Non-contact current measurement system

Systems and methods provide a non-contact current measurement system which operates to measure alternating current flowing through an insulated wire without requiring galvanic contact with the insulated wire. The measurement system may include a magnetic field sensor that is selectively positionable proximate an insulated wire under test. In operation the magnetic field sensor detects a magnetic field generated by the current flowing in the insulated wire. Using an adjustable clamp assembly, the measurement system provides control over the mechanical positioning of the insulated wire relative to the magnetic field sensor to ensure consistent measurements. The non-contact current measurement system may determine information relating to the physical dimensions (e.g., diameter) of the insulated wire. Using the detected magnetic field, the known mechanical positioning, and the determined information relating to the physical dimensions of the insulated wire, the measurement system accurately determines the magnitude of the current flowing through the insulated wire without galvanic contact.

BACKGROUND

Technical Field

The present disclosure generally relates to measurement of electrical characteristics, and more particularly, to non-contact measurement of alternating current (AC) in electrical circuits.

Description of the Related Art

Ammeters are instruments used for measuring current in an electric circuit. Instruments which measure more than one electrical characteristic are referred to as multimeters or digital multimeters (DMMs), and operate to measure a number of parameters generally needed for service, troubleshooting, and maintenance applications. Such parameters typically include alternating current (AC) voltage and current, direct current (DC) voltage and current, and resistance or continuity. Other parameters, such as power characteristics, frequency, capacitance, and temperature, may also be measured to meet the requirements of the particular application.

In order to measure current with a general purpose multimeter, an internal current shunt having a known resistance must be inserted in the current path, requiring a break in the current-carrying conductor. The voltage drop across the current shunt is then measured to determine the current in the current path. General purpose multimeters employing internal current shunts are generally limited to a few amperes maximum because of the capacity of the multimeter test leads and circuitry to carry the current. Furthermore, the multimeter generally must be protected with an internal fuse to prevent excessive current levels from flowing through the multimeter, both for safety reasons and to prevent damage to the multimeter.

With conventional ammeters or multimeters which measure AC current, it may be necessary to bring at least one measurement electrode or probe into galvanic contact with a conductor, which often requires breaking a circuit and/or cutting away part of the insulation of an insulated electrical wire, or providing a terminal for measurement in advance. Besides requiring an exposed wire or terminal for galvanic contact, the step of touching probes to stripped wires or terminals can be relatively dangerous due to the risks of shock or electrocution.

BRIEF SUMMARY

A non-contact current measurement system may be summarized as including: an adjustable clamp assembly which selectively clamps an insulated wire and may locate the wire in a defined position; a position feedback sensor that, in operation, generates a position feedback sensor signal indicative of a diameter of the insulated wire clamped in the adjustable clamp assembly; a magnetic field sensor positioned proximate the adjustable clamp assembly, wherein in operation the magnetic field sensor generates a magnetic field sensor signal that is indicative of at least one characteristic of a current flowing through the insulated wire clamped in the adjustable clamp assembly; and at least one processor communicatively coupled to the position feedback sensor and the magnetic field sensor, wherein in operation the at least one processor: receives the position feedback sensor signal from the position feedback sensor; receives the magnetic field sensor signal from the magnetic field sensor; and determines at least one characteristic of the current flowing through the insulated wire based at least in part on the received position feedback sensor signal and the magnetic field sensor signal.

The adjustable clamp assembly may include a first clamp surface and a second clamp surface, the second clamp surface may face the first clamp surface, and at least one of the first and second clamp surfaces (e.g., “jaws”) may be movable in a direction toward and away from the other of the first and second clamp surfaces to selectively clamp the insulated wire between the first and second clamp surfaces at a defined location. The first clamp surface may include a front end surface of a front end of a housing of the non-contact current measurement system, and the second clamp surface may be disposed on a clamp member that is selectively movable with respect to front end surface. The magnetic field sensor may be positioned proximate the front end surface of the front end of the housing. The adjustable clamp assembly may include a slider clamp assembly, and the position feedback sensor may include a linear position feedback sensor that generates a position feedback signal indicative of a linear position of the slider clamp assembly. The adjustable clamp assembly may include a first clamp portion having a first clamp surface and a second clamp portion having a second clamp surface that faces the first clamp surface, and a biasing member may bias the first clamp portion toward the second clamp portion. The non-contact current measurement system may further include a user interface operatively coupled to the at least one processor, wherein in operation the at least one processor causes the user interface to display the determined at least one characteristic of the current flowing through the insulated wire. The at least one characteristic of the current flowing through the insulated wire may include a magnitude of the current flowing through the insulated wire. The position feedback sensor may include a resistive sensor, a magneto-resistive sensor, a Hall Effect sensor, or an optical sensor. The non-contact current measurement system may further include: a voltage reference signal type sensor that, in operation, senses a reference signal in the insulated wire without galvanically contacting the insulated wire, wherein the at least one processor receives the reference signal and determines the at least one characteristic of the current flowing through the insulated wire driven by a reference voltage based at least in part on the received reference signal. The at least one processor may further determine at least one physical dimension of a conductor inside the insulated wire based at least in part on the received reference signal. The at least one processor may further determine at least one physical dimension of a conductor inside the insulated wire based at least in part on the received reference signal and the received position feedback sensor signal, which provides the outer diameter of the conductor of the insulated wire.

A method of measuring current in an insulated wire without galvanically contacting a conductor in the insulated wire may be summarized as including: clamping, via an adjustable clamp assembly, the insulated wire between first and second clamp surfaces; determining a clamp distance between the first and second clamp surfaces, wherein the clamp distance is indicative of a diameter of the insulated wire clamped between the first and second clamp surfaces; sensing, via a magnetic field sensor positioned proximate the insulated wire clamped between the first and second clamp surfaces, a magnetic field generated by the current flowing through the insulated wire; and determining, via at least one processor, at least one characteristic of the current flowing through the insulated wire based at least in part on the determined clamp distance and the sensed magnetic field generated by the current flowing through the insulated wire.

The first clamp surface may include a front end surface of a front end of a housing and the second clamp surface may include a surface of a clamp member of the adjustable clamp assembly that is movable with respect to the front end surface, and clamping the insulated wire between the first and second clamp surfaces may include clamping the insulated wire between the front end surface and the surface of the clamp member. Sensing the magnetic field generated by the current flowing through the insulated wire may include sensing the magnetic field via the magnetic field sensor, and the magnetic field sensor may be positioned proximate the front end surface of the front end of the housing. Clamping the insulated wire between the first and second clamp surfaces may include clamping the insulated wire between first and second clamp surfaces of a slider clamp assembly, and determining the clamp distance may include determining a linear position of the slider clamp assembly. Any other clamping mechanism in addition to a slider may also be used to provide the position. One other example is a clothespin type of clamping where the wire diameter is proportional the opening angle of the rotary clamping. The first clamp surface may be positioned on a first clamp portion and the second clamp surface may be positioned on a second clamp portion, and the method may further include biasing the first clamp portion toward the second clamp portion. The method may further include: displaying, via a user interface, the determined at least one characteristic of the current flowing through the insulated wire. Determining the at least one characteristic of the current flowing through the insulated wire may include determining a magnitude of the current flowing through the insulated wire. The method of claim may further include: sensing, via a reference signal type sensor positioned in a housing, a reference signal in the insulated wire without galvanically contacting the insulated wire; and determining, via the at least one processor, the at least one characteristic of the current flowing through the insulated wire based at least in part on the sensed reference signal. The method may further include, via the at least one processor, at least one physical dimension of a conductor inside the insulated wire based at least in part on the received reference signal. The method may further include, via the at least one processor, at least one physical dimension of a conductor inside the insulated wire based at least in part on the received reference signal and the received position feedback sensor signal. The reference method may also deliver the position of the wire and both methods of mechanical clamping or reference signal can be used individually or together to determine the wire diameter.

