JP6624638B2 - Photocurrent sensor - Google Patents

Description

  The present invention relates to a photocurrent sensor.

  The photocurrent sensor for measuring the alternating current, for example, guides the light emitted from the light source to the sensor head, modulates the intensity of the light based on the alternating current that is the time-varying alternating current measurement object, and modulates the optical signal. Is converted into an electric signal by a photoelectric conversion element, an AC component and a DC component included in the electric signal are separated, a current signal to be measured is obtained from a 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 a DC component varies. Factors of this drift-like variation include a variation in the light amount of the optical signal emitted from the light source, a variation in the optical loss of the optical fiber transmission line, and a variation in the optical loss of the optical components such as the sensor head and the optical coupler. By calculating AC / DC, these drift-like fluctuations can be cut.

  In this basic measurement method, the influence of light source noise generated from the light source and fluctuating at a relatively high speed affects the sensor output (current value). Therefore, as an invention for removing the influence of such light source noise, for example, there is an “intensity modulation type optical sensor and a 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 a ratio between an AC component and a DC component of the reference signal, and obtains a 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 line accident section detecting device, a system accident judging device, and the like, a sensor head is installed at a position distant from the light source in order to detect an accident or the like occurring in a remote place. Therefore, the transmission path length of the optical fiber transmission path connecting the light source and the sensor head also becomes longer. The transmission path length is, for example, about 10 km to 20 km, and more than that. Further, a photoelectric converter that performs the above-described calculation of the current signal to be measured and the light source noise correction signal and correction processing is installed near the light source.

  Therefore, the reference signal branches off relatively quickly after being emitted from the light source and reaches the photoelectric converter, but the optical signal for obtaining the current signal to be measured travels along a long-distance optical fiber transmission line (outbound path). The light reaches the sensor head, and then travels along the optical fiber transmission path (return path) to reach the photoelectric converter. Therefore, 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 length of the transmission path 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 measured current signal is in a state different from the state of the light source noise when the measured current signal is emitted, and there is a problem that accurate correction cannot be performed.

To solve the problems described above, the present invention includes a light source, a first optical fiber transmission path for transmitting the optical signal emitted from the light source, is connected to the distal end side of the first optical fiber transmission path, A sensor head to which the optical signal is input, a second optical fiber transmission line for transmitting a detection signal output from the sensor head, and a reference signal indicating a part of the optical signal transmitted through the first optical fiber transmission line As a light separating means, a third optical fiber transmission line for transmitting the reference signal extracted by the light separating means, and a photoelectric conversion unit to which the second optical fiber transmission line and the third optical fiber transmission line are respectively connected. Wherein the photoelectric converter has a correction function of subtracting a signal based on the reference signal from a signal based on the input detection signal to perform light source noise correction, and the light separating unit includes a sensor. Place the head side, it is assumed that equal the transmission path length of said third optical fiber transmission path and the transmission path length of said second optical fiber transmission path. The light separating means corresponds to an optical coupler in the embodiment.

  According to the present invention, the light separating means is arranged on the sensor head side, and the optical fiber transmission line length of the second optical fiber transmission line is made equal to the optical fiber transmission line length of the third optical fiber transmission line. The light emitted from the light source enters the photoelectric converter at the same timing from each of the second optical fiber transmission line and the third optical fiber transmission line without generating a time difference. Therefore, even when the installation position of the light source and the sensor head is very far, 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 simultaneously emitted from the light source. The light source noise is based on the light 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.

(1) On the premise described above, an adjustment function for equalizing the DC component of the signal based on the detection signal and the DC component of the signal based on the reference signal is provided, and the subtraction is performed from the AC component of the signal based on the detection signal. , The AC component of the signal based on the reference signal may be subtracted.

  Usually, since the signal levels of the detection signal and the reference signal are 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 between the AC component and the DC component is obtained and normalized. The subtracted signals need to be subtracted. An expensive divider is required for such normalization. In the present invention, since the DC component is equal, the signal level of the signal based on the detection signal is equal to the signal level of the signal based on the reference signal, and the light source noise can be accurately corrected by directly subtracting the AC components. Therefore, since a divider or the like is not required, the photoelectric sensor can be configured at low cost.

(2) As a more specific invention for realizing the invention of (1) , for example, the adjustment function is provided in a stage following the first light receiving element for the detection signal mounted on the photoelectric converter. One automatic amplification adjuster, comprising a second automatic amplification adjuster disposed after the second light receiving element for the reference signal, the DC component of the signal output from the first automatic amplification adjuster, Preferably, the amplification factors of the first and second automatic amplification controllers are feedback-controlled so that the DC components of the signals output from the two automatic amplification controllers are equal.

(3) As a more specific invention for realizing the invention of (1) , for example, the adjusting function includes a first automatic optical variable attenuator mounted on the second optical fiber transmission line, and the third optical fiber. It comprises a second automatic optical variable attenuator mounted on the transmission line, and 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 feedback control of the attenuation 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 is good to be constituted so that.

