JP6563760B2 - Method for improving temperature characteristics of optical CT - Google Patents

Description

  The present invention relates to a method for improving temperature characteristics of an optical CT (a reflection type current sensor or a transmission type current sensor using an optical fiber) using a reflection type current sensor as a temperature sensor.

An optical CT, particularly a reflection type current sensor, is a device that measures the current that generates the magnetic field using the Faraday effect in which the plane of polarization of light passing through an optical fiber is rotated by the action of a magnetic field. It is used to measure the current value in an insulated switchgear (GIS).
In this type of optical CT, since the Faraday rotation angle of the Faraday element generally has temperature dependence, various methods for improving the temperature characteristics of the Faraday element have been proposed.

  First, as a basic idea, there is a method (first prior art) using a Faraday element having a temperature coefficient of Faraday rotation angle at the time of magnetic saturation as small as possible.

  Further, in Patent Document 1, the Faraday rotation angle at the time of magnetic saturation is set to 22.5 degrees + α degrees at a predetermined temperature, and the Faraday rotation angle is changed from 22.5 degrees to α degrees, so that the measured current value is A current measuring device (second prior art) is described in which the fluctuation range of the ratio error is suppressed to ± 0.5 [%], in other words, the gradient of the temperature characteristic of the optical CT is changed to reduce the gradient. Has been.

In Patent Document 2, a signal processing device for measuring the Faraday rotation angle is provided with a temperature sensor for measuring the ambient temperature, and the temperature measured by the temperature sensor is estimated as the ambient temperature of the sensor head, and the estimated temperature is used as a light sensor. A temperature characteristic correcting device (third prior art) for correcting the output of CT is described.
Further, in Patent Document 3 and Non-Patent Document 1, in a signal processing apparatus, two signals obtained by separating light from a Faraday element by a polarization separation element are amplified with different gains, and then one output is inverted. Thus, there is described a temperature characteristic improving method (fourth prior art) in which the gradient of the temperature characteristic of the optical CT is changed to make the gradient small by adding to the other.

JP 2010-271292 A (paragraphs [0048] to [0058] etc.) JP 2010-71934 A (paragraphs [0018] to [0020] etc.) JP 2010-261443 A (paragraphs [0029] to [0047] etc.)

Kondo Reishi, Kurosawa Kiyoshi, “Temperature characteristics improvement method of optical fiber current sensor”, IEEJ Transactions B, Vol. 130, No. 4, 2010

The first prior art focuses on the temperature dependence of the Faraday rotation angle during magnetic saturation. However, the temperature characteristics of optical CT depend on the temperature dependence of the sensor head including the optical fiber for the sensor (lead glass fiber, quartz fiber, etc.) and the optical part and the temperature dependence of the signal processing device. Is determined by the temperature coefficient of the Verde constant of the optical fiber for the sensor and the temperature coefficient of the Faraday rotation angle of the Faraday element constituting the optical unit.
Therefore, even if a Faraday element having a temperature coefficient of the Faraday rotation angle as small as possible is used, the optical CT can be used as long as the temperature dependency of the optical fiber for the sensor is not lost (in the case of lead glass fiber: 0.01 [% / deg]). Has a temperature dependency of about 1.1 [%] in its operating temperature range (−40 to +70 [° C.]).

The second prior art adjusts the temperature coefficient of the Faraday rotation angle to reduce the gradient of the temperature characteristics of the optical CT, and the fourth prior art improves the calculation contents in the signal processing device to obtain the same effect. However, since the temperature dependence of optical CT changes in a curve rather than linearly, the resulting temperature characteristic improvement effect is the accuracy required for optical CT (for current value measurement applied to GIS etc.) In the optical CT, it is difficult to satisfy the fluctuation range of the ratio error within ± 0.2 [%].
Furthermore, it is difficult to adjust the variation in temperature characteristics of individual optical CTs after the optical CTs are assembled.

