Patent Publication Number: US-11644483-B2

Title: System and method for monitoring voltage in a cable

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 16/701,963, filed Dec. 3, 2019, now U.S. Pat. No. 11,137,422, which claims the benefit of U.S. Provisional Application No. 62/774,834, filed Dec. 3, 2018, each of which applications is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Society&#39;s increasing reliance on electric power has resulted in an ever-increasing complexity of electric systems. With the emergence of electric appliances, electric vehicles, and electronics, consumers and businesses are interconnected in ways that were previously isolated. As such, disruptions to services can create massive, cascading consequences. Moreover, companies and consumers are relying on the presence of electric power to operate sensitive, or even lifesaving, technologies. 
     One concern arising from consumer and business dependence on electrical and electronic equipment, is power failure. In complex or remote systems, partial or complete power failure may be difficult to distinguish from other system failures. Communication to the equipment and to adjacent personnel may be partially or fully compromised by loss of power, so an independent means of detecting the presence of power is desired. 
     Detection of power failure has previously been accomplished by placing in-line voltage sensors or with the use of magnetic-field-based current sensors. In-line voltage sensors are complicated to install and generally require interruption of power when installed. Magnetic field based current sensors rely on the flow of current through the power cables and can be unreliable when little or no current is being drawn. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. 
         FIG.  1    includes an illustration of an example sensor device. 
         FIG.  2    includes an illustration of an example configuration of electrodes for use by the sensor device of  FIG.  1   . 
         FIG.  3    includes an illustration of example electrode configurations and circuitry for detecting power in a conductor cable. 
         FIG.  4    includes an illustration of an example configuration of electrodes on a flexible substrate. 
         FIG.  5    and  FIG.  6    include illustrations of an example sensor device. 
         FIG.  7    illustrates example flexible electrode substrates and associated measurement circuitry. 
         FIG.  8    includes a block diagram of an example sensor device. 
         FIG.  9    illustrates an example configuration showing overlapping sense electrodes. 
         FIG.  10    illustrates an example configuration showing two reference electrodes that are connected together. 
         FIG.  11    illustrates an example sensor device for detecting voltage in a conductor cable. 
     
    
    
     The use of the same reference symbols in different drawings indicates similar or identical items. 
     DETAILED DESCRIPTION 
       FIGS.  1 - 11    illustrate embodiments of a voltage sensor device. The voltage sensor device can be used to monitor voltage in a power cable, such as AC voltage in a multi-conductor power cable. The sensor device can include sense electrodes that wrap around unshielded power cable and circuitry to provide real-time indications that the cable is live. The sensor device can communicate wirelessly the voltage status of the cable. For example, the sensor device can be battery-powered and attach around a power cord or cable going in or out of an electrical appliance. No electrical contact is utilized with the power cable, and installation does not utilize unplugging or powering down the equipment. Once installed, the sensor device reports any change in the presence of voltage, providing wireless alerts or trigger events over a radio link. In particular, the sensor device detects electric fields (E-field) around the cable and does not utilize direct electrical connection with conductors of the cable. Accordingly, the sensor device is isolated from the electric power in the cable and provides a safe and reliable system. 
     In some embodiments, the sensor device detects the presence or absence of a voltage, such as an AC voltage, by measuring the E-field of the conductor. The E-field exists whenever voltage (AC or DC) is present, unlike a magnetic field which only exists in a conductor when current is flowing. 
       FIG.  1    includes an illustration of an exemplary sensor device  100  to detect the presence or absence of voltage in a cable  106 . A set of sense electrodes is disposed in a clip or strap  104  wrapped around the cable  106 . The set of electrodes are electrically connected to circuitry within the housing  102 . The circuitry detects the presence or absence of voltage using field-based detection and can report the absence or presence of voltage using a wireless link. 
       FIG.  2    includes an illustration of an example electrode configuration. A cable  202  can include multiple conductors  204 , each of which are insulated individually. In an example, one conductor can be a live conductor, another conductor can be a neutral conductor, and a further conductor can be a ground conductor. 
