Maintaining Paschen breakdown voltage in electrographic printing

Claim 1

A method for determining the applied voltage required for Paschen breakdown to occur between pairs of writing electrodes in an electrographic printing system for use in maintaining the applied writing voltage at an effective minimum operating level based upon existing environmental and physical conditions of the system, the writing electrodes being electrically addressed with an applied voltage having an operating frequency at the Paschen breakdown voltage to form a latent image on a recording medium moving relative to and adjacent to the electrodes, the voltage at which Paschen breakdown occurs being accompanied by an abrupt change in current flow due to the appearance or disappearance of harmonic currents, the method comprising the steps of providing in said system a set of test electrodes having a test gap adjacent to said recording medium, said test electrodes capable of indicating operating characteristics comparable to the writing electrodes, generating a harmonic signal, said harmonic signal having a frequency that is a multiple integer of said operating frequency, applying a sinusoidal voltage across said test gap at said operating frequency, the applied voltage being initially synchronized relative to said harmonic signal, monitoring the applied sinusoidal voltage across said test gap to detect an abrupt appearance or disappearance of a harmonic current at said test gap corresponding in frequency to said harmonic signal, and measuring the magnitude of the applied sinusoidal voltage corresponding to the amplitude of said harmonic current developed across the test gap at the time of said abrupt change.

Claim 2

A method for determining the applied voltage required for Paschen breakdown to occur between pairs of writing electrodes in an electrographic printing system for use in maintaining the applied writing voltage at an effective minimum operating level based upon existing environmental and physical conditions of the system, the writing electrodes being electrically addressed with an applied voltage having an operating frequency at the Paschen breakdown voltage to form a latent image on a recording medium moving relative to and adjacent to the electrodes, the voltage at which Paschen breakdown occurs being accompanied by an abrupt change in current flow due to the appearance or disappearance of harmonic currents, the method comprising the steps of providing in said system a set of test electrodes having a test gap adjacent to said recording medium, said test electrodes capable of indicating operating characteristics comparable to the writing electrodes, generating a harmonic signal, said harmonic signal having a frequency that is a multiple integer of said operating frequency, applying a sinusoidal voltage across said test gap at said operating frequency, the applied voltage being initially synchronized relative to said harmonic signal, monitoring the applied sinusoidal voltage across said test gap to detect an abrupt appearance or disappearance of a harmonic current at said test gap corresponding in frequency to said harmonic signal, and measuring the magnitude of the applied sinusoidal voltage corresponding to the amplitude of said harmonic current developed across the test gap at the time of said abrupt change.

Claim 5

The method according to any one of claims 1, 2 or 3 including the step of monitoring the harmonic current by crosscorrelating the currents developed across said test gap with a sinusoidal signal having a selected frequency that is two or more times the frequency of the applied sinusoidal voltage.

Claim 6

An apparatus for determining the applied voltage required for Paschen breakdown to occur between pairs of writing electrodes in an electrographic printing system for use in maintaining the applied writing voltages at an effective minimum operating level based upon existing environmental and physical conditions of the system, the writing electrodes being electrically addressed with an applied voltage having an operating frequency at the Paschen breakdown voltage to form a latent image on a recording medium moving relative to and adjacent to said electrodes, the voltages at which Paschen breakdown occurs being accompanied by an abrupt change in current flow due to the appearance or disappearance of harmonic currents, and comprising a set of test electrodes in said system, said electrodes having a test gap adjacent to said recording medium, said test electrodes capable of indicating operating characteristics comparable to said writing electrodes, means for generating a harmonic signal having a frequency that is a multiple integer of said operating frequency, means coupled to said generating means to apply a sinusoidal voltage across said test gap at said operating frequency and initially synchronized relative to said harmonic signal, means coupled to said generating means for monitoring said applied sinusoidal voltage across said gap to detect an abrupt appearance or disappearance of a harmonic current at said test gap corresponding in frequency to said harmonic signal, and means to measure the magnitude of said applied sinusoidal voltage corresponding to the amplitude of said harmonic current developed across said test gap at the time of said abrupt change.

Claim 7

An apparatus for determining the applied voltage required for Paschen breakdown to occur between pairs of writing electrodes in an electrographic printing system for use in maintaining the applied writing voltages at an effective minimum operating level based upon existing environmental and physical conditions of the system, the writing electrodes being electrically addressed with an applied voltage having an operating frequency at the Paschen breakdown voltage to form a latent image on a recording medium moving relative to and adjacent to said electrodes, the voltages at which Paschen breakdown occurs being accompanied by an abrupt change in current flow due to the appearance or disappearance of harmonic currents, and comprising a set of test electrodes in said system, said electrodes having a test gap adjacent to said recording medium, said test electrodes capable of indicating operating characteristics comparable to said writing electrodes, means for generating a harmonic signal having a frequency that is a multiple integer of said operating frequency, means coupled to said generating means to apply a sinusoidal voltage across said test gap at said operating frequency and initially synchronized relative to said harmonic signal, means coupled to said generating means for monitoring said applied sinusoidal voltage across said gap to detect an abrupt appearance or disappearance of a harmonic current at said test gap corresponding in frequency to said harmonic signal, and means to measure the magnitude of said applied sinusoidal voltage corresponding to the amplitude of said harmonic current developed across said test gap at the time of said abrupt change.