JPS5820490B2 - Power line carrier communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates generally to power line carrier communication systems, and more particularly to power distribution systems such as automatic reading of metering, performing continuous testing of loads, and selective control of loads. The present invention relates to a power line conveyance system for performing automation functions.

Electric utilities have long used their power lines to communicate with distant switchyards and substations for supervisory and control purposes.

These power transmission lines are ideal for communications because they extend from power plants to switchyards and substations without interference to communication frequencies.

Communication over the power line conductors of the distribution network from distribution substations through distribution transformers to electrical loads is not widely used.

Communication over distribution network power lines is more convenient than over high-voltage transmission lines because the distribution lines have a large number of distribution transformers, which not only cause electrical noise and interference, but also produce poor high-frequency impedance characteristics that rapidly attenuate communication signals. It is difficult.

With the recent increase in the desire to perform certain power distribution automation functions, such as automatic reading of utility meters, selective control of loads, performing continuous testing of loads, etc., attention has been paid to the use of distribution line conductors for communication. However, economically relevant problems inevitably arise in order to obtain a practical communication system.

Furthermore, in order to reduce peak power demand, it is becoming increasingly important to select electrical loads and to control them from a distance.

Furthermore, the content of communication signals can vary widely7. ．． 1', the use of inexpensive encoders with stable characteristics has attracted attention for automatic reading of instruments used.

Load selection control, automatic meter reading, and other power distribution automation functions require some form of communication.

Since electric power services involve distribution lines extending to each party to be communicated with, it is desirable to use distribution line carrier waves for communication purposes if the associated problems can be dealt with economically.

Prior Art U.S. Patent Nos. 3,656,112 and 3,702,46
No. 0, and No. 3,815,119 all disclose some form of communication across an electric power service distribution network.

US Pat. No. 3,656,112 discloses a communication system using a combination of power line and wireless communications.

This radio link is used to bypass transformers and other obstacles on power transmission lines.

U.S. Pat. No. 3,702,460 discloses utilizing the neutral conductor of a distribution line by inserting a parallel resonant circuit between the neutral conductor and the ground point at each ground point of the system. .

A communication circuit connected between this neutral wire and a ground point bypasses the distribution transformer.

U.S. Pat. No. 3,815,119 uses power line conductors on the secondary side of a distribution transformer to transfer readings from various meters connected to this secondary side to a common receiving point. At the receiving point, the readings are stored until they are read out, for example by a motor vehicle that regularly travels in the vicinity of this receiving point and interacts with it by radio contact.

Some inventions have been devised for new and improved devices for communicating by electrical distribution lines, in which a substation district is divided into multiple zones, and when interrogated by a signal from an initiating signal source, those zones are Each responds at a different frequency.

A frequency translation repeater interfaces with the area to augment the signals within the area and differentiate the area.

This multi-frequency arrangement reduces the possibility that the response signal will act as a starting signal.

This invention relates to a communication system that is a further improvement on the newly conceived invention described above, and since there is no direct electrical connection (contact connection) with the high voltage side of the distribution transformer, it is easy to remove obstacles such as the distribution transformer. It can be avoided.

DISCLOSURE OF THE INVENTION Briefly, this invention is a new and improved system that utilizes magnetic field type couplers (inductive couplers) and frequency conversion repeaters to increase signal strength and avoid signal obstructions such as distribution transformers. It is a distribution line carrier communication system.

The only contact point to the high voltage side of the distribution transformer is the start signal input point at the substation.

All initiation signals are transferred from the primary to the secondary side of the distribution network through magnetic field couplers and frequency conversion repeaters, avoiding each distribution transformer.

The response signal is detected from the primary side of the distribution network through another magnetic coupler.

The magnetic field type coupler that detects communication signals from the primary side of the power distribution network is a contact connection type capacitor.

Saves installation time and costs compared to type couplers.