A non-contact current measurement system may be summarized as including: a housing including a front end portion having a front end surface; a clamp member having a clamp member surface that faces the front end surface, wherein the clamp member is movable with respect to the front end surface to selectively clamp an insulated wire between the front end surface and the clamp member surface; a position feedback sensor that generates a position feedback sensor signal that is indicative of a position of the clamp member; a current sensor positioned proximate the front end surface of the housing, wherein in operation the current sensor generates a current sensor signal that is indicative of at least one characteristic of a current flowing through the insulated wire clamped between the front end surface and the clamp member surface; and at least one processor communicatively coupled to the position feedback sensor and the current sensor, wherein in operation the at least one processor: receives the position feedback sensor signal from the position feedback sensor; receives the current sensor signal from the current sensor; and determines at least one characteristic of the current flowing through the insulated wire based at least in part on the received position feedback signal and the current sensor signal.

The current sensor may include a magnetic field sensor. The non-contact current measurement system may further include a display operatively coupled to the at least one processor, wherein in operation the at least one processor causes the display to present a magnitude of the current flowing through the insulated wire. The position feedback sensor may include a resistive sensor, a magneto-resistive sensor, a Hall Effect sensor, capacitive sensor, inductive sensor, or an optical sensor.

DETAILED DESCRIPTION

Systems and methods disclosed herein provide non-contact current measurement systems that measure current flowing through an insulated wire without requiring galvanic contact with the conductor of the insulated wire. In at least some implementations, a non-contact current measurement system includes a magnetic field sensor that is selectively positionable proximate (e.g., adjacent) an insulated wire under test. Non-limiting examples of magnetic field sensors include anisotropic magnetoresistive (AMR) sensors, giant magnetoresistive (GMR) sensors, fluxgate sensors, squid sensors, fiber-optic sensors, optically pumped sensors, nuclear procession sensors, search-coil sensors, magnetotransistor sensors, magnetodiode sensors, magneto-optical sensors, Hall effect sensors, Rogowski coils, current transformers, or other types of magnetic field sensors. The magnetic field sensor detects a magnetic field generated by the current flowing in the insulated wire. The magnitude of the magnetic field surrounding the conductor of the insulated wire is related (e.g., proportional) to the magnitude of current flowing through the conductor of the insulated wire.

In addition to detecting the magnetic field surrounding a conductor, at least some of the implementations of the present disclosure utilize an adjustable clamp assembly to provide control over the mechanical positioning of the insulated wire relative to the magnetic field sensor. Further, in at least some implementations, the non-contact current measurement system determines information relating to at least one physical dimension of the insulated wire under test, such as its outer diameter or gauge of the conductor inside the insulation of the insulated wire. Using the detected magnetic field, the controlled mechanical positioning, and the determined physical dimension information, the non-contact current measurement system accurately determines the magnitude of the current flowing through the conductor of an insulated wire.

As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the context clearly dictates otherwise. In addition, the headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the implementations.

FIG. 1is a pictorial diagram of an environment100in which a non-contact current measurement system102may be used by a technician104to measure AC current present in an insulated wire106without requiring galvanic contact between the non-contact current measurement system and the insulated wire106.FIGS. 2A and 2Bshow enlarged views of the non-contact current measurement system102.

The non-contact current measurement system102includes a housing or body108which includes a grip portion or end110and a front portion or end112opposite the grip portion. The housing108may also include a user interface114which facilitates user interaction with the non-contact current measurement system102. The user interface114may include any number of inputs (e.g., buttons, dials, switches, touch sensor) and any number of outputs (e.g., display, LEDs, speakers, buzzers). The non-contact current measurement system102may also include one or more wired and/or wireless communications interfaces (e.g., USB, Wi-Fi®, Bluetooth®).

As shown inFIGS. 2A and 2B, a magnetic field sensor116(e.g., anisotropic magnetoresistive (AMR) sensor, giant magnetoresistive (GMR) sensor, fluxgate sensor, etc.) is positioned below a top surface118of the front end112. The magnetic field sensor116is used to detect the magnetic field generated by a current flowing in the insulated wire106, which comprises a conductor122surrounded by one or more layers of insulation124. The magnitude of the magnetic field surrounding the conductor122is related (e.g., proportional) to the magnitude of the current flowing through the conductor. Generally, the magnitude of the current flowing in the conductor122may be accurately determined by the magnetic field sensor116when two parameters are met. The first parameter is control over the mechanical positioning of the insulated wire106relative to the magnetic field sensor116, which is controlled by an adjustable clamp assembly126in at least some implementations. The second parameter is physical dimension information of the insulated wire106, such as its outer diameter or the diameter of the conductor inside the insulation of the insulated wire (i.e., gauge), which may be determined or estimated by a position feedback sensor128operatively coupled to the adjustable clamp assembly126. The adjustable clamp assembly126and the position feedback sensor128are discussed further below.

Further, in at least some implementations, physical dimension information regarding the gauge of the insulated wire106may additionally or alternatively be obtained utilizing one or more reference signal sensors that detect a generated reference signal (e.g., reference current signal) between the sensor and the insulated wire106. Various example non-contact measurement systems that implement such a “reference signal” method of detecting physical dimension information for an insulated wire are discussed below with reference toFIG. 7AthroughFIG. 21. For example, in at least some implementations, an adjustable clamp assembly and position feedback sensor may be used to determine the overall diameter of an insulated wire, and the reference signal method may be used to determine the thickness of the insulation of the insulated wire. Using the determined overall diameter of the insulated wire and the determined insulation thickness, the non-contact current measurement system may automatically determine or estimate the diameter of the conductor inside the insulation of the insulated wire (e.g., the diameter of the conductor is equal to the overall diameter of the insulated wire reduced by two times the insulation thickness). The determined diameter of the conductor may then be used in conjunction with the detected magnetic field to accurately determine the magnitude of the current flowing through the insulated wire.

In the illustrated implementation, the mechanical positioning of the insulated wire106is provided by the adjustable clamp or “slider” clamp assembly126which ensures that the insulated conductor is positioned in proper alignment (e.g., adjacent) with the magnetic field sensor116during measurement. The adjustable clamp assembly126includes a clamp member130coupled to the housing108that is selectively movable toward to and away from the top surface118of the front end112. The clamp member130may be referred to herein as a first clamp portion, and the front end112may be referred to herein as a second clamp portion. The clamp member130includes a clamp surface132that faces the top surface118of the front end112and is generally parallel thereto. The clamp surface132and the top surface118together define a variably-sized clamp opening134sized and dimensioned to receive a portion of the insulated wire106therein. In the illustrated example, the clamp member130is selectively movable between a first position P1, in which the clamp opening134is relatively large, and a second position P2, in which the clamp opening is relatively small.

