Toner Density Sensor - Ricoh FW780 Service Manual

Rev. 5/95

4.4.3 Toner Density Sensor

The toner density sensor circuit controls the amount of toner in the developer
mixture.
The toner density sensor is powered by 12 volts from CN104-A11 of the main
board. (The potential of CN104-A11 is 24 V when the connector is disconnected.)
The sensor's sensitivity is based on the feedback signal applied from
CN104-A10. The input signal to the sensor passes from the main board at
CN104-B20.
The active sensor element is a very small transformer with three coils. When iron
ferrite (carrier) is near the sensor element, the inductance of the coils changes,
causing the current through the transformer to change. As the amount of toner in
the developer increases, the effect of the carrier particles decreases and the
voltage applied to CN104-A10 decreases. Conversely, when the toner
concentration drops as toner is used up, the effect of the carrier on the sensor
coils increases and the voltage at CN104-A10 increases.
SM
Toner Density Sensor
Control
Circuit
Coils
2-18
Main Board
2
CN104-A11
[12V]
1
CN104-B20
3 CN104-A10
CN104-B21
4
GND
TS Control
TS. FB
A163