This magnetic field type coupler is used at any distribution-subvoltage level and therefore does not need to be changed when the distribution-subvoltage level is changed.

Furthermore, this magnetic field type coupler does not need to be insulated from the ground point to withstand the primary distribution voltage.
Its manufacturing cost is much lower than that of direct contact type capacitor couplers.

The frequency conversion repeater amplifies the signal detected by the magnetic coupler without limiting the gain due to feedback.

Therefore, the signal strength of the remote receiver can be made sensitive enough that expensive receivers are not required.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and particularly to FIG. 1, there is shown a block diagram of a new and improved power line carrier communication system 10 constructed in accordance with the teachings of the present invention.

The carrier communication system 10 includes an initiation signal source 12 .

The signal source 12 includes an initiation response controller 14, such as a digital computer located at a master control station, such as a utility central office.

The computer is programmed to initiate remote communication terminals coupled to loads connected to the electric utility's distribution lines to obtain data regarding readings of multi-purpose meters, such as electric, gas, or water meters. , and/or require other functions to be performed, such as controlling less important loads.

Electrical loads, such as electric water heaters, are selectively turned off and on to obtain a constant overall demand for power.

Continuous load checks and power shedding operations are also performed.

The initiation signal generated by controller 14 is sent to a given distribution substation with any existing equipment.

Each substation being communicated with includes a central communication terminal that receives an initiation signal from an initiation signal source 12 at a central or master control station and sends a response signal to that source.

As an example, Figure 1 shows that all substations are the same, so
Only one combination of central communication terminal and distribution substation 1
6 is shown.

A convenient means for communication between the main control station signal source 12 and the plurality of distribution substations is by telephone.

The address for each distribution substation is a telephone number that allows the initiation response controller 14 to automatically dial that number to call the given substation.

In a similar manner, when a communications terminal at a substation receives a response signal addressed to signal source 12, the terminal automatically dials the source's telephone number to page the source.

Telephone contact is an economical and convenient method of communicating between signal source 12 and multiple substations, and by way of example assume that the initiation and response portions of the contact are telephone calls.

However, it is to be understood that the communication herein may also be wireless, such as radio, microwave or any other form of communication.

Each distribution substation includes one or more step-down power transformers, such as transformer 18, with a primary winding 20 connected to a high voltage transmission line 21 and a secondary winding connected to the primary distribution network. A winding 22 is provided.

This primary distribution network will be referred to as the first distribution line conductor 23.

The magnitude of the primary distribution network voltage is determined by the distribution transformers 24 and 2.
It is stepped down to the magnitude of the secondary distribution voltage near the connected load by a plurality of distribution transformers such as 6.

Distribution transformer 24 includes a primary winding 28 connected to a first power line conductor 23 and a secondary winding 30 connected to a second distribution network 31, referred to as a second distribution power line conductor.

An electrical load, such as a residential power user, is connected to the second power line conductor 31, such as an electrical load 32, which is connected to the second power line conductor 31 via an electrical meter 33.

Each electrical load 32 has a communication terminal 40 attached to it and has a designated remote communication terminal associated therewith.

The long-distance communication terminals are each connected to a second distribution conductor 31 .

Similarly, the distribution transformer 26 has a primary winding 48 connected to the first power line conductor 23 and a secondary winding 50 connected to the secondary distribution network 51, which will be referred to as the second power line conductor. Contains.

It's a load of 52. An electrical load such as this is connected to the second power line conductor 51.

The electrical load 52 has a designated telecommunications terminal 54 connected thereto, which is connected to the second power line, for example, for reading a meter 56 connected to the load 52 and/or performing other power distribution automation functions. It is connected to the conductor 51.

Each distribution transformer has a frequency conversion repeater connected thereto, the repeaters 60, 62 being connected to the distribution transformers 24, 62, respectively.
26.

these. A frequency conversion repeater is coupled to the power line by a unidirectional coupler on the primary and secondary sides of the distribution transformer, where this unidirectional coupler on the primary side is an inductive or magnetic type coupler and the unidirectional coupler on the secondary side is an inductive or magnetic type coupler. is a capacitive coupler that makes direct contact with one of the secondary power line conductors through a metal contact.

