JP3516766B2 - Electromagnetic induction probe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to impedance measuring devices, and more particularly to an electromagnetic induction probe used in the field of measuring electrical characteristics for quantitative research, inspection and control of the structure of substances in a colloidal state.

[0002]

2. Description of the Related Art Colloids are dispersion systems consisting of a particulate dispersoid and a continuous phase dispersion medium. As a method for evaluating the appearance of such a heterogeneous structure, there is a measurement of electrical characteristics such as conductivity and permittivity. Particularly in recent years, methods for measuring the dielectric constant using impedance measurement have been studied. The applicant of the present application has proposed an electromagnetic induction type conductivity / permittivity meter as an effective means for measuring the capacitance, that is, the permittivity of a solution having a high conductivity in Japanese Patent Application No. 6-172023. This solves the problem of error due to interfacial polarization, which is a drawback of the conventional electrode system, and allows the dielectric constant to be accurately measured without the influence of conductivity. Therefore, we proposed the structure of the probe and a simple correction method. This case is a proposal to improve the structure and further improve the accuracy.

In the electromagnetic induction type permittivity measurement of Japanese Patent Application No. 6-172023, the influence of the change in the conductivity of the solution on the measured permittivity is markedly removed as compared with the electrode type permittivity measurement method. This is because the electrode interface polarization was eliminated in principle. However, if the sensitivity multiplier (so-called cell constant in the electrode system) of the probe is calibrated based on the conductivity, there are the following problems. FIG. 4 shows an example of the true value and the measured value of the dielectric constant of the aqueous solution with respect to the frequency change, which is expressed using the conductivity of the solution as a parameter. The problem is that the measured dielectric constant shows a value lower than the true value, and yet the measured dielectric constant is affected by changes in conductivity. The magnitude of this error may be 30% or more. Further, in the case of a solution in which the product of the dielectric constant and the angular frequency is approximately equal to the electric conductivity within the measurement frequency range, as shown in the figure, the measured value of the dielectric constant also changes due to the frequency change.

Before describing the cause of this, a conventional electromagnetic induction type probe will be described. The first, second and third embodiments of the electromagnetic induction probe proposed in Japanese Patent Application No. 6-172023 are shown in FIGS. 5, 6 and 7, respectively. In the drawings, elements having the same function are designated by the same reference numeral. These elements have the following structure. Impedance measuring instrument body 1
Has a signal source 2, a resistor 3, a voltmeter 4 and an ammeter 5. In addition, the electromagnetic induction probe 8 includes the primary cores 10 and 1
It has a secondary coil 11, a secondary core 12, a secondary coil 13, and a shield 14 having a gap 15, and these are packaged with a packaging resin mold 9. The impedance measuring device body 1 and the probe 8 are connected by coaxial cables 6 and 7. The primary core 10 of the probe shown in FIG.
Has a through hole 16 and the probe of FIG. 7 has a balun 18 and a short circuit wire 17. The equivalent circuit of the balun is shown in 19.

If the structures of FIG. 5, FIG. 6 and FIG. 7 are simplified, all are as shown in FIG. The figure is a view showing a cross section taken along a plane passing through an annular center axis of an annular core of a probe. The figure shows the cross sections of the primary and secondary transformers and the input and output of the transformers as the components of the probe. The exciting current supplied from the signal source 2 is the primary coil 11
And the primary toroidal core 10 is excited, a concentric electric field 31 around the center of the cross section of the primary toroidal core 10 is generated. When the probe is immersed in the solution, an electric field surrounding the probe is caused to flow in the solution by this electric field 31, and as a result, the secondary toroidal core 12 is excited, a current flows in the secondary coil 13, and a value is generated in the ammeter 5. From the vector ratio of this current value and the voltage applied to the primary coil 11 measured by the voltmeter 4, the conductance component and susceptance component of the solution can be obtained. Since the equivalent circuit of a solution is represented by a parallel circuit of a resistance determined by the conductivity of the solution and an electrostatic capacitance determined by the dielectric constant, a method of calculating the dielectric constant from the susceptance component of the solution, that is, the electrostatic capacitance component by calculation processing is Has been done.

FIG. 9 shows a current flowing by the electric field of the primary toroidal core. In the figure, the cross sections of the primary and secondary transformers and the exterior resin mold of the probe are drawn as constituent elements of the probe. Primary toroidal core 1
The electric current flowing by the electric field of 0 includes the electric current 32 flowing only in the solution and the electric current 33 flowing from the solution through the probe to the solution. Although not shown, the inside of the probe is filled with an insulator that insulates the conductor, so that there is stray capacitance due to the dielectric effect of the insulator, and a current flows there. Since the resistance value of the insulator is very high, the current flowing through the resistance component of the insulator can be ignored. The current 33 flowing through this floating capacitance interlinks with the secondary core 12 and reduces the current that should flow. As a result,
Roughly speaking, the dielectric constant is measured smaller than the true value.