  In the third prior art, since it is physically impossible to dispose the signal processing device and the sensor head at the same place, it is inevitable that a difference occurs between the ambient temperatures. For example, when the signal processing device is placed indoors and the sensor head is placed outdoors, the difference in ambient temperature increases depending on the installation environment of the signal processing device and sensor head, and the optical CT output Temperature compensation accuracy decreases.

  In addition, in the field of protective relays and the like, transmissive current sensors are used to measure a large current of 100 to 180 [kA]. These protective transmissive current sensors are also compared in the rated current region. There is a demand for minimizing the error fluctuation range.

  Therefore, a problem to be solved by the present invention is to provide a method for improving the temperature characteristics of an optical CT that satisfies the measurement accuracy required for the optical CT in a predetermined operating temperature range.

In order to solve the above-mentioned problem, the invention according to claim 1 is arranged so as to circulate a conductor through which a current to be measured flows, and an optical fiber for a sensor having a mirror at an end,
An optical unit that includes a polarization / analyzer and a Faraday element, and separates the reflected light incident on the sensor optical fiber and subjected to Faraday rotation by the current to be measured into a first signal and a second signal whose polarization planes are orthogonal to each other And a sensor head, and
The first signal and the second signal are input via a light receiving element, respectively, and the magnitude of the current to be measured based on the degree of modulation calculated from the ratio between the AC component and the DC component of the output signal of the light receiving element. A signal processing device for measuring,
In optical CT configured as a reflective current sensor,
The first modulation factor and the second modulation factor are calculated by normalizing the modulation factors based on the first signal and the second signal, respectively, and calculating the first modulation factor and the second modulation factor independent of the current component. Create a temperature characteristic of the difference in the operating temperature range by calculating the difference with the degree in advance,
Using the temperature characteristic, the ambient temperature of the sensor head is detected from the temperature corresponding to the difference, and temperature characteristic correction data corresponding to the detected ambient temperature is created in advance,
The current to be measured measured by the signal processing device is corrected by the temperature characteristic correction data to compensate the temperature of the current to be measured.

  According to a second aspect of the present invention, in the method for improving temperature characteristics of an optical CT according to the first aspect, the modulation degree based on the first signal and the second signal is divided by the effective value equivalent value of the current to be measured. To normalize.

  According to a third aspect of the present invention, in the temperature characteristic improvement method of the optical CT according to the first or second aspect, the temperature characteristic correction data is an average of modulation degrees based on the first signal and the second signal. The value is data obtained by normalizing the value by an average value at a reference temperature of the modulation degree based on the first signal and the second signal.

The invention according to claim 4 is an optical fiber for sensor arranged so as to go around a conductor through which a current to be measured flows.
A sensor that separates transmitted light incident on the sensor optical fiber from a polarizer and subjected to Faraday rotation by the current to be measured into a first signal and a second signal whose polarization planes are orthogonal to each other. Head and
The first signal and the second signal are input through a light receiving element, respectively, and the magnitude of the current to be measured is based on the modulation degree calculated from the ratio between the AC component and the DC component of the output signal of the light receiving element. Signal processing device for measuring the thickness,
In a light CT in which a transmissive current sensor provided with is disposed in proximity to the reflective current sensor according to any one of claims 1 to 3,
The temperature information detected as the ambient temperature of the sensor head of the reflective current sensor is also used as the ambient temperature of the sensor head of the transmissive current sensor.

According to the present invention, within the operating temperature range of the reflective current sensor for measuring current, the fluctuation range of the ratio error of the measured current value is suppressed to within ± 0.2 [%] and detected by the reflective current sensor. By using the temperature information also for a transmission type current sensor that is used for overcurrent protection or the like, the fluctuation range of the ratio error can be made smaller than that of the related art.
Thereby, it is possible to provide an optical CT capable of realizing a highly accurate current measurement operation and protection operation.