Although it is obvious, distribution transformer 24 includes a unidirectional coupler 6 magnetically coupled to one or more first power line conductors 23.
4 and a unidirectional coupler 66 connected to one or more second power line conductors 31.

The distribution transformer 26 has one or more first power line conductors 2
a unidirectional coupler 68 magnetically coupled to 3 and a unidirectional coupler 7 connected to one or more second power line conductors 51;
0.

Viewing the overall communication system from the perspective of an initiation response signal, an initiation communication is an initiation signal source 12, a communication communication between the initiation signal source 12 and a central communication terminal 16, such as a telephone call, a communication communication between the initiation signal source 12 and the central communication terminal 16, , first power line conductor 23, a plurality of unidirectional couplers, a frequency conversion repeater, one unidirectional coupler in each distribution transformer, such as unidirectional coupler 64;
A plurality of designated remote power line conductors connected to each second power line conductor network, such as a frequency conversion repeater 60, a unidirectional coupler 66, a second power line conductor, such as a second power line conductor 31, and a remote communication terminal 40. Contains communication terminals.

Note that these distribution transformers are not part of the initiation communications.

The response communication link is from each designated remote communication terminal, such as remote terminal 40, through a second power line conductor, such as second power line conductor 31, and from the secondary winding 30 of the distribution transformer 24 to the primary winding 28. From the secondary winding to the primary winding, through the first power line conductor 23, through the unidirectional magnetic coupler 69 in the substation, to the central communication terminal 16, and then through the telephone line. This leads to an initiation response controller 14 located at the central control station.

The device described herein provides an economical way to use power lines for communication purposes, eliminating certain of the problems associated therewith.

For example, if an initiating communication signal must be sent from substation 16 from the primary to the secondary side of a distribution transformer to a remote communications terminal, the signal strength at that remote communications terminal may be weak and unreliable. Even if every remote communication terminal is equipped with an expensive, sensitive receiver without a remote communication terminal, it cannot be trusted that all initiation signals will be properly received.

In contrast, by installing frequency conversion repeaters at each distribution transformer, the desired system reliability can be ensured by providing a strong initiation signal to distant communication terminals, and the signals that are reliably received are Sensitivity can be obtained without the need for expensive receivers.

Magnetic couplers on the primary side of distribution transformers are made very cheaply because they do not come into direct contact with the high voltage primary distribution lines.

Direct contact couplers on the low voltage or secondary side of a distribution transformer are designed so that the secondary distribution voltage with respect to ground is typically 120
Since it is only a port or 240 holt, it can be made at a fairly low cost.

The receiver in the frequency conversion repeater does not have to be highly sensitive since it is subject to the attenuation of the connected distribution transformer after detecting the start signal.

Considering the response signal, the attenuation impedance presented to the communication signal by a distribution transformer is determined by the particular design of that distribution transformer, so that the attenuation from the secondary to the primary of the distribution transformer is equal to the attenuation from the primary to the secondary. The invention takes advantage of the fact that the attenuation to the side is typically about half.

Therefore, the signal strength of the response signal is not attenuated to the same extent as the initiation signal, and since there is only one receiver in the substation,
Rather than using a repeater for response signals at each distribution transformer, it is better to install a highly sensitive receiver at this location, or to connect the entire culm.
Although economical, this repeater also requires an expensive direct contact capacitor type coupler connected to the primary side of the distribution network.

Returning now to the initiation signal source 12, as indicated by the initiation and response controller 14.

In addition to the digital computer that generates the initiation signal and receives the response signal, the central control station also includes a parallel-to-serial converter 72 that provides a baseband binary signal in serial form, which binary signal is connected to the data set interface. 7
4 and then to modem 76.

