JPS62105069A - Magnetic field detecting method - Google Patents

Abstract

PURPOSE:To pickup a magnetic field which is present in an outward field with high sensitivity and to detect a stable, wide-range magnetic field distribution by reducing variation of a voltage induced across detection winding as mush as possible or canceling it by reverse excitation with a current flowed through control winding. CONSTITUTION:A common core AC forms an open magnetic path equipped with exciting winding N1, detection winding N2, and control winding N3. Then, the exciting winding N1 excites the core AC previously to induce a voltage determined by the magnetism characteristics of the core AC across the detection winding N2 by the excitation, and this is used as a reference induced voltage. On the other hand, part of the core AC exposed to a magnetic field is placed in a magnetic field to be measured and magnetized. Variation of magnetic flux caused by the magnetization is detected as variation of the reference induced voltage and the core AC is excited reversely by the control winding N3 to reduce or cancel the variation, thereby detecting the object magnetic field properly from the control current for the reverse oxcitation which reduces or cancels the variation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic field detection method in which the magnetic field of an object to be measured is picked up by a core that is in an excited state in advance, and the magnetic field to be measured is detected based on changes in the magnetic flux.

Prior Art and its Problems Conventionally, a method using a Hall element is known as a typical magnetic field detection method. This method attempts to detect an external magnetic field using the Hall voltage obtained from the magnitude of the magnetic field passing through the Hall element, but it has extremely poor temperature characteristics and is unstable due to changes in environmental temperature. In addition, it is difficult to manufacture a Hall element with a large surface area, and it is unsuitable for detecting a magnetic field to be measured over a wide range, which limits its use.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention applies the principle of the magnetic field flux method to a novel method that picks up magnetic fields existing in the external field with high sensitivity and enables stable detection of magnetic field distribution over a wide range. This provides a magnetic field detection method. The present invention also provides a magnetic field detection method that is compact and has high performance by using an open magnetic path having a short core and three windings as a detector element.

The detailed purpose and effect of the configuration of System II can be understood from the explanation of the embodiment described below, and the gist is that three windings, an excitation winding, a detection winding, and a control winding, are connected to a common core. An open magnetic path is formed, and the core is excited in advance with an excitation winding.
By the excitation, an induced voltage determined by the magnetization characteristics of the core is generated in the detection winding, and this is used as a reference induced voltage, and on the other hand, a part of the core that is exposed to the magnetic field is placed in the magnetic field to be measured and magnetized, The magnetic flux change caused by the magnetization is detected as a change in the reference induced voltage, and the core is reversely excited by the control winding to reduce or offset the change, and the reduction or cancellation is The magnetic field to be measured is appropriately detected from the generated control current for reverse excitation.

Embodiments of the Invention The inventors have already developed and proposed a triangular wave type and integral type current detector using a transformer having four windings as a detection element to which the electromagnetic flux method is applied.

The present invention further aims to develop magnetic field detection methods such as triangular wave method and integral method to which this electromagnetic flux method is applied.

FIG. 1 is a principle diagram of a magnetic field detector according to the present invention that comprehensively represents both of the above-mentioned systems, and FIG. 2 is a specific circuit diagram of the same.

As shown in Figure 1, the core AC is made of a soft magnetic material having at least three windings with an open magnetic path shape sufficient to be magnetized in one direction by the magnetic field to be measured, and the first winding is an excitation winding. line Nl, the second winding is the detection winding N2. The third winding is a control winding N3. The core AC is conditioned to form an open magnetic path as described above, and preferably has a direct shape, and each! ! 8
The part where the wire is wound is shielded from the magnetic field by a magnetic field shielding enclosure K, and a part of the core AC is exposed to the magnetic field, and this is defined as a magnetic field detection part to be measured Act.

The excitation winding Nl and the detection winding N2 are windings for determining how the core AC is magnetized by the magnetic field to be measured Hx, and the excitation winding Nl has a sine wave.

