Patent Publication Number: US-10329942-B2

Title: Apparatus using magnets for harvesting energy on a metrology device

Description:
BACKGROUND 
     Engineers expend great efforts to make devices easy to assemble, reliable to operate, and amenable to maintenance and repair tasks. Hardware constraints can frustrate these efforts because the hardware lacks appropriate functionality and because any improvements can increase costs and/or add complexity to the device. For metrology, the hardware (e.g., gas meters) often suffers from a dearth of power or power generating sources that are resident on the device. 
     SUMMARY 
     The subject matter of this disclosure relates to metrology and metrology hardware. Of particular interest herein are improvements that harvest energy from metering systems, for example, flow meters and the like devices that measure parameters of flowing fluids. These improvements may incorporate an energy harvester to allow the metering system to generate power in situ so as to power on-board electronics, often to replace, supplement, or charge a power source found on-board the metering system. 
     Flow meters may find use in billing applications to charge an end user for fuel (e.g., natural gas). Utility companies may rely on values from the flow meter to assign a monetary value to charge the customer. The values may also serve in custody transfer applications, which transfer fluids (e.g., natural gas, oil, etc.) from a supplier to a recipient, to account for the amount of fluid that transfers between these operators. 
     Some embodiments incorporate an energy harvester that can generate power via operation of the flow meter. The energy harvester may incorporate magnetic devices that cooperate with one another to harvest energy from rotating elements. These devices may include a magnetic core with a wire wound circumferentially about its outside. The magnetic core may reside in a ring magnet that co-rotates with the rotating elements. In use, the rotating ring magnet sets up an alternating magnetic field that induces a signal (e.g., current) in the wire. 
     Some embodiments address a braking effect that has been found to occur in magnet-type energy harvesters. Braking is due to the magnetic attraction between the poles of the ring magnet and the core. In devices with solid cores, it has been found that braking can lead to inaccurate measurements and interrupt rotation of the rotating elements for devices with sold cores. For example, braking increases the minimum flow necessary to start rotation because the breakaway torque increases due to the magnetic attraction between the solid core and the ring magnet. Minimum flow to stop rotation also increases for the same reason. 
     Accuracy of flow meters is a function of speed of a defined volume moving through the device and, also, fluid temperature and pressure in the line (which is corrected to standard conditions). Fluid temperature may be measured at the meter. But fluid pressure is seldom measured because it is known elsewhere in the line and assumed constant. In this regard, braking of the rotating elements may inadvertently introduce a pressure drop across the device that was not accounted for that will cause the resulting flow calculation to produce an error. 
     Some embodiments use “hollow” cores in place of the solid core. As discussed more below, harvesting devices that use the hollow core may be more reliable because the hollow core is much less susceptible to braking effects. Similarly situated devices with hollow cores may also provide more power because the hollow cores can be longer than solid cores, which are likely shorter in length in order to reduce (or eliminate) the braking effect and concomitant loss of accuracy and interruptions in operation. The shorter solid cores increase the gap or distance between the ends of the solid core and the poles of the rotating magnet to reduce braking effect. But, notably, the hollow core improves efficacy of the energy harvester relative to the shorter solid core because the longer hollow core can accommodate more windings of the wire that can lead to greater power generation. 
     Use of the energy harvester may address certain drawbacks of the on-board power source. For example, using the energy harvester to re-charge or reduce duty cycle on the on-board power source may preclude maintenance necessary to check and replace batteries and battery packs found on devices in the field. For gas meters, this feature can save significant costs of labor because these devices can number in the hundreds and thousands in the field and, moreover, often reside in remote areas, both of which may present major logistical challenges that require careful planning. The on-board energy harvester can also improve reliability in the event that batteries die unexpectedly or suffer reduction or total loss of energy prematurely, which is a significant nuisance and unplanned expense for the operator. 
     On-board energy harvesting that is reliable can also address future power needs for gas meters and related metrology devices. For gas meters, the energy harvester may provide sufficient power to meet future data transmission demands that would otherwise exceed the on-board power source by, for example, drawing an unreasonable amount of power from an on-board battery or energy storage unit. On-board energy harvesting can also allow gas meters to expand functionality, for example, in the form of new electronics and sensors including transmitting devices to communicate with a Supervisory Control and Data Acquisition (SCADA) system, cloud-connected product life-cycle management software, and the like. In use, duty cycle for transmitting data may be periodic, which would elevate power demand for brief periods of time. More demanding scenarios might require real-time data transmission to monitor ongoing device health or diagnostics in a connected system, which may require almost-continuous supply of reliable power on the device. 
     The subject matter of this application may relate to commonly owned U.S. Pat. No. 6,886,414, filed on Apr. 21, 2003, and entitled “POWER GENERATING METER.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made briefly to the accompanying figures, in which: 
         FIG. 1  depicts a schematic diagram of an exemplary embodiment of a metering system that is configured for in situ energy harvesting; 
         FIG. 2  depicts an exploded perspective view of an exemplary structure for an energy harvester for use in the metering system of  FIG. 1 ; 
         FIG. 3  depicts an elevation view of the partial cross-section of the energy harvester of  FIG. 2 ; 
         FIG. 4  depicts an elevation view of the partial cross-section of the energy harvester of  FIG. 2 ; 
         FIG. 5  depicts an elevation view of the partial cross-section of the energy harvester of  FIG. 2 ; 
         FIG. 6  depicts an elevation view of the partial cross-section of the energy harvester of  FIG. 2 ; 
         FIG. 7  depicts a perspective view of an example of the energy harvester of  FIG. 2 ; 
         FIG. 8  depicts an elevation view of the cross-section of the energy harvester of  FIG. 7 ; 
         FIG. 9  depicts a perspective view of an example of the energy harvester of  FIG. 2 ; 
         FIG. 10  depicts a perspective view of an example of the energy harvester of  FIG. 2 ; 
         FIG. 11  depicts a perspective view of the front of an example of structure for a metering system; 
         FIG. 12  depicts a perspective view of the back of the example of  FIG. 11 ; 
         FIG. 13  depicts a perspective view of details of the example of  FIG. 12 ; and 
         FIG. 14  depicts an elevation view of the cross-section of the example of  FIG. 11 . 
     
