US20100178887A1 - Blast shield for use in wireless transmission system - Google Patents

Abstract

A blast shield includes a blast resistant housing having a transmission wall which allows transmission of wireless signals therethrough. The shield is especially useful for withstanding external explosions, shock waves and thermal shock such as may occur during the collapse or explosions in underground mines, buildings or other environments while protecting internal components such as wireless transmitters and sensitive electronic equipment. The shield is also configured to prevent electrical arcing or explosions within the housing from escaping the housing and igniting flammable material external to the housing. A wireless transmission system using the blast shield and a method of use are also provided.

Description

BACKGROUND OF THE INVENTION
• 1. Technical Field
• The present invention relates generally to a blast shield for use in wireless transmission. More particularly, the blast shield is configured to house various electronic components such as transmitters so that a wireless signal may be transmitted through a portion of the blast shield. Specifically, the blast shield is typically configured to protect the various components contained therein from external explosions or shock waves while minimizing the possibility of igniting external flammable gasses or other materials in the case of an explosion within the blast shield.
• 2. Background Information
• With the increasing use of wireless mesh networks for communication, controls and data transfer in various industries and applications, there is a need for ruggedized explosion proof enclosures to house various components such as relays, transmitters, antennas and various other types of sensitive electronic equipment. Such enclosures would desirably maximize survivability of the various components in case of catastrophic events such as explosions while also preventing internal explosions from causing secondary explosions external to the enclosure.
BRIEF SUMMARY OF THE INVENTION
• The present invention generally provides a blast shield or enclosure in which various electronic components such as wireless transmitters may be disposed for transmitting wireless signals through a portion of the enclosure. The enclosure is typically configured to prevent internal explosions, flames or arcing from exiting the enclosure in order to prevent ignition of external flammable gasses or the like outside the enclosure. The enclosure may also be configured to withstand external explosions or blast waves or the impact of various types of projectiles in order to protect the internal components. The present invention also includes the wireless transmission system and method of using this system.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• A preferred embodiment of the invention, illustrated of the best mode in which Applicant contemplates applying the principles, is set forth in the following description and is shown in the drawings and is particularly and distinctly pointed out and set forth in the appended claims.
• FIG. 1 is a perspective view of the blast shield of the present invention shown mounted on a wall or other support structure.
• FIG. 2 is a top plan view of the base plate of the blast shield.
• FIG. 3 is a bottom plan view of the transmission wall of the blast shield.
• FIG. 4 is a top plan view of the retaining ring.
• FIG. 5 is a perspective view of the housing of the gland seal.
• FIG. 6 is a top plan view of the blast shield shown mounted on the support structure with one gland seal assembled and the other gland seal disassembled with the gland seal nut separated from the housing.FIG. 6 further shows in dash lines various internal components within the blast shield.
• FIG. 7 is a sectional view taken on line7-7 ofFIG. 6.
• FIG. 8 is an enlarged sectional view of the encircled portion ofFIG. 7.
• FIG. 9 is a sectional view taken on line9-9 ofFIG. 6 illustrating the connection or assembly of the gland seal to provide the seal around the associated cable or wire.
• FIG. 9A is a sectional view taken online9A-9A ifFIG. 6 illustrating the gland seal and the associated fire resistant pathways thereof.
• FIG. 10 is similar toFIG. 9 and shows an alternate embodiment of a gland seal.
• FIG. 11 is a diagrammatic view showing several of the blast shields within a wireless transmission system.
• Similar numbers refer to similar parts throughout the drawings.
DETAILED DESCRIPTION OF THE INVENTION
• The blast shield of the present invention is indicated generally at10 inFIG. 1.Blast shield10 is shown mounted on a wall orother support structure12 and is used to house various internal components14 (shown in dashed lines inFIG. 6) which are part of a wireless transmission system such as shown inFIG. 11. Shield10 is configured in part to protectinternal components14 from damage which may otherwise be sustained by the impact of solid objects or a blast wave such as may occur during an explosion or, for instance, the collapse of an underground mine or the collapse of another type of structure such as a building or the like.Shield10 is also configured to prevent internal sparks, flames, explosions or electric arcs within the blast shield from igniting flammable gasses or other materials which may be disposed adjacent and external to shield10. Shield10 may be configured to meet various requirements such as those established within various industries or by governmental agencies, such as within the underground mining industry, petrochemical industry, manufacturing industry, and the federal Homeland Security agency.
• Before describing the blast shield in greater detail,internal components14 are briefly described.Components14 typically include aradio transceiver unit15, anantenna17 connected thereto, battery-charging power wires19 and optionally signal-transmission lines21.Unit15 may thus serve as a wireless relay and typically includes a radio frequency receiver and radio frequency transmitter for producing signals which are transmitted wirelessly viaantenna17.Unit15 further includes a battery which powers the receiver and transmitter and a battery charger for charging the battery viapower wires19. The charger thus typically includes a rectifier for transforming alternating current to direct current.Unit15 may also include a microprocessor for processing incoming wireless signals and translating them into outgoing signals overtransmission lines21, which may be in the form of fiber optic lines or electric wires for example.