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

It is a figure showing preferred 1st embodiment of a photocurrent sensor concerning the present invention. It is a figure showing the suitable 2nd embodiment of the photocurrent sensor concerning the present invention. It is a figure showing the suitable 3rd embodiment of the photocurrent sensor concerning the present invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. 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 arranged so as to go around a conductor under test 1 through which a current to be inspected flows, a photoelectric converter 20, and an optical fiber connecting them. A transmission path is provided.

  As the light source 10, for example, a light source (ASE) utilizing a phenomenon in which spontaneous emission light generated by exciting a rare earth element-doped fiber with a pumping light source such as a semiconductor laser is amplified as it propagates through the fiber is used. .

  The sensor head 15 includes an optical component 15a including a ferromagnetic Faraday rotator and a polarization splitting element, a sensor fiber 15b, and a mirror 15c connected to a 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 connecting the light source 10 and the sensor head 15, a second optical fiber transmission line 12 connecting the sensor head 15 and the photoelectric converter 20, and a first optical fiber A third optical fiber transmission line 13 connected to the transmission line 11 by an optical coupler 16 is provided. More specifically, the first optical fiber transmission line 11 is connected to an input part of an optical component 15a 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 the 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 a received optical signal into an electric signal, and are both 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 that of the optical signal traveling to the sensor head 15 in consideration of the light loss in 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 become equal.

  With the above configuration, an 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 an input optical signal based on a time-varying AC measurement target, and outputs a modulated optical signal. The output optical signal travels through the second optical fiber transmission line 12 and enters 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 in the third optical fiber transmission line 13 and enters the second light receiving element 22. Thus, the photoelectric converter 20 is provided with the detection signal to the first light receiving element 21 and the reference signal for noise correction to the second light receiving element 22.

  Then, in the present embodiment, the optical coupler 16 is arranged near the sensor head 15. That is, in the conventional examples shown in Patent Document 1 and the like, an optical coupler is arranged near a light source, and a part of an optical signal emitted from the light source is immediately separated and applied to a photoelectric converter. Then, the light source 10 is separated at a position away from the light source 10. The distant position is a position close to the sensor head 15.

  Further, the optical fiber transmission line length L2 of the second optical fiber transmission line 12 was made equal to the optical fiber transmission line length L3 of the third optical fiber transmission line 13. 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 to the optical fiber transmission line length L1 and is ignored. it can. Then, the total fiber transmission path length of the path from the optical signal emitted from the light source 10 to 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 is transmitted 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 without generating a time difference. Incident. Therefore, optical signals that are simultaneously incident on the first light receiving element 21 and the second light receiving element 22 have the same light source noise. 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 object incident from the first light receiving element 21, and the accurate output value is obtained. Can be obtained.

The photoelectric converter 20 having the light source noise correction processing function is specifically configured as follows. The first light receiving element 21 photoelectrically converts an optical signal from the sensor head 15 into an electric signal. The optical signal has a light quantity fluctuation due to factors other than the measurement target in addition to a light quantity fluctuation due to the AC current to be measured. Fluctuations in the light amount due to factors other than the measurement target include a DC component (DC ₁ ) accompanying a drift-like variation and an AC component (AC _N ) accompanying a relatively high-speed variation due to light source noise. Quantity variation due to a measurement target alternating current is an AC component (AC _S). Therefore, the electric 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 downstream of the first light receiving element 21. The signal output from the first light receiving element 21 is input to a first low-pass filter 23 and a 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 to a stage subsequent to the first low-pass filter 23 and the first high-pass filter 24. The first divider _{27, AC (S + N) /} DC 1 to arithmetic processing, and requests the measured current signal _{M (S + N).} The output of the first divider 27 is a current signal to be measured normalized by the DC component, and the drift-like fluctuation of the DC ₁ can be corrected, but includes light source noise.

The second light receiving element 22 photoelectrically converts the incident optical signal (reference signal) into an electric 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 ) accompanying a drift-like variation and an AC component (AC _N ) accompanying a relatively high-speed variation due to light source noise. This AC component has no AC component associated with the AC current to be measured. Therefore, the electric 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 a second low-pass filter 25 and a second high-pass filter 26, respectively, and the electric 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 to a stage subsequent to the second low-pass filter 25 and the second high-pass filter 26. The second divider 28 calculates the light source noise correction signal M _{(N) in} which AC _(N) / DC ₂ is subjected to arithmetic processing and normalized by the DC component, thereby correcting drift-like fluctuation.

  Then, the output of the first divider 27 and the output of the second divider 28 are given to a subtractor 29, and the subtracter 29 subtracts the light source noise correction signal from the current signal to be measured. Since the drift-like fluctuation is corrected by dividing 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) , 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 the present 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 making the optical fiber transmission line length L3 equal to that 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 the first divider 27 and the second divider 28. Since an IC having such a division function is expensive, there is a problem that a 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 arranged between the first light receiving element 21 and each of the filters (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 the reference value. The amplification factor may be more than 1 (increase) or less than 1 (decrease). The output of the first high-pass filter 24 is input to one side (+ side) of the subtractor 29.