As shown inFIG. 2A, a user may position the insulated wire106within the clamp opening134when the clamp surface132of the clamp member130is spaced apart from the top surface118of the front end112by an amount sufficient to easily allow the insulated wire to be moved into the clamp opening. Then, as shown inFIG. 2B, the user may move the clamp member130downward to a third position P3to “clamp” the insulated wire106between the top surface118of the front end112and the clamp surface132, such that the top surface and the clamp surface both contact the insulation layer of the insulated wire on opposite sides. As used herein, the term “clamp” is used to refer to the insulated wire106being contacted by the top surface118and the clamp surface132on opposite sides of the insulated wire to maintain the position of the wire relative to the magnetic field sensor116. That is, the term does not indicate that the top surface118or the clamp surface132necessarily impart any particular amount of force on the insulated wire106.

The position feedback sensor128is operative to sense the position (e.g., linear position) of the clamp member130and generates a position feedback sensor signal (e.g., linear position feedback sensor signal) that is indicative of such. The position feedback signal may be a digital or analog signal, for example. When the insulated wire106is clamped between the clamp surface132and the top surface118of the front end112, the sensed position of the clamp member130may be used to determine or estimate the diameter or gauge of the insulated wire. For example, the position feedback sensor128may provide a position feedback sensor signal that is proportional to the extension of the clamp member130. The position feedback sensor128may be any suitable sensor operative to sense the extension of the clamp member130and determine the diameter of the insulated wire106. For example, the position feedback sensor128may include a resistive sensor, a magneto-resistive sensor, a Hall Effect sensor, an optical sensor, etc. As discussed further below, in at least some implementations a “reference signal” method may additionally or alternatively be used to determine the diameter or dimensions of the conductor inside the insulated wire106, which may further allow the system102to provide accurate current measurements.

In at least some implementations, the clamp member130may be biased toward the second position P2by a suitable biasing member136. For example, the clamp member130may be biased toward the second position P2by a spring coupled between the clamp member and a portion of the housing108. Advantageously, biasing the clamp member130may allow for the clamp assembly126to better retain the insulated wire106in the clamp opening134, while also providing more uniform measurements of the diameter of the insulated wire106.

The mechanical positioning of the insulated wire106relative to the magnetic field sensor116may be important due to the orthogonal relationship between magnetic flux density and current flow (e.g., the “right hand rule” for magnetic flux around a current-carrying conductor). In addition, the physical dimension information provided by the position feedback sensor128may be important due to magnetic flux density, which is tangent to the circumference of the conductor, being higher in conductors with smaller diameters than conductors with larger diameters for the same current flow. Thus, by knowing at least an estimation of the diameter of the insulated wire, the non-contact current measurement system102can more accurately determine the current flowing through the insulated wire by accounting for the impact the diameter of the wire has on the relationship between the sensed magnetic field and the current flowing in the wire.

As discussed further below with reference toFIG. 6, using data from the magnetic field sensor116and the diameter or gauge data from the position feedback sensor128and/or a reference signal sensor, at least one processor of the non-contact current measurement system102may accurately determine at least one characteristic (e.g., magnitude, frequency) of the current flowing through the insulated wire106. Such information may be presented to the user via a display of the user interface114, stored in a nontransitory processor-readable storage medium of the non-contact current measurement system, and/or transmitted to a separate device by a wired or wireless communications interface.

Although the illustrated non-contact current measurement system102includes the magnetic field sensor116, it is appreciated that in other implementations the non-contact current measurement system may include various other types of magnetic field sensors (e.g., a Hall Effect sensor, a Rogowski coil, a current transformer, etc.) capable of sensing the magnetic field generated by a current without requiring galvanic contact with the wire under test.

As discussed further below, in at least some implementations, the non-contact measurement system102may utilize the body capacitance (CB) between the operator104and ground128during the current measurement. Although the term ground is used for the node128, the node is not necessarily earth/ground but could be connected in a galvanically isolated manner to any other reference potential by capacitive coupling.

FIG. 3shows a front elevational view of a non-contact current measurement system300that has a different form factor than the non-contact current measurement system102. The non-contact current measurement system300may be similar or identical to the non-contact current measurement system102discussed above in many respects. Thus, some or all of the discussion above regarding the features of the non-contact current measurement system102may also apply to the non-contact current measurement system300.

The non-contact current measurement system300includes a housing302having a front end304and a grip portion or end306opposite the front end. The housing302includes a user interface308(e.g., display, buttons) positioned on a surface of the housing. The front end304includes a current sensor312(e.g., magnetic field sensor), an optional reference signal sensor313, and a retractable jaw or clamp member314for grasping an insulated wire (e.g., insulated wire106ofFIGS. 1, 2A and 2B). The operation of various reference signal sensors is discussed further below with reference toFIGS. 7A-21. The front end304includes a front end surface316adjacent the current sensor312and the clamp member314includes a clamp surface318opposite the front end surface316. For a further increase of current measurement accuracy, a second magnetic field sensor could be used in clamp member314. The average signal between the current sensor312and an additional sensor located in the clamp member314can then be used for the current calculation. In addition, the difference between both sensors exceeding a limit can be used to identify unreliable situations caused by external stray currents or an incorrectly positioned wire clamped between the clamp members314and316. In use, an insulated wire may be clamped between the front end surface316and the clamp surface318to position the insulated wire adjacent the current sensor312. The clamp member314, as well as other clamp members of the present disclosure, may be permanently attached to the housing302or may be selectively detachable from the housing. The non-contact current measurement system300also includes a position feedback sensor320and optionally includes a biasing member322to bias the clamp member314toward the housing302to clamp an insulated wire between the front end surface316and the clamp surface318. Further discussion of embodiments of a current sensor and a position feedback sensor suitable for use in the non-contact current measurement system300is provided with regard toFIG. 6.

FIG. 4shows a front elevational view of a non-contact current measurement system400that has a different form factor than the non-contact current measurement system102. The non-contact current measurement system400may be similar or identical to the non-contact current measurement systems discussed above in many respects. Thus, some or all of the discussion above regarding the features of the non-contact current measurement systems above may also apply to the non-contact current measurement system400.

The non-contact current measurement system400includes a housing402having a front end404and a grip portion or end406opposite the front end. The housing402includes a user interface408(e.g., display, buttons, dial) positioned on a surface of the housing. The front end404includes a current sensor412(e.g., magnetic field sensor), an optional reference signal sensor413, and a retractable hook or clamp member414for grasping an insulated wire (e.g., insulated wire106ofFIGS. 1, 2A and 2B). The front end404includes a front end surface416adjacent the current sensor412and the clamp member414includes a clamp surface418opposite the front end surface416. In use, an insulated wire may be clamped between the front end surface416and the clamp surface418to position the insulated wire adjacent the current sensor412. The clamp member414may be permanently attached to the housing402or may be selectively detachable from the housing. The non-contact current measurement system400also includes a position feedback sensor420and optionally includes a biasing member422to bias the clamp member414toward the housing402to clamp an insulated wire between the front end surface416and the clamp surface418. Suitable embodiments of a current sensor and position feedback sensor that may be used in the non-contact current measurement system400is provided with regard toFIG. 6.

FIG. 5shows a front elevational view of a non-contact current measurement system500that has a different form factor than the non-contact current measurement system102. The non-contact current measurement system500may be similar or identical to the non-contact current measurement systems discussed above in many respects. Thus, some or all of the discussion above regarding the features of the non-contact current measurement systems above may also apply to the non-contact current measurement system500.

