JP4354058B2 - Data transmission apparatus and automatic meter reading system using the apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a data transmission device and uses the data transmission device to transmit various data such as meter reading data such as gas, electricity and water, or inventory data of vending machines to a remote place via a digital communication network. Therefore, it relates to an automatic meter reading system.
[0002]
[Prior art]
Conventionally, an automatic meter reading system that uses an analog telephone line network to read a meter reading value of a gas usage meter meter installed in each home and transmits it to a meter reading center has been operated. In such an automatic meter reading system, a terminal network control device called T-NCU is installed in the vicinity of an outdoor telephone line entrance, and the T-NCU and meter reading meter are connected by a cable. When there is a call signal from the meter reading center, the T-NCU determines that the incoming call is from the meter reading center, and reads the meter reading data by communicating with the meter meter without ringing the bell of the home phone. This is sent to the meter reading center. According to such an automatic meter reading system, it is not necessary for the meter reader to visit each home individually, the meter reading cost can be greatly reduced, and a number of home meter reading can be completed in a short time.
[0003]
By the way, in recent years, a digital communication line network called ISDN is rapidly spreading in place of a conventional analog telephone line network. In a digital communication network, a DSU (Digital Service Unit) is connected to the end of a subscriber line (existing telephone line) drawn indoors, and a telephone or facsimile transmission / reception is performed via a TA (terminal adapter). It is necessary to connect a TE (Terminal Equipment) such as a machine. Of course, as is well known, DSU and TA may be integrated.
[0004]
FIG. 9 is a schematic configuration diagram of an automatic meter reading system using an ISDN network. An ISDN-dedicated terminal network controller called I-NCU 9 is connected in parallel with TA 7 to DSU 6 connected to the end of subscriber line 3 drawn into subscriber home 4, and the I-NCU 9 reads the meter. Connected to meter 5. When a call signal for meter reading is transmitted from the meter reading center 2, the I-NCU 9 is activated and communicates with the meter meter 5 to acquire meter reading data, and the meter reading data is transmitted via the DSU 6. The data is sent to the meter reading center 2.
[0005]
[Problems to be solved by the invention]
In general, the I-NCU 9 is disposed in the vicinity of the DSU 6, that is, in the house, whereas the meter-reading meter 5 is usually installed outside the house. For this reason, in the said conventional automatic meter-reading system, the cable which connects I-NCU9 and meter-reading meter 5 becomes very long, and also the construction which penetrates the outer wall of the subscriber's house 4 is required. The cost of such construction must be borne by the business operator (for example, a gas company) that benefits from automatic meter reading, and the burden is so large that it is difficult to recover the construction cost even by cost reduction by automatic meter reading. It was a thing. On the other hand, the customer side suffers from the great disadvantage that a long cable is laid in the house and the aesthetic appearance is impaired, and a hole must be drilled in the outer wall of the subscriber house 4.
[0006]
For this reason, the digital communication network is a communication line suitable for data transmission, but the contradiction that remote meter reading becomes difficult with the switching from the analog telephone network to the digital telephone network. Had.
[0007]
On the other hand, the present applicant, in Japanese Patent Application No. 9-275314 (see Japanese Patent Application Laid-Open No. 11-98276), shares an existing subscriber line connected to such a digital communication network, We have proposed a device that sends meter reading data from a meter meter installed outside the home to a terminal network controller installed in the home. According to such a device, it is not necessary to install a new cable for directly connecting the meter-reading meter and the terminal network control device.
[0008]
The present invention is a further improvement of the apparatus according to the present invention. The object of the present invention is to provide a data transmission apparatus that does not require large-scale cable laying work, and that provides benefits to both consumers and operators. An object of the present invention is to provide an automatic meter reading system using the apparatus.
[0009]
[Means for Solving the Problems]
A data transmission apparatus according to the present invention is connected to a telephone line between a station-side OCU (Office Channel Unit) included in a digital communication line network and a subscriber-side DSU. A data transmission device for transmitting data generated by a provided data generating means from a telephone line to a digital communication line network via a DSU,
a1) first signal processing means inserted into the telephone line in the subscriber's house and connected to the I-NCU connected to the DSU;
a2) a second signal processing means inserted into the telephone line on the station side of the first signal processing means and connected to the data generating means;
The first and second signal processing means consist of:
b1) Identification means for identifying or estimating a small amplitude burst signal period transmitted from the OCU among signals in accordance with a time division direction control transmission system transmitted and received between the OCU and the DSU;
b2) selection means for selecting a signal having a predetermined frequency, amplitude or phase according to data to be transmitted between the I-NCU and the data generation means;
b3) a transmission means for superimposing the signal selected by the selection means on at least a part of the burst signal period identified by the identification means, and transmitting it to the telephone line;
b4) separation means for separating and taking out the superimposed signal from the telephone line;
b5) receiving means for restoring the original data in accordance with the frequency, amplitude or phase of the signal extracted by the separating means;
It is characterized by including each.
