Electrometer system

Claim 2

In an electrometer system for non-contact detection of the electrostatic charge on an electrostatographic surface including an electrometer probe containing a probe electrode and an electrometer circuit providing an output signal corresponding to a charge induced on said probe electrode from said surface, wherein said electrometer circuit is mounted in a chassis unit, the improvement wherein: said electrometer probe comprises first and second concentric elongated small diameter conductive hollow tubes relatively movable with respect to one another and electrically shielding said probe electrode, said tubes extending from said chassis unit to define an elongated small diameter probe, said probe electrode extending through said tubes, said first tube containing a relatively small probe window substantially spaced from said chassis in a side of said tube for exposing said probe electrode, and said second tube containing a probe shutter area for covering said probe window in said first tube by said relative movement between said first and second tubes.

Claim 3

The electrometer system of claim 1, wherein said second tube is fixed and overlies said first tube, and wherein said first tube and said probe window therein is movable to open and close said probe window.

Claim 4

The electrometer system of claim 1, wherein said first and second tubes and said probe electrode are all coaxial, and said first and second tubes are cylindrical and have substantially the same internal diameters.

Claim 5

An electrometer system for a non-contact detection of an electrostatic charge on a surface comprising: electrometer probe means containing a probe electrode adapted to be held adjacent to the charged surface for receiving a corresponding DC voltages capacitively induced thereon from said charge on said surface, an electrometer circuit having a highly insulated low leakage electrically floating input circuit, said electrometer circuit providing an output signal corresponding to said DC voltage applied to said input circuit, said input circuit having low-leakage capacitor means for storage and substantially reduction by capacitance ratio division of said DC voltage applied to said input circuit, said electrometer circuit including extremely high input resistance solid state semi-conductive circuit isolation means connecting with said input circuit for providing an isolated DC output responsive to the DC voltage stored in said capacitor means, first switch connector means for selectively connecting said probe electrode to said input circuit, and second switch connector means for selectively grounding both said probe electrode and said input circUit.

Claim 6

An electrometer system for a non-contact detection of an electrostatic charge on a surface comprising: electrometer probe means containing a probe electrode adapted to be held adjacent to the charged surface for receiving a corresponding DC voltages capacitively induced thereon from said charge on said surface, an electrometer circuit having a highly insulated low leakage electrically floating input circuit, said electrometer circuit providing an output signal corresponding to said DC voltage applied to said input circuit, said input circuit having low-leakage capacitor means for storage and substantially reduction by capacitance ratio division of said DC voltage applied to said input circuit, said electrometer circuit including extremely high input resistance solid state semi-conductive circuit isolation means connecting with said input circuit for providing an isolated DC output responsive to the DC voltage stored in said capacitor means, first switch connector means for selectively connecting said probe electrode to said input circuit, and second switch connector means for selectively grounding both said probe electrode and said input circUit.

Claim 7

The electrometer system of claim 4, further including an adjustable voltage comparator circuit connected to the output of said semi-conductive circuit isolation means in said electrometer circuit, and further including a proportional output voltage indicator means connected to said voltage comparator circuit.

Claim 8

The electrometer system of claim 4, wherein said semi-conductive circuit isolation means is a single field effect transistor having a gate input which is connected to said input circuit.

Claim 9

The electrometer system of claim 6, further including an adjustable voltage comparator circuit connected to said field effect transistor in said electrometer circuit, and a proportional output voltage indicator connected to said voltage comparator circuit, and spacing means for maintaining said probe means a constant distance from said surface.

Claim 10

The electrometer system of claim 4, wherein said semi-conductive circuit isolation means in said electrometer circuit has a voltage gain of less than 1.

Claim 11

The electrometer system of claim 6, wherein said field effect transistor in said electrometer circuit is a metal oxide field effect transistor connected to have a voltage gain of less than 1, and wherein said field effect transistor is the only active element in said electrometer circuit.

Claim 12

The electrometer system of claim 6, wherein said input circuit includes protective high resistance means between said probe electrode and said gate of said field effect transistor, and wherein when said first switch connector means directly connects said probe electrode to said gate through only said resistance means, and wherein said capacitor means is connected in parallel with said gate.

Claim 13

The electrometer system of claim 10, wherein said capacitor means, said resistance means and said gate are the only elements of said electrometer circuit connected to said probe electrode.

Claim 14

The electrometer system of claim 10, wherein said probe means has a first capacitance, said gate has a second capicitance, and said capacitor means has a third capacitance substantially exceeding the sum of the first and second capacitances.

Claim 15

The electrometer system of claim 12, wherein said probe electrode has a fourth capacitance relative to said surface and said third capacitance is more than an order of magnitude greater than said fourth capacitance.