It is a whole block diagram of optical CT concerning a 1st embodiment of the present invention. It is a block diagram of the optical part in FIG. It is a block diagram of the analog signal processing part in FIG. FIG. 2 is a functional block diagram of a digital signal processing unit in FIG. 1. It is explanatory drawing of the principal part of FIG. It is a figure which shows the modulation | alteration degree of signal Sig1, Sig2, and the temperature characteristic of the difference. It is a conceptual diagram which shows the procedure which normalizes the modulation degree of signal Sig1, Sig2, and calculates | requires the difference. It is a functional block diagram of the temperature measurement part in FIG. It is a functional block diagram of the temperature correction part in FIG. It is the figure which showed notionally the modulation degree in the temperature correction part of FIG. 9, the average value, and temperature characteristic correction data. It is a figure which shows the ratio error of the to-be-measured current by the reflection type current sensor before temperature characteristic improvement. It is a figure which shows the ratio error of the to-be-measured current by the reflection type current sensor after temperature characteristic improvement in 1st Embodiment of this invention. It is a whole block diagram of 2nd Embodiment of this invention. It is a figure which shows the ratio error of the to-be-measured current by the transmission type current sensor before temperature characteristic improvement. It is a figure which shows the ratio error of the to-be-measured current by the transmission type current sensor after temperature characteristic improvement in 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 is an overall configuration diagram of an optical CT (reflection type current sensor) according to the first embodiment of the present invention, and this optical CT includes a signal processing device 100 and a sensor head 20.

In the signal processing apparatus 100, 10 is a light source unit, 11 is a light source unit, 12 is an optical circulator, 13 is a transmission optical fiber, and light emitted from the light source unit 11 passes through the optical circulator 12 and the transmission optical fiber 13. And sent to the optical unit 21 of the sensor head 20.
The optical unit 21 is configured as shown in FIG. 2, and includes a polarization / analyzer 21a, a lens 21b, a Faraday element 21c made of a Faraday rotator 21d such as a garnet crystal and a permanent magnet 21e, and Faraday rotation. A sensor optical fiber 22 such as a lead glass fiber is disposed on the exit side of the child 21d. Reference numeral 24 denotes a protective tube.

As shown in FIG. 1, the sensor optical fiber 22 is provided with a mirror 23 at its tip, and is arranged so as to go around the conductor through which the current I to be measured flows. Here, the mirror 23 may be a flat mirror fixed to the tip of the sensor optical fiber 22 or a mirror surface formed on the tip of the sensor optical fiber 22 by vapor deposition.
In the optical unit 21 described above, light incident on the Faraday element 21c from the transmission optical fiber 13 via the polarization / analyzer 21a and the lens 21b undergoes Faraday rotation of 22.5 degrees and enters the sensor optical fiber 22. To do. Incident light to the sensor optical fiber 22 undergoes Faraday rotation by the magnetic field generated by the measured current value I, is reflected by the mirror 23, and enters the Faraday element 21c from the sensor optical fiber 22 again. This incident light undergoes an additional Faraday rotation of 22.5 degrees, and is further separated by the polarization / analyzer 21a into two linearly polarized components whose polarized inner surfaces are orthogonal to each other.

  Then, one component enters the second light receiving element (photodiode) PD2 in the signal processing apparatus 100 described later from the transmission optical fiber 72 as the second signal Sig2. The other component returns from the transmission optical fiber 13 to the optical circulator 12, and enters the first light receiving element (photodiode) PD1 in the signal processing device 100 from the transmission optical fiber 71 as the first signal Sig1.

Next, FIG. 3 shows a configuration of the analog signal processing unit 40 in the signal processing apparatus 100.
In FIG. 3, the first signal Sig1 is converted into a current signal by the light receiving element PD1, and converted into a voltage signal by the I / V conversion unit 41a. Since this voltage signal is obtained by superimposing the AC component AC1 on the DC component DC1, the output of the I / V conversion unit 41a is passed through the low-pass filter 42a to extract the DC component DC1, and at the subtraction unit 43a, the I / V The AC component AC1 is extracted by subtracting the DC component DC1 from the output of the V converter 41a.
Similarly, with respect to the second signal Sig2, the DC component DC2 and the AC component AC2 are extracted by the actions of the I / V conversion unit 41b, the low-pass filter 42b, and the subtraction unit 43a.

