JPH09210610A - High-frequency excitation differential transformer for preventing influence of external magnetism and metal, etc. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the influence to an output voltage due to the fluctuation of external magnetism and metal, etc. SOLUTION: A bobbin 1 made of bakelite, and a primary coil 2 which is wound over the entire length of the bobbin 1 by one to two layers are provided. A current power supply feeds an excitation current for exciting the primary coil 2 and has a current frequency of 50-2MHz. Further, the winding ratio with the primary coil 2 is approximately 0.5-2 and a pair of left and right secondary coils 4 are wound around the primary coil 2 while they are directly in contact with the primary coil 2, namely they are wound within the effective magnetic flux of the primary coil 2. A movable core 5 is sealed to a nonmagnetic support rod 5a and is made of a nonmagnetic conductive metal provided within the bobbin 1. Finally, a nonmagnetic protection case 6 protects the movable core 5 and the coils 2 and 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to electric parts, and more particularly to a differential transformer which is an electric sensor for measuring displacement in an analog manner. Above all,
The present invention relates to a differential transformer that can be used in a place where a magnetic field acts and a place where a metal approaches and separates, and is a high-frequency exciting differential transformer that is hardly affected by external magnetism, metal, and the like.

[0002]

2. Description of the Related Art A differential transformer is often used to measure displacement in a so-called bad environment caused by temperature, humidity, vibration, gas and the like. Small and robust analog displacement sensors include potentiometers, strain gauges and differential transformers. In this differential transformer, the coil can be completely sealed, the core moves in the bobbin without contact, and because a differential circuit is used, common mode noise is canceled and stable measurement is possible, and the output voltage is stable. Large and extremely easy to use.

In general, the structure of a differential transformer includes three coils wound on a cylindrical bobbin (that is, one primary coil and two secondary coils excited by the primary coil).
It is made of a metal core that moves inside the bobbin.
Then, the displacement amount of the core can be known by measuring the value of the output voltage by utilizing the property that the displacement amount of the core and the output voltage of the differential transformer maintain a proportional relationship. Therefore, it can be used as a displacement sensor. At this time, the output voltage indicating the amount of displacement of the core is so high that the resolving ability is said to be infinite, so that highly accurate measurement is possible.

The exciting current for exciting the primary coil is generally of a low frequency, but there is also a high frequency of which the size is reduced.

[0005]

As described above, the differential transformer is robust, has high accuracy, and can withstand use in a bad environment. However, since it is a sensor that uses lines of magnetic force, it has drawbacks associated with it. That is, unlike the case of current, this magnetic field line has a property of easily leaking to the outside of the conductor. Therefore, when used in an external magnetic field or when metals are close to each other, it is likely to be affected by them and stable and highly accurate measurement is often difficult.

First, the effect of the magnetic field will be described. For example, when using a differential transformer near an electromagnet, fixing a differential transformer with a permanent magnet, or measuring near a superconducting magnet, a strong magnetic field of up to 1,000 gauss to 4,000 gauss acts. Often happens. In such a strong magnetic field, the ferromagnetic parts such as iron and nickel are strongly magnetized and an attractive force is generated. Not only that, the strong magnetic field lines generated by being magnetized change the distribution state of the magnetic field lines generated from the primary coil of the differential transformer. Therefore, the induced voltage of the two magnetic coils changes and the output voltage of the differential transformer changes.

Of course, the differential transformer can be magnetically shielded, but in most cases there is no room in space. That is, if a magnetic shield cover in which iron plates or permalloy plates are stacked in multiple layers is attached around the differential transformer, the above fluctuation problem does not occur. However, there is usually no place to attach such a large and strong magnetic shield cover. Therefore, the differential transformer
It is usually exposed to strong magnetic fields.

In the low frequency excitation differential transformer having an excitation frequency of 10 KHz or less, the iron core is used because the magnetic permeability is used. Also, as will be described later, the magnetic lines of force generated by the primary coil of the low frequency excitation differential transformer are strong and are 10 mm from the coil.
It reaches a certain degree and is easily affected by external magnetic fields and external metals. Therefore, an iron shield case with a wall thickness of about 1 mm is usually used. However, in the case of iron of about 1 mm, the shielding effect is insufficient, and it is the current situation that the external magnetic field and the influence of metals are always bothered.

