JP2017150890A - Photocurrent sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the accurate measurement by removing a light source noise from a detection signal output from a sensor head even if the sensor head and a light source are disposed very far from each other.SOLUTION: The optical current sensor includes a light source 10, a sensor head 15, a photoelectric converter 20, a first optical fiber transmission path 11 that connects between the light source and the sensor head 15, a second optical fiber transmission path 12 that connects between the sensor head and the photoelectric converter, and a third optical fiber transmission path 13 that connects between the photoelectric converter and a photocoupler 16 provided in the first optical fiber transmission path. The photocoupler is disposed near the sensor head. The transmission path length L2 of the second optical fiber transmission path is equal to the transmission path length L3 of the third optical fiber transmission path. The light emitted from the light source at the same time is incident into the photoelectric converter at the same timing from the second optical fiber transmission path and the third optical fiber transmission path without a time difference.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photocurrent sensor.

  A photocurrent sensor for measuring an alternating current, for example, guides light emitted from a light source to a sensor head, modulates the intensity of light based on an alternating current that is an alternating current measurement object that changes over time, and generates a modulated optical signal. Is converted into an electric signal by a photoelectric conversion element, an alternating current component and a direct current component included in the electric signal are separated, a current signal to be measured is obtained from the ratio (AC / DC), and a current value is measured. is there. The optical signal input to the photoelectric conversion element has a drift-like variation in which the DC component varies. Factors of this drift-like fluctuation include fluctuations in the amount of light of the optical signal emitted from the light source, fluctuations in the optical loss of the optical fiber transmission path, and fluctuations in the optical loss of optical components such as sensor heads and optical couplers. By obtaining AC / DC, these drifting fluctuations can be cut.

  In this basic measurement method, the influence of light source noise generated from a light source and changing at a relatively high speed affects the sensor output (current value). Therefore, as an invention for removing the influence of such light source noise, there is, for example, “intensity modulation type photosensor and photocurrent / voltage sensor” disclosed in Patent Document 1. The invention disclosed in Patent Document 1 obtains a reference signal by separating a part of light emitted from a light source, obtains a light source noise correction signal from the ratio of the AC component and the DC component of the reference signal, The influence of the light source noise is reduced by subtracting the light source noise correction signal from the measured current signal obtained based on the return signal from the sensor head and obtaining the current value based on the subtracted signal.

Japanese Patent No. 4631907

  When the photocurrent sensor is applied to an underground fault section detection device, a system fault determination device, or the like, the sensor head is installed at a point away from the light source in order to detect an accident or the like that occurred in a remote place. Therefore, the transmission line length of the optical fiber transmission line connecting the light source and the sensor head is also increased. This transmission line length is, for example, a long distance of about 10 km to 20 km or more. Further, the photoelectric converter that performs the calculation of the current signal to be measured and the light source noise correction signal and the correction process is installed in the vicinity of the light source.

  For this reason, the reference signal branches relatively quickly after being emitted from the light source and reaches the photoelectric converter. However, the optical signal for obtaining the current signal to be measured travels through the long-distance optical fiber transmission path (outward path). The sensor head is reached, and then the optical fiber transmission path (return path) is advanced to the photoelectric converter. Accordingly, there is a difference between the measured current signal based on the light emitted from the light source at the same time and the time when the light source noise correction signal is generated. As described above, when the transmission path length becomes longer, the transmission time of light traveling through the optical fiber transmission path cannot be ignored.

  Therefore, the light source noise correction signal used when correcting the current signal to be measured is in a state different from the state of the light source noise when the current signal to be measured is emitted, which causes a problem that accurate correction cannot be performed.

  In order to solve the above-described problems, the present invention provides (1) a light source, a first optical fiber transmission line that transmits an optical signal emitted from the light source, and a front end side of the first optical fiber transmission line. A sensor head to which the optical signal is input, a second optical fiber transmission line that transmits a detection signal output from the sensor head, and a part of the optical signal that transmits the first optical fiber transmission line. The optical separation means extracted as a reference signal, the third optical fiber transmission line for transmitting the reference signal extracted by the optical separation means, the second optical fiber transmission line and the third optical fiber transmission line are connected to each other. A photoelectric converter, and the photoelectric converter includes a correction function for performing light source noise correction by subtracting a signal based on the reference signal from a signal based on the input detection signal, and the light separation unit includes Placed Nsaheddo side was equal transmission path length of said third optical fiber transmission path and the transmission path length of said second optical fiber transmission path. The light separation means corresponds to an optical coupler in the embodiment.