The initiation and response controller 14 generates a parallel initiation signal containing the address of the remote communication terminal to be paged.

Data display symbols are also included in the start signal when multiple automation functions are selected and performed.

Modem 76 establishes a telephone communication path with modem 90, which is the main part of the central communication terminal located at the selected distribution substation.

The serial baseband binary signal is used by modulator 92 to modulate a carrier wave.

This modulator 92 preferably uses a modulation format called FSX in which the output frequency of a modulated wave shifts between predetermined values, but any suitable modulation format may be used.

The output of modulator 92 is amplified by transmitter 96 to produce a first frequency band starting signal, designated as Ifl.

A suitable format for the signal f1 is shown in FIG. represents that the signal and, if one or more functions are selected, are modulated by the function identifier.

Signal ■fl is coupled to one of the first power line conductors 23 of the primary distribution network via a unidirectional coupler 97 that includes a 60 Hertz blocking capacitor 98 and an autotransformer 100.

This signal is typically coupled between one of the line conductors and a common neutral return or ground wire.

A capacitor 98 and an autotransformer 100 are connected in series from one of the first power line conductors 23 to a ground point, and the signal from the transmitter 96 is routed between the capacitor and the autotransformer or to a predetermined tap thereof. Can be applied to the grounding point.

Instead of using an autotransformer, it is also suitable to use a two-winding matching transformer.

The modulated carrier wave is detected by a unidirectional magnetic field coupler connected to each repeater, such as unidirectional couplers 64 and 68.

As described for coupler 68, the unidirectional couplers each include a ferrite rod antenna 110 and an amplifier 116 that tune the coil 112 to the frequency band of the starting signal f1 by a capacitor 114.

Figure 2 shows not only coupler 69 but also couplers 64 and 6.
8, this coupler 69 is a schematic representation of a magnetic field type coupler such as to accept a response signal from the first power line conductor 23.

For purposes of illustration, the magnetic coupler shown in FIG. 2 is the magnetic coupler 68 shown in FIG.

The magnetic coupler 68 includes an antenna 110 similar to a ferrite rond radio antenna.

This antenna 110 includes a ferrite rod 111 and a tapped coil 112.
It is tuned to the frequency band of the carrier signal f1 by a capacitor 114 connected to both ends of the carrier signal f1.

Approximately 20
A ferrite rod with 0 turns of thin wire and about 20 turns of taps was found to be an excellent general-purpose antenna.

Connection point 11 between capacitor 114 and one end of coil 112
5 is connected to the ground point 117 via a capacitor 118.

The tap of the coil 112 selected for impedance matching is connected to a first transistor amplifier including an NPN transistor 121.

This coil tap is connected to the base of transistor 121.

The amplifier 120 has a resistor 1 connected from the unidirectional power source to the ground point.
22 and 124 connected in series, the supply of which is represented by terminal 126, a resistor 125 connected from the emitter of transistor 121 to ground 117, and an intermediate stage coupling including primary winding 130. transformer 128
is connected from the power supply 125 to the collector of the transistor 121 and the tapped secondary winding 132.

A capacitor 134 is connected between primary windings 130.

The capacitor 134 and the coupling transformer 128 are connected to the carrier signal ■
It is a bandpass filter for the fl frequency band.

A connection point 136 between resistors 122 and 124 is connected to connection point 115.

The intermediate stage bandpass filter connects one side of the winding 132 to the ground point 1.
Capacitors 138 and 140 connected in series to 17
is provided on the secondary side of the transformer 128.

A voltage divider including resistors 142 and 144 connected in series from power supply 125 to ground point 117 includes a capacitor 138.
The connection point 14 is connected between the resistor connected to the connection point between and 140.
There are 6.

The taps of the secondary winding 132 selected for impedance matching are NPN transistor 152 and resistor 154.15
6, which is connected to a second transistor amplifier including 6;

A tap of secondary winding 132 is connected to the base of transistor 152, a resistor 154 is connected from power supply 126 to the collector of transistor 152, and resistor 156 is connected from the emitter of transistor 152 to ground 116.

