JP2008236457A - Local area network for power line communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a local area network for power line communication capable of securing excellent communication quality even in a severe environment wherein noise is large. <P>SOLUTION: In a configuration wherein signal transmission lines are determined according to whether a necessary communication speed is high or low, equipment (programmable controllers 81 and 83 and IP cameras 82 and 84) which can be operated at slow speed uses power lines 51 to 53 as signal transmission lines, and equipment (personal computers 161 to 164) which requires high speed uses coaxial lines 31 to 33, and 38 to secure better communication quality. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a local area network system for power line communication (PLC) using a power line as a signal transmission path.

  Power line communication is a communication method in which a data communication signal is superimposed on a commercial AC voltage (current) using a power line as a signal transmission line, and has an advantage that there is no need to newly perform communication wiring (for example, non-patent) Reference 1). In recent years, attention has been focused on power line communication using indoor wiring as a communication method for constructing a LAN (local area network) in a home or office.

Interface, pp. 70-81, “Current Status of Power Line Communication (PLC)”, Kiyoshi Eto, CQ Publishing, September 2000

However, for example, when constructing a LAN by power line communication including network equipment in a factory, large noises from a large number of electrical equipment (for example, motors) in the factory enter the power line of the signal transmission path. As a result, when the S / N ratio deteriorates, the communication speed decreases. For this reason, when a large amount of data is transmitted / received between personal computers constituting a LAN, the communication speed is lowered, and the user cannot use it comfortably.
In view of this problem, an object of the present invention is to provide a power line communication LAN system capable of ensuring good communication quality even in a severe environment with large noise.

  A local area network system for power line communication according to the present invention includes a first power line communication device using a power line as a signal transmission path, and a first device connected to the first power line communication device and performing relatively low-speed communication. A second power line communication device using the communication line as a signal transmission path, a second device connected to the second power line communication device and performing relatively high-speed communication, and both the power line and the communication line. A third power line communication device serving as a signal transmission path is included.

  In the local area network system for power line communication as described above, the first device performs relatively low-speed communication using the power line as a signal transmission path, and the second device relatively uses the communication line as a signal transmission path. Perform high-speed communication. The signals of the two signal transmission paths are relayed by the third power line communication device. Communication lines are less attenuated than power lines and are less susceptible to noise.

In the local area network system, the first power line communication device and the first device may be installed in a factory.
In this case, even in a factory where there is no dedicated LAN wiring or coaxial line, it is possible to construct a network using an existing power line, particularly when high-speed communication is not required.

In the local area network system, the communication line may be a coaxial line provided for receiving a television broadcast.
In this case, power line communication can be performed by utilizing an existing coaxial line for receiving a television broadcast.

  According to the local area network system for power line communication of the present invention, a power transmission line that is susceptible to noise in a second device requiring high speed as a configuration in which a signal transmission path is divided depending on whether the necessary communication speed is high or low. Separately, better communication quality can be ensured by using a communication line. Therefore, good communication quality can be ensured even in a harsh environment with large noise.

  Hereinafter, a local area network system (hereinafter referred to as a LAN system) for power line communication according to an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, “power line communication” is basically data communication using a power line as a signal transmission path, but in addition to the power line, a communication line (for example, a coaxial line) wired in a house, a building, or the like. ) Is also used as a signal transmission line, the power line communication is broad.

  FIG. 1 is a block diagram showing an outline of an internal circuit configuration of a power line communication apparatus (hereinafter referred to as a PLC modem). The PLC modem 1 includes a power supply unit 2 that supplies power to an internal circuit, a PLC digital processing unit 3 that performs digital processing of power line communication signals, a PLC analog processing unit 4 that performs analog processing of power line communication signals, and an Ethernet ( A PHY (Physical) unit 5 as a physical layer having a registered trademark interface function, a switching device 6 having a transmission path switching function, and the passage of a frequency signal higher than the signal frequency of power line communication are regulated in both directions. Ethernet connected to the LAN cable 13 and the low-pass filter 7 for filtering, the filter device 8 for allowing commercial AC power to pass between the ports 8a and 8b, and for allowing the power line communication signals to pass bidirectionally between the ports 8a and 8c. Trademark) data communication port 10, coaxial cable connector 11 to which coaxial cable 14 can be connected, and power cord 15 And a power connector 12, units are connected as shown.

  The LAN cable 13 is connected to various network devices in addition to the personal computer 16. The coaxial line 14 can be connected to a coaxial line terminal (television terminal) TV provided on a wall surface or the like for receiving a television broadcast. The power cord 15 is connected to the outlet C.

  The switching device 6, the low pass filter 7 and the filter device 8 constitute an input / output circuit 9. That is, the switching device 6 can select an input / output path as viewed from the PLC analog processing unit 4 by, for example, a manual switching operation. (1) Only the power line, (2) Only the coaxial line, (3) The power line and Any one of the coaxial lines can be selected.