As described in the first embodiment, the electric 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 adjuster 31 to be DC ₁ ′ + AC _{(S + N)} ′, and is separated into respective components by each filter. 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.

Similarly, a second automatic amplification adjuster 32 is arranged between the second light receiving element 22 and each of the filters (the second low-pass filter 25 and the 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 the reference value. The amplification factor may be more than 1 (increase) or 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 adjuster 32 to become DC ₂ ′ + AC _(N) ′, and each component is applied to each filter. Is separated into Therefore, DC ₂ ′ is output from the second low-pass filter 25, and AC _(N) ′ is output from the second high-pass filter 26.

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

As described above, since the DC component of the signal after the amplification process based on the measured current signal and the signal after the amplification process based on the light source noise correction signal are equal, even if the AC components are directly subtracted from each other, the first embodiment Light source noise correction can be performed in the same manner as the subtraction processing of the value obtained by the ratio in the divider. Therefore, in this embodiment, since an expensive divider is not required, the entire photocurrent sensor can be configured at low cost.
Since the other configuration and operation and effect are the same as those of the above-described first embodiment, corresponding members are denoted by the same reference numerals, and detailed description thereof will be omitted.

  FIG. 3 shows a third embodiment of the photocurrent sensor according to the present invention. In the present embodiment, similarly to the second embodiment, the photoelectric converter 20 "that does not use a divider is configured to be used. Specifically, the photoelectric converter 20" is a component of 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 the high-pass filters are input to the subtractor 29, respectively.

  Also, an automatic optical variable attenuator is provided in each of the preceding stages of the photoelectric converter 20 ″ so as to adjust the optical signal traveling through the optical fiber transmission line so that the amount of incident light of the two optical signals to the photoelectric converter 20 ″ is equalized. I made it. That is, the first automatic optical variable attenuator 33 was provided on the second optical fiber transmission line 12, and the second automatic optical variable attenuator 34 was provided on 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 the 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 amount of attenuation so that the output (DC ₂ ′) becomes a reference value.

The reference value in the first automatic optical variable attenuator 33 is equal to the reference value in the second automatic optical variable attenuator. Thereby, 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 fluctuates, both signals are attenuated, so that the state of DC ₁ ′ = DC ₂ ′ can be easily and accurately maintained, which is preferable.

As a result, an electric signal (DC ′ ₁ + AC ′ _{(S + N)} ) input to the first light receiving element 21 and obtained by photoelectric conversion, and an electric signal input to the second light receiving element 22 and obtained by photoelectric conversion Since the DC component of the signal (DC ₂ ′ + AC ′ _(N) ) is equal (DC ′ ₁ = DC ′ ₂ ), the difference between the AC components is obtained as in the second embodiment, thereby obtaining the signal of the first embodiment. Light source noise correction can be performed in the same manner as in the subtraction processing of the value obtained by the ratio in the divider. Therefore, in this embodiment, since an expensive divider is not required, the entire photocurrent sensor can be configured at low cost.
Since the other configuration and operation and effect are the same as those of the above-described first embodiment, corresponding members are denoted by the same reference numerals, and detailed description thereof will be omitted.

DESCRIPTION OF SYMBOLS 1 Conductor under test 10 Light source 11 First optical fiber transmission line 12 Second optical fiber transmission line 13 Third optical fiber transmission line 15 Sensor head 16 Optical coupler (optical separation means)
Reference Signs List 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 adjuster 32 Second automatic amplification adjuster 33 First automatic optical variable attenuator 34 Second automatic optical variable attenuator

Claims (3)

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 and receiving the optical signal,
A second optical fiber transmission line for transmitting a detection signal output from the sensor head,
Light separating means for extracting 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 separating 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 has a correction function of performing light source noise correction by subtracting a signal based on the reference signal from a signal based on the input detection signal,
The light separating means is disposed on the sensor head side, and equalizes the transmission path length of the second optical fiber transmission path and the transmission path length of the third optical fiber transmission path ,
An adjustment function for equalizing the DC component of the signal based on the detection signal and the DC component of the signal based on the reference signal is provided.
The said subtraction subtracts the AC component of the signal based on the said reference signal from the AC component of the signal based on the said detection signal, The photocurrent sensor characterized by the above-mentioned. The adjustment function is a first automatic amplification adjuster disposed after the first light receiving element for the detection signal mounted on the photoelectric converter, and disposed after the second light receiving element for the reference signal. Equipped with a second automatic amplification adjuster,
The first automatic amplification controller and the second automatic amplifier are controlled such that the DC component of the signal output from the first automatic amplification controller is equal to the DC component of the signal output from the second automatic amplification controller. 2. The photocurrent sensor according to claim 1, wherein the amplification factor of the adjuster is 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 a DC component of the detection signal input to the photoelectric converter, 2. The apparatus according to claim 1, wherein an amount of attenuation of the first automatic optical variable attenuator and the amount of attenuation of the second automatic optical variable attenuator are feedback-controlled so that a DC component of the reference signal becomes equal. Photocurrent sensor.

Images