Sensor subsystems for non-contact voltage measurement devices

Systems and methods for measuring alternating current (AC) voltage of an insulated conductor are provided, without requiring a galvanic connection between the conductor and a test electrode. A non-galvanic contact voltage measurement device includes a conductive sensor, an internal ground guard, and a reference shield. A reference voltage source is electrically coupleable between the guard and the reference shield to generate an AC reference voltage which causes a reference current to pass through the conductive sensor. Sensor subsystems may be arranged in layers (e.g., stacked layers, nested layers, or components) of conductors and insulators. The sensor subsystems may be packaged as formed sheets, flexible circuits, integrated circuit (IC) chips, nested components, printed circuit boards (PCBs), etc. The sensor subsystems may be electrically coupled to suitable processing or control circuitry of a non-contact voltage measurement device to allow for measurement of voltages in insulated conductors.

BACKGROUND

Technical Field

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

Description of the Related Art

Voltmeters are instruments used for measuring voltage 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.

With conventional voltmeters or multimeters which measure AC voltage, it is necessary to bring at least two measurement electrodes or probes into galvanic contact with a conductor, which often requires 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 voltmeter probes to stripped wires or terminals can be relatively dangerous due to the risks of shock or electrocution.

A non-contact voltage detector is commonly used to detect the presence of alternating current (AC) voltage, typically high voltage, without requiring galvanic contact with the circuit. When a voltage is detected, the user is alerted by an indication, such as a light, buzzer, or vibrating motor. However, such non-contact voltage detectors provide only an indication of the presence or absence of an AC voltage, and do not provide an indication of the actual magnitude (e.g., RMS value) of the AC voltage.

Thus, there is a need for an AC voltage measurement system which provides convenient and accurate voltage measurements without requiring galvanic contact with the circuit being tested.

BRIEF SUMMARY

A sensor subsystem for a voltage measurement device operative to measure alternating current (AC) voltage in an insulated conductor may be summarized as including a conductive sensor disposed within a housing of the voltage measurement device, the conductive sensor selectively positionable proximate the insulated conductor without galvanically contacting the conductor, wherein the conductive sensor capacitively couples with the insulated conductor; a conductive internal ground guard disposed within the housing, wherein the internal ground guard at least partially surrounds the conductive sensor and is galvanically isolated from the conductive sensor, the internal ground guard sized and dimensioned to shield the conductive sensor from stray currents; and a conductive reference shield which surrounds at least a portion of the housing and is galvanically insulated from the internal ground guard, the conductive reference shield sized and dimensioned to reduce currents between the internal ground guard and an external ground. The conductive internal ground guard and the conductive reference shield may be electrically coupleable to a common mode reference voltage source which, in operation, may generate an alternating current (AC) reference voltage having a reference frequency. The conductive sensor and the conductive internal ground guard may be disposed in layers of a multi-layered circuit. The conductive sensor and the conductive internal ground guard may be disposed in a single layer of a multi-layered circuit. The conductive sensor, the conductive internal ground guard, and the conductive reference shield may be disposed in layers of a multi-layered flexible circuit. At least one of the conductive sensor, conductive internal ground, or conductive reference shield may include conductive tape, a conductive sheet, a conductive plate, or a cured liquid.

The sensor subsystem may further include an insulation layer disposed between the conductive sensor and the conductive internal ground guard. The insulation layer may include plastic, silicon, or ceramic.

The sensor subsystem may further include a high permittivity material disposed above the conductive sensor. The conductive reference shield may be molded into at least a portion of the housing of the voltage measurement device. The conductive sensor and the internal ground guard may be arranged as one of stacked layers or nested components. At least a portion of the sensor subsystem may include formed sheets, a flexible circuit, an integrated circuit chip, nested components, or a printed circuit board. The sensor subsystem may include at least one of a non-contact current sensor, an infrared sensor, an indicator, or an illumination source.

A sensor subsystem for a voltage measurement device operative to measure alternating current (AC) voltage in an insulated conductor may be summarized as including a multi-layered flexible circuit, including: a sensor/guard layer including a conductive sensor portion and a guard portion galvanically isolated from the conductive sensor portion; and a reference shield layer that is galvanically isolated from the sensor/guard layer, wherein the guard portion of the sensor/guard layer and the reference shield layer are electrically coupleable to a common mode reference voltage source which, in operation, generates an alternating current (AC) reference voltage having a reference frequency. The multi-layered flexible circuit may be foldable into a custom shape and, when in the custom shape, the multi-layered flexible circuit may be positionable within a housing of a voltage measurement device.