  According to the present invention, the light separating means is disposed on the sensor head side, and the optical fiber transmission path length of the second optical fiber transmission path is equal to the optical fiber transmission path length of the third optical fiber transmission path. The light emitted from the light source enters the photoelectric converter from the second optical fiber transmission line and the third optical fiber transmission line at the same timing without causing a time difference. Therefore, even when the installation positions of the light source and the sensor head are very far apart, for example, several km to 20 km or more, the detection signal and the reference signal that are simultaneously input to the photoelectric converter are emitted simultaneously from the light source. The same light source noise is applied based on the optical signal. Therefore, by correcting the light source noise using the reference signal, the light source noise is removed from the detection signal, and an accurate output value can be obtained.

  (2) An adjustment function is provided to make the DC component of the signal based on the detection signal equal to the DC component of the signal based on the reference signal, and the subtraction is performed from the AC component of the signal based on the detection signal to the reference signal. The AC component of the based signal may be subtracted.

  Usually, since the signal level of the detection signal and the reference signal is different, even if the reference signal is simply subtracted from the detection signal, appropriate light source noise correction cannot be performed. For example, the ratio of the AC component to the DC component is obtained and normalized. The subtracted signals need to be subtracted. For such normalization, an expensive divider is required. In the present invention, since the DC components are equal, the signal levels of the signal based on the detection signal and the signal based on the reference signal are equal, and the light source noise can be corrected with high accuracy by directly subtracting the AC components. Therefore, since a divider or the like is not necessary, the photoelectric sensor can be configured at low cost.

  (3) As a more specific invention that realizes the invention of (2), for example, the adjustment function is a first arranged in the subsequent stage of the first light receiving element for the detection signal mounted on the photoelectric converter. A first automatic amplification regulator, and a second automatic amplification regulator disposed after the second light receiving element for the reference signal, the DC component of the signal output from the first automatic amplification regulator, and the first The gains of the first automatic amplification regulator and the second automatic amplification regulator may be feedback controlled so that the DC components of the signals output from the two automatic amplification regulators are equal.

  (4) As a more specific invention for realizing the invention of (2), for example, the adjustment function includes a first automatic optical variable attenuator mounted on the second optical fiber transmission line, and the third optical fiber. A second automatic optical variable attenuator mounted on the transmission line, wherein the first automatic optical variable attenuator and the second automatic optical variable attenuator attenuate the signal levels of the detection signal and the reference signal, respectively. Feedback control of attenuation amounts of the first automatic optical variable attenuator and the second automatic optical variable attenuator so that the DC component of the detection signal input to the photoelectric converter is equal to the DC component of the reference signal It may be configured to do so.

  In the present invention, even when the installation positions of the light source and the sensor head are very far apart, for example, several km to 20 km or more, the light source noise is removed from the detection signal output from the sensor head. Good measurements can be made.

It is a figure showing a suitable first embodiment of a photocurrent sensor concerning the present invention. It is a figure which shows suitable 2nd embodiment of the photocurrent sensor which concerns on this invention. It is a figure which shows suitable 3rd embodiment of the photocurrent sensor which concerns on this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not construed as being limited thereto, and various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art without departing from the scope of the present invention.

  FIG. 1 shows a first preferred embodiment of a photocurrent sensor according to the present invention. As shown in FIG. 1, the photocurrent sensor includes a light source 10, a sensor head 15 disposed so as to circulate around a conductor 1 to be measured through which a current to be inspected flows, a photoelectric converter 20, and an optical fiber connecting them. A transmission line is provided.

  As the light source 10, for example, a light source (ASE) using a phenomenon in which spontaneous emission light generated by exciting a rare earth element-added fiber with an excitation light source such as a semiconductor laser is amplified as it is guided in the fiber is used. .