The core AC is excited by passing an AC wave electric FtieX such as a triangular wave or a trapezoidal wave, and an induced voltage ed determined by the magnetization characteristics of the core AC itself and the excitation current iex is generated in the detection coil N2 to generate the magnetic field to be measured. The voltage that does not incorporate Hx is set as a reference induced voltage, and its output (the reference induced voltage or the output of the induced voltage including the variation) is used as the input of a magnetic flux detection circuit shown as a flux net. The magnetic flux detection circuit Fl
The ux port et is connected to the core AC based on the voltage ed induced in the detection winding N2 by the excitation of the excitation winding Nl and the magnetic field to be measured Hx.
detects changes in magnetic flux within the magnetization curve, and outputs a detection output φdet corresponding to the positive/negative asymmetry in the phase or amplitude of the magnetization curve (this is referred to as magnetic flux detection section B).

That is, by placing the detection unit ACI of the core AC exposed to the magnetic field within the magnetic field Hx to be measured, the core AC
is magnetized, and the magnetic flux change caused by the magnetization is detected by the detection winding N2 as a change in the reference induced voltage (induced voltage Hd including the change), and this is output as the detection output φdet.
Output as . A current ic according to the detection output φdet
is applied to the control winding N3 and the core AC is reversely excited, thereby reducing or canceling out the above variation.

In Fig. 1, the target value φr is set to zero, and a control current that cancels out the old change is applied to the control winding fiN3.
rol of ic is based on the above detection signal #de t,
This shows a control current applying circuit that flows an electric current fli, ic through the control winding N3 to reduce or cancel out the above-mentioned change (this is referred to as a control current source C). Detect.

FIG. 3 shows a specific example of a triangular wave type circuit based on the above principle and achieving the same purpose. As shown in the figure, amplifier A
mp, excitation winding Nl, and resistor Rex constitute a current amplifier (excitation current MA).

The excitation current source A supplies a triangular wave current iex having a peak value sufficient to saturate the core AC, thereby exciting the core AC. Further, the magnetic flux detection section B is connected to a waveform shaping circuit E that shapes the voltage waveform induced in the detection winding N by excitation by the triangular wave current iex and the magnetic field to be measured Hx, and a waveform shaping circuit E that shapes the voltage waveform induced in the detection winding N by excitation by the triangular wave current iex and the magnetic field to be measured Hx. A pulse generating circuit P that outputs a pulse (shown as the output of P in FIGS. 3 and 4) having a sufficiently short time I+ according to the period of the triangular wave, and a pulse generating circuit P that samples the triangular wave current by using the pulse output as a sampling pulse. It consists of sample-and-hold circuits SHP and SHN.

A proportional-integral circuit Gs outputs a control current command signal iCr based on the difference ε between φd and target value φr from the control current source C to the detection signal outputted from the magnetic flux detection section B, and the control l
It consists of an amplifier Amp' which inputs the '\L flow command signal icr', and a control winding N3 through which a control current, which is the output of the amplifier, is passed.

Considering an amorphous open core with sharp square characteristics as the soft magnetic material forming the core AC, when the core AC is excited with a triangular wave excitation current source A, the detection winding N
2, an induced voltage ed corresponding to the magnetization characteristics of the amorphous open core is generated.

In a steady state or when the detection part Act of the core AC is placed within the measured magnetic field Hx of the object to be measured and this is zero, the magnitudes of the currents 1exp and iexn are equal and have opposite polarities as shown in Figure 3. . Therefore, the voltage e induced in the detection winding N2
The waveform of d is symmetrical between positive and negative, and the output of the magnetic flux detector has φ
d, that is, the detection of the change is zero.

On the other hand, if the magnetic field to be measured Hx picked up by the detection unit Act of the core AC is not zero, as shown in FIG.
(Hx) causes a sufficient change in the magnetic flux within the core A, and the phase of the voltage ed induced in the detection winding N2 changes accordingly, and the waveform of the induced voltage ed that includes the change is changed by the change in magnetic flux. will be shifted (out of phase) by
In other words, the phase is asymmetrical.

The induced voltage ed of this asymmetrical waveform is applied to the waveform shaping circuit E, and a pulse having a time width sufficiently shorter than the period of the triangular wave is generated in synchronization with the rise of the voltage waveform shaped by the pulse generating circuit P (see FIG. 3).

(shown as the output of P in Fig. 4), and its positive and negative pulse signals are taken as timing signals of sample and hold circuits SHP and SHH, respectively, and the magnitudes of excitation currents 1exPn and 1exNn when the timing signals are generated are This sum is used as the detection output of the change in the induced voltage in the magnetic flux detecting section B, that is, the change in magnetic flux as $d. In this detection output, φd corresponds to the magnitude of the magnetic field to be measured.