     The electrode configuration  200  includes at least one sense electrode. For example, the sense electrode  206  that extends over a region on the surface of the cable  202 . The configuration  200  can also include a sense electrode  208  that extends over a region of the surface of the cable  202 . The sense electrode  206  and the sense electrode  208  have the same or similar axial position relative to the cable  202  and as such, are aligned at the axial position. The sense electrode  206  and the sense electrode  208  are offset circumferentially or angularly and thus, are adjacent in circumferential position. As illustrated, the sense electrodes  206  and  208  have an axial width extending along the axis of the cable  202  and have a circumferential length extending along the circumference of the cable  202 . In an example, the sense electrodes  206  and  208  can have approximately the same axial width and circumferential length. In an example, the sense electrodes do not overlap. In an alternative example, the sense electrodes overlap, as illustrated in  FIG.  9    (showing a cross-sectional view for clarity) which shows an example configuration  900  with sense electrode  908  overlapping sense electrode  906 . Further, the sense electrodes may or may not extend more than the circumference of the cable  202 . 
     The configuration  200  also includes a reference electrode  210  and optionally a reference electrode  212 . The reference electrodes  210  or  212  are positioned at an axial position relative to the axis of the cable  202  adjacent the axial position of the sense electrodes  206  and  208 . The reference electrode  210  or  212  can extend around the circumference of the cable, for example, extending at least the circumferential length of both of the sense electrodes  206  and  208 . The reference electrode  212  can be positioned at an axial position on an opposite side of the axial position of the reference electrode  210  relative to the sense electrodes  206  and  208 . 
     When a conductor  204  of the cable  202  carries a voltage, the difference in the circumferential length covered by a sense electrode and the circumferential length covered by the reference electrode leads to a charge difference between the sense electrode and the reference electrode. When a charge measurement circuit is connected in series between the sense electrode and the reference electrode, a charge can be measured that indicates the presence of the voltage in the conductor  204 . 
     The charge measurement circuit may be an ammeter capable of measuring the current in amperes resulting from the charge differential. The charge measurement circuit may be a voltmeter connected in series between the sense electrode and the reference electrode. The charge measurement circuit may substantially preserve the charge between the sense electrode and the reference electrode, allowing the charge to decay due to the environment or instantaneous conductor voltage. Alternatively, where charge measurement is made using a voltmeter or ammeter, the resistance of the meter provides a decay path. 
       FIG.  3    includes an illustration of circuitry for detecting the absence or presence of voltage in a conductor cable. A conductor cable  302  can include one or more conductors, such as conductors  304 ,  306 , and  308 . In an example, the conductor  304  is a live conductor, the connector  306  is a neutral conductor, and the conductor  308  is a ground conductor. Each of the conductors  304 ,  306 , and  308  can be individually insulated. 
     Sense electrodes  310 ,  312 , or  314  are distributed around the conductor cable  302 . In the illustrated example, the electrodes  310 ,  312  and  314  are distributed at offsets of 120°. While the electrodes  310 ,  312 , and  314  are illustrated as being evenly distributed around the conductor  302 , electrodes may not extend around the full circumference of the conductor  302  or may extend more than once around the conductor  302 , causing some overlap of the sense electrodes. 
     At a separate axial position, a reference electrode  316  can extend around the conductor  302 . In the illustrated example, the reference electrode  316  extends around the full circumference of the conductor cable  302 . Alternatively, the reference electrode  316  can extend partially around the circumference of the conductor cable  302  or can extend more than once around the circumference of the conductor cable  302 , leading to overlap of the reference electrode  316  over itself. In general, the reference electrode  316  extends a greater circumferential length around the cable  302  than any one of the sense electrode  310 ,  312 , and  314 , which leads to a difference in charge between the reference electrode  316  and at least one of the sense electrodes  310 ,  312 , or  314 . 
