JPH0283457A - Voltage measuring apparatus - Google Patents

Abstract

PURPOSE:To prevent the effect of a temp. change by providing a transparent resistor film having a resistance value of 1-1,000MOMEGA or less to the Z-surface of an LiNbO3 single crystal and connecting the same to the voltage applying electrode provided to the X-surface of said crystal. CONSTITUTION:Light is passed through an LiNbO3 single crystal 1 cut vertically in a Z-direction in parallel to the Z-axis of said crystal 1 and an electric field is applied in an x-axis direction by electrodes 3, 3' and this single crystal is placed between a polarizer 4 and a detector 5 along with a 1/4 wavelength plate 6 to constitute a voltage measuring apparatus. Transparent resistors 7, 7' each having a high resistance value M (M=1-1,000MOMEGA) are provided to the Z-surface of the LiNbO3 single crystal 1 and electrically connected to the voltage applying electrodes 3, 3'. Since the resistance value of Z-surface non-treatment is 10<6>MOMEGA, the mounting of the transparent resistors 7, 7' on the Z-surface is effective for discharging and extinguishing the charge generated in the Z-surface by a temp. change and, by this method, a lowering of accuracy due to a temp. change is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a voltage measuring device using the Pockels effect.

(Conventional technology) Optical voltage sensors that measure voltage using the Pockels effect of crystal elements use optical fiber transmission technology, so they can construct a measurement system that has high insulation and is less susceptible to electromagnetic induction noise. So it has been attracting attention in recent years.

Figure 5 is a diagram showing the principle of voltage measurement using the electro-optic effect, and shows the relationship between the applied electric field and the optical axis with respect to the #+Z axis of the LiNbO3 single crystal. Phase difference Δψ2 that occurs in light transmitted in the Z-axis direction when an electric field (EX) is applied in the crystal's axial direction
becomes as follows.

(Reference material: Report of the Institute of Industrial Science, the University of Tokyo, Vol. 28, No. 5, P17-P20) However, λ: wavelength of light no: ordinary ray refractive index γ2□: coefficient indicating the magnitude of electro-optic effect α: Crystal length in Z-axis direction
Ex; the applied electric field is thus LiNb0. Optical retardation due to natural birefringence can be removed by selecting the applied electric field and the direction of light incidence relative to the single crystal axis. That is, it is convenient as a voltage sensor because it is not affected by the spectral characteristics of the light source and can avoid temperature characteristics due to the natural birefringence phase.

On the other hand, LiNb0. Single crystals exhibit a phenomenon called the pyroelectric effect. This is due to temperature changes, LiNb0. This is a phenomenon in which charges are generated on the seven faces of the single crystal, and because of the charges, an electric field other than the measurement electric field is generated in the LiNb3 single crystal, resulting in an error in voltage measurement. Japanese Patent Application Laid-Open No. 57-196166 discloses a voltage measuring device having a configuration that eliminates the above-mentioned drawbacks.
No. 6 has been proposed, and the configuration of the voltage measuring device is shown in FIG.

FIG. 6 shows a LiNb0. Light 2 is passed through the single crystal 1 in a direction parallel to the Z axis, and an electric field is applied by electrodes 3 and 3' in the direction of the Z axis, and this is applied to the 1/4 wavelength plate 6.
A voltage measuring device is constructed by placing the polarizer 4 and the analyzer 5 between the polarizer 4 and the analyzer 5. The output intensity of light 2 incident on the device from the polarizer 4 side is determined by LiNb, which has an electro-optic effect.
It changes depending on the applied voltage Vin applied to the O3 single crystal, and the applied voltage Vin can be detected from this output intensity change.

Furthermore, in FIG. 6, LiNb0. Transparent electrodes 10 and 10' made of a conductive transparent material are provided on two sides of the single crystal.

These transparent electrodes 10 and 10' are electrically connected to each other by a gold lead wire 11. Furthermore, the distance between the voltage applying electrodes 3, 3' and the transparent electrodes 10, 10' is appropriately spaced so as to maintain insulation between them.

