JPH0462354B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an optical measuring device that measures high voltage or large current using light in a non-contact manner.

BACKGROUND ART As shown in FIG. 3, a conventional optical current measuring device passes light emitted from a light emitting element 1 such as a light emitting diode or a laser diode to a Faraday element (magneto-optic effect element, Faraday rotator) through a polarizer 2. ) 3 and this Faraday element 3
The light emitted from the Faraday element 4 is incident on another Faraday element 4, and the light emitted from this Faraday element 4 is sent to an analyzer 5.
The light is made to enter a light receiving element 6 such as a PIN photodiode through the light beam. The Faraday element 3 is placed close to the conductor 7 through which the current I to be detected flows,
A coil 8 is wound around the other Faraday element 4, and an excitation current i is passed through the coil 8 from the power amplifier 9. In addition, the light receiving element 6
The output of is inputted to a minimum value detection circuit 11 via a preamplifier 10, and the output of this minimum value detection circuit 11 is applied as an input to a power amplifier 9.

This optical current measuring device linearly polarizes light emitted from a light emitting element 1 using a polarizer 2, and passes the polarized light through a Faraday element 3. The plane of polarization is rotated by an angle θ ₁ in response to the magnetic field H.

The light whose polarization plane has been rotated by an angle θ ₁ is passed through another Faraday element 4, and in this Faraday element 4, the polarization plane is rotated back to its original state by the excitation current i flowing through the coil 8.

Then, the light emitted from the Faraday element 4 is passed through an analyzer 5 (the analysis plane is perpendicular to the polarization plane of the polarizer 2).
through the light receiving element 6, and this light receiving element 6
After the output is amplified by a preamplifier 10, it is applied to a minimum value detection circuit 11.

In the minimum value detection circuit 11, the preamplifier 10
When the output level of the preamplifier 10 is detected and the input voltage V to the power amplifier 9 is adjusted so that the output level of the preamplifier 10 is minimized, an excitation current i proportional to the input voltage V to the power amplifier 9 flows through the coil 8. The rotation angle θ ₂ of the polarization plane in the Faraday element 4 due to the magnetic field generated by this becomes equal to the polarity of the rotation angle θ ₁ of the polarization plane of the Faraday element 3 due to the current I (θ ₂ = −θ ₁ ). . Current i at this time,
In other words, voltage V is proportional to current I,
If the voltage V is determined, the current I is measured.

Here, the measurement principle will be explained using mathematical formulas. The rotation angle θ' of the plane of polarization in the Faraday element 3 is given by θ, where the length of the Faraday element 3 is l, the magnetic field due to the current I is H, the number of turns of the conductor 7 is N, and v ₁ and v ₁ ' are constants. ₁ = v ₁ Hl = v ₁ 'NI, and the rotation angle θ ₂ of the plane of polarization in the Faraday element 4 is expressed as follows: where i is the excitation current flowing through the coil 8, n is the number of turns of the coil 8, and v ₂ is a constant. Then, θ ₂ =v ₂ ni. Now, if θ ₁ = θ ₂ by adjusting the excitation current i, then v ₁ Hl = v ₁ 'NI = v ₂ ni, and the voltage V and excitation current i are expressed as follows, where k is a constant. Since there is sometimes a relationship of V=ki, if the voltage V is known, the current I or the magnetic field H can be found. Note that if a Pockels element (electro-optic effect element) is used in place of the Faraday element 3, the voltage or electric field can be measured.

Problems to be Solved by the Invention In such a conventional optical current measuring device, it is necessary to accurately match the rotation angle θ ₁ of the polarization plane of the Faraday element 3 with the rotation angle θ ₂ of the polarization plane of the Faraday element 4. Therefore, in order to obtain the necessary measurement accuracy, the preamplifier 10, the minimum value detection circuit 11, and the power amplifier 9 need to be extremely accurate and have little noise.

An object of the present invention is to provide an optical measuring device that can measure current or voltage without requiring highly accurate equipment.

Means for Solving the Problems The optical measuring device of the present invention includes a light emitting element, a light receiving element that receives light emitted from the light emitting element, and a light receiving element arranged on the light emitting element side of an optical path from the light emitting element to the light receiving element. a polarizer disposed on the light-receiving element side of the optical path so that its analysis plane intersects the polarization plane of the polarizer at an angle of 45 degrees; a first light modulation element that is arranged in the polarizer and rotates the plane of polarization of the light emitted from the polarizer according to the signal to be measured; and a first light modulation element that is arranged in the optical path between the polarizer and the analyzer. a second optical modulation element disposed in series with the element; a carrier signal generator that applies a triangular wave or sawtooth carrier signal to the second optical modulation element and rotates the polarization plane at high speed in accordance with the carrier signal; , a DC component extraction circuit that extracts a DC component of the output of the light receiving element, a comparison circuit that compares the levels of the output of the DC component extraction circuit and the output of the light reception element, and a demodulator that demodulates the output of the comparison circuit. The present invention is characterized by having a configuration including a circuit.

