JPS5821471B2 - Terminal connection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a connection method between a network control device and a data terminal device of a data collection system that uses subscriber telephone lines.

1. In recent years, systems have been introduced in which a central device collects data from data terminal devices in remote locations using subscriber telephone lines (hereinafter referred to as telephone lines), such as automatically reading usage amounts of water, gas, electricity, etc. An automatic meter reading system is being considered.

FIG. 1 shows an example of the configuration of the data collection system described above, and the configuration of this system will be briefly described below.

However, FIG. 1 shows everything from the exchange to the data terminal equipment, and the center equipment is omitted.

In the figure, 1 is an exchange, 11 is an incoming trunk (ICT) for subscriber telephones, 12 is a special trunk (SPT) for data collection, 13 is a frame (LLF), 2 is a telephone line, and 3 is a telephone line 2. A connected subscriber telephone (hereinafter referred to as a telephone), 4 a network control unit (hereinafter referred to as NCU) connected to the telephone line 2, and 5A a data terminal device for reading meters of water, gas, etc., are connected.

In the above configuration, in the case of a call to the telephone 3, the connection is made via the incoming trunk 11-frame 13 route, and at the moment of reception, the polarity of the telephone line 2 is reversed, and the 16Hz ringing signal is sent to the telephone 3 via the NCU. Ring the bell.

When the telephone 3 rings and the subscriber answers (off-hook), the direct current circuit of the telephone 3 is closed, a loop current flows, a relay (not shown) in the incoming trunk 11 is activated, and the 16Hz calling circuit is disconnected. (Ring l-IJ knob)
, a communication path is formed, the polarity of the telephone line 2 is restored, and the communication path is maintained until the end of the call.

When the call ends, the exchange 1 returns to its original state.

On the other hand, in the case of a call to a data terminal equipment, special trunk 1
2-frame 13 route, and a call is made using a call signal (hereinafter referred to as a terminal call signal) that does not ring the telephone 3 at a frequency other than 16 Hz and is sent from the center device when the polarity is reversed.

When the NCU 4 detects this terminal call signal, it activates the data terminal device 5A to perform data communication.

During data communication, the DC circuit of the data terminal device 5A is closed and a loop current flows, and a relay (not shown) of the special trunk 12 operates to form a communication path. In contrast, with the polarity of the telephone line 2 reversed, the communication path is maintained until the end of the communication.

When the communication ends, the exchange 1 returns to its original state.

In the above system, NCU4 and data terminal device 5A
When both are operated by the power supply of the exchange (hereinafter referred to as the station power supply), it is necessary to both supply DC current and receive and pass AC signals by connecting the NCU 4 and the data terminal device 5A.

Therefore, simply speaking, this connection requires 2 wires + 2 wires = 4 wires, but minimizing the number of wires is particularly desirable in terms of system operation.

This demand is even greater when, for example, home data terminal equipment 5B, which is different from the subscriber, is connected in parallel as shown in FIG.

The present invention is based on the NCU:! :Data terminal equipment and minimum 2
The purpose is to provide a terminal connection method that connects by wire.

FIG. 2 is a diagram showing an example of the present invention, in which parts corresponding to those in FIG. 1 are designated by the same reference numerals.

Each line 2, 2' of the telephone line is connected to a pair of telephone line side terminals 41, 41' of the NCU 4.

NCU4 data terminal device 5A side terminal pair 42A, 42A
' and the terminal pair 51A, 51A' of the data terminal device 5A.

Connected with 2 wires 6A and 6A'.

Similarly, connections with other data terminal devices 5B are made using two wires 6B and 6.
Perform by B'.

In NCUJ, terminal 41 and terminal 42A are connected,
(between terminal 41' and terminal 42A') This is switch circuit 4
3A is provided.

The same applies to the data terminal device 5B.

44 is a signal detection circuit that detects a terminal call signal sent from a center device (not shown).

When there are two data terminal devices as in this embodiment, the center device sends out different terminal call signals to call each terminal individually, and the signal detection circuit generates a detection output A or B when it detects this.