• With primary reference toFIG. 1,shield10 includes a rigid base mounting structure in the form of a flat circular base orbase plate16, a blast-resistant dome shapedtransmission wall18 and a securing mechanism which secureswall18 toplate16 and includes acircular retaining ring20 andmultiple fasteners22. In the exemplary embodiment, there are sixteenfasteners22 which are circumferentially evenly spaced alongring20.Shield10 further includes a pair ofgland seals24A and24B which are configured to provide a water tight, airtight seal around wires or cables such as flexibleelectric power cable26 and flexiblesignal transmission cable28, respectively, which extend through holes formed intransmission wall18 ofshield10. Each of these cables includes an internal electrical conductor or wire with an outer layer of electrical insulation.Power cable26 is in electrical communication with the internal battery charger via power wires19 (FIG. 6) whenshield10 is assembled.Cable28 is likewise in electrical or optical communication withunit15 viatransmission lines21 so that signals may be transmitted throughlines21 andcable28 frominside shield10 tooutside shield10. Althoughshield10 may be mounted as shown inFIG. 1 on a generally vertical wall, on a floor, on a ceiling or overhanging structure, or in any other desired position, it will be described herein for simplicity as having atop30 and abottom32 so thatplate16 definesbottom32 andtransition wall18 is mounted atopplate16 so as to definetop30, as oriented inFIG. 7. In the orientation shown inFIG. 7, the outer perimeter ofplate16 andring20 are thus concentric about a vertical axis X passing through the center ofshield10. The various substantially circular portions oftransmission wall18 are also substantially concentric about axis X with exceptions noted further below. When assembled,shield10 defines aninterior chamber34 in whichinternal components14 are disposed.
• Top30 andbottom32 define therebetween a height H1 (FIG. 7) which defines the profile ofshield10 or the approximate maximum normal distance whichshield10 will extend outwardly from the surface of a support structure such assupport structure12 when mounted thereon. This distance or height H1 is generally kept to a minimum in order to minimize its interference with personnel or equipment within the area in which the shield is mounted as well as to help minimize the effect of blast waves or the impact of objects which may hitwall18 during an explosion, structural collapse or the like.
• With primary reference toFIGS. 1,2 and7,base plate16 is described in greater detail.Plate16 is in the exemplary embodiment a substantially circular rigid disc typically formed of metal and having a flatcircular top surface36, a parallel flatcircular bottom surface38 and a circularouter perimeter40 extending therebetween. Whenshield10 is in the upright position shown inFIG. 7,surfaces36 and38 are substantially horizontal andbottom surface38 definesbottom32 ofshield10. A plurality of elongated mounting throughholes42 are formed inplate16 adjacentouter perimeter40 and extend fromtop surface36 tobottom surface38. In the exemplary embodiment, there are eightmounting holes42 each of which receives therethrough amounting fastener44 which may be in the form of a bolt, screw or any other suitable fastener depending on the nature of thesupport structure12 on whichshield10 is to be mounted.Holes42 are circumferentially equally spaced from one another and circumferentially elongated to provide for some adjustability during the mounting ofshield10 onsupport structure12 to accommodate for holes instructure12 which may be difficult to accurately form therein. A plurality of threadedholes46 is also formed inplate16 extending fromtop surface36 towardbottom surface38. In the exemplary embodiment, there are sixteen threadedholes46 lying along a common circle which is disposed radially inwardly of the circle along which mountingholes42 lie. Each of these circles is concentric about axis X whenshield10 is assembled.Fasteners22 are typically in the form of bolts having externally threaded shafts which respectively are screwed into threadedholes46 so that eachfastener22 provides a threaded engagement withplate16 within eachrespective hole46 to securering20 andwall18 toplate16. Additional threaded mounting holes (not shown) may be formed radially inwardly ofholes46 for securinginternal components14 toplate16. However, these holes would be blind holes extending fromtop surface36 towardbottom surface38 without communication withbottom surface38.
• With primary reference toFIGS. 1,3 and7,transmission wall18, which is substantially circular as viewed from above, is now described in greater detail. As previously noted,wall18 is generally dome shaped or bowl shaped and generally concentric about axis X whenshield10 is assembled. In accordance with the invention,transmission wall18 is formed of a blast resistant and radio frequency permeable material, which may also be described as having high electromagnetic transparency. The use of such material allows for the transmission of wireless signals such as radio frequency (RF) signals therethrough while also providing a substantial blast resistance primarily to protectinternal components14 from blast waves or solid objects which may serve as projectiles during explosions or structural collapses such as that which may be experienced in an underground mine or otherwise as noted above. Typically,wall18 is formed of a suitable plastic material which provides these properties. In the exemplary embodiment,wall18 is formed of a polycarbonate resin thermoplastic which provides substantial strength and impact resistance, such as the polycarbonate sold under the name LEXAN®.
• Wall18 includes anannular flange48 which in the exemplary embodiment is substantially circular and horizontally flat.Flange48 is substantially concentric about axis X whenshield10 is assembled.Wall18 further includes anannular side wall50 which is rigidly secured to and extends upwardly from the inner perimeter ofannular flange48 to a substantially flat horizontal and circulartop wall52 which is rigidly secured to the top ofside wall50 and extends radially inwardly therefrom. Sixteen throughholes54 are formed inannular flange48 extending from a flat horizontalbottom surface56 thereof to a flat horizontaltop surface58 thereof.Holes54 are circumferentially spaced in the same manner as threadedholes46 andplate16 so as to be vertically aligned therewith for receiving therethroughrespective fasteners22 whenshield10 is assembled.Bottom surface56 has an annular configuration which is circular in the exemplary embodiment and which is also flat and horizontal.Bottom surface56 serves as a flame-arresting or fire-arresting path surface which in the exemplary embodiment is finished to about 250 micro inches.Annular flange48 has circular inner andouter perimeters60 and62 which intersectbottom surface56 and are concentric about axis X whenshield10 is assembled. Inner andouter perimeters60 and62 at their intersections withbottom surface56 define therebetween a distance D1 (FIGS. 3 and 8) which is the shortest distance therebetween as measured alongbottom surface56 and which in the exemplary embodiment is the distance between inner andouter perimeter60 and62 as measured along the intersection betweenbottom surface56 and a vertical plane in which axis X lies whenshield10 is assembled. Distance D1 may also be described as being normal to a tangent toinner perimeter60 or outer perimeter of62. In the exemplary embodiment,flange48 includes anupper ring64 and alower ring66 which is rigidly and non-removably secured at its upper surface to the lower surface ofring64 in order to add to the thickness offlange48. Depending on the specific requirements, the use oflower ring66 may be eliminated. In the exemplary embodiment,lower ring66 definesbottom surface56. Iflower ring66 is not used, then the lower surface ofupper ring64 serves as the flat horizontal bottom surface to provide the fire-arresting path surface offlange48.
