JPS6331054B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a subscriber line resistance measuring device which is important for detecting disconnections in subscriber lines or poor line insulation of telephone exchanges, and for maintaining normal operation of telephone exchanges and calls. Regarding.

A conventional subscriber line resistance measurement method will be explained with reference to a relay system diagram shown in FIG. 1 and a circuit diagram shown in FIG. 2. SUB is the subscriber, LR is the subscriber line (including line resistance), NW is the exchange network,
LTT is the line test trunk, and M is the current meter. A contact t of a relay whose winding of LTT is not shown is operating during line measurement. In operation, by applying -48V to the line and measuring the flowing current, the resistance value written on M's meter MA was read and the line resistance was directly read.

However, the power supply used for measurement is -
Since the voltage is 48V, there are large voltage fluctuations, making it difficult to measure with high precision.Also, since the meter needs to be read by a human, it is difficult to automate this measurement. Furthermore, the subscriber telephone SUB includes ordinary dial telephones, push-button dial (PB) telephones, and even special telephones, especially those that incorporate a rectifier or the like inside the telephone, or those that incorporate a transistor such as a tone ringer. There is something. In such cases, it is currently impossible to accurately measure line resistance (including subscriber telephones) due to the nonlinearity of these semiconductors, that is, the forward voltage drop. Additionally, there are special types of subscriber telephones that may malfunction if -48V is suddenly applied to them. Therefore, it was necessary to lower the measurement voltage for resistance measurement. However, when the measurement voltage is lowered, the error in the measurement value increases due to the nonlinearity of telephones and the like. For example, in the case of a PB telephone, as is already known, there is a rectifier bridge circuit inside the telephone as shown in Figure 3, and the current passing through the telephone passes through two rectifiers. In this case, the maximum forward voltage drop of the rectifier is about 1 to 2 V, and when measured at -48 V, the measurement error is 1 to 2/48, and the measurement error is small, but when the measurement voltage is set to about -5 V, it is 1 to 2 V. ~2/5, and the error is so large that measurement is almost impossible.

As described above, conventional measurement methods have problems with measurement accuracy because they use relatively high and inaccurate voltages, and they also have drawbacks such as difficulty in automating measurements. .

The purpose of the present invention is to eliminate the drawbacks of the conventional method shown above, to enable resistance measurement at a low measurement voltage,
Moreover, it is an object of the present invention to provide a subscriber line resistance measuring device that automates measurement and enables digital measurement.

A subscriber resistance measuring device of the present invention includes: a constant current source connected to one terminal of a subscriber line and having a plurality of output current values; and a detector connected to the terminal and detecting the polarity of voltage on the subscriber line. a full-wave rectifier connected to the terminal, an analog-to-digital conversion circuit connected to the output of the rectifier, and a constant current having a first current value _I1 applied from the constant current source to the subscriber line. The voltage value V ₁ of the subscriber line at the time of levering is determined by the full-wave rectifier and the analog
The data is read through a digital conversion circuit, the polarity is determined by the detection circuit, and a constant current of a second current value I ₂ is applied from the constant current source to the subscriber line to determine the current current of the subscriber line. voltage value
V ₂ is read through the full-wave rectifier and the analog-to-digital conversion circuit, and the polarity is determined by the detection circuit. If the voltage polarity during the two measurements is the same, the difference between the two measured voltage values and the Calculate the ratio between the difference between the two current values, and if the voltage polarities during the two measurements are different, calculate the ratio between the sum of the absolute values of the two measured voltage values and the difference between the two current values. and a control circuit that calculates the resistance of the subscriber line and measures the resistance of the subscriber line.

Next, the present invention will be explained with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention, and to simplify the diagram, NW, LTT in FIG.
is omitted and line testing equipment LTE is connected in place of M. SUB is the subscriber telephone, LR/
2 is a 1/2 value of the subscriber line resistance, A is a constant current source whose constant current can be switched according to instructions from the control device, B is a high input impedance input device, C is a full wave rectifier,
D is an analog-to-digital conversion circuit, E is a control device, and R ₁ is an internal impedance of a constant current source. Note that the relay method for measurement will be explained using the conventional relay method shown in FIG. In the present invention, a negative current source will be described as a constant current source, but this may be a positive current and the current polarity does not limit the present invention.

Under instructions from the control device E, the constant current source A causes a constant current I ₁ to flow through the subscriber line and the subscriber telephone SUB. The voltage V ₁ applied to the line and the internal resistance of the telephone SUB is the constant current I ₁ multiplied by the sum of the line resistance L _R and the telephone internal resistance. It is converted into a positive voltage and input to the analog-to-digital converter D. Note that the high input impedance input device A is intended to minimize the influence on the line. The input voltage is converted into digital information by an analog-to-digital converter D and input to the control device E. The control device E uses, for example, a microcomputer, and calculates the resistance of the subscriber line by calculating the resistance according to the ohmic side of resistance (R)=voltage (V)/current (I). In this example, the line resistance R _L can be determined by calculating line resistance (R _L )=measured voltage (V ₁ )/default constant current (I ₁ ).

