Explanation Of Circuits According To Function; Drum Surface Potential Control Circuit - Printronix L5000 Series Maintenance Manual

Explanation of Circuits According to Function

The following pages provide an introduction to the structure of the main electrical
circuits of this printer.

Drum Surface Potential Control Circuit

The drum surface potential is picked up as an alternating current approximating
640Hz, by interrupting lines of electrical force flowing into a receiving terminal
within the shielded case of the drum surface potential sensor, with a metal tuning
fork. In the drum surface potential measurement circuit, this weak alternating current
is amplified with a low offset operational amplifier, and having been rectified and
smoothed by a absolute value circuit, is converted to 8–bit data by an A/D converter.
On the other hand, the desired surface potential is set as 8–bit data by the sensitized
surface potential setting command from the controller, and stored in the MPU board
data memory. 8–bit observation data sent to the MPU board from the drum surface
potential measurement circuit via I/O board gate array is compared with this target
data called from data memory by the CPU, and based on that comparison result,
8–bit control data is sent to the I/O board main charger current control circuit.
The control data is then converted to analog by a D/A converter, amplified to 0–12
voltage (+HV1 CONT) by an operational amplifier, and sent to the high–voltage
power supply unit. When the +HV1 REM (main charger remote ON/OFF) signal is
asserted, the high voltage power supply unit (that has received input of control
voltage) outputs current (+HV1/+100–1000µA) corresponding to that voltage to the
main charger.
Electrical and Wire Data 6–35