     To measure the difference in charge, each of the sense electrodes  310 ,  312 , and  314  are connected in series through separate ammeters  318 ,  320 , or  322  to the reference electrode  316 . The e-field of a live conductor results in a charge on each of the three sense electrodes  310 ,  312 , or  314 , which cause three electrical currents through the ammeters  318 ,  320 , and  322  when connected in series to the reference electrode. Thus, each of the ammeters  318 ,  320 , and  322  can be viewed as a charge measurement circuit. The sense electrodes  310 ,  312 , and  314  are connected to the reference electrode  316  in parallel relative to each other. The e-fields experienced by each of the sense electrodes  310 ,  312 , or  314  are asymmetric, being influenced by the physical offset of the conductor, the shielding influence of the other conductors, the reinforcement cancellation of other e-fields, or the angular relationship between the conductors and the sense electrodes  310 ,  312 , and  314 . As such, current measurements by the ammeters  318 ,  320 , and  322  are different. The current can be compared to a threshold to detect the presence of a live conductor. 
     The current measurements from the ammeters  318 ,  320 , and  322  can be amplified and filtered and compared to a threshold. For example, the current measurements can be converted to an equivalent voltage, then applied to a simple voltage comparator with a fixed or adjustable reference or can be fed to an analog-to-digital converter for measurement by digital circuit or microprocessor. For on-off voltage detection, the peak measurement can be compared to a reference threshold. Alternatively, the absolute product of the measurements can be used for more dynamic range in the measurement. In an example, the sum of the peaks of the current measurements can be used to determine the presence of voltage in the cable. The electrode-and-sense configuration enables a sensor that can detect voltage independent of the sensor&#39;s position on the cable. A device can mount on the cable in a convenient manner, and mounting can include clamps, clips, or straps, a combination thereof, or other means. 
     The electric configuration establishes a reference and uses multiple sensor electrodes to exploit asymmetry in the cable for measuring the e-fields. The reference electrodes compensate for a lack of ground reference. In particular, the sensor device is a battery-powered wireless device with no external electrical connections and in particular, lacks a connection to the ground. 
     A single reference electrode can be used. Alternatively, additional reference electrodes can be used. For example, a two-reference electrode configuration can be used in which the reference electrodes are located on either axial side of the sense electrodes. The reference electrodes can be electrically coupled, providing an averaging of the reference level over the width of the sensor. Such a configuration is beneficial in cables where the relationship between the sensor and the conductor shifts due to imprecision in the overmolding of the cable jacket. An example configuration  1000  having two reference electrodes  210 ,  212  connected together is illustrated in  FIG.  10   , which also shows two sense electrodes  206 ,  208  and a charge measurement circuit  1018 . 
     In an example, the electrodes can be configured on a flexible substrate, so the electrodes can be wrapped around a cable. For example,  FIG.  4    illustrates a flexible electrode configuration  400  in which electrodes are disposed on a flexible substrate  402  and are electrically connected to an electrical coupling  404  to interface with other circuitry. In the illustrated example, flexible substrate includes sense electrodes  406 ,  408  and  410 , each positioned at an offset to relative to a dimension  430  that when wrapped around the cable becomes a circumference of the cable. Reference electrodes  412  and  414  are positioned on either axial side of the set of sense electrodes  406 ,  408  and  410 , wherein the dimension  432  becomes an axial dimension when the substrate is wrapped around the cable. In the illustrated example, the reference electrodes  410  or  412  extend in the circumferential dimension along the circumferential length of the sense electrodes  406 ,  408 , and  410 . Further, the reference electrodes  412  and  414  are illustrated as having a smaller axial width than the sense electrodes  406 ,  408 , and  410 . 
     Further, the substrate may form an electrostatic discharge (ESD) structure having a conductor with a gap extending between the reference electrodes and the sense electrodes. For example, ESD structures  416 ,  418 , and  420  are formed to between a sense electrode ( 406 ,  408 , or  410 ) and a reference electrode ( 412  or  414 ). 
     The reference electrodes and associated circuitry can be incorporated into a strap and housing configuration. For example, as illustrated in  FIG.  5    and  FIG.  6   , a sensor device  500  includes a housing  502  incorporating a measurement circuitry connected to a strap  504  incorporating the sense and reference electrodes. In the illustrated example, the strap  504  includes an adhesive region  508  incorporating the sense and reference electrodes which can be adhesively coupled around a cable. Optionally, the strap  504  further includes a hook and loop attachment system in which the hooks  506  are attached on one side of the strap  504  and the loops  610  are attached on an opposite side of the strap  504  such that when the strap  504  is wrapped around a cable, the hooks  506  and loops  610  engage to further secure the sensor device  500  to the conductor cable. 
