| 摘要 |
PURPOSE:To measure accurately electric potential of a photosensitive body even if there exist differences more or less in a distance between the photosensitive body and an electric potential sensor or even if stains are formed more or less on the sensor surface. CONSTITUTION:A control section 24 connects an earth brush 22 to escape electric charge on a photosensitive belt 5 to a main body by turning on a relay 23 with every preset copy number when a power is put on, in a switching system to a power supply section of a reference voltage generator 25 to generate reference voltage, and impresses the plural number of different reference voltages successively upon a base layer of the photosensitive belt 5 from the reference voltage generator 25 through the earth brush 22, and corrects a previously memorized A/D converting table (measured value converting data) while using respective electric potential measured values obtained from an electric potential sensor 21 in the case of impressing the respective reference voltages as a reference value, and outputs an abnormal signal when the correction value falls outside a preset specified range. |
