Which displacement sensor is widely used for precise linear measurement and uses a transformer principle?

• A. LVDT
• B. Potentiometer
• C. Hall effect sensor
• D. Capacitive sensor

Answer: (A)

LVDT uses a transformer principle to measure precise linear displacement. It has a single movable ferromagnetic core inside multiple coils: a primary winding is driven with AC, and two secondary windings are connected in series opposition. As the core shifts, the magnetic coupling to the two secondary windings changes, causing a differential voltage between the two secondaries that is proportional to the core’s position relative to a null point. This differential output is then processed to yield a highly accurate displacement measurement.

Because there’s no contact between the moving core and the sensor, wear is minimized and stability and repeatability are excellent over a wide travel range. It also tolerates harsh environments and provides good linearity, making it a preferred choice for precise linear measurement.

The other options don’t fit the transformer-based approach: a potentiometer uses a sliding contact that wears over time and introduces nonlinearities; Hall effect sensors detect magnetic fields rather than transform voltages via coupled windings; capacitive sensors rely on changes in capacitance from distance, not transformer coupling.