JPH0318783B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a current supply circuit that supplies current to a two-wire DC communication line, and in particular, if only one of the wires of the communication line has a ground fault. First, it relates to a track monitoring method that can detect even when both wires are grounded.

(b) Prior art and problems Figure 1 is a diagram showing an example of a conventional track monitoring system. In FIG. 1, a multi-community telephone line is shown as an example of a two-wire DC communication line, and a plurality of communal telephones PT are connected in parallel to the communication line L and accommodated in a multi-community trunk PLT.
The multi-communal trunk PLT connects relay A and
A current is supplied to the other wire a of the communication line L via a current supply path consisting of one winding of each LS, and a communication current is supplied from a DC power supply having a negative potential of -48 volts with respect to the earth. A current is supplied to one wire b of the communication line L via a current supply path constituted by the windings of the other relay A for ground fault detection and relay LS for ground fault detection. When each public telephone PT is in a non-call state, the above-mentioned DC power supplies are applied in series between both wires a and b, and each communal telephone PT
By lighting a neon lamp NL provided at the terminal, it is indicated that the shared communication line L is free. When one of the public telephones PT raises its handset and a DC loop is formed, relay A is operated by the DC current flowing from both DC power sources through both current supply paths and wires a and b, A loop detection signal 1d is output through contact a1. Note that the relay LS does not operate because the magnetic fluxes generated by the direct current flowing through both windings cancel each other out. Line a of such communication line L
If a ground fault occurs in either of and b,
A DC current flows from the +50 volt or -48 volt DC power supply to the ground fault point via both of the current supply paths and either of the wires a and b, the relay LS operates, and the alarm signal a1 is output by the contact LS1. do.
However, if a ground fault occurs in both wires a and b, DC current will flow from both DC power supplies via both current supply paths and wires a and b, so relay LS will It does not operate in the same way as when the handset is raised, and the alarm signal a1 is not output.

As is clear from the above explanation, in the conventional track monitoring system, the lines a and b of the communication line L are
Although it is possible to detect a ground fault that occurs in either one of the lines, it is impossible to detect a ground fault that occurs in both lines a and b.

(c) Purpose of the Invention The purpose of the present invention is to eliminate the shortcomings of the conventional track monitoring system as described above, and to eliminate the problem of ground faults occurring not only in either one of the two wires of a communication line, but also in both wires. The object of the present invention is to realize a track monitoring system that can detect even when

(d) Structure of the Invention The object of the invention is to have a current supply path for supplying current from a DC power supply having a positive potential with respect to the earth on one line of a two-wire DC communication line, and a current supply path that supplies current from a DC power supply having a positive potential with respect to the earth, and a On the other hand, in a current supply circuit having a current supply path that supplies current from a DC power supply having a negative potential, a detection unit that detects a current of a predetermined value or more flowing through each of the wires is individually installed in each of the current supply paths. and a resistor is provided in series with the one detection section to limit the current flowing through the detection section to below a detection limit,
A switching element is provided in parallel with the resistor, and when both of the detection sections detect the current, the switching element is set to a blocking state, and when at least one detection section does not detect the current, the switching element is set to a blocking state. Switching element control means for setting the element to a conductive state is provided, and when both of the detection parts detect the current, and the switching element control means sets the switching element to a blocking state, only one of the detection parts detects the current. If the detection of the current is stopped, it is determined that a ground fault has occurred in both the wires, and if both the detection parts stop detecting the current, a DC loop is formed between the two wires. This is achieved by determining that the

