WO2007011082A1

WO2007011082A1 - System for remote monitoring and safety maintenance of pipe lines buried in the earth

Info

Publication number: WO2007011082A1
Application number: PCT/KR2005/002305
Authority: WO
Inventors: Chee-Woong Hyun; June-Sik Sung; Young-Duk Kim
Original assignee: Samchully Co., Ltd.; Nuri Telecom Co., Ltd.
Priority date: 2005-07-18
Filing date: 2005-07-18
Publication date: 2007-01-25

Abstract

Provided is a system for remote monitoring and safety maintenance of pipe lines buried in the earth in which pipe lines are used as communication lines to monitor state of pipe lines such that costs for establishing the system and operating the same are reduced and rapid and safe management of the pipe lines is performed.

Description

SYSTEM FOR REMOTE MONITORING AND SAFETY MAINTENANCE OF PIPE LINES BURIED IN THE EARTH

Technical Field The present invention relates to a system for remote monitoring and safety maintenance of pipe lines buried in the earth, and more particularly, to an system in which pipe lines buried in the earth are used as communication lines to monitor state of the pipe lines and simultaneously to perform rapidly safety control when abnormality occurs in a pipe line.

Background Art

In general, pipe lines buried in the earth corrode gradually as time elapses. 'Corrosion' means that a material reacts with an ambient environment and the material itself is deformed or the property of the material is changed. Such corrosion is usually generated by an electrochemical reaction caused by movement of electrons and thus is referred as electrochemical corrosion.

When a metallic structure reacts with an ambient environment within an electrolyte, if four conditions of an anode, a cathode, an electric path (or a metallic path), and an ionic path (an electrolyte) are established, a corrosion cell state is formed and a corrosion current is generated. In this case, a more active and lower electrode side becomes an anode and corrodes. As a result, owners of facilities who possess metallic pipe lines buried in the earth have a variety of kinds of anticorrosion facilities so as to increase life spans of the metallic pipes by preventing corrosion. Here, 'anticorrosion' means that at least one condition of factors of the corrosion is removed or suppressed. Generally, it is difficult to remove the corrosion condition completely. Thus, an anode or a cathode reaction is suppressed or the flow of ions is blocked using a corrosion inhibitor, an insulating plate or other methods. Among the methods, a currently most widely used method in consideration of an economical efficiency or a convenience of applicability is cathodic protection which is a kind of methods for suppressing an anode reaction. Cathodic protection is usually called electrolytic protection.

Owners of pipes employing the above-described electrolytic protection facility check regularly whether corrosion is generated in the pipes so as to maintain the pipes stably. A corrosion-checking activity in the field of anticorrosion is performed when an owner of an object to be anti-corroded (a gas pipe, an oil pipeline, an up-and-down water pipe, a variety of kinds of tanks in a petrochemical plant, and other metallic things laid in the underground etc.) requests himself/herself or an anticorrosion-related company to carry out an anticorrosion-checking activity regularly or irregularly in connection with corrosion of the object to be anti-corroded.

At this time, corrosion sensing is intermittently performed by a manual work using an analog meter (a tester) or a portable strip chart recorder. In this case, since a worker should connect a measurement lead line (a pipe line is connected to (+), a reference electrode is connected to (-)) to a test box for measuring a corrosion potential, move to a position where measurement is easily performed, and measure the corrosion potential for a predetermined amount of time, it takes much time for measurement and there are many problems such as economical efficiency and the reliability of measurement. In order to solve the problems, a system in which a test box for measuring corrosion potentials is connected to a wired or wireless public communication network and measurement signals are cyclically transmitted to a management center via the wired or wireless public communication network has been introduced. However, in such a system, a structure for connecting the wired public communication network or the wireless public communication network should protrude and should be installed in each test box for measuring corrosion potential. Thus, it is difficult to install and manage the structure for connecting the public communication network. In addition, much costs for establishing the system and operating the same are required. Furthermore, even in systems for remote monitoring and safety maintenance of pipe lines buried in the earth as well as conventional remote monitoring systems of pipe lines by corrosion potential measurement in this way, there was a problem in that much costs for establishing the system and operating the same are required.

Disclosure of the Invention

The present invention provides a system for remote monitoring and safety maintenance of pipe lines buried in the earth in which the pipe lines are used as communication lines to monitor state of pipe lines such that costs for establishing the system and operating the same are reduced and rapid and safe management of the pipe lines is performed.

According to an aspect of the present invention, there is provided a system for remote monitoring and safety maintenance of pipe lines buried in the earth, the system including: pipe lines being conductive metallic pipes on which a material for anticorrosion is coated, between which an insulator communicated coaxially with the metallic pipes are interposed in a unit of a predetermined length, which are installed in the underground while being electrically divided by the insulator, transmit a fluid and function as an electric signal transmission line; a plurality of first signal sensing terminal units installed in each of the pipes divided by the insulator, measuring corrosion signals on the divided pipes, and transmitting the measurement signals via the pipes; a plurality of signal relay terminal units replaying signals so that an anticorrosion current and a corrosion current flowing through the divided pipes are not transmitted between the pipes divided by the insulator; a plurality of second signal sensing terminal units installed in a valve chamber and/or a static pressure chamber disposed in a predetermined section of the pipes, sensing an environment inside the valve chamber and/or the static pressure chamber and transmitting the sensing signal via the pipes; a control unit installed in the valve chamber and/or the static pressure chamber and controlling a driving mechanism so that a valve installed in the valve chamber and/or the static pressure chamber can be driven to be opened or closed according to control signals transmitted via the second signal sensing terminal units from the pipes; a remote terminal unit (RTU) collecting signals measured and sensed by the plurality of first and second signal sensing terminal units via the pipes and the signal relay terminal units to transmit the signals to a management center device via a public communication network and to transmit control signals from the management center device to the first and second signal sensing terminal units and the signal relay terminal units via the pipes; and a management center device analyzing the signals transmitted from the RTU and when a piping state is abnormal, a valve chamber state is abnormal or a static pressure chamber is abnormal, notifying a patrolman's mobile communication terminal who controls the pipes or valve chamber of static pressure chamber in which abnormality occurs, of abnormality of a corresponding pipe or valve chamber or static pressure chamber via a wireless public communication network.

Brief Description of the Drawings

FIG. 1 is a schematic diagram of a system for remote monitoring and safety maintenance of pipe lines buried in the earth according to an embodiment of the present invention.

FIG. 2 is a block diagram of a corrosion signal sensing terminal unit illustrated in FIG. 1.

FIG. 3 is a block diagram of a corrosion signal sensing/relay terminal unit illustrated in FIG. 1. FIG. 4 is a block diagram of a valve chamber signal sensing terminal unit/control unit illustrated in FIG. 1 ;

FIG. 5 is a block diagram of a static pressure chamber signal sensing terminal unit/control unit illustrated in FIG. 1 ; FIG. 6 illustrates an example of a demodulation signal used in the system of the present invention.

FIG. 7 illustrates an example of a signal data format used in the system of the present invention.

FIG. 8 illustrates a data relay operation state of a corrosion signal sensing/relay terminal unit illustrated in FIG. 3.

FIG. 9 is a block diagram illustrating operations of a remote terminal unit (RTU), a plurality of corrosion signal sensing/relay terminal units, a valve chamber signal sensing terminal unit, a static pressure chamber signal sensing terminal unit, and a corrosion signal sensing terminal unit illustrated in FIG. 1.

FIG. 10 is a flowchart illustrating an operation of receiving signals by the corrosion signal sensing terminal unit and the corrosion signal sensing/relay terminal unit illustrated in FIG. 1.

FIG. 11 is a flowchart illustrating an operation of receiving signals by the valve chamber signal sensing terminal unit and the static pressure chamber signal sensing terminal unit illustrated in FIG. 1.

FIG. 12 is a flowchart illustrating an operation of measuring corrosion signals by the corrosion signal sensing terminal unit and the corrosion signal sensing/relay terminal unit illustrated in FIG. 1. FIG. 13 is a flowchart illustrating an operation of receiving data by the pressure sensor, the temperature sensor, and the water level sensor in the terminal unit illustrated in FIG. 1.

FIG. 14 is a flowchart illustrating an operation of inputting signals from the gas sensor in the terminal unit illustrated in FIG. 1. FIG. 15 is a flowchart illustrating an operation of inputting signals from the open sensor of the manhole or the test box in which each terminal unit is installed in terminal unit illustrated in FIG. 1.

FIG. 16 illustrates an example illustrating a safety control signal processing flow when abnormality is sensed from the corrosion signal sensing/relay terminal unit, the valve chamber signal sensing terminal unit, the static pressure signal sensing terminal unit, and the corrosion signal sensing terminal unit in the system illustrated in FIG. 1.

FIG. 17 illustrates another example illustrating a safety control signal processing flow when abnormality is sensed from the corrosion signal sensing/relay terminal unit, the valve chamber signal sensing terminal unit, the static pressure signal sensing terminal unit, and the corrosion signal sensing terminal unit in the system illustrated in FIG. 1.

Best mode for carrying out the Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

FIG. 1 is a schematic diagram of a system for remote monitoring and safety maintenance of pipe lines buried in the earth according to an embodiment of the present invention. Referring to FIG. 1 , the system includes pipes 10_1 to 10_7 used as communication lines, a corrosion signal sensing terminal unit 52, corrosion signal sensing/relay units 60_1 to 60_6, a valve chamber signal sensing terminal unit 24/a control unit 26, a static pressure signal sensing terminal unit 36/a control unit 38, a remote terminal unit (RTU) 40, a management center 70, and a mobile communication terminal 80.

