# US 10,119,998 B2 · Variable capacitance non-contact AC voltage measurement system

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- Number: US 10,119,998 B2
- Document ID: US10119998B2
- Status: Granted
- Kind: B2
- Application number: 15/345,256
- Filed: 2016-11-07
- Published: 2018-05-10
- Granted: 2018-11-06
- Earliest claimed: 2016-11-07
- Assignees: Fluke Corporation
- Applicants: Fluke Corporation
- Inventors: Paul Andrew Ringsrud; Clark N. Huber; Michael F. Gallavan
- Web page: https://patentgrep.com/patent/US10119998B2

## CPC

- G01R 15/16: using capacitive devices
- G01R 1/22: Tong testers acting as secondary windings of current transformers
- G01R 15/14: Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R 15/142: {Arrangements for simultaneous measurements of several parameters employing techniques covered by groups G01R15/14 - G01R15/26}
- G01R 19/00: Arrangements for measuring currents or voltages or for indicating presence or sign thereof (G01R5/00 takes precedence; for measuring bioelectric currents or voltages A61B5/24)
- G01R 19/2503: {for measuring voltage only, e.g. digital volt meters (DVM's) (G01R19/2506 - G01R19/257 take precedence)}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

Systems and methods for measuring alternating current (AC) voltage of an insulated conductor (e.g., insulated wire) are provided, without requiring a galvanic connection between the conductor and a test electrode or probe. A non-galvanic contact (or “non-contact”) voltage measurement system includes a variable capacitance subsystem which operates to generate a variable capacitive voltage between an insulated conductor under test and earth ground. During measurement, the non-contact voltage measurement system varies the capacitance of the variable capacitance subsystem to change the impedance of a capacitive divider circuit between the insulated conductor under test and earth ground. By sequentially making two (or three) measurements across the variable capacitance subsystem, the AC voltage of the insulated conductor can be determined without requiring any galvanic connection to the insulated conductor. The determined AC voltage of the insulated conductor may then be presented to an operator and/or communicated to an external device.

## Claims

### Claim 1

A system to measure alternating current (AC) voltage in an insulated conductor, the system comprising:
a conductive sensor positionable adjacent the insulated conductor without galvanically contacting the conductor, wherein the conductive sensor capacitively couples with the insulated conductor;
a variable capacitance subsystem which includes a first capacitance subsystem node and a second capacitance subsystem node, the first capacitance subsystem node electrically coupled to the conductive sensor, and the first capacitance subsystem node and the second capacitance subsystem node having a capacitance therebetween which is selectively variable between at least a first capacitance value (C1) and a second capacitance value (C2), the second capacitance value (C2) being different from the first capacitance value (C1);
a voltage measurement subsystem which in operation detects a voltage between the first capacitance subsystem node and the second capacitance subsystem node;
at least one nontransitory processor-readable storage medium that stores at least one of processor-executable instructions or data; and
at least one processor communicatively coupled to the at least one nontransitory processor-readable storage medium, and in operation, in response to execution of the processor-executable instructions or data, the at least one processor:
causes the variable capacitance subsystem to have the first capacitance value (C1) between the first capacitance subsystem node and the second capacitance subsystem node;
causes the voltage measurement subsystem to detect a first voltage (VM1) between the first capacitance subsystem node and the second capacitance subsystem node;
causes the variable capacitance subsystem to have the second capacitance value (C2) between the first capacitance subsystem node and the second capacitance subsystem node;
causes the voltage measurement subsystem to detect a second voltage (VM2) between the first capacitance subsystem node and the second capacitance subsystem node; and
determines the AC voltage (VAC) in the insulated conductor based at least in part on the detected first voltage (VM1) and the detected second voltage (VM2).

### Claim 2 (depends on 1)

The system of claim 1 wherein the at least one processor:
determines the AC voltage (VAC) in the insulated conductor according to the formula: VAC=VM1×[(C1/C2)−1]/[(C1VM1/C2VM2)−1].

