JPH07273855A - Subscriber line measuring method - Google Patents

Abstract

PURPOSE:To provide a subscriber communication line measuring method which prevents the measurement time from being longer without increasing a measuring circuit neither giving a high performance to the circuit. CONSTITUTION:When insulation resistances or capacities between two wires, namely, A and B wires of a two-wire metallic subscriber line and the ground and between the A wire and the B wire are obtained, the insulation resistance or the capacity between the A wire and the ground at the time of short- circuiting the B wire to the ground, that between the B wire and the ground at the time of short-circuiting the A wire to the ground, and that between the A wire or the B wire and the ground at the time of short-circuiting the A wire and the B wire are measured and are converted into target values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for testing a subscriber line in a communication system using a two-wire metallic subscriber line (hereinafter referred to as subscriber line) such as a telephone as a communication medium. It relates to a measuring method.

[0002]

2. Description of the Related Art A subscriber line test is conducted between two lines (hereinafter referred to as A
Line and B line), between the A line and ground, and between the B line and ground, the insulation resistance (hereinafter simply referred to as resistance) and the capacitance are determined. That is, as shown in FIG. 2, the subscriber line is represented by an equivalent circuit using a lumped constant, and its value (hereinafter referred to as line parameter) is obtained. Here, Rag, Rbg, and Rab in FIG.
The resistance between the line and the ground, the resistance between the B line and the ground, and the resistance between the A line and the B line are represented by Cag, Cbg, and Cab.
The capacitance between the A line and the ground, the capacitance between the B line and the ground, and the capacitance between the A line and the B line are shown respectively.

Further, in this equivalent circuit, the conductor resistances of the lines A and B are omitted. Here, for the measurement of resistance and capacitance, for example, a measurement circuit including a measurement power supply, a voltmeter, and an ammeter as shown in FIG. 3 is used. The resistance or capacitance value between the measured terminal and the ground can be obtained by connecting the measured circuit to the measured terminal and measuring the current and voltage. For example, the resistance value is obtained from the measured value in the steady state, and the capacitance value is obtained from the transient response value.

Next, a conventional method for obtaining the line parameters will be described by taking the case of resistance as an example. First, the following four types of measurement are performed. Measurement between line A and ground when line B is open (measurement value Rao), measurement between line B and ground when line A is open (measurement value Rbo),
Measurement between the A line and the ground when the B line is shorted to the ground (measured value Ras), and measurement between the B line and the ground when the A line is shorted to the ground (measured value Rbs). The relationship between the above measured values and line parameters is given by Eqs. (1) to (4) below, and line parameters can be obtained in reverse from this relationship. The description given here can be applied to the case of capacitance, and the line parameters can be obtained in the same manner.

[0005]

[Equation 1]

[0006]

FIG. 4 is a diagram for explaining the problems in the conventional method. Hereinafter, FIG. 4 will be described. The measurement circuit of FIG. 4 is a circuit for measuring the resistance or capacitance between the measured terminal and the ground shown in the example of FIG.
FIG. 4 shows the measurement between the A line and the ground when the B line is opened among the four types of measurement described in the conventional method. The challenge in this measurement is the line capacitance (eg Cab
Alternatively, it takes a long time for the circuit to reach a steady state due to the charge / discharge current due to Rbg) and the capacity of the terminal connected to the line), which leads to a long measurement time. For example,
As a typical value of the subscriber line of about 1 km, the line capacity C
If ab = 1 μF and insulation resistance Rbg = 1 MΩ, the charging / discharging time constant becomes as long as 1 second. It is clear that the same can be said for the measurement between the line B and the ground when the line A is open. The above-mentioned problem that the measurement time, that is, the test time of the subscriber line becomes long, cannot be ignored because it leads to deterioration of the subscriber service quality.

As a solution to the above problems, FIG.
The method shown in can be considered. Hereinafter, FIG. 5 will be described. The measuring circuit is the same as in FIG. Fig. 5 shows the measurement between line A and ground when line B is open, and A
Instead of the measurement between the line B and the ground when the line is open, the measurement between the line A and the ground and between the line B and the ground is simultaneously performed. If they are performed at the same time, the A line and the B line have the same potential, so that no current flows through Cab. Therefore, the above problem does not occur. Since the charging / discharging characteristics in this measurement are determined by Cag or Cbg and the internal impedance of the measuring power source in the measuring circuit, the charging / discharging time can be shortened sufficiently by lowering the internal impedance. The measured values Rac and Rbc according to FIG. 5 are given by equations (5) and (6).
Can be expressed as Therefore, instead of equations (1) and (2),
By using (5) and (6), it is possible to obtain the line parameters in reverse from the equations (3) to (6).