       FIG.  7    illustrates further configurations in which different sized electrode configuration  702  or  704  can be attached to circuitry  706 . Electric interfaces  708  or  710  can be inserted into the electric interface  712  of the circuitry  706 . As such, a single circuitry  706  can be used for smaller or larger cables and size of sense electrodes can be selected based on the size of the cable. 
       FIG.  8    includes an illustration of exemplary circuitry  800  for implementing the sensor device. For example, the sensor device can include computational circuitry  802 , which connects to compare input from sense and reference electrodes  804  to detect the presence or absence of voltage in a cable. The circuitry  802  can communicate the findings through a wireless connection using antennas  808 . For example, the wireless connection can be a proprietary wireless connection or can be a wireless connection using a standard wireless interface, such as Bluetooth, Wi-Fi, or standard in compliance with IEEE 802.xx. 
     The circuitry  802  can be a powered, for example, using a battery  806 . In a particular example, the circuitry is not connected to line power and is not grounded. Optionally, additional interfaces  810  can be provided to access the circuitry  802 . Such interfaces can optionally include a USB interface or other hardwired interfaces. 
     In an example, the computational circuitry can include analog components or digital components. For example, the computational circuitry  802  can include a comparator  814  to compare aspects of a signal, such as a peak value or root mean square value, to a fixed value  812 . In another example, the computational circuitry  802  can include an analog-to-digital converter  816  to provide digital signals that are further processed by microprocessors of the computational circuitry  802 . Such processors can compare peak measurements to a reference threshold. In another example, such processors can utilize the absolute product of the measurements for more dynamic range in the measurement. In an example, the sum of the peaks of the current measurements can be used to determine the presence of voltage in the cable. 
     Embodiments of the above sensor device provide desirable technical advantages over prior art systems. The sensor device provides for simple on/off indication of available AC voltage and can generates alerts within 1 second of voltage failure. No electrical connection is utilized; an electrician is not required for installation. The sensor device connects around insulated (2, 3, 4 or more) conductor appliance cables, and does not access individual conductors. The design can be an ultra-low power design and use a coin cell battery that lasts up to 6 years. One design covers cables over a 2:1 diameter range (e.g. 6 mm to 12 mm diameter). 
     Further, the sensor device is capable of detecting an electric field (E-field) on a conductor even when the conductor is part of a cable containing multiple conductors. In some embodiments, the sensor reliably senses an E-field regardless of cable orientation (e.g., angular orientation). In some embodiments, the sensor is not adversely affected by the stray E-fields of nearby cables and equipment. In some embodiments, the sensor operates at extremely low power (less than 3 uA) including radio operation. In some embodiments, the sensor does not have a reference for ground in either conductor or human-body form. In some embodiments, the e-field sensor is field-attachable to a range of cable sizes. In some embodiments, the sensor amplifies very low-level signals representing the E-field. In some embodiments, the sensor attaches quickly without powering-down the equipment. 
     In some embodiments, the use of a flex circuit minimizes the spacing between the electrodes and the conductors and improves the ratio between the E-field being measured and E-field from other sources. In some embodiments, the sensor works with single-phase, split-phase, and poly-phase cables. In the case of multiple phases, the measurement is based on the collective E-field. In some embodiments, a coiled flex-circuit electrode allows use of the coiled flex-circuit electrode on cables having a diameter range of 2:1 (largest:smallest cable diameter). The sensor compensates for calculating the dimensions of the electrodes to detect voltage presence when the electrodes may be overlapping due to the overlap of the wrap around the cable. Dimensions accommodate three factors with varying degree of overlap: enough E-field asymmetry between the reference plane and the electrodes, enough electrode area, and increasing air-gap due to the thickness of the material as it wraps around the cable. 