The non-contact current measurement system500includes a housing502having a front end504and a grip portion or end506opposite the front end. The housing502includes a user interface508(e.g., display, buttons, dial) positioned on a surface of the housing. The front end504includes a current sensor512(e.g., magnetic field sensor), an optional reference signal sensor513, and a retractable hook or clamp member514for grasping an insulated wire (e.g., insulated wire106ofFIGS. 1, 2A and 2B). The front end504includes a front end surface516adjacent the current sensor512and the clamp member514includes a clamp surface518opposite the front end surface516. In use, an insulated wire may be clamped between the front end surface516and the clamp surface518to position the insulated wire adjacent the current sensor512. The clamp member514may be permanently attached to the housing502or may be selectively detachable from the housing. The non-contact current measurement system500also includes a position feedback sensor520and optionally includes a biasing member522to bias the clamp member514toward the housing502to clamp an insulated wire between the front end surface516and the clamp surface518.FIG. 6below provides additional discussion of embodiments of a current sensor and a position feedback sensor that are suitable for use in the non-contact current measurement system500.

FIG. 6is a schematic block diagram of a non-contact current measurement system or instrument600which provides non-contact current measurement functionality. The non-contact current measurement system600may be similar or identical to any of the non-contact current measurement systems discussed herein.

The non-contact current measurement system600includes a current sensor602(e.g., magnetic field sensor) communicatively coupled to a processor604. The non-contact current measurement system600also includes an adjustable clamp assembly606, and a position feedback sensor608operatively coupled to the adjustable clamp assembly and the processor604. In operation, the position feedback sensor608generates a position feedback sensor signal indicative of the position of the adjustable clamp assembly606, and from the detected position, determines a diameter of an insulated wire clamped in the adjustable clamp assembly606, as discussed above. The processor604receives the position feedback sensor signal from the position feedback sensor608.

The current sensor602may be any suitable non-contact current sensor, such as a magnetic field sensor, Hall Effect sensor, etc. In operation, the current sensor602generates a current sensor signal that is indicative of at least one characteristic of a current flowing through the insulated wire clamped in the adjustable clamp assembly606. For example, the at least one characteristic may include a magnitude of the current or a frequency of the current. In implementations wherein the current sensor602is a magnetic field sensor, the current sensor may generate a magnetic field sensor signal that is indicative of a magnetic field produced by the current flowing through the insulated wire, which magnetic field may be analyzed by the processor604to determine the at least one characteristic of the current flowing through the insulated wire.

The adjustable clamp assembly606may be similar or identical to any of the adjustable clamp assemblies discussed herein. The position feedback sensor608is operative to generate a position feedback sensor signal indicative of a clamp position of the adjustable clamp assembly606, which in turn is indicative of a diameter of the insulated wire clamped by the adjustable clamp assembly. The position feedback sensor608may be any suitable position sensor including, but not limited to, a resistive sensor, a magneto-resistive sensor, a Hall Effect sensor, an optical sensor, etc.

The processor604may include one or more logic processing units, such as one or more central processing units (CPUs), microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), microcontrollers, other programmable circuits, combinations of the above, etc. Generally, the processor604may serve as the computational center of the non-contact current measurement system600by supporting the execution of instructions and reading and writing data to one or more storage devices, I/O interfaces, and communication systems.

The non-contact current measurement system600may also include memory610communicatively coupled to the processor604which stores at least one of instructions or data thereon. The memory610may include one or more solid state memories, for instance flash memory or solid state drive (SSD), which provide nonvolatile storage of computer-readable instructions, data structures, program modules and other data for the non-contact current measurement system600. Although not depicted, the non-contact current measurement system600can employ other nontransitory computer- or processor-readable media, for example a hard disk drive, an optical disk drive, or memory card media drive.

The non-contact current measurement system600may include a user interface612which may include any number of inputs613(e.g., buttons, dials, switches, touch sensor, touchscreen, trigger switches, selectors, rotary switches) and any number of outputs614(e.g., display, LEDs, speakers, buzzers). Non-limiting examples of display devices include a liquid crystalline display (LCD) device, a light emitting diode (LED) device, and/or an organic light emitting diode (OLED) device. The user interface612may include a touch screen, which may be any type of touch screen currently known or later developed. For example, the touch screen may be a capacitive, infrared, resistive, or surface acoustic wave (SAW) device. In implementations wherein the non-contact current measurement system600includes a display, the display may presents readouts and/or waveforms indicative of at least one characteristic (e.g., magnitude, frequency) of the current flowing through the insulated wire under test.

In operation, the processor604receives the sensor signals from the position feedback sensor608and the current sensor602to obtain clamp position and current measurements, respectively. As discussed above, the clamp position measurement is indicative of the diameter of the insulated wire under test, and the current sensor signal may be indicative of at least one characteristic (e.g., magnitude) of the current flowing through the insulated wire. As discussed above, the processor604may utilize such measurements to determine at least one characteristic of the current flowing through the insulated wire under test, such as the magnitude and/or frequency of the current flowing through the insulated wire.

The processor604may provide readouts of one or more of the measured or determined characteristics (e.g., current magnitude, current frequency, diameter of insulated wire), and may provide graphical representations of one or more characteristics. Such graphical representations may include waveforms, harmonic bar graphs, etc.

To communicate with one or more external processor-based devices, the non-contact current measurement system600may include one or more wired and/or wireless communications interfaces616. Non-limiting examples of wireless communications interfaces include Wi-Fi®, Bluetooth®, Bluetooth® Low Energy, ZigBee®, 6LoWPAN®, Optical IR, wireless HART, etc. Non-limiting examples of wired communications interfaces include USB®, Ethernet, PLC, HART, MODBUS, FireWire®, Thunderbolt®, etc.

In addition to sending data to external device, in at least some implementations the non-contact current measurement system600may receive at least one of data or instructions (e.g., control instructions) from an external device via the wired and/or wireless communications interface616.

In at least some implementations, the non-contact current measurement system600may not include a display and instead may be used as a sensor to monitor electrical equipment remotely via an external processor-based device. Such processor-based device may include various types of devices, such as smartphones, tablet computers, laptop computers, wearable computers, servers, cloud computers, etc. The external processor-based device may include a display to present data gathered by the non-contact current measurement system600over a period of time (e.g., minutes, hours, days, weeks).

In at least some implementations, the non-contact current measurement system may include one or more additional electrical sensors618communicatively coupled to the processor604. Such electrical sensors618may include a voltage sensor capable of sensing voltage, a resistance sensor capable of sensing resistance, a capacitive sensor capable of sensing capacitance, etc. In such implementations that include one or more additional sensors618, the non-contact current measurement system600may function as a multimeter that provides a plurality of electrical characteristics (e.g., current, voltage, power, resistance, capacitance).

In at least some implementations, the electrical sensor618may comprise a reference signal sensor that is operative to detect a thickness of the insulation of an insulated wire under test. Various example reference signal sensors are discussed further below with reference toFIGS. 7-21. In such implementations, the adjustable clamp assembly606and position feedback sensor608may be used to determine the overall diameter of an insulated wire, and the reference signal sensor618may utilize a reference signal method, discussed further below, to determine the thickness of the insulation of the insulated wire. Using the overall diameter of the insulated wire determined by the adjustable clamp assembly606and position feedback sensor608, and the determined insulation thickness determined by the reference signal sensor618, the non-contact current measurement system may automatically determine the diameter of the conductor of the insulated wire, which is equal to the overall diameter of the insulated wire reduced by two times the determined insulation thickness. The determined diameter of the conductor may then be used in conjunction with the detected magnetic field to determine the magnitude of the current flowing through the insulated wire.