    
    
     Where applicable like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated. The embodiments disclosed herein may include elements that appear in one or more of the several views or in combinations of the several views. Moreover, methods are exemplary only and may be modified by, for example, reordering, adding, removing, and/or altering the individual stages. 
     DETAILED DESCRIPTION 
     The embodiments disclosed herein employ structure to harvest energy in situ on gas meters and related metrology devices. These devices may quantify parameters (e.g., flow rate, volume, etc.) of fluids and solids, for example, using electro/mechanical means with rotating elements (e.g., impellers) that can generate pulses indicative of the flow. As described below, embodiments may employ magnetic devices that cooperate to generate power in response to rotation of the rotating elements on the device. These embodiments may use a hollow, tubular member (or “core”), however, which proves advantageous to reduce braking and other deleterious effects brought on by interaction with a rotating magnet in these types of devices. Other embodiments are within the scope of the subject matter of this disclosure. 
       FIG. 1  depicts a schematic diagram of an exemplary embodiment of a metering system  100 . This embodiment may couple with a conduit  102  that carries material  104 . Examples of material  104  may include fluids (e.g., liquids and gases), but metering system  100  may also work with solids as well. The metering system  100  may integrate several components (e.g., a first component  106 , a second component  108 , and a third component  110 ). The components  106 ,  108  may operate together to convey information that relates to material  104 . This information may define measured parameters for material  104 , for example, flow rate, volume, and energy; however, this listing of parameters is not exhaustive as relates to applications of the subject matter herein. The third component  110  can operate to harvest energy that might otherwise be lost during operation of the metering system  100 . This harvested energy may find use to power components (e.g., electronics) on the metering system  100 . 
     As noted herein, the metering system  100  may embody a gas meter or like metrology hardware. This type of hardware may be configured to measure defined volumes of flowing gas. These measurements can be used to quantify (and often bill) consumers at residential, commercial, industrial, and municipal locations, but this does not foreclose use of the energy harvesting concepts on other hardware or for other applications. In one implementation, the first component  106  (also “metrology component  106 ”) may include a meter device  112  with a rotating component, for example co-rotating impellers, configured to rotate in response to the material ( 104 ). Although shown separate from the conduit  102 , the meter device  112  may be configured to connect to the conduit  102 , often in-line using flanges or fittings that are common for pipe connections. The second component  108  (also, “processing component  108 ”) may include an indexing unit  114  that can process signals from the meter device  112 . These processes may calculate values for the measured parameters among other functions. As also shown, the third component  110  (also, “energy harvester  110 ”) may couple with the meter device  112 . The energy harvester  110  may have a bifurcated structure with a pair of harvesting units (e.g., a first harvesting unit  116  and a second harvesting unit  118 ). The harvesting units  116 ,  118  can communicate with one another without physical contact, preferably to create a signal  120  in response to movement of elements of the meter device  112 . The units  116 ,  118  may leverage a variety of technologies including photoelectric, inductive, capacitive, and ultrasonic technologies. Other technologies developed after filing of this application may also be acceptable for use in the metering system  100 . 
