JPH01295617A - Ground fault and electric fault detecting circuit - Google Patents

Abstract

PURPOSE:To certainly detect a ground fault or electric fault by identifying the electric potential state of a two-wire communication line, with a plurality of threshold levels according to power source potential fed from a feed circuit. CONSTITUTION:Including the fluctuation of power source potential fed from a feed circuit 1 to a two-wire communication line (a), and the fluctuation of a ground potential difference, a plurality of threshold levels between a time under the worst condition and the time of a normal state are set in a communication line potential identifying means 30. Then, the power source potential fed to the two-wire communication line (a) is always monitored by a power source monitoring means 40 on the basis of a plurality of reference potentials, and the threshold level in the communication line potential identifying means 30 according to the detected power source potential is selected by an alarm signal selecting means 50. As a result, line voltage fed to the two-wire communication line (a) is fluctuated, and even at the time of the worst condition of the fluctuation of the ground potential difference, a ground fault or electric fault can be certainly detected.

Description

[Detailed Description of the Invention] [Summary] By forming a loop at one end, the potential supplied from the power supply circuit to the two-wire telephone line is identified at a predetermined threshold level, thereby preventing a ground fault in the two-wire telephone line. Regarding ground fault detection circuits that detect electrical faults, we have developed a ground fault detection circuit that can reliably detect ground faults or electrical fault conditions even when power supply fluctuations and ground potential difference fluctuations overlap in the worst conditions. A plurality of communication line potential identification means having a plurality of threshold levels and identifying whether the potential state of each line of the ZVA communication line is below the threshold level, and a plurality of communication line potential identification means for supplying power to the two-wire communication line. A ta monitor means that compares the power supply potential supplied from the circuit based on a plurality of reference voltages and sends out a matching signal when they match, and a reference voltage of the power supply monitor means and a plurality of communication line potential identification means are made to correspond to each other. and alarm signal selection means for selecting the identification result of the communication line potential identification means having a threshold level corresponding to the reference voltage that outputs a matching signal from the power supply monitoring means and outputting the same as an alarm.

[Industrial application field]

The present invention detects a ground fault in a two-wire telephone line by identifying the potential supplied from the power supply circuit to the two-wire telephone line at a predetermined threshold level by forming a loop at one end. Related to electric fault detection circuit.

For example, in the case of a telephone loop type telephone line, one end is connected to the battery of the power supply circuit that supplies the power for telephone calls, and the other end is connected to the ground, and one end of the telephone line forms a loop, so that the telephone line cannot be used for telephone calls. It is simple to supply direct current for use.

However, depending on the surrounding conditions, telephone lines may be subject to ground faults or electric faults, such as when the line on the battery side falls into the ground or the line on the ground side comes into contact with the battery, and such situations cannot be detected. Even if the potential at the ground fault circuit changes due to fluctuations in the power source or the state of the ground potential difference, more accurate detection is required.

[Conventional technology]

FIG. 3 shows a block diagram illustrating a conventional example.

The communication line in this example (al is a two-wire line with A line for battery and B line for ground air, power supply in power supply circuit 1 EC=50V) is supplied with power as described above.

For example, the call f on the opposite end to that connected to the power supply circuit l side
i (When the A line and B line of al form a loop, the communication line (
The power supply E (-50V) of the power supply circuit 1 is supplied to a), thereby causing a direct current to flow.

The ground fault detection circuit 2 draws in the communication line (alOB line) through the Zener diode D1, and draws in the AvA of the communication line (a) through the Zener diode D2.

Note that the power supply E-50V normally fluctuates between 42V and 56V171, and the Zener voltages of the Zener diodes D1 and D2 are each 41V.

If the impedances of the AwA and B lines of the communication line (al) are balanced in the above state and DC current is flowing normally, the voltage applied to Zener diodes p1 and D2, VD, is 25V. becomes.