That is, as shown in FIG. 6, LiNb0. LiNb0. The charges generated on the seven faces of the single crystal can cancel each other out, making it possible to prevent the generation of an electric field that causes measurement errors due to the charges.

(Problem to be solved by the invention) However, in the configuration shown in FIG.
′ is made of a conductive material, so it becomes an electrically floating electrode, and in this example, it is approximately at the midpoint potential of the applied voltage. Therefore, the conductive surface 8 inside the LiNb0a single crystal 1 becomes as shown in FIG. When a voltage is applied exactly in the direction of the machining axis, Li
Nb0. Inside the single crystal, in addition to the electric field in the C-axis direction, there is
An axial electric field will also be present. In this case, as can be seen from Figure 7, if e and Q□ are exactly equal and the optical axis coincides with the crystal axis, the influence of the electric field in the Z-axis direction will be ignored. It is very difficult to implement the measuring device. Therefore, the influence of the electric field in the Z-axis direction cannot be ignored, resulting in an error in voltage measurement.

Further, the transparent electrodes 10 and 10' need to be electrically connected to each other by the gold lead wire 11.
The thickness of 0' is very thin (on the order of a few numbers), and this connection work also requires some ingenuity. Further transparent electrode 10.10'
It is necessary to ensure insulation between the electrodes 3, 3' and the voltage applying electrodes 3, 3', which increases the size of the LiNΩ single crystal, making it difficult to measure up to a high frequency range.

This is because electro-optic crystals have a piezoelectric effect.

At this resonance point, which exhibits a mechanical resonance phenomenon at a specific frequency, birefringence occurs in the crystal due to the photoelastic effect due to the stress generated by the piezoelectric effect.

This birefringence appears by superimposing the electro-optic effect due to the applied voltage, so care must be taken when measuring signals containing high frequency components such as surge voltages.In order to increase this resonance frequency, LiNb0. It is necessary to miniaturize single crystals.

The present invention improves the drawbacks of the conventional device described above.
It is an object of the present invention to provide a voltage measuring device which has good workability and is capable of accurately measuring voltage even when the environmental temperature changes.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a transparent resistive film with a high resistance value on seven sides of a LiNb0a single crystal, and electrically connects these transparent electrodes to voltage application electrodes provided on the machined surface. are doing.

(Function) By attaching a transparent resistive film with a high resistance value electrically connected to the voltage applying electrode, LiNb0. Since the charges generated on the seven planes of the single crystal disappear and the electric field distribution inside the LiNb0z single crystal only has a component in the direction of the axis, it is possible to prevent the generation of electric fields that cause measurement errors. Furthermore, since the transparent resistive film is vapor-deposited from the two sides, the vapor deposition material also adheres to the cut side, so the transparent resistive films on the seven sides are easily electrically connected to the voltage application electrodes on the cut side.

(Example) As an example of the present invention, as shown in FIG.
．． Transparent resistive films 7 and 7' having a high resistance value (R [MΩ]) are provided on the seven sides of the single crystal 1, and these transparent resistors lI7゜7' are electrically connected to voltage application electrodes 3 and 3'. The configuration can be shown in the equivalent circuit of FIG.

Here, Cp is LiNb0. The capacitance of single crystal 1 is
Now, if we use LINbO as a single crystal in the form of a cube with dimensions of 3 x 3 x 3 mm, Cp '' = 2 [pF
].

In the above, the discharge time constant (c[5]) of charges generated on the 7th surface due to temperature change is τ=cP-RX 10-"[
mS], and there is a relationship shown in Table 1.

Table 1 Therefore, when measuring a surface circumference frequency of 50 Hz, the resistance value of the 7th surface must be 100 [M
Less than Ω is desirable.

Normally, the resistance value of two untreated surfaces is 10' [MΩ] or more, so providing a transparent resistance value that satisfies the above resistance value on the seventh side is effective in discharging and extinguishing the charge generated on the seventh side due to temperature changes. This is an effective method.