     In a first aspect, an example of which is conceptually shown in  FIG.  11   , a sensor device  1100  for detecting voltage in a conductor cable  1104  includes a sense electrode  1102  to be disposed over a surface of the conductor cable  1104  to cover a sense region having a sense axial width and a sense circumferential length, and a reference electrode  1106  to be disposed over the surface of the conductor cable  1104  to cover a reference region. The reference region has an axial position adjacent the axial position of the sense region and has a reference circumferential length greater than the sense circumferential length. The sensor device  1100  further includes a charge measurement circuit  1112  connected in series between the sense electrode  1102  and the reference electrode  1106  to measure a charge measurement, and circuitry to compare the charge measurement to a threshold to detect a presence of the voltage in the conductor cable. In the example sensor device  1100 , such circuitry includes a comparator  1114  for comparing the charge measurement against a reference threshold  1116 , and for generating a signal  1118  indicating voltage presence. 
     In an example of the first aspect the sensor device of claim  1 , further comprising a second sense electrode to be disposed over the surface of the conductor cable to cover a second sense region having a second axial width and a second circumferential length, the second sense region having an axial position aligned with the sense region and having a circumferential position adjacent the sense region. In an example, the sense device further includes a second charge measurement circuit connected in series between the second sense electrode and the reference electrode to provide a second charge measurement. In an additional example, the circuitry is to compare the second charge measurement to the threshold to detect the presence of the voltage in the conductor cable. In a further example, the sense electrode and the second sense electrode overlap when disposed over the surface of the conductor cable. In another example, the sensor device further includes a third sense electrode to be disposed over the surface of the conductor cable to cover a third sense region having a third axial width and a third circumferential length, the third sense region having an axial position aligned with the sense region and the second sense region and having a circumferential position adjacent the sense region and the second sense region. In an additional example, the sensor device further includes a third charge measurement circuit connected in series between the third sense electrode and the reference electrode to measure a third charge measurement. 
     In another example of the first aspect and the above examples, the sensor device further includes a second reference electrode to be disposed over the surface of the conductor cable to cover a second reference region, the second reference region having an axial position adjacent the axial position of the sense region on an opposite axial side of the sense region as the axial position of the reference region and having a second reference circumferential length greater than the sense circumferential length. For example, the second reference electrode is electrically connected to the reference electrode. 
     In a further example of the first aspect and the above examples, the circuitry is free of a connection to ground. 
     In an additional example of the first aspect and the above examples, the sensor device is an e-field sensor and wherein the sense and reference electrodes are responsive to the e-field. 
     In another example of the first aspect and the above examples, the conductor cable includes a line conductor, a neutral conductor, and a ground conductor. 
     In a further example of the first aspect and the above examples, the conductor cable is a split-phase or three-phase cable. 
     In an additional example of the first aspect and the above examples, the sensor device further includes an electrostatic discharge structure electrically coupled between the sense electrode and the reference electrode. 
     In another example of the first aspect and the above examples, the circuitry includes a voltage comparator. For example, the sensor device further includes a fixed reference applied to the voltage comparator. 
     In a further example of the first aspect and the above examples, the circuitry includes an analog-digital converter and a processor to compare signals. 
     In an additional example of the first aspect and the above examples, the sense and reference electrodes are disposed in a strap to wrap around the conductor cable. In an example, the circuitry is disposed on a case attached to the strap. In another example, the strap has an adhesive region to secure a portion of the strap to the conductor cable. In a further example, the strap includes a hook region on a first side and a loop region on a second side to form a hook and loop coupling. 
     In a second aspect, a sensor device for detecting voltage in a conductor cable includes a plurality of sense electrodes to be disposed over the surface of the conductor cable, each sense electrode of the plurality of sense electrodes to cover a unique sense region having an axial length and a circumferential width, the unique region having an axial position aligned with unique sense regions associated with other sense electrodes of the plurality of sense electrodes and having a circumferential position adjacent the unique sense regions associated with other sense electrodes of the plurality of sense electrodes; a reference electrode to be disposed over the surface of the conductor cable to cover a reference region, the reference region having an axial position adjacent the axial position of the unique regions and extending to cover the circumferential positions of the unique regions; a plurality of charge detectors, the each sense electrode of the plurality of sense electrodes electrically connected to the reference electrode through a charge detector of the plurality of charge detectors, the charge detector to detect a charge measurement; and circuitry to compare the charge measurement to a threshold to detect the voltage in the conductor cable. 