Resistor 156 is a load resistor, and the signal to the receiver portion of repeater 62 is coupled across resistor 156.

Although the description of the magnetic coupler stated that it is tuned to the carrier frequency, it is possible to detune the magnetic coupler to a frequency that is slightly displaced from the carrier frequency, especially if the primary distribution line is subject to fairly large amplitude transients. It turned out to be convenient.

This detuning of the magnetic coupler ensures that no harmful ringing or waveform distortion occurs at the starting signal frequency.

An example of the use of magnetic field coupler 68 in an airborne power distribution network with a power line communication system where the initiation signal 1f1 transmitted on the carrier wave is at a nominal frequency of 100 kilohertz is given below.

The primary distribution line conductor 23 shown in FIG. 2 has an effective value of 10 m.
A high voltage conductor 170 is provided carrying a starting signal current indicated by arrow 172, assumed to be A.

The return signal, assumed to be 8 mA rms, is shown by arrow 174 on common neutral or ground wire 176.

It is thought that these differential currents of 2 mA are returned through another circuit.

A common neutral return or ground wire 176 is mounted directly above the high voltage conductor 170, with a spacing of 1 meter, for example, as shown at 180, and is connected to the antenna 110, as shown by a spacing of 182.
is provided below the high voltage conductor 170, for example, with a distance of 2 m.

Depending on the receiver design, 20 mV rms is a fairly large signal.

As a result, the filtering and current limiting required to remove the unnecessary 60 Hz component can be performed with a simple and inexpensive circuit.

The frequency conversion repeater 62 changes the frequency and at the same time amplifies the 22 mV start signal ``fl'' so as to obtain the start signal If2 in a frequency band that does not overlap with the frequency band of the signal ``fl''.

It has been found that an output signal of only 1 volt rms is sufficient to provide a 100 mV rms signal to a remote communication terminal over a long distance secondary line.

This equally large communication signal used by remote communication terminals can be used in simple and inexpensive receivers.

The amplified starting signal f1 obtained by each unidirectional coupler is applied to its associated frequency converting repeater, such as repeaters 60 and 62.

Since each repeater is of the same construction, only one repeater 62 will be discussed in detail.

The repeater 62 includes a receiver 111, which typically includes a general-purpose limiter to remove noise and amplify the carrier signal Ifl, and a demodulator circuit to produce a baseband logic signal.

The output of the receiver 111 is applied to a frequency converting amplifying transmitter 113 which produces a modulated carrier start signal f2.

The output of this transmitter 113 is applied to the second power line conductor 51 via a unidirectional coupler 70.

As explained in FIG. 4, the frequency band F3-F occupied by the question signal If2 obtained by the transmitter 113 is the frequency band F1-F of the signal f1 received by the receiver 111.
It does not overlap with 2.

Because of this change in frequency, the transmitted signal f2 is prevented from being fed back through the transformer 26 and from acting as an input to the receiver 111, so that the gain of the transmitter 113 is reduced due to the feedback and oscillation. You can choose without being restricted by the problem.

FIG. 3 is detailed with repeaters 60 and 62, each shown in slightly different arrangements to define the two appropriate types of frequency converting repeaters used.

The repeater 60 includes a limiter 190, which reduces distortion and noise in the received start signal f1, and then the start signal is applied to a detector 192 that demodulates the signal and processes it for adjustment, and a start response controller. The original baseband binary logic signal prepared by 14 is recovered.

This baseband binary logic signal is then applied to a modulator and oscillator circuit 194 in which the baseband signal is used to modulate a transmit frequency in a frequency band outside the frequency band of the received signal f1. is used as a modulating wave.

This modulated transmission carrier signal is passed through a bandpass filter 19 tuned to the frequency band of the carrier signal, and the signal expressed as a λ signal f2 is amplified by an amplifier 198 and applied to the second power line conductor 31 via a capacitor coupler 66. It will be done.