  These direct current components DC1 and DC2 and alternating current components AC1 and AC2 are converted into digital signals by the AD converter 50 in FIG. 1 and input to a digital signal processing unit 60 such as an FPGA (Field-Programmable Gate Array).

FIG. 4 is a functional block diagram realized by software in the digital signal processing unit 60.
The modulation degree calculation means 61 divides the AC component AC1 of the signal Sig1 by the DC component DC1, and similarly divides the AC component AC2 of the signal Sig2 by the DC component DC2, thereby obtaining the modulation degree ( AC1 / DC1) and (AC2 / DC2) are calculated. Note that the modulation degrees of the signals Sig1 and Sig2 are opposite to each other.

These modulation degrees (AC1 / DC1) and (AC2 / DC2) are input to the current component calculation means 62, and by obtaining the difference between the modulation degrees as shown in FIG. 5, the Faraday rotation angle by the measured current value I is obtained. Current component (current component that is not temperature compensated) I _k can be obtained. Variations in detection sensitivity due to changes in received light power and variations in characteristics of the light receiving elements PD1, PD2, etc., due to normalization by the DC component of the AC component in the modulation degree calculating means 61 and averaging processing in the current component calculating means 62. Can be canceled.

Here, the modulation degrees (AC1 / DC1) and (AC2 / DC2) of the signals Sig1 and Sig2 calculated by the modulation degree calculation means 61 are actually curves, but these are approximated by a linear line and predetermined. When the temperature characteristics in the ambient temperature range (for example, −40 ° to +80 [° C.]) are obtained, the characteristic lines P1 (Δ plots) and P2 (■ plots) in FIG. 6 are obtained. Further, the difference between the two is as shown by the characteristic line P3 in FIG.
These characteristic lines P1, P2, and P3 can be obtained in advance, and the ambient temperature of the sensor head 20 can be estimated by using the characteristic line P3.

  However, the modulation degrees (AC1 / DC1) and (AC2 / DC2) of the signals Sig1 and Sig2 are signals proportional to the measured current value I, and do not change only by the ambient temperature. Therefore, when the ambient temperature is estimated based on the difference of each modulation degree, each modulation degree is normalized so as not to depend on the measured current value I, and each modulation degree that does not depend on the current value and the temperature characteristics of the difference. Need to get.

Now, the modulation factor (AC1 / DC1) of the first signal Sig1 is m1 · sin (ωt), and the modulation factor (AC2 / DC2) of the second signal Sig2 that is in reverse phase to the signal Sig1 is − Let m2 · sin (ωt).
When the measured current component of the modulation degree is m · sin (ωt), the effective value equivalent value is (m / √2). Note that m = m1 − (− m2) = m1 + m2. When the modulation degree of the signals Sig1 and Sig2 is respectively divided and normalized by the effective value equivalent value (m / √2), Expressions 1 and 2 are obtained.
[Formula 1]
M1 = m1 · sin (ωt) / (m / √2) = √2 · m1 · sin (ωt) / m
[Formula 2]
M2 = −m2 · sin (ωt) / (m / √2) = − √2 · m2 · sin (ωt) / m

  FIG. 7A conceptually shows the normalization described above, and the degree of modulation of the signals Sig1 and Sig2 is divided by the effective value equivalent value (m / √2) of the measured current component. The obtained characteristics (temperature characteristics) M1 and M2 are as shown in the lower part of FIG. FIG. 7B shows the extracted characteristics M1 and M2.