Each of the two switch circuits 43A and 43B is composed of a transistor or a SIRISK, and conduction is controlled by the detection outputs A and B described above.

At this time, the terminals 41' and 42A' and the terminals 41' and 42B' are connected with almost no loss in both direct current and alternating current.

The data terminal device 5A includes an interface section 52 and a data terminal circuit section 53.

This interface unit 52 supplies DC current from the station power source to the data terminal circuit unit 53 for its operation; at the same time, it separates the AC signal from the center device that is superimposed on this DC current, and conversely supplies it to the data terminal circuit unit 53. This is for superimposing AC signals from the

That is, although this is just an example, it is composed of a transformer 521 for separating and superimposing exchange signals, and a known constant voltage power supply circuit consisting of a transistor 523, a resistor 524, and a constant voltage diode 525 for supplying DC current. .

Note that the capacitor 522 is used to prevent direct current from flowing through the transformer 521, and has extremely low impedance in terms of alternating current.

These configurations are also the same for the data terminal device 5B.

After the exchange controls the connection between the center device and the telephone circuit 2 during data collection, if the center device sends out a terminal call signal to select, for example, the data terminal device 5A, the signal detection circuit 44 of the NCU 4 detects this signal. It is detected and produces an output A, which controls the conduction of the switch circuit 43A.

Then, the data terminal circuit section 53 is immediately supplied with direct current from the station power supply through the constant voltage power supply circuit, and as a result, a loop current flows through the telephone line 2, making data communication possible.

Since the equivalent load resistance of the data terminal circuit section 53 can be kept almost constant, by using a constant voltage power supply circuit for DC current supply, its impedance changes depending on the length of the telephone line 2. However, the DC current flowing there, that is, the loop current, remains almost constant.

This is also a great advantage for the switching equipment when setting the loop current value.

In addition, since the AC impedance on the collector side of the transistor 523 of the constant voltage power supply circuit is extremely high,
There is very little influence on the AC signal passing through the transformer 521.

As explained above, according to the present invention, a switch circuit whose conduction is controlled during data collection is provided in a network control device, and a switch circuit for separating direct current and alternating current signals,
By providing the ink face section for superimposing, these devices can be connected with a minimum of two wires, and wiring can be simplified.

Furthermore, while the first data terminal device is in operation, the small data terminal device is disconnected from the telephone line by a switch circuit, and therefore the impedance seen from the telephone line side or the impedance seen from the operating data terminal device side is , is constant regardless of the number of data terminal devices, and high communication quality can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a data collection system according to the present invention, and FIG. 2 is a diagram showing main parts of the configuration of an embodiment of the present invention. 1... Switchboard, 2, 2'... Subscription telephone line, 3... Telephone, 4... Network control device, 5A, 5B... ...Data terminal equipment, 41,4
1'...Network control device subscriber telephone line side terminal pair,
42A, 42A', 42B. 42B/-... Data terminal device side terminal pair of network control device, 43A, 43B... Switch circuit, 44
...Signal detection circuit, 51A, 5'fA', 51
B, 51B'...Terminal pair of data terminal equipment, 5
2... Ink face section, 53... Data terminal circuit section.

Claims (1)

[Claims] 1 In systems that supply power from a switching system via subscriber telephone lines to a network control device and a plurality of selectively driven data terminal devices for their operation, and collect data from each data terminal device, the network control device A switch circuit is provided between each data terminal device side terminal pair and the subscriber telephone line side terminal pair, and conduction is controlled to pass DC current and AC signals during data collection, and each data terminal device side terminal pair of the network control device is and the terminal pair of each data terminal device with two wires, and each data terminal device has a data terminal circuit section and a subscriber telephone line by supplying direct current from the power supply of the exchange to the data terminal circuit section. 1. A terminal connection method characterized by comprising an interface unit that closes a DC loop of the data terminal circuit unit, separates an AC signal to a data terminal circuit unit, and superimposes an AC signal from the data terminal circuit unit.