This modulation may be of the FSK type, or any other suitable type of frequency or phase modulation may be used.

The repeater 62 is shown as being of the type that heterodynes the starting signal to a new frequency band.

For example, the signal from the magnetic field type coupler 68 is transmitted to the limiter 20.
0 and then mixed with the signal from local oscillator 202 by mixer 204.

The output of the mixer 204 is in a frequency band F3 to F4 that does not overlap the frequency band Fl to F2 of the original start signal f1.
The bandpass filter 206 selects the sum and difference of the desired frequencies or their collapse such that the starting signal is at
given to.

The signal f2 from the bandpass filter 206 is amplified by an amplifier 208 and applied to the second power line conductor 51 via a capacitor coupler 70.

The remote communication terminal 54 includes a bidirectional coupler and detector 162 connected to one or more of the second power line conductors 51.
Equipped with

Start signal f detected by coupler and detector 162
2 is applied to the receiver.

The receiver demodulates the signal and applies it to a serial-to-parallel conversion and decoding circuit.

If the received initiation signal is designated to the remote communication terminal to be noted down by an appropriate comparator, the function identifier is decoded and the required function is performed.

The receiver, demodulator, series to parallel converter, comparator and decoder are generally indicated at 164.

It controls the reading function of the meter used and the number of times the electrical load is turned on and off.

If the required function is to read a meter such as an electricity, waste, water meter, etc., then all are required, such as parallel-to-series converters, demodulators, and amplified transmitters, such as broadly indicated at 172. an encoder 17 for providing meter reading data such as obtained by meter 56 to a device producing a response signal;
0 is driven.

The serialized response signal, called Rf3, is the signal f1
and f2 from the associated transmitter portion, indicated by the link 172, whose signal occupies the frequency band f2, to the coupler and detector 162, which in turn applies a response signal to one of the second power line conductors 51; Can be given.

FIG. 4 shows a suitable format for this signal Rf3.

This signal includes some kind of identification label for the response signal source, as well as any take that is sent back to the interrogation signal source, such as a meter reading.

For purposes of illustration, this identification label is shown as a unique address used in the initiation signal, but any suitable identification signal may be used.

Encoder 170 may be of the type described in the aforementioned US Pat. No. 3,820,073, or any other suitable encoder may be used.

Second power line conductor 51 via coupler and detector 162
The response signal Rf3 applied to the first power line conductor 23 passes through the distribution transformer 26.

This response signal R43 is sent to the first
It is detected from the power line conductor 23 and applied to a receiving and demodulating circuit (response receiving device) 280.

This circuit 280 demodulates the response signal to a data configuration interface 28 similar to data configuration interface 74.
Give it to 2.

Modem 90 sends the signal over a communications link to a central control station where it is received by modem 76 and applied to initiation response controller 14.

Now, the start signal ■f1 created by the controller 14
The initiation response cycle started by completes.

SUMMARY OF THE INVENTION A new and improved electrical distribution network power line communication system is herein disclosed that avoids distribution transformers for initiating communication connections by a combination of magnetic field couplers and frequency conversion repeaters.

This combination provides a fairly simple and inexpensive device for communicating through obstacles such as distribution transformers, voltage regulators, etc., and also because the output frequency from the repeater is different from its input frequency. , other advantages are obtained, such as being able to produce the desired amplifier gain.

Therefore, oscillation due to feedback is not a problem.

Furthermore, expensive high-voltage coupling capacitors are not required, since the start signal is detected from the high-voltage side of the distribution network by means of a magnetic coupler that is not connected to the power line.

Magnetic field type couplers do not make contact with power lines, so they can be installed quickly and inexpensively, and the couplers are general-purpose.
There is no need to replace the coupler when the primary distribution voltage level changes.