(e) Embodiment of the invention An embodiment of the invention will be described below with reference to the drawings. FIG. 2 is a diagram showing a line monitoring system according to an embodiment of the present invention. Note that the same reference numerals indicate the same objects throughout the figures. Further, in FIG. 2, only the communication line L and the multiple communal trunk PLT are shown, and the communal telephone PT is omitted. In Fig. 2, the current supply circuit that supplies DC current from a DC power supply having a positive potential of +50 volts to the ground to the wire a of the communication line L is constituted by a detection unit FDa, and also has a positive potential of -48 volts to the ground. A current supply path for supplying direct current from a direct current power supply having a negative potential to the wire b of the communication line L is constituted by the detection unit FDb. Note that there is a relay between the detection part FDa and the filament a.
A resistor R is inserted in which the contact ls'1 of LS' is connected in parallel. The resistor R is short-circuited when the contact ls′1 is in the closed state, and the resistance R is short-circuited when the contact ls′1 is in the closed state, and the
Although it has no effect on the current flowing to FDb and FDb, if contact ls′1 is open, the detection
It has a resistance value that limits the current flowing through FDa or the detection parts FDa and FDb to below the detection limit of the detection parts FDa and FDb. If a ground fault occurs in wire a of communication line L, the detection unit will be connected to the +50 volt DC power supply.
A direct current flows to the ground fault point via FDa and wire a. The detection unit FDa detects the DC current and transmits a detection signal sa to the control unit CTL. Control unit CTL
receives only the detection signal sa, determines that a ground fault has occurred in the wire a, and outputs an alarm signal a1. Further, when a ground fault occurs in the wire b of the communication line L, a DC current flows from the -48 volt DC power source to the ground fault point via the detection unit FDb and the wire b. The detection unit FDb detects the DC current and outputs a detection signal.
sb is transmitted to the control unit CTL. By receiving only the detection signal sb, the control unit CTL determines that a ground fault has occurred in the wire b, and outputs an alarm signal a1. Furthermore, if both wires a and b of the communication line L have a ground fault, the detection unit will be
FDa and FDb control the detection signals sa and sb.
Communicate to CTL. When the control unit CTL receives both detection signals sa and sb, it drives relay LS′,
Contact ls'1 is opened. As a result, the DC current flowing through the detection unit FDa becomes below the detection limit of the detection unit FDa, and the transmission of the detection signal sa to the control unit CTL is stopped. However, the DC current flowing through the detection unit FDb does not change at all, and the detection signal sa continues to be transmitted. sb is transmitted to the control unit CTL. When only the detection signal sb is stopped by driving the relay LS', the control unit CTL determines that both the wires a and b have caused a ground fault, and outputs an alarm signal a1. At this time, the control unit CTL is a relay
LS' is held and the state of the detection signal sa is monitored. When the detection signal sa is restored, the relay LS' is restored and returned to its initial state. On the other hand, public telephone PT (1st
When either of the above (Figure) raises the transmitter and a DC loop is formed, DC current is supplied from both DC power sources via both current supply paths and wires a and b, and FDa and FDb are detected signals
The sa and sb are transmitted to the control unit CTL. control part
CTL drives relay LS′ in the same way as above, and contacts
Let ls′1 be in an open state. As a result, the DC currents flowing through the detection units FDa and FDb are both limited to below the detection limit, and the transmission of the detection signals sa and sb to the control unit CTL is stopped. Control unit CTL is a relay
When LS' is driven, both detection signals sa and sb are stopped, and it is determined that one of the communal telephones PT has lifted the handset, and a loop detection signal 1d is outputted, and relay LS' is restored.

As is clear from the above description, according to this embodiment, the detection units FDa and FDb are individually provided corresponding to the lines a and b of the communication line L, and the detection units FDa
By inserting a resistor R in series with the wires, it becomes possible to output the alarm signal a1 even if both wires a and b become a ground fault.

Note that FIG. 2 is only one embodiment of the present invention, and for example, the resistor R and the contact ls' are not limited to those inserted between the detection part FDa and the filament a; Although insertion between FDb and filament b is also considered, the effects of the present invention remain unchanged in such a case. Further, the configuration of the current supply path for both filaments a and b is not limited to that shown in the drawings, and many other modifications may be considered, but the effects of the present invention will not change in any case. Further, the object of the present invention is not limited to the multi-joint trunk PLT, and many other modifications may be considered, but the effects of the present invention remain the same in any case.

(f) Effects of the Invention As described above, according to the present invention, in the current supply circuit, it is possible to detect not only a ground fault in either one of the two wires of the communication line, but also when both wires have a ground fault. This improves the reliability of the communication line.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional track monitoring system, and FIG. 2 is a diagram showing a track monitoring system according to an embodiment of the present invention. In the figure, A, LS and LS' are relays, a and b are wires, a1, ls1 and ls'1 are contacts, and a
1 is the alarm signal, CTL is the control unit, D is the diode,
FDa and FDb are detection units, L is a communication line, 1d is a loop detection signal, NL is a neon lamp, PLT is a multiple common trunk, PT is a common telephone, R is a resistor,
sa and sb indicate detection signals.

Claims (1)

[Claims] 1 One wire of a two-wire DC communication line has a current supply path that supplies current from a DC power source with a positive potential with respect to the earth, and the other wire has a current supply path that supplies current from a DC power source with a negative potential with respect to the earth. In a current supply circuit having a current supply path for supplying a current, a detection section for detecting a current of a predetermined value or more flowing through each of the wires is individually provided in each of the current supply paths, and the detection section is connected in series to one of the detection sections. A resistor is provided to limit the current flowing through the detection section to below a detection limit, a switching element is provided in parallel with the resistance, and when both of the detection sections detect the current, the switching element is set to a blocking state. , a switching element control means is provided for setting the switching element to a conductive state when at least one of the detection parts does not detect the current, and both of the detection parts detect the current, and the switching element control means When the switching element is set to a blocking state, if only one detection unit stops detecting the current, it is determined that a ground fault has occurred in both the wires,
A track monitoring system characterized in that when both the detection units stop detecting the current, it is determined that a DC loop is formed between the two wires.