| 摘要 |
A toner concentration detecting apparatus is disclosed wherein developing powder including magnetic carrier and pigmented toner is carried on a magnet roller and transported thereby to a surface of a photosensitive drum, and after development a portion of the developing powder is removed off the surface of the magnet roller and passed through a hollow body containing a detection coil to determine a concentration of the toner in the developing powder based on a magnitude of an inductance of the detection coil. A flow condition of the developing powder is at the same time determined by detecting a rippled voltage induced by the detection coil. Accuracy of detection is enhanced by an electric circuit for pulsating the rippled voltage and counting the number of pulses produced thereby. The flow of the developing powder is accelerated by a vibrator mounted on the hollow body responding to an output signal of the electric signal if the flow of developer powder stops. If the toner concentration falls below a predetermined range, a toner supply means supplies toner to the chamber. The toner is supplied only when the developing powder is flowing through the hollow body. |