As described above, the measured value of permittivity shows a value lower than the true value, and the measured value of permittivity is affected by the change in conductivity because the closed-circuit current generated by electromagnetic induction is The cause is that a part is shunted to the stray capacitance in the probe. As a countermeasure, it is conceivable to reduce the stray capacitance of the probe, but this is very difficult to realize due to many structural restrictions of the probe. Therefore, the applicant
Reference number 40950002 filed on December 29, 1994
We proposed a method to reduce the effect of stray capacitance by “correction method of electromagnetic induction probe”. This proposal has a drawback in that the operation for obtaining the floating capacitance by calibration is necessary.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art in which the dielectric constant is measured to be smaller than the true value, and the measured dielectric constant is affected by changes in conductivity. It is an object of the present invention to provide an electromagnetic induction probe capable of highly accurate dielectric constant measurement, which does not require calibration for obtaining a floating capacitance.

[0009]

SUMMARY OF THE INVENTION The present invention has devised a combined structure of a primary core and a secondary core. Specifically, by enclosing the primary core with a secondary core or vice versa, a closed circuit current generated by electromagnetic induction is probed. By realizing a probe that does not divert the internal stray capacitance, the measurement that is not affected by the stray capacitance is realized.

[0010]

1 is a conceptual diagram of an embodiment of the present invention in which a closed current generated by electromagnetic induction is not shunted to a stray capacitance in a probe. The figure is a view showing a cross section taken along a plane passing through an annular center axis of an annular core of a probe. In the drawings, elements having the same functions as those of the conventional technique are designated by the same reference numerals. The feature of this structure is that the secondary core 12 surrounds the primary core 10 and the cross sections of both cores are concentric. The primary coils 11 and 2 are provided in a part of the secondary core.
A hole through which the lead wire of the next coil 13 passes is provided. Since the cross sections of both cores are concentric, the electric field 31 generated by the excitation of the primary core is concentric so as to surround the two cores. As a result, all the electric fields 31 are in the tangential direction of the cross-sectional circle of the core, have no normal direction component, and no current flows from the solution to the core. That is, no current flows from the solution to the stray capacitance existing in the probe. As a result, all the closed-circuit current in the solution generated by the electromagnetic induction flows in the solution and excites the secondary core 12. Although the secondary core has a tubular shape, since the secondary coil 13 is wound so as to surround the cross section of the secondary core 12, a current flows through the secondary coil 13 by excitation as in a normal transformer. The ammeter 5 measures this current, and the impedance of the solution can be measured. The structure of the present invention has a symmetry condition of the structure of the Japanese Patent Application No. 6-172023, that is, "the two central axes of the two cores are coincident with each other and the center points of the circles are coincident with each other. By the way, the structure “symmetrical with respect to a plane perpendicular to the central axis” is satisfied. In the present invention, the plane on which the circular locus drawn by the centers of the cross sections of the two cores rides is the symmetrical plane.

FIG. 2 is a schematic diagram of FIG. 1 in which shields 14a and 14b, coaxial cables 6 and 7, and a balun 18 are provided.
It is the detail drawing which added the short circuit wire 17. The shield is
It is applied to prevent electrostatic coupling between the primary coil and the secondary coil. Therefore, the inner shield 14a and the outer shield 1
4b is a structure surrounding the secondary coil 13. Further, a gap 15 is provided at a position having a symmetrical structure with respect to the plane of symmetry so that the shield does not become a short ring with respect to the secondary coil. Balun 18 and short-circuit wire 17
Is provided for compensating the breaking of symmetry in the connection and extraction structure of the coaxial cables 6 and 7 and the coil. This operates similarly to the balun 18 and the short-circuit line 17 shown in FIG. 7 of the prior art. If the signal source 2, the voltmeter 4 and the ammeter 5 are not grounded, the balun 18 and the short-circuit wire 17 are unnecessary. The balun 18 and the short-circuit line 17 are unnecessary.

An embodiment of an assembling method for realizing the structure of the present invention is shown in FIG. The drawings are drawn for the purpose of showing the order of assembly and the wire connection of the coil, and details of the secondary core and the shield relating to the lead wire of the coil are omitted. Further, the positions of the lead lines of the coils are shown in a dispersed manner so that the connection of the coils can be easily understood. In order to realize the structure in which the primary core 10 is surrounded by the secondary core 12, the feature of this embodiment is that the secondary core is divided into a structure in which the secondary coil is wound inside the secondary core and outside. It consists of a coil to be wound. (1) The primary coil 11 is applied to the primary core 10. The winding start of the coil is 41 and the winding end is 42. (2) The inner shield 14a is provided on the primary coil.
A gap 15 is provided in the shield. (3) Inner winding 13 of the secondary coil on this shield
Apply a. The winding start is 43 and the winding end is 44. (4) The secondary core 12 is a plane that passes through the center of the ring and is perpendicular to the center axis of the ring and can be divided as shown in the figure. The assembly of the previous section is placed in this secondary core. (5) Outer winding 13b of the secondary coil on the outside of the secondary core
Give. The start of winding is 45 and the end of winding is 46. The inner winding 13a and the outer winding 13b have the same number of turns. Then, 13a and 13b are connected in series. The connection has a polarity such that a magnetic flux is generated only in the secondary core when a current is applied to the coil. That is, if the winding directions of the inner coil and the outer coil are similar (similar to the screw rotation and advancing direction), connect the winding start and the winding end as coil terminals, or connect the winding ends. And use the beginning of winding as the coil terminal. In the figure, the winding ends 44 and 46 are connected, and the winding start 43
And 45 are shown as terminals of the coil. Also,
If the winding directions of the inner coil and the outer coil are opposite, the winding start and winding end are connected, and the other winding end and winding start are used as the coil terminals. (6) Although not shown, an outer shield and an exterior mold are further applied to complete the assembly. Also, although the above does not mention insulation between the coil and the shield,
Insulate if necessary.

