JPH0748782B2 - Input circuit of network controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a data transmission system using a general subscriber telephone line, which is connected between a data terminal and a subscriber telephone line and activated by an activation signal. The present invention relates to an input circuit of a network control device for connecting a data terminal to a subscriber telephone line only when the above situation occurs, and particularly to an improvement for preventing various tests of the subscriber telephone line from being adversely affected.

[Conventional technology]

In recent years, a small amount of data scattered over a wide area from the parent station, such as automatic meter reading to monitor the usage of water, gas, electricity, etc., or monitoring of various electric power equipment, survey of the usage of vending machines, etc. As a simple method for collecting data, there is a data collection system in which a data terminal device is connected to a subscriber telephone line, each data terminal is activated in order from the master station, and data is transmitted from each data terminal to the subscriber telephone line. It is attracting attention as an economically powerful person. Such a system has a very wide range of application fields and is expected to be widely used in the future.

The cost of the above-mentioned system is influenced by the cost of the terminal system, and in order to reduce the terminal cost, it is not a good idea to use the commercial power supply as the power supply for operating each terminal, and the power is supplied from the exchange through the subscriber telephone line. It is necessary to operate using the electric power that is generated. For this reason, the power supply circuit is turned on only when the power of a specific polarity is supplied from the subscriber telephone line, and the network control device for connecting the data terminal system to the subscriber telephone line is connected to the data terminal and the subscriber telephone by a specific start signal. It is interposed between the lines. Since the network control device and the data terminal system are supplied with only a power supply having a specific polarity, they have no influence on the power supply such as a normal call current supply.

However, various test voltages or test currents having different polarities from the power supply for supplying the call current may be sent to the subscriber telephone line for testing the line and / or the telephone. This test is, for example, a line test for insulation and capacitance measurement performed on the subscriber telephone line from the station side. Specifically, a certain voltage is applied to the subscriber telephone line from the station side and the capacity is measured by the voltage at the time of transient response at that time, or the absolute value is measured by measuring the current in a steady state after a certain period of time. Based on the result, it is determined whether or not a plurality of telephones are connected to the subscriber telephone line or whether there is a ground fault.

During such a test, if the current value flowing through the subscriber telephone line is not less than a certain value, it is determined that the line test is defective.Therefore, the current consumption during operation of the data terminal device is determined to be normal during the line test. If the current value is equal to or higher than the current value, the line test fails if the data terminal device is connected. In this way, when it is determined that various voltages applied to the input terminals are not in the test state, it is necessary to activate the network control device and the data terminal device.

By the way, if the polarities of the test voltage and the current are the same as the polarities of the network control device (A line ground, B line positive), the test current flows into the power supply circuit for operating them. It will make a mistake in the judgment such as the line test. Therefore, conventionally, according to the type of test voltage, using an overvoltage detection circuit that detects an overvoltage above a certain voltage and a low voltage detection circuit that detects a low voltage below a certain value, a test voltage of 200V system or 48V or less, For example, when a test voltage of a low voltage level system of 36V is detected, the power supply circuit of the network control device is turned off. Of course, the power consumption of the overvoltage detection circuit and the low voltage detection circuit is designed to be extremely small, and the test result will not be erroneous due to the current consumption of these detection circuits.

[Problems to be Solved by the Invention]

However, when the same voltage as the voltage used for normal call or data transmission from the data terminal device, that is, a test voltage of about 48V (A line ground, B line positive) is applied, the above-mentioned overvoltage detection circuit is applied. The low voltage detection circuit cannot prevent the test current from flowing into the power supply circuit of the network controller.
Therefore, the network control device is activated, and it is monitored that a specific activation signal is input.If the activation signal is not received within a certain period of time, the switch circuit is controlled and the power supply circuit is switched from the subscriber telephone line. I'm trying to shut it off. After the switch circuit is turned off, the test current does not flow into the power supply circuit and the test can be performed normally.
By the way, when a test voltage of about 48 V is applied, a resistor of 1 kΩ, 10 kΩ, or 100 kΩ may be inserted in series with the power supply on the exchange side. So, for example, 100k
When a high resistance of Ω is inserted, the current supplied to the power supply circuit of the network control device becomes small and the terminal voltage of the power supply circuit drops, so that the network control device can operate normally. Therefore, operations such as monitoring the specific start signal and disconnection control of the switch cannot be performed.
Therefore, the switch circuit is not turned off, and the test current flows into the power supply circuit of the network control device, resulting in an erroneous determination such as a line test.

