JP2717410B2 - Optical demodulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device for detecting a current flowing through a cable,
In particular, the present invention relates to an apparatus that allows a value detected by an optical magnetic field sensor provided on a single-core cable to be displayed through a circuit of an automatic gain control system so as to display a change state of only an AC component.

(Prior Art) In order to know a current flowing through a power transmission cable or the like, or a state of a leakage current or the like in the cable, a current detecting means is provided for the cable, and the conductor of the cable or It has been generally practiced to detect a current flowing through a cable sheath.

As a detection means therefor, an optical magnetic field sensor or the like using a Faraday element is often used because of its relatively simple configuration and high reliability. In the device such as the optical magnetic field sensor, the Faraday element utilizes the phenomenon that the plane of polarization of light rotates according to the magnetic field strength. Is used as a device for detecting the intensity of the magnetic field when the occurrence occurs.

In such a magnetic field detector, a polarizer and a right-angle prism are arranged on both sides of a Faraday element, an optical fiber is connected to such members via a lens, and light between the light emitting unit and the light receiving unit is detected. The used magnetic field detection circuit is configured.

In the conventionally used optical magnetic field sensor as described above, information of light detected by the optical magnetic field sensor is, for example, using a signal processing circuit as shown in JP-A-59-225372. The change in the current of the cable that has been processed and detected by the optical magnetic field sensor can be displayed on the display unit.

The conventional signal processing circuit as described above is configured as shown in FIG. 3, and the optical signal received by the light receiving unit 10 from the optical magnetic field sensor is O / E (optical-electrical signal). It is converted into an electric signal by the conversion circuit 21, and thereafter,
The signals are input to two filter circuits 22, 22a arranged in parallel, and are divided into an AC component and a DC component, respectively.

Then, each signal is amplified by the amplifier circuits 23 and 23a and input to the division circuit 25, and the output of the division circuit 25 is output to the amplification circuit
The signal is amplified at 27 and output to the display circuit 28, and the state of change of the optical signal is displayed on the display unit.

By configuring the signal processing circuit as described above, the output from the optical magnetic field sensor can be transmitted to the signal processing means using one optical fiber, and the configuration of the signal processing circuit can be simplified. It is said that it can exhibit the advantage of becoming.

(Problems to be Solved by the Invention) However, in the conventional signal processing circuit as described above, it is necessary to divide the voltage of the O / E conversion circuit into a DC component and an AC component by using two filter circuits. Further, it is necessary to perform the above-described division of the two components by the division circuit.

Therefore, in the case of using the above-described signal processing circuit, it is necessary to use two filter circuits and to provide a dividing circuit, which causes a problem that the configuration of the signal processing circuit is complicated. .

In addition, since the division circuit is a device having relatively small tolerance in frequency characteristics, temperature characteristics, and the like, when those conditions change, the reliability of the output value may decrease. In addition, there is a problem that the performance of the optical demodulator depends on the above-described conditions.

(Object of the Invention) The present invention solves the above-mentioned drawbacks of the conventionally used optical demodulator and aims at directing only a change in the AC component to a display circuit without providing a division circuit. It is an object of the present invention to provide a device that enables output and simplifies the configuration of a signal processing circuit.

(Means and Actions for Solving the Problems) The present invention relates to an apparatus provided with an optical magnetic field sensor for a power transmission cable and configured to detect a current or the like flowing through the cable by the optical magnetic field sensor.

In the present invention, when the light of the optical magnetic field sensor is converted into an electric signal through an optical-electrical signal conversion circuit or the like, and is processed in the signal processing circuit, the signal processing circuit includes an amplification circuit and a parallel connection to the amplification circuit. A feedback resistor provided with a function of adjusting the amplification degree of the amplifier circuit by controlling the resistance value to make the DC component a constant value, and comparing the output of the amplifier circuit with the signal of the reference voltage circuit. An automatic gain control type signal processing circuit comprising a comparison circuit for causing the output signal to be fed back to the feedback resistor is provided, and an output from the auto gain control type signal processing circuit is input to a filter circuit. Removes the DC component and outputs only the AC component to the amplifier circuit, and outputs the signal amplified by the amplifier circuit to the display circuit. It is configured so as.

Therefore, in the optical demodulator of the present invention, of the voltage obtained by the O / E conversion circuit, the DC component is maintained as a constant value by the circuit of the auto gain control method,
Since only the change in the AC component can be output, it is possible to simplify the signal processing circuit, and reduce the manufacturing cost of the optical demodulator by not using the division circuit.
It is possible to improve the reliability of the device.

(Example) The configuration of the optical demodulator of the present invention will be described with reference to the illustrated example.

In the embodiment of the present invention shown in FIG. 1, an optical signal output from the optical magnetic field sensor 1 to the light receiving unit 10 is output to the signal processing circuit as an output voltage via the O / E conversion circuit 11. .

The signal processing circuit of the optical demodulator includes an amplifier circuit 12, a feedback resistor 15 provided in parallel with the amplifier circuit 12, and a comparison circuit for comparing the output of the amplifier circuit 12 with the signal of the reference voltage circuit 14. The circuit 13 constitutes an automatic gain control type circuit.

The output value of the comparison circuit 13 is fed back to the feedback resistor 15 as a control signal, so that the DC component of the output voltage from the O / E conversion circuit 11 can be maintained at a constant value.

The feedback resistor 15 in the circuit of this embodiment is
Is controlled, and the larger the resistance value is, the larger the amplification degree is. Then, in the control circuit of the present invention, by controlling the resistance value by the feedback resistor, the amplification degree in the amplifier circuit 12 is adjusted so that the DC component can be controlled to a constant value. ing.