       FIG. 2  illustrates an exemplary structure for the energy harvester  110  in partially-exploded form. The harvesting units  116 ,  118  may embody magnetic units (e.g., a first magnetic unit  122  and a second magnetic unit  124 ). The magnetic units  122 ,  124  can generate a magnetic field F, preferably as permanent magnets or continuous magnetic sources. On the first harvesting unit  116 , the first magnetic unit  122  may form an annular ring  126  with a center axis  128 . The annular ring  126  may have magnetic poles (e.g., first pole  130  and a second pole  132 ) diametrically opposed from one another across an opening  134 . Construction of the annular ring  126  may include additional magnetic poles that are dispersed about the device. The second magnetic unit  124  may itself comprise constituent components, shown here as a conductor  136  and a core  138 . The conductor  136  may embody a thin-diameter wire  140  forming windings  142  that circumscribe the core  138 . The windings  142  may couple with one or more leads (e.g., a first lead  144  and a second seal  146 ). The leads  144 ,  146  may extend to electronics  148  found on-board the metering system  100  ( FIG. 1 ). The electronics  148  may include devices  150  and operative circuitry  152 . Exemplary devices  150  may include sensors, micro-controllers and related processors; however, the metering system  100  ( FIG. 1 ) may also benefit from on-board energy storage units (e.g., rechargeable batteries). The core  138  may have a body  154  with a longitudinal axis  156  that extends between a pair of ends (e.g., a first end  158  and a second end  160 ). A bore  162  may penetrate into the body  154  along the longitudinal axis  156  to form a peripheral wall  164 . 
       FIG. 3  depicts an elevation view of a partial cross-section of the energy harvester  110  taken at line  3 - 3  of  FIG. 2 . As shown, the bore  162  may extend through the body  154 . This feature creates a “hollow” structure in the form of an elongate tube with openings at the ends  158 ,  160 . Form factors for the body  154  may include cylinders, as shown, but other form factors with different cross-sections (e.g., square, rectangle, elliptical, ovoid, etc.) may comport with the proposed concepts as well. In one implementation, the body  154  measures approximately 8 mm in length (L), although the length L may fall within a range of from approximately 7 mm to approximately 9 mm. The peripheral wall  164  may have a wall thickness (t) in a range of from approximately 0.5 mm to approximately 1.6 mm. The wire  140  may be formed from 47 gauge copper wire. Windings  142  may form approximately 12,500 turns or coils about the core  138 ; however, the number of turns may vary to maximize or optimize functioning of the device, for example, from approximately 8,000 to approximately 14,000. When assembled, the core  138  may reside inside the opening  134  at an orientation with the longitudinal axis  156  that is radially offset from the center axis  128 . The radial offset may be 90° so that the axes  128 ,  156  are perpendicular to one another, as shown. This orientation may form a gap  166  between the ends  158 ,  160  and the interior surface of the annular ring  126 . This disclosure does contemplate configurations in which the radial offset is such that the longitudinal axis  156  aligns with the center axis  128 . 
     With reference also to  FIG. 2 , the exemplary structure for the energy harvester  110  may generate the signal  120  in response to relative movement between the units  122 ,  124 . In use, rotation of the annular ring  126  changes the annular position of the poles  130 ,  132  around the center axis  128 . The motion sets up an alternating magnetic field that induces signal  120  in the wire  140 , typically as a sinusoidal alternating current (“SAC”). Leads  144 ,  146  may conduct the SAC to the electronics  148  for use by devices  150 . Operative circuitry  152  may be useful to convert the SAC to direct current (DC) that is better suited for devices  150 . The operative circuitry  152  may include one or more discrete electrical components like a rectifier for this purpose. 
     The “hollow” body  154  of the core  138  has been found to improve performance of the harvesting component  110 . The design is less susceptible to “braking” that may occur as the poles  130 ,  132  of the rotating annular ring  126  pass in close proximity to the ends  158 ,  160  of the body  154 . In turn, the length L of body  154  can be set to maximize the number of windings  142  of the conductor  136 . This feature permits the harvesting component  110  to more effectively generate the SAC. As an example, Table 1 below compares power achieved from a “solid” core design and the power achieved from the “hollow” body  154  disclosed herein. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Power Comparison 
                   
