Self-biased scorotron grid power supply and electrostatic voltmeter

Abstract

An electrophotographic system including a corona charging device for applying a charge to a surface and having a coronode driven to a corona producing condition; a conductive grid interposed between the surface to be charged and the coronode; the conductive grid having a self-biasing arrangement to control the voltage thereon produced by corona current from the coronode, the self-biasing arrangement including a current sinking device between the conductive grid and a common; and a power supplying takeoff, electrically connected between the conductive grid and the current sinking device, and having a voltage thereat controlled by the current sinking device. An electrostatic voltmeter drivable by such an arrangement includes a probe for detecting voltage on a surface and producing a representative voltage signal; a low current, high voltage supply such as that available at the conductive grid; a constant current source; a current sinking device connected to the constant current source and having a constant voltage drop thereacross, and providing first and second floating voltages and a relative common therebetween; and a voltage controller variably controlling the voltage level at the current sinking device in response to the representative voltage signal; a signal processing device for conditioning the representative voltage signal for variably controlling the voltage controller; the amplifier driven by the first and second floating voltages.