JPH07221862A - Terminal equipment system - Google Patents

Abstract

PURPOSE:To attain communication with high reliability in which level fluctuation of a communication signal is suppressed by varying a resistance of a resistor inserted in a loop of a telephone line with number of terminal equipments to be connected so as to always set an optimum resistance of the semi-loop closed resistor independently of number of the terminal equipments to be connected when plural terminal equipments are connected to the system. CONSTITUTION:When one terminal equipment is connected to the system, a control section 6 activates only a light emitting diode 50-b only of a photocoupler to control a light receiving transistor(TR) 50-a of the photocoupler to be conductive, then a rectifier circuit 14 forms a closed circuit via a resistor 53. When three terminal equipments are connected to the system, the control section 6 activates the light emitting diode 50-b of a photocoupler to control only the light receiving transistor(TR) 50-a of the photocoupler to be conductive, then the rectifier circuit 14 forms a closed circuit via a resistor 55. That is, a loop is formed to a subscriber telephone line via the resistor 55. Thus, the resistance of the resistor inserted in a closed circuit of the telephone line is varied with the change in number of terminal equipments to be connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal device system for monitoring the state of a sensor provided at a remote place using a telephone line.

[0002]

2. Description of the Related Art In recent years, a device for monitoring a plurality of sensors provided at a remote place from a monitoring center by using a telephone line has become popular. For example, gas, water,
A so-called automatic meter reading system has been introduced, in which the meter automatically measures the amount of electricity used, etc., periodically using a telephone line.

In this automatic meter reading system, a no-ringing service is used to call a plurality of connected terminal devices from a monitoring center without ringing the bell of a telephone of a general home to connect to a desired specific terminal device, and a predetermined terminal device is connected. A method of performing data communication according to a procedure and collecting an indicated value such as a meter value has been put into practical use.

Such a no-ringing service is a special service realized by adding a special device called a no-ringing trunk having a special function to the exchange of the telephone station. Data communication is performed by designating a target terminal device by a DTMF signal in a half-closed state of the telephone line. As such a device, there is JP-A-2-70165 (terminal device of network control device).

[0005]

When a call is received from the monitoring center, a terminal device connected to a plurality of subscriber telephone lines of a general home detects polarity reversal and simultaneously puts the subscriber telephone lines in a semi-closed state. Then, the loop resistance that is semi-closed differs depending on the number of connected units. Since the loop resistance decreases as the number of connected devices increases, even if a signal of a certain level is transmitted from the center, the reception level of the terminal device on the receiving side varies depending on the number of connected devices.

Therefore, normal communication may not be possible depending on the number of connected devices.

[0007]

A storage unit for storing the number of connected terminal devices which are connected to a telephone line to transmit and receive monitoring data, and a polarity monitoring circuit for monitoring the polarity of the telephone line.
It is composed of a control unit that monitors the signal of the polarity monitoring circuit, a switch circuit controlled by the control unit, and a loop resistance circuit that variably closes the loop resistance of the telephone line according to the operation of the switch circuit. In the terminal system, when the polarity reversal signal of the telephone line is detected from the polarity monitoring circuit,
The loop resistance of the telephone line is variably connected according to the number of connected terminal devices stored in the storage unit.

[0008]

Function: The loop resistance of the telephone line is variably connected according to the number of connected terminal devices, so that communication is performed in an optimum state regardless of the number of connected devices.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram. Reference numeral 1 denotes a terminal device, which is connected to a monitoring center (not shown) via a telephone line 2.

Reference numeral 8 is an incoming call signal detection circuit, which is a telephone line 2
When the incoming call signal is detected from, the control unit 6 is connected so as to be input.

Reference numeral 9 denotes a line current detection circuit, which is used for the terminal device 1.
The control unit 6 monitors whether or not the telephone 19 connected via the telephone is used by detecting the current flowing through the telephone line 2.

Reference numeral 10 is a capacitor, and 11 is an insulating transformer, which is connected to the telephone line 2 with high impedance and supplies a signal to the terminal identification signal receiving circuit 12 for monitoring by the control section 6.

