BLAST SHIELD FOR USE IN WIRELESS TRANSMISSION SYSTEM
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.
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 INVENTIONThe 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.
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.
Similar numbers refer to similar parts throughout the drawings.
DETAILED DESCRIPTION OF THE INVENTIONThe blast shield of the present invention is indicated generally at 10 in
Before describing the blast shield in greater detail, internal components 14 are briefly described. Components 14 typically include a radio transceiver unit 15, an antenna 17 connected thereto, battery-charging power wires 19 and optionally signal-transmission lines 21. Unit 15 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 via antenna 17. Unit 15 further includes a battery which powers the receiver and transmitter and a battery charger for charging the battery via power wires 19. The charger thus typically includes a rectifier for transforming alternating current to direct current. Unit 15 may also include a microprocessor for processing incoming wireless signals and translating them into outgoing signals over transmission lines 21, which may be in the form of fiber optic lines or electric wires for example.
With primary reference to
Top 30 and bottom 32 define therebetween a height H1 (
With primary reference to
With primary reference to
Wall 18 includes an annular flange 48 which in the exemplary embodiment is substantially circular and horizontally flat. Flange 48 is substantially concentric about axis X when shield 10 is assembled. Wall 18 further includes an annular side wall 50 which is rigidly secured to and extends upwardly from the inner perimeter of annular flange 48 to a substantially flat horizontal and circular top wall 52 which is rigidly secured to the top of side wall 50 and extends radially inwardly therefrom. Sixteen through holes 54 are formed in annular flange 48 extending from a flat horizontal bottom surface 56 thereof to a flat horizontal top surface 58 thereof. Holes 54 are circumferentially spaced in the same manner as threaded holes 46 and plate 16 so as to be vertically aligned therewith for receiving therethrough respective fasteners 22 when shield 10 is assembled. Bottom surface 56 has an annular configuration which is circular in the exemplary embodiment and which is also flat and horizontal. Bottom surface 56 serves as a flame-arresting or fire-arresting path surface which in the exemplary embodiment is finished to about 250 micro inches. Annular flange 48 has circular inner and outer perimeters 60 and 62 which intersect bottom surface 56 and are concentric about axis X when shield 10 is assembled. Inner and outer perimeters 60 and 62 at their intersections with bottom surface 56 define therebetween a distance D1 (
Annular side wall 50 is substantially circular as viewed from above and tapers upwardly and radially inwardly from its circular annular connection to the inner perimeter of flange 48 to its circular annular connection to the outer perimeter of circular top wall 52. Side wall 50 has a generally frustoconical configuration and has an inner surface 68 which communicates with inner perimeter 60 and an outer surface 70 which communicates with top surface 58 of flange 48. Inner surface 68 faces generally radially inwardly and downwardly while outer surface 70 faces generally radially outwardly and upwardly. Side wall 50 includes an annular lower side wall section 72 connected to and extending upwardly from the inner perimeter of flange 48, and an annular upper side wall section 74 connected to and extending upwardly from lower section 72 to the circular outer perimeter of top wall 52. In the exemplary embodiment, the sectional view of sidewall 50 illustrated in
Annular side wall 50 includes a pair of generally triangular flats or flat sections 71 configured for mounting thereon respective gland seals 24A and 24B. Each section 71 includes a generally triangular flat inner surface 73 and a substantially matching generally triangular outer surface 75 which is parallel to inner surface 73. Each section 71 tapers upwardly at a constant angle from adjacent the inner perimeter of flange 48 to the outer perimeter of top wall 52. A cable-receiving through hole 77 is formed generally centrally in section 71 extending from inner surface 73 to outer surface 75 to provide communication between interior chamber 34 and atmosphere external to shield 10 when assembled. Four mounting through holes 79 are likewise formed through each section 71 and spaced outwardly from hole 77 which is positioned at the center of holes 79.
Top wall 52 in the exemplary embodiment is a flat horizontal circular disc having a flat horizontal upwardly facing top outer surface 76 and a flat horizontal downwardly facing bottom inner surface 78 which is parallel to surface 76. Top and bottom surfaces 76 and 78 define therebetween a thickness of top wall 52 which is substantially the same as the thickness of side wall 50 as defined between inner and outer surfaces 68 and 70 thereof and typically slightly less than the thickness of upper ring 64 of flange 48 although this may vary. In the exemplary embodiment, transmission wall 18 is formed by blow molding or vacuum molding such that side wall 50 and top wall 52 are thinned somewhat during the formation process while upper ring 64 substantially retains its original thickness. Inner surfaces 78 and 68 and inner perimeter 60 define therewithin a downwardly opening bowl-shaped cavity 80. Cavity 80 thus has a bottom entrance opening 81 which is completely covered by plate 16 when shield 10 is assembled. Entrance opening 81 is at the bottom or lowermost portion of transmission wall 18 and is in the exemplary embodiment the widest or largest diameter portion of cavity 80, which is thus defined by the lowermost portion of inner surface 68 or inner diameter 60. When lower ring 66 is used, inner perimeter 60 thus serves as the lowermost portion of the inner surface of transmission wall 18. The volume of cavity 80 is substantially the same as that of interior chamber 34 when shield 10 is assembled inasmuch as interior chamber 34 is defined between the flat top surface 36 of plate 16 and the inner perimeter 60 and inner surfaces 68 and 78 of transmission wall 18.