[0010]
This data transmission apparatus is suitable for an automatic meter reading system that sends meter reading data such as usage amount of gas, electricity, water, etc. to a remote meter reading center. That is, the automatic meter reading system according to the present invention includes a meter reading center connected to the digital communication network, and the data generation means is a meter reading meter for acquiring meter reading data, and a predetermined signal is transmitted from the meter reading center. The I-NCU and the meter-reading meter send and receive data via the first and second signal processing means, and the meter-reading data is sent from the DSU to the meter-reading center via the digital communication network. .
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
In the data transmission apparatus according to the present invention, a burst signal for a normal time division direction control transmission system (so-called ping-pong transmission system) is transmitted through a telephone line connecting the first signal processing means and the second signal processing means. Bidirectional transmission of other data in a multiplexed format. On the telephone line near the DSU, the burst signal transmitted from the OCU is attenuated and has a small amplitude, whereas the burst signal transmitted from the DSU has a large amplitude because it is hardly attenuated. Therefore, in view of the power power of the signal to be superimposed, it is more advantageous to superimpose in the burst period having a small amplitude.
[0012]
Therefore, for example, when a data transmission request signal is sent from the I-NCU to the data generation means, the first signal processing means operates as follows. That is, the discriminating unit discriminates or estimates a period of a small amplitude among burst signals that appear periodically. In practice, it is easier to detect a large-amplitude burst signal that is hardly attenuated. Therefore, the identification means detects the rising or falling of a large-amplitude burst signal, and a predetermined period when a predetermined time elapses therefrom. May be configured to estimate that the burst period is a small amplitude. The transmission means performs signal conversion such as associating signals of different frequencies, amplitudes or phases with binary values of “0” or “1”, for example, according to the data to be transmitted received from the I-NCU. The signal is superimposed every burst period of amplitude.
[0013]
On the other hand, the second signal processing means estimates a small-amplitude burst period in the same manner as the first signal processing means, and frequency-separates, for example, signals superimposed in the period. Then, the original data is restored by discriminating the frequency, amplitude or phase of the signal, and the restored data is sent to the data generation means. On the other hand, when data is sent from the data generation means to the I-NCU, similarly, the data is transmitted in the order of the transmission means of the second signal processing means → the telephone line → the reception means of the first signal processing means. Sent.
[0014]
In the data transmission apparatus according to the present invention, as long as the frequency band of the burst signal by the normal time division direction control transmission through the telephone line is separated from the frequency of the superimposed signal, the operation of the DSU or OCU is impaired. There is no. Therefore, the data transmission apparatus according to the present invention can perform local data transmission / reception without interfering with such normal transmission. In order to prevent the superimposed signal from being sent to the DSU or OCU side as described above, a high-pass type or band cut-off type filter may be inserted into the telephone line as necessary.
[0015]
Further, in the automatic meter reading system according to the present invention, when the meter reading center sends a call signal for automatic meter reading to a predetermined consumer's house, the DSU at the consumer's house detects the incoming call and detects the I-NCU. The I-NCU sends a meter reading execution instruction signal to the meter reading meter via the first and second signal processing means as described above. The meter-reading meter receives this, for example, acquires usage data at that time, and sends it back to the I-NCU via the second and first signal processing means. Further, this data is sent from the DSU to the digital communication network in a predetermined format, and finally reaches the meter reading center. As a result, the meter reading center can calculate a charge for the amount of gas used in the customer's home for the past month, for example.
[0016]
Therefore, according to the automatic meter reading system of the present invention, data transmission / reception between the meter reading meter and the I-NCU is performed using the existing telephone line. It is only necessary to perform the construction for inserting the first and second signal processing means into the housing, and the construction for penetrating the outer wall of the subscriber's house as in the prior art is unnecessary, and the newly added wiring is short. That's it. Therefore, since there is little damage to the aesthetics of the house without damaging the outer wall, the consumer (subscriber) has no resistance to the construction. In addition, for the business side, the cost burden is greatly reduced because the construction is small.
