Magnetostrictive vs. LVDT vs. Potentiometer: How to Choose a Displacement Measurement Solution
Disclaimer: Germanjet supplies only magnetostrictive linear displacement/position sensors; descriptions of other displacement-measurement technologies below are for technical comparison only.
Displacement measurement is not magnetostriction alone. Potentiometers, LVDTs and even vision each do their work on their own ground. This article puts the three most common — magnetostrictive, LVDT and potentiometer — side by side, focusing on each technology's shortcomings so that you are not led by one-sided promotion in a specification meeting.
Three technologies in one sentence each
- Magnetostrictive: non-contact, absolute position, long life; suited to medium-to-long strokes and harsh conditions;
- LVDT (linear variable differential transformer): a classic contacting/non-contacting device, high accuracy and small size, suited to short-stroke laboratory or precision benches;
- Potentiometer (contacting): simple construction and the lowest cost, suited to short strokes where life is not demanding.
Comparison: accuracy / life / stroke / environment / cost
| Criterion | Magnetostrictive | LVDT | Potentiometer |
|---|---|---|---|
| Typical accuracy | non-linearity <0.02%FS, repeatability ±0.002 mm | ±0.1%–0.01% | ±0.1%–1% |
| Life | Very long (non-contact) | Long | Short (brush wear) |
| Applicable stroke | 50 mm to several metres | typically <300 mm | typically <1 m |
| Environmental tolerance | Strong (IP67–69K) | Moderate (dislikes oil sludge) | Moderate |
| Relative cost | Medium–high | Medium | Low |
Shortcomings of each (stated objectively)
- Magnetostrictive shortcomings: susceptible to strong alternating magnetic fields; cost per point higher than potentiometer types; concentricity of the position magnet is required — a poor installation weakens the signal.
- LVDT shortcomings: needs an AC excitation supply, so the electronics are more complex than magnetostrictive; short measuring range, unsuitable for long strokes; installation is sensitive to concentricity — offset degrades linearity.
- Potentiometer shortcomings: brush wear requiring periodic replacement; poor linearity on long strokes; high-speed reciprocation tends to chatter.
Selection advice
In one sentence: harsh conditions, medium-to-long stroke, maintenance-free → magnetostrictive; short-stroke precision benches → LVDT; short stroke, cost-sensitive, modest life requirement → potentiometer. For extra-long strokes, prefer a flexible magnetostrictive sensor (for example 19F). Nothing comprehensively outperforms everything else; there is only fit or unfit.
Our entire range is magnetostrictive displacement sensors, covering general-purpose, mobile hydraulic, in-cylinder integrated, externally mounted linear displacement and process fieldbus applications. If you have confirmed the magnetostrictive route, start from Series 13 or Series 17.
Practical tips for engineers
- 19F front dead zone: 50 mm when stroke <8000 mm, 130 mm when stroke >8000 mm; always subtract this when calculating effective stroke.
- Total sensor length tolerance: +8 mm when stroke <8000 mm, +15/-5 mm when stroke >8000 mm; this tolerance does not affect the measuring stroke.
- 19F minimum stroke 250 mm; for shorter strokes choose another series.