The pipes 10_1 to 10_7 are pipes on which consist of conductive metallic pipes on which a material for preventing corrosion is coated and the internal metallic pipes are utilized as communication lines. Here, the pipes may be polyethylene-coated line pipes (PLP). An insulator 15 communicated coaxially with the pipes 10_1 to 10_7 is interposed between the pipes 10_1 to 10_7 in the unit of a predetermined length (about 300 m to 1 km) so that the adjacent pipes 10_1 to 10_7 can be insulated by the insulator 15. In this way, the pipes 10_1 to 10_7 are installed in the underground while being electrically divided by the insulator 15 in a state where the insulator 15 is interposed therebetween, so that they transmit a fluid such as a city gas and also function as a signal transmission line.

Here, the insulator 15 is interposed between the pipes 10_1 to 10_7 in the unit of the predetermined length because a corrosion current that promotes corrosion of the pipes 10_1 to 10_7 flows through the pipes 10_1 to 10_7 and an anticorrosion current flows through the pipes 10_1 to 10_7 for anticorrosion of the pipes 10_1 to 10_7 and signal interference is eliminated between measurement sections of adjacent corrosion signals generated when the insulator 15 is interposed between the pipes 10_1 to 10_7 according to a measurement section unit of corrosion signals of the pipes 10_1 to 10_7.

The corrosion signal sensing terminal unit 52 (hereinafter, simply referred to as a 'signal sensing terminal unit') is installed in a test box 50, for example, is positioned at the shortest portion of the pipes 10_1 to 10_7, for example, measures corrosion signals with respect to the divided pipe 10_7 and transmits the measurement signals via the pipe 10_7. The detailed block construction of the signal sensing terminal unit 52 is shown in FIG. 2. In FIG. 1 , reference numeral AS denotes a unit for measuring corrosion signals, such as sacrificial anode, a reference electrode, and a pipe measurement point in the case of electrolytic protection. S1 to Sn denote a pressure sensor, a water level sensor, a temperature sensor, a gas sensor or a test box open sensor of a pipe, installed in test boxes 50, 60_1A to 60_6A, a valve chamber 20, and a static pressure chamber 30 and sensing an environment of each of the test boxes 50, 60_A to 60_6A, the valve chamber 20, and the static pressure chamber 30. Here, these sensors may be selectively installed at the test box 50 of the signal sensing terminal unit 52 and the test boxes 60_A to 60_6A of the corrosion signal sensing/relay terminal units 60_1 to 60_6.

Referring to FIG. 2, the signal sensing terminal unit 52 includes a measurement interface 52_1 , an analog/digital converter 52_2, a sensing interface 52_3, a controller 52_4, a storing unit 52_5, a signal modulator

52_6, a signal demodulator 52_7, a transmitter 52_8, and a receiver

52_9.

Here, the signal sensing terminal unit 52 is installed inside a test box or manhole 50 in the underground, for example. A cover support portion 56 that contacts a manhole cover 54 at an upper portion of the manhole 50 is generally formed of cast iron, contacts the earth, has humidity and can keep a ground resistance of less than about 50 ohms. Thus, the cover support portion 56 has a sufficient condition for a communication ground of the signal sensing terminal unit 52. Thus, in the current embodiment of FIG. 2, the cover support portion 56 is utilized as a communication ground of the signal sensing terminal unit 52 by electrically connecting a ground line 59 to the cover support portion 56. In addition, when corrosion signal sensing/relay terminal units 60_1 to 60_6 which will be described later, as well as the signal sensing terminal unit 52 are installed in the test boxes or manholes 60_1A to 60_6A, the cover support portion 56 may be utilized as a communication ground of the corrosion signal sensing/relay terminal units 60_1 to 60_6. A conductive structure which contacts the ground of the valve chamber 20 and the static pressure chamber 30 and keeps humidity may be utilized as a communication ground even in the signal sensing terminal units 24 and 36 installed in the valve chamber 20 and the static pressure chamber 30. Meanwhile, the signal sensing terminal unit 52, the corrosion signal sensing/relay terminal units 60_1 to 60_6, and the signal sensing terminal units 24 and 36 are communication grounds and may use a low-resistance metallic conductor (less than of about 50 ohms) additionally installed in the underground.

The measurement interface 52_1 measures a corrosion signal from a sacrificial anode 5OB installed in the underground, for example, formed of magnesium, a reference electrode 5OA formed of copper, for example, and a pipe measurement point 5OC on the pipe 10_7. Here, the measurement signals include a potential Eon between the sacrificial anode and the reference electrode, a potential Eoff between the pipe and the reference electrode, and a current Ecorr between the sacrificial anode and the pipe. Preferably, the measurement interface 52_1 eliminates the effect of a communication signal on the measurement signals via the pipes 10_1 to 10_9 by filtering a signal having the same frequency band as the pipe communication signal (in the current embodiment, a frequency shift keying (FSK) signal) among the measurement signals and by eliminating it.

Sensing signals are inputted to the sensing interface 52_3 from sensors S1 to Sn for sensing an environment of the test box or manhole 5tO. The sensor S1 is a test box open sensor for sensing opening of the cover 54 of the test box or manhole 50, and the sensors S2 to Sn may be a pressure sensor for sensing pressure of the pipe 10_7, a water level sensor for sensing a water level when water stays in the test box or manhole 50, a temperature sensor for sensing temperature inside the test box or manhole 50, and a gas sensor for sensing gas leakage of the pipe 10_7. The analog/digital converter 52_2 converts analog measurement signals inputted from the measurement interface 52_1 and analog sensing signals inputted from the sensing interface 52_3 into digital measurement signals and digital sensing signals. The storing unit 52_5 makes the digital measurement signals and the digital sensing signals as a database according to control of the controller 52_4 and stores them and temporarily stores signals received by the receiver 52_9 and demodulated by the signal demodulator 52_7.

Here, in the exemplary embodiment of the present invention, the signals transmitted via the pipes 10_1 to 10_7 are FSK modulation signals. As shown in FIG. 6, the FSK modulation signals are signals in which regarding binary data represented by "01101", "0" is modulated into a first frequency signal ASK1 and "1" is modulated into a second frequency signal ASK2 using two different frequency signals ASK1 and ASK2. The inventors of the present invention have carried out experiments on several communication methods regarding the pipes 10_1 to 10_7. As a result of experiments, it was ascertained that the FSK modulation signals are most suitable for communication signals via the pipes 10_1 to 10_7 and frequencies of the FSK modulation signals are preferably in a low frequency range of 1-40 kHz. The receiver 52_9 is electrically connected to the pipe 10_7 and receives the FSK modulation signal from the pipe 10_7. The signal demodulator 52_7 demodulates the FSK modulation signal received by the receiver 52_9 and converts the demodulated FSK signal into an original data format represented by "0" and "1". The signal modulator 52_6 modulates data to be transmitted, represented by "0" and "1", into an FSK signal, as shown in FIG. 6. The transmitter 52_8 is electrically connected to the pipe 10_7 and transmits the FSK signal to the pipe 10_7.

The controller 52_4 controls the system to make digital measurement signals and digital sensing signals inputted from the analog/digital converter 52_2 as a database and to store them in the storing unit 52_5. Here, the measurement signals are cyclically measured, for example, per 60 second. In this case, preferably, each of measurement signals (for example, Eon, Eoff, and Ecorr) is made as a database together with its measurement time data. The sensing signals may be always monitored by the controller 52_4 and may be cyclically made as a database together with time data. In addition, for example, the sensing signals may be made as a database together with time data even when a specific event is generated by sensing signals such as cover opening sensing, abnormal pressure sensing, abnormal water level sensing, abnormal temperature sensing, and gas leakage sensing. In addition, the storing unit 52_5 may have a sufficient storing capacity for about 6 months.

The controller 52_4 controls the system to temporarily store a signal received by the receiver 52_9 and demodulated by the signal demodulator 52_7 in the storing unit 52_5, to interpret the demodulated signal, for example, a signal having a format shown in FIG. 7, to check whether a destination ID is its own identification code and a source ID is the RTU 40, and then, if itself is a signal designated as a destination and is a command for transmitting measurement signal data and/or sensing signal data from the RTU 40, to insert an identification code of the RTU 40 as the destination ID and to insert its own identification code as the source ID, as shown in FIG. 6, and then to convert the measurement data into a format having a shape attached to a data area, to generate a measurement signal data message, to transmit the measurement signal (or sensing signal) data message to the signal modulator 52_6, to modulate the measurement signal data message into an FSK signal using the signal modulator 52_6 and then to be transmitted to the pipe 10_7 using the transmitter 52_8, so as to read the measurement signal data stored in the storing unit 52_5 to be transmitted to the RTU 40. Meanwhile, the controller 53 interprets the signal received by the receiver 52_8, demodulated by the signal demodulator 52_6 and then temporarily stored in the storing unit 52_5 and if the destination ID is not its own identification code, discards and ignores the corresponding signal.

In addition, the controller 52_4 controls the system, if it is determined that the digital measurement signal inputted from the analog/digital converter 52_2 is not normal, that is, as a result of analyzing a potential Eon between a sacrificial anode and a reference electrode, a potential Eoff between a pipe and the reference electrode, and a current Ecorr between the sacrificial anode and the pipe, if it is determined that the state of the pipe is damaged or cut, or if it is determined that the digital sensing signal inputted from the analog/digital converter 52_2 is abnormal, for example, if it is determined that a cover opening sensing signal, an abnormal pressure sensing signal, an abnormal water level sensing signal, an abnormal temperature sensing signal or a gas leakage sensing signal is inputted, for example, as shown in a format of FIG. 7, to use the destination ID as an identification code for the RTU 40 and to use the source ID as its own identification code, to fill a data area with measurement signal and/or sensing signal abnormal state data, to generate a measurement signal (or sensing signal) abnormal message and to modulate the measurement signal abnormal message into an FSK signal using the signal modulator 52_6 and then to be transmitted to the pipe 10_7 using the transmitter 52_7, so as to transmit its measurement signal and/or its sensing signal abnormal state to the RTU 40.

