Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2001-03-30
2002-07-09
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S315000, C340S010200, C340S315000
Reexamination Certificate
active
06417762
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
This invention relates to a method and system for transmitting high frequency communication signals over a preexisting building power line network. More particularly, the present invention relates to a method and system for using anti-resonance isolation and virtual earth ground signaling to transmit communication signals over wires of a power line network.
2. The Relevant Technology
The ability to freely access data on a network and to transfer information between electrical apparatus can dramatically increase productivity and efficiency. Networking is beneficial for businesses, as well as for residential uses. Transfer of data over a network is typically accomplished with a telephone line or cable. Accordingly, many buildings are wired for local access network (LAN) connectivity. Some buildings, however, particularly older residential, business, and military buildings, are not appropriately wired for LAN. These buildings must either be rewired, or an alternative means for networking must be used. Because the costs of rewiring a building can be prohibitive, it is desirable to provide an efficient means of networking over preexisting building wires. One such means includes the transfer of communication signals over preexisting power transmission lines.
The use of power transmission lines as a communication network is well known in the art. Early inventors contemplated sending communication signals directly over the load carrying conductors of the power line. There are problems, however, associated with transmitting communication signals over load carrying conductors (wires). Perhaps the most significant problem, is ‘noise,’ which is resident in all power line networks.
Noise is generated in the load carrying conductors by the high voltage alternating power, the discontinuities in impedances caused by various branch circuits, transients and impedance changes produced by power load switching, and isolation of the power line network into separate circuits. Noise makes it difficult to transmit high frequency signals over long distances due to line losses, radiation, and impedance mismatches.
Noise also interferes with the transmission of communication signals by limiting the capacity of the network to transmit reliable communication signals. The constraining effect of noise on data transmission is defined by the Hartley-Shannon Law, in which C=B*log
2
(1+P/N)bits/s. In this equation, C establishes the upper limit for the rate of reliable information that can be transmitted over the conductor, B is the bandwidth, P is the average power of the transmitted signal, and N is the average power of the noise component. Accordingly, as the noise in the conductor increases, the capacity of the conductor to transmit reliable data decreases.
Various approaches have been proposed to overcome the constraints of noise and to enable reliable transmission of communication signals over power line networks. For example, in one approach, which is disclosed in U.S. Pat. No. 4,697,166, issued to Warnagiris et al., selective filters are used to separate power signals and communication signals at the transmitting and receiving ports of a communication system on a power line network. In another approach, which is disclosed in U.S. Pat. No. 4,864,589, issued to Endo, different transmission frequencies (frequency hopping) and “spread spectrum” systems are utilized to transmit communication signals over a power line network. In yet another approach, as disclosed in U.S. Pat. No. 5,982,276, issued to Stewart, electromagnetic signals are transmitted through magnetic modulation of the magnetic flux surrounding the load carrying wires. These various approaches disclose various means of transmitting communication signals over the main current carrying conductors of a power line network. They do not, however, directly address or overcome the underlying problems associated with noise, namely, limited bandwidth and slow transfer rates. Rather they simply enable the transmission of communication signals over the resident noise.
To effectively overcome slow transfer rates and limited bandwidth of noisy channels, communication signals may be transmitted over conductors with less noise, such as between the earth ground and the power line neutral, instead of using the “hot” power line, as disclosed in the prior art. By transferring communication signals between the earth ground and the power line neutral, the effects of noise are minimized because these conductors have less noise. One problem with this approach, however, is that to transmit signals between the building ground and neutral power lines, it is necessary that the two conductors be electrically isolated, which they are not.
In the prior art, as disclosed in U.S. Pat. No. 3,702,460, issued to Blose, adequate isolation between the building ground and neutral lines is accomplished by placing a transformer winding between the two conductors at the transmitting end and at the receiving end of the power line network. Although this resolves many of the problems associated with noise when using the current carrying wires of the power line network, this method is not appropriate for buildings that are wired to current electrical codes. In present residential and commercial buildings, for example, the uniform electrical code requires that the building ground, earth ground and the power line neutral be conductively tied into a common heavy bus or “tie” at the service panel. This “tie” is commonly referred to as a ground bar.
In U.S. Pat. No. 4,433,326, issued to Howell, an alternative method of isolating the building ground from the neutral line is proposed, which involves replacing the “tie” at the service panel with an inductor or transformer. This modification is intended to isolate the ground and neutral lines at high frequencies for transmitting communication signals while at the same time enabling a tie between the conductors at lower power line frequencies, so as to satisfy the safety codes. This, however, requires modification to the building wiring at the service panel and generally requires the services of a licensed electrician and the use of a special approved inductor, which can be costly. This prior art also does not resolve problems of parasitic capacitive coupling between the neutral and building ground wires.
Furthermore, by replacing the “tie” with an inductor or transformer, the problems associated with having to rewire a building to enable network connectivity are not resolved. In particular, costly professional rewiring of the power line network is still required. Accordingly, it would be desirable to provide a method and system for networking over preexisting power lines without requiring any electrical modifications to the preexisting power lines or service panel.
BRIEF SUMMARY OF THE INVENTION
In accordance with the invention as embodied and broadly described herein, a system and method for sending and receiving high-frequency signals over a previously installed building power line network is provided. A suitable environment for practicing the present invention is a previously installed building power line network that includes an electrical service panel, a building ground line, a hot line, and a neutral/earth ground line. The service panel connects a utility phase I power line, a utility neutral power line, and a utility 115V phase II power line to preexisting building wires that include the hot line, the neutral/earth ground line and the building ground line. To comply with electrical safety standards, the service panel also includes a ground bar that provides a common conductive ‘tie’ for various ground and neutral wires, including an earth ground wire that connects the ground bar to the physical ground (earth).
The building wires are insulated and routed through cabling to various power outlets throughout the building. The power outlets include at least one set of three electrical contacts that are correspondingly connected to the hot, neutral and ground power lines. Each
Comcircuits
Hofsass Jeffery
Previl Daniel
Workman & Nydegger & Seeley
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