Now, for example, if line A of the communication line (a) becomes grounded as shown in Figure 3, the impedance balance between line A and line B will be lost, and 50V will be applied across the Zener diode DI. Therefore, when a voltage equal to or higher than the Zener voltage of 41 V is applied to the Zener diode D1, the Zener diode D1 enters the operating state.

As a result, the transistor TRI becomes conductive.

The transistor TR2 becomes conductive, and the output, which had been at the "H" level, becomes the "L" level, and the ground fault of the A line is sent as an alarm to, for example, a monitoring panel (not shown).

Note that even if the B line is in an electrical circuit state, 50V will be applied to the Zener diode D2, so the transistor TR2 will be in a conductive state, and the electrical fault in the B line will be sent out as an alarm.

[Problem to be solved by the invention]

When detecting a ground fault as described above, if a voltage equal to or higher than the Zener voltage (-41V) of the Zener diodes DI, D2 is applied to the Zener diodes DI, D2, the Zener diodes Di, D2 become conductive. Become.

On the other hand, the power supply E-50V fluctuates between 42V and 56V as mentioned above, and when the ground potential difference fluctuation (usually considered to be 6 ■) is added to this, the Zener diodes DI and D2 will The applied voltage is Zener voltage (= 4
1 V) or less.

In this case, even if a ground fault or electric fault occurs, the Zener diodes DI and D2 cannot become conductive, and the state may be regarded as a tight state without being detected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a ground fault/electrical fault detection circuit that can reliably detect a ground fault or electrical fault state even when power supply fluctuations and ground potential difference fluctuations overlap under the worst conditions.

[Means to solve the problem]

FIG. 1 shows a block diagram illustrating the invention in detail.

In the diagram of the principle of the present invention shown in FIG. 1, 1 is a power supply circuit that feeds direct current to the two-wire communication line (a) by forming a loop at one end, and 20 is a power supply circuit provided with the following means 30 to 50. 30 is a short circuit detection circuit, and 30 is a communication line potential identification means that has a plurality of threshold levels and identifies whether or not the potential state of each line A and B of the two-wire communication line (a) is below the threshold level. 40 is an IS monitor means for comparing the power supply potential supplied from the power supply circuit 1 to the two-wire communication line &i (a) based on a plurality of reference voltages and sending out a coincidence signal when they match; Reference numeral 50 associates the reference voltage of the power source monitoring means 40 with the plural communication line potential identifying means 30, and the power source monitoring means 4
Alarm signal selection means that selects the identification result of the communication line potential identification means 40 having a threshold level corresponding to the reference voltage that outputs a matching signal from 0, and by providing such means, this problem is solved. It will be used as a means to achieve this goal.

[For production]

zvA type telephone line, %1 When (a) is in a ground fault or electrical fault state, the threshold level for identifying the ground fault or electrical fault state by the applied voltage is determined by the two-wire telephone line (a). A plurality of threshold levels from the worst condition to the normal condition are set in the communication line potential identification means 30, taking into account the fluctuations in the power supply potential supplied from the power supply circuit 1 to the power supply circuit 1 and the fluctuations in the ground potential difference.

At the same time, the power supply potential supplied to the two-wire telephone line (a) is constantly monitored based on a plurality of reference potentials, and the telephone line potential identification means 30 having a threshold level corresponding to the detected power supply potential is selected as an alarm signal. By configuring the selection by the means 50, it is possible to ensure that a ground fault or electric line condition is detected even under the worst conditions in which the power supply voltage supplied to the two-wire communication line (AL fluctuates and the ground potential difference also fluctuates). It becomes possible to detect

〔Example〕

The gist of the present invention will be specifically explained below with reference to an embodiment shown in FIG.

FIG. 2 shows a block diagram illustrating the invention in detail. Note that the same reference numerals refer to the same objects throughout the plan.