The present invention solves such a problem, and although a test voltage that is substantially equal to the voltage used for a call arrives, its supply power is low and the switch cannot be cut off while the network control device is still connected. It is an object of the present invention to provide an input circuit of a network control device that can avoid a situation that adversely affects a test.

[Means for Solving the Problems]

The input device of the network control device of the present invention is interposed between the subscriber telephone line and the data terminal device, and connects the data terminal device and the subscriber telephone line in response to a specific activation signal coming from the subscriber telephone line. A rectifier that is connected to the input of the network controller to be connected and that passes only the polarity used for talking on the subscriber telephone line and a first voltage higher than the voltage used for talking on the output side of this rectifier (for example, An overvoltage detection circuit that cuts off a voltage of + 200V or more, and a low voltage detection circuit that detects that the output voltage of the rectifier is a second voltage lower than the voltage used for communication (eg + 36V) or less, A network including a switch circuit that is off-controlled by a detection output of a low-voltage detection circuit, and a power supply circuit that supplies power from the subscriber telephone line to the network control device and the data terminal device when the switch circuit is on. Control device In this input circuit, when the DC voltage between these input terminals is connected in parallel with the input terminal of the power supply circuit and falls below a certain value, the switch circuit is turned off assuming that the DC power resistance of the subscriber telephone line is below a predetermined value. A high resistance value detection circuit is provided.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. That is, the input terminal 11 connected to the A and B lines of the subscriber telephone line, the rectifier 12 connected to the input terminal 11 and turned on by a voltage having a specific polarity, and the first terminal connected to the output of the rectifier 12
Overvoltage detection circuit 13 that is turned off at a voltage equal to or higher than (for example, about 200V), a low voltage detection circuit 14 that detects that the output voltage of the overvoltage detection circuit 13 is lower than a second voltage (for example, 36V), and a low voltage A switch circuit connected to the output of the detection circuit 14 and controlled to the off state by the detection output of the low voltage detection circuit 14
15 and a high resistance value detection circuit 16 that is connected to the output of the switch circuit 15 and turns off the switch circuit 15 when it detects that the resistance value on the subscriber telephone line side is a certain resistance or higher.
And a power supply circuit 17 for supplying operating power to the network control device 18 and the data terminal 19 by receiving power supplied from the subscriber telephone line via the switch circuit 15.

The network control device 18 has a built-in circuit for determining a start signal based on a specific AC signal (for example, 2 kHz). The network control device 18 is activated by the power supplied from the power supply circuit 17, and when the specific start signal is received, the data terminal 19 If you do not receive the above activation signal within a certain time,
The switch circuit 15 is controlled to be turned off.

The switch circuit 15 is normally on, but once it is controlled to be off, it remains off until the voltage supply from the rectifier 12 side is interrupted. That is, it is initialized when the test from the exchange is completed and the polarity of the subscriber telephone line is reversed, that is, when the line is disconnected.

However, when the power supply resistance value on the subscriber telephone line side is high resistance, the current supplied from the power supply circuit 17 is not sufficient, the input terminal voltage of the power supply circuit 17 is lowered, the determination of the start signal and the above The OFF control operation of the switch circuit 15 cannot be performed as in the above-described conventional example.