That is, when the low frequency excitation differential transformer is exposed to a strong magnetic field, in addition to the attractive force generated in the iron shield case and core of the differential transformer, the differential transformer is differentiated by the magnetized iron case. The output voltage of the transformer changes. According to the experiment, when a permanent magnet of about 2,000 gauss is brought close to the iron case, the output voltage changes by 10%.
%. Thus, in a strong magnetic field, a low frequency excitation differential transformer cannot perform stable and highly accurate measurement.

Next, the influence of adjacent metals will be described. The magnetic field lines in the iron shield case of the low-frequency excitation differential transformer are affected by the metal approaching the case, and the distribution state of the magnetic field lines also changes. If the distribution state of the magnetic field lines in the iron shield case changes, it affects the inside and changes the distribution state of the magnetic field lines generated by the primary coil. Therefore, the output voltage of the differential transformer fluctuates. According to the experiment, when a 30 mm square mild steel was brought close to the case, an output voltage of about 2% was generated. As described above, in the low frequency excitation differential transformer, the influence of the external magnetic field and the adjacent metal is considerably large, and it is necessary to give sufficient consideration to the measurement.

The differential transformer which the applicant of the present invention previously invented and applied for a patent (Japanese Patent Publication No. 1-54845) has a differential transformer of 50 KHz.
It is a so-called high frequency excitation differential transformer that uses a high excitation frequency of up to 2 MHz. In the case of this high frequency excitation differential transformer, as will be described later, the strength of the magnetic field lines generated in the primary coil thereof is about 1/10 of that of the low frequency excitation type.
Therefore, it is relatively unaffected by external magnetic fields and external metals. However, the lines of magnetic force tend to leak and are distributed over a considerable distance. Therefore, as in the case of the low frequency excitation differential transformer, it is natural that the external magnetic field 7 and the external metal are affected.

Therefore, the high frequency excitation differential transformer will be examined. First, the influence of the magnetic field of the high frequency excitation differential transformer will be described. In a high-frequency excitation differential transformer that uses an iron core and an iron shield case, attractive force is generated between the iron core and the iron shield case. And with it,
The iron shield case is magnetized, and the lines of magnetic force affect the inside. Therefore, the output voltage of the differential transformer fluctuates. In a high-frequency excitation differential transformer that uses a non-magnetic conductive metal that produces an eddy current effect such as copper or aluminum instead of an iron core and uses an iron shield case, the core is not magnetized. Therefore, no suction force is generated in the shield case. However, the iron shield case is magnetized as in the previous case to generate an attractive force, and the magnetic flux generated by the magnetization causes the output voltage of the differential transformer to fluctuate.

This output fluctuation is smaller than that of the low-frequency excitation differential transformer, but according to experiments, it is observed that when a permanent magnet of about 2,000 gauss is brought close to the high-frequency excitation differential transformer using an iron shield case (described later). Output fluctuation is about 5%
Met. From the above, it can be said that the high-frequency excitation differential transformer cannot measure with high accuracy because its output voltage fluctuates in a strong magnetic field.

Next, the influence of the metal that comes close to or away from the high frequency excitation differential transformer will be described. The effect is small compared to the magnetic field, but the output voltage of the differential transformer slightly changes depending on the metal that approaches or leaves. This is because the distribution state of magnetic lines of force in the iron shield case changes depending on the metal that approaches or leaves. However, since the strength of the magnetic field lines generated in the primary coil of the high frequency excitation differential transformer is smaller than that of the low frequency excitation differential transformer, the amount of fluctuation is small. According to the experiment (described later), the output voltage fluctuation when the 30 mm square soft iron was brought close to was 0.2%.

Summarizing the above results, in both the low-frequency excitation differential transformer and the high-frequency excitation differential transformer, the output voltage fluctuates considerably in a strong magnetic field, and the output voltage also fluctuates slightly depending on the adjacent metal. To do. As you can see, the conventional differential transformer has a magnetic field,
When there is a metal approaching, it is difficult to perform stable and highly accurate measurement.