               
            
           
           
               
               
               
            
               
                 Rotation Speed 
                 “Solid” Core 
                 “Hollow” Core 
               
               
                   
               
               
                  200 RPM 
                   670 μWatts 
                   840 μWatts 
               
               
                  300 RPM 
                  1,320 μWatts 
                   1650 μWatts 
               
               
                  400 RPM 
                  2,370 μWatts 
                   2960 μWatts 
               
               
                  500 RPM 
                  3,760 μWatts 
                   4700 μWatts 
               
               
                  600 RPM 
                  5,290 μWatts 
                   6610 μWatts 
               
               
                  700 RPM 
                  6,970 μWatts 
                   8710 μWatts 
               
               
                  800 RPM 
                  8,380 μWatts 
                 10,470 μWatts 
               
               
                  900 RPM 
                 10,820 μWatts 
                 13,520 μWatts 
               
               
                 1000 RPM 
                 13,910 μWatts 
                 17,390 μWatts 
               
               
                 1100 RPM 
                 16,520 μWatts 
                 20,650 μWatts 
               
               
                 1200 RPM 
                 18,920 μWatts 
                 23,650 μWatts 
               
               
                 1300 RPM 
                 23,330 μWatts 
                 29,160 μWatts 
               
               
                 1400 RPM 
                 25,500 μWatts 
                 31,880 μWatts 
               
               
                 1500 RPM 
                 29,150 μWatts 
                 36,420 μWatts 
               
               
                 1600 RPM 
                 33,300 μWatts 
                 41,620 μWatts 
               
               
                 1700 RPM 
                 36,240 μWatts 
                 45,300 μWatts 
               
               
                 1800 RPM 
                 38,750 μWatts 
                 48,430 μWatts 
               
               
                 1900 RPM 
                 41,360 μWatts 
                 51,700 μWatts 
               
               
                 2000 RPM 
                 43,530 μWatts 
                 54,410 μWatts 
               
               
                 2100 RPM 
                 46,020 μWatts 
                 57,520 μWatts 
               
               
                 2200 RPM 
                 49,300 μWatts 
                 61,620 μWatts 
               
               
                 2500 RPM 
                 55,430 μWatts 
                 69,290 μWatts 
               
               
                   
               
            
           
         
       
     
