JP3100701B2 - Cable disconnection detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a disconnection of a subscriber telephone line at a telephone exchange.

[0002]

2. Description of the Related Art Hitherto, a test device attached to a telephone exchange has been used to perform tests on a subscribed telephone line such as insulation deterioration, short circuit, and crosstalk.

[0003]

In this case, these tests need to be performed on a daily basis as maintenance. In addition, in order to perform the tests without the trouble of the subscriber, it is necessary to perform the tests when the line is not used. As described above, since the test can be performed only when the terminal is open, that is, when the DC loop is open, the disconnection and the normal line non-use state cannot be determined. For this reason, the disconnection is detected when the subscriber uses the telephone, and it has been desired that the disconnection be detected in advance by the telephone exchange in order to maintain the line.

An object of the present invention is to provide a cable disconnection detecting method which can detect a disconnection failure of a telephone line from a telephone exchange side without troublesome subscribers.

[0005]

That is, the present invention measures and stores the capacitance of a cable under test in a normal state, and then measures the capacitance of the cable under test when a cable disconnection is detected. In a cable disconnection detection method for detecting a disconnection of a cable by comparing with a capacitance at the time, a reference capacitor, a DC power supply, and a voltage measurement circuit are provided, and the cable under test and the reference capacitor are charged by the DC power supply. After, after charging, disconnect the DC power supply , connect the cable under test and the reference capacitor with opposite polarities,
A cable disconnection detection method is to measure a voltage after charge cancellation due to the connection of the opposite polarity by the voltage measurement circuit, and to obtain a capacitance of the cable under test from the measured voltage.

[0006]

In the cable disconnection detecting method configured as described above, first, when detecting an insulation failure of a telephone line, a DC power supply is connected via a series resistor to a circuit in which a cable under test and a reference capacitor are connected in parallel. In the state where
Measure the voltage across the reference capacitor. In this case, if the insulation of the cable under test is reduced, the reference capacitor is charged by the voltage obtained by dividing the power supply voltage by the series resistance and the fault resistance of the insulation reduction. The voltage becomes lower than the power supply voltage, and the insulation failure of the cable under test can be detected.

Next, when the disconnection of the telephone line is detected, in a state where each of the cable under test and the reference capacitor is charged with a DC power supply, the combined capacitor of the cable under test and the reference capacitor is reversely connected. Voltage V
e, that is, the difference voltage Ve, the power supply voltage V, and the capacitance C of the reference capacitor when the charges of both capacitors are canceled.
The capacitance CX of the cable under test is calculated from R and Ask for. In this case, the capacitance CX of the cable under test in a normal state without disconnection is determined in advance, and the capacitance CX of the cable under test when measured later is the capacitance CX in the normal state measured earlier. If it is smaller, it can be determined that the wire is broken.

[0008]

As a result, the present invention has an effect that a telephone line disconnection fault can be easily found from the telephone exchange side without troublesome subscribers.

[0009]

Next, the structure of an embodiment of the present invention will be described with reference to the drawings. The DC power supply B has resistors R1 and R2 at both ends.
And the cables under test L1 and L2 of the telephone line are connected via the switches SW1 and SW2.
A reference capacitor CR is connected between both ends via switches SW3 and SW4, and the reference capacitor CR is reversely connected via switches SW5 and SW6 between both ends of a series circuit of the DC power source B and the resistors R1 and R2. The reference capacitor CR is connected at both ends to a voltage measuring circuit (not shown) through switches SW7 and SW8.

Next, the operation of this embodiment will be described.
In the cable disconnection detection circuit thus configured,
First, prior to measuring the capacitance, the cables under test L1,
Switches SW1, SW2, SW3 for performing insulation test of L2
, SW4 as shown in FIG. 1, a charging current flows from the DC power supply B to the reference capacitor CR for measurement and the cables under test L1, L2 via the resistors R1, R2. After the charging is completed, the switches SW1, SW2, SW3, S
W4 is opened, switches SW7 and SW8 are closed, and the voltage across the reference capacitor CR is measured. Here, if the insulation state of the cables under test L1 and L2 is good, the voltage between the cables under test L1 and L2 and between both ends of the reference capacitor CR becomes equal to the voltage V of the DC power supply B. If the insulation is reduced, a DC current flows through a closed circuit formed by the DC power source B, the resistors R1 and R2, and the fault resistor RX between the cables under test L1 and L2. R1
, R2 appears across the reference capacitor CR.

