Measuring Linear Displacement with an LVDT

Linear displacement is movement in one direction along a single axis. The linear variable differential transformer (LVDT) is a sensor that measures linear displacement. LVDTs operate on the principle of a transformer and consist of a stationary coil assembly and moveable core. An LVDT measures displacement by associating a specific signal value for any given position of the core.

LVDT signal conditioners generate a sine wave for the primary output signal and synchronously demodulate the secondary output signal. The demodulated output is passed through a lowpass filter to remove high-frequency ripple. The resulting output is a DC voltage proportional to core displacement. The sign of the DC voltage indicates whether the displacement is to the left or right.

LVDTs typically come in 4-wire (open wire) and 5-wire (ratiometric wire) configurations. Wires from the sensor connect to a signal conditioning circuit that translates the output of the LVDT to a measurable voltage. The method of signal conditioning used differentiates the 4-wire and 5-wire configurations.