  Now, when the ΔM characteristic is obtained so that the difference ΔM between the characteristics M1 (20) and M2 (20) when the reference temperature of the ambient temperature is 20 ° C., for example, is 0, as shown in FIG. Become. This ΔM characteristic indicates the relationship between the ambient temperature T [° C.] and the modulation degree difference ΔM, and can be obtained for each sensor head, so it is prepared in advance in the form of a table or the like.

FIG. 8 is a functional block diagram of the temperature measurement unit 65a in the temperature measurement / correction means 65 of FIG. 4 for realizing the above-described processing.
In FIG. 8, 81 and 86 to 88 are addition / subtraction means, 82 is an effective value equivalent value calculation means, 83 and 84 are division means, 85 is a memory, and 89 is a temperature conversion means provided with ΔM characteristics by a table or the like. The memory 85 stores the values of M1 (20) and M2 (20) in order to perform an operation for setting the difference ΔM when the ambient temperature is 20 [° C.] to 0, and the subsequent addition / subtraction means 86 and 87 respectively subtract M1 (20) and M2 (20) from M1 and M2, and the difference between the results is obtained by the addition / subtraction means 88 to obtain the ΔM characteristic of FIG.

  The temperature measurement unit 65a in the temperature measurement / correction means 65 shown in FIG. 4 sets the modulation degree (AC1 / DC1) and (AC2 / DC2) of the first and second signals Sig1 and Sig2 to an effective value equivalent value (m / √2) to obtain the characteristics M1 and M2, and the ambient temperature T [° C.] (for example, T = 60 [° C.]) according to the difference ΔM between them is based on the ΔM characteristics shown in FIG. To identify.

Next, the temperature correction unit 65b in the temperature measurement / correction means 65 of FIG. 4 will be described.
FIG. 9 is a functional block diagram of the temperature correction unit 65b. In FIG. 9, m1 · sin (ωt) = P1 which is the modulation degree (AC1 / DC1) of the first signal Sig1, and −m2 · sin (ωt) which is the modulation degree (AC2 / DC2) of the second signal Sig2. ) = P2 is input to the addition / subtraction means 91, and further multiplied by 1/2 by the multiplication means 92 to obtain an average value (P = (P1 + P2) / 2). This average value P is input to the memory 93 and the dividing means 94.
Here, FIG. 10A is a diagram conceptually showing the above P1, P2, and P.

The memory 93 of FIG. 9 stores an average value P (20) = (P1 (20) + P2 (20)) / 2 when the reference temperature of the ambient temperature is set to 20 [° C.], for example, and this average value P (20) is input to the dividing means 94.
The dividing means 94 divides and normalizes the average value P output from the multiplying means 92 by the average value P (20), so that the ratio of the average value P to the average value P (20) at the reference temperature, that is, P / P (20) is calculated. The ratio P / P (20) is stored in the memory 95 as the temperature characteristic correction data E _m.

Figure 10 (b) is a conceptual diagram of a temperature characteristic correction data E _m described above, is normalized ratio P / P (20) at ambient temperature is 20 [° C.] 1.0.
P1, P2, P in FIG. 10 (a) that can be obtained in advance for each sensor head 20, the temperature characteristic correction data _{E m} shown in FIG. 10 (b) can also be calculated in advance. If it the temperature characteristic correction data E _m is stored in the memory 95 of FIG. 9, it is possible to obtain the temperature characteristic correction data E _m corresponding to the ambient temperature T the temperature measuring portion 65a described above is determined by the FIG.

Returning to FIG. 9, the temperature characteristic correction data E _m read from the memory 95 according to the ambient temperature T is sent to the division means 96. In this division means 96, by dividing the current component I _k of the current component calculation means 62 in FIG. 4 is calculated by the temperature characteristic correction data E _m, temperature corrected current value I _n is obtained.
This current value I _n, after correcting the non-linearity of the modulation degree for the current to be measured in a non-linearity correction unit 63 of FIG. 4, performs the adjustment of the conversion ratio by the final adjustment means 64, the current flowing through the conductor I Is output as the measured value. The non-linearity correction means 63 and the final adjustment means 64 can achieve the intended purpose by the present invention not essential requirement to obtain the current value I _n the temperature correction unit 65b.