[0017]
【Example】
An embodiment of an automatic meter reading system using a data transmission apparatus according to the present invention will be described below with reference to the drawings.
[0018]
FIG. 1 is a schematic configuration diagram of the automatic meter reading system. 9 is different from the conventional configuration shown in FIG. 9 in that the first multiplexing control device 11 and the second multiplexing control device 21 are in the middle of the subscriber line 3 distributed from the ISDN line network 1 to each home. That is, the data transmission device 10 is inserted. The I-NCU 9 is connected to the first multiplexing control device 11 with a relatively short cable, and the meter meter 5 for measuring the usage amount of gas, electricity, water, etc. is connected to the second multiplexing control device 21. ing. Thereby, a long cable for connecting the I-NCU 9 and the meter-reading meter 5 as in the prior art becomes unnecessary. In FIG. 1, the second multiplexing control device 21 and the meter-reading meter 5 are arranged outside the subscriber house 4 and other parts are arranged in the house, but such an arrangement is not necessarily required. Absent.
[0019]
FIG. 2 is a configuration diagram of a main part centering on the data transmission apparatus 10 in FIG. The OCU 1a installed in the telephone office and the DSU 6 installed in the subscriber home 4 are connected by a two-wire metallic balanced cable (subscriber line 3).
[0020]
FIG. 3 is a diagram illustrating a signal waveform of a signal transmission method between the OCU 1a and the DSU 6, that is, a so-called ping-pong transmission method. In the OCU 1a, the continuous transmission pulse signal is time-axis compressed to ½ or less, converted into a burst-like pulse train at a predetermined cycle, and sent to the subscriber line 3. The standard amplitude at the time of sending out is 6V _0-p , and the signal is attenuated by passing through the subscriber line 3, and reaches the DSU 6 after being attenuated by 50 dB at the maximum. The DSU 6 extends such a burst-like pulse train in the time axis, reversely converts it into a continuous pulse train, and sends it to the TA 7. When signals are transmitted in the reverse direction, that is, from the subscriber side to the station side, the idle time between bursts is used to transmit the same burst-like pulse train. The burst period T is 2.5 ms, and the transmission rate during the burst signal period is typically 320 kbps. In the following description, data transmitted between the station side and each subscriber side (that is, OCU 1a and DSU 6) is referred to as main data, and first and second multiplexing are described as will be described later. Data transmitted / received only between the control devices 11 and 21 is defined as sub-data, and the two are distinguished.
[0021]
In the transmission system using the ISDN line network, the OCU 1a supplies a constant current of 39 mA to the DSU 6 in addition to the data transmission as described above in order to supply power to the DSU 6, TA 7 and TE 8 of each subscriber. . The power supply voltage (line voltage and ground voltage) by this is 60V at the maximum. Upon receiving such power supply, the DSU 6 can supply a power source power of up to 420 mW to the TA 7 and TE 8.
[0022]
As shown in FIG. 2, as part of the configuration of the first multiplexing control device 11, an AC coupling unit 12 including a coil or the like is connected to the subscriber line 3. The apparatus 11 includes a modulation / demodulation processing unit 13 and a transmission / reception unit 14. Further, the second multiplexing control device 21 has the same configuration as the first multiplexing control device 11.
[0023]
FIG. 4 is a diagram illustrating an internal configuration of the modulation / demodulation processing units 13 and 23. The modulation / demodulation processing units 13 and 23 modulate the data received through the transmission / reception units 14 and 24 and place them on the subscriber line 3 via the AC coupling units 12 and 22. A low-pass filter (LPF) 37 and a frequency discriminating unit for demodulating a signal received from the subscriber line 3 through the AC coupling units 12 and 22 and sending them to the transmitting and receiving units 14 and 24. 38, a receiving-side buffer memory 39 is provided. Furthermore, a burst detection unit 31, a timing generation unit 32, and a memory control unit 33 are provided to supply control signals necessary for the operation of each unit.
[0024]
The operation of the data transmission apparatus 10 shown in FIGS. 2 and 4 will be described with reference to the timing chart of FIG. FIG. 5A is a diagram showing a burst signal observed at the insertion position of the first multiplexing control device 11. The pulse of the burst signal is a ternary signal that swings on both sides of “+ V” and “−V” with respect to “zero” as an AC signal, so that it can swing positively and negatively around a DC voltage component by constant current feeding. It has a shape. For example, when transmitting predetermined digital data from the I-NCU 9 side to the meter-reading meter 5 side, when the modulation / demodulation processing unit 13 receives data from the I-NCU 9 via the transmission / reception unit 14 in the first multiplexing control device 11. The data is stored in the transmission side buffer memory 34 in response to a control signal from the memory control unit 33. The transmission-side buffer memory 34 (same as the reception-side buffer memory 39) absorbs the difference in data rate (speed) between when data is received from the transmission / reception unit 14 and when data is sent to the variable frequency oscillation unit 35. It has a function to do.