Function The optical measurement device of the present invention has a polarizer and an analyzer arranged between a light emitting element and a light receiving element so that the polarization plane and the analysis plane form an angle of 45 degrees, and further includes a polarizer and an analyzer. A first and a second light modulation element are arranged in series between the two, and the first light modulation element optically modulates the signal to be measured, and the second light modulation element modulates a triangular wave or sawtooth wave carrier. By optically modulating the signal, extracting the DC component of the output of the light-receiving element, and comparing the levels of this DC component and the output of the light-receiving element, the measured signal is pulse-width-modulated to create a pulse-width modulated wave, By passing this pulse width modulated wave through a demodulation circuit, a voltage signal proportional to the signal being measured is extracted, so measurements can be performed without the need for high-precision, low-noise equipment as in conventional methods. Furthermore, since pulse width modulation is performed by detecting the coincidence of the rotation angle of the first light modulation element and the rotation angle of the second light modulation element, the amount of light of the light emitting element and the amount of attenuation of the optical path change over time. Not affected by change at all.

Embodiment An embodiment of the present invention will be described based on FIGS. 1 and 2. This optical current measuring device
As shown in the figure, light emitted from a light emitting element 1 such as a light emitting diode or a laser diode is incident on a Faraday element 3 which is a first light modulation element through a polarizer 2, and the light emitted from this Faraday element 3 is transmitted to a second Faraday element 3. The light enters the Faraday element 4, which is a light modulation element, and the light emitted from the Faraday element 4 is passed through an analyzer 5 (the analysis plane is inclined at 45 degrees with respect to the polarization plane of the polarizer 2) to a PIN photodiode, etc. It is configured such that the light is incident on the light receiving element 6 of.

The Faraday element 3 is placed close to the conductor 7 through which the current I to be detected flows, and the other Faraday element 4 is wound with a coil 8, and this coil 8 receives the triangular wave output from the triangular wave carrier signal generator 12. A carrier signal is now added. In this case, the frequency of the triangular wave carrier signal is desirably 10 times or more the maximum frequency included in the signal to be measured. For example, if the frequency range of the signal to be measured is 2 KHz or less, the frequency of the triangular wave carrier signal is 20 KHz or more.

Further, a DC component of the output of the light receiving element 6 is extracted by a DC extraction circuit 13, and this DC component extraction circuit 13
The current I to be measured (signal to be measured) is converted into a pulse width modulated signal obtained by pulse width modulating the triangular wave carrier signal by comparing the DC component extracted by the comparator circuit 14 with the output of the light receiving element 6. , the high frequency components in this pulse width modulation signal are demodulated by the demodulation circuit 1.
5, a voltage signal proportional to the current I is extracted.

To explain in more detail, this optical current measuring device linearly polarizes light emitted from a light emitting element 1 using a polarizer 2, and passes the polarized light through a Faraday element 3, which causes the Faraday element 3 to generate a current I. The plane of polarization is rotated according to the solid line _A1 in FIG.

Next, the light emitted from the Faraday element 3 enters the Faraday element 4.
Since a triangular wave carrier signal is added to
In the Faraday element 4, the rotation angle of the plane of polarization of the light changes as shown by the solid line _A2 in FIG.
In this case, since the polarization plane of the polarizer 2 and the analysis plane of the analyzer 5 intersect at an angle of 45 degrees, the rotation angle of the polarization plane due to the current I and the rotation angle of the polarization plane due to the triangular wave carrier signal are synthesized. There is a relationship (1 + cos2 (θ-45°)) between the rotation angle and the amount of light passing through the analyzer 5 as shown by the solid line _A3 in Figure 2, and it becomes zero when the composite rotation angle is -45 degrees. , reaches its maximum at +45 degrees. Therefore, the above rotation angle needs to be within the range of ±45 degrees.

Now, if the rotation direction of the polarization plane by the triangular wave carrier signal is set to be opposite to the rotation of the polarization plane by the current I, the light receiving element 6 receives the light emitted from the Faraday element 4 through the analyzer 5. The output has a signal waveform that is a combination of the current I and the triangular carrier signal, as shown by the solid line _A4 in FIG. The output of the light receiving element 6 shown by this solid line _A4 is an output component (second
(shown by the broken line _A5 in the figure) and the output component according to the change in rotation angle due to the triangular wave carrier signal (shown by the broken line A5 in Fig. 2).
A ₆ ) is synthesized.

