A sensing apparatus for a turbomachine comprises: a magnet; a sensing coil; a power supply; and a processor. The magnet is arranged to produce a magnetic field and the sensing coil is at least partially disposed in the magnetic field. The power supply is operable to provide a voltage across the sensing coil. The processor is operable to determine a periodicity of a voltage across the sensing coil. The processor is further operable to determine a quantity indicative of temperature dependent characteristic of the sensing coil.