The output from the circuit of the auto gain control system is input to a filter circuit 16, the DC component is removed by the filter circuit 16, and only the AC component is output to the amplifier circuit 17, which is amplified by the amplifier circuit 17. The output signal is output to the display circuit 18.

Then, by configuring the circuit as described above, in the optical demodulator of the present invention, the DC voltage of the output voltage from the O / E conversion circuit 11 can be maintained at a constant value. Without being affected by changes in
The output of the O / E conversion circuit can be obtained as a detection value of only the AC component.

That is, as shown in FIG. 1 described above, when the circuit of the auto gain control method is configured by the amplifier circuit 12, the comparison circuit 13, the reference voltage circuit 14, and the feedback resistor 15, the circuit shown in FIG. As shown in the graph, O / E
Even if the incident light power of the conversion circuit 11 changes between 1 μw and 20 μw, the DC component value pdc can be maintained at a constant value of about 9.5V.

Then, the processing of the DC component as described above is performed by the circuit of the signal processing circuit, whereby the filter circuit 16 is processed.
In this case, the DC component can be easily removed, and only the AC component can be input to the amplifier circuit 17 in a separated state, amplified, and output to the display circuit 18.

When the optical demodulator of the present invention is configured as described above, it is unnecessary to provide two filter circuits in parallel and to provide a division circuit, as shown in the conventional example of FIG. Thus, the configuration of the signal processing circuit in the optical demodulator can be simplified.

Further, in the optical demodulator of the present invention, since a circuit such as a division circuit which is affected by temperature or the like is not provided, the magnetic field due to the current flowing through the cable line is not generated without the influence of the environmental temperature. The change can be accurately detected.

As an optical magnetic field sensor for transmitting detection information of a change in a magnetic field in a cable line to the optical demodulator as described above, for example, an apparatus as shown in FIG. 2 can be used. . In the optical magnetic field sensor 1 shown in FIG. 2, a YIG (Yttrium-Iron-Gallium) sensor is disposed along a cable line and detects a change in a magnetic field due to a change in current in the line.
A known Faraday element 2 such as a system or a lead glass system can be used.

In the optical magnetic field sensor 1, a polarizer 3 is arranged on the light input side of the Faraday element 2, and an analyzer 4 and a right-angle prism 5 are arranged on the opposite side. Optical fibers 7 and 7a are connected to the polarizer 3 and the right-angle prism 5 through lenses 6 and 6a, respectively, and connected to a light emitting unit 8 including an LED or the like and a light receiving unit 10, respectively. I do.

When a current flowing in the cable in which the Faraday element 2 is set causes a leak or the like to occur in a single wire of any phase in the cable line and a change occurs in the current in another cable, the current of the current is reduced. Due to the change in the magnetic field accompanying the change, the surface of the light passing through the Faraday element is rotated by a predetermined angle.

Therefore, the detection voltage by the light receiving unit changes due to the rotation of the light in the above-mentioned Faraday element. By processing the signal of the change by the optical demodulator, a change in the current in the cable line can be accurately detected. Can be done.

The circuit configuration according to the present invention can be used as it is even for an electric field sensor using the Pockels effect.

(Effect of the Invention) Since the optical demodulator of the present invention has the above-described configuration, by providing an auto gain control type circuit, the DC component is kept constant, and the information of only the change of the AC component is obtained. Can be output to the display circuit, so that an accurate detection value can be obtained.

Further, the optical demodulator of the present invention does not require the use of a plurality of filter circuits and a division circuit unlike the conventionally used signal processing circuit, and thus the configuration of the signal processing circuit is not required. Since it can be simplified, and furthermore, since a division circuit is not used, a highly reliable detection value can be obtained without being affected by environmental temperature or the like.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing the configuration of an optical demodulator of the present invention, FIG. 1a is a graph showing the state of a DC component obtained by an auto gain control type circuit, and FIG. It is an explanatory view showing a configuration of a magnetic field sensor,
FIG. 3 is a circuit diagram of a conventional optical demodulator. Reference numeral 1 in the drawing: optical magnetic field sensor 2, Faraday element 3, polarizer 4, analyzer 5, right angle prism 6, lens 6, optical fiber 7, light emitting unit , 10 light receiving section, 11 O / E conversion circuit, 12 amplifier circuit, 13 comparison circuit, 14 reference voltage circuit, 15 feedback resistor, 16 filter circuit, 17 Amplifier circuit, 18 Display circuit.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yukio Morita 4-3 Ikejiri, Itami City, Hyogo Prefecture, Itami Works, Mitsubishi Electric Wire & Cable Co., Ltd. (56) References JP-A-64-88372 (JP, A)

Claims (1)

(57) [Claims] An apparatus configured to provide an optical magnetic field sensor for a power transmission cable and to detect a current or the like flowing through the cable by the optical magnetic field sensor, wherein light from the optical magnetic field sensor is converted into an optical-electrical signal. When converting into an electric signal through a circuit or the like and processing the signal in the signal processing circuit, the signal processing circuit includes an amplifier circuit, and an amplification degree of the amplifier circuit is adjusted by controlling a resistance value provided in parallel with the amplifier circuit. An automatic gain including a feedback resistor having a function of setting a DC component to a constant value, and a comparison circuit for comparing an output of the amplifier circuit with a signal of a reference voltage circuit and feeding back the output signal to the feedback resistor. A signal processing circuit of a control system is provided, and an output from the signal processing circuit of the auto gain control system is input to a filter circuit; Removing the DC component by over circuit outputs only the AC components to the amplifier circuit, an optical demodulator, characterized in that configured to output to the display circuit the signals amplified by the amplifying circuit.