The embodiment of the present invention shown in FIG. 2 uses a Zener diode D31. Detection unit 31 having D32. Zener diode D33 with Zener voltage v2. Detection unit 32 having D34. Zener diode D35 with Zener voltage ■3. A communication line potential identification section 30a consisting of a detection section 33 having a D36, a comparison circuit 41-43 for comparing the reference power supplies E1-E3 and the power supply E of the power supply circuit 1 as a power supply monitor means 40, and a stable reference power supply E1- Zener diode D41. to obtain E3. Power supply monitor unit 4as consisting of capacitor C and resistors R40 to R49 Power supply monitor unit 40a as alarm signal selection means 50
The three detection units 3 of the communication line potential identification unit 30a connected to the input side are detected by the signals ■ to ■ of the internal comparison circuits 41 to 43.
This is an example configured with a selector circuit 50a that selects one of 1 to 33.

The ground fault detection circuit 20a of this embodiment includes the above-mentioned call vA potential identification section 30a, power supply monitor section 40a, and selector circuit 5.
0a.

Note that the part (b) in the communication line potential identifying section 30a has the same configuration as the part (b) in the earth fault detection circuit 2 shown in FIG.

Moreover, the Zener diode D31 in the communication line potential identification section 30a
．． D33. D35 is for ground fault detection, and Zener diode D32. D34. D36 is provided for detecting an electric fault.

Furthermore, a Zener diode D31. D33. D35 or Zener diode D32. D34. D36 notsena voltage v
1 to v3 are set to Vl>V2>V3.

Therefore, in this embodiment, for example, the Zener voltage Vl-
41V, Zener voltage V2-39.5V.

Assume that the Zener voltage is V3-36V.

Further, the selector circuit 50a selects the output of the detection section 31 when a match signal is output from the comparison circuit 41, selects the output of the detection section 32 when a match signal is output from the comparison circuit 42, When a match signal is output from the comparison circuit 43, the output of the detection section 33 is selected.

That is, a power supply circuit 1 that supplies direct current to the telephone line (a)
When the internal power source E fluctuates in the direction of lowering, the threshold level of the communication line potential identifying section 30a is also detected at a lower level, so that detection signal is selected as an alarm.

By processing as described above, the A line can be effectively and reliably treated against fluctuations in power supply and ground potential difference.

It becomes possible to detect a ground fault in the two-gland communication line (a) consisting of the B line.

〔Effect of the invention〕

According to the present invention as described above, it is possible to provide a ground fault detection circuit that can reliably follow fluctuations in power supply and ground potential difference.

[Brief explanation of the drawing]

FIG. 1 is a block diagram explaining the present invention in detail, FIG. 2 is a block diagram explaining the present invention in detail, and FIG. 3 is a block diagram explaining a conventional example. In the figure, 1 is a power supply circuit, 2.20.20a is a ground fault detection circuit, 30 is a communication line potential identification unit, 30a is a communication line potential identification unit, 31 to 33 are detection units, 40 is a power supply monitor unit, 40a is a power supply monitor section, 41 to 43 are comparison circuits, 50 is an alarm signal selection means, and 50a is a selector circuit. Hon'i Muyo Tsuki no Harajiri Σ Word Shizuki Su Block Diagram 1st Area

Claims (1)

[Claims] A circuit (20) for detecting ground faults and electrical faults in a two-wire communication line ((a)) to which DC current is supplied from the power supply circuit (1) by forming a loop at one end. and a plurality of communication line potential identifiers having a plurality of threshold levels to identify whether or not the potential state of each line (line A, line B) of the two-wire communication line ((a)) is below the threshold level. means (30), comparing power supply potentials supplied from the power supply circuit (1) to the two-wire communication line ((a)) based on a plurality of reference voltages, and if they match, transmitting a match signal; Power supply monitor means (4
0), and the reference voltage of the power supply monitoring means (40) is made to correspond to the plurality of communication line potential identification means (30), respectively, and the matching signal is outputted from the power supply monitoring means (40) to correspond to the reference voltage. A ground fault/electrical fault detection circuit comprising: alarm signal selection means (50) for selecting the identification result of the communication line potential identification means (30) having a threshold level and outputting the selected result as an alarm output.