Linear variable differential transformer

LVDTs are robust, absolute linear position/displacement transducers; inherently frictionless, they have a virtually infinite cycle life when properly used.

LVDTs have been widely used in applications such as power turbines, hydraulics, automation, aircraft, satellites, nuclear reactors, and many others.

In practice minor variations in the way in which the primary is coupled to each secondary means that a small voltage is output when the core is central.

It is a nuisance in closed loop control systems as it can result in oscillation about the null point, and may also be unacceptable in simple measurement applications.

Modern systems, particularly those involving safety, require fault detection of the LVDT, and the normal method is to demodulate each secondary separately, using precision half wave or full wave rectifiers, based on op-amps, and compute the difference by subtracting the DC signals.

If sufficient digital processing capacity is available, it is becoming commonplace to use this to generate the sinusoidal excitation via a DAC and possibly also perform the secondary demodulation via a multiplexed ADC.

Because the sliding core does not touch the inside of the tube, it can move without friction, making the LVDT a highly reliable device.

LVDTs are commonly used for position feedback in servomechanisms, and for automated measurement in machine tools and many other industrial and scientific applications.