Meanwhile, the corrosion signal sensing/relay terminal units 60_1 to 60_6 (hereinafter, simply referred to as "signal sensing/relay unit") are respectively installed at both sides of the insulator 15 for electrically dividing the pipes 10_2 and 10_3, sense corrosion signals at the respective pipes 10_2 and 10_3 and connect signal transmission lines blocked by the insulator 15 of the pipes 10_2 and 10_3. The detailed block construction of the signal sensing/relay units 60_1 to 60_6 is shown in FIG. 3.

Referring to FIG. 3, the signal sensing/relay units 60_1 to 60_6 includes measurement interfaces 61 and 61 A, sensing interfaces 61' and 61 A', analog/digital converts 62 and 62A, controllers 63 and 63A, storing units 64 and 64A, signal modulators 65 and 65A, signal demodulators 66 and 66A, transmitters 67 and 67A, receivers 68 and 68A, and communication interfaces 69 and 69A.

The measurement interfaces 61 and 61A measure corrosion signals from sacrificial anodes 6OB and 6OB' installed in the underground, for example, formed of magnesium, reference electrodes 6OA and 6OA' formed of copper, for example, and pipe measurement points 6OC and 6OC of the pipes 10_2 and 10_3. Here, the measurement signals include a potential Eon between the sacrificial anode and the reference electrode, a potential Eoff between the pipe and the reference electrode, and a current Ecorr between the sacrificial anode and the pipe. Preferably, the measurement interfaces 61 and 61 A eliminate the effect of a communication signal on the measurement signals via the pipes 10_1 to 10_7 by filtering a signal having the same frequency band as the pipe communication signal (in the current embodiment, a frequency shift keying (FSK) signal) among the measurement signals and by eliminating it.

Sensing signals sensed by the sensors S1 to Sn are inputted to the sensing interfaces 61' and 61 A'. Here, the sensors S1 to Sn sense environments of the test boxes or the manholes 60_1A to 60_6A. The sensors S1 to Sn may be a test box open sensor for sensing cover opening of the test boxes or manholes 60_1A to 60_2A, a pressure sensor for sensing pressure of the pipes 10_2 and 10_3, a water level sensor for sensing a water level when water stays in the test boxes or manholes 60_1A to 60_2A, a temperature sensor for sensing temperature inside the test boxes or manholes 60_1A to 60_2A, and a gas sensor for sensing gas leakage of the pipes 10_2 and 10_3.

The analog/digital converters 62 and 62A convert analog measurement signals inputted from the measurement interfaces 61 and 61 A and analog sensing signals inputted from the sensing interfaces 61' and 61A' into digital measurement signals and digital sensing signals. The storing units 64 and 64A make the digital measurement signals and the digital sensing signals as a database according to control of the controllers 63 and 63A and stores them and temporarily store signals received by the receivers 68 and 68A and demodulated by the signal demodulators 66 and 66A. The receivers 68 and 68A receive FSK modulation signals from the pipes 10_2 and 10_3 or the communication interfaces 69 and 69A of the adjacent signal sensing/relay units 60_1 to 60_6 via the communication interfaces 69 and 69A electrically connected to the pipes 10_2 and 10_3 and connected to the communication interfaces 69A and 69 of the adjacent signal sensing/relay units 60_1 to 60_6.

The signal demodulators 66 and 66A demodulate the FSK modulation signals received by the receivers 68 and 68A and convert the demodulated FSK signals into an original data format represented by "0" and "1". The signal modulators 65 and 65A modulate data to be transmitted, represented by "0" and "1", into FSK signals, as shown in FIG. 6. The transmitters 67 and 67A transmit the FSK signals modulated by the signal modulators 65 and 65A to the communication interfaces 69 and 69A electrically connected to the pipes 10_2 and 10_3 and connected to the communication interfaces 69A and 69 of the adjacent signal sensing/relay units 60_1 to 60_6.

The communication interfaces 69 and 69A are switching controlled to be electrically connected to the pipes 10_2 and 10_3 and to be electrically connected to the communication interfaces 69A and 69 of the adjacent signal sensing/relay units 60_1 to 60_6, to transmit the FSK modulation signals received from the pipes 10_2 and 10_3 and the communication interfaces 69A and 69 of the adjacent signal sensing/relay units 60_1 to 60_6 according to control of the controllers 63 and 63A to the receivers 68 and 68A and to transmit the FSK modulation signals from the transmitters 67 and 67A to the pipes 10_2 and the communication interfaces 69A and 69 of the adjacent signal sensing/relay units 60_1 to 60_6. The controllers 63 and 63A control the system to make digital measurement signals and digital sensing signals inputted from the analog/digital converters 62 and 62A as a database and to store them in the storing units 64 and 64A. Here, the measurement signals are cyclically measured, for example, per 60 second. In this case, preferably, each of measurement signals (for example, Eon, Eoff, and Ecorr) is made as a database together with its measurement time data. The sensing signals may be always monitored by the controller 52_4 and may be cyclically made as a database together with time data. In addition, for example, the sensing signals may be made as a database together with time data even when a specific event is generated by sensing signals such as cover opening sensing, abnormal pressure sensing, abnormal water level sensing, abnormal temperature sensing, and gas leakage sensing. In addition, the storing units 64 and 64A may have a sufficient storing capacity for about 6 months.

The controllers 63 and 63A control the system to temporarily store signals received by the receivers 68 and 68A and demodulated by the signal demodulators 66 and 66A in the storing units 64 and 64A, to interpret the demodulated signals, for example, signals each having a format shown in FIG. 7, to check whether a destination ID is its own identification code and a source ID is the RTU 40, and then, if itself is a signal designated as a destination and is a command for transmitting measurement signal data and/or sensing signals from the RTU 40, to insert an identification code of the RTU 40 as the destination ID and to insert its own identification code as the source ID, as shown in FIG. 7, and then to convert the measurement data and/or sensing signals into a format having a shape attached to a data area, to generate measurement signal (or sensing signal) data messages, to transmit the measurement signal (or sensing signal) data messages to the signal modulators 65 and 65A, to modulate the measurement signal (or sensing signal) data messages into FSK signals using the signal modulators 65 and 65A and then to be transmitted to the communication interfaces 69A and 69 of the adjacent signal sensing/relay units 60_1 to 60_6 or the pipes 10_2 and 10_3 using the transmitters 67 and 67A and the communication interfaces 69 and 69A, so as to read the measurement signal data stored in the storing units 64 and 64A to be transmitted to the RTU 40.

Here, the controller 63 of the signal sensing/relay unit 60_1 controls the system, if the signal received by the receiver 68 is interpreted and a destination ID is not its own identification code and a source ID is the RTU 40, to determine that the corresponding signal signals from the RTU 40 to the terminal unit positioned at a lower stream that its position via the pipe 10_2, to read demodulation data temporarily stored in the storing unit 64 and corresponding to the corresponding signal and then to modulate the demodulation data using the signal modulator 65 and then to transmit the modulated data to the communication interface 69A of the adjacent signal sensing/relay unit 60_2 via the transmitter 67 and the communication interface 69. In addition, the controller 63 controls the system, if the signal received by the receiver 68 is interpreted and the destination ID is the RTU 40, to determine that the corresponding signal is transmitted from the terminal unit positioned at a lower stream that its position to the RTU 40 and is received via the communication interface 69A of the adjacent signal sensing/relay unit 60_2, to read demodulation data temporarily stored in the storing unit 64 and corresponding to the corresponding signal and then to modulate the demodulation data using the signal modulator 65 and then to transmit the modulated data to the pipe 10_2 via the transmitter 67 and the communication interface 69.

Meanwhile, the controller 63A of the signal sensing/relay unit 60_2 controls the system, if the signal received by the receiver 68 is interpreted and a destination ID is not its own identification code and a source ID is the RTU 40, to determine that the corresponding signal is received from the RTU 40 to the terminal unit positioned at a lower stream that its position via the communication interface 69 of the adjacent superior-position signal sensing/relay unit 60_1 , to read demodulation data temporarily stored in the storing unit 64A and corresponding to the corresponding signal and then to modulate the demodulation data using the signal modulator 65A and then to transmit the modulated data to the pipe 10_3 via the transmitter 67A and the communication interface 69A. In addition, the controller 63A controls the system, if the signal received by the receiver 68 is interpreted and the destination ID is the RTU 40, to determine that the corresponding signal is transmitted from the terminal unit positioned at a lower stream that its position to the RTU 40 and is received via the pipe 10_3, to read demodulation data temporarily stored in the storing unit 64A and corresponding to the corresponding signal and then to modulate the demodulation data using the signal modulator 65A and then to transmit the modulated data to the communication interface 69 of the adjacent superior-position signal sensing/relay unit 60_1 via the transmitter 67A and the communication interface 69A.

