| 摘要 |
PURPOSE:To make it possible to easily detect the trouble of a light emitting diode or a signal cable, by setting first and second two-phase pulses and inverse phase pulses respectively corresponding thereto as pairs and generating a signal when a pair of same logical levels are generated. CONSTITUTION:Four kinds of slits SA, SA', SB, SB' provided to a fixed disc 15 are respectively constituted of four slits mutually shifted in a phase by 360 deg. and four slits coincide with the slit 12A of the disc 12. The slits SA, SA' are arranged so as to be made different by 180 deg. in a phase and the slits SA, SB are arranged so as to be made different by 90 deg. in a phase. Output signals A2, B2 and output signals -A2, -B2 each having a phase inverse to that of each of the slits A2, B2 are respectively outputted from comparators 16A-16D. That is, when the signal A2 is a H-level, the signal -A2 is a L-level and, when the signal A2 is a L-level, the signal -A2 is a H-level and both of the signals A2, -A2 take no same output state. The same output state is obtained when the a light emitting diode 13A or the signal wires for the signals A2, -A2 is discon nected. Therefore, by monitoring the signals A2, -A2, the detection of trouble can be easily performed.
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