SAMPLED AC REFERENCE
Original Publication Date: 1978-Jun-30
Included in the Prior Art Database: 2004-Mar-31
Xerox Disclosure Journal
An electrometer and associated circuitry for measuring elec-trostatic charge levels on a text surface 10 such as a photoreceptor utilized in xerographic copying machines. The charge on the surface 10 is sensed by probe 12 and con-verted to a corresponding voltage level by a variety of known circuits in the head 14, with this level being represented by curve C in Figure 2. A constant amplitude AC reference signal B derived, for example, from a typical AC transformer sup-plying signal A, is coupled to the head 14 and to a zero detector 16. When signals C and B are at the same potential, zero detector 16 supplies a signal D to a sample and hold circuit 18 through optical isolator 20. Consequently, circuit 18 provides an output signal E representative of the potential on test surface 10 by reading the instantaneous voltage level of signal B at the time when it corresponds to the potential on test surface 10.