Patent ID: 9297635
Filing Date: 2016-03-29
CPC Classification: G01B,G01D,G01R

Claim Text:
1. A magnetic sensor system comprising a scale and a magnetic sensor that are arranged in a relative positional relationship variable in a first direction, the magnetic sensor system being configured to detect a physical quantity associated with the relative positional relationship between the scale and the magnetic sensor, wherein the magnetic sensor includes a first detection circuit disposed at a first position and a second detection circuit disposed at a second position, the first detection circuit outputs a first detection signal that varies depending on a first magnetic field applied to the first detection circuit, the second detection circuit outputs a second detection signal that varies depending on a second magnetic field applied to the second detection circuit, each of the first and second detection circuits includes a plurality of magnetoresistive elements connected in series, each of the plurality of magnetoresistive elements includes: a magnetization pinned layer having a magnetization in a pinned direction; a free layer having a magnetization that varies depending on an applied magnetic field; and a tunnel barrier layer interposed between the magnetization pinned layer and the free layer, each of the first and second magnetic fields changes its direction periodically in response to a change in the relative positional relationship between the scale and the magnetic sensor, and the first position and the second position differ from each other by 1.25% of one pitch or less, where one pitch is an amount of a change in the relative positional relationship between the scale and the magnetic sensor that changes the direction of each of the first and second magnetic fields by one period, the magnetic sensor system further comprising a computing unit, the computing unit being configured to generate an abnormal-event determination signal by computation using the first detection signal and the second detection signal, and to determine whether the magnetic sensor is normal or has an abnormal event by monitoring whether the abnormal-event determination signal falls within a predetermined range specified by an upper limit and a lower limit, the upper limit and the lower limit being established to determine the presence of an abnormal event in the first or second detection circuit caused by a short circuit between the magnetization pinned layer and the free layer in one of the plurality of magnetoresistive elements included in the first or second detection circuit, and to thereby allow for determination of an abnormal event in the magnetic sensor.