When winding a toroidal core, as in the case of the primary coil shown in FIG. 3, if the ring of the core is wound once from the beginning of winding to the end of winding, an air-core coil in which this ring forms one winding Is formed. Therefore, if the secondary coil has the same winding, there is a transformer coupling of one air core between the primary coil and the secondary coil. However, 2 of the present invention
In the secondary transformer, if the winding directions of the windings 13a and 13b are the same, the secondary coil returns from the inner winding start (or the winding end) to the outer winding start (or the winding end) and makes one round of the core ring. Therefore, the one-turn air core coil is not formed. Therefore, there is no coupling between the primary coil and the secondary coil by the air-core one-turn transformer, and it is effective in strengthening the isolation between the primary and the secondary. Although the embodiments of the present invention have been described above, the exemplary forms, partial shapes, arrangements, etc. are not limited, and modifications of the configuration are allowed as necessary without losing the gist of the present invention. Especially for convenience of explanation, 1
Although the secondary core is the inner side and the secondary core is the outer side, it is not limited to either one in practice.

[0014]

EFFECT OF THE INVENTION An improvement of the electromagnetic induction type probe proposed in Japanese Patent Application No. 6-172023 was proposed. According to the invention,
Since no current flows through the stray capacitance in the probe, it became possible to further eliminate the influence of the change in the conductivity of the solution on the measured dielectric constant. As a result, the solution dielectric constant can be measured with high accuracy, which is useful for practical use.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic structure of an embodiment of the present invention.

FIG. 2 is a diagram showing a detailed structure of an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a mounting method according to an embodiment of the present invention.

FIG. 4 is a diagram showing a tendency of a dielectric constant measurement value measured by a conventional technique.

FIG. 5 is a diagram showing a first example of a conventional probe.

FIG. 6 is a diagram showing a second example of a conventional probe.

FIG. 7 is a diagram showing a third example of a conventional probe.

FIG. 8 is a simplified diagram of the structure of a prior art probe.

FIG. 9 is a diagram showing a current path of a conventional probe.

[Explanation of symbols]

1: Impedance measuring device body 2: Signal source 3: resistance 4: Voltmeter 5: Ammeter 6: Coaxial cable 7: Coaxial cable 8: Electromagnetic induction type probe 9: Exterior resin mold 10: 1 primary toroidal core 11: primary coil 12: Secondary toroidal core 13: secondary coil 13a: inner secondary coil 13b: outer secondary coil 14: Shield 14a: inner shield 14b: outer shield 15: Gap 16: Core through hole 17: Short-circuit line 18: Balun 19: Balun equivalent circuit 31: Electric field induced by primary toroidal core 32: Current flowing only in solution 33: Current through both solution and probe 41: winding start terminal of primary coil 42: Terminal of winding end of primary coil 43: Winding start terminal of inner secondary coil 44: Terminal of winding end of inner secondary coil 45: Winding start terminal of outer secondary coil 46: Terminal of winding end of outer secondary coil

Claims (4)

(57) [Claims] 1. An electromagnetic induction probe having a primary transformer and a secondary transformer for measuring a dielectric constant of a solution, wherein the primary core and the secondary core are cut along a plane passing through an annular central axis of an annular core of the transformer. The electromagnetic induction probe, wherein the two transformers are configured such that the centers of the cross sections of the following cores overlap each other. 2. The cross section of the secondary core circulates concentrically with the cross section of the primary core, and
The primary core and the secondary core are arranged such that the centers of the cross sections of the secondary cores overlap each other, and the inner secondary coil wound inside the secondary core and the outer secondary coil wound outside are connected in series. The electromagnetic induction probe according to claim 1, wherein a coil of the secondary core is formed. 3. A structure in which the secondary core can be divided by a plane that passes through the annular center of the annular core and is perpendicular to the central axis of the annular shape, or substantially parallel thereto, A primary coil is wound, an electrostatic shield is provided on the outside of the primary coil, and the inside 2 is provided on the outside of the electrostatic shield.
An assembly in which a secondary coil is wound is housed inside the secondary core, an outer secondary coil is wound outside the secondary core, and winding start or winding end of the inner secondary coil and the outer secondary coil are mutually The electromagnetic induction probe according to claim 2, wherein the secondary coil is connected to form a secondary coil. 4. The electromagnetic induction probe according to claim 2, wherein the electromagnetic induction probe has a structure in which a primary transformer and a secondary transformer are replaced with each other.