The sensor subsystem may further include at least one of a non-contact current sensor, an infrared sensor, an indicator, or an illumination source coupled to the multi-layered flexible circuit.

The sensor subsystem may further include at least one of a Rogowski coil, a fluxgate sensor, or a Hall Effect sensor coupled to the multi-layered flexible circuit.

The sensor subsystem may further include a shielding layer disposed above the sensor/guard layer, the shielding layer having an opening therein that is aligned with the conductive sensor portion of the sensor/guard layer, wherein the shielding layer is galvanically isolated from any conductive components of the sensor subsystem.

A sensor subsystem for a voltage measurement device operative to measure alternating current (AC) voltage in an insulated conductor may be summarized as including a housing including an opening that defines a first interior volume; a guard insulator disposed within the first interior volume of the housing, the guard insulator including an opening that defines a second interior volume; a conductive guard disposed within the second interior volume of the guard insulator, the conductive guard including an opening that defines a third interior volume; a sensor insulator disposed within the third interior volume of the conductive guard, the sensor insulator including an opening that defines a fourth interior volume; and a conductive sensor disposed within the fourth interior volume of the sensor insulator.

The sensor subsystem may further include a printed circuit assembly electrically coupled to the conductive guard and the conductive sensor.

The sensor subsystem may further include a reference shield molded into the housing, wherein the conductive guard and the reference shield are electrically coupleable to a common mode reference voltage source which, in operation, generates an alternating current (AC) reference voltage having a reference frequency.

DETAILED DESCRIPTION

Systems and methods of the present disclosure are directed to sensor subsystems for non-contact voltage measurement devices. The non-contact voltage measurement devices are operative to measure alternating current (AC) voltage in an insulated (e.g., insulated wire) or blank uninsulated conductor (e.g., bus bar) without requiring a galvanic connection between the conductor and a test electrode or probe. Generally, a non-galvanic contact (or “non-contact”) voltage measurement device is provided which measures an AC voltage signal in an insulated conductor with respect to ground using a capacitive sensor. Such devices which do not require a galvanic connection are referred to herein as “non-contact.” As used herein, “electrically coupled” includes both direct and indirect electrical coupling unless stated otherwise.

The sensor subsystems disclosed herein may include a coupled capacitor or “capacitive sensor,” guarding and/or shielding, and a reference signal or voltage existing independently of each other. The components of the sensor subsystems discussed herein may be arranged in layers (e.g., stacked layers, nested layers) of conductors and insulators, for example. Each of the conductors may include any suitable types of conductor, such as conductive tape, conductive sheet, conductive plate, conductive cured liquid, etc. The insulators may include any suitable type of material that blocks an electrical charge, such as plastic, silicon, ceramic, etc. The insulation layer may be made of a high permittivity material disposed above the sensor to focus the field to the sensor, increasing sensitivity and reducing stray effects (seeFIG. 16). The sensor subsystems may be packaged in any form, including formed sheets, one or more flexible circuits, one or more integrated circuit (IC) chips, nested components, printed circuit boards (PCBs), etc. The sensor subsystems may be electrically coupled to suitable processing or control circuity of a non-contact voltage measurement device to allow for measurement of voltages in insulated conductors.

Initially, with reference toFIGS. 1A-4, examples of non-contact voltage measurement devices are discussed. Then, with reference toFIGS. 5-16, various examples of sensor subsystems for non-contact voltage measurement devices are discussed.

FIG. 1Ais a pictorial diagram of an environment100in which a non-contact voltage measurement device102of the present disclosure may be used by an operator104to measure AC voltage present in an insulated wire106without requiring galvanic contact between the non-contact voltage measurement device and the wire106.FIG. 1Bis a top plan view of the non-contact voltage measurement device102ofFIG. 1A, showing various electrical characteristics of the non-contact voltage measurement device during operation. The non-contact voltage measurement device102includes a housing or body108which includes a grip portion or end110and a probe portion or end112, also referred to herein as a front end, opposite the grip portion. The housing108may also include a user interface114which facilitates user interaction with the non-contact voltage measurement device102. 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 voltage measurement device102may also include one or more wired and/or wireless communications interfaces (e.g., USB, Wi-Fi®, Bluetooth®).