As a result, the fault resistance RX between the cables under test L1 and L2, that is, the insulation resistance RX of the cables under test L1 and L2, is expressed assuming that the voltage across the reference capacitor CR is Ve and the voltage of the DC power supply B is V. , Given by: If the insulation resistance RX is equal to or less than the reference value, it is determined that the insulation is defective, an alarm or the like is taken, and the next disconnection test is stopped at the same time. The energization / measurement shown in FIGS. 1 and 2 can be performed in an inverted state as shown in FIGS.

Next, when the disconnection of the telephone line is detected, as shown in FIG. 5, the switches SW1, SW2, SW5, S5
Only W6 is closed to charge the reference capacitor CR for measurement and the cables under test L1 and L2.
As shown in FIG. 6, the switches SW1, SW2, SW5,
When the switch SW6 is opened and only the switches SW3 and SW4 are closed, the reference capacitor CR and the cables under test L1 and L2 are connected. However, since the charging voltage has the opposite polarity, only the difference between the charges remains. That is, the capacitance of the reference capacitor CR is CR, the capacitance of the cables under test L1, L2 is Cx,
Assuming that the voltage of the DC power supply B is V, the charge stored in the reference capacitor CR is QR, and the charge stored in the cables under test L1 and L2 is Qx, Qx is given by the following equation. Qx = CxV QR = CRV Here, as shown in FIG. 6, when the reference capacitor CR and the cables under test L1 and L2 are connected in opposite polarities, the respective charges are canceled and the difference remains. On the other hand, since the capacity of the combined capacitor is the sum of CR and Cx, the finally combined voltage Ve across the capacitor is given by the following equation. Accordingly, the capacitance Cx of the cables under test L1 and L2 is as follows. In this case, if the cables under test L1 and L2 are disconnected, the capacitances CX of the cables under test L1 and L2 decrease.
2 is stored in a storage device, such as a flexible disk, using a personal computer or the like, and the newly obtained capacitance CX is stored during the test. If the newly obtained capacitance CX is smaller than the stored normal capacitance CX, it can be determined that the wire is disconnected. Note that a personal computer can be used for the arithmetic circuit. In this case, a large-capacity data can be stored by using a flexible disk device for the storage device. A voltmeter provided with an interface for measuring instruments such as an analog / digital conversion board and GP-IB which can be built in the ASIC can be used.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a cable disconnection detection circuit during energization at the time of detection of insulation failure.

FIG. 2 is a circuit diagram of a cable disconnection detection circuit during measurement at the time of detection of insulation failure.

FIG. 3 is a circuit diagram of a cable disconnection detection circuit at the time of reversal energization at the time of detection of insulation failure.

FIG. 4 is a circuit diagram of a cable disconnection detection circuit at the time of measurement at the time of detection of insulation failure.

FIG. 5 is a circuit diagram of a cable disconnection detection circuit during charging at the time of disconnection detection.

FIG. 6 is a circuit diagram of a cable disconnection detection circuit at the time of a short circuit at the time of disconnection detection.

FIG. 7 is a circuit diagram of a cable disconnection detection circuit during measurement at the time of disconnection detection.

FIG. 8 is a circuit diagram of a cable disconnection detection circuit before disconnection detection.

[Explanation of symbols]

 B DC power supply R1 resistance R2 resistance CR reference capacitor SW1 to SW8 switch

Claims (1)

(57) [Claims] After measuring and storing the capacitance of the cable under test in a normal state, the capacitance of the cable under test is measured when a cable disconnection is detected, and is compared with the capacitance in a normal state. in cable break detection method for detecting the disconnection of the cable, and a reference capacitor DC power supply and a voltage measuring circuit is provided, after the said cable under test and the reference capacitor has been charged by the DC power source, the DC after charging
The power supply is disconnected and the cable under test and the reference capacitor are connected in opposite polarities, and the voltage after charge cancellation by the connection of the reverse polarity is measured by the voltage measurement circuit, and the capacitance of the cable under test is measured from the measured voltage. Cable disconnection detection method, wherein