Abstract:
A Rogowski coil in a sensor unit has voltage induced by a conductor surrounded by the Rogowski coil. The voltage is integrated to represent current which is converted to digital data representing current in the conductor and sent wirelessly to a multimeter. The sensor unit may receive control signals from the multimeter. A plurality of sensor units may be networked and controlled by a remote control apparatus.

Description:
BACKGROUND 
       [0001]    Multimeters, also called digital multimeters or “DMMs”, are adapted for measuring a number of parameters generally needed for service, troubleshooting, and maintenance applications. Such parameters typically include a.c. (alternating current) voltage and current, d.c. (direct current) voltage and current, and resistance or continuity. Other parameters, such as 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 flow. 
         [0002]    General purpose multimeters employing internal current shunts are generally limited to ten 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. The difficulty in removing a blown fuse, coupled with the time and cost necessary to procure a replacement fuse, make it desirable to obtain a non-contact current measuring instrument that requires no internal fuse. 
         [0003]    Clamp-on multimeters provide improved capability for measuring current over general purpose multimeters by employing an integral current clamp which senses the current in the current-carrying conductor without having to cut the current-carrying conductor or break the circuit including the current-carrying conductor. A current clamp is typically provided in the same housing with a multimeter which measures other parameters such as voltage and resistance in the conventional manner using separate test probes. The current clamp is closed around the current-carrying conductor, which may include copper wires and buss bars, to sense the magnetic field created by the current flow. The current clamp provides a voltage signal for measurement by the multimeter which calculates and displays the measured current level. Because there is no current shunted from the current-carrying conductor through the clamp-on multimeter, the constraint on the maximum current that may be measured has largely been eliminated. Likewise, the internal fuse has been eliminated in clamp-on multimeters. 
         [0004]    In order to obtain a valid current measurement, the magnetic core in the current clamp must completely encircle the current-carrying conductor so that the current clamp is completely closed. The current clamp must be mechanically actuated to open the jaws, the current-carrying conductor inserted, and the jaws then closed around the current-carrying conductor. In tight physical spaces such as an electrical cabinet, inserting the clamp-on multimeter and using this technique to make a current measurement is inconvenient and difficult. Moreover, the jaws must be aligned to complete the magnetic core for obtaining a valid current measurement. Clamp-on multimeters are therefore difficult to use in confined spaces and require a large physical space in which to open the jaws of the current clamp. 
         [0005]    Clamp-on multimeters also tend to be physically heavy because of the substantial amount of iron used on the magnetic core. Furthermore, high levels of current may saturate the magnetic core. The current measuring capacity of the clamp-on multimeter is accordingly limited to current levels that do not saturate the magnetic core. The clamp-on multimeters and wired Rogowski coil are both able to sense alternating current flowing through a conductor surrounded by the clamp or Rogowski coil. There are, however, a number of differences between the Rogowski coil and the clamp. For example, a Rogowski coil is more flexible and has a smaller cross-section than the substantially rigid clamp of the multimeter. The Rogowski coil can accordingly be used in confined spaces that are too tight and/or too small for the clamp-type multimeter. Further, the loop of a Rogowski coil can be reshaped to surround conductors having cross-sections that the clamp cannot close around. Another difference is the greater current measuring capability of the Rogowski coil as compared to the clamp. Specifically, an air core does not become saturated at levels of current that saturate the magnetic material of the cores of the clamp. 
         [0006]    However, the Rogowski coil is limited by the parasitic resistance, capacitance and inductance of the connecting cable. To minimize parasitic effects, it is desired to keep the length of the connecting cable as short as practical. The length of the connecting cable also limits the distance between the placement of the Rogowski coil and the position of a technician viewing the measurements taken with the coil. The conductor enclosed by the Rogowski coil may be in a room or cabinet with limited room for the person operating the multimeter. The conductor may carry large voltage and currents that represent a danger to the technician because accidental contact with an exposed conductor could be harmful and possibly fatal. Despite the progress made by systems such as those shown and described in U.S. Pat. No. 8,330,449, there remains an unmet need for improved convenience and safety that cannot be provided by a Rogowski coil wired to a multimeter. 
       SUMMARY 
       [0007]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0008]    The embodiments described and shown herein are for a wireless remote controlled Rogowski coil, a system that controls the wireless Rogowski coil, and a method for remotely measuring the current in a conductor surrounded by a Rogowski coil. In particular, the wireless remote-controlled Rogowski coil is a sensor unit having an elongated Rogowski coil. A conductor surrounded by the coil induces a voltage in the Rogowski coil. The voltage is integrated by an integrator circuit or device to provide an output signal representative of current in the conductor. The current signal is converted into digital signals by an analog to digital converter. The digital signal representing the current is wirelessly transmitted by a transceiver that sends the digital data and receives control signals. A multimeter or other control apparatus has a wireless transceiver for receiving the digital data from the sensor transceiver and for sending control signals to the transceiver of the Rogowski coil. 
