Magnetostrictive Displacement Sensor Applications: Cylinders, Moulding Machines, Rolling Mills

Magnetostrictive displacement sensors are chosen for three properties — non-contact, high precision and long life — and those properties decide where they are used: hydraulic cylinders, harsh environments and applications that cannot be serviced often. This article walks five typical application cases, then gives the pros and cons in one place.

Five typical cases

1. In-cylinder (injection moulding, die casting, hydraulic presses)

The rod goes through the cylinder head, the ring rides on the piston, and position is read through the oil. High-frequency cycling, oil and pressure make contact solutions short-lived — non-contact magnetostrictive is the standard. In-cylinder series 16 / 19.

2. Roll gap and lift tables (steel plants)

Roll gap screwdowns and lift tables run in heat, scale dust and vibration. Use heat-rated, sealed external sensors and protect the rod from scale. External series 17 / 18.

3. Press brake slide position

Slide position decides the bend angle, so repeatability is the priority. Mount on the slide or the side cylinders and feed the value to the CNC. External, high-repeatability version.

4. Gate opening and lift platforms

Water gate opening, stage lifts and logistics platforms need long stroke and reliability. Long-stroke external magnetostrictive is proven here — no wear, no maintenance.

5. TBM thrust cylinders (wet, vibrating, unserviceable)

Dozens of thrust cylinders push a tunnel boring machine; each carries a sensor to compute advance direction. Once installed it is very hard to service, so non-contact (no wear) and IP68 are essential. In-cylinder, IP68.

Pros and cons in one line

Pros: non-contact (no wear, long life, no maintenance), high resolution (down to 0.005 mm) and repeatability, strong resistance to oil, vibration and temperature, long stroke from tens of millimetres to metres.

Cons: higher price than a potentiometer electronic ruler, in-cylinder mounting needs the cylinder design to accept the rod, and the field around the ring must stay clean of strong magnets.

When to choose magnetostrictive

• Accuracy requirement at 0.01 mm or better.
• Oily, vibrating, wet or hot environment.
• Frequent cycling or a location that is hard to service.
• Long stroke or long-life requirement.

If the requirement is low precision and the environment is clean, a conductive plastic ruler is the economical choice — see selection method. For the heavy-industry details, see displacement sensors in five heavy industries.