| 摘要 |
PURPOSE:To detect the deterioration of a powder developer accurately, by providing a developer resistance detecting means consisting of a high frequency power source and counter electrodes for detecting variation in the resistance of the developer. CONSTITUTION:A detection coil is inserted in a toner density detector 10 and a toner density variation signal based upon variation in the inductance of the coil is supplied to a control part 15 and compared with a reference value, when the signal is lower than the reference value, a density decrease signal is outputted to rotate a supplementing roll 14 to hold the toner density constant. The counter electrodes 11 fitted in parallel to the flow of the developer are impressed with a constant voltage from the high frequency power source 16 and the AC voltage across a resistance R connected in series is rectified 17 and compared by a comparator 18 with a threshold level Vs. Thus, as the resistance between the counter electrodes 11 increases, a DC voltage V drops and when it drops below the level Vs, a comparator 18 operates to display the deterioration of the developer. |