         [0009]    The sensor unit may have a memory and a controller. The integrator and analog to digital converter may be distinct devices or circuits or incorporated into the controller. 
         [0010]    The control signals are configured to place the sensor transceiver in an idle mode, command the sensor unit to exit the idle mode and take one or more readings of the current in the conductor, or periodically transmit readings of the current in the conductor. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0011]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a schematic illustration of a multimeter with a wireless Rogowski coil sensor unit according to an embodiment of the present disclosure for measuring alternating current; 
           [0013]      FIG. 2  is a schematic illustration of components of a Rogowski coil according to an embodiment of the present disclosure; and 
           [0014]      FIG. 3  is a block diagram of components of a multimeter according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Specific details of embodiments according to the present disclosure are described below with reference to electrical circuits including a conductor. Other embodiments of the disclosure can have configurations, components, features or procedures different than those described in this section. A person of ordinary skill in the art, therefore, will accordingly understand that the disclosure may have other embodiments with additional elements, or the disclosure may have other embodiments without several of the elements shown and described below with reference to  FIGS. 1-3 . 
         [0016]      FIG. 1  is a schematic illustration of the multimeter  100  wirelessly coupled to the Rogowski coil sensor  200 . The multimeter  100  includes a housing  120  having a slender shape whereby a user (not shown) is able to comfortably hold the housing  120 . 
         [0017]    A clamp  140  is provided on the housing  120 . The clamp  140  includes a pair of clamp portions  142   a  and  142   b  having cores  144   a  and  144   b,  respectively. The clamp cores  144   a  and  144   b  can include windings (not shown) around a core made of a magnetizable material, e.g., iron. The first clamp portion  142   a  is movably attached, e.g., pivotally attached, to the housing  120  and capable of moving to an arrangement shown with one-dot-chain lines. The second clamp portion  142   b  can be fixed with respect to the housing  120 . The clamp portions  142   a  and  142   b  include ends  146   a  and  146   b , respectively, and are accordingly capable of being positioned in an open arrangement with the ends  146   a  and  146   b  separated by a gap. The clamp portions  142   a  and  142   b  are also capable of being positioned in a closed arrangement with the ends  146   a  and  146   b  being contiguously engaged. Thus, the closed arrangement of the clamp  140  shown in solid lines in  FIG. 2  has an approximately ring-like shape. A lever  150  fixed to the first clamp portion  142   a  can be used to move the first clamp portion  142   a  relative to the second clamp portion  142   b  and/or the housing  120 . The clamp  140  is configured to inductively sense a flow of alternating current in a conductor C surrounded by the clamp  140  in the closed arrangement. The clamp  140  may include a Hall effect current sensor (not shown) for, e.g., sensing a direct current flowing in the conductor C. The clamp  140  can sense the flow of current without breaking an electrical circuit (not shown in  FIG. 2 ) that includes the conductor C. The clamp  140  may produce a first signal in a first voltage range corresponding to the current flow. 
         [0018]    The housing  120  includes a port  180  that has one or more terminals  181 ,  182 ,  183  for sensing other electrical parameters. Plugs on the ends of lead wires of other sensors (not shown) may be connected to the port  180  to introduce to the multimeter  100  various signals that indicate voltage, resistance and/or temperature. 
         [0019]    The housing can include a display  130 , for example, a liquid crystal display (LCD). The display  130  shows measured parameters such as alternating current, or alternating current frequencies that are inductively sensed by the clamp  140 . In particular, a signal is induced in the clamp  140  by a flow of current in the conductor C that is surrounded by the clamp  140 . The display  130  also shows the electrical parameters sensed by signals received via the port  180 . If desired, another Rogowski coil with a three prong plug may be inserted into the port  180 . Such a wired Rogowski coil is shown and described in U.S. Pat. No. 8,330,449, which is assigned to the assignee of this patent, and whose entire content is hereby incorporated by reference for all purposes. 
         [0020]    The housing  120  includes one or more selectors  190 , e.g., push-buttons  192  and/or a rotary switch  194 . The selectors  190  may turn on and off a power source (not shown) for the multimeter  100  and/or change the measuring modes of the multimeter  100 . For example, the rotary switch  194  can be turned to select a mode for measuring alternating current with the clamp  140 . Other modes for measuring voltage, resistance, temperature, etc., can be selected with the selectors  190 . According to embodiments of the present disclosure, the selectors  190  can also be used to select a mode for measuring alternating current with the Rogowski coil sensor  200 . 