The high frequency excitation differential transformer according to the present invention for preventing the influence of external magnetism or metal is improved in order to eliminate these drawbacks. In conclusion, a non-magnetic material such as aluminum or copper is used. This is a structure of a high frequency excitation differential transformer using a conductive metal as a core, which uses a protective case made of a non-magnetic material. Although the basic structure of the differential transformer itself is completely the same as that of the above-mentioned invention, by making the material of the protective case a non-magnetic material, it is hardly affected by the external magnetic field and the approaching metal. Therefore, the output voltage of the differential transformer hardly changes, and stable and highly accurate measurement can be performed.

Before explaining the effect of the non-magnetic material case,
It will be explained that the performance of the high frequency excitation differential transformer does not change even if the case of a non-magnetic material is used. The reason for this is simple, but as will be described later, the effective reach of the magnetic field lines generated in the primary coil of the high-frequency excitation differential transformer is only about 1 mm, so the case is installed at a position 1 mm or more away from the primary coil. In that case, there is no need for a shield effect against the magnetic field due to the case, so a non-magnetic material such as
It turns out that brass, aluminum, stainless steel, bakelite, etc. are all appropriate.

Generally, in a differential transformer, a lead wire from the coil is soldered to the coil wire, so that it is usual to provide a space of 2 mm or more on the coil. Therefore, the case is usually 2 mm from the primary coil.
It is installed far away. Since it suffices to use a non-magnetic material for this case, this improvement has no practical problem.

Next, the strength of the lines of magnetic force generated in the primary coil of the differential transformer quoted in various parts of the description will be described numerically. In conclusion, the effective magnetic field lines generated in the primary coil reach about 10 mm in the low frequency excitation differential transformer and about 1 mm in the high frequency excitation differential transformer. Will be described below with an example of a practical differential transformer.

Generally, in designing a primary coil of a differential transformer, an exciting current of about 10 to 30 ma is made to flow at an applied voltage of 2 to 3V. The impedance of the primary coil of both the low-frequency excitation differential transformer and the high-frequency excitation differential transformer is approximately 200Ω to 500Ω, which are about the same.
Since the impedance is a value obtained by combining the DC resistance and the AC resistance, most (95%) of the high-frequency excitation differential transformer is AC resistance, and the DC and AC resistance of the low-frequency excitation differential transformer are almost equal. Now, assuming that the impedance of the primary coil of the low frequency excitation and high frequency excitation differential transformer is 200Ω, the AC impedance of the primary coil of the high frequency excitation differential transformer is about 190Ω, and the AC of the low frequency excitation differential transformer is The impedance is

200 / √2 ≈ 140Ω Z = AC impedance of coil f = Magnetic frequency N = Number of turns of coil D = Diameter of coil K1 = Proportional constant

Then, the following equation is generally established. Z = K1 · f · (D × N) ² ··· (1) The coil diameter D of the high frequency excitation differential transformer and the low frequency excitation differential transformer is the same, and the excitation of the high frequency excitation differential transformer If the frequency is 100 KHz, the number of turns is N1, the excitation frequency of the low frequency excitation differential transformer is 1 KHz, and the number of turns is N2, then from equation (1), 190 = K1 · 100 · (D × N1) ² 140 = K1 · 1 -Two equations of (D x N2) ² are established. From this equation, the following equation is derived.