In the control current source C, this detection output has φd and target value φ.
A control current command signal icr is outputted from the proportional-integral circuit Gs based on φd=ε for the difference φr- of r, and the control current ic is caused to flow through the control winding Nc via the amplifier Amp'.

The core AC is reverse excited by this control current IC, thereby reducing or canceling out the change in the magnetic flux, that is, the change in the reference induced voltage. The magnetic field to be measured Hx is detected from the current ic flowing through the control winding Nc in order to reduce or offset this change. Rd is a resistor for taking out this detection as a voltage, and the detection signal φxdet is taken out as a voltage Rdic.

Although the case where a triangular wave method is applied as a magnetic field detection method has been described here, a corresponding result can also be obtained by a zero magnetic flux method using an integral method according to the principle shown in FIG.

The above-mentioned refinement method focuses on the fact that the positive and negative amplitudes of the voltage waveform induced in the detection winding N2 differ depending on the magnetic field to be measured, and slices the positive and negative voltages, which are asymmetrically distorted, at a certain amplitude or more. , by adding this, integrating over one cycle of the excitation current, and sampling and holding the final value, a detection output corresponding to the magnetic flux change is obtained, and the core AC
It is possible to know how the magnetic field Hx is biased by the magnetic field to be measured Hx.

As in the case of the triangular wave method, the control current i is controlled by the control current source C so as to always offset or attenuate the above variation.
By flowing the control current ic, the magnetic field to be measured Hx can be detected from the control current ic.

Effects of the Invention As explained above, the present invention makes it possible to provide a compact and high-performance magnetic flux detection device by using an open magnetic path having three windings: an excitation winding, a detection winding, and a control winding. Ta. That is, the present invention adopts a method of detecting the magnetic field to be measured from the current value by reducing or canceling the change in the induced voltage due to the detection winding as much as possible by the current flowing through the control winding. The detection range of the magnetic field to be measured has been significantly expanded, and by arbitrarily selecting the winding thickness, core size, circuit capacity, etc., magnetic field detection has the ability to handle all measurement objects that have a magnetic field within the detection range. Equipment could be provided. or,
It has the advantage of enabling stable magnetic field detection that is not affected by disturbance factors such as external temperature.

[Brief explanation of drawings]

Fig. 1 is a flowchart of a magnetic field detection method showing an embodiment of the present invention with a principle diagram, Fig. 2 is a specific circuit diagram applying this to a triangular wave type zero magnetic flux method, and Fig. 3 is a diagram of the device to be measured. FIG. 4 is a waveform diagram when the magnetic field is zero, and a waveform diagram when a measured magnetic field is detected. AC... Core forming an open magnetic path, Act... Measured magnetic field detection section, N1... Excitation winding, N2... Detection winding, N3... Control winding, A... Excitation current source, B...
Magnetic flux detection section, E... waveform shaper of the same detection section, P...
Pulse generator, C... control current source. Patent applicant Meguro Electric Seizo Co., Ltd. Figure 3 Figure 4 □ Procedural amendment document June 6, 1988 Patent Application No. 245851 2 Name of the invention Magnetic field detection method 3 Person making the amendment/IS matter Relationship between Patent applicant name Meguro Electric Manufacturing Co., Ltd. 4th agent Address: 144 5 Date of amendment order Voluntary action (1) "Induced voltage HdJ" on page 5, line 14 of the specification
Correct it to "induced voltage ed". (2) Same page 6: Correct "Figure 3" in line 56 to "Figure 2." (3) "Correct the above core ACJ to the above core ACJ" on the 10th line of page 6. (4) Correct "by the r period" on the 16th line of page m6 to "from the period"

Claims (1)

[Claims] A core forming an open magnetic path is excited by an excitation winding wound around the core, a reference induced voltage is generated in a detection winding wound around the core by the excitation, and the other is placed in a state exposed to the magnetic field. A part of the core is placed in the magnetic field to be measured and magnetized, and the magnetic flux change caused by the magnetization is detected as a change in the reference induced voltage by the detection winding, and based on the change. Magnetic field detection that reduces or cancels the change by flowing a control current through a control winding wound around the core to reverse excite the core, and detects the magnetic field to be measured from the control current that causes the reduction or cancellation. Law.