The following discussion provides examples of systems and methods which utilize a “reference signal” method for measuring at least one physical dimension (e.g., insulation thickness) of an insulated wire without requiring a galvanic connection between the conductor of an insulated wire and a sensor or electrode (“reference signal sensor”). As noted above, in at least some implementations, a non-contact current measurement system may utilize the reference signal method, with or without mechanical position feedback, to determine or estimate one or more physical dimensions (e.g., diameter of a conductor) of an insulated wire. As also discussed below, the reference signal method may additionally or alternatively be utilized to measure alternating current (AC) voltage of an insulated or blank uninsulated conductor (e.g., insulated wire) without requiring a galvanic connection between the conductor and the test electrode or probe. The implementations disclosed below may be referred to herein as “reference signal type” sensors or systems.

FIG. 7Ais a pictorial diagram of an environment700in which a non-contact measurement system702that includes a reference signal type voltage sensor or system may be used by an operator704to measure AC current present in an insulated wire706without requiring galvanic contact between the non-contact measurement system and the wire706. The non-contact measurement702may include some or all of the components and functionality of the non-contact current measurement systems discussed above.FIG. 7Bis a top plan view of the non-contact measurement system702ofFIG. 7A, showing various electrical characteristics of the non-contact measurement system during operation. The non-contact measurement system702includes a housing or body708which includes a grip portion or end710and a probe portion or end712, also referred to herein as a front end, opposite the grip portion. The housing708may also include a user interface714which facilitates user interaction with the non-contact measurement system702. The user interface714may include any number of inputs (e.g., buttons, dials, switches, touch sensor) and any number of outputs (e.g., display, LEDs, speakers, buzzers). The non-contact measurement system702may also include one or more wired and/or wireless communications interfaces (e.g., USB, Bluetooth®).

In at least some implementations, as shown best inFIG. 7B, the probe portion712may include a recessed portion716defined by first and second extended portions718and720. The recessed portion716receives the insulated wire706(see FIG.7A). The insulated wire706includes a conductor722and an insulator724surrounding the conductor722. The recessed portion716may include a reference signal sensor or electrode726which rests proximate the insulator724of the insulated wire706when the insulated wire is positioned within the recessed portion716of the non-contact measurement system702. Although not shown for clarity, the sensor726may be disposed inside of the housing708to prevent physical and electrical contact between the sensor and other objects.

As shown inFIG. 7A, in use the operator704may grasp the grip portion710of the housing708and place the probe portion712proximate the insulated wire706so that the non-contact measurement system702may accurately measure the current present in the wire, as discussed above. Although the probe end712is shown as having the recessed portion716, in other implementations the probe portion712may be configured differently. For example, in at least some implementations the probe portion712may include a selectively movable clamp, a hook, a flat or arcuate surface which includes the sensor, or other type of interface which allows a sensor of the non-contact measurement system702to be positioned proximate the insulated wire706. Examples of various adjustable clamp assemblies and position feedback sensors are discussed above with reference toFIGS. 1-6. Examples of various probe portions and sensors are discussed below with reference toFIGS. 16-21.

The operator's body acting as a reference to earth/ground may only be in some implementations. The non-contact measurement functionality discussed herein is not limited to applications only measuring with respect to earth. The outside reference may be capacitively coupled to any other potential. For example, if the outside reference is capacitively coupled to another phase in three phase systems, the phase-to-phase voltages are measured. In general, the concepts discussed herein are not limited to reference with respect to earth only using a body capacitive coupling connected to a reference voltage and any other reference potential.

As discussed further below, in at least some implementations, the non-contact measurement system702may utilize the body capacitance (CB) between the operator704and ground728during measurements. Although the term ground is used for the node728, the node is not necessarily earth/ground but could be connected in a galvanically isolated manner to any other reference potential by capacitive coupling.

The particular systems and methods used by the non-contact measurement system702are discussed below with reference toFIGS. 8-21.

FIG. 8shows a schematic diagram of various internal components of the non-contact measurement system702also shown inFIGS. 7A and 7B. In this example, the conductive sensor726of the non-contact measurement system702is substantially “V-shaped” and is positioned proximate the insulated wire706under test and capacitively couples with the conductor722of the insulated wire706, forming a sensor coupling capacitor (CO). The operator704handling the non-contact measurement system702has a body capacitance (CB) to ground. Thus, as shown inFIGS. 7B and 8, the AC voltage signal (VO) in the wire722generates an insulated conductor current component or “signal current” (IO) over the coupling capacitor (CO) and the body capacitance (CB), which are connected in series. In some implementations, the body capacitance (CB) may also include a galvanically isolated test lead which generates a capacitance to ground or any other reference potential.

The AC voltage (VO) in the wire722to be measured has a connection to an external ground728(e.g., neutral). The non-contact measurement system702itself also has a capacitance to ground728, which consists primarily of the body capacitance (CB) when the operator704(FIG. 7A) holds the non-contact measurement system in his hand. Both capacitances COand CBcreate a conductive loop and the voltage inside the loop generates the signal current (IO). The signal current (IO) is generated by the AC voltage signal (VO) capacitively coupled to the conductive sensor726and loops back to the external ground728through the housing708of the non-contact measurement system and the body capacitor (CB) to ground728. The current signal (IO) is dependent on the distance between the conductive sensor726of the non-contact measurement system702and the insulated wire706under test, the particular shape of the conductive sensor726, and the size and voltage level (VO) in the conductor722.

To compensate for the distance variance and consequent coupling capacitor (CO) variance which directly influences the signal current (IO), the non-contact measurement system702includes a common mode reference voltage source730which generates an AC reference voltage (VR) which has a reference frequency (fR) different from the signal voltage frequency (fo).

To reduce or avoid stray currents, at least a portion of the non-contact measurement system702may be surrounded by a conductive internal ground guard or screen732which causes most of the current to run through the conductive sensor726which forms the coupling capacitor (CO) with the conductor722of the insulated wire706. The internal ground guard732may be formed from any suitable conductive material (e.g., copper) and may be solid (e.g., foil) or have one or more openings (e.g., mesh).

Further, to avoid currents between the internal ground guard732and the external ground728, the non-contact measurement system702includes a conductive reference shield734. The reference shield734may be formed from any suitable conductive material (e.g., copper) and may be solid (e.g., foil) or have one or more openings (e.g., mesh). The common mode reference voltage source730is electrically coupled between the reference shield734and the internal ground guard732, which creates a common mode voltage having the reference voltage (VR) and the reference frequency (fR) for the non-contact measurement system702. Such AC reference voltage (VR) drives an additional reference current (IR) through the coupling capacitor (CO) and the body capacitor (CB).

The internal ground guard732which surrounds at least a portion of the conductive sensor726protects the conductive sensor against direct influence of the AC reference voltage (VR) causing an unwanted offset of reference current (IR) between the conductive sensor726and the reference shield734. As noted above, the internal ground guard732is the internal electronic ground738for the non-contact measurement system702. In at least some implementations, the internal ground guard732also surrounds some or all of the electronics of the non-contact measurement system702to avoid the AC reference voltage (VR) coupling into the electronics.

As noted above, the reference shield734is utilized to inject a reference signal onto the input AC voltage signal (VO) and as a second function minimizes the guard732to earth ground728capacitance. In at least some implementations, the reference shield734surrounds some or all of the housing708of the non-contact measurement system702. In such implementations, some or all of the electronics see the reference common mode signal which also generates the reference current (IR) between the conductive sensor726and the conductor722in the insulated wire706. In at least some implementations, the only gap in the reference shield734may be an opening for the conductive sensor726which allows the conductive sensor to be positioned proximate the insulated wire706during operation of the non-contact measurement system702.