     The power output of the “hollow” structure of the body  154  is seen in Table 1 to be significantly greater, up to 25%, effectively maximizing the available space within the similar-sized envelope as compared to the “solid” core design. By way of comparison, the spacing or gap distance of a prior art solid core sensor was approximately 0.030 inches less on each end, resulting in significantly less coils (approximately 2000 less turns) and less power generation. 
       FIG. 4  depicts an elevation view of the cross-section of the energy harvester  110  taken at line  4 - 4  of  FIG. 2 . Generally, the peripheral wall  164  may embody a thin-walled structure  168  that comprises materials with properties suitable to function as part of the energy harvester  110 . Exemplary materials include steel, although a variety of metals and metallic composites may be useful as well. Likewise, material composition for the thin-walled structure may or may not be homogeneous throughout. Machining techniques like turning and milling may be used to form the form factor with bore  162 . 
       FIGS. 5 and 6  depict an elevation view of the cross-section of exemplary configurations for the thin-walled structure  168  of the energy harvester  110 . In  FIG. 5 , the configuration leverages multiple layers (e.g., a first layer  170 , a second layer  172 , and a third layer  174 ). The layers  170 ,  172 ,  174  may form a laminate structure that features sheets of material wrapped circumferentially about the longitudinal axis  156  or, possibly, individual hollow cylinders of varying diameters. Adhesives may attach the layers  170 ,  172 ,  174  together to form the thin-walled structure  168 . In operation, materials selection may set the amount of energy available from each of the layers  170 ,  172 ,  174 . The SAC that the energy harvester  110  generates will correspond with the sum of that generated by each layer  170 ,  172 ,  174 . In  FIG. 6 , the configuration assumes a spiral design that forms the layers  170 ,  172 ,  174  contiguously or at least semi-contiguously with one another. This spiral design may result from winding one or more sheets of material about the longitudinal axis  156 . 
       FIG. 7  depicts a perspective view of an example of the second magnetic unit  124  for use in the energy harvester  110  of  FIG. 2 . At a high level, the magnetic field F may be represented by magnetic flux lines that extend between the ends  158 ,  160  of the body  154 . The density of these flux lines typically decreases with radial distance away from the body  154 . As shown in  FIG. 7 , a field shaper  176  may be useful to shape or manipulate the flux lines to increase power generation of the harvesting component  110 . The field shaper  176  may comprise a bent wire  178 , typically copper wire or other conductive metals. The bent wire  178  assumes a position on the device to collapse the flux lines closer to or in proximity of the vicinity of the windings  142 . This structure may increase the magnetic flux density to increase power generated by the harvesting component  110 . 
       FIG. 8  depicts an elevation view of the cross-section of the second magnetic unit  124  taken at line  8 - 8  of  FIG. 7 . The bent wire  178  may have ends  180  disposed in the bore  162 . The ends  180  are spaced apart from one another and from the peripheral wall  164 . Potting or insulation may be useful to retain the ends  180  in position relative to the body  154 . The bent wire  178  may have a unitary structure with bends that form segments at varying orientations relative to the longitudinal axis  156 . In one implementation, the segments may include a pair of short, longitudinal segments  182  that extend longitudinally away from the ends  180 . The segments  182  may terminate at first bends  184  to give way to a pair of radial segment  186  disposed at or near 90° to the longitudinal axis  156 . Each of the segments  186  may terminate at a pair of second bends  188  that couple with an elongate longitudinal segment  190 , possibly parallel to the longitudinal axis  156 . Each of the radial segments  186  may be offset from the ends  158 ,  160  by a distance L 1 , which may be in a range of from approximate 1 mm to approximately 5 mm. The longitudinal segment  190  may be offset from the surface of the body  154  by a distance R 1 , which may be in a range of from approximately 1 mm to approximately 10 mm. 
       FIG. 9  depicts a perspective view of an example of the second magnetic unit  124  for use in the energy harvester  110  of  FIG. 2 . In this example, the field shaper  176  comprises a plurality of shaping members  192  disposed in an array  194 . The shaping members  192  may be radially spaced apart from one another by an angle α, preferably so that the members  192  are equally spaced circumferentially apart from one another about the longitudinal axis  156 . In one implementation, each of the shaping members  192  may conform to the shape of the bent wire  178  ( FIGS. 7 and 8 ). The number of shaping members  192  may be determined by the practical limits of manufacturing, or by the practical aspect of diminishing returns, whereby increasing the number of shaping member  192  beyond a high limit results in decreasing performance. 
       FIG. 10  depicts a perspective view of another example of the second magnetic unit  124 . The field shaper  176  may comprise a pair of magnetic end caps (e.g., a first end cap  196  and a second end cap  198 ). The end caps  196 ,  198  reside on each end  158 ,  160  of the body  154 . The end caps  196 ,  198  may be useful to reshape the magnetic field density around the center of the core  138 . The diameter of the end caps  196 ,  198  may be sized greater than the effective diameter D of the core  138 , where the effective diameter D is the diameter of the body  154  plus windings  142 . In one example, the diameter of the end caps  196 ,  198  is between 10% and 100% greater than the effective diameter, although the diameter may also be 20% to 50% greater than the effective diameter. 