[0024]

(Equation 1) It can be seen from the equation (2) that the number of turns N2 of the coil of the low frequency excitation differential transformer is close to 9 times, that is, about 10 times the number of turns N1 of the high frequency excitation differential transformer. Next, the strength of the magnetic field line (ampere turn) is calculated. S = strength of magnetic field line I = exciting current N = number of turns of coil K2 = proportional constant

Then, the following equation is generally established. S = K2 · I · N (3) Since the excitation voltage is the same and the impedance is the same, the excitation current I of the high frequency and low frequency excitation differential transformers is the same value. Now, let S1 be the strength of the magnetic field lines of the primary coil of the high frequency excitation differential transformer, and S2 be the strength of the magnetic field lines of the primary coil of the low frequency excitation differential transformer. From equation (3), S1 = K2 · I · N1 S2 = K2, I, N2

## EQU1 ## Therefore, the ratio of the magnetic field lines of both differential transformers is S2 / S1 = N2 / N1 = 9 (substituting equation (2)). That is, the strength of the magnetic field lines of the primary coil of the low frequency excitation differential transformer is 9 times that of the magnetic field lines of the high frequency excitation differential transformer.
It turns out that it is about double. Therefore, the reaching distance of the effective magnetic field lines of the primary coil of the low frequency excitation differential transformer is about 10
If it is mm, it can be seen that the effective magnetic field line of the primary coil of the high frequency excitation differential transformer reaches about 1 mm.

This means that in the low frequency excitation differential transformer, the magnetic field lines of the primary coil are strong and reach a considerable distance from the coil. Therefore, it is necessary to provide an iron shield case to block external influences. On the other hand, in the high frequency excitation differential transformer, the magnetic field lines reach only about 1 mm. Therefore, when the case is installed outside it, it is not necessary to consider the shield effect against the magnetic field. Therefore, it can be seen that the case of a non-magnetic material may be used since the protective function of merely preventing the damage of the coil may be fulfilled, and the performance is not changed at all.

[0028]

In view of the above technical problems, a high frequency excitation differential transformer for preventing the influence of external magnetism, metal, etc. according to the present invention has a high frequency excitation difference of an excitation frequency of 50 KHz to 2 MHz. In a dynamic transformer, a nonmagnetic conductive metal that produces an eddy current effect such as copper or aluminum is used as a core, and a structure having a case of a nonmagnetic material, that is, copper, aluminum, stainless steel, bakelite, or the like is used.

The specific structure of the high-frequency excitation differential transformer for preventing the influence of external magnetism, metal, etc. according to the present invention will be described below in detail. First, the configuration of the invention described in claim 1 of the present invention will be described. First of all, there is a bobbin. Next is the primary coil. The primary coil is formed by winding one or two layers over the entire length of the bobbin. And there is an exciting current power supply. This exciting current power source sends an exciting current for exciting the primary coil, and has a frequency of the current of 50 KHz to 2 MHz.

Further, there is a pair of left and right secondary coils. The pair of left and right secondary coils has a winding ratio of about 0.5 to 2 times with the above primary coil, and is wound directly on the above primary coil. It is wound within the effective magnetic flux of the primary coil. Then, there is a movable core fixed to a non-magnetic support rod. The movable core is made of a non-magnetic conductive metal provided inside the bobbin. Finally, there is a non-magnetic protective case. The non-magnetic protective case protects the movable core and the coil.

Next, the structure of the invention according to claim 2 of the present invention will be described. The present invention is the same as the configuration of the first aspect of the present invention except for the following points. Therefore, the entire text of the above description of the configuration of the invention of claim 1 is incorporated herein, and the following description of the configuration is added thereto. The difference from the configuration of the invention of claim 1 is the above case.
This case is composed of a movable core fixed to a non-magnetic support rod and a diamagnetic material having a relative magnetic permeability close to 1 such as copper or brass that protects the coil.

[0032]

The high-frequency excitation differential transformer for preventing the influence of external magnetism, metal, etc. according to the present invention has the following actions because of the above-mentioned configuration. That is, the core and the case are non-magnetic materials. Therefore, since it is not magnetized by the external magnetic field, no attractive force is generated. In addition, the magnetic field lines do not change due to the magnetization. Therefore, there is no fluctuation in the output voltage of the differential transformer. Since the protective case is not magnetized, the line of magnetic force does not change even when a metal approaches the outside, and the output voltage from the secondary coil does not change.

Therefore, the high frequency excitation differential transformer which uses a non-magnetic and conductive metal that produces an eddy current effect as a core and uses a case of a non-magnetic material is affected by the external magnetic field or even when the metal approaches the outside. Absent. Therefore, since the output voltage of the differential transformer does not change, stable and highly accurate measurement can be performed.

