KR100645639B1 - Co-axial type lf/rf dielectric sensor and dielectric spectrum measuring system using the same - Google Patents

Abstract

The present invention relates to an LF / RF common dielectric sensor and a dielectric spectrum measuring system using the same, which can accurately measure the dielectric spectrum of a liquid in common in the LF and RF domains. A cylindrical outer pipe 13 to be formed; An inner rod 15 arranged coaxially inside the outer pipe to form the other electrode of the sensor; A rod supporter 17 which maintains a constant gap between the outer pipe and the inner rod to prevent contact between electrodes; A sensor connector 18 for connecting the sensor to the sensor fixture; And a lid 11 which prevents the outflow of the liquid sample in the sensor and has a hole for inserting the thermocouple, and provides a dielectric spectrum measurement system using the common dielectric sensor. According to the present invention, a single common dielectric sensor can obtain a dielectric spectrum in two regions of LF and RF, and an accurate dielectric spectrum of a sample can be measured.

Dielectric Sensor, Spectrum, Complex Dielectric Constant, Impedance Meter, Dielectric Relaxation

Description

CO-AXIAL TYPE LF / RF DIELECTRIC SENSOR AND DIELECTRIC SPECTRUM MEASURING SYSTEM USING THE SAME}

1 is a diagram showing a measurement region of dielectric spectroscopy in the electromagnetic spectrum.

Figure 2 is a view showing the disassembled and assembled state of the coaxial LF / RF common dielectric sensor according to the present invention.

Figure 3 is a schematic diagram of a dielectric spectrum measurement system using a coaxial LF / RF common dielectric sensor in accordance with the present invention.

4A and 4B are graphs showing the spectra of the LF and RF regions and relative errors at each frequency measured using a sensor having a length of 30 mm of an inner rod.

5A and 5B are graphs showing the spectra of the LF and RF regions and the relative errors at each frequency measured using a sensor having a length of 70 mm of the inner rod.

6A and 6B are graphs showing the spectra of the LF and RF regions and the relative errors at each frequency measured using a sensor having a length of 50 mm of the inner rod.

Figure 7 is a graph measuring the dielectric spectrum using a dielectric sensor dedicated to LF and RF and synthesized the results.

Figure 8 is a graph measuring the dielectric spectrum using the LF / RF common dielectric sensor according to the present invention and synthesized the results.

9 is a schematic diagram of a dielectric spectrum measurement system using a coaxial LF / RF common dielectric sensor with a low temperature thermostat;

※ Explanation of symbols about main part of drawing ※

1: dielectric sensor 13: outer pipe

15: inner rod 17: rod support

18: sensor connector 11: lid

2: thermostat 21: heating wire

22: heated lid 23: thermocouple

24: Thermostat 3: Sensor Fixture

31: Fixture connector 4: Impedance meter

5: Computer 6: Low Temperature Thermostat

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coaxial LF / RF common dielectric sensor and a dielectric spectrum measurement system using the same. In particular, the dielectric spectrum of a liquid is commonly used at low and high frequencies. The present invention relates to a dielectric sensor and a dielectric spectrum measurement system capable of accurately measuring spectrum.

The dielectric sensor according to the invention is particularly suitable for measuring the dielectric spectrum of hydrocarbons having a low dielectric constant and a low loss factor.

Low frequency (LF) used in the present invention refers to a region of 300 kHz or less in the electromagnetic spectrum, and RF (radio frequency) refers to a region of 300 kHz to 300 MHz in the electromagnetic spectrum.

Dielectric spectroscopy is a method of characterizing a material by measuring its complex dielectric constant, which indicates a change in polarization and conductivity of a material in the electromagnetic spectrum below the infrared ray.

Figure 1 shows the application area of dielectric spectroscopy and optical spectroscopy in the electromagnetic wave region.

In dielectric spectroscopy, when an alternating electric field with a relatively low voltage (100 kV to 1 V) is applied to two electrodes installed at both ends of a material, the current component used for the accumulation of current and charge lost by the resistive component depending on the electrical properties of the material The response will appear. Dielectric spectrum is measured by changing the frequency at a constant temperature and measuring by changing the temperature at a constant frequency. The complex permittivity can be obtained from the relationship between the current and the voltage, and various physical properties of the material can be found from the tendency of the frequency or temperature change of the real part and the imaginary part of the complex dielectric constant.