As shown in
Referring now to
Shield 10 is shown in its assembled configuration in
With primary reference to
Gland nut 96 includes a hexagonal head 134 and an externally threaded portion 136 connected thereto. Head 134 may be engaged by a wrench or the like for rotatably tightening and loosening nut 96 via the threaded engagement between threaded portion 136 and the internal threaded portion 128 of cylinder 112. A through passage is formed through nut 96 which communicates with the gland chamber and atmosphere external to shield 10 whereby one of cables 26 and 28 is inserted through said passage as well as through gland 94, bushings 95, the gland chamber, hole 132, hole 77, and a central cable receiving hole 140 formed in the center of back plate 98 whereby said cable 26 or 28 extends from outside shield 10 to inside shield 10 within interior chamber 34. Like mounting plate 110, back plate 98 includes four mounting holes 142 extending therethrough for receiving the threaded shafts of bolts 102 so that the threaded engagement of bolts 102 and nuts 104 secures the respective gland seal 24 on transmission wall 18 with mounting section 71 clamped or sandwiched between mounting plates 98 and 110 under suitable pressure to provide at atmospheric pressure a gas or airtight and water tight seal therebetween. A lock wire hole 138 is formed through head 134 of nut 96 such that hole 138 and holes 124 in the lock tabs 122 may receive a wire threaded therethrough to secure nut 96 in place when it is in a tightened position to prevent nut 96 from loosening.
There are additional fire resistant paths illustrated in
As previously noted, blast shield 10 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 wall 18 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 the shield 10 is assembled. However, transmission wall 18 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 of top wall 52, which is illustrated at axis X in
In addition, transmission wall 18 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 the shield 10 in assembled form although transmission wall 18 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 the transmission wall 18 or shield 10. 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 the entire shield 10 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 shield 10 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 For Explosion 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 or blast shield 10 under specific circumstances while the shield is disposed within a gallery or explosion test chamber. In short, the explosion-proof container or blast shield 10 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 as blast shield 10 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 shield 10 is configured to undergo these sixteen tests and pass all of the various criteria required by ASTP 2137. Thus, blast shield 10 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.
Shield 10 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. Shield 10 is configured to have at least an IP 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. The IP 66 rating thus specifies that blast shield 10 is dust tight or totally protected against dust, and is protected against powerful jets of water from any direction. The IP 67 rating specifies that blast shield 10 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 against solid objects 50 mm or greater; 2=protected against solid objects 12 mm or greater; 3=protected against solid objects 2.5 mm or greater; 4=protected against solid 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 shield 10 is thus obviously also protected at all of the IP ratings less than IP 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 wall 18 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).
With reference to
With continued reference to
As noted above, unit 172 may utilize a transmitter without the use of an inertial sensor, and thus unit 172 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 at 170 in
Blast shield 10 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, shield 10 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. Shield 10 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, shield 10 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
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 of claim 1 wherein the transmission wall comprises an annular sidewall.
3. The blast shield of claim 2 wherein the annular sidewall tapers upwardly and radially inwardly.
4. The blast shield of claim 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 of claim 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 of claim 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 of claim 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 of claim 7 wherein the transmission wall comprises a top wall extending radially inward from the annular sidewall.
9. The blast shield of claim 1 wherein the transmission wall has a bowl-shaped configuration.
10. The blast shield of claim 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 of claim 1 further comprising a wireless transmitter in the interior chamber.
12. The blast shield of claim 11 further comprising a cavity defined by the transmission wall; and wherein the transmitter is within the cavity.
13. The blast shield of claim 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 of claim 13 further comprising a gland seal around the cable adjacent the transmission wall.
15. The blast shield of claim 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 of claim 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 of claim 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 of claim 1 wherein the housing has at least an IP 66 rating in accordance with IEC Publication 60529.
19. The blast shield of claim 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 of claim 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.
Type: Application
Filed: Jan 11, 2010
Publication Date: Jul 15, 2010
Inventor: Michael J. Millam (Norfolk, VA)
Application Number: 12/685,236
International Classification: H04B 1/034 (20060101); H05K 5/00 (20060101);