In addition, the controller 63 and 63A control the system, if it is determined that the digital measurement signals inputted from the analog/digital converters 62 and 62A are not normal, that is, as a result of analyzing a potential Eon between a sacrificial anode and a reference electrode, a potential Eoff between a pipe and the reference electrode, and a current Ecorr between the sacrificial anode and the pipe, if it is determined that the state of the pipe is damaged or cut, or if it is determined that the digital sensing signals inputted from the analog/digital converters 62 and 62A are abnormal, for example, if it is determined that a cover opening sensing signal, an abnormal pressure sensing signal, an abnormal water level sensing signal, an abnormal temperature sensing signal or a gas leakage sensing signal is inputted, for example, as shown in a format of FIG. 7, to use the destination ID as an identification code for the RTU 40 and to use the source ID as its own identification code, to fill a data area with measurement signal [and/or sensing signal] abnormal state data, to generate measurement signal [and/or sensing signal] abnormal messages and to modulate the measurement signal [and/or sensing signal] abnormal messages into FSK signals using the signal modulators 65 and 65A and then to be transmitted to an upper stream side 10_9 using the transmitters 67 and 67A and the communication interfaces 69 and 69A, so as to transmit its measurement signal abnormal state and/or its sensing signal abnormal state to the RTU 40. Here, the controller 63 of the superior-position signal sensing/relay unit 60_1 controls the system so that the FSK signal can be transmitted to the pipe 10_2 via the transmitter 67 and the communication interface 69, and the controller 63A of the subordinate signal sensing/relay unit 60_2 controls the system so that the FSK signal can be transmitted to the communication interface 69 of the superior-position signal sensing/relay unit 60_1 via the transmitter 67A and the communication interface 69A.

In other words, for example, when the RTU 40 transmits a signal to the signal sensing/relay unit 60_3 (see FIG. 1 ), as shown by solid-line arrow of FIG. 8, the signal passes the pipe 10_2, the communication interface 69, the receiver 68, the controller 63, the transmitter 67, and the communication interface 69 of the superior-position signal sensing/relay unit 60_1 , and is transmitted to the pipe 10_3 via the communication interface 69A, the receiver 68A, the controller 63A, the transmitter 67A, and the communication interface 69A of the subordinate signal sensing/relay unit 60_2.

Meanwhile, for example, when the signal sensing/relay unit 60_3 (see FIG. 1 ) transmits a signal to the RTU 40, as shown by dotted-line arrow of FIG. 8, the signal passes the pipe 10_3, the communication interface 69A, the receiver 68A, the controller 63A, the transmitter 67A, and the communication interface 69A of the subordinate signal sensing/relay unit 60_2 and is transmitted to the pipe 10_2 via the communication interface 69, the receiver 68, the controller 63, the transmitter 67, and the communication interface 69 of the superior-position signal sensing/relay unit 60_1.

The signal sensing terminal unit 24, the control unit 26, the driving mechanism 28 for opening and closing the valve 22, and the sensors S1 to Sn for sensing an environment of the valve chamber 20 may be installed in the valve chamber 20, as shown in FIG. 4.

Here, the sensors S1 , S2, . . . may be an entrance open sensor for sensing opening of an entrance of the valve chamber 20, a water level sensor for sensing a water level when water stays in the valve chamber 20, a temperature sensor for sensing temperature inside the valve chamber 20, and a gas sensor for sensing gas leakage of the pipes 10_6 and 10_5. The sensor Sn is a pressure sensor for sensing pressure of the pipe 10_6. The signal sensing terminal unit 24 includes a sensing interface

24_1 , an analog/digital converter 24_2, a controller 24_3, a storing unit 24_4, a signal modulator 24_6, a signal demodulator 24_5, a transmitter 24_8, a receiver 24_7, and a communication interface 24_9.

Sensing signals are inputted to the sensing interface 24_1 from the sensors S1 to Sn for sensing an environment of the valve chamber 20. The analog/digital converter 24_2 converts analog sensing signals inputted from the sensing interface 24_1 into digital sensing signals. The storing unit 24_4 makes the digital sensing signals as a database according to control of the controller 24_3 and simultaneously temporarily stores the signals received by the receiver 24_7 and demodulated by the signal demodulator 24_5.

The receiver 24_7 receives FSK modulation signals from the pipe 10_6 via the communication interface 24_9 electrically connected to the pipe 10_6 and connected to the communication interface 26_1 of the control unit 26. The signal demodulator 24_5 demodulates the FSK modulation signals received by the receiver 24_7 and converts the demodulated FSK signals into an original data format represented by "0" and "1". The signal modulator 24_6 modulates data to be transmitted, represented by "0" and "1", into FSK signals, as shown in FIG. 6. The transmitter 24_8 transmits the FSK signals modulated by the signal modulator 24_6 to the pipe 10_ via the communication interface 24_9.

The communication interface 24_9 is switching controlled to be electrically connected to the pipe 10_6 and to be electrically connected to the communication interface 26_1 of the control unit 26, to transmit the FSK modulation signals received from the pipe 10_6 to the receiver 24_7, to transmit the FSK modulation signals from the transmitter 24_8 to the pipe 10_6, and to transmit a control signal of the controller 24_3 to the communication interface 26_1 of the control unit 26. The controller 24_3 controls the system to make digital sensing signals inputted from the analog/digital converters 24_2 as a database and to store them in the storing unit 24_4. Even in this case, the sensing signals may be always monitored by the controller 24_3 and may be cyclically made as a database together with time data. In addition, for example, the sensing signals may be made as a database together with time data even when a specific event is generated by sensing signals such as cover opening sensing, abnormal pressure sensing, abnormal water level sensing, abnormal temperature sensing, and gas leakage sensing. In addition, the storing unit 24_4 may have a sufficient storing capacity for about 6 months.

The controller 24_3 control the system to temporarily store signals received by the receiver 24_7 and demodulated by the signal demodulator 24_5 in the storing unit 24_4, to interpret the demodulated signals, for example, signals each having a format shown in FIG. 7, to check whether a destination ID is its own identification code and a source ID is the RTU 40, and then, if itself is a signal designated as a destination and is a command for transmitting sensing signals from the RTU 40, to insert an identification code of the RTU 40 as the destination ID and to insert its own identification code as the source ID, as shown in FIG. 7, and then to convert the sensing signals data into a format having a shape attached to a data area, to generate sensing signal data messages, to transmit the sensing signal data messages to the signal modulator 24_6, to modulate the sensing signal data messages into FSK signals using the signal modulator 24_6 and then to be transmitted to the pipe 10_6 via the transmitter 24_8 and the communication interface 24_9, so as to read the sensing signal data stored in the storing unit 24_4 from the storing unit 24_4 to be transmitted to the RTU 40.

In addition, if a destination ID of the demodulated and received signal is its own identification code, a source ID thereof is the RTU 40 and is a command signal for driving opening and closing the valve 22 via the driving mechanism 28 from the RTU 40, the controller 24_3 transmits the command signal to the communication interface 26_1 of the control unit 26 via the communication interface 24_9. Meanwhile, the controller 24_3 interprets the signal received by the receiver 24_7 and if a destination ID is not its own identification code, the controller 24_3 discards and ignores the corresponding signal.

In addition, the controller 24_3 controls the system, if it is determined that the digital sensing signals inputted from the analog/digital converter 24_2 is abnormal, for example, if it is determined that a cover opening sensing signal, an abnormal pressure sensing signal, an abnormal water level sensing signal, an abnormal temperature sensing signal or a gas leakage sensing signal is inputted, for example, as shown in a format of FIG. 7, to use the destination ID as an identification code for the RTU 40 and to use the source ID as its own identification code, to fill a data area with sensing signal abnormal state data, to generate a sensing signal abnormal message and to modulate the sensing signal abnormal message into FSK signals using the signal modulator 24_6 and then to be transmitted to the pipe 10_6 via the transmitter 24_8 and the communication interface 24_9.

The control unit 26 includes a controller 26_2 for controlling a driver 26_3 for driving the driving mechanism 28 according to the control signal of the RTU 40 inputted from the controller 24_3 of the signal sensing terminal unit 24 via the communication interfaces 24_9 and 26_1. Here, the driving mechanism 28 is a well-known mechanism for driving opening and closing the valve 22. In addition, the driver 28 may be a well-known circuit for driving the driving mechanism 28. Meanwhile, the static pressure chamber 30 is a facility for controlling a fluid that flows from a high-pressure pipe to an intermediate-pressure pipe or from the intermediate-pressure pipe to a low-pressure pipe, for example, pressure of a gas. A signal sensing terminal unit 36, a control unit 38, driving mechanisms 35 and 37 for opening and closing valves 34 and 32, and sensors S1 to Sn and Sn+1 for sensing an environment of the static pressure chamber 30 may be installed in the static pressure chamber 30, as shown in FIG. 5.

Here, the sensors S1 , S2, . . . may be an entrance open sensor for sensing opening of an entrance of the static pressure chamber 30, a water level sensor for sensing a water level when water stays in the static pressure chamber 30, a temperature sensor for sensing temperature inside the static pressure chamber 30, and a gas sensor for sensing gas leakage of the pipe 10_2. The sensors Sn and Sn+1 are pressure sensor for sensing pressure of the pipe 10_2. Functions of a sensing interface 36_1 , an analog/digital converter

36_2, a controller 36_3, a storing unit 36_4, a signal modulator 36_6, a signal demodulator 36_5, a transmitter 36_8, a receiver 36_7, and a communication interface 36_9, which constitute the signal sensing terminal unit 36, will be substantially the same as those of the sensing interface 24_1 , the analog/digital converter 24_2, the controller 24_3, the storing unit 24_4, the signal modulator 24_6, the signal demodulator 24_5, the transmitter 24_8, the receiver 24_7, and the communication interface 24_9, which constitute the signal sensing terminal unit 24 described with reference to FIG. 4.