  The sensor head 15 includes an optical component 15a including a ferromagnetic Faraday rotator and a polarization separation element, a sensor fiber 15b, and a mirror 15c connected to the tip of the sensor fiber 15b. The sensor fiber 15b is wound once around the conductor 1 to be measured.

  The optical fiber transmission line includes a first optical fiber transmission line 11 that connects the light source 10 and the sensor head 15, a second optical fiber transmission line 12 that connects the sensor head 15 and the photoelectric converter 20, and a first optical fiber. A transmission line 11 and a third optical fiber transmission line 13 connected by an optical coupler 16 are provided. More specifically, the first optical fiber transmission line 11 is connected to the input part of the optical component 15 a constituting the sensor head 15. The second optical fiber transmission line 12 has one end connected to the output part of the optical component 15 a constituting the sensor head 15 and the other end connected to the first light receiving element 21 of the photoelectric converter 20. The third optical fiber transmission line 13 has one end connected to the first optical fiber transmission line 11 by the optical coupler 16 and the other end connected to the second light receiving element 22 of the photoelectric converter 20.

  Each of these three optical fiber transmission lines uses, for example, a single mode optical fiber. Further, the second light receiving element 22 and the first light receiving element 21 convert the received optical signal into an electric signal, and both are constituted by photodiodes.

  The optical coupler 16 has a function of separating and extracting a part of an optical signal traveling in the first optical fiber transmission line 11. The extracted optical signal travels through the third optical fiber transmission line 13. The extracted optical signal has a signal level smaller than the optical signal traveling to the sensor head 15 in consideration of the optical loss at the sensor head 15. The respective lights transmitted through the second optical fiber transmission line 12 and the third optical fiber transmission line 13 are set so that the input light amounts of the optical signals incident on the photoelectric converter 20 are equal.

  By adopting the above configuration, the optical signal emitted from the light source 10 is input to the sensor head 15 through the first optical fiber transmission line 11. The sensor head 15 modulates the intensity of the input optical signal based on the alternating current measurement object that changes over time, and outputs the modulated optical signal. The output optical signal travels through the second optical fiber transmission line 12 and is input to the first light receiving element 21.

  On the other hand, the optical signal separated from the first optical fiber transmission line 11 by the optical coupler 16 travels through the third optical fiber transmission line 13 and enters the second light receiving element 22. Thus, the detection signal is supplied to the first light receiving element 21 and the reference signal for noise correction is supplied to the second light receiving element 22 in the photoelectric converter 20.

  In this embodiment, the optical coupler 16 is disposed near the sensor head 15. That is, in the conventional example shown in Patent Document 1 or the like, an optical coupler is disposed near the light source, and a part of the optical signal emitted from the light source is immediately separated and applied to the photoelectric converter. Then, it was made to isolate | separate in the position away from the light source 10. FIG. The separated position is a position close to the sensor head 15.

  Furthermore, the optical fiber transmission line length L2 of the second optical fiber transmission line 12 and the optical fiber transmission line length L3 of the third optical fiber transmission line 13 were made equal. The optical fiber transmission line length L1 of the first optical fiber transmission line 11 is very long, for example, 10 km to 20 km, and the length from the optical coupler 16 to the sensor head 15 is extremely short compared with the optical fiber transmission line length L1 and ignored. it can. Then, the total fiber transmission path length of the path where the optical signal emitted from the light source 10 reaches the photoelectric converter 20 via the sensor head 15 can be approximated to L1 + L2. Therefore, from L1 + L2 = L1 + L3, the light emitted from the light source 10 at the same time does not cause a time difference and is sent from the second optical fiber transmission line 12 and the third optical fiber transmission line 13 to the photoelectric converter 20 at the same timing. Incident. Therefore, the same light source noise is carried on the optical signals that are simultaneously incident on the first light receiving element 21 and the second light receiving element 22. Therefore, by correcting the light source noise using the optical signal incident on the second light receiving element 22, the light source noise is removed from the optical signal based on the AC measurement target incident from the first light receiving element 21, and an accurate output value is obtained. Can be obtained.