The internal ground guard732and the reference shield734may provide a double layer screen around the housing708(seeFIGS. 7A and 7B) of the non-contact measurement system702. The reference shield734may be disposed on an outside surface of the housing708and the internal ground guard732may function as an internal shield or guard. The conductive sensor726is shielded by the guard732against the reference shield734such that any reference current flow is generated by the coupling capacitor (CO) between the conductive sensor726and the conductor722under test.

The guard732around the sensor726also reduces stray influences of adjacent wires close to the sensor.

As shown inFIG. 8, the non-contact measurement system702may include an input amplifier736which operates as an inverting current-to-voltage converter. The input amplifier736has a non-inverting terminal electrically coupled to the internal ground guard732which functions as the internal ground738of the non-contact measurement system702. An inverting terminal of the input amplifier736may be electrically coupled to the conductive sensor726. Feedback circuitry737(e.g., feedback resistor) may also be coupled between the inverting terminal and the output terminal of the input amplifier736to provide feedback and appropriate gain for input signal conditioning.

The input amplifier736receives the signal current (IO) and reference current (IR) from the conductive sensor726and converts the received currents into a sensor current voltage signal indicative of the conductive sensor current at the output terminal of the input amplifier. The sensor current voltage signal may be an analog voltage, for example. The analog voltage may be fed to a signal processing module740which, as discussed further below, processes the sensor current voltage signal to estimate or determine the thickness of the insulation layer724of the insulated wire706and/or to determine the AC voltage (VO) in the conductor722of the insulated wire706. As discussed above, a determined thickness of the insulation layer724of the insulated wire706may be used at least in part to estimate or determine at least one physical dimension (e.g., diameter) of the conductor722, which may be used along with a magnetic field measurement to determine the current flowing through the conductor722of the insulated wire. The signal processing module740may include any combination of digital and/or analog circuitry.

The non-contact measurement system702may also include a user interface742(e.g., display) communicatively coupled to the signal processing module740to present the determined current and/or the determined voltage (VO) or to communicate by an interface to the operator704of the non-contact measurement system.

FIG. 9is a block diagram of a non-contact measurement system900which shows various signal processing components of the non-contact measurement system.FIG. 10is a more detailed diagram of the non-contact measurement system900ofFIG. 9.

The non-contact measurement system900may be similar or identical to the non-contact measurement system702discussed above. Accordingly, similar or identical components are labeled with the same reference numerals. As shown, the input amplifier736converts the input current (IO+IR) from the conductive sensor726into a sensor current voltage signal which is indicative of the input current. The sensor current voltage signal is converted into digital form using an analog-to-digital converter (ADC)902.

The AC voltage (VO) in the wire722is related to the AC reference voltage (VR) by Equation (1):

VOVR=IO×fRIR×fO(1)
where (IO) is the signal current through the conductive sensor726due to the AC voltage (VO) in the conductor722, (IR) is the reference current through the conductive sensor726due to the AC reference voltage (VR), (fO) is the frequency of the AC voltage (VO) that is being measured, and (fR) is the frequency of the reference AC voltage (VR).

The signals with indices “0,” which are related to the AC voltage (VO), have different characteristics like frequencies than the signals with indices “R,” which are related to the common mode reference voltage source730. In the implementation ofFIG. 10, digital processing, such as circuitry implementing a fast Fourier transform (FFT) algorithm906, may be used to separate signal magnitudes with different frequencies. In the implementation ofFIG. 11discussed below, analog electronic filters may also be used to separate “O” signal characteristics (e.g., magnitude, frequency) from “R” signal characteristics.

The currents (IO) and (IR) are dependent on the frequencies (fO) and (fR), respectively, due to the coupling capacitor (CO). The currents flowing through the coupling capacitor (CO) and the body capacitance (CB) are proportional to the frequency and thus, the frequency (fO) of the AC voltage (VO) in the conductor722under test may need to either be measured to determine the ratio of the reference frequency (fR) to the signal frequency (fO), which is utilized in Equation (1) listed above or the reference frequency is already known because it is generated by the system itself.

After the input current (IO+IR) has been conditioned by the input amplifier736and digitized by the ADC902, the frequency components of the digital sensor current voltage signal may be determined by representing the signal in the frequency domain using the FFT906. When both of the frequencies (fO) and (fR) have been measured, frequency bins may be determined to calculate the fundamental magnitudes of the currents (IO) and (IR) from the FFT906.

The magnitude of the current (IR) and/or the current (IO) may vary as a function of distance between the reference signal sensor or electrode (e.g., electrode726) and the conductor722of the insulated wire706. Thus, the system may compare the measured current (IR) and/or the current (IO) to expected respective currents to determine the distance between the reference signal sensor or electrode and the conductor722. Since during measurement the insulated wire706may be positioned adjacent the reference signal sensor or electrode (e.g., via an adjustable clamp assembly), the distance between the reference signal sensor and the conductor722of the insulated wire706is approximately equal to the thickness of the insulation layer724. As discussed above, a position feedback sensor operatively coupled to an adjustable clamp assembly provides the overall diameter of the insulated wire706. Thus, using the determined overall diameter of the insulated wire and the determined thickness of the insulation layer724, the system may accurately determine the diameter or gauge of the conductor722inside the insulated wire706. This information, along with the magnetic field measured by a magnetic field sensor (e.g., sensors116,312,412, or512), may be used to by the system to accurately determine the magnitude of the current flowing through the conductor722inside the insulated wire706.

As indicated by a block908, the ratio of the fundamental harmonics of the currents (IR) and (IO), designated IR,1and IO,1, respectively may be corrected by the determined frequencies (fO) and (fR), and this factor may be used to calculate the measured original fundamental or RMS voltage by adding harmonics (VO) in the wire722, which is done by calculating the square root of the squared harmonics sum, and which may be presented to the user on a display912in implementations wherein the non-contact measurement system also determines AC voltage in the insulated wire706.

The coupling capacitor (CO) may generally have a capacitance value in the range of approximately 0.02 pF to 1 pF, for example, depending on the distance between the insulated conductor706and the conductive sensor726, as well as the particular shape and dimensions of the sensor726. The body capacitance (CB) may have a capacitance value of approximately 20 pF to 200 pF, for example.

From Equation (1) above, it can be seen that the AC reference voltage (VR) generated by the common mode reference voltage source730does not need to be in the same range as the AC voltage (VO) in the conductor722to achieve similar current magnitudes for the signal current (IO) and the reference current (IR). The AC reference voltage (VR) may be relatively low (e.g., less than 5 V) by selecting the reference frequency (fR) to be relatively high. As an example, the reference frequency (fR) may be selected to be 3 kHz, which is 50 times higher than a typical 120 VRMS AC voltage (VO) having a signal frequency (fO) of 60 Hz. In such case, the AC reference voltage (VR) may be selected to be only 2.4 V (i.e., 120 V±50) to generate the same reference current (IR) as the signal current (IO). In general, setting the reference frequency (fR) to be N times the signal frequency (fO) allows the AC reference voltage (VR) to have a value that is (1/N) times the AC voltage (VO) in the wire722to produce currents (IR) and (IO) which are in the same range as each other to achieve a similar uncertainty for IRand Ia.

