When initially introduced fifty years ago, all LVDT linear position sensors were AC-operated and required external oscillators, carrier amplifiers, demodulators and filers to operate.
The introduction of high-density microelectronics enabled the incorporation of signal conditioning and processing functions inside the LVDT housing rather than requiring an external box. The DC-operated LVDT maintains all the desirable characteristics of the AC-operated LVDT, but has the simplicity of DC operation. It is comprised of an AC-operated LVDT and a carrier generator/signal conditioning module.
So why haven’t DC-operated linear position sensors replaced the original AC-operated versions? While DC-LVDTs eliminate the need for calibration and additional equipment, AC-LVDTs continue to possess their own set of benefits.
AC-operated linear position sensors offer unlimited mechanical and electrical life. The absence of friction and contact between the coil and core means there is nothing to wear, resulting in infinite mechanical life that is important in high reliability mechanisms and systems. The frictionless operation of the LVDT combined with the induction function by which it operates, provides for truly infinite resolution, with the only limitation on resolution posed by the readability of the external electronics.
Without the need for internal electronic components, AC-LVDTs can be offered in smaller package sizes to fit in compact locations. AC units also have better shock and vibration resistance and can operate over higher temperature ranges.