Patent ID: 7138795

Claim:
A rotational angle detection device having: a rotating rotor; an exciting coil secured to the rotor and having one end thereof to which an alternating-current exciting current is applied and the other end thereof connected to an earth wire; and a stator coil stationarily provided around the rotor and having one end thereof for taking out an output voltage and the other end thereof connected to the earth wire, the stator coil being for outputting the voltage which is made as a result that an alternating-current bias voltage, caused by an impedance of the earth wire and the exciting current, is superimposed on an alternating-current rotational angle voltage the amplitude of which fluctuates in dependence on the rotational angle of the rotor; the improvement of the rotational angle detection device further comprising: memory means for storing data necessary to calculate values of temperature-dependent components in connection with the passing time from a reference time; rotational angle voltage detection means for calculating the alternating-current rotational angle voltage by subtraction means for subtracting the data stored in the memory means; bias detection means for calculating the alternating-current bias voltage by addition means for adding the data stored in the memory means; and means for calculating an amplitude value of the alternating-current rotational angle voltage, a phase difference of the alternating-current rotational angle voltage from the reference time, an amplitude value of the alternating-current bias voltage, and a phase difference of the alternating-current bias voltage from the reference time, based on values sampled by the rotational angle voltage detection means and the bias detection means at at least two different time points.