Reference numeral 3 is a polarity monitoring circuit, which is the telephone line 2
The polarity reversal due to the no-ringing signal from is detected and monitored by the control unit 6.

Reference numerals 13-1, 13-2, and 13-3 denote relay contacts, respectively, the telephone line 2, the telephone 19, the loop resistance circuit 4, and the dial circuit 15 which will be described later.
It is for switching the connection with such as, and is interlocked via the relay drive circuit 17.

Reference numeral 14 denotes a rectifying circuit, which prevents the terminal device 1 from having a polarity when it is connected to the telephone line 2, and a loop resistance circuit 4 and a dial circuit 15, which are semi-closed during no ringing communication, And signal modulation / demodulation circuit 1
6 is connected.

The dial circuit 15 sends a dial signal for calling the monitoring center when the terminal device 1 transmits data to the monitoring center.
The signal modulation / demodulation circuit 16 is a circuit that transmits and receives communication data.

The loop resistance circuit 4 is controlled by the control unit 6, but is controlled to be connected to the control unit 6 via the switch unit 5 so as to be insulated from the telephone line 2.

Reference numeral 18 denotes an off-hook detection circuit, which is used when the terminal device 1 is connected to the telephone line 2.
9 is a circuit for detecting the off-hook of 9 and inputting it to the control unit 6. 20 is a meter interface circuit, which is a meter 2
1 is a circuit for connecting the control unit 6 and the meter 21.
It relays the transmission and reception of signals to and from.

Reference numeral 22 denotes a sensor interface circuit, which is a circuit for connecting a sensor 23 such as a gas leak alarm, and which relays transmission / reception of signals between the control unit 6 and the sensor 23.

Reference numeral 24 denotes a data input interface circuit, which is a circuit (not shown) to which a data input device is connected to input data of the terminal device 1 necessary for operating the automatic meter reading system.

The meter interface circuit 20, the sensor interface circuit 22, and the data input interface circuit 24 are respectively monitored by the control section 6, and the state is stored in the storage section 7 as necessary. .

The operation of the above configuration will be described below.

The operation of transmitting data from the terminal device 1 to the monitoring center will be described by taking the case of detecting a gas leak as an example.

When the control unit 6 detects a gas leak signal from the gas leak alarm, which is the sensor 23, via the sensor interface circuit 22, the control unit 6 checks the incoming call signal detection circuit 8 and the line current detection circuit 9. Then, after confirming that the telephone call from the third party or the telephone 19 is not being used, the relay drive circuit 17 is controlled to invert the relay contacts 13-1, 13-2 and 13-3, The telephone line 2 is connected to the dial circuit 15.

If a telephone call is being made by a third party or the telephone 19 is being used, the telephone 19 waits until the use of the telephone 19 is completed.

When the telephone line 2 and the terminal device 1 are connected, the control unit 6 reads out the preset telephone number of the monitoring center from the storage unit 7 and controls the dial circuit 15 to send a selection signal. .

When the monitoring center responds to the call, the terminal device 1 confirms the response of the monitoring center through the signal modulation / demodulation circuit 16 and sends out data indicating that gas has leaked from the signal modulation / demodulation circuit 16. Send to surveillance center.

When the monitoring center receives the transmission data from the terminal device 1, it transmits a confirmation signal to open the telephone line 2.

Upon receiving this confirmation signal, the terminal device 1 controls the relay drive circuit 17 to relay-contact 13-.
1, 13-2, and 13-3 are restored, and the communication ends.

Next, the operation of reading the measured value of the meter 21 from the monitoring center will be described.

When the telephone number of the ordinary home and the number of the terminal device 1 which the user wants to read using the no ringing line are dialed from the monitoring center, the telephone line 2 is called from the no ringing trunk with a signal that does not ring the telephone 19 of the ordinary home. A signal is input.

In the terminal device 1, when the polarity monitoring circuit 3 receives the polarity inversion signal of the telephone line 2, the control unit 6 controls the relay driving circuit 17 to control the relay contact 13-.
Telephone line 2 by reversing 1, 13-2, and 13-3
Is connected to the rectifier circuit 14.