Here, FIG. 11 shows the ratio error of the current to be measured by the reflection type current sensor before the temperature characteristic improvement, and FIG. 12 shows the reflection type current sensor after the temperature characteristic improvement in the first embodiment of the present invention. Shows the ratio error of the current under measurement.
As is clear from these figures, according to the first embodiment, in the range of −40 to +80 [° C.], the variation range of the ratio error is approximately −0.1 [%] or less, and GIS or the like. As a result, sufficient temperature characteristics are obtained as the light CT for current value measurement.

Next, a second embodiment of the present invention will be described.
Since the transmissive current sensor for protection used in protective relays and the like does not use the Faraday element like the reflective current sensor, the Faraday element is used as the ambient temperature sensor of the sensor head as in the first embodiment. Can not do it. Here, in general, in the optical CT, a reflective current sensor for measurement for measuring current with high accuracy and a transmissive current sensor for protection for performing overcurrent protection or the like are installed close to each other. .
Therefore, if the ambient temperature information detected by the reflective current sensor for measurement according to the first embodiment is also used as the ambient temperature information of the sensor head of the protective transmission type current sensor, the current to be measured by the transmission type current sensor is measured. Temperature compensation can be performed. The second embodiment of the present invention focuses on this point.

  As is well known, a transmission-type current sensor is composed of a sensor optical fiber arranged so as to circulate around a conductor through which a current to be measured flows, and a current to be measured that is incident on the sensor optical fiber from a polarizer. A sensor head having an analyzer for separating the transmitted light subjected to Faraday rotation into a first signal and a second signal whose polarization planes are orthogonal to each other, and the first and second signals are transmitted through the light receiving element. At least a signal processing device is provided that measures the magnitude of the current to be measured based on the modulation degree respectively inputted and calculated from the ratio between the AC component and the DC component of the output signals of these light receiving elements.

  FIG. 13 is an overall configuration diagram of the second embodiment. In FIG. 13, reference numeral 200A denotes a signal processing board of a reflection type current sensor to which the first embodiment is applied, and constitutes a main part of the signal processing apparatus 100 shown in FIG. Reference numeral 200B in FIG. 13 denotes a signal processing board for a protective transmission type current sensor, which similarly constitutes a main part of the signal processing apparatus for the transmission type current sensor.

As a schematic operation of this embodiment, for example, temperature data (temperature T) measured by the above-described temperature measurement unit 65a and temperature-corrected current data (current value I) from the signal processing board 200A of the reflective current sensor. _n ) is transmitted to the communication board 300, and the temperature data is transmitted from the communication board 300 to the signal processing board 200B of the transmission current sensor.
In the signal processing board 200 </ b> B, temperature compensation is performed on the current detection data by the transmission type current sensor by the same operation as that of the first embodiment using the temperature data, and temperature-corrected current data is generated. Then, this current data is transmitted to the communication board 300.

  The synchronous I / F board 400 transmits the 1PPS synchronization signal to the communication board 300, and the communication board 300 receives the current data of the reflection type current sensor and the transmission type current sensor synchronized with the 1PPS synchronization signal from the signal processing boards 200A and 200B. Read and transmit to the synchronous I / F board 400. Then, the synchronous I / F board 400 transmits the current data after the temperature correction of the reflection type current sensor and the transmission type current sensor to the outside as the optical CT output.

FIG. 14 shows a ratio error of the current to be measured by the transmission current sensor before the temperature characteristics are improved, and FIG. 15 shows a measurement by the transmission current sensor after the temperature characteristics are improved in the second embodiment of the present invention. The current ratio error is shown.
As is clear from these comparisons, according to the second embodiment, in the range of −40 to +80 [° C.], the fluctuation range of the ratio error is suppressed to approximately ± 0.2 [%] or less, and protection is achieved. As a result, sufficient temperature characteristics can be obtained as a light CT.