In at least some implementations, as shown best inFIG. 1B, the probe portion112may include a recessed portion116defined by first and second extended portions118and120. The recessed portion116receives the insulated wire106(seeFIG. 1A). The insulated wire106includes a conductor122and an insulator124surrounding the conductor122. The recessed portion116may include a sensor or electrode126which rests proximate the insulator124of the insulated wire106when the insulated wire is positioned within the recessed portion116of the non-contact voltage measurement device102. Although not shown for clarity, the sensor126may be disposed inside of the housing108to prevent physical and electrical contact between the sensor and other objects.

As shown inFIG. 1A, in use the operator104may grasp the grip portion110of the housing108and place the probe portion112proximate the insulated wire106so that the non-contact voltage measurement device102may accurately measure the AC voltage present in the wire with respect to earth ground (or another reference node). Alternatively a direct connection to earth ground128, such as via a test lead139, can be used. Although the probe end112is shown as having the recessed portion116, in other implementations the probe portion112may be configured differently. For example, in at least some implementations the probe portion112may 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 voltage measurement device102to be positioned proximate the insulated wire106. Examples of various sensor subsystems are discussed below with reference toFIGS. 5-16.

The operator's body acting as a reference to earth/ground may only be used in some implementations. The non-contact measurement functionality discussed herein is not limited to applications only measuring against 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 against 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 voltage measurement device102may utilize the body capacitance (CB) between the operator104and ground128during the AC voltage 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.

The particular systems and methods used by the non-contact voltage measurement device102to measure AC voltage are discussed below with reference toFIGS. 2-4.

FIG. 2shows a schematic diagram of various internal components of the non-contact voltage measurement device102, also shown inFIGS. 1A and 1B. In this example, the conductive sensor126of the non-contact voltage measurement device102is substantially “V-shaped” and is positioned proximate the insulated wire106under test and capacitively couples with the conductor122of the insulated wire106, forming a sensor coupling capacitor (CO). The operator104handling the non-contact voltage measurement device102has a body capacitance (CB) to ground. Thus, as shown inFIGS. 1B and 2, the AC voltage signal (VO) in the wire122generates 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 wire122to be measured has a connection to an external ground128(e.g., neutral). The non-contact voltage measurement device102itself also has a capacitance to ground128, which consists primarily of the body capacitance (CB) when the operator104(FIG. 1) holds the non-contact voltage measurement device in his hand. Both capacitances COand CBcreate a conductive loop for AC 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 sensor126and loops back to the external ground128through the housing108of the non-contact voltage measurement device and the body capacitor (CB) to ground128. The current signal (IO) is dependent on the distance between the conductive sensor126of the non-contact voltage measurement device102and the insulated wire106under test, the particular shape of the conductive sensor126, and the size and voltage level (VO) in the conductor122.

To compensate for the distance variance and consequent coupling capacitor (CO) variance which directly influences the signal current (IO), the non-contact voltage measurement device102includes a common mode reference voltage source130which generates an AC reference voltage (VR) which has a reference frequency (fR).

To reduce or avoid stray currents, at least a portion of the non-contact voltage measurement device102may be surrounded by a conductive internal ground guard or screen132which causes most of the current to run through the conductive sensor126which forms the coupling capacitor (CO) with the conductor122of the insulated wire106. The internal ground guard132may be formed from any suitable conductive material (e.g., copper) and may be solid (e.g. sheet metal, sputtered metal inside plastic enclosure), flexible (e.g., foil), or have one or more openings (e.g., mesh).