         [0021]    The Rogowski coil sensor  200  includes a loop  210 , a pendant  230 , a signal cable  240 , and a wireless controller  250 . Additionally, referring to  FIG. 2 , the loop  210  includes a toroidal coil  212  having a central wire surrounded by the same wire wound in a helix around a flexible, non-magnetic core  214  and sheathed in a flexible covering  216 . As a result, one end of the coil is taken through the coil itself and brought out the other side so that both ends of the coil are on the same side  212   a.  According to one embodiment of the present disclosure, the non-magnetic core  214  includes air. The covering  216  can be sufficiently rigid to protect the form of the toroidal coil  212  and still be sufficiently flexible to allow the loop  210  to be adjusted in length and/or shape. The length of the loop  210  can be adjusted with the pendant  230 . A start turn of the toroidal coil  212   a  and an end turn of the toroidal coil  212   b  are electrically connected by the signal cable  240  to the wireless controller  250  ( FIG. 3 ). The end turn  212   b  has an insulated cap  232  that plugs into an insulated bushing  234  of pendant  230 . A technician opens the loop  210  by removing end  212   b  from the pendant  230 , positioning the loop around a conductor, and reclosing the loop by inserting the cap  232  into bushing  234 . 
         [0022]    The wireless controller  250  sends data signals to the multimeter  100  and receives control signals from the multimeter  100  or other control apparatus. The clamp  140  and the Rogowski coil sensor  200  are both able to sense alternating current flowing through a conductor surrounded by the clamp  140  or the loop  210 . There are, however, a number of differences between the Rogowski coil sensor  200  and the clamp  140 . For example, the loop  210  is more flexible and has a smaller cross-section than the substantially rigid clamp portions  142   a  and  142 . The Rogowski coil sensor  200  can accordingly be used in confined spaces that are too tight and/or too small for the clamp  140 . Further, the loop  210  can be reshaped to surround conductors having cross-sections that the clamp  140  cannot close around. Another difference is the greater current measuring capability of the Rogowski coil sensor  200  as compared to the clamp  140 . Specifically, an air core does not become saturated at levels of current that saturate the magnetic material of the cores  144   a  and  144   b.  Yet another difference is the Rogowski coil sensor  200  is spaced from the multimeter  100  by the signal cable  240  whereas the relative position of the clamp  140  is fixed with respect to the multimeter  100 . Thus, the clamp  140  and the multimeter  100  can be handled as a single unit whereas the Rogowski coil sensor  200  allows the user to position the Rogowski coil sensor unit  200  around a conductor and hold the multimeter  100  a safe location removed from proximity to the conductor. 
         [0023]      FIG. 3  is a block diagram of components of a system including the multimeter  100  and the Rogowski coil sensor unit  200  according to an embodiment of the present disclosure. The multimeter  100  includes the display  130 , the clamp  140 , and the port  180 , a wireless transceiver  104 , the selectors  190  and a processor  110 . The wireless transceiver  105  communicates with the Rogowski coil sensor unit  200  by sending control signals and receiving data signals from the Rogowski coil sensor unit  200 . The control signals may include commands to the sensor unit  200  to power up from an idle or sleeping mode, power down to an idle or sleeping mode, provide current readings of voltage sensed by the loop  210 , or provide periodic readings of the voltage sensed by the loop  210 . The clamp  140  includes a winding that inductively senses alternating current without breaking the electrical circuit and produces a first signal in a first voltage range corresponding to the alternating current. For example, the first voltage range may be measured in terms of millivolts. The first signal is received by the processor  110  which outputs a signal to the display  130 . Similarly, other signals from the port  180  are also received by the processor  110 . According to certain embodiments, the selector  190  selects the signal(s) that the processor  110  uses to present the desired measurements on the display  130 . 
         [0024]    The Rogowski coil sensor unit  200  inductively senses alternating current without breaking the electrical circuit and produces a second signal in a second voltage range corresponding to the alternating current. For example, the second voltage range may be measured in terms of microvolts. The Rogowski coil sensor  200  has a wireless control unit  250  that sends data wirelessly to multimeter  100  and receives one or more commands from the multimeter  100  or other control apparatus. The wireless control unit  250  has a controller  300 , a signal conditioning circuit  301 , a memory  302 , a transceiver  304 , an antenna  305 , and a power supply  306 . The controller  300  may be a microprocessor, a digital signal processor, an application-specific circuit or a programmable logic controller. The signal conditioning circuit may comprise one or more circuits for a filter, an integrator, an analog-to-digital converter, or any other circuit for configuring the signal from the Rogowski coil loop  210  to be acceptable for processing by controller  300  and for storage in memory  302 . In other embodiments, the one or more conditioning circuits are incorporated directly into the controller  300 . In still further embodiments, there is at least an analog-to-digital circuit to convert the voltage signal from the loop  210  into digital data signals that are sent to multimeter  100  or stored until demanded by the multimeter  100 . 