• FIGS. 3 and 8 also illustrate a distance D2 which is the shortest distance along the fire arresting path surface56 offlange48 betweeninner perimeter60 and a given one ofholes54. Distance D2 in the exemplary embodiment is the distance betweeninner perimeter60 and the closest portion ofhole54 as measured along the intersection betweenbottom surface56 and a vertical plane in which axis X lies whenshield10 is assembled. In addition, distance D2 in the exemplary embodiment is normal to a tangent ofinner perimeter60.
• Annular side wall50 is substantially circular as viewed from above and tapers upwardly and radially inwardly from its circular annular connection to the inner perimeter offlange48 to its circular annular connection to the outer perimeter of circulartop wall52.Side wall50 has a generally frustoconical configuration and has aninner surface68 which communicates withinner perimeter60 and an outer surface70 which communicates withtop surface58 offlange48.Inner surface68 faces generally radially inwardly and downwardly while outer surface70 faces generally radially outwardly and upwardly.Side wall50 includes an annular lowerside wall section72 connected to and extending upwardly from the inner perimeter offlange48, and an annular upperside wall section74 connected to and extending upwardly fromlower section72 to the circular outer perimeter oftop wall52. In the exemplary embodiment, the sectional view ofsidewall50 illustrated inFIG. 7 shows that as viewed from the side, outer surface70 alonglower section72 is concavely curved whileinner surface68 alonglower section72 in convexly curved. As also viewed from the side, outer surface70 alongupper section74 is convexly curved whileinner surface68 alongupper section74 is concavely curved.Annular side wall50 in cross section thus has a gently curving and generally open S-shaped configuration which extends from the outer perimeter oftop wall52 to the inner perimeter offlange48 along the intersection with a vertical plane in which axis X lies.Inner surface68 as viewed from below (FIG. 3) is generally circular and concavely curved while outer surface70 as viewed from above is generally circular and convexly curved.
• Annular side wall50 includes a pair of generally triangular flats orflat sections71 configured for mounting thereonrespective gland seals24A and24B. Eachsection71 includes a generally triangular flatinner surface73 and a substantially matching generally triangularouter surface75 which is parallel toinner surface73. Eachsection71 tapers upwardly at a constant angle from adjacent the inner perimeter offlange48 to the outer perimeter oftop wall52. A cable-receiving throughhole77 is formed generally centrally insection71 extending frominner surface73 toouter surface75 to provide communication betweeninterior chamber34 and atmosphere external to shield10 when assembled. Four mounting throughholes79 are likewise formed through eachsection71 and spaced outwardly fromhole77 which is positioned at the center ofholes79.
• Top wall52 in the exemplary embodiment is a flat horizontal circular disc having a flat horizontal upwardly facing topouter surface76 and a flat horizontal downwardly facing bottominner surface78 which is parallel to surface76. Top andbottom surfaces76 and78 define therebetween a thickness oftop wall52 which is substantially the same as the thickness ofside wall50 as defined between inner andouter surfaces68 and70 thereof and typically slightly less than the thickness ofupper ring64 offlange48 although this may vary. In the exemplary embodiment,transmission wall18 is formed by blow molding or vacuum molding such thatside wall50 andtop wall52 are thinned somewhat during the formation process whileupper ring64 substantially retains its original thickness.Inner surfaces78 and68 andinner perimeter60 define therewithin a downwardly opening bowl-shapedcavity80.Cavity80 thus has a bottom entrance opening81 which is completely covered byplate16 whenshield10 is assembled. Entrance opening81 is at the bottom or lowermost portion oftransmission wall18 and is in the exemplary embodiment the widest or largest diameter portion ofcavity80, which is thus defined by the lowermost portion ofinner surface68 orinner diameter60. Whenlower ring66 is used,inner perimeter60 thus serves as the lowermost portion of the inner surface oftransmission wall18. The volume ofcavity80 is substantially the same as that ofinterior chamber34 whenshield10 is assembled inasmuch asinterior chamber34 is defined between the flattop surface36 ofplate16 and theinner perimeter60 andinner surfaces68 and78 oftransmission wall18.
• As shown inFIG. 7,wall18 has a height H2 which is the normal distance defined betweenbottom surface56 andtop surface76. Height H2 is preferably kept to a minimum in keeping with the desire to minimize the total profile ofshield10, which is represented by height H1 as previously discussed.FIG. 7 also shows thatannular wall50 has a maximum diameter D3 measured at its base, which is substantially the same as the diameter ofinner perimeter60. Generally speaking, diameter D3 is substantially greater than height H2 and in the exemplary embodiment, the ratio of diameter D3 to height H2 is on the order of about 5:1 and often falls within the range of about 4.5:1 to 5.5:1. Generally speaking, this ratio is preferably at least 4:1 or 4.5:1. The relatively minimal profile ofwall18 in combination with its overall shape substantially aids in its ability to deflect blast waves or projectiles from an external explosion or the like. More particularly, the overall circular configuration ofwall18 aids in this deflecting ability. In addition, the configuration ofannular side wall50 also aids in this deflecting ability.
• Referring now toFIGS. 1,4 and7, retainingring20 is described in greater detail.Ring20 is a substantially flat annular wall having flat circular top andbottom surfaces82 and84 which are parallel to one another and horizontal.Ring20 further includes circular inner andouter perimeters86 and88 with sixteen throughholes90 formed therein extending fromtop surface82 tobottom surface84.Holes90 are circumferentially evenly spaced from one another so that they align withholes54 inflange48 and holes46 inplate16 to receive therethroughrespective fasteners22 whenshield10 is assembled.Ring20 in the exemplary embodiment is formed of a rigid material which is typically a metal such as steel or the like althoughring20 by itself may be somewhat flexible or easily bent due to the fact that it is typically relatively thin.Ring20 helps to provide an even dispersion of the force applied by the heads offasteners22 when they are screwed into threadedholes46 so thatbottom surface56 ofannular flange48 forms at atmospheric pressure a substantially airtight and water tight seal against the mating flat annular portion oftop surface36 ofplate16.Shield10 is configured to withstand without breaking an internal pressure of at least 50 pounds per square inch (psi) withininterior chamber34, although this specification may vary depending on specific requirements. Preferably, the internal pressure whichshield10 is configured to withstand without breaking is, for instance, at least 60, 70, 80, 90, 100, 110, 120, 130 140 or 150 psi withininterior chamber34.Ring20 helps minimize the flexing ofwall18 during an internal explosion and helps prevent flames or the like from escapingshield10 to prevent ignition of external gasses or other materials.
