JPS5896256A - Electric field sensor employing liquid crystal - Google Patents

Abstract

PURPOSE:To supply inexpensively an electric field sensor of high sensitivity by constituting the sensor by using a liquid crystal panel. CONSTITUTION:A liquid crystal panel is connected to a light source and a detector by optical fibers. The panel is TN-type liquid crystal panel having the same structure as a display panel of a conventional desk-type electronic computer, and is constituted by two glass plates 1 and 2, a liquid crystal cell 3 sealed in between the glass plates, and polarizing plates 6 and 7 which are bonded on the outer surfaces of the glass plates and whose polarizing directions cross at right angles. The liquid crystal may have any quality on condition that it shows a TN effect, and it is possible to adjust the sensitivity of this sensor by utilizing the difference in a threshold voltage of the operation of the panel according to the quality of the liquid crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION As an optical electric field sensor, one that uses the anisotropy of the refractive index change in response to the application of an electric field to an electro-optic crystal due to the Pockels effect is conventionally known. However, this method has drawbacks such as the operating characteristics largely depend on processing accuracy and the angle of the cut surface with respect to the crystal axis must be selected and polished with high precision during manufacturing. In addition, detection sensitivity is adjusted by changing the light transmission distance, so if you aim for high sensitivity, the detection light intensity will decrease due to transmission loss. A drawback is that it is difficult to connect the light guide and the electro-optic crystal during use. Furthermore, when using LiT 014 L i N 60 s tubes with relatively large electro-optic constants, the temperature dependence of their birefringence properties is very large, and the structure becomes complex to compensate for temperature changes in the refractive index. There are drawbacks to doing so.

Due to the above-mentioned drawbacks, nine electric field sensors using electro-optic crystals have low sensitivity and are expensive to manufacture.

The present invention aims to provide a highly sensitive electric field sensor at a low cost by configuring the sensor using a liquid crystal panel of the same quality as that currently widely used for displays on desktop electronic computers, etc. . These liquid crystal panels do not require the conventional work that requires the precision of crystal polishing.

In an experiment on the gold side of a common TN type liquid crystal panel (referring to one equipped with a polarizing plate), when a DC voltage of 2cm is applied to a liquid crystal cell with an electrode spacing of 1071m, 9
A change in light transmittance of 0s is obtained. On the other hand, Pockels cell (
Half-wavelength voltage V, = 104 V, thickness 1 m) When an electric field of the same intensity is applied, the transmittance change is 0.1%. From this, it can be seen that the electric field sensor using a liquid crystal panel has much higher sensitivity than the sensor using an electro-optic crystal. ease. In addition to the above, even if a liquid crystal panel has a polarizing plate glued on it, the thickness of the panel is t1.
m, and coupling of incident light and transmitted light through an optical fiber becomes easy.

In the case of the sensor of the present invention, since the operating characteristics are determined only by the structure in the thickness direction of the liquid crystal panel, a portion of the sensor can be made extremely small by using incident light with a small beam cross section. This means that disturbances in the surrounding electric field can be reduced.

Figure wcI shows an example of the structure of this sensor. ! FIG. 1a is an enlarged sectional view of the sensor portion 11 of FIG. Here, the liquid crystal panel, light source, and detector are connected with optical fibers, but l! It is sufficient that the light travels straight through the liquid crystal panel in the thickness direction, and an abbreviated configuration using other optical systems such as lenses and mirrors is also possible. The liquid crystal panel is a TN type liquid crystal panel with a structure similar to the display panel of a normal desktop computer, and consists of two glass plates 1, 2, a liquid crystal cell 3 sealed between the glass plates, and a liquid crystal cell 3 sealed between the glass plates. It is composed of polarizing plates 6 and 7 whose polarization directions are orthogonal to each other and which are glued to each other. The material of the liquid crystal may be any material as long as it exhibits the TN effect, and the sensitivity of this sensor can be adjusted by utilizing the difference in the voltage value of panel operation depending on the material.

1! Figure 1: The electrical part including the light source, LED, and detector PDt is a long optical fiber 12.1:1m! m serisa 1
It is connected to 111. This configuration is effective in suppressing disturbances in the constant electric field 611, protecting electrical devices and observers from strong electric fields, enabling remote measurement, and reducing the space occupation rate of the guide part.

As shown in FIG. 1aK, the original fibers 12 and 13 and the liquid crystal panel are coated and bonded using a fiber reinforcing material 10 to be integrated. The reinforcement is made of an opaque insulating material (such as an epoxy resin containing a black pigment) to shade the fiber joints and the panel. If necessary, the surroundings of the light source detection section PD, LED, etc. may be further reinforced by painting or resin molding, and the light tracing may be strengthened.

FIG. 2 is an example of applied voltage-transmittance characteristics of a TN type liquid crystal panel. In a typical TN liquid crystal panel with *' cell width of 10 μm, the l value voltage Vth = 1.5 (to) and the saturation voltage Vs a t = approximately 2 V, so this is 2
Electric field strengths up to 000 V/cm can be determined.