     In an example of the second aspect, the unique region and a second unique region associated with a second sense electrode of the plurality of sense electrode overlap when disposed over the surface of the conductor cable. 
     In another example of the second aspect and the above examples, the sensor device further includes a second reference electrode to be disposed over the surface of the conductor cable to cover a second reference region, the second reference region having an axial position adjacent the axial position of the unique regions on an opposite axial side of the unique regions as the axial position of the reference region and extending to cover the circumferential positions of the unique regions. For example, the second reference electrode is electrically connected to the reference electrode. 
     In a further example of the second aspect and the above examples, the circuitry is free of a connection to ground. 
     In an additional example of the second aspect and the above examples, the sensor device is an e-field sensor and wherein the plurality of sense electrodes and the reference electrode are responsive to the e-field. 
     In another example of the second aspect and the above examples, the conductor cable includes a line conductor, a neutral conductor, and a ground conductor. 
     In a further example of the second aspect and the above examples, the conductor cable is a split-phase or three-phase cable. 
     In an additional example of the second aspect and the above examples, the plurality of sense electrodes and the reference electrode are disposed in a strap to wrap around the conductor cable. For example, the circuitry is disposed on a case attached to the strap. In an example, the strap has an adhesive region to secure a portion of the strap to the conductor cable. In another example, the strap includes a hook region on a first side and a loop region on a second side to form a hook and loop coupling. 
     In a third aspect, a method for detecting voltage in a conductor cable includes detecting a first signal using a first charge measurement circuit connected in series between a reference electrode and a first electrode, the first electrode disposed over a surface of the conductor cable to cover a first region having a first axial width and a first circumferential length, the reference electrode disposed over the surface of the conductor cable to cover a reference region, the reference region having an axial position adjacent the axial position of the first region and having a reference circumferential length greater than the first circumferential length; and comparing with a circuitry the first signal to a threshold to detect the presence of the voltage in the conductor cable. 
     In an example of the third aspect, comparing the first signal to a threshold includes applying the voltage to a voltage comparator with a fixed reference. 
     In another example of the third aspect and the above examples, comparing the first signal to a threshold includes converting the first signal using an analog to digital converter to provide a first digital signal and comparing the first digital signal using a processor. 
     In a further example of the third aspect and the above examples, comparing includes comparing a peak measurement of the first signal. 
     In an additional example of the third aspect and the above examples, comparing includes comparing an absolute product of the first signal. 
     In another example of the third aspect and the above examples, the first electrode and the reference electrode are disposed in a flexible circuitry, the method further comprising wrapping the first electrode and the reference electrode around the conductor cable. For example, wrapping is performed without disconnecting power from the conductor cable. 
     In a further example of the third aspect and the above examples, the method further includes detecting a second signal using a second charge measurement circuit connected in series between a reference electrode and a second electrode, the second electrode disposed over a surface of the conductor cable to cover a second region having a second axial width and a second circumferential length, the reference region having an axial position adjacent the axial position of the second region and having a reference circumferential length greater than the sum of the first circumferential length and the second circumferential length, the second region offset from the first region along the circumference; and comparing with a circuitry the second signal to a threshold to detect the presence of the voltage in the conductor cable. For example, the method further includes detecting a third signal using a third charge measurement circuit connected in series between a reference electrode and a third electrode, the third electrode disposed over a surface of the conductor cable to cover a third region having a third axial width and a third circumferential length, the reference region having an axial position adjacent the axial position of the third region and having a reference circumferential length greater than the sum of the first circumferential length, the second circumferential length, and the third circumferential length, the third region offset from the first region and the second region along the circumference; and comparing with a circuitry the third signal to a threshold to detect the presence of the voltage in the conductor cable. 