• Shield10 is shown in its assembled configuration inFIG. 7, which illustrates that the threadedfasteners22 are tightened to provide a secure threaded engagement within the corresponding threadedholes46 ofplate16 in order to provide at atmospheric pressure the substantially airtight and water tight seal betweenbottom surface56 offlange48 and the corresponding annular circular portion oftop surface36 which engagesbottom surface56. In the exemplary embodiment, this seal is formed by the direct contact betweenbottom surface56 andtop surface36. This seal can in certain circumstances be formed with the use of an O-ring which is made of rubber or an elastomer for instance, or with the use of gaskets or sealing compounds. However, some regulations may not allow for the use of these types of configurations. For instance, the Mine Safety and Health Administration (MSHA) does not allow the use of gaskets or sealing compounds in the formation of such seals. It is noted thatshield10 is configured to meet all applicable MSHA requirements although this may vary depending on the specific circumstances in whichshield10 may be used. Depending on the circumstances, it may be required that distance D1 and distance D2 meet at least a minimum value, which is true in the case of the MSHA requirements for example. More particularly, the interface betweenbottom surface56 andtop surface36 betweeninner perimeter60 and the closest portion of eachhole46 is a continuous mating interface between two surfaces which are sufficiently smooth and held against one another tightly enough to provide a fire arresting or fire resistant path with a minimum distance D2. Likewise, the interface betweenbottom surface56 andtop surface36 extending between inner andouter perimeters60 and62 should be a continuous interface between mating surfaces which are sufficiently smooth and held together tightly enough to provide a fire resistant path of a minimum distance D1. These fire resistant paths thus normally extend along part of or all of the substantially airtight and water tight seal previously discussed. In the exemplary embodiment, all of the fire resistant path surfaces which form any of the fire resistant paths noted herein are finished to about 250 micro inches although this may vary depending on the requirements and materials used.
• With primary reference toFIGS. 5 and 9, eachgland seal24 is described in greater detail. Eachgland seal24 includes ahousing92 which houses acompressible gland94 and a pair ofbushings95 on opposed ends of the gland. Each gland seal also includes a hollow gland nut orfollower96, an interior mounting backplate98, and fourfasteners100 which in the exemplary embodiment include abolt102, anut104 threadedly secured to bolt102 along with a pair offlat washers106 and alock washer108. With primary reference toFIG. 5,housing92 is described in greater detail.Housing92 includes a substantially flatsquare mounting plate110 and acylinder112 which is rigidly secured along its base to mountingplate110 via anannular weld114.Square plate110 has substantially flat and parallel upper andlower surfaces116 and118. Four mounting throughholes120 are formed throughplate110 adjacent its corners extending fromupper surface116 tolower surface118 for receiving therethrough the threaded shafts ofbolts102. A pair oflock wire tabs122 are secured to and extend upwardly fromupper surface116 ofplate110 on opposite sides ofcylinder112 and define throughholes124 therein for receiving a lock wire (not shown) for securingnut96 in place as noted further below.Cylinder112 defines aninterior chamber126 having an upper portion defined by an upper threadedsection128 ofcylinder112 and a lower gland chamber defined by a lowernon-threaded portion130 ofcylinder112. A cable-receiving through hole132 (FIG. 9) is formed in the center ofplate110 and communicates with the gland chamber for receiving therethrough a portion of one ofcables26 or28.
• Gland nut96 includes ahexagonal head134 and an externally threadedportion136 connected thereto.Head134 may be engaged by a wrench or the like for rotatably tightening and looseningnut96 via the threaded engagement between threadedportion136 and the internal threadedportion128 ofcylinder112. A through passage is formed throughnut96 which communicates with the gland chamber and atmosphere external to shield10 whereby one ofcables26 and28 is inserted through said passage as well as throughgland94,bushings95, the gland chamber,hole132,hole77, and a centralcable receiving hole140 formed in the center ofback plate98 whereby saidcable26 or28 extends fromoutside shield10 toinside shield10 withininterior chamber34. Like mountingplate110, backplate98 includes four mountingholes142 extending therethrough for receiving the threaded shafts ofbolts102 so that the threaded engagement ofbolts102 andnuts104 secures therespective gland seal24 ontransmission wall18 with mountingsection71 clamped or sandwiched between mountingplates98 and110 under suitable pressure to provide at atmospheric pressure a gas or airtight and water tight seal therebetween. Alock wire hole138 is formed throughhead134 ofnut96 such thathole138 andholes124 in thelock tabs122 may receive a wire threaded therethrough to securenut96 in place when it is in a tightened position to preventnut96 from loosening.FIG. 9 shows the mounting of one ofcables26 and28 asnut96 is rotated to thread the nut into the cylinder and compressgland94 in the direction shown by arrow A inFIG. 9 such thatgland94 applies radially outward force against the inner surface ofcylinder112 and radially inward force against the outer surface of thecable26 or28 in order to secure the cable and provide at atmospheric pressure substantially a gas or airtight, water tight seal betweengland94 and each of the inner surface ofcylinder112 and the outer surface of the cable.
• There are additional fire resistant paths illustrated inFIGS. 9 and 9A having respective minimum distances D4, D5 and D6. More particularly,bottom surface118 of mountingplate110 andouter surface75 of mountingsection71 form a continuous mating interface between the edges ofholes132 or77 and the closest part of the outer perimeter ofplate10 where it intersects withbottom surface118 so that this interface provides a fire resistant path having a minimum distance D4 wherein the continuous interface typically provides at atmospheric pressure an airtight and water tight seal betweensurfaces118 and75.FIG. 9A illustrates a similar continuous interface serving as a fire resistant path betweenbottom surface118 andtop surface75 wherein this fire resistant path extends the shortest distance between the edge ofhole77 and the edge of one ofholes79, or between the edge ofhole132 and the edge of one ofholes120, such that this fire resistant path has a minimum distance D5.FIG. 9A also illustrates a fire resistant path which is the continuous interface between the outer surface ofcable26 or28 and the inner perimeter ofgland94 and is measured in the direction of the length of the cable. This fire resistant path has a minimum distance D6. Similarly,FIG. 9A illustrates an additional fire resistant path between the inner surface ofnon-threaded portion130 ofcylinder112 and the outer perimeter surface ofgland94 as measured in the direction in which the cable is elongated in the region ofgland94. This fire resistant path also has a minimum distance D6. Each of distances D4, D5 and D6 typically equal or exceed the MSHA minimum requirements for such fire resistant paths.
