| 摘要 |
The photoconductive layers on the drum, in which the latent electrostatic image is produced in the conventional way, is precharged in the normal way by a corona discharge electrode assembly fed by the rectified EHT output of the mains transformer in the charging power supply unit. To enable positive negative originals to be used, the polarity of the precharge is changed by a polarity inverter switch in the EHT leads. To compensate for the differences in contrast in the two cases, the precharge on the drum is varied with polarity by coupled top changer in the transformer primary or by a switched in series resistor in the EHT supply or alternatively the lamp intensity is altered by changing its feed voltage or insertion of a grey filter.
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