Further, to avoid currents between the internal ground guard132and the external ground128, the non-contact voltage measurement device102includes a conductive reference shield134. The reference shield134may be formed from any suitable conductive material (e.g., copper) and may be solid (e.g. sheet metal, sputtered metal inside plastic enclosure), flexible (e.g., foil), or have one or more openings (e.g., mesh). In at least some implementations, the reference shield134may be positioned within the housing of the voltage measurement device, for example, molded into at least a portion of the housing. The common mode reference voltage source130is electrically coupled between the reference shield134and the internal ground guard132, which creates a common mode voltage having the reference voltage (VR) and the reference frequency (fR) for the non-contact voltage measurement device102. Such AC reference voltage (VR) drives an additional reference current (IR) through the coupling capacitor (CO) and the body capacitor (CB).

The internal ground guard132which surrounds at least a portion of the conductive sensor126protects the conductive sensor against direct influence of the AC reference voltage (VR) causing an unwanted offset of reference current (IR) between the conductive sensor126and the reference shield134. As noted above, the internal ground guard132is the internal electronic ground138for the non-contact voltage measurement device102. In at least some implementations, the internal ground guard132also surrounds some or all of the electronics of the non-contact voltage measurement device102to avoid the AC reference voltage (VR) coupling into the electronics.

As noted above, the reference shield134is utilized to inject a reference signal onto the input AC voltage signal (VO) and, as a second function, minimizes the guard132to earth ground128capacitance. In at least some implementations, the reference shield134surrounds some or all of the housing108of the non-contact voltage measurement device102. 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 sensor126and the conductor122in the insulated wire106. In at least some implementations, the only gap in the reference shield134may be an opening for the conductive sensor126which allows the conductive sensor to be positioned proximate the insulated wire106during operation of the non-contact voltage measurement device102.

The internal ground guard132and the reference shield134may provide a double layer screen around the housing108(seeFIGS. 1A and 1B) of the non-contact voltage measurement device102. The reference shield134may be disposed on an outside surface of the housing108and the internal ground guard132may function as an internal shield or guard. The conductive sensor126is shielded by the guard132against the reference shield134such that any reference current flow is generated by the coupling capacitor (CO) between the conductive sensor126and the conductor122under test. The guard132around the sensor126also reduces stray influences of adjacent wires close to the sensor.

As shown inFIG. 2, the non-contact voltage measurement device102may include an input amplifier136which operates as an inverting current-to-voltage converter. The input amplifier136has a non-inverting terminal electrically coupled to the internal ground guard132which functions as the internal ground138of the non-contact voltage measurement device102. An inverting terminal of the input amplifier136may be electrically coupled to the conductive sensor126. Feedback circuitry137(e.g., feedback resistor) may also be coupled between the inverting terminal and the output terminal of the input amplifier136to provide feedback and appropriate gain for input signal conditioning.

The input amplifier136receives the signal current (IO) and reference current (IR) from the conductive sensor126and 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 module140which, as discussed further below, processes the sensor current voltage signal to determine the AC voltage (VO) in the conductor122of the insulated wire106. The signal processing module140may include any combination of digital and/or analog circuitry.

The non-contact voltage measurement device102may also include a user interface142(e.g., display) communicatively coupled to the signal processing module140to present the determined AC voltage (VO) or to communicate by an interface to the operator104of the non-contact voltage measurement device.

FIG. 3is a block diagram of a non-contact voltage measurement device300which shows various signal processing components of the non-contact voltage measurement device.FIG. 4is a more detailed diagram of the non-contact voltage measurement device300ofFIG. 3.

The non-contact voltage measurement device300may be similar or identical to the non-contact voltage measurement device102discussed above. Accordingly, similar or identical components are labeled with the same reference numerals. As shown, the input amplifier136converts the input current (IO+IR) from the conductive sensor126into 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)302.

The AC voltage (VO) in the wire122is related to the AC reference voltage (VR) by Equation (1):

VOVR=IO×fRIR×fO(1)
where (IO) is the signal current through the conductive sensor126due to the AC voltage (VO) in the conductor122, (IR) is the reference current through the conductive sensor126due 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 “O,” which are related to the AC voltage (VO), have different frequencies than the signals with indices “R,” which are related to the common mode reference voltage source130. In the implementation ofFIG. 4, digital processing, such as circuitry implementing a fast Fourier transform (FFT) algorithm306, may be used to separate signal magnitudes. In the implementation ofFIG. 5discussed below, analog electronic filters may 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 conductor122under test needs either to 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 amplifier136and digitized by the ADC302, the frequency components of the digital sensor current voltage signal may be determined by representing the signal in the frequency domain using the FFT306. 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 FFT306.

