Combined AC-DC electrometer with AC feedback for drift compensation
Patent 4149119 Issued on April 10, 1979. Estimated Expiration Date: 
May 20, 1997. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
May 20, 1997. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References 2714136 2741668 3852667 InventorAssigneeApplicationNo. 05/799051 filed on 05/20/1977US Classes:324/458, Using modulation-type electrometer330/9WITH PERIODIC SWITCHING INPUT-OUTPUT (E.G., FOR DRIFT CORRECTION)ExaminersPrimary: Corcoran, Robert J.Attorney, Agent or FirmInternational ClassesG01R 15/16 (20060101)G01R 29/24 (20060101) G01R 15/14 (20060101) AbstractAn electrostatic voltmeter or electrometer which includes a probe sensor element for receiving electrostatic charge from a test surface whose potential level is desired to be measured. The probe is conditioned to receive both A.C. and D.C. signals which are amplified by a D.C. amplifier, with the A.C. signal from the probe being fed back to the D.C. amplifier to stabilize its output. In a preferred embodiment, a portion of the probe sensor element is periodically exposed to the test surface to impress the A.C. signal thereon which is utilized to correct the drift in the D.C. amplifier output.Other References
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