[Equation 2]

The method according to FIG. 5 can avoid the problem of lengthening the measuring time, but causes the following new problems. That is, two measurement circuits are required for simultaneous measurement, and high performance of the measurement circuit itself is required in order to make the voltage of the A line and the B line the same regardless of the load imbalance between the two. is there. An object of the present invention is to provide a measuring method that can avoid a long measuring time without increasing the number of measuring circuits or improving the performance.

[0009]

In order to solve the above-mentioned problems, according to the present invention, between the A line of the subscriber line and the ground, and the B line.
A when the B line is shorted to the ground when obtaining the insulation resistance or capacitance between the line and the ground and between the A line and the B line
Insulation resistance or capacitance between line and ground, insulation resistance or capacitance between B line and ground when A line is shorted to ground, and A line or B line and ground when A line and B line are shorted It is characterized by measuring the insulation resistance or capacitance between them.

[0010]

According to the method of the present invention, it is possible to prevent the measurement time from becoming long in the measurement having a large charge / discharge time, and to realize it by shorting the equipotentials of the A line and the B line. Therefore, multiple measurement circuits and higher performance can be avoided.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining one embodiment of the present invention. Hereinafter, FIG. 1 will be described. As the measuring circuit in the figure, the same circuit as the conventional measuring circuit for measuring the resistance or capacitance between the terminal to be measured and the ground shown in FIG. 3 can be used. In FIG. 1, line A and line B are short-circuited and connected to the measurement circuit. That is, in this measurement, the A line and the B line have the same potential, so that the measurement current does not flow in the resistance and the capacitance between the A line and the B line, which can be ignored.
This means that the combined resistance Rp or combined capacitance Cp between the line and the ground is being measured. Therefore, the measuring current having a large charging / discharging time constant as described with reference to FIG. 4 of the conventional embodiment does not flow, and the lengthening of the measuring time can be avoided.

This principle is the same as the method of FIG. 5 described in the conventional embodiment, but in the present invention and the method of FIG.
The difference is that the lines are short-circuited and the potentials of the lines A and B are made the same. That is, in the present invention, therefore, only one measuring circuit is required, and the potentials of the A and B lines can be made to be the same regardless of the load unbalance, so that there is no need to improve the performance of the measuring circuit. As described above, according to the present invention, the new problem caused by the method of FIG. 5 can be avoided. The measured value Rp by this method can be expressed as in equation (7). If the line parameters are obtained from Equation (3), Equation (4), and Equation (7) in reverse, Equations (8) to (10) are obtained.

[0013]

[Equation 3]

Similarly, with respect to the capacity, equations (11) to (13) to equations (14) to (16) are obtained.

[Equation 4] Here, Cas, Cbs, and Cp are the measured values of the capacitance between the A line and the ground when the B line is shorted to the ground, respectively.
It is the measured value of the capacitance between the B line and the ground when the A line is shorted to the ground, and the measured value of the capacitance between the A line or the B line and the ground when the A line and the B line are shorted.

[0015]

As described above, according to the present invention,
A line when the B line is shorted to the ground when obtaining the insulation resistance or the capacitance between the A line and the ground, between the B line and the ground, and between the A line and the B line of the two-wire metallic subscriber line. Insulation resistance or capacitance between the A and B lines, the insulation resistance or capacitance between the B line and the ground when the A line is shorted to the ground, and the A line or the B line and the ground when the A line and the B line are shorted Since it is obtained by measuring the insulation resistance or capacitance of the above, it is possible to avoid the measurement time from becoming long in the measurement with a large charge / discharge time, and by shorting the A line and the B line, Since the same electric potential is realized, it is possible to obtain an advantage that a plurality of measurement circuits and higher performance can be avoided.

[Brief description of drawings]

FIG. 1 is a diagram showing a measuring method according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit in which a two-wire metallic subscriber line is represented by a lumped constant.

FIG. 3 is a diagram showing an example of a measuring circuit used in the conventional example and the present example.

FIG. 4 is a diagram for explaining a problem in the conventional example.

FIG. 5 is an explanatory diagram of an embodiment that solves the problems of the conventional embodiments but creates new problems.

[Explanation of symbols]

 Insulation resistance between Rag A line and ground Rbg Insulation resistance between B line and ground Rab Insulation resistance between A line and B line Cag Capacitance between A line and ground Cbg Capacitance between B line and ground Cab A line and B line Capacity between

Claims (1)

[Claims] 1. A B line when determining the insulation resistance or capacitance between two lines of a two-line metallic subscriber line (hereinafter referred to as A line and B line) and ground and between A line and B line. Insulation resistance or capacitance between line A and ground when A is shorted to ground, insulation resistance or capacitance between line B and ground when A line is shorted to ground, and line A and B are shorted A method of measuring a subscriber line, which comprises measuring an insulation resistance or a capacitance between the A line or B line and the ground at the time.