Here, various cases of the magnetic field will be briefly described. Generally, there are static magnetic fields and dynamic magnetic fields (including alternating magnetic fields). Most of the magnetic fields encountered in normal measurement are the case of a uniform static magnetic field that does not change with time or a uniform dynamic magnetic field that slowly changes. In addition to this, when a commercial frequency alternating magnetic field generated by a power line or a strong magnetic field passes at high speed (for example, the magnetic field due to superconductivity moves at a speed of 500 km / h on the Linear Shinkansen, so it passes a width of 10 cm. The time is 0.7ms).

Of these, the size of the differential transformer is extremely small with respect to the region where the magnetic field changes, except for the state where the magnetic field moves at high speed. For example, it may be considered that the magnetic field acts uniformly on a coil wound on a bobbin of about 5 mm in general. If a uniform magnetic field acts on the differential transformer, it will give a similar magnitude change to the two secondary coils. Since the secondary coils are differentially connected, this change corresponding to in-phase noise is canceled by each other, and the output voltage of the differential transformer does not change.

When the magnetic field passes at a high speed, the placement of the differential transformer may be devised so that the change in the magnetic field acts on the two secondary coils in the same phase. That is, if the direction of the bobbin of the differential transformer and the direction of the magnetic field are made to coincide with each other, the same line of magnetic force simultaneously passes through the two secondary coils.
Therefore, the same magnitude of change occurs in each secondary coil, so that the changes cancel each other out and the output voltage of the differential transformer does not change.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high frequency excitation differential transformer for preventing the influence of external magnetism, metal, etc. according to the present invention will be described below in detail with reference to the accompanying drawings using an embodiment thereof. As shown in the sectional view of the differential transformer S shown in FIG. 1 and its wiring diagram shown in FIG. 2, there is a bakelite bobbin 1 first. On this bobbin 1, three disk-shaped collars 1a are adhered to both ends and the center of the bobbin 1. These three disk-shaped collars 1
Since a has a slit process of about 0.5 to 3 mm, it can be freely wired through this slit when winding a coil or when processing a coil wire. Next is the primary coil 2. This primary coil 2
Is obtained by winding one to two layers over the entire length of the bobbin 1. Then, there is an exciting current power source 3 (see the wiring diagram of FIG. 2 and the cross section / wiring diagram shown in FIG. 3). The exciting current power supply 3 sends an exciting current for exciting the primary coil 2 and has a frequency of 50 KHz to 2 MHz.

Further, there is a pair of left and right secondary coils 4.
The pair of left and right secondary coils 4 has a winding number ratio of about 0.5 to 2 times with the above-mentioned primary coil 2, and is wound in close contact with the above-mentioned primary coil 2 directly. That is, it is wound within the effective magnetic flux of the above primary coil. Then, there is a movable core 5. The movable core 5 is fixed to a non-magnetic support rod 5a and is made of a non-magnetic conductive metal provided in the bobbin 1. Finally, there is a non-magnetic protective case 6. The nonmagnetic protective case 6 protects the movable core 5 and the coils 2 and 4. The case 6 may be made of a diamagnetic material having a relative magnetic permeability close to 1 such as copper or brass that protects the movable core and the coil.

However, in the high frequency excitation differential transformer S using the movable core 5 due to the eddy current effect, when the case of the non-magnetic material is used, the influence of the external magnetic field and the approaching metal is different from the case of the iron case. In order to demonstrate that the case 6 shown in FIG. 1 is hardly received, the cases 6 made of various materials were prepared, and the influence of the magnetic field and the metal when each case was used was measured. The structure of the high frequency excitation differential transformer used is the same as that of FIG. 2, and the materials and dimensions of each component are as follows.

