U.S. patent application number 12/685236 was filed with the patent office on 2010-07-15 for blast shield for use in wireless transmission system.
Invention is credited to Michael J. Millam.
Application Number | 20100178887 12/685236 |
Document ID | / |
Family ID | 42319419 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100178887 |
Kind Code |
A1 |
Millam; Michael J. |
July 15, 2010 |
BLAST SHIELD FOR USE IN WIRELESS TRANSMISSION SYSTEM
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.
Inventors: |
Millam; Michael J.;
(Norfolk, VA) |
Correspondence
Address: |
SAND & SEBOLT
AEGIS TOWER, SUITE 1100, 4940 MUNSON STREET, NW
CANTON
OH
44718-3615
US
|
Family ID: |
42319419 |
Appl. No.: |
12/685236 |
Filed: |
January 11, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61204953 |
Jan 13, 2009 |
|
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|
Current U.S.
Class: |
455/128 ; 174/50;
174/520 |
Current CPC
Class: |
H04B 1/034 20130101 |
Class at
Publication: |
455/128 ; 174/50;
174/520 |
International
Class: |
H04B 1/034 20060101
H04B001/034; H05K 5/00 20060101 H05K005/00 |
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.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] 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.
[0003] 2. Background Information
[0004] 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
[0005] 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
[0006] 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.
[0007] FIG. 1 is a perspective view of the blast shield of the
present invention shown mounted on a wall or other support
structure.
[0008] FIG. 2 is a top plan view of the base plate of the blast
shield.
[0009] FIG. 3 is a bottom plan view of the transmission wall of the
blast shield.
[0010] FIG. 4 is a top plan view of the retaining ring.
[0011] FIG. 5 is a perspective view of the housing of the gland
seal.
[0012] 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.
[0013] FIG. 7 is a sectional view taken on line 7-7 of FIG. 6.
[0014] FIG. 8 is an enlarged sectional view of the encircled
portion of FIG. 7.
[0015] FIG. 9 is a sectional view taken on line 9-9 of FIG. 6
illustrating the connection or assembly of the gland seal to
provide the seal around the associated cable or wire.
[0016] FIG. 9A is a sectional view taken on line 9A-9A if FIG. 6
illustrating the gland seal and the associated fire resistant
pathways thereof.
[0017] FIG. 10 is similar to FIG. 9 and shows an alternate
embodiment of a gland seal.
[0018] FIG. 11 is a diagrammatic view showing several of the blast
shields within a wireless transmission system.
[0019] Similar numbers refer to similar parts throughout the
drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The blast shield of the present invention is indicated
generally at 10 in FIG. 1. Blast shield 10 is shown mounted on a
wall or other support structure 12 and is used to house various
internal components 14 (shown in dashed lines in FIG. 6) which are
part of a wireless transmission system such as shown in FIG. 11.
Shield 10 is configured in part to protect internal components 14
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. Shield
10 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 shield 10. Shield 10 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.
[0021] 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.
[0022] With primary reference to FIG. 1, shield 10 includes a rigid
base mounting structure in the form of a flat circular base or base
plate 16, a blast-resistant dome shaped transmission wall 18 and a
securing mechanism which secures wall 18 to plate 16 and includes a
circular retaining ring 20 and multiple fasteners 22. In the
exemplary embodiment, there are sixteen fasteners 22 which are
circumferentially evenly spaced along ring 20. Shield 10 further
includes a pair of gland seals 24A and 24B which are configured to
provide a water tight, airtight seal around wires or cables such as
flexible electric power cable 26 and flexible signal transmission
cable 28, respectively, which extend through holes formed in
transmission wall 18 of shield 10. Each of these cables includes an
internal electrical conductor or wire with an outer layer of
electrical insulation. Power cable 26 is in electrical
communication with the internal battery charger via power wires 19
(FIG. 6) when shield 10 is assembled. Cable 28 is likewise in
electrical or optical communication with unit 15 via transmission
lines 21 so that signals may be transmitted through lines 21 and
cable 28 from inside shield 10 to outside shield 10. Although
shield 10 may be mounted as shown in FIG. 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 a top 30 and a bottom 32 so that plate 16 defines bottom
32 and transition wall 18 is mounted atop plate 16 so as to define
top 30, as oriented in FIG. 7. In the orientation shown in FIG. 7,
the outer perimeter of plate 16 and ring 20 are thus concentric
about a vertical axis X passing through the center of shield 10.