Next, as indicated by a block308, 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 wire122, which may be presented to the user on a display312.

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 conductor106and the conductive sensor126, as well as the particular shape and dimensions of the sensor126. 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 source130does not need to be in the same range as the AC voltage (VO) in the conductor122to 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 wire122to produce currents (IR) and (IO) which are in the same range as each other to achieve a similar uncertainty for IRand IO.

Any suitable signal generator may be used to generate the AC reference voltage (VR) having the reference frequency (fR). In the example illustrated inFIG. 3, a Sigma-Delta digital-to-analog converter (Σ-Δ DAC)310is used. The Σ-Δ DAC310uses 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 DAC310may generate a waveform that is in phase with the window of the FFT306to reduce jitter. Any other reference voltage generator can be used, such as a PWM which may use less computing power than a Σ-Δ DAC.

In at least some implementations, the ADC302may have 14 bits of resolution. In operation, the ADC302may sample the output from the input amplifier136at 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 FFT306) ready for processing by the FFT306. For 60 Hz input signals, the sampling frequency may be 12.28 kHz, for example. The sampling frequency of the ADC302may 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 FFT306and 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 source130generates 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 source130is selected to be a frequency that is least likely to be affected by harmonics of an AC voltage (VO) in the conductor122under test. As an example, the common mode reference voltage source130may be switched off when the reference current (IR) exceeds a limit, which may indicate that the conductive sensor126is approaching the conductor122under test. A measurement (e.g., 100 ms measurement) may be taken with the common mode reference voltage source130switched 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.

FIG. 5is a perspective view of an example sensor and guard assembly or subsystem500for a non-contact voltage measurement device, such as any of the non-contact voltage measurement devices discussed above. In this example, the sensor and guard assembly500includes a conductive sensor502, an internal ground guard504, and an isolating layer506disposed between the sensor and the internal ground guard. Generally, the sensor assembly500should provide good coupling capacitance (CO) between the sensor502and the wire under test and should suppress the capacitance to other adjacent wires and the capacitance to the external ground. The sensor assembly500should also minimize the capacitance (CSENS-REF) between the sensor502and the reference shield (e.g., reference shield134).

As a simple example, the sensor502, guard504and isolating layer506may each comprise a piece of foil. The guard504may be coupled to a carrier (seeFIG. 6), the isolating layer506(e.g., Kapton® tape) may be coupled to the guard, and the sensor502may be coupled to the isolating layer.

FIG. 6shows a sectional view of an example for a sensor realization of a probe or front end600of a non-contact voltage measurement device, which includes a housing layer602(e.g., plastic) which covers the sensor assembly500to avoid direct galvanic contact between the sensor assembly and any objects. The front end600may be similar or identical to the front end112of the non-contact voltage measurement device102shown inFIGS. 1A and 1B. In this illustration, the sensor assembly500, including the sensor502, guard504and isolating layer506, are shaped in the form of a “U” or “V,” to allow the sensor assembly500to surround insulated wires of different diameters, to increase the coupling capacitance (CO), and to better shield, by the guard, against adjacent conductive objects. A reference shield (e.g., reference shield134) may be disposed in the housing layer (e.g., molded therein) to surround at least a portion of the sensor502and guard504, and/or other portions of the voltage measurement device.

In the example shown inFIG. 6, the sensor assembly500is shaped to accommodate insulated wires of various diameters, such as an insulated wire604with a relatively large diameter or an insulated wire606with a relatively small diameter. In each case, the sensor assembly500substantially surrounds the wire when the wire is positioned in a recessed portion608of the front end600. A wall of the front end600, which defines the recessed portion608and is positioned between the sensor assembly500and the wire under test, may be relatively thin (e.g., 1 mm, 3 mm, 5 mm) to provide galvanic isolation while still allowing for suitable capacitive coupling. Due to the “V” shape of the recessed portion608, thicker wires604have more distance than thinner ones606to reduce the wide range of coupling capacitance and also to reduce the environmental capacitance to be less dependent of wire diameter.