       FIGS. 11 and 12  depict a perspective view of an exemplary structure  200  for the metering system  100  from the front ( FIG. 11 ) and the back ( FIG. 12 ), each in partially-exploded form. Starting with the front view of  FIG. 11 , the structure  200  may include a meter body  202  having a central cylinder  204  and a pair of covers (e.g., a first cover  206  and a second cover  208 ) that attach to opposing ends. The central cylinder  204  may form a fluid coupling  210  with inlet/outlets  212 . The inlet/outlets  212  may interface with the conduit  102  ( FIG. 1 ) to allow material  104  ( FIG. 1 ) to transit the interior of the central cylinder  204 . The meter device  112  may comprise a mechanical assembly, shown here having cylinder cover plates  216  that secure on opposite sides of the fluid coupling  210 . The cover plates  216  enclose and seal an inner cavity  218  on the fluid coupling  210  that houses impellers  220 . On the front end, the mechanical assembly may also include a gear assembly  222  having a pair of gears  223 . The gears  223  can couple with the impellers  206 , typically by way of one or more shafts that extend through the first cover plate  206  to engage with the impellers  220 . 
     The impellers  220  work in concert to displace a fixed volume of material  104  that transits the fluid coupling  210  between inlet/outlets  212 . In one implementation, the impellers  220  counter-rotate in response to flow of material  104  ( FIG. 1 ). The rate at which the impellers  220  rotate relates to the rate at which material  104  flows through the fluid coupling  210 . For many applications, the rate of rotation of the impellers  220  is directly proportional to the flow rate of material  104  ( FIG. 1 ) through the fluid coupling  210  so that with each full revolution of the impellers  220  and, in turn, corresponding impeller shafts, a precise volume of material  104  ( FIG. 1 ) moves through the meter body  202 . In use, flow volume can be ascertained by counting the revolutions of the impeller shafts, typically by way of the gear assembly  222  and related counting technology of the mechanical assembly. 
     The back view of  FIG. 12  shows generally the hardware that may implement the harvesting component  110  on the structure  200 . On the back end, the structure  200  may include a harvester assembly  224  with a bifurcated structure having parts configured to permit relative movement between the magnetic units  122 ,  124 . For rotation, the parts may couple with impellers  220 , preferably by way of one or more shafts that extend through the cover plate  216 . These rotating parts may support the first harvesting unit  116  so that the annular ring  126  can co-rotate with the impellers  220 . The parts of the harvester assembly  224  may also secure the second harvesting unit  122  in proximity to the annular ring  126 , as described herein. 
       FIG. 13  shows a perspective view of details of the harvester assembly  224  of the structure  200  of  FIG. 12  in exploded form. The harvester assembly  224  may include a mounting bracket  226  and an extension cup  228 . Both parts may align co-axially with one another on an axis  230 . The mounting bracket  226  may have a central aperture  232  extending between a first end  234  and a second end  236 . On the first end  234 , the mounting bracket  226  may form a flange  238  with openings  240  dispersed circumferentially about the axis  230 . The second end  236  may form a cup portion  242  having a reduced diameter relative to the diameter of the flange  238 . Proximate the cup portion  242 , the extension cup  228  may have a receiving part  244  with a peripheral outer wall  246  that bounds an inner opening  248 . The peripheral outer wall  246  may include one or more flexible tabs (e.g., first flexible tab  250  and second flexible tab  252 ), shown here dispersed diametrically opposite one another. In one implementation, the extension cup  228  may reduce in diameter from peripheral outer wall  246  to a tapered section  254  with support ribs  256  disposed circumferentially from a shoulder portion to an outer surface. The annular ring  126  may be configured as a short, cylindrical magnet  258  having detents  260  disposed diametrically opposite from one another. The detents  260  may penetrate the magnet  258  a depth suitable to interface with the flexible tabs  250 ,  252 . 
       FIG. 14  shows an elevation view of the cross-section of the structure  200  in assembled form taken at line  14 - 14  of  FIG. 12 . The extension cup  244  may insert at the tapered section  254  onto one end of an impeller shaft  262 . The fit may be snug, as each of extension cup  244  and the impeller shaft  262  may be configured with features  264  for use to receive and secure a fastener (e.g., a bolt or screw). The magnet  258  is shown to install into the inner opening  248  so that the flexible tabs  250 ,  252  engage the detents  260 . The fit between the peripheral outer wall  246  and the magnet  258  may be snug to prevent relative annular movement with the extension cup  224 . The flexible tabs  250 ,  252  may help ensure this fit as well as to prevent longitudinal movement of the magnet  258  out of the extension cup  244 . The flange  238  of the mounting bracket  226  may abut part of the second cover  208 . Fasteners  266  may populate the openings  240  on the flange  238  to secure the mounting bracket  226  in place. As shown, the cup portion  242  extends into the inner opening  248  of the extension cup  224  to locate the second harvesting unit  124  inside of the magnet  258 . 
     As used herein, an element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 
     In light of the foregoing discussion, the embodiments herein incorporate improvements that are useful to harvest energy from revolution of the impellers on gas meters and related metrology hardware. These devices often reside in remote areas that lack electrical power so as to place emphasis on battery power for energy. Powering the electronics by battery power alone presents two common problems. First, the battery life was finite so the batteries had to be periodically replaced according to a maintenance schedule. Second, sometimes batteries died prematurely and unexpectedly, requiring an expensive emergency field replacement. In this regard, the examples below include certain elements or clauses one or more of which may be combined with other elements and clauses describe embodiments contemplated within the scope and spirit of this disclosure.