• As previously noted,blast shield10 in the exemplary embodiment is configured to meet or exceed all of the MSHA requirements with regard to explosion-proof enclosures. Some of these requirements or standards will now be discussed in greater detail. For example,transmission wall18 is configured to undergo without breaking an impact test in accordance with ASTP 2132 Version 2008-03-26 of the MSHA Approval and Certification Center, the title of which is “Lens Impact Test 18.66(a)”, which is incorporated herein by reference in its entirety. This test is typically conducted while theshield10 is assembled. However,transmission wall18 is configured to pass this test as a stand alone component. The impact test requires that the center of the lens is to be the point of impact, which in this case is the center oftop wall52, which is illustrated at axis X inFIG. 6. The test is more particularly formed using a drop weight test apparatus which is shown and described in ASTP 2132. The test apparatus includes a four pound weight, the bottom of which includes a one inch hemispherical striking surface which is used to strike the center of the lens when dropped. A height adjustment mechanism such as a height adjustment screw is used to control the height from which the weight is dropped during the test. The drop distance is defined as the distance (prior to dropping the weight) between the striking surface of the drop weight and the top of the accessory, namely the center of the lens which in the present case is the center oftop wall52 when positioned horizontally. For round windows or lenses, the height of the fall or distance that the drop weight is to be dropped varies depending of the diameter of the lens. For a lens having a diameter of one inch to less than four inches, the height of fall is six inches; where the diameter is greater than or equal to four inches and less than five inches, the height of fall is nine inches; when the diameter is greater than or equal to five inches and less than six inches, the height of fall is fifteen inches; and when the diameter is equal to or greater than six inches, the height of fall is twenty-four inches. ASTP 2132 also provides the height of fall for windows or lenses which are irregularly shaped, although those are not stated here for brevity.
• In addition,transmission wall18 is configured to undergo without breaking or other defined defect a thermal shock test in accordance with ASTP 2131 Version 2008-04-23 of the MSHA Approval and Certification Center, which is a thermal shock test on windows or lenses, which is incorporated herein by reference in its entirety. This test is conducted with theshield10 in assembled form althoughtransmission wall18 is also configured to pass this test as a stand alone component. In order to pass this thermal shock test, ASTP 2131 requires that the lens after the test may not have any defects greater than as defined in ACRI 2102. To that effect, ACRI 2102 Version 2008-11-26 of the MSHA Approval and Certification Center, having a title of “Criteria for the Evaluation Of A Window Or Lens Used As Part Of An Explosion-Proof Enclosure”, is incorporated herein by reference in its entirety. ASTP 2131 indicates that a defect shall be defined as a crack, chip, break, flaw, fracture, warpage or crazing observed on the sample or assembly, thus namely thetransmission wall18 orshield10. ACRI 2102 provides the definition of a crack as being a separation of material throughout its thickness; and the definition of craze as defects that appear as surface cracks and have a silvery appearance when light is passed through the material. An abbreviated description of the thermal shock test of ASTP 2131 is now described. In short, the thermal shock test involves the heating of the lens to a certain temperature and the immersing of the lens into water at a lower temperature. A drum or tank of water is provided which is of a sufficient size in order to allow the entire sample to be immersed, namely theentire shield10 where tested as assembled. The volume of the water is also to be sufficient to cool the sample without raising the temperature of the water by more than 5° C. To perform the test, the shield is heated in an oven so that the temperature of the lens or transmission wall reaches 115° C. (240° F.) for a polycarbonate lens or 150° C. (302° F.) for a glass lens. The water in the tank is to be between 15° C. (59° F.) and 20° C. (68° F.) prior to immersing the heated sample. Once the temperature of the lens has stabilized for a period of fifteen minutes, the sample is removed from the oven and immediately immersed in the cooler water and allowed to cool to the temperature of the water. The sample is then removed from the water and inspected for visual defects such as breakage or the other defects noted above.
• Furthermore,blast shield10 is configured to pass the test as described in ASTP 2137 Version 2005-11-08 of the MSHA Approval and Certification Center, having a title of “Requirements ForExplosion Testing Per 30 CFR 18.62”, which is incorporated herein by reference in its entirety. In short, this test creates an internal explosion within the interior chamber of the enclosure orblast shield10 under specific circumstances while the shield is disposed within a gallery or explosion test chamber. In short, the explosion-proof container orblast shield10 is positioned within an explosion test gallery or chamber with the enclosure and test chamber filled with an explosive mixture, and a single spark plug is positioned in order to ignite the explosive mixture within the enclosure such asblast shield10 to determine if the enclosure meets various requirements.
• In order to fully meet the requirements of ASTP 2137, the enclosure must undergo a minimum of sixteen of such tests.Blast shield10 is configured to undergo these sixteen tests and pass all of the various criteria required by ASTP 2137. Thus,blast shield10 is likewise capable of undergoing any lesser number of these tests, that is, any number from one to fifteen of the tests, while passing any number of the criteria required by ASTP 2137. The test more particularly requires that the enclosure is filled with and surrounded by an explosive mixture of natural gas and air or methane and air. If natural gas is used, the content of methane and ethane shall total at least 98% by volume with nitrogen and propane the remainder. The internal mixture within the enclosure is ignited by an electrical spark of 100 millijoules or greater. ASTP 2137 describes the various tests in much greater detail, including several variables which are used to meet the full requirements of the explosion test. ASTP 2137 even requires that the test must be conducted under conditions most likely to result in test failure, such as 9.6% CH4 (methane) gas-air mixture, optimum spark location and testing with and without dummies, which are defined as parts substituted during explosion testing for internal electrical components. Some of the tests also include placing coal dust within the enclosure prior to ignition. The passing criteria or acceptable performance for the tested explosion-proof enclosure is, as a result of the ignition and internal explosion within the enclosure, no discharge of flame from the enclosure; no ignition of the explosive mixture in the gallery or explosion test chamber; no development of after burning, which is defined as the combustion of a flammable mixture that is drawn into an enclosure after an internal explosion has occurred; no rupture of any part of the enclosure; no permanent distortion of any planar surface of the enclosure exceeding 0.040 inch per linear foot; no excessive clearances along flame-arresting paths following retightening of fastenings, as required; no pressure exceeding 125 psi, unless the enclosure has withstood a static pressure of twice the highest value recorded in the test; and no looseness or physical damage to a window or lens.
