JPS601582A - Measuring apparatus for both ac and dc magnetic fields - Google Patents

Abstract

PURPOSE:To achieve a higher reliability with a better temperature characteristic by making a combined light of two kinds of lights different in the wavelength incident into a Faraday rotary type magnetic field sensor to separate the light emitted for photoelectric conversion. CONSTITUTION:Lights different in the wavelength from light sources 1a and 1b are combined with a wavelength synthesizer 2 and enters a Faraday rotary type magnetic field sensor with polarizing elements 4a and 4b and a Faraday element 5 via an optical fiber 3c so that the light different in the wavelength is rotated at the angle of Faraday rotation according to a magnetic field. Then, the light is separated with an optical fiber 3d and a wavelength separator 6 and converted into electricity with light receiving elements 7c and 7d. With such an arrangement, temperature characteristic or the like of fibers 3c and 3d and a magnetic sensor will be the same with respect to lights with a different wavelength and the number of the optical fibers also are reduced thereby improving the reliability with a better temperature characteristic of a measuring apparatus for both AC and DC magnetic fields.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alternating current magnetic field measuring device, and more particularly to an optical alternating current magnetic field measuring device using a Faraday one-rotation type field sensor.

FIGS. 1 and 2 are block diagrams of conventional AC and DC magnetic field measuring devices, respectively. In FIG. 1, 1 is a light source, 3 is an optical fiber, 4α and 4b are polarizing elements each consisting of a polarizing plate or a polarizing prism, and 5 is a Faraday element for applying a measurement magnetic field.
Now, this constitutes a Faraday one-rotation type sensor.

7 is a light receiving element, 8 is an amplifier, 9 is a subtracter, 10 is a divider, and 11 is a reference DC voltage generator.

In FIG. 1, light of one wavelength is used, and on the receiving side there is a reference DC voltage generator 11 that generates a DC pressure that cancels the output voltage of the amplifier 8 when no measurement magnetic field is applied to the Faraday element 5. is provided, the output voltage and the output voltage of the amplifier 8 are manually input to the subtracter 9, and the output of the subtracter 9 and the output voltage of the reference DC voltage generator 11 are manually input to the divider 10, When a measurement magnetic field is applied to the Faraday element 5, v, -v, /v2 (v□ is the output voltage of the amplifier 8, V2 is the output voltage of the reference DC voltage generator 11) are calculated, and the results are It is designed to be output as a measured value of the measured magnetic field. However, this has the following drawbacks.

(1) Even if the output light level of light source 1 is stabilized,
The light emitted from the optical fiber 6 fluctuates due to temperature changes in the magnetic field sensor, temperature characteristics, vibrations, stress changes, etc. of the optical fiber 6, and this affects the output voltage of the amplifier 8, making it impossible to measure a high degree of aperture.

(2) Furthermore, a modification of this method in which two optical fibers are used, one of which does not pass through the magnetic field sensor, has the same drawbacks as in (1) above.

In FIG. 2, the polarizing element on the exit side of the Faraday cycle i-type magnetic field sensor is used as a wave splitting element 4c, and the respective lights are connected to optical fibers 6α, ? ll, the light receiving elements 7a, 7
The output currents of the light-receiving elements 7α and 7b are amplified and converted into voltage by amplifiers 8α and 8b, respectively, and the output voltages of the amplifiers 8α and 8b are input to the subtracter 9 and adder 12, respectively. The output of 9 and the output of adder 12 are input to a divider 10, and the output of the divider 10 is used as the measured value of the measured magnetic field. Figure 2 is an improved version of Figure 1.
If there is no imbalance in the emitted light from the magnetic field sensor, it is very stable and has the advantage of not being affected by the characteristics of the light source 1 and the input optical fiber B. The output side optical fibers 3a, 3
There may be an unbalance in the coupling loss to b, and there may be a difference in transmission loss between the two output one-law optical fibers 6cL and 6b.
When different vibrations and stresses are applied to both optical fibers 6α and 3b, an imbalance occurs in the output light level, and the amplifier 8
There is a drawback that the output voltages of α and 8b vary greatly.

The present invention has been made in view of the above, and an object of the present invention is to provide an AC/DC magnetic field measuring device with good temperature characteristics and high reliability.

A feature of the present invention is that the light input to the Faraday rotary magnetic field sensor, which has a configuration in which a Faraday element for applying a measurement magnetic field is sandwiched between polarizing elements, is generated by combining light from two light sources with different wavelengths. The one light source generates light of a wavelength such that the Faraday rotation angle in the Faraday element is sufficiently smaller than the Faraday rotation angle of the light generated from the other light source, and the light from the magnetic field sensor The current configuration is such that it is transmitted through a single optical fiber, and the output light is separated into two wavelengths and then subjected to wake conversion.

The present invention will be explained in detail below using the embodiment shown in FIG.

FIG. 6 is a configuration diagram showing an embodiment of the AC/DC magnetic field dividing measuring device of the present invention. In Figure 6, 1α.