10: light source unit 11: light source unit 12: optical circulators 13, 71, 72: transmission optical fiber 20: sensor head 21: optical unit 21a: polarization / analyzer 21b: lens 21c: Faraday element 21d: Faraday rotator 21e: Permanent magnet 22: Sensor optical fiber 23: Mirror 24: Protection tube 40: Analog signal processing unit 41a, 41b: I / V conversion unit 42a, 42b: Low pass filter 43a, 43b: Subtraction unit 50: AD converter 60: Digital signal Processing unit (FPGA: Field-Programmable Gate Array)
61: Modulation degree calculation means 62: Current component calculation means 63: Non-linearity correction means 64: Final adjustment means 65: Temperature measurement / correction means 65a: Temperature measurement part 65b: Temperature correction parts 81, 86, 87, 88, 91 : Addition / subtraction means 82: effective value equivalent value calculation means 83, 84, 94: division means 85, 93, 95: memory 89: temperature conversion means 92: multiplication means 96: division means 100: signal processing devices 200A, 200B: signal processing Substrate 300: Communication substrate 400: Synchronous I / F substrate PD1, PD2: Light receiving element

Claims (4)

An optical fiber for a sensor which is arranged so as to circulate around a conductor through which a current to be measured flows, and which has a mirror at an end;
An optical system that includes a polarization / analyzer and a Faraday element, and separates reflected light incident on the sensor optical fiber and subjected to Faraday rotation by the current to be measured into a first signal and a second signal whose polarization planes are orthogonal to each other. A sensor head having a portion, and
The first signal and the second signal are input through a light receiving element, respectively, and the magnitude of the current to be measured is based on the modulation degree calculated from the ratio between the AC component and the DC component of the output signal of the light receiving element. A signal processing device for measuring the thickness,
In optical CT configured as a reflective current sensor,
The first modulation factor and the second modulation factor are calculated by normalizing the modulation factors based on the first signal and the second signal, respectively, and calculating the first modulation factor and the second modulation factor independent of the current component. Create a temperature characteristic of the difference in the operating temperature range by calculating the difference with the degree in advance,
Using the temperature characteristic, the ambient temperature of the sensor head is detected from the temperature corresponding to the difference, and temperature characteristic correction data corresponding to the detected ambient temperature is created in advance,
A method for improving the temperature characteristics of an optical CT, wherein the current measured by the signal processing device is corrected by the temperature characteristic correction data to compensate the temperature of the current to be measured. In the temperature characteristic improvement method of optical CT described in Claim 1,
A method for improving the temperature characteristics of an optical CT, wherein the modulation degree based on the first signal and the second signal is respectively divided and normalized by an effective value equivalent value of the current to be measured. In the temperature characteristic improvement method of optical CT as described in Claim 1 or Claim 2,
The temperature characteristic correction data is obtained by normalizing an average value of the modulation degree based on the first signal and the second signal by an average value at a reference temperature of the modulation degree based on the first signal and the second signal. A method for improving the temperature characteristics of optical CT, characterized in that the data is obtained. An optical fiber for a sensor arranged so as to go around a conductor through which a current to be measured flows;
A sensor that separates transmitted light incident on the sensor optical fiber from a polarizer and subjected to Faraday rotation by the current to be measured into a first signal and a second signal whose polarization planes are orthogonal to each other. Head and
The first signal and the second signal are input through a light receiving element, respectively, and the magnitude of the current to be measured is based on the modulation degree calculated from the ratio between the AC component and the DC component of the output signal of the light receiving element. Signal processing device for measuring the thickness,
In the optical CT in which a transmissive current sensor provided with is disposed in proximity to the reflective current sensor according to any one of claims 1 to 3,
A method for improving temperature characteristics of optical CT, wherein temperature information detected as the ambient temperature of the sensor head of the reflective current sensor is also used as the ambient temperature of the sensor head of the transmissive current sensor.

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