  When (1) is selected, signal transmission between the switching device 6 and the low-pass filter 7 is blocked. When (2) is selected, signal transmission between the switching device 6 and the filter device 8 is interrupted. When (3) is selected, the switching device 6 performs signal transmission with both the low-pass filter 7 and the filter device 8, and the PLC analog processing unit 4 uses two systems of power lines and coaxial lines as input / output paths. It becomes a state to do. Thereby, the function of simultaneously outputting the same power line communication signal to the two systems of the power line and the coaxial line and inputting the power line communication signal from each system is achieved.

  In this way, the input / output circuit 9 (selection is made by the switching device 6) capable of two-way input / output and selective input / output enables the transmission of the signal even for a single PLC modem as a product. The system can be properly used according to the environment of the installation site.

  FIG. 2 is a graph showing the frequency characteristics of the low-pass filter 7. The horizontal axis represents frequency and the vertical axis represents input / output ratio. The low-pass filter 7 allows the signal to pass through almost 46 MHz without being attenuated. However, when the frequency exceeds about 46 MHz, the attenuation suddenly increases, and exhibits a very large attenuation characteristic for frequencies above about 60 MHz. . A signal with a frequency of 2 to 30 MHz is used for power line communication, while a signal with a frequency of 90 MHz or more is used for television broadcasting. Accordingly, the passage of television broadcast signals is restricted by the low-pass filter 7. Thereby, it is possible to prevent a television broadcast signal from being input to the PLC analog processing unit 4. Moreover, although the use frequency of power line communication is up to 30 MHz as above-mentioned, the harmonic of the frequency (frequency range of a television broadcast) exceeding this occurs. However, the passage of harmonics of power line communication exceeding about 46 MHz is restricted by the low-pass filter 7. Therefore, it is possible to prevent the harmonics from affecting the reception of the television broadcast.

The low-pass filter 7 is inserted to avoid interference with other communication services on the coaxial line. If the influence of interference can be avoided at a frequency higher or lower than 46 MHz, the cut frequency is changed. May be. Further, in the case where the influence of interference can be avoided without inserting the low-pass filter 7 or there is no other communication service itself, the low-pass filter 7 may be omitted.
Further, signals may be output to both the coaxial line connector 11 and the power connector 12 except for the switching device 6.

  FIG. 3 is a connection diagram showing an example of a LAN system for power line communication using the PLC modem 1. Here, a LAN system in the case where the factory 20 and the office exist in one campus will be described. The office is, for example, a monitoring room 21 and a meeting room 22, which are provided adjacent to the factory 20. Among the wirings in the figure, a thick line is a power line, and a thin line is a coaxial line (coaxial cable) or a LAN cable. The coaxial line is used for video transmission, Ethernet communication (10BASE-5, 10BASE-2, etc.) and the like.

  In the figure, an output signal from a television broadcast receiving antenna (not shown) is distributed by a distributor 30. The coaxial lines 31 and 32 that transmit the output signals of the distributor 30 are connected to the coaxial line terminal TV1 of the monitoring room 21 and the coaxial line terminal TV2 of the conference room 22, respectively. A PLC modem 1 </ b> M is connected to the coaxial line terminal TV <b> 1 of the monitoring room 21 using a coaxial line 33. The PLC modem 1M is connected to the hub 35 via a LAN cable 34. The personal computer 161 is connected to the hub 35 via the LAN cable 36. The hub 35 is also connected to the corporate network via the LAN cable 37. In the PLC modem 1M, the above-mentioned “(2) Coaxial line only” is selected as the input / output path.

  On the other hand, the PLC modem 1 </ b> R is connected to the coaxial line terminal TV <b> 2 of the conference room 22 using the coaxial line 38. The PLC modem 1R is connected to the hub 40 by a LAN cable 39. The personal computers 162, 163, and 164 are connected to the hub 40 via LAN cables 41, 42, and 43, respectively. The power cord 44 of the PLC modem 1R is connected to the outlet C0. The outlet C0 is connected to the distribution board 50 via a power line 51 of indoor wiring. In the PLC modem 1R, the above-mentioned “(3) power line and coaxial line” is selected as the input / output path.

  In the factory 20, power lines are laid from the distribution board 50 to each production line. Here, for example, power lines 52 and 53 are laid on two production lines A and B, and outlets C1 to C4 are provided. And A power cord 61 of the PLC modem 1S1 is connected to the outlet C1, and the PLC modem 1S1 is connected to, for example, a programmable controller 81 via a LAN cable 71. The programmable controller 81 has a function of monitoring operation information (contact on / off) of the mechanical equipment and various analog measurement value information controlled thereby, and a network function.

  On the other hand, the power cord 62 of the PLC modem 1S2 is connected to the outlet C2, and the PLC modem 1S2 is connected to, for example, an IP camera 82 for line monitoring via the LAN cable 72. The IP camera 82 has an imaging function and a network function.

Similarly, the power cord 63 of the PLC modem 1S3 is connected to the outlet C3, and the PLC modem 1S3 is connected to the programmable controller 83 via the LAN cable 73. The power cord 64 of the PLC modem 1S4 is connected to the outlet C4, and the PLC modem 1S4 is connected to the IP camera 84 via the LAN cable 74.
In the PLC modems 1S1, 1S2, 1S3, and 1S4, the above-mentioned “(1) power line only” is selected as the input / output path.

