JP2806593B2 - Fault detection method for communication lines - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a communication line fault detection system.

[Prior Art] A conventional fault detection method for a communication line of this kind is described in the second section.
This will be described with reference to the drawings.

In FIG. 2, a conventional fault detection system for a communication line uses communication devices 1 to n + 1, Na connected in cascade through the communication line.
And a power supply station 10 for supplying DC power to the communication devices 1 to n + 1 and Na.

When the switching circuit 11 of the power supply station 10 is on the a side, the communication devices 1, 2,..., N, n + 1, N connected in cascade from the DC constant current power supply 12
Power is supplied to a (an integer of n1), and each communication device receives a constant voltage by the Zener diode 22 and uses it as a power source for each communication device.

The power supply current from the DC constant current power supply 12 is looped back by the communication device Na at the final point to form a loop returning to the DC constant current power supply 12.

Now, if the point A between the communication devices n and n + 1 is disconnected, the power supply is stopped and the communication is interrupted. Therefore, in order to search for the line disconnection point A, the switching circuit 11 of the power supply station 10 is set to the b side, a current for fault point detection is passed from the DC constant voltage power supply 14, and the current is measured by the ammeter 13. At this time, the polarity of the DC constant voltage power supply 14 is opposite to the polarity of the DC constant current power supply 12 for power supply.

The fault point current for exploration flows respective resistors 24, diodes 23 in the communication device 1~n up before the cutting point A, the respective currents I _1, I _2, ..., When I _n, resistor The resistance value R [Ω] of 24 is the resistance value r of the DC resistance 21 of the communication line.
Since the value is much larger than [Ω], if the voltage value of the DC constant voltage power supply 14 is V [v], Holds. Therefore, the current measured by the ammeter 13 is I
[A], So that It can be known that the line between the nth and (n + 1) th communication devices has been disconnected.

[Problems to be solved by the invention]

In the conventional communication line fault detection method described above, in the communication device Na at the final point where the supply current is turned back as shown in FIG. 2, the diode resistance is similar to that of many communication devices 1, 2,..., N + 1. Since the connection is not established, if the line is not disconnected, a large amount of current flows only into the communication device Na, and the DC constant voltage power supply 14 is in an overcurrent state, and measurement is impossible. That is, in the conventional communication line fault detection method, it is unknown whether or not the line is disconnected. However, if a communication failure occurs for any reason, for example, if the line is disconnected, it is not possible to determine the disconnection by the above method. Although possible, it has the drawback that if it is not disconnected, it cannot be checked whether the communication line is short-circuited.

[Means for solving the problem]

The fault detection system for a communication line according to the present invention is a fault detection system for a communication line in a communication system in which a cascade-connected communication device supplies DC constant current via a communication line. A value that is sufficiently larger than the first element that passes only the current, the second element that passes only the fault detection current having a polarity opposite to the connection direction of the first element, and the series resistance of the communication line. It has a parallel circuit for connecting a resistor in series with a circuit for connecting a certain resistor in series.

〔Example〕

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

 FIG. 1 is a block diagram showing an embodiment of the present invention.

In FIG. 1, the present embodiment has the same components as those of the conventional example shown in FIG. Communication device N is diode 30
And a series circuit of a resistor 24 and a diode 24 connected in series with the opposite polarity to the diode 30 and connected in parallel to the Zener diode 22.

When the switching circuit 11 of the power supply station 10 is set to the a side, power is supplied from the DC constant current power supply 12 to the cascade-connected communication devices 1 to n + 1 and N.
A constant voltage is received by the Zener diode 22 and used as a power source in each communication device. When the power supply current is turned back by the communication device N, a loop is formed in which the power supply current passes through the diode 30 and returns to the DC constant current power supply 12.

 Next, the operation of the present embodiment will be described.

When a failure occurs in the communication line for some reason, the switching circuit 11 of the power supply station 10 is set to the b side, and a failure detection current flowing from the DC constant voltage power supply 14 is measured by the ammeter 13. If the cause of the communication line failure is the line disconnection, the disconnection section can be obtained as described in the background art. If the communication line is not disconnected, the fault detecting current flows normally through the resistors 24 and the diodes 23 of the communication devices 1 to n + 1 and N, and the normal connection of the line can be confirmed in the same manner. If the fault detection current value is much larger than the normal value, it is possible to know that there is a short circuit in the communication line.

〔The invention's effect〕

As described above, the present invention provides a device that passes only a DC supply current to a communication device that wraps a power supply, and a device and a connection that allow only a fault detection current having a reverse polarity to pass through the device and a DC resistance component of a line. By connecting a resistor having a very large value in series with a circuit in which a resistor is connected in series, there is an effect that not only disconnection of the communication line but also confirmation of short-circuiting of the communication line can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a block diagram showing an example of a conventional fault detection system for a communication line. 1,2 to n, n + 1, N, Na ... communication device, constant current power supply, 13 ... ammeter, 14 ... DC constant voltage power supply, 21 ... DC resistance of line, 22 ... Zener diode, 23 , 30 …… Diode, 24 …… Resistance.

Continuation of front page (56) References JP-A-1-213039 (JP, A) JP-A-58-63260 (JP, A) JP-A-59-27476 (JP, U) (58) Fields investigated (Int) .Cl. ⁶ , DB name) H04B 3/46

Claims (1)

(57) [Claims] In a communication line fault detecting system in a communication system in which a cascade-connected communication device supplies DC constant current via a communication line, only a DC supply current is passed to a communication device which is returning power supply. The first element, a second element that allows only a fault detection current having a polarity opposite to the connection direction of the first element, and a resistor having a value sufficiently larger than the series resistance of the communication line are connected in series. A fault finding method for a communication line, comprising: a parallel circuit for connecting in parallel with a circuit to perform the communication, and performing a fault determination at least on whether or not the communication line is disconnected.