Since the output level of the transmitter section of the repeater can be quite high, a fairly low gain is required, thus allowing the use of inexpensive receivers in the remote communication terminal.

Since the output impedance of the transmitter portion of the frequency conversion repeater can be much lower, matching of the transmitter to the secondary power distribution network is not critical.

Therefore, the transmission voltage has little to do with the secondary line impedance.

The invention also discloses the use of a magnetic field type coupler in a substation receiver that allows the use of only one matching transformer to couple the substation transmitter to the primary distribution line.

[Brief explanation of the drawing]

FIG. 1 is a drawing partially showing in blocks and partially schematically a distribution power line carrier communication system constructed according to the present invention using a magnetic field type coupler and a frequency conversion repeater;
Figure 2 is a schematic diagram of a magnetic field type coupler used in the distribution power line carrier communication system shown in Figure 1, and Figure 3 is a part of a frequency conversion repeater used in the distribution power line carrier communication system shown in Figure 1. FIG. 4 is a diagram showing in blocks and in part diagrammatically, not only that the signals are in non-overlapping frequency bands, but also a suitable form of the initiation response signal. In the drawing, relay devices...60, 62, remote communication terminals...40, 54, starting signal sources...12, 16, first communication path...23, second communication path... 31゜51, Frequency converter...111, Response receiving device...
280°

Claims (1)

[Claims] 1. A start signal source provided in the main control station and generating a start signal, a plurality of relay devices connected to this start signal source and converting the frequency of the start signal, and connected to each relay device. a first remote communication terminal configured to connect the start signal source and each relay device via a first power line conductor and a magnetic field type coupler;
a second power line conductor connected to the first power line conductor via a distribution transformer; a second communication path connecting the relay device and the remote communication terminal via the second power line conductor; a frequency converter provided in each of the relay devices, which converts the start signal into a second frequency band that does not overlap with the first frequency band of the start signal; and a device which applies the output of the frequency converter to the second communication path. , a response receiving device connected to the first communication path and configured to receive a response signal generated by a called remote communication terminal, each remote communication terminal being coupled to the second power line conductor; an apparatus for forming a response communication link extending through the distribution transformer with the response receiver, and coupling the response receiver to the first power line conductor such that a remote communication terminal is designated by the initiation signal; Then, each remote communication terminal includes a device for giving a response signal to the response receiving device, and each remote communication terminal
A power line carrier communication system that operates to provide a response signal in a third frequency band that does not overlap with the first and second frequency bands to the second communication link when called by a start signal through the communication link. 2. Claim No. 2, comprising an encoder for encoding the readings of the multi-purpose meter into the response signal produced by the remote communication terminal when only one remote communication terminal is designated by the initiation signal. The power line carrier communication system according to item 1. 3. The power line carrier communication system according to claim 1 or 2, wherein the remote communication terminal has a coder for adding its unique address to the response signal. 4. The start signal source generating the start signal includes a central communication terminal that applies a first modulated carrier signal 1f in a first frequency band to the first power line conductor in response to the start signal, and the relay device A modulated carrier signal is received, and a second modulated carrier signal I41 corresponding to the start signal is transmitted to a second power line conductor coupled to the carrier signal, and the second modulated carrier signal is in the first frequency band. in second non-overlapping frequency bands, the remote communication terminals each include a serial-to-parallel converter decoding device for receiving and processing the second modulated carrier signal, and the remote communication terminal is designated by the second modulated carrier signal. The power line carrier communication system according to any one of claims 1, 2, and 3, wherein when the remote communication terminal sends a response signal to the associated second power line conductor. 5. The power line carrier communication system according to any one of claims 1 to 4, wherein the relay device includes a device for amplifying the start signal in the second frequency band. 6. The magnetic field type coupler includes a ferrite rod antenna provided on the magnetic W near the first power line conductor, a bandpass filter tuned to the first frequency band, and an amplifier according to any one of claims 1 to 5. A power line carrier communication system described in .