaged insulation, common on high-temperature, humid or corrosive-gas sites. Insulation problems usually need a return to the factory; they are hard to repair on site. Also check in passing whether the cable is open-circuit — an internal break produces complete no-output.

Step 5: distinguish body vs. installation

If supply, output, insulation and the magnet are all normal but the reading is wrong, focus on installation: whether the position magnet is coaxial with the rod, whether there is mechanical interference, whether the range has entered a dead zone (dead zones exist at both ends of the effective range), and whether a loose mounting is causing position drift. A test magnet at a known position as a comparison can further separate "body" from "installation".

Summary

After the five steps, the large majority of problems can be located to a specific link: power/wiring → sensor body → position magnet → insulation → installation. Return to the factory only after the body is confirmed faulty; other problems can be handled on site. If questions remain after troubleshooting, remote diagnostic support is available.