What is the type of transformer used for measuring linear displacement (position)?

What is the type of transformer used for measuring linear displacement (position)?

• A. A potentiometer
• B. A servo transformer
• C. A magnetostrictive sensor
• D. A linear variable differential transformer

Answer: (D)

The key idea is using a transformer-based sensor that converts linear position into a proportional electrical signal without contact. An LVDT, or linear variable differential transformer, does exactly that. It has a movable ferromagnetic core inside a coil assembly with a primary coil and two secondary coils. When an AC excitation is applied to the primary, the magnetic coupling to the secondary windings depends on the core’s position. The voltages from the two secondary coils are compared (differenced) to produce a signal that varies in proportion to the core’s displacement. Because this relies on mutual inductance rather than physical contact, it offers very high resolution, good linearity over a wide range, and long life with little wear. Potentiometers measure position with a sliding contact on a resistive element, which wears over time and isn’t a transformer-based method. Magnetostrictive sensors use the magnetostrictive effect and a timing or phase approach to determine position, not a transformer-based differential voltage. A servo transformer isn’t a standard device for measuring linear position. So the LVDT is the best choice for measuring linear displacement using a transformer mechanism.

The key idea is using a transformer-based sensor that converts linear position into a proportional electrical signal without contact. An LVDT, or linear variable differential transformer, does exactly that. It has a movable ferromagnetic core inside a coil assembly with a primary coil and two secondary coils. When an AC excitation is applied to the primary, the magnetic coupling to the secondary windings depends on the core’s position. The voltages from the two secondary coils are compared (differenced) to produce a signal that varies in proportion to the core’s displacement. Because this relies on mutual inductance rather than physical contact, it offers very high resolution, good linearity over a wide range, and long life with little wear.

Potentiometers measure position with a sliding contact on a resistive element, which wears over time and isn’t a transformer-based method. Magnetostrictive sensors use the magnetostrictive effect and a timing or phase approach to determine position, not a transformer-based differential voltage. A servo transformer isn’t a standard device for measuring linear position. So the LVDT is the best choice for measuring linear displacement using a transformer mechanism.