LVDTs are selected when reliable, robust, and accurate position sensing is critical. Learn Why…
The single primary coil is centered in the housing and energized with an AC signal. Magnetically coupled by the core, a voltage is induced in each of two symmetrical secondary windings connected in a series-opposing circuit. The effective voltage and LVDT output is the difference between each secondary.
When the core moves away from the center of the LVDT, known as the null point, the signal from the primary will be coupled to one secondary more than the other. In Figure 1, as the core moves over S1, the voltage output of S1 increases. As the core moves over S2, the output of S2 increases. The value of (S1 ‑ S2) and (S2 – S1) becomes a linear function of the core position as it moves toward S1 and S2, respectively.
Being an inductive transformer, the LVDT requires an AC excitation voltage across the primary and produces an AC output across the secondaries. In modern LVDTs, excitation signal requirements are around 3 Vrms and frequencies ranging from 1kHz to 10 kHz. Support electronics and signal conditioners supply the excitation signal and measure output. Signal conditioners demodulate the low-amplitude AC output and produce DC voltage, current, or digital output that can be measured by most meters and control systems.
LVDTs can be used for many different applications. In this example, see how an AC LVDT can be used in conjunction with a signal conditioner to monitor the position of a valve.