The RTU 40 monitors and controls the entire operations of the signal sensing/relay units 60_1 to 60_6, the signal sensing terminal unit 52, and the signal sensing terminal units 24 and 36/control units 26 and 38 positioned in its own jurisdiction region, cyclically collects measurement signal data and/or sensing signal data from the signal sensing/relay terminal units 60_1 to 60_6, the signal sensing terminal unit 52, and the signal sensing terminal units 24 and 36 via the pipe 10_2, transmits the collected signal data to the management center 70 cyclically or in real-time via a wireless data communication network or a wired data communication network which is a public communication network and when receiving a measurement signal abnormal message and/or a sensing signal abnormal message from the signal sensing/relay units 60_1 to 60_6, the signal sensing terminal unit 52, and the signal sensing terminal units 24 and 36/control units 26 and 38 in real-time, transmits the measurement signal abnormal message and/or sensing signal abnormal message to the management center 70 immediately via the wireless data communication network or the wired data communication network.

A system unit of the management center 70 analyzes and monitors the state of the pipe in a wide area unit based on signals transmitted from a plurality of RTU 40 and when receiving the measurement signal abnormal message, analyzes it, checks mobile communication terminal information (for example, a telephone number) of a patrolman who controls the corresponding abnormal signal message sending place in a database (not shown), transmits data including corresponding mobile communication terminal information, abnormal signal message sending place information, and abnormal signal message information to a short message service center (SMSC) 100 of a mobile communication network, as a wireless data communication network, for example, and notifies the patrolman's mobile communication terminal of arrival of an abnormal signal message from the abnormal signal message sending place. As a result, the patrolman who patrols a corresponding district immediately runs to the abnormal signal message sending place and exactly checks situations generated by the abnormal signal message and then transmits a circumstantial report to the management center 70 via the mobile communication network using the mobile communication terminal. Thus, the system unit of the management center 70 rapidly confronts the abnormal signal message.

Here, the system unit of the management center 70 may analyze the abnormal signal message when receiving it, if it is determined that a serious danger occurs in the corresponding abnormal signal message sending place, may transmit a control message for allowing the control signal to be transmitted to the signal sensing terminal unit of the corresponding valve chamber of static pressure chamber, so as to intercept a fluid (for example, gas) flowing into the corresponding abnormal signal message sending place via the pipe.

In the underground piping state remote monitoring and safety control system having the above structure according to the present invention, regarding a signal transmission system of the RTU 40, the plurality of signal sensing/relay units 60_1 to 60_n, the signal sensing terminal unit 52, the signal sensing terminal unit 24 of the valve chamber, and the signal sensing terminal unit 36 of the static pressure chamber, the case where a command signal for uploading measurement signal data and sensing signal data from the RTU 40 to the signal sensing terminal unit 52 is transmitted and the measurement signal data and the sensing signal data are uploaded to the RTU 40 from the signal sensing terminal unit 52 according to the command signal will be described with reference to FIG. 9. That is, the RTU 40 generates a command signal in which a destination ID is an identification code of the signal sensing terminal unit 52, a source ID is an identification code of the RTU 40 and data is a command for uploading the measurement signal data and/or the sensing signal data in the format of FIG. 7, performs FSK modulation and transmits the FSK modulated signal. Then, the signal sensing/relay unit 60_1 receiving the command signal through the pipe demodulates an FSK signal, performs FSK modulation because the destination ID is not its own identification code and transmits the FSK modulated signal to a down stream side terminal unit. Similarly, the signal sensing/relay units 60_2 to 60_n receiving command signals demodulate FSK signals, perform FSK modulation because the destination ID is not its own identification code and transmit the FSK modulated signals to the down stream side terminal unit. As a result, the signal sensing terminal unit 52 finally receiving the command signal reads measurement signal data and sensing signal data stored in its own storing unit, generates a measurement signal data message and sensing signal data message in which a destination ID is an identification code of the RTU 40 in the format of FIG. 7 and a source ID is an identification code of the signal sensing terminal unit 52 and data is the measurement signal data and the sensing signal data, performs FSK modulation and transmits the FSK modulated signal via the pipe.

Then, the signal sensing/relay terminal unit 60_n, receiving FSK signals regarding to the measurement signal data message and the sensing signal data message via the pipe, demodulates the FSK signals, performs FSK modulation for the FSK demodulated signals because the destination ID is an identification code of the RTU 40, and transmits the FSK modulated signals to the upper stream side terminal unit. Similarly, the signal sensing/relay terminal units 60_n-1 to 60_1 , receiving the FSK signals regarding to measurement signal data message and the sensing signal data message via the pipe, demodulate the FSK signals, perform FSK modulation the FSK demodulated signals because the destination ID is an identification code of the RTU 40, and transmit the FSK modulated signals to the RTU 40. As such, the RTU 40 receives and demodulates the measurement signal data message and the sensing signal data message from the signal sensing terminal unit 52 to collect measurement data and sensing data of the signal sensing terminal unit 52.

A control operation to be performed when the signal sensing/relay units 60_3 to 60_n receive signals will now be described with reference to FIGS. 10 and 3.

First, if FSK signals are received by the receivers 68 and 68A, the FSK signals are transmitted to the signal demodulators 66 and 66A and are demodulated and then are transmitted to the controllers 63 and 63A, and the demodulation signal is temporarily stored in the storing units 64 and 64A by the controllers 63 and 63A (operations S10-S14).

After that, the controllers 63 and 63A interpret the demodulated data, check a destination ID, check a destination of the corresponding receiving data and determine whether the destination is itself (operations S16-S18). As a result of determination in operation S 18, if it is determined that the destination ID is its own identification code (that is, if the destination is itself), the controllers 63 and 63A interpret commands in a data area of the demodulation data and perform a control operation according to the command (operation S20). Here, for example, if the command in the data area of the demodulated data is an upload command of the measurement data and/or the sensing data, the controllers 63 and 63A control the system to read measurement signal data and/or sensing signal data stored in the storing units 64 and 64A, to insert an identification code of the RTU 40 as the destination ID, to insert its own identification code as the source ID, to insert the read measurement signal data and/or sensing signal data in the data area, to generate a measurement signal data message and/or sensing signal data message, to send the measurement signal data message and/or sensing signal data message to the signal modulators 65 and 65A, to perform FSK modulation and then to transmit the FSK modulated signal to the upper stream side via the transmitters 67 and 67A and the communication interfaces 69 and 69A.

As a result of determination in operation S18, if it is determined that the destination ID is not its own identification code (that is, if the destination is not itself), the controllers 63 and 63A control the system to read the demodulation data temporarily stored in the storing units 64 and 64A, to transmit the read demodulated data to the signal modulators 65 and 65A, to perform FSK modulation, and then to transmit the FSK modulated signal to the down stream side via the transmitters 67 and 67A and the communication interfaces 69 and 69A (operations S22-S26). A control operation to be performed when the signal sensing terminal units 24 and 36 receive signals will now be described with reference to FIGS. 11 , 4, and 5.

First, if FSK signals are received by the receivers 24_7 and 36_7, the FSK signals are transmitted to the signal demodulators 24_5 and 36_5 and are demodulated and then are transmitted to the controllers 24_3 and 36_3, and the demodulation data is temporarily stored in the storing units 24_4 and 36_4 by the controllers 24_3 and 36_3. The controllers 24_3 and 36_3 interpret the demodulation data, check a destination ID and determine whether a destination is itself (operations S30 to S36).

As a result of determination in operation S36, if it is determined that the destination ID is not its own identification code (that is, if the destination is not itself), the controllers 24_3 and 36_3 discard and ignore the demodulation data (operation S38) and control returns to operation S30 and the controllers 24_3 and 36_3 control the system to check whether other data is received. Meanwhile, as a result of determination in operation S36, if it is determined that the destination ID is its own identification code (that is, if the destination is itself), the controllers 24_3 and 36_3 interpret a command in a data area of the demodulation data (operation S40). As a result of interpretation of the command in operation S40, it is checked whether the command is a data transmission command (operation S42), if the command in the data area of the demodulation data is an upload transmission command of sensing data, the controllers 24_3 and 36_3 control the system to read sensing signal data stored in the storing units 24_4 and 36_4, to insert an identification code of the RTU 40 as a destination ID, to insert its own identification code as a source ID, to insert the read sensing signal data in the data area, to generate a sensing signal data message, to perform FSK modulation, and then to transmit the FSK modulated signal to the signal modulators 24_6 and 36_6 via the transmitters 24_8 and 36_8 and the communication interfaces 24_9 and 36_9. After that, control returns to operation S30 and the controllers 24_3 and 36_3 control the system to check whether other data is received.

Meanwhile, as a result of determination of operation S42, if it is checked that the command in the data area of the demodulation data is not the upload transmission command of the sensing data, the controllers 24_3 and 36_3 check whether the command in the data area of the demodulation data is a control command for the control units 26 and 38 (operation S46). If it is checked in operation S48 that the command is a control unit control command, the controllers 24_3 and 36_3 transmit the checked control command to the control units 26 and 38 via the communication interfaces 24_9 and 36_9. After that, control returns to operation S30 and the controllers 24_3 and 36_3 control the system to check whether other data is received. Meanwhile, the controller 26_2 and 38_2 of the control units 26 and 38 which receive control signals from the signal sensing terminal units 24 and 36 via the communication interfaces 26_1 and 38_1 , interpret the control signal, check whether a command from the RTU 40 is a command for opening the valves 22(34 and/or 32) or a command for closing the valves 22(34 and/or 32), and control the drivers 26_3 and 38_3 to open or close the valves 22(34 and/or 32) by the driving mechanism 28(35 and/or 37) according to the checked result.