The light source does not have to be monochromatic; it can be anything that has an effective wavelength that is sufficiently small compared to the twist pitch of the liquid crystal, and has a stable output intensity, for example, as shown in this figure. LEDs can be used for Optical electric field sensors that use the Pockels effect have the disadvantage that the light source must be monochromatic and require the use of a laser or a narrow band wavelength filter, whereas this sensor
It has the special purpose of being able to use various light sources such as LEDs and incandescent lamps.

Note that the temporal response of the transmitted light intensity to the applied electric field of a TN type liquid crystal panel is a decrease of several hundred B@ec to several tens of g for both the rise and fall times with DC and step pulse voltages, and when an AC electric field is applied, The molecular orientation at time is proportional to the average absolute value of the electric field.

Therefore, the transmittance during AC is several KH compared to that at DC value.
It is equivalent to z t. Changes in Transmittance When it is desired to follow changes in the electric field or to facilitate amplification after detection, the light source is intensity-modulated at an appropriate frequency (for example, 10 KHz) to achieve the purpose.

The detector may be of any type as long as it can follow the modulation frequency of the light source, or if the intensity of the light source is constant, it can follow the response of the liquid crystal panel to the application of a stepped electric field. Although the light source and detector may be placed at a large distance from each other, Figure 1 shows a case where the light source and detector are placed close to each other, and a portion of the light source output is taken out and guided to the detector. This shows what is directly compared with the detected light.

In addition, as shown in Figure 2, the applied voltage-transmittance characteristic has a fixed threshold value, so by adjusting the threshold value by selecting the material of the TN type liquid crystal described above, the sensor itself can have a level detection function. Depending on the application, level detection by an electric circuit after detection may be omitted, and the presence of an electric field above a certain value can be immediately and effectively detected. If you want to detect the electric field around a conductor and keep the potential of the conductor constant without contact, you can adjust the sensitivity by changing the relative position of the sensor and the conductor to be measured (in addition to adjusting the sensitivity using the liquid crystal material mentioned above). and the FJ value level can be adjusted.

Figure 3 aFi shows an example in which the electric field strength t-S+ is actually determined using this sensor, and the electric field 'till of a commercial alternating current applied to a straight conductor 31 having a PVC coating 32' is determined.

Figure 3 shows the change in the detected light intensity caused by the ground voltage, measured as a distance t between the conductor and the sensor, and plotted as a graph.
A change in the detected light intensity of about 50 - with respect to the V range) is observed, indicating that this sensor has sufficiently high sensitivity, and also shows that the sensitivity changes depending on the placement position.

As a result, this sensor is easier to manufacture, smaller, and smaller than conventional optical electric field sensors based on the Pockels effect.
It is also highly sensitive and has characteristics at KM value, so it has been shown that it is particularly effective in detecting not only a constant electric field and voltage, but also the presence or absence of an electric field strength above a certain value.

The application of this sensor is to handle strong electric fields in the power field.
It can be used in exactly the same way as a conventional optical electric field sensor, such as non-contact measurement of constant and voltage with high insulation and high impedance.

Because of its high sensitivity, it is suitable for live wires of distribution lines of several KV or less.
One example is that it can be easily fixed from a distance. Since it is small in size, it can be said to be an industrially useful invention that can be effectively used for measuring a spatial electric field while moving the detection section, and for inserting into a narrow place.

[Brief explanation of drawings]

FIG. 1(b) shows 1. of the present invention. FIG. 2 is a diagram showing the configuration of an embodiment of a field sensor. FIG. 1 (1) is an enlarged sectional view of the detection section. Figure 2 is a diagram of the applied voltage-transmittance characteristics of a TN type liquid crystal panel. Figure 93 (ml is a diagram of the detection status of the embodiment of the present invention. Figure W43) is a graph of its detection characteristics. 1. 2. Glass plate 3, 11 crystal 41 Sealing agent 5, Spacer 6.7. Polarizing plate 8.9. Reinforcement plate 10, Reinforcement material (paint or mold) 11, Sensor part 12, Input optical fiber 13, Output optical fiber P ,D, Photodiode LED, Light emitting diode 14, Comparator, Distributor OUT, Output the Dark value voltage vlt, Saturation voltage 5iPD, Silicon photodiode d, Distance between copper wire and liquid crystal panel 31, Copper wire 32, PVC coated Patent issuer: Toyo Tsushinki Co., Ltd. - f4 - LED ≦ 1 + + PD Electrical conductor of 1 conductor (KV) Procedural amendment C Fang Gen 1, case indication 1932 RN g + petition No. 1D!θlΔ No. 2, Name of the month 5 and m・Ilt! Request 3, Relationship with the case of the person making the amendment Applicant 5, Number of inventions increased by the amendment 0 6, Correction target rlJk). 7. Contents of correction-14-PD Electricity and pressure of one conductor (KV)

Claims (1)

[Claims] (1) Light transmittance or reflection depending on electric field strength
1. In an optical electric field sensor using an element that changes overtones,
A TN type liquid crystal panel is used as a detection element, light from a light source is guided to the liquid crystal panel through a light guide such as an optical fiber, and the transmitted light of the corpse liquid crystal is guided again to a photodetector by the light guide, and the light intensity of the light source and A sensor that calculates the transmittance of the liquid crystal panel from the detected light intensity of the light collection detector.