     In a fourth aspect, a sensor device for detecting voltage in a conductor cable includes a first electrode to be disposed over a surface of the conductor cable to cover a first region having a first axial length and a first circumferential width; a second electrode to be disposed over the surface of the conductor cable to cover a second region having a second axial length and a second circumferential width, the second region having an axial position aligned with the first region and having a circumferential position adjacent the first region; a reference electrode to be disposed over the surface of the conductor cable to cover a reference region, the reference region having an axial position adjacent the axial position of the first and second regions and extending to cover the circumferential positions of the first and second regions; a first charge measurement circuit connected in series between the first electrode and the reference electrode, the first charge measurement circuit providing a first charge measurement; a second charge measurement circuit connected in series between the second electrode and the reference electrode, the second charge measurement circuit providing a second charge measurement; and circuitry to compare the first charge measurement or the second charge measurement to a threshold to detect the voltage in the conductor cable. 
     In an example of the fourth aspect, the first region and the second region overlap. 
     In another example of the fourth aspect and the above examples, the sensor device further includes a third electrode to be disposed over the surface of the conductor cable to cover a third region having a third axial length and a third circumferential width, the third region having an axial position aligned with the first and second regions and having a circumferential position adjacent the first and second regions. For example, the reference region extends along the circumferential lengths of at least the first, second, and third regions. In another example, the sensor device further includes a third charge measurement circuit connected in series between the third electrode and the reference electrode, the third ammeter providing a third charge measurement. 
     In a further example of the fourth aspect and the above examples, the sensor device further includes a second reference electrode to be disposed over the surface of the conductor cable to cover a second reference region, the second reference region having an axial position adjacent the axial position of the first and second regions on an opposite axial side of the first and second regions as the axial position of the reference region and extending to cover the circumferential positions of the first and second regions. For example, the second reference electrode is electrically connected to the reference electrode. 
     In an additional example of the fourth aspect and the above examples, the circuitry is free of a connection to ground. 
     In another example of the fourth aspect and the above examples, the sensor device is an e-field sensor and wherein the first, second, and reference electrodes are responsive to the e-field. 
     In a further example of the fourth aspect and the above examples, the conductor cable includes a line conductor, a neutral conductor, and a ground conductor. 
     In an additional example of the fourth aspect and the above examples, the conductor cable is a split-phase or three-phase cable. 
     In another example of the fourth aspect and the above examples, the first, second, and reference electrodes are disposed in a strap to wrap around the conductor cable. For example, the circuitry is disposed on a case attached to the strap. In an example, the strap has an adhesive region to secure a portion of the strap to the conductor cable. In another example, the strap includes a hook region on a first side and a loop region on a second side to form a hook and loop coupling. 
     In a fifth aspect, a method for detecting voltage in a conductor cable includes detecting a first charge signal using a first charge measurement circuit connected in series between a reference electrode and a first electrode, the first electrode disposed over a surface of the conductor cable to cover a first region having a first axial length and a first circumferential width, a second electrode disposed over the surface of the conductor cable to cover a second region having a second axial length and a second circumferential width, the second region having an axial position aligned with the first region and having a circumferential position adjacent the first region, the reference electrode disposed over the surface of the conductor cable to cover a reference region, the reference region having an axial position adjacent the axial position of the first and second regions and extending to cover the circumferential positions of the first and second regions; detecting a second charge signal using a second charge measurement circuit connected in series between the second electrode and the reference electrode; and comparing with a circuitry the first charge signal or the second charge signal to a threshold to detect the voltage in the conductor cable. 
     In an example, the method further includes detecting a third charge signal with a third charge measurement circuit connected in series between the reference electrode and a third electrode, the third electrode disposed over the surface of the conductor cable to cover a third region having a third axial length and a third circumferential width, the third region having an axial position aligned with the first and second regions and having a circumferential position adjacent the first and second regions. 
     Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. 
     In the foregoing specification, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention. 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive-or and not to an exclusive-or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
     Also, the use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
     Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. 
     After reading the specification, skilled artisans will appreciate that certain features are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, references to values stated in ranges include each and every value within that range.