Light sources 1b each emit light of a different wavelength; for example, the light source 1a is a semiconductor laser with a wavelength of λ, and the light source 1b is a semiconductor laser with a wavelength of λ. 2 is light source 1a and 1b
The light from the wavelength synthesizer 2 is transmitted through an optical fiber 6C, and is sent to a Faraday rotation type magnetic field sensor consisting of a polarizing element 4α, a Faraday element 5 that applies a measurement magnetic field, and a polarizing element 4b. incident. The light from this magnetic field sensor is transmitted by one optical fiber 6d, the light emitted from the optical fiber 6d is separated into two wavelengths by a wavelength demultiplexer B, and the light with a wavelength λ 1 is transmitted to a light receiving element 7c with a wavelength λ . The output signal is subjected to awakening conversion at , and is applied to a subtracter 9 and a divider 10 through an amplifier 8α.

On the other hand, the light having the wavelength λ2 is converted by the light receiving element 7d having the wavelength λ2, passes through the amplifier 8b, and is applied to the p-attenuator 9.

Note that the light sources 1α and lb are stabilized by housing both lasers in the same case to stabilize the temperature. Further, one of the light sources 1α and 1b, 1cL, has a Faraday rotation angle in the Faraday element 5 that is different from that of the other light source 1b.
The wavelength combiner 2 is a light source that generates light with a wavelength that is sufficiently smaller than that of the light generated by the Faraday effect. In contrast, it shall have a film that completely reflects that light.

Further, the optical fibers 3c and 3d have low loss in both wavelength bands. Further, as the light receiving elements 7a and 7, for example, a silicon photodiode or an InGaAs photodiode is used. Further, the light receiving elements 7α, 7b and the signal processing circuit are housed in the same case, and installed in a place where the temperature is constant from 0 to 40°C.

Now, when the voltage at the output of the amplifier 8α is T72 and the output voltage of the amplifier 8b is V, when no measurement magnetic field is applied to the Faraday element 5, V1=V.

The gain of the 1st converter 8b is adjusted in advance so that . Here, a measurement magnetic field is applied to the Faraday element 5,
If the Faraday rotation angle of the light with wavelength λ2 at that time is ψ, then V2kiV.

Here, Vo is the output voltage when there is no measurement magnetic field.

Therefore, the subtracter 9 calculates vl-v2, and the divider 1
If the calculation of V□-V2/V' is performed at 0, a voltage proportional to 5in2ψ can be obtained as an output voltage.

According to the embodiment described above, the optical fibers 3C, 6
The change in the transmission characteristics of d and the temperature characteristics of the magnetic field sensor are determined by the wavelength λ 1. The same holds true for the light of λ2, so it is not affected by these effects. In particular, it has excellent temperature characteristics. Therefore, highly accurate magnetic field measurement is possible. Furthermore, since light is guided to the magnetic field sensor through one optical fiber 6C, and light from the magnetic field sensor is transmitted through one optical fiber 6d, handling is easy. Further, it is also possible to diagnose the transmission system without affecting the optical signal containing magnetic field information by using light with a wavelength that is ineffective for the Faraday effect.

As explained above, according to the present invention, there are advantages in that temperature characteristics are good, reliability is low, and highly accurate magnetic field measurement is possible.

[Brief explanation of the drawing]

FIGS. 1 and g2 are block diagrams of conventional AC/DC magnetic field measuring devices, respectively, and FIG. 6 is a block diagram showing an embodiment of the AC/DC magnetic field meters i1+ and lI of the present invention. 1α, 1b; Light source, 2; Wavelength combiner, 6 c, 3 d; Optical fiber, 4a, 4b: iB optical element, 5; Faraday element, 6; Wavelength demultiplexer, 7c, 7
d: light receiving element, 8 a r 8 b: amplifier, 9 - subtracter, 10: divider. 1st item

Claims (2)

[Claims] (1) In an alternating orthogonal side magnetic field measuring device that measures a magnetic field using a Faraday single rotation type sensitive field sensor configured by sandwiching a Faraday element that applies a measurement magnetic field between polarizing elements, the light that is manually applied to the magnetic field sensor is the generated light. Light from two light sources with different wavelengths is passed through a multiplexer, and one of the light sources has a Faraday rotation angle in the Faraday element that is more than the Faraday rotation angle of the light generated from the second light source. An orthogonal side magnetic field measurement device that generates light with a decreasing wavelength. (2) The light emitted from the magnetic field sensor is separated into three wavelengths using a demultiplexer on the light receiving side, and then photoelectrically converted by two light receiving elements that match each wavelength. After passing through an amplifier whose gain is adjusted so that the respective output voltages are equal when no magnetic field is applied to the Faraday element, the amount of light at a wavelength that is effective for Faraday rotation is Pl, and the amount of light at a wavelength that is ineffective for Faraday rotation. The alternating current side magnetic field measuring device according to claim 1, wherein when P2 is determined, the calculation of (P□-P2)/P2 is performed and the result is output as a magnetic field measurement value.