• Shield10 is also configured to meet certain ingress protection standards, such as those set forth by the International Electrical Commission (IEC), that is, protection against the ingress or entry of solid objects and liquids into an enclosure.Shield10 is configured to have at least anIP 66 rating or IP 67 rating in accordance with IEC Publication 60529 (IEC 60529), which is incorporated herein by reference. In the rating, IP stands for ingress protection, the first number indicates the level of protection against ingress of solid objects, and the second number indicates the level of protection against ingress of liquids. TheIP 66 rating thus specifies thatblast shield10 is dust tight or totally protected against dust, and is protected against powerful jets of water from any direction. The IP 67 rating specifies thatblast shield10 is dust tight or totally protected against dust, and is protected against temporary immersion in water at a depth between 15 cm and 1 meter. This rating system, or rating itself, is sometimes referred to as the IP Code, International Protection Rating or Ingress
• Protection Rating. Under IEC 60529, the first number ratings basically mean the following: 0=no special protection; 1=protected againstsolid objects 50 mm or greater; 2=protected againstsolid objects 12 mm or greater; 3=protected against solid objects 2.5 mm or greater; 4=protected againstsolid objects 1 mm or greater; 5=protected against dust (no harmful deposit); and 6=totally protected against dust. Under IEC 60529, the second number ratings basically mean the following: 0=not protected; 1=protected against vertically dripping water; 2=protected against vertical dripping water when enclosure is tilted up to 15° from the vertical; 3=protected against direct sprays of water up to 60° from the vertical; 4=protected against splashing water from any direction; 5=protected against low pressure jets of water from any direction; 6=protected against powerful jets of water from any direction (temporary flooding of water, e.g. for use on ship decks against heavy seas); 7=protected against temporary immersion in water at a depth between 15 cm and 1 meter; and 8=protected against continuous or long periods of immersion at a depth greater than 1 meter.Blast shield shield10 is thus obviously also protected at all of the IP ratings less thanIP 66.
• IP ratings sometimes include a third number, from earlier versions of IEC 60529, which related to resistance to mechanical impact, which was identified as energy measured in joules which the impacted enclosure could withstand without breaking. There is also a newer IK number or rating which is in many cases now used in place of the earlier specifications. The IK number is specified in IEC 62262 or European standard EN 62262 (formerly known as EN 50102), each of which is incorporated herein by reference. These impact tests are generally similar to the MSHA impact test discussed further above. Using one of these impact tests,transmission wall18 is configured to undergo or withstand without breaking an impact energy of at least 5 joules, which is equivalent to an impact from dropping a 1.7 kg (3.3 lbs.) weight from a height of 29.5 cm (15.75 inch), or 6 joules, which is equivalent to an impact from dropping a 1.5 kg (3.75 lbs.) weight from a height of 40 cm (11.6 inch).
• FIG. 10 illustrates analternate gland seal146 which may be used with analternate transmission wall18A. This arrangement would typically be used when the requirements regarding the flame path are less stringent than those associated with the use ofgland seal24.Alternate transmission wall18A is very similar towall18 except that it includes one ormore mounting sections71A which are analagous to mounting sections of71 but have only a singlecable receiving hole77A formed therethrough without the use of mounting holes corresponding to mountingholes79 of the mountingsection71 ofwall18.Hole77A is typically somewhat larger thanhole77 to accommodate thealternate gland seal146.Gland seal146 includes an externally threadedtube148 which extends throughhole77A, an internally threadedgland nut150 which threadedly engages one end oftube148, and agland152 which is disposed within a gland chamber formed withingland nut150. Anoutside mounting nut154 and aninside mounting nut156 are threaded onto externally threadedtube148 so thatoutside nut154 engages the outer surface of mountingsection71A and insidenut156 engages the inner surface of mountingsection71A in order to securegland seal146 to mountingsection71A. The basic operation ofgland seal146 is similar to that ofgland seal24 in that the tightening ofgland nut150 ontube148 compresses thegland152 in order to provide at atmospheric pressure the gas or airtight and water tight seal between the gland, the cable and inner surface ofnut150.Cable26 or28 thus passes throughtube148 andgland nut150 to extend from outside the blast shield to inside its interior chamber.
• With reference toFIG. 11, a wireless transmission system in which shields10 are used is now described. There are a number of operational environments in which the wireless transmissionsystem utilizing shields10 may be typically used.FIG. 11 is a diagrammatic view illustrating the operational environment as being anunderground mine160. However, the system may be used in other underground environments such as a subway. In addition, the system is suited for use in various industries (typically above ground), especially within large plants in which wireless mesh networks are particularly desirable. Wireless mesh networks are advantageous in one regard in that they eliminate a large amount of electrical wiring or other signal transmission lines which would otherwise be used. The system is also configured for use in petrochemical industry or other industries which utilize volatile liquids or include flammable gasses. As previously noted, shields10 are specifically configured to prevent any internal arcing or explosions from igniting such flammable gasses external to the shield. Other industries which utilize highly flammable materials such as gun powder or fine dust particles which could easily be ignited may also be served well with the present system.