Any suitable signal generator may be used to generate the AC reference voltage (VR) having the reference frequency (fR). In the example illustrated inFIG. 9, a Sigma-Delta digital-to-analog converter (Σ-Δ DAC)910is used. The Σ-Δ DAC910uses a bit stream to create a waveform (e.g., sinusoidal waveform) signal with the defined reference frequency (fR) and AC reference voltage (VR). In at least some implementations, the Σ-Δ DAC910may generate a waveform that is in phase with the window of the FFT906to reduce jitter.

In at least some implementations, the ADC902may have 14 bits of resolution. In operation, the ADC902may sample the output from the input amplifier736at a sampling frequency of 10.24 kHz for nominal 50 Hz input signals to provide 2nsamples (1024) in 100 ms (10 Hz bins for the FFT906) ready for processing by the FFT906. For 60 Hz input signals, the sampling frequency may be 12.288 kHz, for example, to get the same number of samples per cycle. The sampling frequency of the ADC902may be synchronized to full numbers of cycles of the reference frequency (fR). The input signal frequency may be within a range of 40-70 Hz, for example. Depending on the measured frequency of the AC voltage (VO), the bins for the AC voltage (VO) may be determined using the FFT906and use a Hanning window function for further calculations to suppress phase shift jitter caused by incomplete signal cycles captured in the aggregation interval.

In one example, the common mode reference voltage source730generates an AC reference voltage (VR) which has a reference frequency (fR) of 2419 Hz. This frequency is in between the 40thharmonic and the 41stharmonic for 60 Hz signals, and between the 48thharmonic and 49thharmonic for 50 Hz signals. By providing an AC reference voltage (VR) which has a reference frequency (fR) that is not a harmonic of the expected AC voltage (VO), the AC voltage (VO) is less likely to influence measurement of the reference current (IR).

In at least some implementations, the reference frequency (fR) of the common mode reference voltage source730is selected to be a frequency that is least likely to be affected by harmonics of an AC voltage (VO) in the conductor722under test. As an example, the common mode reference voltage source730may be switched off when the reference current (IR) exceeds a limit, which may indicate that the conductive sensor726is approaching the conductor722under test. A measurement (e.g., 100 ms measurement) may be taken with the common mode reference voltage source730switched off to detect signal harmonics at a number (e.g., three, five) of candidate reference frequencies. Then, the magnitude of the signal harmonics in the AC voltage (VO) may be determined at the number of candidate reference frequencies to identify which candidate reference frequency is likely to be least affected by the signal harmonics of the AC voltage (VO). The reference frequency (fR) may then be set to the identified candidate reference frequency. This switching of the reference frequency may avoid or reduce the impact of possible reference frequency components in the signal spectrum, which may increase the measured reference signal and reduce accuracy, and may create unstable results. Other frequencies besides 2419 Hz that have the same characteristics include 2344 Hz and 2679 Hz, for example.

FIG. 11is a block diagram of a signal processing portion1100of a non-contact measurement system which implements electronic filters. The signal processing portion1100may receive a sensor current voltage signal that is proportional to the conductive sensor726current (IO+IR) from a current measurement subsystem (e.g., input amplifier736).

As discussed above, the signal current (IO) has a different frequency than the reference current (IR). To isolate the signal current (IO) from the reference current (IR), the signal processing portion1100may include a first filter1102which operates to pass the signal current (IO) and reject the reference current (IR). The filtered signal may then be rectified by a first rectifier1104and digitized by a first ADC1106. The digitized signal may be fed to a suitable processor1108for use in calculations, as discussed above. Similarly, to isolate the reference current (IR) from the signal current (IO), the signal processing portion1100may include a second filter1110which operates to pass the reference current (IR) and reject the signal current (IO). The filtered signal may then be rectified by a second rectifier1112and digitized by a second ADC1114. The digitized signal may be fed to a suitable processor1108for use in calculations. The first and second filters1102and1110may be any suitable analog filters, and may each include a number of discrete components (e.g., capacitors, inductors).

FIG. 12is a schematic circuit diagram of portions of a non-contact measurement system, such as any of the non-contact measurement systems discussed above, showing the loop formed by the common mode reference voltage source730, the body capacitance (CB), the coupling capacitor (CO), the wire722, the external ground728, and the internal ground738.

FIG. 13Ais a schematic diagram of the non-contact measurement system702, which shows various leakage and stray capacitances. Generally, removal of the influences of different stray capacitors seen by the system (e.g., sensor726) cannot be completely achieved by special sensor design and screening methods even with sophisticated shielding techniques. As discussed above, implementations of the present disclosure utilize the common mode reference voltage source730to generate a reference voltage with a reference frequency (fR) that is different from the measured signal frequency (fo) to compensate for the stray capacitances seen by the system.

In particular, in addition to the coupling capacitor (CO),FIG. 13Ashows the body capacitance (CB), a capacitance (CX), a capacitance (CSENS-REF), and a capacitance (CG). The body capacitance (CB) is in series with the coupling capacitor (CO) and, in typical applications, the body capacitance (CB) is much greater than the coupling capacitor (CO). Thus, the body capacitance (CB) only impacts the magnitudes of the currents (IO+IR), but does not impact the ratio (IO/IR) of the currents.

As shown inFIGS. 13A and 14, the capacitance (CX) is the sensor capacitance between the conductive sensor726and the external ground728. The coupling capacitor (CO) is not the only capacitance between the wire722and the sensor726. There is also the capacitance (CX) between the sensor726and the external ground728, especially for thin wires which do not substantially cover the area of the sensor726. The capacitance (CX) has a capacitive voltage divider effect for the signal current (IO), and may result in a lower voltage measurement for the AC voltage (VO). The capacitance (CX) therefore reduces the magnitudes of the currents (IO+IR). However, the reference current (IR) is divided by the same ratio and, thus, also compensates for the stray capacitor (CX), so the ratio (IO/IR) is not impacted. To also avoid any internal current flows to outside the non-contact measurement system, as discussed above in at least some implementations the whole measurement system except for the sensing area may be shielded by the reference shield734from the outside environment and connected to the output of the common mode reference voltage source730to create the reference current (IR).

As shown inFIG. 13A, the capacitance (CSENS-REF) is the remaining capacitance between the reference shield734and the conductive sensor726. The capacitance (CSENS-REF) causes an offset for the sensor current (IO+IR) which is present even when the AC voltage (VO) in the wire706is not being measured.

As shown inFIGS. 13A and 15A, the capacitance (CG) is the capacitance between the internal ground738and the external ground728or reference potential. The capacitance (CG) is a parallel path for the reference current (IR), and reduces the reference current. Thus, the capacitance (CG) causes an increase in the calculated result for the AC voltage (VO) in the wire706. SeeFIG. 15B, which shows the impact of the capacitance (CG). In particular, the capacitance (CG) influences IRand IOdifferently, and therefore influences the ratio IO/IR.

As can be seen from equations (2)-(5) above, the ratio IO/IRdepends on CB/CG. The capacitance CGis much smaller when a reference screen is around the whole enclosure and sensor of the non-contact measurement system702.

FIG. 13Bshows an implementation which provides compensation for the impact that the reference voltage (VR) has on the sensor726by using an inverted reference signal (−VR) and an arrangement which couples the inverted reference signal to the sensor726.FIG. 13Cshows an example sensor arrangement which includes the inverted reference signal compensation.

InFIG. 13B, an adjustable inverting amplifier741is used to provide an inverted reference signal (−VR) to the sensor726to compensate for the impact that the reference voltage (+VR) has on the sensor. This may be achieved by a capacitive coupling (CC) positioned proximate the sensor726. The capacitive coupling (CC) may be in the form of a wire, screen, shield, etc., positioned proximate the sensor. The compensation may be particularly advantageous when the insulated conductor706has a relatively small diameter because, in such instances, the reference voltage (VR) from the reference shield734may have the greatest impact on the sensor726.

