JPH0382968A - Insulating type level detector - Google Patents

Abstract

PURPOSE:To detect the level of a very small quantity of input electricity by subjecting an input current to resistance-type potential division and outputting the circuit on the side connected to a control power supply when a circuit detecting the level of a very small quantity of electricity is operated. CONSTITUTION:The current inputted from a terminal 1 is introduced into a resistance-type potential divider circuit consisting of resistors R2 - R5, and resistors R7 and VR1. When the input current becomes a definite value or more, since the voltage between a gate G and a source S exceeds pinch-off voltage, a field-effect transistor TR1 is turned ON and a drain D and the source S become conductive. As a result, voltage is induced between both terminals of a resistor R6 and a transistor TR2 is turned ON and a photocoupler (PC1) 6 is turned ON. By this method, the level of the input current is detected and the current is outputted to the secondary part of the photocoupler 6 connected to a control power supply at the terminals 3, 4 thereof and a transistor TR3 is turned OFF. Therefore, when the input current becomes a level detection value or less, the transistor TR3 is turned ON and an auxiliary relay X is operated to act as a monitor relay on the daughter side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an electrical quantity level detection device that requires insulation.

(Prior art) Fig. 2 is an example of a connection diagram of an indicator line monitoring device, in which a constant monitoring current is constantly passed through the indicator line for an indicator line relay that protects the power system, and the indicator line 18 changes due to changes in this current. Indicates that the presence or absence of an abnormality is detected. Since the secondary monitoring relay 12 has a simpler function than the conventional coarse monitoring relay 9, it is configured to operate when the monitoring current decreases below a certain level.

In FIG. 2, two display line relays 19 are connected to isolated current transformers 1. It is connected via Oa, 10b and display wirework 8.

The presence or absence of an abnormality in the display wire 18 installed between the substations is monitored by the coarse side monitoring relay 9 and the secondary side monitoring relay 12, and the power supply of the coarse side monitoring relay 9 is used to send a direct current to the display line 18. Abnormalities in the display line are detected by changes in the current. Note that the neutralization reactor 11a, 11. b and capacitor 22. The resistor 23 is for preventing the application of high voltage based on the indicator line induced voltage to the rough side and child side monitoring relays, and the capacitor 24 is for superimposing DC current to the AC indicator line circuit on the indicator line relay side. It is. In addition, conventionally, the coarse side monitoring relay insulates the DC power supply with a D/D converter or the like, applies a DC voltage to the display line circuit, and flows the monitoring current.

(Problems to be Solved by the Invention) Although polarized relays have conventionally been used as the child-side monitoring relay 12, there is a strong demand for an electronic circuit to replace this.

To this end, a compact, low-burden isolation circuit that can detect levels of minute inputs that have never been seen before is absolutely necessary.

Therefore, an object of the present invention is to provide an insulated level detection device capable of detecting the level of a minute amount of input electricity.

[Structure of the invention]

(Means for solving problems) A description will be given below based on an example of the diagram of the king.

The input current is divided into resistive voltages (R2-R5), the field effect transistor TRI is used to detect the level of minute amounts of electricity, and the resistive voltage divided by R
7 and the level detection circuit (LD) 3 from the VRI,
This level detection circuit (LD) 3 includes an ONL during operation, and an output circuit consisting of a photocoupler (PCI) 6 that outputs an output signal to a photocoupler output side circuit connected to a control power source.

(Function) The current input from the terminal is guided to a resistive voltage divider circuit consisting of resistors R2 to R1 (5) and resistors R7 and VRI.

When the input current exceeds a certain value, the voltage between the gate (G) and source (S) of the field effect transistor 1 to transistor TRI exceeds the pinch-off voltage of the field effect transistor TRI, so that the field effect transistor TR1, drain (D) and the source (S) are electrically connected. As a result, a voltage is induced across the resistor R6, so that the transistor TR2 is ONL.
, drives a photocoupler (Pct) 6.

In this way, the level of the input current is detected, and the resulting output signal is the result of two sets of output signals. 11 Output to the photocoupler output side circuit connected to the power supply.