The various substantially circular portions of transmission wall 18
are also substantially concentric about axis X with exceptions
noted further below. When assembled, shield 10 defines an interior
chamber 34 in which internal components 14 are disposed.
[0023] Top 30 and bottom 32 define therebetween a height H1 (FIG.
7) which defines the profile of shield 10 or the approximate
maximum normal distance which shield 10 will extend outwardly from
the surface of a support structure such as support structure 12
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 hit wall 18 during an explosion, structural
collapse or the like.
[0024] With primary reference to FIGS. 1, 2 and 7, base plate 16 is
described in greater detail. Plate 16 is in the exemplary
embodiment a substantially circular rigid disc typically formed of
metal and having a flat circular top surface 36, a parallel flat
circular bottom surface 38 and a circular outer perimeter 40
extending therebetween. When shield 10 is in the upright position
shown in FIG. 7, surfaces 36 and 38 are substantially horizontal
and bottom surface 38 defines bottom 32 of shield 10. A plurality
of elongated mounting through holes 42 are formed in plate 16
adjacent outer perimeter 40 and extend from top surface 36 to
bottom surface 38. In the exemplary embodiment, there are eight
mounting holes 42 each of which receives therethrough a mounting
fastener 44 which may be in the form of a bolt, screw or any other
suitable fastener depending on the nature of the support structure
12 on which shield 10 is to be mounted. Holes 42 are
circumferentially equally spaced from one another and
circumferentially elongated to provide for some adjustability
during the mounting of shield 10 on support structure 12 to
accommodate for holes in structure 12 which may be difficult to
accurately form therein. A plurality of threaded holes 46 is also
formed in plate 16 extending from top surface 36 toward bottom
surface 38. In the exemplary embodiment, there are sixteen threaded
holes 46 lying along a common circle which is disposed radially
inwardly of the circle along which mounting holes 42 lie. Each of
these circles is concentric about axis X when shield 10 is
assembled. Fasteners 22 are typically in the form of bolts having
externally threaded shafts which respectively are screwed into
threaded holes 46 so that each fastener 22 provides a threaded
engagement with plate 16 within each respective hole 46 to secure
ring 20 and wall 18 to plate 16. Additional threaded mounting holes
(not shown) may be formed radially inwardly of holes 46 for
securing internal components 14 to plate 16. However, these holes
would be blind holes extending from top surface 36 toward bottom
surface 38 without communication with bottom surface 38.
[0025] With primary reference to FIGS. 1, 3 and 7, transmission
wall 18, which is substantially circular as viewed from above, is
now described in greater detail. As previously noted, wall 18 is
generally dome shaped or bowl shaped and generally concentric about
axis X when shield 10 is assembled. In accordance with the
invention, transmission wall 18 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 protect internal
components 14 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, wall 18 is formed of a suitable plastic
material which provides these properties. In the exemplary
embodiment, wall 18 is formed of a polycarbonate resin
thermoplastic which provides substantial strength and impact
resistance, such as the polycarbonate sold under the name
LEXAN.RTM..
[0026] 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 (FIGS. 3 and 8) which is the shortest distance
therebetween as measured along bottom surface 56 and which in the
exemplary embodiment is the distance between inner and outer
perimeter 60 and 62 as measured along the intersection between
bottom surface 56 and a vertical plane in which axis X lies when
shield 10 is assembled. Distance D1 may also be described as being
normal to a tangent to inner perimeter 60 or outer perimeter of 62.
In the exemplary embodiment, flange 48 includes an upper ring 64
and a lower ring 66 which is rigidly and non-removably secured at
its upper surface to the lower surface of ring 64 in order to add
to the thickness of flange 48. Depending on the specific
requirements, the use of lower ring 66 may be eliminated. In the
exemplary embodiment, lower ring 66 defines bottom surface 56. If
lower ring 66 is not used, then the lower surface of upper ring 64
serves as the flat horizontal bottom surface to provide the
fire-arresting path surface of flange 48.