FIG. 13Cshows an example sensor arrangement739for use in an implementation which provides the aforementioned reference signal compensation. The sensor arrangement739includes a sensor739a, an insulating layer739b(e.g., Kapton® tape), an internal ground guard739c, an inverted reference signal layer739d(−VR), an insulating layer739e, and a reference signal layer739f(+VR).

FIG. 16is a perspective view of an example sensor and guard assembly1600for a non-contact measurement system, such as any of the non-contact measurement systems discussed above. In this example, the sensor and guard assembly1600comprises a conductive sensor1602, an internal ground guard1604, and an isolating layer1606disposed between the sensor and the internal ground guard. Generally, the sensor assembly1600should provide good coupling capacitance (CO) between the sensor1602and the wire under test and should suppress the capacitance to other adjacent wires and the capacitance to the external ground. The sensor assembly1600should also minimize the capacitance (CSENS-REF) between the sensor1602and the reference shield (e.g., reference shield734).

As a simple example, the sensor1602, guard1604and isolating layer1606may each comprise a piece of foil. The guard1604may be coupled to a carrier (seeFIG. 17), the isolating layer1606(e.g., Kapton® tape) may be coupled to the guard, and the sensor1602may be coupled to the isolating layer.

FIG. 17shows a sectional view of an example for a sensor realization of a probe or front end1700of a non-contact measurement system, which includes a housing layer1702(e.g., plastic) which covers the sensor assembly1600to avoid direct galvanic contact between the sensor assembly and any objects. The front end1700may be similar or identical to the front end712of the non-contact measurement system702shown inFIGS. 7A and 7B. In this illustration, the sensor assembly1600, including the sensor1602, guard1604and isolating layer1606, are shaped in the form of a “U” or “V,” to allow the sensor assembly1600to surround insulated wires of different diameters, to increase the coupling capacitance (CO), and to better shield, by the guard, against adjacent conductive objects.

In the example shown inFIG. 17, the sensor assembly1600is shaped to accommodate insulated wires of various diameters, such as an insulated wire1704with a relatively large diameter or an insulated wire1706with a relatively small diameter. In each case, the sensor assembly1600substantially surrounds the wire when the wire is positioned in a recessed portion1708of the front end1700. A wall of the front end1700which defines the recessed portion1708and is positioned between the sensor assembly1600and the wire under test may be relatively thin (e.g., 1 mm), to provide galvanic isolation while still allowing for suitable capacitive coupling. Due to the “V” shape of the recessed portion1708, thicker wires1704have more distance than thinner ones1706to reduce the wide range of coupling capacitance and also to reduce the environmental capacitance to be less independent of wire diameter.

FIG. 18shows an elevational view of an arcuate-shaped front end1800of a non-contact measurement system. The front end1800includes a recessed portion1802defined by first and second extended portions1804and1806. The recessed portion1802includes a relatively large upper arcuate-shaped portion1808which receives an insulated wire1810having a relatively large diameter. The recessed portion1802also includes a relatively small lower arcuate-shaped portion1812, below the portion1808, which receives an insulated wire1814having a relatively small diameter. A sensor assembly1816, which may be similar to the sensor assembly1600shown inFIG. 16and which is covered by the portions1808and1812, may have a shape that substantially conforms to the arcuate-shaped portions1808and1812so that the sensor assembly1816substantially surrounds wires having a relatively large diameter (e.g., wire1810) and wires having a relatively small diameter (e.g., wire1814).

FIG. 19is a perspective view of a cylindrically shaped front end1900of a non-contact measurement system. In this example, the front end1900includes a cylindrically shaped internal ground guard1902which has a sidewall1904and a front surface1906which may be positioned proximate a wire under test. The front surface1906of the internal ground guard1902includes a central opening1908. A conductive sensor1910, which forms the coupling capacitor (CO) together with a wire under test, is recessed behind the opening1908of the internal ground guard1902to avoid capacitive coupling with adjacent objects. The sensor1910may be recessed by a distance (e.g., 3 mm) from the front surface1906of the internal ground guard1902, for example.

The sidewall1904of the internal ground guard1902maybe surrounded by a cylindrically shaped reference shield1912, which is isolated from the internal ground guard by an isolating layer1914. A common mode reference voltage source (e.g., voltage source730) may be connected between the internal guard ground1902and the reference shield1912to provide the functionality discussed above.

FIGS. 20A and 20Bshow top views of a front end2000of a non-contact measurement system, andFIG. 21shows a perspective view of a portion of the front end. In this example, the front end2000includes an internal ground guard2002which includes front surface2004against which a wire2006(FIG. 21) under test may be positioned. The front surface2004includes an edge2007, in this case rectangular-shaped, which defines an opening2008in the front surface. This small long rectangular opening accommodates the wire shape having also a longer but thin shape seen from the side. This again reduces adjacent wire influence and also has a high reduction of environmental capacitance related to the sensor. This results in high accuracy independent of wire size. A conductive sensor2010, which forms the coupling capacitor (CO) with a wire under test, is recessed behind the opening2008of the front surface2004of the internal guard ground2002by a distance (e.g., 3 mm).

The internal ground guard2002also includes sidewalls2012and2014which extend forward (toward the wire under test) from lateral edges of the front surface2004. The sidewalls reduce sensor stray capacitance and direct reference signal coupling. The internal ground guard2002may also include a conductive guard ring clamp2016which includes a first clamp arm2016A and a second clamp arm2016B. The clamp arms2016A and2016B may be selectively moved into an opened position, shown inFIG. 20B, to allow a wire under test to be positioned adjacent the front surface2004of the internal ground guard2002. Once the wire is in position, the clamp arms2016A and2016B may be selectively moved into a closed position, shown inFIG. 20A, to provide a shield around the sensor2010from capacitances with the external environment (e.g., adjacent conductors, adjacent objects). When in the closed position, the guard ring clamp2016may be substantially in the shape of a cylinder which has a height that extends above and below the sensor2010, for example. The clamp arms2016A and2016B may be selectively movable using any suitable manual or automated actuation subsystem2018. For example, the clamp arms2016A and2016B may be biased toward the closed position (FIG. 20A) by a spring or other biasing mechanism which functions as the actuation system2018, which bias may be overcome by an operator to move the clamp arms into the opened position (FIG. 20B) so that a wire under test may be positioned proximate the front surface2004of the internal ground guard2002.

Those of skill in the art will recognize that many of the methods or algorithms set out herein may employ additional acts, may omit some acts, and/or may execute acts in a different order than specified. As an example, in at least some implementations a non-contact current measurement system may not utilize a processor to execute instructions. For example, a non-contact current measurement system may be hardwired to provide some or all of the functionality discussed herein. Additionally, in at least some implementations a non-contact current measurement system may not utilize a processor to cause or initiate the different functionality discussed herein.

The various implementations described above can be combined to provide further implementations. To the extent that it is not inconsistent with the specific teachings and definitions herein, U.S. Provisional Patent Application No. 62/421,124, filed Nov. 11, 2016; U.S. patent application Ser. No. 15/345,256, filed Nov. 7, 2016; U.S. patent application Ser. No. 15/413,025, filed Jan. 23, 2017; and U.S. patent application Ser. No. 15/412,891, filed Jan. 23, 2017, are incorporated herein by reference, in their entirety.