Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Reexamination Certificate
2000-05-15
2002-10-22
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
C174S1130AS, C174S116000
Reexamination Certificate
active
06469251
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The preferred embodiments of the present invention generally relate to communications and electronics cabling, and in particular to a vapor proof cable, such as for high speed communications and network interconnect cable, and a method of manufacturing the same.
2. Background Art
Communications and electronics cables are used today in a broad array of applications, many of which require that the cable carry high frequency signals over long distances. The operating frequency range for modem cable is significantly higher than the range needed for past applications, due in part to the evolution of communications and electronics equipment. In addition, today's applications require that cable operate under environmental conditions that are significantly more demanding than in the past.
Communications and electronics applications have been proposed that require cables capable of supporting ethernet protocols, while submerged for extended periods of time in fluid, such as oil, gas, water and the like. In at least one application, networking cables are installed at gasoline service stations to interconnect fuel pump electronics and point of sale (POS) equipment. The point of sale equipment communicates with the fuel pump via an ethernet data transmission protocol, such as established in accordance with the IEEE 802.3 10Base-T standard. Interconnect cable used in service station applications is exposed to petroleum fumes and, in some instances, may be submerged in fuel. Other protocols that cable can be used for include asynchronous transfer mode communication.
Heretofore, local area networks, such as used at service stations, typically use category 5 cable as the interconnect cable. Category 5 represents a standard set forth by ANSI, and the TIA/EIA group. Conventional category 5 cable includes twisted groups of insulated conductors. Each twisted group may include two or more conductors forming pairs. Twisted pair cable includes air gaps between an inner surface of the cable jacket and the twisted pair insulated conductors. Twisted pair cable also includes a hollow core between the multiple twisted pair insulated conductors within the cable. The air gaps and hollow core both facilitate the migration of fumes or vapors along the length of the cable. Hence, the potential exists that the cable may transport explosive vapors from the pump to the facility where the clerk is located.
In the past, attempts have been made to vapor proof category 5 cable in order to prevent fumes from migrating to the service station and to comply with safety regulations. One method in the past includes stripping away the cable jacket at multiple discrete regions along the length of the cable when the cable is installed to expose the insulated conductors. A potting material is applied to the conductors at each exposed area to form a vapor blocking seal. The potting material is applied at multiple discrete points along the length of the cable to provide a series of discrete or sectional vapor locks. Multiple vapor locks are necessary since the potting material may develop cracks or be improperly applied, thereby permitting vapor to enter the cable and migrate through a vapor lock. Also, the jacket may become damaged between the service station and any given vapor lock, thereby permitting vapor to enter the jacket and migrate toward the service station upstream of a vapor lock. The existing practice of stripping cables and adding potting material is labor intensive, expensive and unreliable and is undesirable.
FIG. 1
illustrates a category 5 cable that has been used for ATM and ethernet interconnections heretofore. The cable
10
includes a jacket
12
enclosing four twisted pairs
14
-
17
of conductors arranged in a helix configuration and surrounding a hollow core
18
. The twisted pairs
14
-
17
contact one another and the inner surface
20
of the jacket
12
. The relative positions of the twisted pairs
14
-
17
remain substantially constant with respect to one another. The twisted pairs
14
-
17
are also twisted to form one large helix. The outer boundary of each twisted pair
14
-
17
is denoted by dashed line
28
. Do to the very nature of a helix, the cable
10
includes several peripheral air gaps
24
-
27
located between the inner surface
20
of the jacket
10
and the outer peripheral sections of the twisted pairs
14
-
17
, and air gaps
38
within each twisted pair
14
-
17
.
Each twisted pair
14
-
17
comprises two wires
30
and
32
enclosed in insulators
34
and
36
, respectively. A rip cord (not shown) may be provided proximate the inner surface
20
of the jacket
12
. The wires
30
and
32
are copper and the insulators
34
and
36
are formed of a polyolefin or fluoropolymer insulator. The jacket
12
is constructed of riser or plenum rated PVC or fluoropolymer.
The cable
10
is arranged in a specific geometry and constructed from materials having a set of desired electrical and physical properties that interact with one another in a particular manner. The overall geometric and material combination affords physical and electrical characteristics that satisfy the requirements of the category 5 standard. Therefore, the cable
10
is approved for use in telecommunications and electronics applications that require category 5 cable.
Air is provided in the cable
10
in the core
18
and gaps
24
-
27
and
38
, to achieve specific electrical characteristics. The geometric configuration and dielectric constants for the materials used in the cable
10
, along with the dielectric constant of air in the core
18
and in air gaps
24
-
27
and
38
interact to achieve a desired characteristic impedance and to minimize cross talk between signals transmitted over the twisted pairs
14
-
17
, and interact to minimize attenuation and skew. Therefore, the inclusion of air in the cable
10
is necessary and desirable for category 5 cable. By way of example, the cable
10
exhibits standard electrical characteristics.
The cable
10
is able to meet the requirements of the TIA/EIA-568-A standard for the category 5 cable by including air around the insulated conductors
14
-
17
.
In certain networking applications, data transmission protocols may be used that differ from the category 5 standard. For instance, in certain ethernet networks, data transmission protocols are used that meet a less strict standard, such as the 10Base-T standard. By way of example, the ethernet network used at service stations, such as in the example explained above, may utilize a data transmission protocol that satisfies the 10Base-T standard.
A need remains for an improved network cable that is vapor proof and gas impermeable, while continuing to offer the electrical characteristics needed for high speed data transmissions. It is believed that the preferred embodiments of the present invention, satisfy this need and overcome other disadvantages of conventional cabling which will become more readily apparent from the following discussion.
BRIEF SUMMARY OF THE INVENTION
In accordance with at least one preferred embodiment of the present invention, a quad cable is provided including a jacket and at least one quad of insulated signal conductors encased within the jacket. The insulated signal conductors contact one another and are arranged in a helix configuration defining a hollow core. A vapor proof filler substantially fills the hollow core. The jacket and filler fill the gaps and crevices around each insulated conductor to form a hermetic seal along the length of the insulated signal conductors, thereby preventing vapor migration along a length of the cable. In one embodiment, the jacket includes a gas impermeable outer jacket and an inner jacket, while in another embodiment the jacket includes a single unitary jacket. In both embodiments, the single jacket and inner jacket have a dielectric constant higher than a dielectric constant of the insulation on the insulated signal conductors to afford desirable electrical characteristics. The jacket constitutes a pres
Mayo III William H.
Reichard Dean A.
Tyco Electronics Corporation
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