[0027] FIGS. 3 and 8 also illustrate a distance D2 which is the
shortest distance along the fire arresting path surface 56 of
flange 48 between inner perimeter 60 and a given one of holes 54.
Distance D2 in the exemplary embodiment is the distance between
inner perimeter 60 and the closest portion of hole 54 as measured
along the intersection between bottom surface 56 and a vertical
plane in which axis X lies when shield 10 is assembled. In
addition, distance D2 in the exemplary embodiment is normal to a
tangent of inner perimeter 60.
[0028] 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 FIG. 7 shows that as viewed from the side, outer
surface 70 along lower section 72 is concavely curved while inner
surface 68 along lower section 72 in convexly curved. As also
viewed from the side, outer surface 70 along upper section 74 is
convexly curved while inner surface 68 along upper section 74 is
concavely curved. Annular side wall 50 in cross section thus has a
gently curving and generally open S-shaped configuration which
extends from the outer perimeter of top wall 52 to the inner
perimeter of flange 48 along the intersection with a vertical plane
in which axis X lies. Inner surface 68 as viewed from below (FIG.
3) is generally circular and concavely curved while outer surface
70 as viewed from above is generally circular and convexly
curved.
[0029] 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.
[0030] 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.
[0031] As shown in FIG. 7, wall 18 has a height H2 which is the
normal distance defined between bottom surface 56 and top surface
76. Height H2 is preferably kept to a minimum in keeping with the
desire to minimize the total profile of shield 10, which is
represented by height H1 as previously discussed. FIG. 7 also shows
that annular wall 50 has a maximum diameter D3 measured at its
base, which is substantially the same as the diameter of inner
perimeter 60. 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 of wall 18 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 of wall 18 aids in
this deflecting ability. In addition, the configuration of annular
side wall 50 also aids in this deflecting ability.
[0032] Referring now to FIGS. 1, 4 and 7, retaining ring 20 is
described in greater detail. Ring 20 is a substantially flat
annular wall having flat circular top and bottom surfaces 82 and 84
which are parallel to one another and horizontal. Ring 20 further
includes circular inner and outer perimeters 86 and 88 with sixteen
through holes 90 formed therein extending from top surface 82 to
bottom surface 84. Holes 90 are circumferentially evenly spaced
from one another so that they align with holes 54 in flange 48 and
holes 46 in plate 16 to receive therethrough respective fasteners
22 when shield 10 is assembled. Ring 20 in the exemplary embodiment
is formed of a rigid material which is typically a metal such as
steel or the like although ring 20 by itself may be somewhat
flexible or easily bent due to the fact that it is typically
relatively thin. Ring 20 helps to provide an even dispersion of the
force applied by the heads of fasteners 22 when they are screwed
into threaded holes 46 so that bottom surface 56 of annular flange
48 forms at atmospheric pressure a substantially airtight and water
tight seal against the mating flat annular portion of top surface
36 of plate 16. Shield 10 is configured to withstand without
breaking an internal pressure of at least 50 pounds per square inch
(psi) within interior chamber 34, although this specification may
vary depending on specific requirements. Preferably, the internal
pressure which shield 10 is configured to withstand without
breaking is, for instance, at least 60, 70, 80, 90, 100, 110, 120,
130 140 or 150 psi within interior chamber 34. Ring 20 helps
minimize the flexing of wall 18 during an internal explosion and
helps prevent flames or the like from escaping shield 10 to prevent
ignition of external gasses or other materials.
[0033] Shield 10 is shown in its assembled configuration in FIG. 7,
which illustrates that the threaded fasteners 22 are tightened to
provide a secure threaded engagement within the corresponding
threaded holes 46 of plate 16 in order to provide at atmospheric
pressure the substantially airtight and water tight seal between
bottom surface 56 of flange 48 and the corresponding annular
circular portion of top surface 36 which engages bottom surface 56.
