lvdt transducers are commonly used in industrial, test and measurement, aerospace, and research settings because they provide very high accuracy, resolution, and reliability. They are able to measure displacement with very fine resolution by using a magnetic field that moves a moving core in relation to a set of transmitting and receiving coils, and then measuring the changes in the coupling between them.
A LVDT consists of a former with one main winding in the middle and two secondary windings on each side. During operation, an AC excitation signal is applied to the primary winding. The movable soft iron core is made of high permeability material which helps in reducing harmonics and increasing sensitivity. In order to cut down eddy current losses, the core is additionally laminated. The whole assembly is installed inside a stainless steel to offer electromagnetic and electrostatic shielding.
The output voltage of an LVDT is a linear function of core displacement. The change in o/p polarity or phase of this output voltage indicates the direction of core displacement, which can be classified into three cases as shown below.
CASE I: LVDT Core Moved Left of Null Position
When the LVDT core is moved to the left of null position, more flux links with coil S1 than with S2, hence the resulting output voltage V0=V1-V2 is positive. In case the core is moved to the right of the null position, more flux links with coils S2 than with S1, causing the resulting output voltage to be negative.