Magnet Ring and Coaxial Mounting: Common Field Faults
A magnetostrictive sensor reads position from where the magnet ring sits. The ring wears nothing itself, yet it decides whether the reading is stable: reversed and the number runs backwards, eccentric and the last digit jitters, poorly fixed and any knock shows up as a spike.
01Selection and working gap
- How to Choose the Position Magnet for a Magnetostrictive Displacement Sensor: Remanence, Gap, Mounting
The ring magnet is not stronger-is-better. For a magnetostrictive displacement sensor, weak remanence loses the echo; match remanence, gap, mount.
- Multi-Magnet Measurement: Several Positions on One Waveguide
Several magnets on one rod: a magnetostrictive displacement sensor reads 2-4 positions in echo order, but Series 19 needs 76 mm minimum spacing.
- CANopen Multi-Magnet Reading: 8-Byte Frame Limits and PDO Mapping
One waveguide, several magnets, an 8-byte frame. A TPDO holds just two INT32 positions, so three magnets need SYNC batches; minimum spacing is 76 mm.
02Mount it coaxial
- How Much Off-Centre Is Too Much: Telling Coaxiality, Parallelism and Squareness Apart
Walk the full stroke by hand and the reading shudders at one or two fixed stretches while the rest is steady. A new unit behaves the same way. This is rarely the part — it is the rider magnet sitting off-centre on the rod. Eccentricity is not simply a weaker signal: it modulates the return amplitude at the phase where the offset is greatest. Coaxiality, parallelism and squareness are defined first, then how much is allowed, how to measure it, and how to adjust.
- Installing a Magnetostrictive Displacement Sensor: Magnet, Zero, Noise
Wild readings come from mounting, not failure. On a magnetostrictive displacement sensor, set magnet coaxiality, two-point zero, screened earthing.
- Five Magnet-Fit Pitfalls on a Magnetostrictive Displacement Sensor
Jumpy readings trace back to the magnet, the only moving part. Five fit defects - coaxiality, gap, reversed polarity, loose fasteners, ferrous parts.
03Reversal and polarity
- Magnet Ring Installed Backwards: Symptoms and Correction
A reversed magnet does not fail immediately; it makes readings subtly wrong. Four symptoms visible on site, two polarity checks that need no disassembly, three details that matter when correcting the position, and how to confirm a replacement ring matches.
- Magnetostrictive Displacement Sensor: No Output in Three Checks
A magnetostrictive sensor with no reading points to one broken link. Do not open the head: check +24 V at the plug, trace the loop, move the magnet.
04Field diagnosis
- Commissioning a Magnetostrictive Displacement Sensor: Use a Test Magnet to Split Body Faults from Install Problems
Body bad or install wrong? Take a magnetostrictive displacement sensor off-line, feed 24 V, sweep a known magnet; a smooth read proves it sound.
- Ten Injection Presses, One Jittering Ejector Sensor: A Thin Mounting Plate Acting as a Tuning Fork
We ran all ten injection moulding machines on site up to maximum ejector speed. Only one reading jittered; the other nine stayed steady. The cause was not the sensor: on that smaller machine the mounting plate was not rigid enough and too thin, so at speed the plate resonated like a tuning fork and fed high-frequency vibration down the cantilever into the sensor core. A replacement sensor would not have helped. Fitting an anti-vibration base cleaned the waveform immediately. A second, separate fault turned up in the same batch: installation over-travel, with the slider passing the black mark on the housing at the bottom of the stroke on several machines.
05Related products
Frequently Asked Questions
Q: What happens if the magnet ring is installed back to front?
The position runs backwards: as the piston advances, the reading falls. Some models show a mirrored range instead, or sit pinned at one end on power-up. You do not need to take anything apart: push the ring a short distance along the rod and watch whether the number rises or falls. Correcting it means flipping the ring over, taking care that the locating face does not end up on the wrong side.
Q: How much eccentricity counts as out of tolerance?
The criterion is coaxiality, not how straight it looks. When the gap between ring bore and probe is uneven around the circumference and exceeds the allowance, torsional wave coupling weakens, which shows up as a jittering last digit or drift over a short stretch of stroke. The field method is to rotate around the rod and measure the gap; if the difference between the largest and smallest exceeds half the design clearance, reposition the ring seat.
Q: Can the magnet ring sit further from the probe?
Radial gap sets the magnetic coupling strength. Beyond the working range the reading first becomes unstable, then drops positions locally, and finally loses output over the whole stroke. In-cylinder designs deserve particular attention: wear in the piston guide pushes the ring progressively off-centre, which is an ageing fault that appears after months of service rather than at installation.
Q: How do I tell a magnet problem from a sensor problem?
Swap in a known-good test ring. If the reading recovers with the test ring, the problem is the original ring or how it is mounted; if nothing changes, go back to the body, the wiring and the controller. This one step filters out most unnecessary rework and is the cheapest fork in the road.