JPH0264474A - Earth detection circuit - Google Patents

Abstract

PURPOSE:To detect an earth state without being affected by the voltage of a power supply by a method wherein the voltage of a Zener diode and the voltage of one telephone line are respectively subtracted from the voltage of the power supply to calculate difference voltages which are, in turn, divided by resistance to obtain voltages and both voltages are inputted to a DC amplifier to take out difference. CONSTITUTION:When a telephone line (a) is in a normal state, the reference voltage V1 inputted to the reference terminal of a DC amplifier 21 is one obtained by dividing the voltage, which is calculated by subtracting the potential VZD of a Zener diode ZD2 from the voltage VE of a power supply, by the resistance values of resistors R10, R20. The voltage V2 inputted to the other terminal of said amplifier 21 is one obtained by dividing the difference between the voltage VE of the power supply and the voltage VS of a B-line by the resistance values of resistors R30, R40. In this case, because of voltage V1 voltage V2, the output of the amplifier 21 becomes almost zero to be sent out as H. Next, when the telephone line (a) is in an earth state, the voltage V1 is one obtained by dividing the voltage between the earth G and VE by the resistance values of the resistors R30, R40 and shows no change. The difference between the input voltages V2, V1 is taken out through a resistor 50 and displayed to accurately detect an earth state.

Description

[Detailed description of the invention] [Summary] Detects a ground fault condition in a two-wire communication line that supplies voltage from a power supply circuit to a partner station device connected by the two-wire communication line by forming a loop at one end. Regarding ground fault detection circuits, we aim to provide a ground fault detection circuit that can reliably detect ground fault conditions under conditions that are not affected by power supply fluctuations. , a first resistor and a second resistor that divide the fluctuating potential taken out by the Zener diode to obtain a first potential, and the potential appearing at the connection point between the two-wire telephone line and the power supply circuit and the power supply voltage. A third resistor and a fourth resistor divide the potential into a second potential, and a DC amplifier detects and outputs the difference between the first potential and the second potential. Configure.

[Industrial application field]

The present invention relates to a ground fault detection circuit that detects a ground fault state of a two-wire communication line that has one end formed into a loop to supply voltage from a power supply circuit to a partner station device connected to the two-wire communication line.

For example, in a two-wire loop telephone line, one of the lines is a battery in the power supply circuit that supplies power for telephone calls;
Generally, the other end of the communication line is connected to the ground, and the other end of the communication line forms a loop to supply direct current for communication.

However, depending on the surrounding conditions, a two-wire telephone line may fall to the ground and become a ground fault, and the detection of such a situation is difficult because the potential at the time of the ground fault fluctuates due to fluctuations in the power supply or ground potential difference. Even in such cases, reliable detection is required.

[Conventional technology]

FIG. 3 is a diagram illustrating a conventional example, and FIG. 4 is a diagram illustrating a ground fault detection situation in the conventional example.

In this example, the communication line (a) is usually A line ground air and B line battery 2
It is a wire line, and the type source E (for example, 50V
) is fed via the B line of the communication line fa) and forms a loop above the ground on the A line side.

That is, for example, if wires A and B of the communication line (a) connected to the other party's device 3 side connected to the power supply circuit 1 side become a loop, the power supply E of the power supply circuit 1 is fed to the communication line fat. ,
As a result, direct current is supplied to the other party's station device 3 via the communication line fa).

The ground fault detection circuit 2 draws in the B line of the communication line (a) via a Zener diode ZDl. For example, when the voltage SE is 50V, it normally fluctuates between 42V and 56V.

Also, the zener voltage of the zener diode ZDI is several ■,
It is assumed that the power source E of the ground fault detection circuit 2 and the power source E of the power supply circuit 1 are the same.

Note that the direction of the arrow in the power supply circuit 1 shown in FIG. 3 indicates the direction of direct current, and the same goes for the direction of the arrow in the partner station device 3.

In the ground fault detection circuit 2, when a specified Zener voltage of several volts or less is applied to the Zener diode ZDI, the transistor TRI in the ground fault detection circuit 2 is in an off state, and therefore its output side is connected to the resistor R. The connected +5■ is sent out and becomes the "H" state.

Next, if, for example, a two-wire communication line (al A line or B line) is in a ground fault condition with the ground G as shown in FIG. is several volts or more, which is defined as the zener voltage.

As a result, the Zener diode ZD1 becomes in the 4-way state, and the transistor TRI connects the power source E to the resistor R1 and the resistor R.
It is turned on by applying a potential divided by 2 to the base, and its output becomes an "L" state, and a ground fault state is detected.

[Problem to be solved by the invention]

In the conventional example shown in FIG. 3 mentioned above, the voltage is set using the power supply E as a reference voltage, and the Zener diode ZDI's voltage 1-2 voltage 1! i! However, as shown in Figure 4, the power supply voltage, which is the reference voltage, is 42V. It fluctuates between
), even if the voltage applied to the Zener diode ZDI is in a ground fault state under the worst conditions, the detection level ■ will be displayed as a non-detection state in Figure 4.
2□ (= several volts) or less, and there is a possibility that the ground fault condition cannot be detected.

An object of the present invention is to provide a ground fault detection circuit that can reliably detect a ground fault state under conditions that are not affected by power supply fluctuations.

[Means to solve the problem]

FIG. 1 shows a detailed illustration of the invention.

