Patent ID: 8319492

Claim:
A rotary encoder comprising a magnet, AMR or GMR sensors arranged to generate two signals and means for evaluating the said two signal created by the sensors, the means for evaluating comprising two means for digitising the said two signals generated by the sensors, one of the two means arranged to provide a lower resolution digital representation of the said two signals than the other means, the encoder arranged to be switched to a power saving state for a predetermined period of time, to be at least partially re-activated after the predetermined period of time and to compare a current value derived from the signal with a stored previous value derived from the signal; wherein a magnetic field generated by the magnet is not monitored in the power saving state; wherein the encoder is arranged to, when partially activated, create a current digital representation of the said two signals using the lower resolution digitisation means, to compare the current digital representation of the signal with a stored previous digital representation of the said two signals, to reactivate further if the comparisons indicates that the current and previous digital representations differ and to create, using the higher resolution digitisation means when further activated, a digital representation of the said two signal having a higher resolution than the digital representation of the signal created when partially activated.