Specifically, the photoelectric converter 20 having the light source noise correction processing function is configured as follows. The first light receiving element 21 photoelectrically converts the optical signal from the sensor head 15 into an electrical signal. The optical signal has a light amount variation due to factors other than the measurement target in addition to the light amount variation associated with the alternating current that is the measurement target. Light quantity fluctuations due to factors other than the measurement target include a DC component (DC ₁ ) accompanying drift-like fluctuations and an AC component (AC _N ) accompanying relatively high-speed fluctuations caused by light source noise. The light amount fluctuation accompanying the alternating current to be measured is an AC component (AC _S ). Therefore, the electrical signal output from the first light receiving element 21 is DC ₁ + AC _{(S + N)} .

A first low-pass filter 23 and a first high-pass filter 24 are connected in parallel at the subsequent stage of the first light receiving element 21. The signal output from the first light receiving element 21 is input to the first low-pass filter 23 and the first high-pass filter 24, respectively, and the electric signal is separated into a DC component and an AC component by these filters. Therefore, DC ₁ is output from the first low-pass filter 23, and AC _{(S + N)} is output from the first high-pass filter 24.

A first divider 27 is connected downstream of the first low pass filter 23 and the first high pass filter 24. The first divider 27 calculates AC _{(S + N)} / DC ₁ and obtains a measured current signal M _{(S + N)} . The output of the first divider 27 is a current signal to be measured normalized by a DC component, and drift fluctuations of the DC ₁ can be corrected, but includes light source noise.

The second light receiving element 22 photoelectrically converts an incident optical signal (reference signal) into an electrical signal. This optical signal is separated by the optical coupler 16 before reaching the sensor head 15, and is equivalent to the optical signal emitted from the light source 10. Therefore, the optical signal includes a DC component (DC ₂ ) associated with drift-like fluctuations and an AC component (AC _N ) associated with relatively high-speed fluctuations due to light source noise. This AC component has no AC component associated with the AC current to be measured. Therefore, the electrical signal output from the second light receiving element 22 is DC ₂ + AC _(N) .

A second low-pass filter 25 and a second high-pass filter 26 are connected in parallel at the subsequent stage of the second light receiving element 22. The signal output from the second light receiving element 22 is input to the second low-pass filter 25 and the second high-pass filter 26, respectively, and the electrical signal is separated into a DC component and an AC component by these filters. Therefore, DC ₂ is output from the second low-pass filter 25, and AC _(N) is output from the second high-pass filter 26.

A second divider 28 is connected downstream of the second low pass filter 25 and the second high pass filter 26. The second divider 28 calculates AC _(N) / DC ₂ and normalizes it with a DC component to obtain a light source noise correction signal M _(N) that corrects drifting fluctuations.

  Then, the output of the first divider 27 and the output of the second divider 28 are respectively supplied to the subtractor 29, and the subtractor 29 subtracts the light source noise correction signal from the current signal to be measured. Since the drift-like fluctuation is corrected by dividing each by the divider and normalizing, two signals based on the light emitted from the light source 10 at the same time (current signal to be measured and light source noise correction signal) Thus, the light source noise component can be accurately removed.

  FIG. 2 shows a second embodiment of the photocurrent sensor according to the present invention. In this embodiment, similarly to the first embodiment, the installation position of the optical coupler 16 connected to the first optical fiber transmission line 11 is set to the sensor head 15 side, and the optical fiber transmission line length L2 of the second optical fiber transmission line 12 is set. The basic configuration of equalizing the optical fiber transmission line length L3 of the third optical fiber transmission line 13 is the same, and the internal configuration of the photoelectric converter 20 ′ is changed.

  That is, the photoelectric converter 20 used in the first embodiment includes a first divider 27 and a second divider 28. Since an IC having such a division function is expensive, there is a problem that the photocurrent sensor becomes expensive. In order to solve such a problem, in the present embodiment, a photoelectric converter 20 ′ capable of performing light source noise correction without using a divider is realized.

