TONER CONCENTRATION DETECTION

摘要

A toner concentration detecting device for detecting a toner concentration of a two component developer includes a differential transformer (1) which is connected to an oscillating drive (2) and a phase detecting circuit (3). A variable capacitance diode (VCD) is connected between a primary coil (101) and the secondary coils (102, 103) and a variable resistor (VR) is provided to supply the variable capacitance diode (VCD) with a variable DC voltage thereby to select the capacitance of the diode (VCD).