On the other hand, in the embodiment of the present invention, the voltage application electrodes 3', 3
When an AC voltage (E [V]) is applied to ', the transparent resistive films 7 and 7' on the seven sides lose [V
].

Electrical equipment generally has a withstand voltage test specification, and for example, high-voltage electrical equipment must withstand lightning impulses of 7000 [V] for 2000 [711 minutes] AC.

Table 2 shows the relationship between the resistance value (R [MΩ]) of the transparent resistive film and the generated loss CP [V]) when an AC voltage of 2000 [V] is applied.

Table 2 From this, it can be seen that there is a lower limit to the resistance value of the transparent resistive film.

Therefore, LiNb0. The resistance value of the transparent resistive film is 1 [M
[Ω] or more is desirable, and by providing such a high resistance value, sufficient dielectric strength against lightning impulses can be ensured.

As described above, the resistance value of the transparent resistive film is desirably 1 [MΩ] or more and 1000 [MΩ], and this resistance value can be obtained by appropriately selecting the conditions for depositing ZnO1 or SnO.

In addition, in the vapor deposition of transparent resistive films, it is possible to set the vapor deposition conditions so that the vapor deposition material adheres to the work surface by performing vapor deposition from the two sides, and the transparent resistive films 7 and 7' on the two sides can be set on one side. It is easily electrically connected to the voltage applying electrode 3.3'.

Note that if the corners of the 7th plane and the X plane are acute, there is a risk that the electrical connection between the transparent resistive films on the 2nd plane and the cut plane may be lost depending on the handling after vapor deposition. Therefore, by chamfering the corner 9 as shown in FIG. 4(a) or chamfering the corner as shown in FIG. , reliability can be increased.

〔Effect of the invention〕

LiNb0. By providing a transparent resistive film with a resistance value of 1 [MΩ] or more and 1000 [:MΩ] or less on seven sides of the single crystal, and electrically connecting these transparent resistance values to the voltage application electrode provided on the machined surface. , LiNb0 due to temperature change
．． As the charges generated on the seven faces of the single crystal disappear, L
Since the electric field distribution within the iNb0□ single crystal is limited to the component in the direction of the transverse axis, it is possible to prevent the generation of electric fields that cause measurement errors, thereby providing a voltage measuring device that can accurately measure voltage even when the environmental temperature changes. can do.

Furthermore, with the transparent resistance value according to the present invention, since the vapor deposition agent can be applied to the cut surface by vapor deposition from the two sides, it is possible to easily electrically connect the transparent resistive films on the seven sides and the voltage application electrodes on the cut surface.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a voltage measuring device according to the present invention, and FIG.
The figure shows LiNb0. A schematic diagram showing equipotential surfaces inside a single crystal, FIG. 3 is an electrical equivalent circuit of the present invention, and FIG.
5 is a schematic diagram showing another embodiment of the present invention, FIG. 5 is a block diagram explaining voltage measurement using an electro-optic crystal, FIG. 6 is a block diagram showing a conventional voltage measuring device, and FIG. 7 is a block diagram showing a conventional voltage measuring device. Conventional L
FIG. 3 is a schematic diagram showing equipotential surfaces inside an iNbO3 single crystal. 1...LiNb0. Single crystal 2...light beam 3
．． 3'...Electrode for voltage application 4...Polarizer 5...Analyzer 6...1
/4 wavelength plate 7f7'...transparent resistive film 8...
Equipotential surface 9, 9'... Corner chamfer 10...
・Transparent electrode 11...Gold lead wire agent Patent attorney Noriyuki Chika Ken Yudo Daishimaru Ken (oL) Cb) Figure

Claims (1)

[Claims] In a voltage measuring device using an electro-optic crystal, each Z-plane of the electro-optic crystal has a resistance of 1 MΩ or more and 1000 MΩ.
1. A voltage measuring device comprising: transparent resistive films having the following resistance values; these transparent resistive films are electrically connected to a voltage applying electrode provided on the x-plane.