### Claim 3 (depends on 1)

The system of claim 1 wherein the voltage measurement subsystem comprises at least one analog-to-digital converter (ADC).

### Claim 4 (depends on 1)

The system of claim 1 wherein the measurement subsystem has an effective resolution of at least 20 bits.

### Claim 5 (depends on 1)

The system of claim 1 wherein the variable capacitance subsystem comprises at least a first capacitor and a second capacitor which are each selectively electrically coupled between the first capacitance subsystem node and the second capacitance subsystem node.

### Claim 6 (depends on 1)

The system of claim 1 wherein the variable capacitance subsystem comprises a first capacitor electrically coupled between the first capacitance subsystem node and the second capacitance subsystem node, and a second capacitor which is selectively electrically coupled between the first capacitance subsystem node and the second capacitance subsystem node.

### Claim 7 (depends on 1)

The system of claim 1 wherein a ratio (C1:C2) of the first capacitance value (C1) to the second capacitance value (C2) is between 2:5 and 1:10 inclusive.

### Claim 8 (depends on 1)

The system of claim 1 wherein the first capacitance value (C1) is selectively variable to accommodate different values of input signals and input capacitance.

### Claim 9 (depends on 1)

The system of claim 1, further comprising:
a user interface communicatively coupled to the at least one processor, wherein the at least one processor presents the determined AC voltage (VAC) via the user interface.

### Claim 10 (depends on 9)

The system of claim 9 wherein the user interface comprises at least one of a display or a plurality of light emitters.

### Claim 11 (depends on 1)

The system of claim 1 wherein, in operation, the second capacitance subsystem node is electrically coupled to a reference node via the body of a user operating the system.

### Claim 12 (depends on 1)

The system of claim 1, further comprising:
a reference connection which electrically couples the second capacitance subsystem node to earth ground.

### Claim 13 (depends on 1)

The system of claim 1 wherein the first capacitance subsystem node and the second capacitance subsystem node have a capacitance therebetween which is further selectively variable between at least the first capacitance value (C1), the second capacitance value (C2) and a third capacitance value (C3), and in response to execution of the processor-executable instructions or data in the nontransitory processor-readable storage medium, the at least one processor:
causes the variable capacitance subsystem to have the third capacitance value (C3) between the first capacitance subsystem node and the second capacitance subsystem node;
causes the voltage measurement subsystem to detect a third voltage (VM3) between the first capacitance subsystem node and the second capacitance subsystem node; and
determines the AC voltage (VAC) in the insulated conductor based at least in part on the detected first voltage (VM1), second voltage (VM2), and third voltage (VM3).

### Claim 14 (depends on 13)

The system of claim 13 wherein the at least one processor:
determines the AC voltage (VAC) in the insulated conductor according to the formula: VAC=C3VM3×[(VM2−VM1)/(C1VM1−C2VM2)]+VM3.

### Claim 15

A system to measure alternating current (AC) voltage in an insulated conductor, the system comprising:
a conductive sensor positionable adjacent an insulated conductor without galvanically contacting the conductor, wherein the conductive sensor capacitively couples with the insulated conductor;
a variable capacitance subsystem electrically coupled to the conductive sensor;
a voltage measurement subsystem which in operation detects a voltage across the variable capacitance subsystem;
at least one nontransitory processor-readable storage medium that stores at least one of processor-executable instructions or data; and
at least one processor communicatively coupled to the at least one nontransitory processor-readable storage medium, and in operation, in response to execution of the processor-executable instructions or data, the at least one processor:
causes the variable capacitance subsystem to have a first capacitance value (C1);
detects, via the voltage measurement subsystem, a first voltage (VM1) across the variable capacitance subsystem when the conductive sensor is positioned adjacent the insulated conductor;
causes the variable capacitance subsystem to have a second capacitance value (C2);
detects, via the voltage measurement subsystem, a second voltage (VM2) across the variable capacitance subsystem when the conductive sensor is positioned adjacent the insulated conductor; and
determines the AC voltage (VAC) in the insulated conductor based at least in part on the detected first voltage (VM1) and the detected second voltage (VM2).