• With continued reference toFIG. 11,mine160 includes a mine shaft which may branch as shown and include a mine portal orentrance162 or multiple entrances. As is well known in the mining industry, some underground mines are very extensive and may extend for miles in various directions with multiple branches.FIG. 11 further shows anelectric power source164 withelectric power lines166 in electrical communication withpower source164 andpower cables26 of several blast shields10. As previously noted, the battery of theinternal components14 is kept charged via its charger by this connection topower source164. As shown inFIG. 11, some of the shields are marked10A andothers10B. The ones marked10A utilizepower cable26, but do not utilize thesignal transmission cable28. Thus, blast shields10A may be formed withoutcable28,gland seal24B and the associated mountingsection71 shown in the previous figures. On the other hand, the shields which are generally closer toentrance162 are marked asshields10B and include thetransmission cable28 in addition to thepower cable26. The system further includescommunication lines168 which are in communication withtransmission cables28 and also with an information receiving unit which is external to the mine.Unit170 may represent a variety of devices which typically include some sort of processing unit for translating data received vialines168 into information which may, for example, be tracked by a computer or viewed on a screen.Unit170 may thus include a computer for running a suitable program for processing or translating information received thereby.
• FIG. 11 also shows severalinertial sensor units172 havingantennas174. One ofunits172 is shown at a battery charging and resetstation176 which is in electrical communication withpower source164. Eachinertial sensor unit172 typically includes a housing containing a radio frequency transmitter, an inertial sensor, a micro processor and a battery for powering the unit. The inertial sensor during movement produces velocity data which the micro processor translates into a signal which is transmitted by the transmitter viaantenna174 to any of the receivers which are housed within blast shields10 within the transmission range of the givenunit172.Shields10 are typically spaced 500 to 1000 feet apart from one another and thus serve as nodes or relays for receiving transmissions either fromunit172 or from another transmitter within adifferent shield10 and relaying the signal via its transmitter to any other receivers within its transmission range. Radio frequency signals may thus be transmitted from outside to inside the blast shield to be received by the internal receiver as well as transmitted from the internal transmitter from inside to outside the blast shield throughtransmission wall18 due to the fact that it is formed of a material which is sufficiently permeable to radio frequency or sufficiently electromagnetically transparent to allow for the radio waves to pass therethrough. Althoughunit172 may include an inertial sensor as noted, it may also include devices other than inertial sensors for producing signals to be transmitted to the relay stations provided within eachshield10.Inertial sensor units172 may be positioned at charging and resetstation176 in order to charge the onboard battery as well as to set or reset the alignment of the inertial sensor to a home position. In the underground mine setting, this setting or resetting process is typically accomplished utilizing a pair of underground geodetic survey monuments. The specific use of such an underground inertial sensor tracking system is described in greater detail in U.S. Pat. No. 7,400,246 granted to Breeding, which is incorporated herein by reference.Inertial sensor units172 may be hand held units which can be carried by hand by miners or other personnel and or they may be carried by an individual by, for example, securingunit172 to a belt which can be worn by an individual or some other type of body wearable pack.Units172 may also be mounted on mining machinery or other mobile machines for tracking their movement.
• As noted above,unit172 may utilize a transmitter without the use of an inertial sensor, and thusunit172 also represents more broadly a transmitter unit which may be configured to transmit signals related to any kind of information or data packets with which the wireless transmission system of the invention may be used. One feasible use for the present system relates to life cycle monitors which may be used on various types of machines for the purpose of tracking or monitoring the life of a given machine in order to ascertain when the machine needs to be repaired or replaced. For example, vibration sensors or temperature sensors may be mounted on or near such a machine in order to monitor the machine's vibrations and temperature, which can provide pertinent information as to what stage the machine is in its life cycle. Such sensors may produce signals which can be wirelessly transmitted via the electric mesh network of the present invention to a computer or the like at a remote location as generally indicated at170 inFIG. 11. The signals from the life cycle sensors or the like may enter the wireless mesh network initially either via a wireless transmission or via transmission lines. For instance, a machine's life cycle sensor may be in communication with its own transmitter which transmits wireless signals to a receiver within one ofshields10 for retransmission via the transmitter within the shield. Such life cycle sensors could also be wired via transmission lines such aslines28 to transmit the signal via the transmission line into the interior chamber of the shield so that the internal transmitter thereof would itself begin the wireless transmissions within the network. The present invention may also be useful in process control such that various types of sensors could similarly produce signals which could be transmitted over the wireless mesh network to, for example, a remote controller such as indicated generally at170 which would control a device associated with the process control sensors in accordance with the signals received therefrom.Controller170 could thus provide return signals over the wireless mesh network so that the transmitted signal would control the given device. This would allow for the remote control of various types of machines or devices within a large manufacturing plant, for example.
• Blast shield10 thus provides an enclosure for housing various electronic components including a wireless transmitter so that a wireless mesh network may be used in various environments. For instance, shield10 provides a blast resistant or blast proof enclosure for protecting the internal electronic components from blast waves or shock waves or various materials which may impact the shield during explosions or the collapse of a mine or other structure.Shield10 also provides a gas tight enclosure with suitable fire resistant or fire arresting paths to prevent the escape of flames or electrical sparks from inside the shield which could otherwise ignite flammable materials external to the enclosure. In addition,shield10 provides a dust proof and water proof or water resistant enclosure which thus protects the internal components from dusty and moist environments.
• In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed.
• Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described.