In the exemplary embodiment, this seal is formed by the direct
contact between bottom surface 56 and top surface 36. 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 that shield 10 is configured to meet all applicable
MSHA requirements although this may vary depending on the specific
circumstances in which shield 10 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
between bottom surface 56 and top surface 36 between inner
perimeter 60 and the closest portion of each hole 46 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 between bottom surface 56 and
top surface 36 extending between inner and outer perimeters 60 and
62 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.
[0034] With primary reference to FIGS. 5 and 9, each gland seal 24
is described in greater detail. Each gland seal 24 includes a
housing 92 which houses a compressible gland 94 and a pair of
bushings 95 on opposed ends of the gland. Each gland seal also
includes a hollow gland nut or follower 96, an interior mounting
back plate 98, and four fasteners 100 which in the exemplary
embodiment include a bolt 102, a nut 104 threadedly secured to bolt
102 along with a pair of flat washers 106 and a lock washer 108.
With primary reference to FIG. 5, housing 92 is described in
greater detail. Housing 92 includes a substantially flat square
mounting plate 110 and a cylinder 112 which is rigidly secured
along its base to mounting plate 110 via an annular weld 114.
Square plate 110 has substantially flat and parallel upper and
lower surfaces 116 and 118. Four mounting through holes 120 are
formed through plate 110 adjacent its corners extending from upper
surface 116 to lower surface 118 for receiving therethrough the
threaded shafts of bolts 102. A pair of lock wire tabs 122 are
secured to and extend upwardly from upper surface 116 of plate 110
on opposite sides of cylinder 112 and define through holes 124
therein for receiving a lock wire (not shown) for securing nut 96
in place as noted further below. Cylinder 112 defines an interior
chamber 126 having an upper portion defined by an upper threaded
section 128 of cylinder 112 and a lower gland chamber defined by a
lower non-threaded portion 130 of cylinder 112. A cable-receiving
through hole 132 (FIG. 9) is formed in the center of plate 110 and
communicates with the gland chamber for receiving therethrough a
portion of one of cables 26 or 28.
[0035] 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. FIG. 9 shows the mounting of one of cables 26
and 28 as nut 96 is rotated to thread the nut into the cylinder and
compress gland 94 in the direction shown by arrow A in FIG. 9 such
that gland 94 applies radially outward force against the inner
surface of cylinder 112 and radially inward force against the outer
surface of the cable 26 or 28 in order to secure the cable and
provide at atmospheric pressure substantially a gas or airtight,
water tight seal between gland 94 and each of the inner surface of
cylinder 112 and the outer surface of the cable.
[0036] There are additional fire resistant paths illustrated in
FIGS. 9 and 9A having respective minimum distances D4, D5 and D6.
More particularly, bottom surface 118 of mounting plate 110 and
outer surface 75 of mounting section 71 form a continuous mating
interface between the edges of holes 132 or 77 and the closest part
of the outer perimeter of plate 10 where it intersects with bottom
surface 118 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 between surfaces 118 and 75. FIG. 9A illustrates a
similar continuous interface serving as a fire resistant path
between bottom surface 118 and top surface 75 wherein this fire
resistant path extends the shortest distance between the edge of
hole 77 and the edge of one of holes 79, or between the edge of
hole 132 and the edge of one of holes 120, 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 of cable 26 or 28 and the inner perimeter of gland 94
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 of non-threaded portion 130 of cylinder 112 and the outer
perimeter surface of gland 94 as measured in the direction in which
the cable is elongated in the region of gland 94. 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.
[0037] 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 FIG. 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 of top wall 52 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.
[0038] 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.degree. C. To perform the test, the shield
is heated in an oven so that the temperature of the lens or
transmission wall reaches 115.degree. C. (240.degree. F.) for a
polycarbonate lens or 150.degree. C. (302.degree. F.) for a glass
lens. The water in the tank is to be between 15.degree. C.
(59.degree. F.) and 20.degree. C. (68.degree. 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.
[0039] 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.
[0040] 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.
[0041] 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
[0042] 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.degree. from the vertical;
3=protected against direct sprays of water up to 60.degree. 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.
[0043] 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).
