In an LVDT, the secondary windings are connected in series.

• A. In series
• B. In parallel
• C. Isolated
• D. Independently excited

Answer: (A)

Two secondary windings are connected in series (and usually with opposite polarity) so that the voltages they generate add as a differential signal. The end-to-end voltage is proportional to the core’s position because the two windings respond differently as the core moves: at the centered position their induced voltages are equal and opposite, canceling to zero. Move the core, and one winding’s induced voltage increases while the other decreases, so the series connection produces a net voltage that grows with displacement. This setup also gives a larger, linear output and lets the signal be measured as a single differential voltage.

If the secondaries were in parallel, you’d just duplicate the same voltage across both windings instead of creating a position-dependent differential signal, reducing sensitivity and losing the null at the center. Isolated or independently excited secondaries would remove the direct, reference-based relationship to the primary excitation and would not yield the straightforward, proportional output relied on in LVDTs.