An evaluation method for an output signal of a sensing device for scanning a cyclic movement, consisting of a rotatable pole wheel provided with equidistant teeth and an inductive sensor, permits recognition and display of damage to the pole wheel, in particular defective or missing teeth. Contrary to known evaluation processes, where error monitoring of the output signal is carried out for a relatively short time period comprising few signal cycles of the output signal, an observation of the output signal is effected for a sufficiently long time span in the evaluation process according to the invention, such that within the time span, at least two complete revolutions of the pole wheel are completed. To detect damage to the pole wheel, the sudden changes in the output signal occurring in the course of a complete revolution are recorded and are compared with changes recorded in previous, complete revolutions. If the numbers of changes are in at least approximate agreement, an error signal which can be displayed, for example optically, is produced.
A magnetic rotation detector includes a magnetic rotor having magnetic bodies, a detecting body that detects a change in magnetic flux that is caused by the magnetic bodies as the magnetic rotor rotates; and an abnormality determination portion that monitors an apparent fluctuation in rotational speed of the magnetic rotor based on a result detected by the detecting body and that determines that the magnetic rotor is in an abnormal state if the fluctuation occurs at a specific position of the magnetic rotor. The abnormality determination portion detects the occurrence of the fluctuation at the specific position of the magnetic rotor by making a determination on a distance between apparent positions of the magnetic bodies which correspond to the apparent fluctuation in rotational speed and calculates the distance on the basis of a product of an interval of generation of noise in an output signal detected by the detecting body and a rotational speed of the magnetic rotor at the time of generation of noise.
Numbers of teeth of respective rotors are obtained once and stored in an EEPROM. Then, when an ignition switch is initially turned on, vehicle wheel speeds for the respective vehicle wheels are derived based on the information about the numbers of teeth stored in the EEPROM. Accordingly, it is possible to obtain the vehicle wheel speeds even during a calculation period while the number of teeth of each rotor is being calculated each time the ignition switch is turned on. Further, it also becomes possible to perform ABS control prior to when the vehicle wheel speed calculation is completed.