(Example) An example of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram of an insulated level detection device used in a slave station monitoring relay or the like.

The terminal is connected to a limiter circuit consisting of a Zener diode ZDl and a resistor R2 via a diode and a resistor R1.
A voltage dividing circuit consisting of ~R5, a level detection circuit 1 consisting of a resistor R6 and a field effect transistor TRI, a voltage dividing circuit consisting of a resistor R7 and VRI, and a photovoltaic circuit consisting of a transistor TR2, a photocoupler PC1, a resistor R8, and a diode D4. It is connected in parallel with the coupler primary side circuit, and connected to the terminal ■ through the diode D2.

The secondary side collector terminal of the photocoupler PCI is connected to the control power supply terminal (2) via resistors R9, R13, and R11, and the secondary side emitter terminal of the photocoupler PCI is connected to the control power supply terminal (2). Furthermore, the emitter side of the photocoupler PCI is a Zener diode ZD2. Zn2. It is connected to transistors TR1 to TR3 that drive auxiliary relay X through a circuit including resistor 10.

A diode D5 is connected in parallel to the auxiliary relay X.

Next, the effect will be explained.

The current input from the terminal is introduced into a voltage dividing circuit made up of resistors R2 to R5 and a voltage dividing circuit made up of resistors R7 and VRI.

When the input current exceeds a certain value, the voltage between the gate (G) and source (S) of field effect transistor TRI exceeds the pinch-off voltage of field effect transistor TRI, so field effect transistor T turns on. drain(
A current is passed between D) and the source (S).

Therefore, a voltage is generated across the resistor R6 and the transistor TR
2 and turn on the photocoupler Pct. The secondary side of the photocoupler has terminals ■ and ■! Since it is connected to the Ilf# power supply, when the photocoupler PCI turns on, the resistors R9, R13, R11, and Zener diode ZD
2゜Due to the current flowing through Zn2, the above current in transistor TR3, which was ONL, no longer flows, and transistor T
R3 is turned OFF.

When transistor TR3 turns off, auxiliary relay X, which had been on until then, turns off.

From the above, it can be seen that, conversely, when the current input to the terminal falls below the level detection value, auxiliary relay X operates, closes the a contact, opens the b contact, and functions as a child side monitoring relay. .

As described above, the present invention makes it possible to realize a small, low-impact passive insulator capable of detecting the level of minute amounts of input electricity.

It also has the advantage of being much smaller and cheaper than devices that use isolated amplifiers or the like.

For example, an isolated level detection device with a detection current r-)C2mA, an input impedance 2 of Ω or less, and a load of 8ml or less has conventionally required the use of an expensive and large circuit such as an isolated amplifier, but the present invention can be used. For example, the device can be realized in a small size and at low cost.

The present invention is not limited to application to the monitoring relay described in the embodiments, but can be applied to various electrical equipment, control devices, and electronic devices that require the above-mentioned detection, and its contribution to the industry as a whole is immeasurable.

〔Effect of the invention〕

The present invention makes it possible to provide a small, inexpensive, low-burden, passive, isolated level detection device capable of detecting the level of minute amounts of input electricity.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an insulated level detection device of the present invention, and FIG. 2 is a configuration diagram of a secondary monitoring relay device. 1. Input terminal, 2 Zener diode, 3.
・Level detection circuit (using FET), 4. Variable resistor,
5, 6...Photocoupler, 7 8...Relay, 9]Oa, 10b...Isolation transformer. 11, a, 1.1b...neutralization reactor, 12. slave side monitoring relay, T-work...circulating current.・Transistor, Transistor, ・Coarse side monitoring relay

Claims (1)

[Claims] A level detection circuit that divides an input electrical quantity using a voltage dividing circuit and uses a field effect transistor to generate an output when the input electrical quantity exceeds a certain level based on the pinch-off voltage of the field effect transistor; The output of the circuit drives the primary side of the photocoupler, and this photocoupler 2
An insulated level detection device comprising: an output circuit that obtains an output signal by making the next side conductive.