In the above example, there is no non-linear element in the subscriber line, and the line resistance value can be simply determined. However, if the subscriber telephone SUB is a PB telephone as shown in Figure 3, the current and Since the circuit uses semiconductor elements whose voltage relationship is not linear, it is not possible to simply determine the line resistance R _L.
The relationship between line current and line voltage in such a case is shown in FIG. Here, V _F is a voltage applied to a nonlinear element such as a semiconductor element. Strictly speaking, V _F
varies depending on the line current, but is ignored here. It will be explained below that the line resistance R _L can be determined from FIG. 5. Let the current flowing through the subscriber line be I ₁
I ₂ and the voltages at that time are V ₁ and V ₂ , the line resistance R _L under each condition is according to Ohm's law R _L = V ₁ − _{V F} /I ₁ ... R _L = V ₂ − V _F /I ₂ ... is required. However, the line resistance R _L to be determined must be equal to the equation. Therefore, when calculating V _F here, it becomes V _F = I ₂ V ₁ − I ₁ V ₂ /I ₂ − I ₁ . Substituting this V _F into the equation gives R _L = V ₂ - V ₁ / I ₂ - I ₁ ..., and the line resistance R _L to be sought can be found. Fifth
In the figure, the value of the current I ₂ is set to twice that of I ₁ , and the line resistance R _L is R _L =V ₂ −V ₁ /I ₁ . . . .

As explained above, the constant current source according to the present invention allows the current to flow to the subscriber line by switching between I ₁ and I ₂ , converts the voltages V ₁ and V ₂ at that time into analog-to-digital, and calculates the equation using the control device. It is understood that the desired line resistance R _L can be found.

Note that in the above formula, I ₂ is set to twice I ₁ to simplify the calculation, and this does not particularly limit the present invention.

Next, measurement when there is a ground potential difference, which is another feature of the present invention, will be described. Measurement of subscriber line is not only carried out when the subscriber line is normal, but also when the subscriber line is cut off due to an accident and the part is in contact with the ground, and the ground air has earth potential. be. Figure 6 shows a model of such a case, and Figure 6a shows that the earth potential is negative (-).
In this case, FIG. 6b is positive (+).

Now, to explain the case in Figure 6a, if the external ground potential is negative, it acts in the direction of reducing the constant current from the constant current source (as mentioned above, the constant current source is assumed to be negative). This only strengthens the effect of this constant current source (which is provided by the constant current source), and the polarity of the line voltage does not change even if the constant current is switched. However, in the case shown in FIG. 6b, a problem occurs because the external ground potential is positive.

This case will be explained using a specific numerical example with reference to FIG.

Figure 7 shows an example where the earth potential is +3V, the line resistance is 2KΩ, and the currents from the constant current source are 2mA and 1mA. In the analog-to-digital conversion circuit in the case of FIG. 7a, 1V is input. In addition, in the case of Fig. 7b, the polarity is the same as Fig. 7a in the full-wave rectifier circuit, and the voltage is 1V.
shows. When the control device E calculates the line resistance value R _L using the formula, it shows 0Ω. Here, the function of the voltage polarity detection circuit F shown in FIG. 4 is important. In other words, the control device E is the polarity detection circuit F.
If the polarity of _the input voltage is positive by inputting _the polarity of _{the input} voltage from Good things are understood. In some cases, the polarity of both V ₁ and V ₂ may be positive; in this case, it is understood that the difference between V ₁ and V ₂ should be taken.

In this way, by measuring the subscriber line voltage twice with a constant current and calculating the results to find the resistance, it is possible to measure the resistance with high accuracy that can ignore the nonlinearity of the subscriber line and the ground potential difference. It becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a relay system diagram for measuring subscriber line resistance in the conventional method and in accordance with the present invention, FIG. 2 is a circuit diagram showing the conventional measuring method in more detail, and FIG. A circuit diagram showing an example of a PB telephone,
FIG. 4 is a block diagram showing one embodiment of the present invention;
Figure 5 is a diagram showing an example of the relationship between line current and line voltage when there is a forward voltage drop V _F of a non-linear element such as a semiconductor on the line, and Figures 6a and b are diagrams when there is a ground potential difference. Figures 7a and 7b are diagrams showing specific sequences in the case of Figures 6a and b. SUB...Subscriber telephone, LR...Subscriber line and its resistance, NW...Switch network,
LTT...Line test trunk, M...Current measuring meter,
LTE...Line testing equipment, AM...Ammeter, A...
Constant current source, B... High impedance input device, C...
...Full wave rectifier circuit, D...Analog-digital converter, E...Control circuit, F...Input voltage polarity detection circuit.

Claims (1)

[Scope of Claims] 1. A constant current source connected to one terminal of a subscriber line and having a plurality of output current values; A detection circuit connected to the terminal and detecting the polarity of voltage on the subscriber line; a full-wave rectifier connected to the terminal; an analog-to-digital conversion circuit connected to the output of the rectifier; and a constant current of a first current value _I1 from the constant current source applied to the subscriber line. The voltage value V ₁ of the subscriber line is converted to the full-wave rectifier and the analog
The data is read through a digital conversion circuit, the polarity is determined by the detection circuit, and a constant current of a second current value I ₂ is applied from the constant current source to the subscriber line to determine the current current of the subscriber line. voltage value
V ₂ is read through the full-wave rectifier and the analog-to-digital conversion circuit, and the polarity is determined by the detection circuit. If the voltage polarity at the time of the two measurements is the same, the difference between the two measured voltage values and the Calculate the ratio between the difference between the two current values, and if the voltage polarities during the two measurements are different, calculate the ratio between the sum of the absolute values of the two measured voltage values and the difference between the two current values. A subscriber line resistance measuring device comprising: a control circuit that calculates the resistance of the subscriber line and measures the resistance of the subscriber line.