         [0025]    The memory  302  may be a separate memory, may be directly incorporated into circuitry for the controller  300 , or may be both a separate memory and a second memory in the controller  300 . The memory  302  may store system and application programs for interpreting and responding to commands received by the transceiver  304 . The transceiver  304  is any suitable radio transmitter and receiver. In some embodiments the transceiver complies with original Bluetooth standards. Other embodiments comply with 
         [0026]    Bluetooth Low Energy standards. Still other embodiments comply with Wi-Fi standards. Alternative embodiments comply with any other suitable radio frequency standards. A power supply  306  provides power directly or indirectly to the controller  300 , signal conditioning circuitry  301 , memory  302 , transceiver  304  and antenna  305 . The power supply may comprise batteries including, and not limited to, rechargeable batteries. 
         [0027]    In other embodiments a remote control apparatus  400  is operated by an attendant  404  to receive information from one or more Rogowski coil sensor units  200  and multimeters  100  as well as send control signals to one or more Rogowski coil sensor units  200  and multimeters  100 . The remote control apparatus may communicate with the Rogowski coil sensor units via one or more networks including, and not limited to, a local wireless network in range of the transceivers  304 . 
         [0028]    The embodiments described above overcome one or more of the drawbacks and solve one or more of the problems that arise when Rogowski coils are wire-coupled to multimeters. The wireless units  100 ,  200  provide virtually unlimited flexibility for allowing a technician to safely place a Rogowski coil sensor unit  200  on a target conductor and move safely away from the conductor before manipulating the multimeter  100  to take readings of the conductor. The connecting cable  240  may be very short and may be integral with the bottom of the pendant  230 , thereby reducing the potential adverse influence of parasitic factors such as the resistance, capacitance and inductance of the connecting cable  240 . In other embodiments the wire  240  is enclosed in a relatively short rigid insulated conduit. 
         [0029]    Some embodiments of the disclosure have wireless sensor units that include an integrator circuit coupled to the Rogowski coil, an analog to digital converter coupled to the output of the integrator and a wireless transmitter coupled to the output of the analog to digital converter. The wireless transmitter continuously transmits the output of the analog to digital converter. Existing multimeters, such as those shown in U.S. Pat. No. 8,330,449, could be modified to have a receiver or transceiver wire-connected via port  180  so that the current data could be received and displayed on multimeter  100 . Accordingly, the disclosure is not limited to the particular placement of any one type of circuitry in the sensor unit  200  of the multimeter  100 . 
         [0030]    In some embodiments the multimeter  100  may also receive a wired Rogowski coil in port  180 . Such multimeters also include an integrator  112  to scale the second signal from the wired Rogowski coil to the first voltage range, e.g., to scale a microvolt output of the Rogowski coil up to a millivolt signal that the processor  110  can process. The housing  120  of the multimeter  100  includes the processor  110 , the integrator  112 , the display  130 , the clamp  140 , the port  180 , and the selectors  190 . 
         [0031]    In other embodiments of the disclosure, other master or control apparatus may be substituted for the multimeter  100 . For example, other digital multimeters with a wireless transceiver but without a clamp  140  may be substituted for the multimeter  100 . Still other embodiments may use other apparatus to control the sensor unit including and not limited to tablets, smartphones, personal digital assistants (PDA) and personal computers (PC) equipped with a transceiver may receive signals from the sensor unit  200  and send control signals to the sensor unit. Such DMMs, tablets, smartphones, PDAs and PCs may have condition circuitry and/or software to receive unprocessed signals representative of processed current from sensor units  100  or the sensor units  100  may have conditioning circuitry and/or software to transmit processed signals representative of measured current. 
         [0032]    Specific details of the embodiments of the present disclosure are set forth in the description and in the figures to provide a thorough understanding of these embodiments. A person skilled in the art, however, will understand that the invention may be practiced without several of these details, or that additional details can be added to the invention. Well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the present disclosure. 
         [0033]    Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to. Additionally, the words “herein,” “above,” “below,” and words of similar connotation, when used in the present disclosure, shall refer to the present disclosure as a whole and not to any particular portions of the present disclosure. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or”, in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
         [0034]    The above detailed description of embodiments is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
         [0035]    While certain aspects of the invention are presented below in certain claim forms, the inventors contemplate the various aspects of the invention in any number of claim forms. Accordingly, the inventors reserve the right to add additional claims after filing the application to pursue such additional claim forms for other aspects of the invention. 
         [0036]    While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.