Further, the control section 6 drives the switch circuit 5 to bring the loop resistance circuit 4 into an operating state.

In this case, the loop resistance circuit 4 is changed in accordance with the number of connected terminal devices 1 stored in the storage unit 7 in advance and brought into an operating state.

This operation will be described in detail with reference to the detailed diagram shown in FIG.

The loop resistance circuit 4 comprises a series circuit of light receiving transistors 50-a, 51-a and 52-a of the photocoupler and resistors 53, 54 and 55, respectively. It is connected in parallel.

On the other hand, the switch circuit 5 is composed of a series circuit of light emitting diodes 50-b, 51-b and 52-b of photocouplers and resistors 56, 57 and 58, and each is controlled by the control unit 6. ing.

When the number of connected terminal devices 1 is 1,
The control unit 6 operates only the light emitting diode 50-b of the photocoupler to operate the light receiving transistor 50- of the photocoupler.
The rectifier circuit 14 forms a closed circuit via the resistor 53 in order to control only a in the conductive state. That is, the telephone line 2 forms a loop via the resistor 53.

Next, when the number of connected terminal devices 1 is three, the control unit 6 controls the light emitting diode 5 of the photocoupler.
2-b is operated, and the light receiving transistor 5 of the photocoupler
The rectifier circuit 14 forms a closed circuit via the resistor 55 in order to control the 2-a in the conductive state.

That is, a loop is formed in the subscriber telephone line via the resistor 55.

As described above, even if the number of connected terminal devices 1 changes, the resistance value for closing the telephone line 2 is changed according to the number of connected devices.

When the loop of the telephone line 2 is formed, the control unit 6 controls the signal modulation / demodulation circuit 16 to transmit / receive data, communicate with the monitoring center, and in response to the request from the monitoring center. The measured value of the meter 6 is transmitted.

When the monitoring center normally receives the meter reading data from the terminal device 1, it sends a confirmation signal and opens the telephone line 2.

On the other hand, when the terminal device 1 receives the confirmation signal from the monitoring center, the control unit 6 causes the switch circuit 5 to operate.
All of the operations described above are stopped to open the loop of the telephone line 2, the relay drive circuit 16 is driven, the relay contacts 13-1, 13-2, and 13-3 are restored, and the communication ends. .

[0046]

As described above, according to the present invention,
Even if multiple terminal devices are connected to the same telephone line, they can always be connected to the telephone line with an appropriate half-loop closing resistance, so that fluctuations in the communication signal level can be suppressed by suppressing loss fluctuations in the line loop. Since it is possible to hold down, it is possible to provide a useful terminal device system in which communication with the monitoring center is not possible depending on the number of connected devices.

[Brief description of drawings]

FIG. 1 is a block diagram of a terminal device system showing an embodiment of the present invention.

FIG. 2 is a specific circuit diagram of a loop resistance circuit in the terminal device system showing the embodiment of the present invention.

[Explanation of symbols]

 1 terminal device 2 telephone line 3 polarity monitoring circuit 4 loop resistance circuit 5 switch circuit 6 control unit 7 storage unit

Front Page Continuation (72) Inventor Kuniaki Ito 3-3, Shinjyojiyo, Kashiwa-shi, Chiba, Japan 1 (72) Inventor, Junichi Shimizu 1-3, Shinjyujiyo, Kashiwa-shi, Chiba, 1

Claims (1)

[Claims] 1. A storage unit (7) for storing the number of connected terminal devices (1) connected to a telephone line (2) for transmitting and receiving monitoring data, and a polarity monitor for monitoring the polarity of the telephone line (2). Circuit (3), control section (6) for monitoring the signal of the polarity monitoring circuit (3), switch circuit (5) controlled by the control section (6), and operation of the switch circuit (5) In a terminal device system comprising a loop resistance circuit (4) that variably closes the loop resistance of the telephone line (2) according to the above, a polarity inversion signal of the telephone line (2) is detected from a polarity monitoring circuit (3). At this time, the terminal device system is characterized in that the loop resistance of the telephone line (2) is variably connected according to the number of connected terminal devices (1) stored in the storage unit (7).