  The PLC modem 1M is set as a master unit, the PLC modem 1R is set as a slave unit that also serves as a repeater, and the other PLC modems 1S1, 1S2, 1S3, and 1S4 are set as slave units. The setting can be performed from the personal computer 161 connected to the PLC modem 1M, for example.

  In the LAN system as described above, the slave PLC modems 1S1 to 1S4 can communicate with the PLC modem 1R through the power lines 52 and 53, the distribution board 50, and the power line 51. On the other hand, the PLC modem 1R can perform power line communication with the PLC modem 1M as a master unit via the coaxial lines 38 and 32, the distributor 30, and the coaxial lines 31 and 33. By relaying the PLC modem 1R, communication between all the PLC modems becomes possible. Therefore, information from the programmable controllers 81 and 83 and the IP cameras 82 and 84 can be monitored by the personal computer 161 in the monitoring room 21 (also can be monitored by the personal computers 162 to 164). The personal computer 161 in the monitoring room 21 and the personal computers 162 to 164 in the conference room 22 can access each other using a coaxial line as a signal transmission path.

  As described above, power line communication using a coaxial line as a signal transmission path has no branching in the coaxial line and has a shield structure. It is hard to receive. Therefore, the communication speed is faster than that of the power line, and long-distance communication is possible. For example, PLC modems connected to each other by a coaxial line can communicate up to a distance of about 300 m, which is about three times the communicable distance by Ethernet (10 / 100BASE-T) (registered trademark). .

  Although a large amount of data communication is often performed between the personal computer 161 and the personal computers 162 to 164, high-speed communication is performed by using a coaxial line as a signal transmission path. On the other hand, the communication between the personal computer 161 (same for 162 to 164), the programmable controllers 81 and 83, and the IP cameras 82 and 84 is communication using the power line as a signal transmission path, so the S / N ratio decreases due to branching or noise. As a result, it is slower than the coaxial line. However, the information from the programmable controllers 81 and 83 and the IP cameras 82 and 84 has a relatively small amount of data, and there is no particular problem even if there is a minute communication delay. Therefore, these devices do not cause inconvenience even with relatively low-speed communication.

  Thus, in the LAN system, devices such as the programmable controllers 81 and 83 and the IP cameras 82 and 84 perform relatively low-speed communication using the power line as a signal transmission path, and devices such as the personal computers 161 to 164 High-speed communication can be performed using the coaxial line as a signal transmission path. The signals of the two signal transmission paths are relayed by the PLC modem 1R. Since the coaxial line is less attenuated than the power line and is less susceptible to noise, better communication quality can be ensured by using the coaxial line.

In addition, the coaxial line is often an existing facility on the premises for receiving television broadcasts, as in the case of the power line. Therefore, better communication quality can be ensured by utilizing the existing facility.
In addition, such a LAN system makes it possible to construct a network using an existing power line even in a factory without a dedicated LAN wiring or coaxial line, particularly when high-speed communication is not required, thereby expanding the application range of power line communication. .

In the above embodiment, it is assumed that power lines are used for all power line communications in the factory 20, but coaxial lines can be used in the factory 20, and conversely, in the monitoring room 21. It is also possible to use power lines.
Moreover, although the said embodiment demonstrated the LAN system of the power line communication in a factory, not only a factory but other various offices which are noisy environments construct | assemble the same LAN system, and can perform better communication. It can contribute to quality assurance.
In addition to the coaxial line in the above embodiment, various signal lines can be used. For example, a telephone line, an Ethernet line (10 / 100BASE-T), an interphone line, or the like can be used. Since these signal lines have few or no branches, a relatively high communication speed can be obtained.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined not by the above-mentioned meaning but by the scope of claims for patent, and is intended to include all modifications within the scope and meaning equivalent to the scope of claims for patent.

The outline of the internal circuit structure of a PLC modem (power line communication apparatus) is represented by a block diagram. It is a graph which shows the frequency characteristic of a low-pass filter. It is a connection diagram showing an example of a LAN system for power line communication using a PLC modem.

Explanation of symbols

1S1 to 1S4 PLC modem (first power line communication device)
1M PLC modem (second power line communication device)
1R PLC modem (third power line communication device)
20 factories 31 to 33, 38 coaxial line 51 to 53 power line 81, 83 programmable controller (first device)
82,84 IP camera (first device)
161-164 PC (second device)

Claims (3)

A first power line communication device using a power line as a signal transmission path;
A first device connected to the first power line communication device and performing relatively low-speed communication;
A second power line communication device using the communication line as a signal transmission path;
A second device connected to the second power line communication device and performing relatively high-speed communication;
A local area network system for power line communication, comprising: a third power line communication device using both the power line and the communication line as signal transmission paths.   The local area network system for power line communication according to claim 1, wherein the first power line communication device and the first device are installed in a factory.   2. The local area network system for power line communication according to claim 1, wherein the communication line is a coaxial line provided for receiving a television broadcast.

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