A control operation of measuring corrosion signals by the signal sensing terminal unit 52 and the signal sensing/relay terminal units 60_1 and 60_2 will now be described with reference to FIGS. 12, 2, and 3. First, the controllers 52_4, 63, and 63A start time count (operation

S50), measure corrosion signals [including a potential Eon between a sacrificial anode and a reference electrode, a potential Eoff between a pipe and the reference electrode, and a current between the sacrificial anode and the pipe] via the measurement interfaces 52_1 , 61 , and 61 A and receive the measurement signals via the analog/digital converters 52_2, 62, and 62A (operation S52).

After that, the controllers 52_4, 63, and 63A make the measurement signals received via the analog/digital converters 52_2, 62, and 62A as a database together with its measurement time and store them in the storing units 52_4, 64, and 64A (operation S54).

The controllers 52_4, 63, and 63A analyze the measurement signals and determine whether the measurement signals are abnormal, like that the measurement signals are classified into signals indicating a worry about damages or cut of the pipe, for example (operation S56). If it is determined in operation S56 that the measurement signals are abnormal, the controllers 52_4, 63, and 63A control the system to insert an identification code of the RTU 40 as the destination ID, to insert its own identification code as the source ID, to insert data for identifying a signal indicating abnormality of the measurement signal in the data area together with the read measurement signal data, to generate a measurement signal abnormal message, to send the measurement signal abnormal message to the signal modulators 52_6, 65, and 65A, to perform FSK modulation and then to transmit the FSK modulated signal to the upper stream side via the transmitters 52_8, 67, and 67A (operation S58). If it is determined in operation S56 that the measurement signal is not abnormal or after the system is controlled to transmit the measurement signal abnormal message in operation S58, the controllers 52_4, 63, and 63A check whether the counted time T reaches a predetermined setting time T1 (for example, 60 seconds) (operation S60).

If it is checked in operation S60 that the counted time T reaches the predetermined setting time T1 , the controllers 52_4, 63, and 63A reset the count values (operation S62) and the control operation proceeds to the above operation S50. A control operation of receiving data from a pressure sensor, a temperature sensor, and a water level sensor from the signal sensing terminal units 24 and 26 will now be described with reference to FIGS. 13, 4, and 5. Here, only for simplification of explanation, only the control operation in the signal sensing terminal units 24 and 26 has been described. However, it will be easily understood that a control operation can be performed when data is received from the pressure sensor, the temperature sensor and the water level sensor even in the corrosion signal sensing terminal unit and the corrosion signal sensing/relay terminal unit illustrated in FIGS. 2 and 3. First, the controllers 24_3 and 36_3 monitor digital sensing signals which are inputted from pressure sensors Sn and (Sn, Sn+1 ), a temperature sensor (for example, S1) and a water level sensor (for example, S2) via the sensing interfaces 24_1 and 36_1 and are converted into digital signals by the analog/digital converters 24_2 and 36_2 (operation S70) and start time count (operation S72). After that, if the digital sensing signals converted into the digital signals by the analog/digital converters 24_2 and 36_2 are inputted, the controllers 24_3 and 36_3 check whether the inputted sensing signals of the sensors are abnormal (operations S74 to S76). Here, the controllers 24_3 and 36_3 have threshold values with respect to pressure sensing signals of the pressure sensors (Sn)(Sn, Sn+1 ), a temperature sensing signal of the temperature sensor (for example, S1 ), and a water level sensing signal of the water level sensor (for example, S2) and check whether, whenever each sensing signal is inputted, a threshold value of the sensing signal is greater than or smaller than each threshold value. The threshold values may be properly set in consideration of the case where a pressure sensing signal indicates a very high pressure or very low pressure and there is a worry about a damage or destruction of a pipe, the case where a temperature sensing signal is too high and there is a worry about a damage of an electronic device in a static pressure chamber or valve chamber or destruction of a gas pipe or the case where a water level sensing signal indicates a very high water level and there is a worry about a damage of the electronic device in the static pressure chamber of valve chamber. If it is checked in operation S76 that the inputted sensing signals are abnormal, the controllers 24_3 and 36_3 control the system to insert an identification code of the RTU 40 as a destination ID, to insert its own identification cod as a source ID, to insert data for identifying a signal notifying a data area of sensing signal abnormality together with the sensing signal data to generate a sensing signal abnormal message, to transmit the sensing signal abnormal message to the signal modulators 24_6 and 36_6, to perform FSK modulation and then to transmit the FSK modulated signals to the pipes 10_6 and 10_2 via the transmitters 24_8 and 36_8 (operation S78). If it is determined in operation S76 that the sensing signals are not abnormal, the controllers 24_3 and 36_3 check whether the counted time T reaches a predetermined setting time T1 (for example, 60 seconds) (operation S80).

If it is checked in operation S80 that the counted time T does not reach the predetermined setting time T1 (for example, 60 seconds), the controllers 24_3 and 36_3 control the system so that control can return to operation S74.

If it is checked in operation S80 that the counted time T reaches the predetermined setting time T (for example, 60 seconds) or if a sensing signal abnormal message is transmitted in operation S78, the controllers 24_3 and 36_3 control the system to make the inputted sensing signals as a database together with its sensing time and to store them in the storing units 24_4 and 36_4 (operation S80).

Subsequently, the controllers 24_3 and 36_3 control the system to reset the count values (operation S82) and to allow control to return to operation S72.

A control operation of receiving data from a gas sensor from the signal sensing terminal units 24 and 26 will now be described with reference to FIGS. 14, 4, and 5. Here, only for simplification of explanation, only the control operation in the signal sensing terminal units 24 and 26 has been described. However, it will be easily understood that a control operation can be performed when data is received from the gas sensor installed around the corrosion signal sensing terminal unit and the corrosion signal sensing/relay terminal unit illustrated in FIGS. 2 and 3 even in the corrosion signal sensing terminal unit and the corrosion signal sensing/relay terminal unit illustrated in FIGS. 2 and 3.

First, the controllers 24_3 and 36_3 monitor and analyze digital sensing signals which are inputted from the gas sensor via the sensing interfaces 24_1 and 36_1 and are converted into digital signals by the analog/digital converters 24_2 and 36_2 (operations S90 to S94). After that, the controllers 24_3 and 36_3 check whether the inputted sensing signals indicate gas leakage as a result of analysis (operation S96). If it is checked that the inputted sensing signals do not indicate gas leakage, operation S90 is repeatedly performed.

If it is checked that the inputted sensing signals indicate gas leakage, the controllers 24_3 and 36_3 control the system to insert an identification code of the RTU 40 as a destination ID, to insert its own identification cod as a source ID, to insert data for identifying a signal notifying a data area of sensing signal abnormality (that is, gas leakage sensing) together with the sensing signal data to generate a sensing signal abnormal message, to transmit the sensing signal abnormal message to the signal modulators 24_6 and 36_6, to perform FSK modulation and then to transmit the FSK modulated signals to the pipes 10_6 and 10_2 via the transmitters 24_8 and 36_8 (operation S98). Subsequently, the controllers 24_3 and 36_3 control the system so that control can return to operation S90. A control operation of receiving data from a manhole (an entrance) open sensor from the signal sensing terminal units 24 and 26 will now be described with reference to FIGS. 15, 4, and 5. Here, only for simplification of explanation, only the control operation in the signal sensing terminal units 24 and 26 has been described. However, it will be easily understood that a control operation can be performed when data is received from the manhole (the entrance) open sensor as a manhole or a test box in which a terminal unit is accommodated is opened even in the corrosion signal sensing terminal unit and the corrosion signal sensing/relay terminal unit illustrated in FIGS. 2 and 3. First, the controllers 24_3 and 36_3 monitor manhole (entrance) sensing signals which are inputted from the manhole (entrance) open sensor via the sensing interfaces 24_1 and 36_1 and are converted into digital signals by the analog/digital converters 24_2 and 36_2 (operations S100 to S110). After that, the controllers 24_3 and 36_3 check whether sensing signals indicating manhole (entrance) opening are inputted (operation S120). If it is checked that the inputted sensing signals are not manhole (entrance) open signals, operations S100 and S110 are repeatedly performed.

If it is checked that the inputted sensing signals are manhole (entrance) open signals, the controllers 24_3 and 36_3 control the system to insert an identification code of the RTU 40 as a destination ID, to insert its own identification cod as a source ID, to insert data for identifying a signal notifying a data area of manhole (entrance) opening together with the sensing signal data to generate a manhole (entrance) open message, to transmit the manhole (entrance) open message to the signal modulators 24_6 and 36_6, to perform FSK modulation and then to transmit the FSK modulated signals to the pipes 10_6 and 10_2 via the transmitters 24_8 and 36_8 (operation S130). Subsequently, the controllers 24_3 and 36_3 control the system so that control can return to operation S 100.

An embodiment of a safety control signal processing flow by abnormality of measurement signals or sensing signals in the corrosion signal sensing/relay terminal unit 52 or the signal sensing terminal unit 24 of a valve chamber as a terminal unit, for example will now be described with reference to FIGS. 16 and 1. Here, only for simplification of explanation, only the control operation in the corrosion signal sensing terminal unit 52 or the signal sensing terminal unit 24 of the valve chamber has been described. However, it will be easily understood that safety control signal processing caused by abnormality of measurement signals or sensing signals in the corrosion signal sensing/relay terminal units 60_1 to 60_6 and the signal sensing terminal unit 36 of a static pressure chamber can be performed with the same flow.

