JPH0654886B2 - Line characteristics measurement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a line to which a device having an arbitrary input impedance is connected, the line being connected to the device without being affected by the device. The present invention relates to a line characteristic measuring method for accurately measuring the characteristics of the.

[Conventional technology]

For example, in order to detect faults in telephone lines, line insulation resistance, capacitance, etc. have been conventionally measured, but these measurements can be performed by direct current measurement because the measurement circuit configuration is simple. Has been done. FIG. 7 shows an equivalent circuit when a device having an arbitrary DC input impedance is connected to the line. The device 12 having the input resistance R _i is connected between one ends of the pair of lines 11, and the DC power supply 13 is connected between the other ends. The insulation resistance R _x between the pair of lines 11 (hereinafter simply referred to as line insulation resistance R _x ) is connected in parallel with the input resistance R _i . When measuring the insulation resistance R _x of the line 11 from the terminals 14 and 15 of the DC power supply 13, the measurement result is affected by the input resistance R _i of the device, and the resistance value R _x · R of the parallel connection of R _x and R _i is _i / (R _x + R _i ). Therefore line 1
The error from the insulation resistance R _{x of} 1 is −R _x ² / (R _x +
R _i ), and when the input resistance R _i of the device 12 decreases, the error increases and there is a problem that accurate measurement cannot be performed.

[Means for solving problems]

The present invention, when measuring the line characteristics, the device having the arbitrary input impedance is mechanically connected to the line, but is configured to be electrically disconnected from the line,
This enables accurate line characteristic measurement.

In the present invention, will be conducting in the voltage V _o is applied to the line in normal use, the circuit for blocking a lower than the predetermined voltage V _M than V _o, devices having any of the input impedance and a pair of lines Insert it between each and
At the time of measuring the line characteristic, the line characteristic is measured by applying a voltage equal to or lower than the predetermined voltage V _M to the line.

〔Example〕

FIG. 1 is a diagram for explaining the principle of the present invention, in which parts corresponding to those in FIG. 7 are designated by the same reference numerals. Between the device 12 having an arbitrary input impedance R _i and the line 11, a circuit 16 in which the resistance R _z changes according to the applied voltage V _i at the end of the pair of lines 11 on the device 12 side is inserted. This resistance R
The ideal characteristic of the circuit 16 in which _z changes is shown in FIG. Normally the voltage V _o is applied to the line 11, but power the device 12 is performed, the resistance R _z of the circuit 16 whose resistance varies this time O (Omega), i.e. a conductive state, the power feeding action It has no effect. In general the applied voltage V _o
In the case of a telephone line, the voltage of the opposite polarity is used for an incoming call signal or the like, but in this case as well, the resistance R _{z of the} circuit 16 is O (Ω), and therefore has no effect.

Now, when a voltage V _M smaller than the voltage V _o is applied to the line 11, the resistance R _{z of the} circuit 16 is ∞ (Ω), that is, a cutoff state. Therefore, from terminals 14 and 15,
The input impedance R _i of the device 12 is no longer observed, and the insulation resistance R _x of the line 11 can be measured accurately.

FIG. 3 is one of the concrete implementation examples of the circuit 16, and is an example in which the circuit 16 in which the resistance R _z is changed by the applied voltage V _i is configured by the Zener diode Z _D. Here, it is assumed that a voltage having a positive polarity is normally applied to the terminal 14 and a voltage having a negative polarity is applied to the terminal 15, and the cathode of the Zener diode Z _D is on the terminal 14 side. By setting the Zener voltage of the Zener diode Z _D into the V _M, practical characteristics shown in Figure 2 can be realized.

FIG. 4 shows another implementation example of the circuit 16. As the circuit 16, a diode 17 and an enhancement type FET 18 are used.
Is connected in series with the line 11, and a shunt is connected to the line 11 via a Zener diode 19 and a resistor 20 at the line side connection point.
The connection point of 9 and the resistor 20 is connected to the gate of the FET 18. Normally a Zener voltage higher than the voltage _{V o} of the Zener diode 19 is applied between terminals 14 and 15, the Zener diode 19 is rendered conductive, the conduction current flows through the resistor 20, the voltage drop across the resistor 20 is FET18 Applied to the gate, which causes the FET 18
Turns on. However, when measuring line characteristics, terminal 1
A measurement voltage equal to or lower than the Zener voltage of the Zener diode 19 is applied between 4 and 15, the Zener diode 19 becomes non-conductive, no current flows through the resistor 20, and the gate and the source of the FET 18 have the same potential. Is in the off state because it is an enhancement type and the device 1
The two sides are electrically separated.

In this example, the Zener diode 1 is different from the configuration shown in FIG.
9 has a feature that a small capacity can be applied.

5 and 6 show embodiments of the present invention.
A circuit 16 is inserted between each of the pair of lines 11 and the device 12 to form a balanced type. 5 and 6 are respectively shown between both ends of the device 12 and the line 11, FIG.
The circuit 16 shown in FIG. 4 is inserted, and the ground impedances of the pair of lines 11 become equal to each other, so that it is possible to secure an unbalanced ground attenuation amount. In FIG. 6, FETs 18 and 18 '
Has the opposite conductivity type and is turned on or off at the same time.

〔The invention's effect〕

As described above, according to the present invention, the line characteristic measurement is performed at the voltage V _{M which is} lower than the normal applied voltage V _o , so that the device having an arbitrary input impedance can be electrically connected while being mechanically connected. Since it can be disconnected from the line, there is an advantage that the line characteristics can be accurately measured. Moreover, since it is of the balanced type, it is possible to secure the amount of attenuation to the ground, and it is applied to a wideband digital signal transmission system and does not affect the waveform transmission of the digital signal.

Although the measurement of the communication line has been described here as an example, the present invention is naturally applicable to the characteristic measurement of the power line and other various lines.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the principle of the present invention, FIG. 2 is a diagram showing ideal characteristics of a circuit 16 in which a resistance R _z is changed by an applied voltage V _i, and FIG. 3 is a realization of the circuit 16 in FIG. FIG. 4 is a circuit diagram showing one example, FIG. 4 is a circuit diagram showing another implementation example of the circuit 16 in FIG. 1, and FIG. 5 is a diagram showing an example in which the embodiment of FIG. FIG. 6 is a diagram showing an example in which the embodiment of FIG. 4 is made into a balanced form, and FIG. 7 is an equivalent circuit diagram when a device having an arbitrary DC input impedance is connected to a line. 11: line, 12: device having arbitrary input impedance R _i , 13: direct current power supply, 16: circuit in which resistance R _z changes according to applied voltage V _i .

Claims (1)

[Claims] 1. A device having an arbitrary input impedance is connected between one ends of a pair of lines, a DC power source is connected between the other ends of the pair of lines, and a normal power source is connected between the DC power source and the pair of lines. in the transmission system voltage V _o is applied, the pair of lines, between the device having the arbitrary input impedance, conducting the normal applied voltage V _o from each said DC power source, the applied A circuit for cutting off at a predetermined voltage V _M or less smaller than the voltage V _o is inserted, and a line characteristic measurement is performed by applying a voltage of the voltage V _M or less between the pair of lines when measuring the line characteristic. Measuring method for line characteristics.