Patent ID: 8380092
Filing Date: 2013-02-19
Classification: G03G

Abstract:
1. A toner concentration sensor comprising: a first oscillation circuit having a detection coil which is placed relative to a two-component developing unit so that inductance of the detection coil varies with varying magnetic permeability of a toner-and-carrier mixture contained in the two-component developing unit; a second oscillation circuit having a reference coil which is placed relative to the two-component developing unit so that inductance of the reference coil is not influenced by magnetic permeability of any toner-and-carrier mixture contained in the two-component developing unit, and which shows an inductance-temperature characteristic equivalent to that of the detection coil; a calculating section calculating a difference between oscillation frequencies of the first and second oscillation circuits; a storage section storing a target value; and a detecting section detecting a difference between a mixing ratio of the toner-and-carrier mixture in the two-component developing unit and a preset mixing ratio based on a relationship between the target value and the difference calculated by the calculating section.