Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Reexamination Certificate
2001-06-18
2004-01-06
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
C361S117000
Reexamination Certificate
active
06674626
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to lightning suppression systems. More particularly, the present invention relates to devices for reducing the effect of a lightning strike as it moves along transmitting and receiving wires. More particularly, the present invention relates to devices for protecting electronic equipment associated with T1 or DSL lines.
2. Description of Related Art
Lightning conceivably may have provided humankind with a first source of fire, but lightning has otherwise been a destructive force throughout human history. Strategies and apparatus for reducing the likelihood of damage by lightning are fairly old, including, for instance, lightning rods that have been use for approximately 200 years. While the use of such rods and other precautionary steps and safety devices reduce the damage and injury that would otherwise result from lightning today, it remains an enormously dangerous natural phenomenon that claims hundreds of lives worldwide every year and destroys a substantial amount of property. Somewhat paradoxically, advances in other areas of technology have increased, rather than diminished, the damaged caused by lightning. This is because relatively low voltage and current levels can damage integrated circuits and other modern electronic components, with the result that many electronic devices are more susceptible to lightning damage today than ever before. Many devices to which microprocessors technology has been added are more susceptible to lightning damage as a result of such improvements. Additionally, lightning is capable of inducing substantial currents not only in electrical circuits directly struck by it but also in circuits located within the magnetic field induced by a nearby lightning strikes, giving each strike enormous destructive potential.
One of the most common areas of lightning strikes are large telecommunications and camera towers that extend upwardly from the earth. Typically, such towers include an electronic device at the top which serves to transmit or receive information. Since lightning will follow a path of least resistance on its way to the earth, the towers are very attractive to lightning. It is well known that lightning is particularly attracted to areas of positive ions and is repelled by areas of negative ions. Since the electronic devices at the top of towers often operate on AC power, an attractive source of positive ions is generated at the top of the tower.
A variety of communication technologies are competing to provide high speed access to the home. For example, asymmetric digital subscriber lines (ADSL), cable modems, satellite broadcasts, wireless LANs, and direct fiber connections to the home have all been suggested. Of these technologies, the asymmetric digital subscriber line can utilize the POTS subscriber line (the wire currently being utilized for POTS) between the home user (the residence) and the telephone company (the central office). DSL networks and protocols were developed in the early 1990's to allow telephone companies to provide video-on-demand service over the same wires that were being used to provide POTS. DSL technologies include discrete multitone, carrierless amplitude and phase modulation, high speed DSL and other technologies. DSL technology allows telephone companies to offer high speed internet access and also allows telephone companies to remove internet traffic from the telephone switch network. Typically, a conventional asymmetric DSL system includes a copper twisted pair analog telephone subscriber line, a DSL modem, and a band splitter.
The Bell telephone system in the United States has widely used a digital time-domain multiplexing pulse code modulation system known as the T1 transmission system. Each T1 transmission system carries 24 8-KB/second voice or data channels on two (2) pairs of exchange grade cables. One pair of cables provides communication in each direction. For convenience and simplification of terminology, the pair of cables carrying signals from the central office to the customer premises equipment may be referred to as a “transmit” line, and the pair of cables transmitting data from the customer premises equipment to the central office may be referred to as the “receive” line. These designations are made only as a matter of convenience; when an observer (such as a testing technician) changes position from a central office to a customer premises, what used to be a “transmit” line can become a “receive” line, and what used to be a “receive” line can become a “transmit” line.
In the T1 system, the data to be transmitted over the lines, such as speech, is sampled at a rate of 8,000 Hertz, and the amplitude of each sample is measured. The amplitude of each sample is compared to a scale of discreet values and assigned a numeric value. Each discreet value is then encoded into binary form. Representative binary pulses appear on the transmission lines. The binary form of each sample pulse consists of a combination of seven pulses, or bits. An eighth bit is periodically added to allow for signaling.
In certain circumstances, the cables from the central office to the customer premises can become affected by either a direct strike by lightning or by a ground effective lightning. As a result, the lightning wavefront can travel along the transmit lines and the receive lines so as to affect the communications with the customer. Additionally, the lightning wavefront can travel toward the central office so as to directly affect the transmitter and the electronic equipment associated therewith. As such, a need has developed in order to effectively prevent the affect of such lightning strikes.
In the past, various patents issued on such lightning suppression equipment. For example, U.S. Pat. No. 5,844,766, issued on Dec. 1, 1998 to L. Miglioli, describes a lightning suppression system comprising a directional coupler, a quarter-wavelength stub, a first cylindrical capacitor, a second cylindrical capacitor and a lightning suppression circuit. The lightning suppression circuit suppresses high voltage direct current and low frequency signals such as those produced by near lightning strikes.
U.S. Pat. No. 5,167,537, issued on Dec. 1, 1992 to Johnescu et al., describes a high density MLV contact assembly employing a multi-layered varistor as the transient suppression device. The varistor is mounted in a notch and a sleeve and connected to ground by way of a ground sleeve.
In typical DSL and T1 systems, a suppressor, such as a varistor, is connected between the pairs of cables and the electronic equipment. However, these types of suppressors are usually only effective against minor voltage spikes. They are generally too slow to effectively suppress the effects of a lightning wavefront. When a lightning wavefront passes through the suppressor to the electronic equipment, the high speed telecommunications equipment can cost $20,000 to repair. As such, a need has developed so as to provide an effective lightning suppression attenuator that prevents lightning strikes from affecting the equipment associated with T1 lines and DSL lines.
It is an object of the present invention to provide a lightning suppression system that effectively prevents lightning strikes from affecting the equipment associated with T1 and DSL lines.
It is another object of the present invention to provide a lightning suppression system that will cushion the shock of the lightning wave front from adversely affecting the existing suppressor equipment associated with the T1 and DSL lines.
It is another object of the present invention to provide a lightning suppression system that will minimize the damaging effects of lightning.
It is a further object of the present invention to provide a lightning suppression attenuator which is easy to install, relatively inexpensive and easy to manufacture.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
BRIEF SUMMARY OF THE INVENTION
Fowler Benjamin P.
Fowler William J.
Harrison & Egbert
Leja Ronald W.
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