Therefore, in this embodiment, when the high resistance value detection circuit 16 detects that the subscriber telephone line side has high resistance, the switch circuit 15 is turned off by the detection output of the high resistance value detection circuit 16. The high resistance value detection circuit 16 has, for example, a built-in resistor, and the voltage across the resistor is equal to or lower than a predetermined value, that is, since the subscriber telephone line side has high resistance, the current supplied is small and the input terminal voltage of the power supply circuit 17 is small. Thus, it is possible to easily detect that the resistance value on the subscriber telephone line side is large.

Next, the operation of this embodiment will be described.

A telephone 10 is connected in parallel to the input terminal 11, and when the telephone 10 is on-hook and data collection is not performed, earth is supplied to the line A of the subscriber telephone line from the exchange side and B Zero to negative battery voltage (0 to -25
0V) is supplied. Therefore, the rectifier 12 is off by the voltage of the opposite polarity and has no effect on the telephone connection.

When the telephone 10 connected in parallel to the input terminal 11 makes a call, the telephone rings by 16 Hz ringing, and when the telephone goes off-hook, the exchange reverses the polarities of the A and B lines, and the A line ground and B line + 48V. Battery voltage is supplied. This causes a call current. At this time, the rectifier 12 is turned on, and the voltage of the subscriber telephone line becomes the overvoltage detection circuit 13,
It is input to the power supply circuit 17 via the low voltage detection circuit 14 and the switch circuit 15, and the power for operation is once supplied to the network control device 18 and the data terminal 19. However, in the case of a telephone call, the activation signal (2kHz) does not arrive within a certain time, so
The network controller 18 turns off the switch circuit 15. Therefore, the telephone call on the telephone is not affected. After the call is completed, the potential of the B line becomes negative, so that the rectifier 12 is turned off, the entire circuit is initialized, and the normal standby state is set.

At the time of data collection, the data terminal 19 is called with no ringing from the device (center device) that wants to collect the data. That is, in the exchange, the polarities of the A and B lines are inverted and the + 48V battery voltage is supplied to the B line without sending a 16 Hz ringing signal, and a specific start signal (2 kHz) is sent immediately thereafter. As a result, the telephone line is connected to the network control device 18.

When the + 48V battery voltage is supplied to the B line, the rectifier 12 is turned on and the supply voltage from the subscriber telephone line is supplied to the power supply circuit 17 via the overvoltage detection circuit 13, the low voltage detection circuit 14 and the switch circuit 15. Is entered. The power supply circuit 17 receives the above voltage and supplies power for operation to the network control device 18 and the data terminal 19. Further, when the activation signal is input from the exchange side, the network control device 18 receives the activation signal and sends the data from the data terminal 19 to the subscriber telephone line via the switch circuit 15.

Next, the case where the test voltage is applied to the subscriber telephone line will be described. In this case, when the polarity of the test voltage becomes positive on the B line, the rectifier 12 is turned on.
Supply to 17 must be avoided.

When the test voltage is the 200V system, the overvoltage detection circuit 13 detects a high voltage and turns off, and the circuits thereafter are cut off. The electric power required for the above operation of the overvoltage detection circuit 13 is extremely small, and the test result is not affected by the shunting of the test current to the overvoltage detection circuit 13. As the overvoltage detection circuit 13, for example, a semiconductor element including a voltage detection circuit and a switch that is cut off when the output of the voltage detection circuit exceeds a predetermined value is used.

When the test voltage is a low voltage system of 48 V or less, for example 36 V system,
The low voltage detection circuit 14 detects this and turns off the switch circuit 15. Therefore, even in this case, the test is not affected. As the low voltage detection circuit 14, for example,
A semiconductor element which has a built-in voltage detection circuit and outputs a control signal to the switch circuit 15 when the detected value is less than or equal to a predetermined value is used.

When the test voltage is 48V and the DC resistance inserted in the power supply on the exchange side is about 1 kΩ, power is supplied to the power supply circuit 17 by the test voltage, and the power supply circuit 17 uses the supplied power to control the network controller. Supply power for operation to 18. Therefore, the network control device 18 is in the operating state and is in the monitoring state of the activation signal. However, since the activation signal is not received, the switch circuit 15 is turned off after a certain period of time. When the switch circuit 15 is turned off, a normal test becomes possible.