Specifically, the first automatic amplification adjuster 31 is disposed between the first light receiving element 21 and each filter (the first low-pass filter 23 and the first high-pass filter 24). Then, the first automatic amplification adjuster 31 feeds back the output (DC ₁ ′) of the first low-pass filter 23 and adjusts the amplification factor so that the output (DC ₁ ′) becomes a reference value. There are cases where the amplification factor exceeds 1 (increase) and becomes less than 1 (decrease). Further, the output of the first high-pass filter 24 is input to one (+ side) of the subtractor 29.

As described in the first embodiment, the electrical signal output from the first light receiving element 21 is DC ₁ + AC _{(S + N)} . Then, the signal is amplified by the first automatic amplification regulator 31 to become DC ₁ '+ AC _{(S + N)} ', and is separated into respective components by each filter. Therefore, the first low-pass filter 23 outputs DC ₁ ′, and the first high-pass filter 24 outputs AC _{(S + N)} ′.

Similarly, a second automatic amplification adjuster 32 is disposed between the second light receiving element 22 and each filter (second low-pass filter 25, second high-pass filter 26). Then, the second automatic amplification adjuster 32 feeds back the output (DC ₂ ′) of the second low-pass filter 25 and adjusts the amplification factor so that the output (DC ₂ ′) becomes a reference value. There are cases where the amplification factor exceeds 1 (increase) and becomes less than 1 (decrease). The output of the second high pass filter 26 is input to the other (− side) of the subtractor 29.

Then, the electric signal (DC ₂ + AC _(N) ) output from the second light receiving element 22 is amplified by the second automatic amplification regulator 32 to become DC ₂ ′ + AC _(N) ′, and each component is received by each filter. Separated. Therefore, the second low-pass filter 25 outputs DC ₂ ′, and the second high-pass filter 26 outputs AC _(N) ′.

The reference value in the first automatic amplification regulator 31 and the reference value in the second automatic amplification regulator 32 are made equal. Thus, 'the output of the second low-pass filter 25 _(DC 2 output of the first low-pass filter 23 _(DC 1)') are equal.

Thus, since the DC component of the signal after amplification processing based on the current signal to be measured and the signal after amplification processing based on the light source noise correction signal are equal, even if the AC components are subtracted directly, This is similar to the subtraction process of the value obtained by the ratio by the divider, and light source noise correction can be performed. Therefore, in this embodiment, since an expensive divider is not required, the entire photocurrent sensor can be configured at low cost.
In addition, since another structure and effect are the same as that of 1st embodiment mentioned above, the same code | symbol of a corresponding member is attached | subjected and the detailed description is abbreviate | omitted.

  FIG. 3 shows a third embodiment of the photocurrent sensor according to the present invention. In the present embodiment, as in the second embodiment, a photoelectric converter 20 ″ that does not use a divider is used. Specifically, the photoelectric converter 20 ″ includes the first light receiving element 21. The first low-pass filter 23 and the first high-pass filter 24 are connected in parallel at the subsequent stage, and the second low-pass filter 25 and the second high-pass filter 26 are connected in parallel at the subsequent stage of the second light receiving element 22. The outputs of both high-pass filters are input to the subtractor 29, respectively.

  In addition, an automatic optical variable attenuator is provided in the preceding stage of the photoelectric converter 20 ″ so as to adjust the optical signal traveling through the optical fiber transmission line so that the incident light amounts of the two optical signals to the photoelectric converter 20 ″ are equalized. I made it. That is, the first automatic optical variable attenuator 33 is provided in the second optical fiber transmission line 12, and the second automatic optical variable attenuator 34 is provided in the third optical fiber transmission line 13.

Then, the first automatic optical variable attenuator 33 feeds back the output (DC ₁ ′) of the first low-pass filter 23 and adjusts the attenuation so that the output (DC ₁ ′) becomes a reference value. The second automatic optical variable attenuator 34 feeds back the output (DC ₂ ′) of the second low-pass filter 25 and adjusts the attenuation so that the output (DC ₂ ′) becomes a reference value.