FIG. 7shows an elevational view of an arcuate-shaped front end700of a non-contact voltage measurement device.FIG. 8shows a sectional elevational view of the front end700, which shows a sensor subsystem716of the front end. The front end700includes a housing701that has a recessed portion702defined by first and second extended portions704and706. The recessed portion702includes a relatively large upper arcuate-shaped portion708which receives an insulated wire710having a relatively large diameter. The recessed portion702also includes a relatively small lower arcuate-shaped portion712, below the portion708, which receives an insulated wire714having a relatively small diameter. The sensor subsystem or assembly716may have a shape that generally conforms to the shape of the recessed portion702so that at least a portion of the sensor subsystem716at least partially surrounds wires having a relatively large diameter (e.g., wire710) and wires having a relatively small diameter (e.g., wire714).

The sensor subsystem716includes a reference signal layer718that is molded into the housing701(e.g., plastic housing). The reference signal layer718may be electrically coupled to a reference voltage source, such as the reference voltage source130shown inFIGS. 2-4. The reference signal layer718may surround at least a portion of the other components of the sensor subsystem716, and may also surround at least some other portions (e.g., electronics) of the voltage measurement device of which the front end700is a part.

The sensor subsystem716also includes a guard layer720disposed below the reference signal layer718and above a conductive sensor722. The guard layer720may include an opening or window724such that the guard layer does not occlude sensor722from the wires under test. Similar to the guard132shown inFIGS. 2 and 4, the guard layer720may be coupled to a ground of the voltage measurement device.

The guard layer720and the sensor722may each be coupled to a printed circuit assembly (PCA)726. The PCA726may include various processing circuitry of the voltage measurement device, such as the circuitry shown inFIGS. 2-4discussed above. Additionally or alternatively, the PCA726may include one or more connectors that allow for connection of the guard layer720and the sensor722to such circuitry.

FIGS. 9-12show various views of a front end sensor subsystem900of a voltage measurement device that includes a plurality of nested components. The sensor subsystem900includes a housing902(e.g., plastic housing) that has a front portion903which defines a recess904that, in operation, receives an insulated wire906under test.

The sensor subsystem900includes the housing902, a guard insulator908nested inside an interior volume of the housing, a guard910nested inside an interior volume of the guard insulator, a sensor insulator912nested inside an interior volume of the guard insulator, a sensor914nested inside an interior volume of the sensor insulator, and a PCA916electrically coupled to at least the sensor914and the guard910. Fasteners918(e.g., screws) are provided to secure the PCA916and the other components to the housing902. A reference signal layer (not shown) may be incorporated into the housing902. For example, a reference signal layer may be molded into at least a portion of the housing902.

As best shown inFIG. 11, the guard910may include an opening or window920, which prevents the guard from occluding the sensor914from the wire906under test.

FIG. 13shows an exploded view of an example multi-layer flexible circuit1300that may be used to implement a sensor subsystem for a voltage measurement device. The flexible circuit1300may in at least some implementations comprise a portion of an expanded sensor subsystem, such as a sensor subsystem1400shown inFIGS. 14A-Cand15A-E.

The flexible circuit1300comprises a plurality of stacked layers. In particular, the flexible circuit1300includes a conductive shielding layer1302, an adhesive backing layer1304, a first insulation layer1306, a conductive sensor/guard layer1308comprising a conductive sensor portion1308aand a guard portion1308bseparated by a gap1309, a second insulation layer1310, a connector layer1312, and a third insulation layer or cover-lay1314. In at least some implementations, the flexible circuit1300may include additional or fewer layers. The conductive layers may be formed from copper or other suitable conductive material. The insulation layers may be formed from any material that blocks electrical charge, such as plastic, silicon, ceramic, etc.

The conductive shielding layer1302may be “free-floating” and insulated from the conductive sensor/guard layer1308by the first insulation layer1306. The conductive shielding layer1302includes a central opening1316so the shielding layer1302does not block the sensor from a wire under test. The first insulation layer1306includes plurality of openings1318therein which allows the adhesive backing layer1304to contact the guard portion1308bof the sensor/guard layer1308to bond the layers1302-1308together.

