9 Inductive position sensing

Inductive angle sensors offer some advantages over magnetic sensors. Their main advantage is inherent magnetic immunity to external DC fields. Additionally, inductive technology requires only a conductive metal target – and no magnet – to be in proximity with the sense coils in order to determine the metal target position as it spins about the shaft.

Figure 7 shows an absolute encoder using two LDC5072-Q1 inductive sensors, one for each sense coil. Nonius encoding requires two sense coils: the outer sensor target may have 16 metal positions; the inner target, 15. Evenly spacing both targets forces a unique pattern across a complete rotation, providing the ability to know the absolute angle with high precision.

Mechanical resolvers perform the same function as absolute inductive encoders, but have size and weight disadvantages. It is possible to build inductive encoding solutions directly on a printed circuit board, while resolvers are built on thick steel laminations with copper-wire-wound teeth. Resolvers are also expensive to build because of their mechanical structure. Finally, power consumption can be an issue, as resolvers easily consume 500mW of power (assuming 70mA at 7V_RMS).