1 in the diagram showing the embodiment of the present invention shown in FIG. 1 is a power supply circuit that feeds DC current to the two-wire communication line fat by forming a loop at one end, and ZD2 is the power supply voltage V of the power supply circuit 1. This is a Zener diode that takes out potential fluctuations, and R10 and R20 are a first resistor R10 and a second resistor R20 that divide the fluctuating voltage (2°) taken out by the Zener diode ZD2 to obtain a first potential (1). , R30 and R40 are the third voltage V2 which divides the potential between the voltage V appearing at the connection point between the two-wire communication line (a) and the power supply circuit I and the voltage VE of the power aE to obtain the second potential V2. resistor (R30
) and a fourth resistor (R40), and 21 is a DC amplifier that detects and outputs the difference between the first potential V and the second potential V2 as a reference, and is equipped with such means to detect a ground fault. Configuring the detection circuit 20 is a means for solving this problem.

[For production]

Voltage V input to the reference terminal of DC amplifier 21.

It is assumed that the difference obtained by subtracting the voltage v2° of the resistor of the Zener diode ZD2 from the power supply voltage V5 is divided by the resistor R1°0°R20.

On the other hand, the voltage ■2 input to the other terminal of the DC amplifier 21 is
If the 2nd wire 2 telephone line (a) is in a ground fault state, the ground
and power supply E (Ve-vl)) is the voltage between resistors R30 and R
It is divided by 40.

Now, when there is a fluctuation in the power supply E, the voltage input to the other terminals of the DC amplifier 21 (2) The voltage V input to the reference terminal of the DC amplifier 210 (inspection level) also removes the influence of the power fluctuation. Since the ground fault voltage varies depending on the direction, it is possible to always detect a ground fault condition at a test level suitable for the ground fault voltage to be tested.

〔Example〕

The gist of the present invention will be specifically explained below with reference to embodiments shown in FIGS. 1 and 2.

FIG. 2 is a diagram illustrating a ground fault detection situation in an embodiment of the present invention. Note that the same reference numerals indicate the same objects throughout the figures.

Similarly to the ground fault detection circuit 2 shown in FIG. 3, the ground fault detection circuit 20 of the present invention shown in FIG. When a ground fault condition is detected, an "L" level signal is sent to a control section (not shown) or the like.

That is, when the communication line (al) is in a normal state, the DC amplifier 2
The voltage V1 applied to the reference terminal 1 is the voltage V of the power supply E, minus the potential VZO2 of the Zener diode ZD2, divided by resistors R10 and R20, and this is the reference voltage of the DC amplifier 21. do.

On the other hand, to other terminals, the voltage V2 is obtained by dividing the difference between the power supply voltage ■2 and the B line voltage ■8 by resistors R30 and R40, and in this case, the voltage V1#voltage ■2, so the DC amplifier 2
The output becomes approximately zero and is sent out as "H".

In addition, the voltage (2) is lower than the voltage of the worst value of the voltage variation between the A line and the B line of the communication line (a).
, R40.

Next, when the communication line (al) is in a ground fault state, the voltage between the earth G and the power supply voltage 70 is divided by resistors R30 and R40, and this becomes the voltage V2 that is applied to the DC amplifier 21.At this time, the DC The voltage 1 applied to the reference terminal of the amplifier 21 remains unchanged.

The DC amplifier 21 takes out the difference between the input voltage 2 and the voltage V1 through the resistor R50, and sends it out as "L", thereby indicating the ground fault condition to a control section (not shown) or the like.

Now, if the ground fault state detection special power source E fluctuates, the difference between the voltage V of the power source E and the voltage vzoz extracted from the Zener diode ZD2 will increase by the amount of the fluctuation in the power source E, and therefore the voltage Vl input to the reference terminal will also increase. As shown in FIG. 3, the voltage changes to correspond to the voltage (2) that changes due to power supply fluctuations.

That is, the values of the resistors R10 and R20 are set so that the ground fault detection level is suitable for the changed value of the voltage v2 from among the difference changes from the voltage vzoz due to power supply fluctuations.

As described above, the voltage Vt input to the reference terminal changes in accordance with the variation in the voltage v2 input to the other terminal of the DC amplifier 21 due to fluctuations in the power supply, so it is possible to effectively detect a ground fault condition. .

In the figure, 1 is a power supply circuit, 2.20 is a ground fault detection circuit, 3 is the partner station device, 2 are shown respectively.

1 is a DC amplifier. [Effects 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 power fluctuations.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the present invention in detail, Fig. 2 is a diagram for explaining the ground fault detection situation in the embodiment of the present invention, Fig. 3 is a diagram for explaining the conventional example, and Fig. 4 is a diagram for explaining the conventional example. Figures illustrating the ground fault detection situation are shown, respectively. Figure 2 Diagram explaining the ground fault detection situation in the conventional example Figure 4

Claims (1)

[Claims] A ground fault detection circuit (20) that detects a ground fault state of a two-wire communication line ((a)) to which direct current is supplied from the power supply circuit (1) by forming a loop at one end. There is a Zener diode (ZD2) that takes out the potential fluctuation of the power supply voltage (V_E) of the power supply circuit (1), and a fluctuating potential (V_Z_) taken out by the Zener diode (ZD2).
A first resistor (R10) and a second resistor (R20) that divide D) to a first potential (V_1), the two-wire communication line ((a)), and the power supply circuit ( A third resistor (R30) and a fourth resistor ( R40) and the second potential (V_2) with reference to the first potential (V_1) and a DC amplifier (21
).