Claims (20)

1. A blast shield comprising:

a blast resistant housing;

an interior chamber formed in the housing and substantially sealed from atmosphere external to the housing; and

a transmission wall of the housing formed of a material through which a wireless signal is transmittable from inside the interior chamber to outside the housing.

2. The blast shield ofclaim 1 wherein the transmission wall comprises an annular sidewall.

3. The blast shield ofclaim 2 wherein the annular sidewall tapers upwardly and radially inwardly.

4. The blast shield ofclaim 3 wherein the transmission wall comprises an annular flange extending radially outwardly from the annular sidewall; and the annular sidewall tapers upwardly and radially inwardly from adjacent the annular flange.

5. The blast shield ofclaim 4 wherein the transmission wall comprises a top wall extending radially inward from the annular sidewall; and the annular sidewall tapers upwardly and radially inwardly from adjacent the annular flange to adjacent the top wall.

6. The blast shield ofclaim 2 wherein the annular sidewall comprises an annular lower sidewall section and an annular upper sidewall section connected to and extending upwardly from the lower sidewall section; the lower sidewall section has an outer surface which is concavely curved as viewed from the side; and the upper sidewall section has an outer surface which is convexly curved as viewed from the side.

7. The blast shield ofclaim 2 wherein the transmission wall comprises an annular flange extending radially outwardly from the annular sidewall; and the annular sidewall extends upwardly from the annular flange.

8. The blast shield ofclaim 7 wherein the transmission wall comprises a top wall extending radially inward from the annular sidewall.

9. The blast shield ofclaim 1 wherein the transmission wall has a bowl-shaped configuration.

10. The blast shield ofclaim 1 further comprising a retaining ring; an annular flange of the transmission wall; and a base of the housing; and wherein the flange is clamped between the retaining ring and the base.

11. The blast shield ofclaim 1 further comprising a wireless transmitter in the interior chamber.

12. The blast shield ofclaim 11 further comprising a cavity defined by the transmission wall; and wherein the transmitter is within the cavity.

13. The blast shield ofclaim 1 further comprising a through hole formed in the transmission wall; and a cable which extends from outside the transmission wall through the hole into the interior chamber.

14. The blast shield ofclaim 13 further comprising a gland seal around the cable adjacent the transmission wall.

15. The blast shield ofclaim 14 further comprising an internal plate; an external plate; a gland seal housing secured to one of the plates; and a portion of the transmission wall clamped between the plates.

16. The blast shield ofclaim 1 further comprising a first component of the housing; a first fire-arresting surface on the first component; a second component of the housing; a second fire-arresting surface on the second component; an interface between the first and second fire-arresting surfaces to provide a fire resistant path configured to prevent electrical arcing or an explosion within the interior chamber from exiting the housing so as to present a danger of igniting flammable material external to the housing.

17. The blast shield ofclaim 1 wherein the housing is configured to withstand an internal pressure of at least 50 pounds per square inch within the interior chamber without breakage of the housing.

18. The blast shield ofclaim 1 wherein the housing has at least an IP 66 rating in accordance with IEC Publication 60529.

19. The blast shield ofclaim 1 wherein the transmission wall is configured to undergo without breaking one of (a) an impact energy of at least 5 joules; (b) an impact test in accordance with ASTP 2132 Version 2008-03-26 of the Mine Safety and Health Administration (MSHA) Approval and Certification Center; and (c) a thermal shock test in accordance with ASTP 2131 Version 2008-04-23 of the Mine Safety and Health Administration (MSHA) Approval and Certification Center.

20. The blast shield ofclaim 1 wherein the housing is configured to undergo an explosion within the interior chamber in accordance with ASTP 2137 Version 2005-11-08 of the Mine Safety and Health Administration (MSHA) Approval and Certification Center with a result selected from the group consisting of (a) no discharge of flame from within the interior chamber to atmosphere external to the housing; (b) no rupture of any part of the housing; (c) no permanent distortion of any planar surface of the housing exceeding 0.040 inch per linear foot; (d) no ignition of an explosive mixture in an explosion test chamber in which the blast shield is disposed during the explosion; and (e) no combustion of a flammable mixture that is drawn into the interior chamber after the explosion has occurred while the blast shield is disposed within an explosion test chamber filled with an explosive mixture.

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