Ricoh FT8680 Service Manual page 30

PROCESS CONTROL
1.3.1 Drum Potential Sensor Calibration
[A]
The drum potential sensor [A] is located just above the development unit. The
sensor has a detector which detects the electric lines of force from the
electric potential on the drum. The output of the sensor depends of the
number of electric lines of force.
Since the output of the sensor is affected by environmental conditions, such
as temperature and humidity, the sensor output is calibrated during process
control data initialization.
The drum current detection board has two relay contacts. Usually RA2
grounds the drum. However, during the initialization, the main PCB turns RA1
on and RA2 off and applies the development bias to the drum shaft.
By measuring the outputs of the drum potential sensor when +100 V and
+800V are applied to the drum, the sensor output is calibrated automatically.
A171D585.img
Potential Sensor
Bias
P.P.
2-6
Drum
RA2
RA1
Drum Current
Detection PCB
Relay
TRIG 1 (800V)
TRIG 2 (100V)
PWM
Sensor
Main PCB
A171D511.wmf
31 July 1995
Case
Sensor
Output
Amp.
A171D512.wmf