(1) Bobbin 1 is a bakelite pipe,
The outer diameter is 5.3 mm, the inner diameter is 4.3 mm, and the length is 46 mm. (2) The collar 1a is a bakelite disc with an outer diameter of 9.8 mm and an inner diameter of 5.3.
mm, width 2 mm, and bonded to bobbin 1. (3) The primary coil 2 is a polyurethane wire having a diameter of 0.1 mm wound closely in parallel in one layer over the entire length of the bobbin 1, and the number of turns is 350 turns. (4), (5) The two secondary coils 4 are divided from the center of the bobbin 1 into the right and left, and two layers of polyurethane wire with a diameter of 0.1 mm are directly wound on the primary coil 2 in close contact (generally 2 In order to wind the next coil neatly, the primary coil is wrapped with insulating paper, etc., and then the secondary coil is wound on it, but it is wound directly without this). The number of turns is 350 turns each. Is.

(6) The movable core 5 is a brass pipe with an outer diameter of 4 mm,
It has an inner diameter of 3 mm and a length of 22 mm and is adhered to the support rod 5a. (7) The support rod 5a is a non-magnetic stainless round bar,
The diameter is 3 mm and the length is about 70 mm. Protective case 6 here
Is a pipe having an outer diameter of 12 mm, an inner diameter of 10 mm and a length of 46 mm, and is made of iron, stainless steel, aluminum, bakelite and brass as described below.

The electrical conditions of this differential transformer S are as follows. The frequency of the exciting current power source 3 for exciting the primary coil 2 is 100 KHz, the exciting voltage is 2 V, and its electric circuit is adjusted so that the output voltage ± 5 V can be obtained for the displacement of the movable core 5 ± 5 mm. . Further, the magnetic field method was performed with the position of the movable core 5 at the time of measuring the fluctuation of the output voltage caused by the influence of the approaching metal being fixed to an appropriate output voltage of + 3V to + 5V. The influence of the external magnetic field was measured by the magnitude of the fluctuation of the output voltage generated when the 2,000 Gauss permanent magnet Mg was moved closer to the protective case 6 as shown in FIG. The effect of external metal is to prepare iron and brass with a length of 30 mm and a length of about 50 mm, and the fluctuation of the output voltage that occurs when each metal Mt is brought close to the case of the differential transformer as shown in FIG. The size was measured.

Next, the fluctuation rate of the output voltage in each measurement is shown below. In the iron case, variation by magnet: 5% Variation by steel: 0.2% Variation by brass: 0% In non-magnetic stainless case Variation by magnet: 0.5% Variation by steel: 0.05% Fluctuation due to brass ... 0.05%

Fluctuations due to magnets in aluminum case ・ ・ ・ 0.6% Fluctuations due to steel ・ ・ ・ 0% Fluctuations due to brass ・ ・ ・ 0% Fluctuations due to magnets in Bakelite case ・ ・ ・ 0.2% Fluctuations due to steel ・ ・ ・・ ・ 0.2% Fluctuation due to brass ・ ・ ・ 0.2% Fluctuation due to magnet in brass case ・ ・ ・ 0.06% Fluctuation due to steel ・ ・ ・ 0% Fluctuation due to brass ・ ・ ・ 0%

As can be seen from the above measurement results, the variation of the output voltage due to the magnetic field is 5% which is a considerably large value in the iron case, but is 1% or less in all cases of the non-magnetic material, which is extremely good. The effect of metal is 0.2% or less in the case of non-magnetic material, which is extremely small and practically sufficient. As described above, in the high frequency excitation differential transformer S having the movable core 5 such as copper or aluminum which is a non-magnetic conductor due to the eddy current effect, by using the non-magnetic case 6, the external magnetic field Mg and the external metal Mt are The influence of can be extremely reduced. Therefore, the external magnetic field Mg
It is possible to perform stable and highly accurate measurement even in the presence of the external metal Mt.

Fluctuating external magnetic field Mg and contacting / separating metal Mt
In order to reduce the influence of the above, it is possible to use the case 6 of the non-magnetic material, as shown in the embodiment. In this embodiment, the brass case is particularly effective. The reason for the large effect is due to the characteristics of this material, and the non-permeability of copper is extremely close to 1 as compared with other materials. Moreover, it has a property of diamagnetism. That is, by using a case of a diamagnetic material having a relative magnetic permeability close to 1, it is possible to manufacture a high frequency excitation differential transformer which is extremely less affected by an external magnetic field and a nearby metal, so that the effect is very large.