### Claim 16 (depends on 15)

The system of claim 15 wherein the at least one processor:
determines the AC voltage (VAC) in the insulated conductor according to the formula: VAC=VM1×[(C1/C2)−1]/[(C1VM1/C2VM2)−1].

### Claim 17 (depends on 15)

The system of claim 15 wherein the voltage measurement subsystem has an effective resolution of at least 20 bits.

### Claim 18 (depends on 15)

The system of claim 15 wherein the variable capacitance subsystem comprises at least a first capacitor, a second capacitor, and a switch coupled to at least one of the first capacitor and the second capacitor, wherein the switch is selectively operable by the at least one processor to cause the variable capacitance subsystem to have the first capacitance value (C1) and the second capacitance value (C2).

### Claim 19

A method of operating a system to measure alternating current (AC) voltage in an insulated conductor, the system comprising a conductive sensor positionable adjacent an insulated conductor without galvanically contacting the conductor, and a variable capacitance subsystem electrically coupled to the conductive sensor; the method comprising:
causing, by at least one processor, the variable capacitance subsystem to have a first capacitance value (C1);
detecting, by at least one processor, a first voltage (VM1) across the variable capacitance subsystem when the conductive sensor is positioned adjacent the insulated conductor;
causing, by at least one processor, the variable capacitance subsystem to have a second capacitance value (C2);
detecting, by at least one processor, a second voltage (VM2) across the variable capacitance subsystem when the conductive sensor is positioned adjacent the insulated conductor; and
determining, by at least one processor, the AC voltage (VAC) in the insulated conductor based at least in part on the detected first voltage (VM1) and the detected second voltage (VM2).

### Claim 20 (depends on 19)

The method of claim 19 wherein determining the AC voltage (VAC) in the insulated conductor comprises determining the AC voltage (VAC) in the insulated conductor according to the formula: VAC=VM1×[(C1/C2)−1]/[(C1VM1/C2VM2)−1].

### Claim 21 (depends on 19)

The method of claim 19 wherein detecting each of the first voltage (VM1) and the second voltage (VM2) comprises detecting each of the first voltage (VM1) and the second voltage (VM2) via at least one analog-to-digital converter (ADC) coupled to the variable capacitance subsystem.

### Claim 22 (depends on 19)

The method of claim 19 wherein detecting each of the first voltage (VM1) and the second voltage (VM2) comprises detecting each of the first voltage (VM1) and the second voltage (VM2) at an effective resolution of at least 20 bits.

### Claim 23 (depends on 19)

The method of claim 19 wherein causing the variable capacitance subsystem to have a second capacitance value (C2) comprises causing the variable capacitance subsystem to have a second capacitance value, wherein a ratio (C1:C2) of the first capacitance value (C1) to the second capacitance value (C2) is between 2:5 and 1:10 inclusive.

### Claim 24 (depends on 19)

The method of claim 19, further comprising:
presenting, by the at least one processor, the determined AC voltage (VAC) via a user interface.

### Claim 25 (depends on 19)

The method of claim 19, further comprising:
causing, by at least one processor, the variable capacitance subsystem to have a third capacitance value (C3);
detecting, by at least one processor, a third voltage (VM3) across the variable capacitance subsystem when the conductive sensor is positioned adjacent the insulated conductor; and
determining, by at least one processor, the AC voltage (VAC) in the insulated conductor based at least in part on the detected first voltage (VM1), second voltage (VM2), and third voltage (VM3).

### Claim 26 (depends on 25)

The method of claim 25 wherein determining the AC voltage (VAC) of the insulated conductor comprises determining the AC voltage (VAC) in the insulated conductor according to the formula: VAC=C3VM3×[(VM2−VM1)/(C1VM1−C2VM2)]−VM3.