The conductive sensor portion1308aand the guard portion1308bof the sensor/guard layer1308may be electrically coupled to the connector layer1312through vias1320and1322, respectively, in the second insulation layer1310. The connector layer1312may include a pad1324to which a connector (not shown) may be attached (e.g., soldered). The connector may be coupled to a main circuit board of the voltage measurement device that includes the various processing circuitry discussed herein. The third insulation layer1314may comprise an acrylic cover-lay that include an opening1326sized and dimensioned to allow the connector coupled to the connector layer1312to pass therethrough.

As noted above, the flexible circuit1300may form a portion1402(FIG. 14A) of the expanded flexible circuit1400shown inFIGS. 14A-Cand15A-E. In this example, the flexible circuit1400is manufactured as a flat multi-layered circuit, as shown inFIGS. 14A-14C. During manufacturing, the flexible circuit1400may be folded or bent along fold or tangent lines1404shown inFIGS. 14B and 14Cinto the shape shown inFIGS. 15A-15E, and positioned into a front end portion of a housing of a voltage measurement device. Several of the various portions of the flexible circuit1400are labeled inFIGS. 14B and 15A-E for clarity. In at least some implementations, the multi-layer flexible circuit1400may include an insulated reference signal layer (e.g., reference signal layer134) disposed in one or more of the portions of the circuit. For example, in at least some implementations, the flexible circuit1400may include a reference signal layer disposed in some or all of the portions of the circuit except the portion1402which includes the conductive sensor portion1308a(seeFIG. 13).

In at least some implementations, one or more additional components1430(FIG. 15B) may be coupled to the flexible circuit1400to provide additional functionality. Such other components may include AC measurement devices, such as a non-contact current sensor (e.g., Rogowski coil, Hall Effect sensor, fluxgate sensor), one or more indicators (e.g., LEDs), illumination equipment (e.g., LED flashlight), one or more infrared (IR) sensors, etc. By including such additional components, the functionality of the flexible circuit1400may be extended to facilitate additional applications. Also, using multiple sensor arrangements (e.g., split signal-Reference sensor, multi-parameter sensor) is supported by a flexible sensor structure including switching or signal conditioning electronics. For example, illumination equipment may allow the voltage measurement device to illuminate a work area in which conductors are to be measured. An IR sensor may be used to detect heat profiles for circuitry under examination. A current sensor may be used to measure current, which measurement may be combined with the voltage measurement to determine other AC characteristics, such as power characteristics, phase characteristics, etc.

FIG. 16shows an example sensor subsystem1600that includes a conductive sensor1602, a guard1604, a positive reference shield1606, a negative reference shield1608, an isolation layer1610, and a high permittivity material1612(e.g., plastic) disposed between the sensor and a conductor under test. The high permittivity material1612disposed above the sensor1602focuses the field to the sensor, thereby increasing sensitivity and reducing stray effects.

The negative reference shield1608may be provided to compensate for the impact that the positive reference voltage (VR) has on the sensor1602by using an inverted reference signal (−VR) coupled to the negative reference shield. As an example, an adjustable inverting amplifier may be used to provide an inverted reference signal (−VR) to compensate for the impact that the reference voltage (+VR) has on the sensor1602. This may be achieved by a capacitive coupling positioned proximate the sensor1602. The capacitive coupling may be in the form of a wire, screen, shield, etc., positioned proximate the sensor. The compensation may be particularly advantageous when the insulated conductor under test has a relatively small diameter because, in such instances, the reference voltage (VR) from the reference shield1606may have the greatest impact on the sensor1602.

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 voltage measurement device may not utilize a processor to execute instructions. For example, a non-contact voltage measurement device may be hardwired to provide some or all of the functionality discussed herein. Additionally, in at least some implementations a non-contact voltage measurement device may not utilize a processor to cause or initiate the different measurements discussed herein. For example, such non-contact voltage measurement device may rely on one or more separate inputs, such as a user-actuated button which causes measurements to occur.

The various implementations described above can be combined to provide further implementations. To the extent that they are not inconsistent with the specific teachings and definitions herein, U.S. Provisional Patent Application No. 62/421,124, filed Nov. 11, 2016 and U.S. patent application Ser. No. 15/413,025, filed Jan. 23, 2017, are incorporated herein by reference, in their entirety. Aspects of the implementations can be modified, if necessary, to employ systems, circuits and concepts of the various applications to provide yet further implementations.