First, a sensing signal abnormal or measurement signal abnormal message caused by abnormality of measurement signals or by abnormality of sensing signals in the corrosion signal sensing terminal unit 52 or the signal sensing terminal unit 24 of the valve chamber passes pipes (10_7, 10_6, 10_5, 10_4, 10_3)(10_6, 10_5, 10_4, 10_3) and corrosion signal sensing/relay terminal units 60_6, 60_5, 60_4, 60_3, 60_2)(60_4, 60_3, 60_2) and is transmitted to the corrosion signal sensing/relay terminal unit 60_1 (operation S200). Here, sensing signal abnormality may be a gas leakage sensing signal from a gas sensor, an abnormal pressure sensing signal from a pressure sensor, an abnormal temperature sensing signal from a temperature sensor, an abnormal water level sensing signal from a water level sensing sensor, and an open signal from a manhole (a test box or an entrance) open sensor. The corrosion signal sensing/relay terminal unit 60_1 outputs the message to the pipe 10_2 because a destination of the message is not itself, and the message is transmitted to the RTU 40 via a pipe of the static pressure chamber 30 and the pipe 10_1 (operation S210).

The RTU 40 analyzes the received message and checks that the received message is a sensing signal abnormal or measurement signal abnormal message from the corrosion signal sensing terminal unit 52 or the signal sensing terminal unit 24 of the valve chamber and then transmits the sensing signal abnormal or measurement signal abnormal message to the system unit of the management center 70 via a wired data communication network or a wireless data communication network which is a public communication network (operation S220).

The system unit of the management center 70 which receives the sensing signal abnormal message or measurement signal abnormal message analyzes the received message and checks that the received message is a sensing signal abnormal or measurement signal abnormal message from the corrosion signal sensing terminal unit 52 or the signal sensing terminal unit 24 of the valve chamber and then, searches mobile communication terminal information of a patrolman who controls a region in which the corrosion signal sensing terminal unit 52 or the signal sensing terminal unit of the valve chamber is positioned, from a database (not shown) and obtains patrolman's mobile communication terminal information (for example, mobile phone number) (operation S230).

After that, the system unit of the management center 70 transmits a message including corresponding mobile communication terminal information (for example, mobile phone number) and abnormal signal message sending place information [that is, information about the corrosion signal sensing terminal unit 52 or the signal sensing terminal unit 24 of the valve chamber] and abnormal signal message information to a short message service center (SMSC) 100 of a mobile communication network, as a wireless data communication network, for example, and requests to transmit an emergency message including abnormal signal message sending place information [that is, information about the corrosion signal sensing terminal unit 52 or the signal sensing terminal unit 24 of the valve chamber] and abnormal signal message information to the corresponding mobile communication terminal.

As a result, the SMSC 100 analyzes the emergency message and transmits the emergency message of the above-described contents to the corresponding mobile communication terminal 80 (operation S240). The patrolman who carries out the mobile communication terminal 80 which receives the emergency message checks the emergency message, rapidly checks situations in the abnormal signal message sending place [that is, the position of the corrosion signal sensing terminal unit 52 or the position of the signal sensing terminal unit 24 of the valve chamber], and rapidly transmits a circumstantial report to the system unit of the management center 70 via the SMSC 100 of the mobile communication network using the mobile communication terminal

80 (operations S260 and S270). Thus, the system unit of the management center 70 rapidly confronts the abnormal signal message.

Another embodiment of a safety control signal processing flow by abnormal sensing signals in the signal sensing terminal unit 24 of a valve chamber as a terminal unit, for example will now be described with reference to FIGS. 17 and 1. Here, only for simplification of explanation, only the control operation in the corrosion signal sensing terminal unit 52 or the signal sensing terminal unit 24 of the valve chamber has been described. However, it will be easily understood that safety control signal processing caused by abnormal sensing signals in the corrosion signal sensing terminal unit 52, the corrosion signal sensing/relay terminal units 60_1 to 60_6, and the signal sensing terminal unit 36 of the valve chamber illustrated in FIG. 1 can be performed with the same flow.

First, a sensing signal abnormal message caused by abnormality of sensing signals in the signal sensing terminal unit 24 of the valve chamber passes pipes 10_6, 10_5, 10_4, 10_3 and corrosion signal sensing/relay terminal units 60_4, 60_3, 60_2 and is transmitted to the corrosion signal sensing/relay terminal unit 60_1 (operation S300). Here, abnormal sensing signals may be gas leakage sensing signals from a gas sensor and abnormal pressure sensing signals from a pressure sensor.

The corrosion signal sensing/relay terminal unit 60_1 outputs the message to the pipe 10_2 because a destination of the message is not itself, and the message is transmitted to the RTU 40 via a pipe of the static pressure chamber 30 and the pipe 10_1 (operation S310).

The RTU 40 analyzes the received message and checks that the received message is a sensing signal abnormal message from the signal sensing terminal unit 24 of the valve chamber and then transmits the sensing signal abnormal message to the system unit of the management center 70 via a wired data communication network or a wireless data communication network which is a public communication network (operation S320).

The system unit of the management center 70 which receives the sensing signal abnormal message analyzes the received message, if it is determined that the received message is a sensing signal abnormal message [for example, a gas leakage sensing or abnormal pressure sensing message] from the signal sensing terminal unit 24 of the valve chamber and there is a very high possibility for accident caused by gas leakage sensing or abnormal pressure sensing, and then, transmits a control signal message for intercepting all of the valves 32 and 34 of the static pressure chamber as well as the valve 22 of the valve chamber 20, for example, adjacent to the signal sensing terminal unit 24 of the valve chamber 20 to the RTU 40 via the wired data communication network or the wireless data communication network (operation S330).

The RTU 40 which receives the control signal message generates a first control signal message for intercepting the valve 22 using the signal sensing terminal unit 24, transmits the first control signal message to the pipe 10_1 , generates a second control signal message for intercepting all of the valves 32 and 34 of the static pressure chamber and transmits the second control signal message to the RTU 40 (operation S340).

As a result, as the first and second control signal messages are received by the signal sensing terminal unit 36 of the static pressure chamber 30 via the pipe 10_1 , the signal sensing terminal unit 36 ignores the first control signal message because its destination is not itself, and transmits a control signal to the control unit 38 based on the second control signal message whose destination is itself. Thus, the control unit 38 controls the system to close the valves 34 and 32 by driving the driving mechanisms 35 and 37 using the driver 38_3.

Meanwhile, as the first control signal message transmitted to the pipe 10_1 is received by the signal sensing terminal unit 24 of the valve chamber 20 via the pipe 10_2, the corrosion signal sensing/relay terminal units 60_1 and 60_2, the pipes 10_3 and 10_4, the corrosion signal sensing/relay terminal units 60_3 and 60_4, and the pipe 10_6, the signal sensing terminal unit 24 transmits a control signal to the control unit 26 based on the first control signal message because a destination of the first control signal message is itself. Thus, the control unit 26 controls the system to close the valve 22 by driving the driving mechanism 28 using the driver 26_3 (operation S360).

Meanwhile, as a result of operation S320, the system unit of the management center 70 which receives the sensing signal abnormal message searches mobile communication terminal information of a patrolman who controls a region in which the signal sensing terminal unit 24 of the valve chamber 20 is positioned, from a database (not shown) and obtains patrolman's mobile communication terminal information (for example, mobile phone number) (operation S370). After that, the system unit of the management center 70 transmits a message including corresponding mobile communication terminal information (for example, mobile phone number) and abnormal signal message sending place information [that is, information about the signal sensing terminal unit 24 of the valve chamber] and abnormal signal message information to a short message service center (SMSC) 100 of a mobile communication network, as a wireless data communication network, for example, and requests to transmit an emergency message including abnormal signal message sending place information [that is, information about the signal sensing terminal unit 24 of the valve chamber] and abnormal signal message information to the corresponding mobile communication terminal.

As a result, the SMSC 100 transmits the emergency message of the above-described contents to the corresponding mobile communication terminal 80 (operation S390). The patrolman who carries out the mobile communication terminal

80 which receives the emergency message checks the emergency message, rapidly checks situations in the abnormal signal message sending place [that is, the position of the signal sensing terminal unit 24 of the valve chamber], and immediately transmits a circumstantial report to the system unit of the management center 70 via the SMSC 100 of the mobile communication network using the mobile communication terminal 80 (operations S400 and S410). Thus, the system unit of the management center 70 rapidly confronts the abnormal signal message.

Although the above embodiments have been described to limit the case where an FSK modulation signal is used as a communication signal via a pipe, according to the present invention, an amplitude shift keying

(ASK) modulation signal may be used as the communication signal via the pipe.

The above description just concerns embodiments of the present invention. The present invention is not restricted to the above embodiments, and various modifications can be made thereto within the scope defined by the attached claims. For example, the shape and structure of each member specified in the embodiments can be changed.

Industrial Applicability As described above, according to the present invention, pipes buried in the earth are used as communication lines to monitor state of the pipes such that costs for establishing the system and operating the same can be reduced and rapid and safe management of the pipes can be performed.