Dielectric sensors come in various shapes and structures depending on the application. The most common type is a parallel plate type dielectric sensor, in which two metal plates facing each other serve as electrodes, and a sample to be measured is inserted between the two metal plates. The dielectric sensor having such a structure is easy to measure in the solid state, but requires a special structure to prevent the liquid from flowing down in the liquid state, which may increase the appearance of the device. In addition, in order to increase the sensitivity of the parallel plate dielectric sensor, it is necessary to reduce the distance between the electrodes and increase the cross-sectional area. However, reducing the electrode distance reduces the amount of sample to be measured, making it difficult to measure the average characteristic of the sample, and increasing the cross-sectional area has the disadvantage of increasing the size of the dielectric sensor. US Pat. Nos. 4,448,909 and 4,448,943 disclose such parallel plate dielectric sensors.

Another type, called a digitized fringing field type sensor, is a type in which several small electrode patterns are formed on a base material, thereby increasing the sensitivity of the sensor by increasing the number of patterns. Some sensors of this type can be used to measure the dielectric constant of a polymer material mainly by contacting the surface of the polymer material, or have a special design to be used for on-line control of a molding apparatus. Examples of such sensors are found in US Pat. Nos. 5,208,544 and 3,696,369. However, the fringing field type sensor is not robust and may cause problems in long-term use, and its use is limited because the frequency range that can be used is limited to the LF region.

Another form is a coaxial type dielectric sensor. This type is a form in which the inner rod and the outer pipe are coaxially aligned to serve as electrodes, and in principle, are similar to parallel plate dielectric sensors. However, compared to the parallel plate dielectric sensor, the sensitivity can be increased even at the same size, and the connector can be processed in the sensor itself, which reduces the size of the entire system. The sample can be contained inside the sensor to measure the liquid sample. Therefore, the handling of the liquid sample is easy. There is an example of such a coaxial dielectric sensor in US Pat. No. 3,846,073.

Since these conventional dielectric sensors can be mainly used in the frequency region below the LF, it is not suitable for measuring the dielectric spectrum of a sample exhibiting a dielectric relaxation phenomenon in the RF region. Large numbers of liquid samples could span the dielectric relaxation frequency from the end of the LF region to the RF region, so that the LF-only dielectric sensor could not accurately observe the dielectric spectrum. Therefore, in order to obtain the full spectrum, it is necessary to obtain the dielectric spectrum by synthesizing each of the dielectric spectra using a dedicated sensor and system for each region of the LF and the RF, and obtaining the entire spectrum. In this case, since two types of sensors are used, when the dielectric spectrum is measured by changing the temperature, the degree of thermal expansion of the sensors at each temperature is different so that the shape of the synthesized dielectric spectrum may not be smooth, and thus accurate dielectric spectrum may not be obtained. .

The present invention can be commonly used in the area of LF and RF to solve the above problems, and provides a coaxial LF / RF common dielectric sensor capable of measuring an accurate dielectric spectrum, using the coaxial common dielectric sensor The purpose is to provide a system that can accurately measure the dielectric spectrum.

In addition, the present invention adds a temperature control function to measure the dielectric spectrum of the sample from a low temperature (-180 ℃) near the liquid nitrogen temperature to a high temperature of several hundred degrees (200 ℃), cleaning and maintenance of the sensor Another purpose is to make the structure easier to use.

In order to achieve the above object, the coaxial LF / RF common dielectric sensor according to the present invention comprises a cylindrical outer pipe (13) forming one electrode of the sensor; An inner rod 15 arranged coaxially inside the outer pipe to form the other electrode of the sensor; A rod supporter 17 which maintains a constant gap between the outer pipe and the inner rod to prevent contact between electrodes; A sensor connector 18 for connecting the sensor to the sensor fixture; And a lid 11 which prevents outflow of the liquid sample in the sensor and has a hole for inserting the thermocouple.

In addition, the dielectric spectrum measurement system according to the present invention includes the coaxial LF / RF common dielectric sensor (1); A thermostat device (2) for adjusting the temperature of the sensor, comprising a cylindrical hot wire lid wound around the sensor wire, a thermostat, and a thermocouple connecting the dielectric sensor to a thermostat; An impedance measuring device (4) connected to the sensor body to measure an impedance of a sample in the sensor body; A sensor fixture (3) connecting the sensor body and an impedance meter; And a computer 5 for controlling the thermostat and impedance meter and analyzing the measurement data.

Hereinafter, a coaxial LF / RF common dielectric sensor and a dielectric spectrum measurement system using the dielectric sensor according to the present invention will be described with reference to the accompanying drawings.