[0044] FIG. 10 illustrates an alternate gland seal 146 which may be
used with an alternate transmission wall 18A. This arrangement
would typically be used when the requirements regarding the flame
path are less stringent than those associated with the use of gland
seal 24. Alternate transmission wall 18A is very similar to wall 18
except that it includes one or more mounting sections 71A which are
analagous to mounting sections of 71 but have only a single cable
receiving hole 77A formed therethrough without the use of mounting
holes corresponding to mounting holes 79 of the mounting section 71
of wall 18. Hole 77A is typically somewhat larger than hole 77 to
accommodate the alternate gland seal 146. Gland seal 146 includes
an externally threaded tube 148 which extends through hole 77A, an
internally threaded gland nut 150 which threadedly engages one end
of tube 148, and a gland 152 which is disposed within a gland
chamber formed within gland nut 150. An outside mounting nut 154
and an inside mounting nut 156 are threaded onto externally
threaded tube 148 so that outside nut 154 engages the outer surface
of mounting section 71A and inside nut 156 engages the inner
surface of mounting section 71A in order to secure gland seal 146
to mounting section 71A. The basic operation of gland seal 146 is
similar to that of gland seal 24 in that the tightening of gland
nut 150 on tube 148 compresses the gland 152 in order to provide at
atmospheric pressure the gas or airtight and water tight seal
between the gland, the cable and inner surface of nut 150. Cable 26
or 28 thus passes through tube 148 and gland nut 150 to extend from
outside the blast shield to inside its interior chamber.
[0045] With reference to FIG. 11, a wireless transmission system in
which shields 10 are used is now described. There are a number of
operational environments in which the wireless transmission system
utilizing shields 10 may be typically used. FIG. 11 is a
diagrammatic view illustrating the operational environment as being
an underground mine 160. 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, shields 10 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.
[0046] With continued reference to FIG. 11, mine 160 includes a
mine shaft which may branch as shown and include a mine portal or
entrance 162 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 an electric power source 164 with electric power
lines 166 in electrical communication with power source 164 and
power cables 26 of several blast shields 10. As previously noted,
the battery of the internal components 14 is kept charged via its
charger by this connection to power source 164. As shown in FIG.
11, some of the shields are marked 10A and others 10B. The ones
marked 10A utilize power cable 26, but do not utilize the signal
transmission cable 28. Thus, blast shields 10A may be formed
without cable 28, gland seal 24B and the associated mounting
section 71 shown in the previous figures. On the other hand, the
shields which are generally closer to entrance 162 are marked as
shields 10B and include the transmission cable 28 in addition to
the power cable 26. The system further includes communication lines
168 which are in communication with transmission cables 28 and also
with an information receiving unit which is external to the mine.
Unit 170 may represent a variety of devices which typically include
some sort of processing unit for translating data received via
lines 168 into information which may, for example, be tracked by a
computer or viewed on a screen. Unit 170 may thus include a
computer for running a suitable program for processing or
translating information received thereby.
[0047] FIG. 11 also shows several inertial sensor units 172 having
antennas 174. One of units 172 is shown at a battery charging and
reset station 176 which is in electrical communication with power
source 164. Each inertial sensor unit 172 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 via antenna 174 to any of the receivers which are
housed within blast shields 10 within the transmission range of the
given unit 172. Shields 10 are typically spaced 500 to 1000 feet
apart from one another and thus serve as nodes or relays for
receiving transmissions either from unit 172 or from another
transmitter within a different shield 10 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 through transmission wall 18 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.
Although unit 172 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
each shield 10. Inertial sensor units 172 may be positioned at
charging and reset station 176 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 units
172 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, securing unit 172 to a belt which can be worn by an
individual or some other type of body wearable pack. Units 172 may
also be mounted on mining machinery or other mobile machines for
tracking their movement.
[0048] 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 FIG.
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 of
shields 10 for retransmission via the transmitter within the
shield. Such life cycle sensors could also be wired via
transmission lines such as lines 28 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 at 170 which would control a device associated
with the process control sensors in accordance with the signals
received therefrom. Controller 170 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.
[0049] 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.
[0050] 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.
[0051] Moreover, the description and illustration of the invention
is an example and the invention is not limited to the exact details
shown or described.
* * * * *