Claims

What is claimed is:

1. A system for remote monitoring and safety maintenance of pipe lines buried in the earth, the system comprising: pipe lines being conductive metallic pipes on which a material for anticorrosion is coated, between which an insulator communicated coaxially with the metallic pipes are interposed in a unit of a predetermined length, which are installed in the underground while being electrically divided by the insulator, transmit a fluid and function as an electric signal transmission line; a plurality of first signal sensing terminal units installed in each of the pipes divided by the insulator, measuring corrosion signals on the divided pipes, and transmitting the measurement signals via the pipes; a plurality of signal relay terminal units replaying signals so that an anticorrosion current and a corrosion current flowing through the divided pipes are not transmitted between the pipes divided by the insulator; a plurality of second signal sensing terminal units installed in a valve chamber and/or a static pressure chamber disposed in a predetermined section of the pipes, sensing an environment inside the valve chamber and/or the static pressure chamber and transmitting the sensing signal via the pipes; a control unit installed in the valve chamber and/or the static pressure chamber and controlling a driving mechanism so that a valve installed in the valve chamber and/or the static pressure chamber can be driven to be opened or closed according to control signals transmitted via the second signal sensing terminal units from the pipes; a remote terminal unit (RTU) collecting signals measured and sensed by the plurality of first and second signal sensing terminal units via the pipes and the signal relay terminal units to transmit the signals to a management center device via a public communication network and to transmit control signals from the management center device to the first and second signal sensing terminal units and the signal relay terminal units via the pipes; and a management center device analyzing the signals transmitted from the RTU and when a piping state is abnormal, a valve chamber state is abnormal or a static pressure chamber is abnormal, notifying a patrolman's mobile communication terminal who controls the pipes or valve chamber of static pressure chamber in which abnormality occurs, of abnormality of a corresponding pipe or valve chamber or static pressure chamber via a wireless public communication network.

2. The system of claim 1 , wherein the second signal sensing terminal unit installed in the valve chamber and/or the static pressure chamber comprises: a communication interface connected to the pipes to communicate therewith and connected to a communication interface of the control unit to communicate therewith; a sensing interface which senses an environment inside the valve chamber and/or the static pressure chamber and to which sensing signals from at least one sensor of a pressure sensor, a water level sensor, a temperature sensor, a gas sensor, and an entrance open sensor of the pipes are inputted; an analog/digital converter converting analog sensing signals inputted from the sensing interface into digital sensing signals; a storing unit storing the digital sensing signals by making the digital sensing signals as a database; a receiver receiving signals from the pipes via a communication interface electrically connected to the pipes; a signal demodulator demodulating the signals received from the receiver; a transmitter transmitting the signals to the pipes via the communication interface electrically connected to the pipes; a signal modulator modulating the signals to be transmitted to the transmitter; and a controller controlling the system to store the digital sensing signals inputted from the analog/digital converter in the storing unit by making the digital sensing signals as a database, if the signal demodulated by the signal demodulator is temporarily stored in the storing unit, the demodulation signal is interpreted and a destination of the interpretation signal is itself and the interpretation signal is a command for transmitting its own sensing signal data from the RTU, controlling the system to modulate the interpretation signal using the signal modulator and then to be transmitted using the transmitter, so as to read the corresponding sensing signal data from the storing unit to transmit to the RTU, if the destination of the interpretation signal is itself and the interpreted signal is an open/closing driving control command of a driving mechanism by the control unit, controlling the system to transmit the command to the control unit via the communication interface and if the destination of the demodulation signal is not itself, controlling the system to discard the modulation signal temporarily stored in the storing unit, and if it is determined that the digital sensing signals inputted from the analog/digital converter is not normal, and controlling the system to modulate the digital sensing signals using the modulator and then to be transmitted using the transmitter, so as to transmit abnormal state data of the sensing signals to the RTU.

3. The system of claim 2, wherein, excluding the first signal sensing terminal units positioned at the shortest portion of the pipes, each first signal sensing terminal unit and each signal relay terminal unit constitute a signal sensing/relay terminal unit in one body.

4. The system of claim 3, wherein the signal sensing terminal unit positioned at the shortest portion of the pipes comprises: a measurement interface measuring a corrosion signal from a sacrificial anode installed in the underground, a reference electrode, and a pipe measurement point; an analog/digital converter converting analog measurement signals inputted from the measurement interface into digital measurement signals; a storing unit storing the digital measurement signals by making the digital measurement signals as a database; a receiver being electrically connected to the pipes and receiving signals from the pipes; a signal demodulator demodulating the signals received from the receiver; a transmitter being electrically connected to the pipes and transmitting the signals to the pipes; a signal modulator modulating the signals to be transmitted to the transmitter; and a controller controlling the system to store the digital measurement signals inputted from the analog/digital converter in the storing unit by making the digital measurement signals as a database, if the signal demodulated by the signal demodulator is temporarily stored in the storing unit, the demodulation signal is interpreted and the interpretation signal is a command for transmitting measurement signal data from the

RTU, controlling the system to modulate the interpretation signal using the signal modulator and then to be transmitted using the transmitter, so as to read the corresponding measurement signal data from the storing unit to transmit to the RTU, and if it is determined that the digital measurement signals inputted from the analog/digital converter is not normal, and controlling the system to modulate the digital measurement signals using the modulator and then to be transmitted using the transmitter, so as to transmit abnormal state data of the measurement signals to the RTU.

5. The system of claim 4, wherein the signal sensing/relay terminal unit is connected to a signal sensing/relay terminal unit of an adjacent pipe electrically divided by the insulator to communicate therewith via a communication interface and a signal line, and wherein the signal sensing/relay terminal unitce comprises: a measurement interface measuring a corrosion signal from a sacrificial anode installed in the underground, a reference electrode, and a pipe measurement point; an analog/digital converter converting analog measurement signals inputted from the measurement interface into digital measurement signals; a storing unit storing the digital measurement signals by making the digital measurement signals as a database; a receiver receiving signals from the pipes via a communication interface electrically connected to the pipes and receiving signals from the adjacent signal sensing/relay terminal units via the communication interface; a signal demodulator demodulating the signals received from the receiver; a transmitter transmitting the signals to the pipes via the communication interface electrically connected to the pipes and transmitting the signals to the adjacent signal sensing/relay units via the communication interface; a signal modulator modulating the signals to be transmitted to the transmitter; and a controller controlling the system to store the digital measurement signals inputted from the analog/digital converter in the storing unit by making the digital measurement signals as a database, if the signal demodulated by the signal demodulator is temporarily stored in the storing unit, the demodulation signal is interpreted and a destination of the interpretation signal is itself and the interpretation signal is a command for transmitting its own measurement signal data from the RTU, controlling the system to modulate the interpretation signal using the signal modulator and then to be transmitted using the transmitter, so as to read the corresponding measurement signal data from the storing unit to transmit to the RTU, if the destination of the interpretation signal is not itself, controlling the system to modulate the interpretation signal using the signal modulator and then to be transmitted to the communication interface of the pipes or the adjacent signal sensing/relay terminal units using the transmitter and the communication interface, so as to transmit the demodulation signal temporarily stored in the storing unit to the destination, and if it is determined that the digital measurement signals inputted from the analog/digital converter is not normal, and controlling the system to modulate the digital measurement signals using the modulator and then to be transmitted using the transmitter, so as to transmit abnormal state data of the measurement signals to the RTU.

6. The system of claim 5, wherein the first signal sensing terminal unit and the signal sensing/relay terminal unit further comprise a sensing interface which senses an environment inside a test box of the signal sensing terminal unit or a test box of the signal sensing/relay terminal unit and to which sensing signals from at least one sensor of a pressure sensor, a water level sensor, a temperature sensor, a gas sensor, and an entrance open sensor of the pipes are inputted to be transmitted to the analog/digital converter, wherein the controller of each first signal sensing terminal unit and each signal sensing/relay terminal unit controls the system to store the digital sensing signals inputted from the analog/digital converter in the storing unit by making the digital sensing signals as a database, if a destination of the interpretation signal is itself according to the result of interpretation of the demodulation signal and the interpretation signal is a command for transmitting its own sensing signal data from the RTU, controlling the system to modulate the interpretation signal using the signal modulator and then to be transmitted using the transmitter, so as to read the corresponding sensing signal data from the storing unit to transmit to the RTU, and if it is determined that the digital sensing signals inputted from the analog/digital converter is not normal, and controlling the system to modulate the digital sensing signals using the modulator and then to be transmitted using the transmitter, so as to transmit abnormal state data of the sensing signals to the RTU.

7. The system of claim 6, wherein the controller of each signal sensing/relay terminal unit controls, if the signals received by the receiver are interpreted, a destination ID is not its own identification code and a source ID is a remote terminal unit (RTU), determines that the signals are received from an upper stream side and controls the transmitter and the communication interface so that the corresponding signals can be transmitted to a down stream side via the transmitter and the communication interface, and if the signals received by the receiver are interpreted and the destination ID is the RTU, determines that the corresponding signals are transmitted to the RTU from the terminal unit positioned at a lower stream than its own position and controls the transmitter and the communication interface so that the corresponding signals can be transmitted to the upper stream side via the transmitter and the communication interface.

8. The system of claim 7, wherein two adjacent signal sensing/relay terminal units, the insulator of the pipes being interposed between the signal sensing/relay terminal units are installed in one test box.

9. The system of any one of claims 1 through 8, wherein the signals communicating via the pipes are frequency shift keying (FSK) modulation signals or amplitude shift keying (ASK) modulation signals.

10. The system of claim 9, wherein a frequency of the FSK modulation signals or ASK modulation signals are in the range of 1-40 kHz.

11. The system of claim 10, wherein the pipes are polyethylene-coated line pipes (PLP).

12. The system of claim 11 , wherein the first and second signal sensing terminal units and the signal sensing/relay terminal unit use a conductor portion contacting the ground as a communication ground at a manhole, a valve chamber or a static pressure chamber in which the first and second signal sensing terminal units and the signal sensing/relay terminal unit are accommodated in the underground.