Figure 2 shows the disassembled and assembled state of the coaxial LF / RF common dielectric sensor according to the present invention.

The coaxial LF / RF common dielectric sensor 1 according to the present invention includes an outer rod 13 forming one electrode of the sensor and an inner rod 15 forming the other electrode, the outer pipe 13 and the inner rod. (15) to maintain a constant gap between the rod support 17 to prevent contact between these electrodes, the sensor connector (18) for connecting to the sensor holder (3) and the leakage of the liquid sample during the measurement of the dielectric spectrum It consists of a lid 11 to prevent it.

The inner rod 15 is firmly coupled with the rod support 17, the combined inner rod 15 and the rod support 17 are in contact with the rod contact portion 14 of the outer pipe, and then the sensor connector 18 again. It is to be firmly coupled by the screw (19). The sensor 1 coupled as described above is fixed to the pin 16 and the sensor connector 18 of the lower end by the male / female role and the female / male of the holder connector 31 of the sensor holder (3). Therefore, if necessary, the sensor 1 can be disassembled and washed, and then reassembled to facilitate the use.

The encapsulation support 17 is made of a material such as Teflon, which does not have much deformation at high temperature, and other parts are made of a metal body, and if necessary, gold-plating is used to improve electrical conductivity and contact with a corrosive sample. Prevents corrosion of metal parts.

The lid 11 is formed with a hole 12 for inserting the thermocouple 23.

3 is a schematic diagram of a system for measuring dielectric spectrum using a coaxial LF / RF common dielectric sensor according to the present invention.

Dielectric spectrum measurement system according to the present invention comprises a coaxial LF / RF common dielectric sensor (1), temperature control device (2), impedance measuring instrument (4), sensor fixture (3) and computer (5).

The temperature control device 2 is formed on the heating wire 21 for generating heat and controlling the temperature, the heating wire lid 22 covering the outside of the dielectric sensor 1 in a cylindrical shape to wind the heating wire, and a cover of the sensor. And a thermocouple 23 and a thermostat 24 for connecting the sensor to the thermostat through the aperture.

The temperature controller 24 is composed of a PID controller and a power controller with an autotuning function.

The impedance measuring instrument 4 may be a commercially available product such as a frequency response analyzer such as Solartron SI 1260 or an RF impedance analyzer such as HP 4291A. However, other models of equivalent performance can be used, or a dedicated measuring instrument can be used. If continuous measurement is required, it can be used as an automatic continuous measurement device by installing inlet and outlet in the sensor body and installing a pump.

Table 1 shows the diameter (2b) and an inner rod, the outside diameter (2a) and an inner rod length (l _e) of the sample volume inside the sensitivity (C ₀₎ and a sensor of the sensor according to the outer pipe 13. The sensitivity of the sensor can be adjusted by adjusting the length l _e of the inner rod 15 which has less influence on the structure of the sensor. In order to obtain an optimal spectrum, an appropriate inner rod length is selected according to the electrical characteristics of the impedance measuring instrument 4 and the characteristics of the sample.

division 2a (mm) 2b (mm) l _e (mm) C ₀ (pF) V _sample (cm 3) C1-1 9 12 10 1.93 0.49 C1-2 9 12 30 5.80 1.48 C1-3 9 12 50 9.67 2.47 C1-4 9 12 70 13.54 3.46 C1-5 9 12 90 17.40 4.45 C1-6 9 12 110 21.27 5.44

4A and 4B show three standard samples without dielectric relaxation in the LF / RF region when the length of the inner rod 15 is 30 mm, (10) -monochlorobenzene (03). Relative errors between the dielectric spectrum and true values of) -n-heptane ((03) -n-heptane) and (01) -air ((01) -air) are shown. When the length of the inner rod 15 is 30 mm, the error of the LF region is greater than that of the RF region. Thus, the electrical characteristics of the sensor at this length are suitable for measuring the RF region and not for the LF region.

5A and 5B show relative errors of dielectric spectra and true values of three standard samples without dielectric relaxation in the LF / RF region when the length of the inner rod 15 is 70 mm. As shown in FIG. 5, when the length of the inner rod 15 is 70 mm, the error of the RF region is greater than that of the LF region. Therefore, the electrical characteristics of the sensor at this length are suitable for the measurement of the LF region and not for the measurement of the RF region.