[0025]
Since the AC coupling unit 12 passes only an AC voltage, the burst detection unit 31 is given a signal as shown in FIG. 5A (hereinafter, this signal is referred to as “main signal”). The burst detector 31 detects the start timing of a large-amplitude burst signal (that is, a signal output from the DSU 6 side) by determining the voltage level of the main signal, and has a pulse shape as shown in FIG. Outputs burst start signal. The appearance interval of this burst start signal is 2.5 ms. The timing generation unit 32 generates a window signal having a predetermined time width t2 from the time when the predetermined time t1 has elapsed after the burst start signal appears (see FIG. 5C). T1 and t2 are determined so that this window signal corresponds to a period of a burst signal having a small amplitude (that is, a signal output from the OCU 1a side).
[0026]
The memory control unit 33 reads the data stored in the transmission side buffer memory 34 bit by bit in synchronization with the burst start signal, and supplies the data to the variable frequency oscillation unit 35. The frequency variable oscillating unit 35 oscillates at a frequency of 10 kHz when the binary signal input from the transmission side buffer memory 34 is “0”, and oscillates at a frequency of 12 kHz when the binary signal is “1”. Then, the sine wave signal having one of the two wavelengths is output for the period of the window signal given from the timing generation unit 32. As a result, the output driver 36 outputs an intermittent sine wave signal as shown in FIG. Thereby, only the sine wave signal of the two wavelengths is superimposed only in the burst signal period of small amplitude (hereinafter, the superimposed signal is referred to as “sub signal”). As described above, the transmission rate of the main signal is 320 kbps. However, depending on the original data, a plurality of “0” or “1” may be continuous, so the frequency spectrum of the main signal is up to about 50 kHz. Exists. Still, since the frequency can be completely separated from the superimposed 10 kHz or 12 kHz sine wave signal using a filter, each data can be transmitted and received without interfering with each other. The modulation / demodulation processing unit 13 may add and output additional data, error detection data, or the like as needed.
[0027]
When such sub-signals are superimposed and transmitted, the second multiplexing control device 21 operates as follows. The burst detection unit 31 and the timing generation unit 32 generate a window signal during a period in which a small-amplitude burst signal exists, similar to the operation on the transmission side. The LPF 37 has an appropriate cutoff frequency set between 12 kHz and 50 kHz so as to pass the superimposed 10 kHz or 12 kHz sine wave signal and cut off the main signal. The frequency discriminating unit 38 identifies the frequency of the sine wave signal extracted by the LPF 37 only during the window signal period, and outputs “0” when it is 10 kHz and “1” when it is 12 kHz. The output signal of the frequency discriminating unit 38 is sequentially stored in the reception side buffer memory 39. Then, the memory control unit 33 reads data from the reception side buffer memory 39 at a predetermined cycle, and sends it to the meter reading meter 5 via the transmission / reception unit 24. As described above, when other data is added by the modulation / demodulation processing unit 13 at the time of transmission, the modulation / demodulation processing unit 23 extracts only the original data obtained from the I-NCU 9 and supplies it to the transmission / reception unit 24.
[0028]
When meter reading data such as a measured value is sent from the meter reading meter 5 side to the I-NCU 9 side, the processing completely opposite to the above may be executed.
[0029]
Note that the binary signal “0” or “1” is not associated with sine wave signals of two different frequencies (10 kHz and 12 kHz in the above example), but a plurality of consecutive binary signals are assigned to a plurality of different types. You may make it match | combine with the sine wave signal of a frequency. For example, if two adjacent binary signals “00”, “01”, “10”, and “11” are associated with different sine wave signals having frequencies f1, f2, f3, and f4, data of 2 bits is obtained every 2.5 ms. Therefore, the transmission rate can be doubled as compared to the above embodiment. Of course, if frequency discrimination is possible, three or more consecutive binary signals can be associated with signals of different frequencies.
