Abstract Presented is a system, including apparatus and methods of operation thereof, for effecting isolated measurement and sensing of line to ground voltages, differential voltages, currents, insulation leakage and resistances, Corona levels, and other parameters in insulated conductors and related systems associated with low and high power, low and high voltage electrical and electronic systems. The system includes a high input impedance meter unit actuated by a solid-state amplifier circuit including a pair of feedback circuits that cooperate with transistor amplifiers to maintain substantially constant the ratio of input and output from the circuit over a wide range of AC and DC voltages and currents. In its different applications, the high input impedance meter including solid-state amplifier circuit is used in conjunction with a variety of probes, both low voltage and high voltage types, for measurements of various voltages, and may be utilized with a proximity probe for direct sensing of AC fields. The high input impedance of the meter movement and solidstate circuit also permits the use of Corona voltage level and detecting probes for both high voltage direct and low voltage indirect or proximity measurement of various levels of voltages. Inasmuch as it is important that systems of this type be predictably accurate and operative, the system also includes a high voltage portable test unit to test the voltmeter and probes. To insure complete reliability of values being measured, the high voltage portable test source itself is subject to test to determine that it is operating properly before it is used to test the voltmeter and probes, and for this purpose a high voltage megohmmeter insulation leakage current-emission detecter is provided to test the high voltage portable test voltage source, and to measure the high voltage insulation associated with the high voltage point or terminal being measured. Inasmuch as the high input impedance metering system is used in conjunction with high voltages, a collapsible and detachable insulating ''''hot stick'''' is provided to isolate the high voltage components from human contact while in use.
A high input impedance probe for use in conjunction with a high input impedance metering system comprising: a. an electrically conductive input terminal adapted to be brought into close proximity or contact with an electrically conductive circuit; b. an output terminal adapted for electrical connection to said meter; c. a hollow dielectric housing disposed between said input and output terminals and mechanically supporting said input and output terminals in spaced relation; d. a capacitor and a resistor serially connected between said input and output terminals within said housing; and e. an electrically conductive shield structure surrounding said capacitor and resistor to effectively shield said probe from stray electrical fields; f. said hollow dielectric housing being provided with a reentrant tubular portion coaxially arranged within the housing, and said shield comprising a metallic tube coaxially disposed between the inner surface of the housing and the reentrant tubular portion, said reentrant tubular portion being supported at one end on the housing and provided with an end wall at its other end, and said capacitor and resistor being supported on said end wall of the reentrant tubular portion.
Claim 2
Dependent Claim
185 words
A high input impedance probe for use in conjunction with a high input impedance metering system comprising: a. an electrically conductive input terminal adapted to be brought into close proximity or contact with an electrically conductive circuit; b. an output terminal adapted for electrical connection to said meter; c. a hollow dielectric housing disposed between said input and output terminals and mechanically supporting said input and output terminals in spaced relation; d. a capacitor and a resistor serially connected between said input and output terminals within said housing; and e. an electrically conductive shield structure surrounding said capacitor and resistor to effectively shield said probe from stray electrical fields; f. said hollow dielectric housing being provided with a reentrant tubular portion coaxially arranged within the housing, and said shield comprising a metallic tube coaxially disposed between the inner surface of the housing and the reentrant tubular portion, said reentrant tubular portion being supported at one end on the housing and provided with an end wall at its other end, and said capacitor and resistor being supported on said end wall of the reentrant tubular portion.
Claim 3
Dependent Claim
18 words
The combination according to claim 1, in which the value of said resistor is at least 20 megohms.
Claim 4
Dependent Claim
19 words
The combination according to claim 1, in which a capacitor is interposed between said input circuit and said shield.
Claim 5
Dependent Claim
37 words
The combination according to claim 1, in which said resistive circuit includes a second resistor and a capacitor in parallel connection thereto, connected between said input circuit and said shield to provide over-voltage protection for said meter.