When the test is completed, the line A is in the ground state and the line B is in the state of waiting for incoming call or call waiting in which -48V is applied. In this state, the rectifier 12 does not apply a voltage to the circuits after the rectifier, so that the power supply of the network control device 18 is turned off and the switch circuit is turned off.
15 is also initialized and turned on, and returns to the initial state of waiting for incoming calls or waiting for outgoing calls before reversing the polarity of the subscriber telephone line.

The above operation is equivalent to the conventional operation. The feature of this embodiment is that the test voltage is 48V system, and 10 kΩ on the exchange side.
Or it is in operation when high resistance such as 100kΩ is inserted. Such a test is performed with the subscriber telephone line open, and even if the open circuit voltage is 48 V, the current flowing through the load is small when the load is connected. For this reason, the input terminal overvoltage of the power supply circuit 17 is lowered, and the power for operating the network control circuit normally cannot be obtained, and the switch circuit 15 is off-controlled by the signal from the network control device 18 as it is. I can't. Therefore, this is detected by the high resistance value detection circuit 16, and the switch circuit 15
Turn off. Therefore, also in this case, it is possible to prevent the judgment of the line test or the like from being adversely affected. After the test is completed, the B line becomes a negative potential, and the circuits after the rectifier 12 are initialized.

〔The invention's effect〕

As described above, the present invention includes the overvoltage detection circuit, the low voltage detection circuit, and the high resistance value detection circuit, and the switch circuit that is off-controlled by the detection output of the low voltage detection circuit and the high resistance value detection circuit. When a test voltage with a high resistance inserted on the exchange side is input, this is detected by the high resistance value detection circuit and the switch circuit is turned off, so network control is performed even during the high resistance insertion test. There is an effect that it is possible to prevent a phenomenon in which the determination signal of the test cannot be determined by the device and the adverse effect on the determination result of the test by the test voltage occurs without turning off the switch circuit.

[Brief description of drawings]

The figure is a block diagram showing an embodiment of the present invention. 11 …… Input terminal, 12 …… Rectifier, 13 …… Overvoltage detection circuit, 14 …… Low voltage detection circuit, 15 …… Switch circuit, 16…
… High resistance value detection circuit, 17 …… Power supply circuit, 18 …… Network control device, 19 …… Data terminal.

Claims (1)

[Claims] 1. A network control device which is interposed between a subscriber telephone line and a data terminal device and which connects the data terminal device and the subscriber telephone line in response to a specific activation signal coming from the subscriber telephone line. A rectifier that is connected to the input and that passes only the voltage of the polarity that is used for calls on the subscriber telephone line, and a voltage that is connected to the output side of this rectifier and that is higher than the first voltage that is higher than the voltage used for calls is detected. At this time, an overvoltage detection circuit that cuts off the voltage of each circuit connected to the output terminal, and a low voltage detection circuit that detects that the output voltage of the rectifier is equal to or lower than a second voltage lower than the voltage used for communication. A switch circuit that is off-controlled by the detection output of the low-voltage detection circuit; and when the switch circuit is on, the power from the subscriber telephone line is made into a constant voltage so that the network control device and the data terminal device are provided. In the input circuit of the network control device having a power supply circuit for supplying power, a voltage drop occurs in the subscriber telephone line due to the current connected to the power supply circuit input terminal in parallel and supplied to the network control device and the data terminal device. The DC voltage between the input terminals of the power supply circuit is monitored, and the power supply circuit has a voltage drop caused by the sum of the high resistance value inserted in the subscriber telephone line and the resistance value of the subscriber telephone line during the high resistance insertion test. A high resistance value detection circuit is provided to turn off the switch circuit when the direct current voltage between the input terminals is a voltage that cannot supply the current required to operate the network control device and the data terminal device. Input circuit of the network control circuit.