| 摘要 |
PROBLEM TO BE SOLVED: To enhance the detecting accuracy of toner concentration by installing a conductor on an opposite-side surface to the concentration detecting surface of a base plate and setting the thickness of the conductor within a specified range. SOLUTION: A detection coil 12 formed to be plane is provided on the base plate 11. The coil 12 is a plane coil pattern formed by providing a silver foil on the surface of the base plate 11 and etching it, and is formed to be a vortex having 50 to 100μm width and about 100 to 200μm pitch. The conductor 13 made of metal or the like having a shielding effect is provided on the back side of the base plate 11. However, the expected effect is not obtained if the conductor 13 does not have the specified thickness. Then, the thickness d[m] of the conductor 13 is set to satisfy a relational expression d>=503×√(ρ/f×μs). Provided thatρis the resistivity [Ω.m],μs is the relative permeability of the conductor and (f) is the oscillation frequency [Hz]. By providing the conductor 13 having the specified thickness as a shielding member, influence associated with temperature change is decreased and the detecting accuracy is enhanced. |