6A and 6B show relative errors between dielectric spectra and true values of three standard samples without dielectric relaxation in the LF / RF region when the length of the inner rod 15 is 50 mm. As shown in FIG. 6, when the length of the inner rod 15 is 50 mm, the relative error is within 1% in the LF and RF region, and is suitable for measuring the LF and RF region at the length of the inner rod 50 mm. You can see that.

7 is a result of measuring the dielectric spectrum of the sample during the refining process using a common dielectric sensor having a length 50mm of the inner rod 15 according to the present invention at 140 ℃ and the dielectric spectrum of each of the LF and RF individual dielectric sensors The synthesis results are shown. As shown in FIG. 7, when a spectrum measured by each of the dedicated dielectric sensors is synthesized, discontinuity occurs at the connection portion (log f = 6.0) of the LF and the RF. The main reason for this discontinuity is that the sensor is thermally expanded during high temperature measurement, and the degree of expansion is different depending on the sensor of LF and RF, so that the result of sensor calibration at room temperature (20 ° C) is applied. Because the results are different from each other.

FIG. 8 is a result of measuring the dielectric spectrum of a sample during the same refining process as shown in FIG. 7 using the common dielectric sensor according to the present invention and synthesizing the entire spectrum. In this case, the influence by temperature is the same. Therefore, discontinuity does not occur at the connecting part (log f = 6.0).

FIG. 9 shows a dielectric spectrum measurement system having a low temperature thermostat 6 for measuring the dielectric spectrum of a sample in a temperature range from low temperature (−180 ° C.) to room temperature (20 ° C.). This system adds two lids to the temperature control device 2 of FIG. 3 and injects liquid nitrogen into the lids to control the temperature by injecting liquid nitrogen. The low temperature temperature controller 28 receives the input of the thermocouple 23 to control the heating wire 21 and the low temperature metering pump 27 to adjust the temperature. The first low-temperature lid 25 uses a good thermal conductivity metal material, the second low-temperature lid 26 uses a low thermal conductivity insulating material. Using the temperature control device, in addition to the high temperature range controlled by the temperature control device of FIG. 3, accurate temperature control is possible in the temperature range from liquid nitrogen temperature (-180 ° C.) to room temperature.

In the case of using the common dielectric sensor according to the present invention as described above, since a dielectric spectrum in two regions of LF and RF can be obtained with a single common dielectric sensor, the effects of temperature expansion or contraction on the high and low temperature measurements are the same. Therefore, discontinuity does not occur in the synthesized dielectric spectrum after measurement, thereby enabling accurate measurement of the dielectric spectrum of the sample. Therefore, the common dielectric sensor according to the present invention can be suitably used to study the electrical characteristics of various types of liquid samples exhibiting dielectric relaxation and impedance relaxation in the LF and RF domains.

In addition, using the common dielectric sensor according to the present invention can obtain the spectrum of a very opaque sample that could not be obtained by conventional optical spectroscopy method can also be used to study the physical properties of the sample therefrom have.

Claims (4)

A cylindrical outer pipe forming one electrode; An inner rod arranged coaxially within the outer pipe to form the other electrode; A rod support for maintaining a constant gap between the outer pipe and the inner rod to prevent contact between electrodes; A sensor connector for connecting to the sensor fixture; And A coaxial LF / RF common dielectric sensor, comprising: a lid for preventing leakage of a liquid sample in the sensor and having a hole for inserting a thermocouple. Claim 1 coaxial LF / RF common dielectric sensor; A thermostat device for adjusting the temperature of the sensor, comprising a cylindrical hot wire lid wound around the sensor, a thermostat, and a thermocouple connecting the dielectric sensor to a thermostat; An impedance meter connected to the sensor main unit to measure an impedance of a sample in the sensor main unit; A sensor fixture connecting the sensor body and an impedance meter; And And a computer for controlling the temperature controller and the impedance meter and analyzing the measurement data. 3. The apparatus of claim 2, further comprising: a low temperature thermostat comprising a thermally conductive inner wall covering the cylindrical hot wire lid, an insulating outer wall covering the inner wall, and a low temperature thermostat connected to the thermocouple to control the temperature; And And a low temperature quantitative pump for controlling temperature by injecting liquid nitrogen between the inner and outer walls by controlling the low temperature thermostat. The dielectric spectrum measurement system according to claim 2 or 3, wherein the sensitivity of the dielectric sensor is adjusted by varying the length of the inner rod according to the type of the impedance measuring instrument and the sample.

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