The output of the light-receiving element 6 is added to the DC component extraction circuit 13 to extract the DC component (the light-receiving element output level corresponding to the composite rotation angle of 0 degrees), and the output of the light-receiving element 6 is combined with the DC component. If level comparison is performed in the comparator circuit 14, a pulse width modulated wave as shown by the solid line _A7 in FIG. A voltage signal proportional to is obtained, and if this voltage is determined, the current I is measured.

In this way, in this embodiment, the rotation angle of the Faraday element 3 is changed by the current I, and the rotation angle of the Faraday element 4 is changed in the opposite direction by the triangular wave carrier signal, and the analysis by the analyzer 5 is performed. The plane and the polarization plane of the polarizer 2 are arranged so that they intersect at an angle of 45 degrees, and the light is analyzed in a region where the combined rotation angle of the Faraday elements 3 and 4 and the output of the light receiving element 6 are approximately proportional. By doing this, a composite signal of the current I and the triangular wave carrier signal is extracted from the light receiving element 6, and by comparing the level of this composite signal with the DC component contained therein, a pulse width modulated wave is created and this is demodulated. This eliminates the need for zero adjustment as in the conventional example, and eliminates the need for high-precision, low-noise equipment. Furthermore, since pulse width modulation is performed, the timing at which the rotation angles of the planes of polarization in the Faraday elements 3 and 4 coincide is simply detected, and the magnitude of the light amount of the light emitting element 1 is irrelevant to the measured value. It is completely unaffected by changes over time in the amount of light from the light emitting element 1 or the amount of attenuation of the optical path.

In addition, in the above embodiment, pulse width modulation was performed using a triangular wave carrier signal, but pulse width modulation can also be performed using a sawtooth wave as a carrier signal. are also included within the scope of this invention.

Further, in the above embodiment, the Faraday element 3 is used to measure the current, but a Pockels element (electro-optic effect element) can be used to measure the voltage. Further, although the Faraday element 4 is used for modulation, a pocket element may also be used for modulation.

Further, current or voltage can also be measured by performing phase modulation using a sine wave as a carrier. In this case, the light receiving element output Q is:
If X and Y are constants, ω _C is the carrier frequency, and ω _S is the signal frequency, it is expressed as Q=Xcos(sin ω _C t−Ysin ω _S t).

Effects of the Invention The optical measuring device of the present invention has a polarizer and an analyzer arranged between a light emitting element and a light receiving element so that the polarization plane and the analysis plane form an angle of 45 degrees, and further includes a polarizer and an analyzer. A first and a second light modulation element are arranged in series between the two, and the first light modulation element optically modulates the signal to be measured, and the second light modulation element modulates a triangular wave or sawtooth wave carrier. optically modulate the signal,
By extracting the DC component of the output of the light receiving element and comparing the levels of this DC component and the output of the light receiving element, a pulse width modulated wave is created by pulse width modulating the measured signal, and this pulse width modulated wave is Since the voltage signal proportional to the measured signal is extracted by passing it through a demodulation circuit, measurement can be performed without the need for high-precision, low-noise equipment as in conventional methods. Since pulse width modulation is performed by detecting the coincidence of the rotation angle of the first light modulation element and the rotation angle of the second light modulation element, it is completely unaffected by changes over time in the light amount of the light emitting element and the amount of attenuation of the optical path. Never.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of its operation, and FIG. 3 is a block diagram of a conventional example. DESCRIPTION OF SYMBOLS 1... Light emitting element, 2... Polarizer, 3... Faraday element (first light modulation element), 4... Faraday element (second light modulation element), 5... Analyzer, 6
... Light receiving element, 13 ... DC component extraction circuit, 14 ...
... Comparison circuit, 15 ... Demodulation circuit.

Claims (1)

[Claims] 1. A light-emitting element, a light-receiving element that receives light emitted from the light-emitting element, a polarizer disposed on the light-emitting element side of the optical path from the light-emitting element to the light-receiving element, and an analysis surface on the light-receiving element side of the optical path. an analyzer arranged to intersect the polarization plane of the polarizer at an angle of 45 degrees; and an analyzer arranged in the optical path between the polarizer and the analyzer to measure the polarization plane of the light emitted from the polarizer. a first light modulation element rotated according to a signal; a second light modulation element disposed in series with the first light modulation element in the optical path between the polarizer and the analyzer; a carrier signal generator that applies a triangular wave or sawtooth carrier signal to the second optical modulation element and rotates the polarization plane at high speed according to the carrier signal; and a DC component extraction circuit that extracts the DC component of the output of the light receiving element. An optical measuring device comprising: a comparison circuit that compares the levels of the output of the DC component extraction circuit and the output of the light receiving element; and a demodulation circuit that demodulates the output of the comparison circuit.