[0030]
As described above, the sub-signal superimposed on the main signal can arbitrarily use the frequency band between the lower limit frequency and the upper limit frequency determined as follows. First, the lower limit frequency needs to be 800 Hz or more in order to superimpose a signal having one or more AC periods within a half of the burst period of 2.5 ms of the main signal. Considering the ability of the filter to extract (generally several cycles are required) and the fact that signal detection with a stable margin is performed, the design is easy if it is several kHz or more. On the other hand, the upper limit frequency needs to be the lower limit of the spectrum due to the repetitive pulse of the main signal as described above, about 50 kHz or less, and practically considering the ability of the filter to extract the sub-signal band, etc. If it is 30 to 40 kHz or less, the design is easy.
[0031]
In the above embodiment, as a sub-signal modulation method, so-called frequency modulation is performed in which the original binary signal is associated with a signal having a different frequency, but the amplitude is obtained by using a sine wave signal of a certain frequency as a carrier wave. Modulation may be performed. FIG. 6 is an example of a timing diagram in the case of using amplitude modulation. As shown in FIG. 6 (d), for example, the carrier frequency is 10 kHz, and the sine wave for binary signals “0” and “1”. The peak voltage of the signal is made to correspond to two types of V1 and V2. At the time of demodulation, amplitude determination may be performed instead of frequency discrimination. Of course, even in such amplitude modulation, a plurality of continuous binary signals (for example, “00”, “01”, “10”, and “11”) are changed to a plurality of different voltage levels within a range in which the amplitude can be identified. You may make it match | combine.
[0032]
Furthermore, as the sub-signal modulation method, various modulation methods used in a normal analog subscriber telephone line can be used. That is, amplitude modulation, frequency modulation, phase modulation, etc. may be used in combination. However, the usable frequency band is preferably in the range of several kHz to 40 kHz as described above.
[0033]
In the above description, it is assumed that the signal sent from the OCU 1a is greatly attenuated at the insertion position of the data transmission apparatus 10. However, there are cases where the subscriber's home 4 is close to the OCU 1a and the signal attenuation is small. In such a case, an attenuator may be inserted at a position indicated by L1 in FIG. 2 to forcibly attenuate the signal. As described above, the frequency band of the sub-signal and the frequency band of the main signal in the period in which the sub-signal is superimposed can be completely separated, but normal in the DSU 6 configured on the assumption that there is no signal superimposition. There is also a risk that the operation cannot be performed. In such a case, a high-pass filter or a band removal filter may be inserted at a position indicated by L2 in FIG. 2 to remove the frequency band of the superimposed signal.
[0034]
The power sources of the first and second multiplexing control devices 11 and 21 are generally used such as a commercial AC power source (AC100V), a primary battery, a secondary battery, a solar battery (and a combination with a storage means such as a capacitor). In addition to the various power sources, a part of the power source current supplied to the subscriber line 3 by local power supply may be branched and used within a range that does not hinder the operation of other devices such as TA. Of course, a combination of these power sources may be used.
[0035]
Next, the operation when performing automatic meter reading in the automatic meter reading system according to the present embodiment will be described with reference to the flowchart of FIG.
The DSU 6 repeatedly determines whether there is an incoming call (step S1). If there is an incoming call, the DSU 6 determines whether the incoming call is an incoming call from the meter-reading center 2 (step S2). When performing automatic meter reading, the meter-reading center 2 sends a call signal to a meter-reading subscriber via the ISDN network 1. When an incoming call is detected in response to this call signal, the I-NCU 9 operates (step S3), and the read instruction signal is changed from I-NCU 9 → first multiplexing control device 11 → second multiplexing control device 21 → meter meter 5 (Step S4). The operations of the first and second multiplexing control devices 11 and 21 at this time are as described above.
[0036]
When the meter-reading meter 5 receives the reading instruction signal, for example, the metering value at that time is read according to the instruction, and the meter-reading meter 5 → second multiplexing control device 21 → first multiplexing control device 11 → I as meter-reading data. -Reply with NCU9 (step S5). The I-NCU 9 stores the meter reading data via the DSU 6, for example, in the B channel of the burst signal and sends it to the subscriber line 3. Of course, it is also possible to send by using D or B channel packet, UUI, etc. instead of the B channel. The meter reading center 2 receives the meter reading data through the ISDN line network 1, and calculates a charge from the amount of gas used for the past one month, for example (step S6). If it is determined in step S2 that the incoming call is not from the meter reading center 2, since it is a normal telephone call signal, TE8 is operated via TA7.
