(19)
(11) EP 0 292 130 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
14.06.1989 Bulletin 1989/24

(43) Date of publication A2:
23.11.1988 Bulletin 1988/47

(21) Application number: 88303863.0

(22) Date of filing: 28.04.1988
(51) International Patent Classification (IPC)4: G03G 15/08
(84) Designated Contracting States:
DE FR GB

(30) Priority: 19.05.1987 JP 74869/87

(71) Applicant: TDK Corporation
Chuo-ku, Tokyo-to 103 (JP)

(72) Inventors:
  • Nakagawa, Shiro
    Chiba-shi Chiba-ken (JP)
  • Domon, Taisuke
    Ichikawa-shi Chiba-ken (JP)
  • Imai, Takehiro
    Ichikawa-shi Chiba-ken (KP)
  • Takahashi, Eiji
    Ichikawa-shi Chiba-ken (JP)

(74) Representative: Rackham, Stephen Neil et al
GILL JENNINGS & EVERY, Broadgate House, 7 Eldon Street
London EC2M 7LH
London EC2M 7LH (GB)


(56) References cited: : 
   
       


    (54) Toner concentration detection


    (57) 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).







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