In general, the term non-magnetic material refers to ferromagnetic materials such as iron, nickel and cobalt. All materials are slightly magnetized, but non-magnetic materials are less magnetized. Usually, it does not cause a problem when a strong magnetic field does not act or when precise measurement is not necessary, but it causes a problem because the measurement of the sensor has an influence depending on the degree of magnetization. Non-magnetic materials include paramagnetic materials that magnetize in the direction of the magnetic field (eg, aluminum, platinum, air, etc.) and diamagnetic materials that magnetize in the direction opposite to the magnetic field (eg, copper, zinc, gold, water, etc.). There is.

Next, the relative magnetic permeability (1 in vacuum) of some materials is shown. Aluminum: 1.00022 Water: 1.000088 Air: 1.000037 Copper: 1.0000094

As can be seen from the value of the relative magnetic permeability, copper has a value extremely close to 1 as compared with other materials. Vacuum is 1
Therefore, a value close to 1 indicates that the material is hard to be magnetized. That is, since it is difficult to magnetize, the brass case is extremely unlikely to be affected by the external magnetic field or metal. Further, being a diamagnetic material, when magnetized, it is magnetized in the direction opposite to the magnetic field. Therefore, it acts in a direction to cancel the influence of the external magnetic field. Therefore, the influence of the external magnetic field is further reduced. Of course, it is natural that the degree of magnetization (relative permeability) has a greater influence on the external magnetic field than the direction of magnetization, and a material having a relative permeability closer to 1 is more effective. Is.

[0050]

The high-frequency excitation differential transformer for preventing the influence of external magnetism, metal, etc. according to the present invention has the following great effects because of the above-mentioned effects. That is,
By using the case of non-magnetic material, the influence of fluctuating external magnetic field and metal moving close to and away from it has been greatly reduced.

[Brief description of drawings]

FIG. 1 is a front cross-sectional view of a high frequency excitation differential transformer for preventing the influence of external magnetism, metal, etc. according to the present invention.

FIG. 2 shows a wiring diagram of that of FIG.

FIG. 3 shows a front sectional view and a wiring diagram of that of FIG.

FIG. 4 is an explanatory perspective view showing the differential transformer of FIG. 1 and its fluctuating external magnetic field in place of a magnet.

5 is an explanatory perspective view showing the differential transformer of FIG. 1 and its varying external metal in place of a metal rod.

[Explanation of symbols]

 1 bobbin 2 primary coil 3 exciting current power source 4 secondary coil 5 movable core 5a support rod 6 non-magnetic protective case

Claims (2)

[Claims] 1. A bobbin, a primary coil wound in one or two layers over the entire length of the bobbin, an exciting current power source for exciting the primary coil, the frequency of which is 50 KHz to 2 MHz, and the primary coil described above. And a pair of left and right secondary windings having a winding number ratio of about 0.5 to 2 times and wound directly in close contact with the primary coil, that is, in the effective magnetic flux of the primary coil. A coil, a movable core fixed to a non-magnetic support rod made of a non-magnetic conductive metal provided in the bobbin, and a protective case made of a non-magnetic material for protecting the movable core and the coil. A high-frequency excitation differential transformer that prevents the effects of external magnetism and metals. 2. A bobbin, a primary coil wound by one to two layers over the entire length of the bobbin, an exciting current power source for exciting the primary coil, the frequency of which is 50 KHz to 2 MHz, and the primary coil described above. And a pair of left and right secondary windings having a winding number ratio of about 0.5 to 2 times and wound directly in close contact with the primary coil, that is, in the effective magnetic flux of the primary coil. A coil, a movable core fixed to a non-magnetic support rod made of a non-magnetic conductive metal provided in the bobbin, and a relative magnetic permeability of 1 such as copper or brass for protecting the movable core and the coil. A high-frequency excitation differential transformer for preventing the influence of external magnetism, metal, etc., which is composed of a protective case made of a close diamagnetic material.