[0037]
In the above embodiment, as shown in FIG. 1, the DSU 6, the I-NCU 9, the first multiplexing control device 11, the second multiplexing control device 21, and the meter-reading meter 5 have independent configurations. The data transmission apparatus of the invention is not limited to this, and can take various forms in which a plurality of components are integrated. Specifically, for example, the I-NCU 9 and the first multiplexing control device 11 may be integrated, or the DSU 6, I-NCU 9 and the first multiplexing control device 11 may be integrated. it can. On the other hand, the 2nd multiplexing control apparatus 21 and the meter-reading meter 5 can also be integrated. FIG. 8 is a diagram showing an example of the configuration in that case. Since the meter-reading meter 5 often has to be arranged at a predetermined position, the function of the second multiplexing control device 21 is incorporated in the meter-reading meter 5 and is connected to the end of the branch line 3 a connected to the subscriber line 3. The second multiplexing control device 21 is connected. In general households, the length of the branch line 3a is 20 to 30 m or less, so even with such a configuration, it is possible to send and receive sub-data without interfering with the original call or the like.
[0038]
In addition to the above-described remote automatic meter reading system for gas, electricity, water, etc., the present invention can be applied from a remote location via a digital telephone network, such as a remote management system that sends inventory management data of vending machines to a central management center. It can be applied to various systems for automatically obtaining various data.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an automatic meter reading system according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a main part centering on the data transmission apparatus in FIG. 1;
FIG. 3 is a diagram showing a signal transmission method between an OCU and a DSU.
4 is an internal configuration diagram of a modulation / demodulation processing unit in FIG. 2;
FIG. 5 is a timing chart for explaining a multiplexing method of a main signal and a sub signal in the present embodiment.
FIG. 6 is a timing diagram for explaining a multiplexing method of a main signal and a sub signal according to another embodiment of the present invention.
FIG. 7 is a flowchart showing an operation when automatic meter reading is performed in the present embodiment.
FIG. 8 is a schematic configuration diagram of an automatic meter reading system according to another embodiment of the present invention.
FIG. 9 is a schematic configuration diagram of a conventional automatic meter reading system.
[Explanation of symbols]
1 ... ISDN network 1a ... OCU
2 ... Meter reading center 3 ... Subscriber line 3a ... Branch line 4 ... Subscriber house 5 ... Meter reading meter 6 ... DSU
9 ... I-NCU
DESCRIPTION OF SYMBOLS 10 ... Data transmission apparatus 11 ... 1st multiplexing control apparatus 21 ... 2nd multiplexing control apparatus 12, 22 ... AC coupling part 13, 23 ... Modulation / demodulation processing part 14, 24 ... Transmission / reception part 31 ... Burst detection part 32 ... Timing generation Unit 33 ... Memory control unit 34 ... Transmission side buffer memory 35 ... Variable frequency oscillation unit 36 ... Output driver 37 ... Low pass filter (LPF)
38 ... Frequency discriminating unit 39 ... Reception side buffer memory

Claims (2)

Connected to the telephone line between the OCU on the station side and the DSU on the subscriber side included in the digital communication line network, the data generated by the data generating means provided on the subscriber side is digitally transmitted from the telephone line via the DSU. A data transmission device for transmitting to a communication network,
a1) first signal processing means inserted into the telephone line in the subscriber's house and connected to the I-NCU connected to the DSU;
a2) a second signal processing means inserted into the telephone line on the station side of the first signal processing means and connected to the data generating means;
The first and second signal processing means consist of:
b1) Identification means for identifying or estimating a small amplitude burst signal period transmitted from the OCU among signals in accordance with a time division direction control transmission system transmitted and received between the OCU and the DSU;
b2) selection means for selecting a signal having a predetermined frequency, amplitude or phase according to data to be transmitted between the I-NCU and the data generation means;
b3) a transmission means for superimposing the signal selected by the selection means on at least a part of the burst signal period identified by the identification means, and transmitting it to the telephone line;
b4) separation means for separating and taking out the superimposed signal from the telephone line;
b5) receiving means for restoring the original data in accordance with the frequency, amplitude or phase of the signal extracted by the separating means;
A data transmission device comprising: The automatic meter reading system using the data transmission device according to claim 1, further comprising a meter reading center connected to the digital communication network, wherein the data generating means is a meter meter for acquiring meter reading data, When a predetermined signal is sent from the I-NCU, the I-NCU and the meter-reading meter send and receive data via the first and second signal processing means, and the meter-reading data is sent from the DSU to the meter-reading center via the digital communication network. An automatic meter reading system characterized by being

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