| 摘要 |
PURPOSE:To detect the abnormality of connection between a detecting coil and a control circuit and the disconnection of the detecting coil by providing a circuit which outputs an abnormality signal if the detection voltage inputted to a toner density discriminating circuit reaches an abnormality reference voltage. CONSTITUTION:A voltage V0 of a detecting coil 10 which discriminates the toner density in accordance with an inductance is set to 9-10V, and an abnormality reference voltage VSE of a comparator 24 which detects an abnormal reduction of the detection voltage V0 is set to 0-9V. If the connection between the detecting coil 10 and the control circuit is not normal or the detecting coil 10 is disconnected to reduce the detection voltage V0, an output TERR of the comparator 24 becomes low-level to operate an alarm device 27, and a toner supply valve is closed to stop the toner supply. Consequently, the abnormality of the connection between the detecting coil and the control circuit and the disconnection of the detecting coil are detected to control the toner supply. |