The reference value in the first automatic optical variable attenuator 33 and the reference value in the second automatic optical variable attenuator 34 are made equal. As a result, the DC components (DC ₁ ′, DC ₂ ′) of the optical signals output from the first automatic optical variable attenuator 33 and the second automatic optical variable attenuator 34 become equal. Even if the DC component of the optical signal emitted from the light source 10 may fluctuate, both signals are attenuated, so that the state of DC ₁ ′ = DC ₂ ′ can be easily and accurately maintained.

As a result, the electric signal (DC ′ ₁ + AC ′ _{(S + N)} ) input to the first light receiving element 21 and obtained by photoelectric conversion, and the electric signal input to the second light receiving element 22 and obtained by photoelectric conversion are obtained. Since the DC components of the signal (DC ₂ '+ AC' _(N) ) are equal (DC ' ₁ = DC' ₂ ), the difference between the AC components is obtained in the same manner as in the second embodiment. This is similar to the subtraction process of the value obtained by the ratio by the divider, and light source noise correction can be performed. Therefore, in this embodiment, since an expensive divider is not required, the entire photocurrent sensor can be configured at low cost.
In addition, since another structure and effect are the same as that of 1st embodiment mentioned above, the same code | symbol of a corresponding member is attached | subjected and the detailed description is abbreviate | omitted.

DESCRIPTION OF SYMBOLS 1 Conductor 10 Light source 11 1st optical fiber transmission path 12 2nd optical fiber transmission path 13 3rd optical fiber transmission path 15 Sensor head 16 Optical coupler (light separation means)
20 photoelectric converter 20 ′ photoelectric converter 20 ″ photoelectric converter 21 first light receiving element 22 second light receiving element 23 first low pass filter 24 first high pass filter 25 second low pass filter 26 second high pass filter 27 first divider 28 Second divider 29 Subtractor 31 First automatic amplification regulator 32 Second automatic amplification regulator 33 First automatic optical variable attenuator 34 Second automatic optical variable attenuator

Claims (4)

A light source;
A first optical fiber transmission line for transmitting an optical signal emitted from the light source;
A sensor head connected to the distal end side of the first optical fiber transmission line, to which the optical signal is input;
A second optical fiber transmission line for transmitting a detection signal output from the sensor head;
A light separating means for taking out a part of the optical signal transmitted through the first optical fiber transmission line as a reference signal;
A third optical fiber transmission line for transmitting the reference signal extracted by the light separation means;
A photoelectric converter to which the second optical fiber transmission line and the third optical fiber transmission line are respectively connected;
The photoelectric converter includes a correction function for performing light source noise correction by subtracting a signal based on the reference signal from a signal based on the input detection signal,
The photocurrent sensor is characterized in that the light separation means is disposed on the sensor head side, and the transmission path length of the second optical fiber transmission path is equal to the transmission path length of the third optical fiber transmission path. An adjustment function is provided to equalize the DC component of the signal based on the detection signal and the DC component of the signal based on the reference signal,
The photocurrent sensor according to claim 1, wherein the subtracting subtracts an AC component of a signal based on the reference signal from an AC component of a signal based on the detection signal. The adjustment function is arranged in a subsequent stage of the first automatic amplification adjuster arranged in the subsequent stage of the first light receiving element for the detection signal mounted in the photoelectric converter and in the subsequent stage of the second light receiving element for the reference signal. A second automatic amplification regulator,
The first automatic amplification regulator and the second automatic amplification so that the DC component of the signal output from the first automatic amplification regulator and the DC component of the signal output from the second automatic amplification regulator are equal. The photocurrent sensor according to claim 2, wherein the amplification factor of the regulator is configured to be feedback-controlled. The adjustment function includes a first automatic optical variable attenuator mounted on the second optical fiber transmission line, and a second automatic optical variable attenuator mounted on the third optical fiber transmission line,
The first automatic optical variable attenuator and the second automatic optical variable attenuator attenuate the signal levels of the detection signal and the reference signal, respectively, and input the DC component of the detection signal to the photoelectric converter, The feedback control of the attenuation amounts of the first automatic optical variable attenuator and the second automatic optical variable attenuator is performed so that the DC components of the reference signal are equal to each other. Photocurrent sensor.

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