JPH0638101B2 - Magnetic field detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus for detecting an extremely small magnetic field with high sensitivity and high speed response.

Conventional technology For detecting an extremely small magnetic field of, for example, 10 ^-9 Tesla or less, there are conventional flux gate type magnetic detectors, superconducting quantum interferometers, etc.
The detection limit is limited by the magnetic noise of the magnetic material used for the core, and no superconducting quantum interferometer has yet appeared, for example, that does not require a cryogenic maintenance device at this time. Therefore, special technology, expensive materials and equipment are required at present.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention has solved the above problems,
In other words, regarding magnetic noise, avoid the discontinuous magnetization range due to internal strain and compositional inhomogeneity of the magnetic material used as the core, voids and impurities, and make the nonlinear region larger than the discontinuous magnetization range the dynamic of the sensor core. By causing magnetic excursion to reach the magnetization level (excitation region), magnetic noise is effectively reduced from appearing in the output, and by applying the zero magnetic field method, it has excellent linearity and exists in the outside world. It is possible to detect a magnetic field with high sensitivity and to detect a magnetic field in a stable and wide range. Further, the present invention can be carried out without using a particularly expensive device such as a liquefied gas and a device for maintaining the same, and enables highly sensitive detection of an extremely small magnetic field that could not be measured without a superconducting quantum interferometer. At the same time, this makes it possible to provide a high-sensitivity magnetic detection device that is simple and inexpensive for the user.

Means and Actions for Solving Problems The dynamic magnetization level of the sensor core excited by the alternating current is determined by the external magnetic field (hereinafter, detected magnetic field H _X
That is, the magnitude of the dynamic differential permeability of the core also changes accordingly. Therefore, if the change in magnetic permeability caused by the detected magnetic field H _X is detected as the transformer electromotive force generated in the secondary winding with respect to the high-frequency exciting current, the magnitude and polarity of the detected magnetic field can be known. it can. However, if the dynamic magnetization level of the sensor core is in the discontinuous magnetization range, harmful electro-magnetic noise that is not based on the detected magnetic field may be superimposed on the transformer electromotive force generated in the secondary winding. Is recognized.

The present invention applies a DC excursion magnetic field to the sensor core at the same time as excitation by the AC current to excite the excitation region of the core to a nonlinear region larger than the discontinuous magnetization range, and to detect the detected object in the excitement excitation region. A magnetic field is sensed, and a control current is caused to flow through the control winding added to the sensor core based on the change in the induced electromotive force generated in the secondary winding of the sensor core, and the sensor core is reverse-excited. By doing
The problem is solved by canceling or canceling the change, and detecting the magnetic field to be detected from the control current that causes the cancel or cancel.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. The example shows a case where two sensor cores are used as a representative example.

A and B are transformers, a and b are sensor cores in each transformer, and primary windings A ₁ and B of the sensor cores a and b are provided.
_One input terminal 2 and 5 are connected to each other, and an AC power source E and a DC power source D are connected to the other input terminals 1 and 6 in series as shown by the solid line in FIG. And the resistance C ₁ is connected in series to the series or parallel power supply circuit. In the case of the parallel power supply circuit, the resistances C ₂ and C _{3 are connected.}
Are connected in series, and one output end 4 of the secondary winding A ₂ of the sensor core a and one output end 7 of the secondary winding B ₂ of the sensor core b are connected. , And a low noise amplifier F between the output terminals 3 and 8 of the secondary windings A ₂ and B _2.
The synchronous rectifier G and the frequency selective attenuator H are connected via the.

Here, the “•” marks attached to the four windings A ₁ , B ₁ , A ₂ , and B ₂ indicate the polarities of the windings, and the primary windings A ₁ and B ₁ of the sensor cores a and b are shown. the winding direction is reversed phase with respect to the detected magnetic field H _X, winding directions of the secondary winding a _2, B ₂ are in phase with respect to the detected magnetic field.

Further, a third winding is added to each of the sensor cores a and b, and these are used as control windings A ₃ and B ₃ in the zero magnetic field method. The control windings A ₃ and B ₃ are arranged so that their winding directions are opposite to the magnetic field to be detected, and one of the winding terminals 16 and 1
Connect 7 to each other. Further, as a control system of the control windings B ₃ and A ₃ , a control current command signal is generated based on a difference ε between the detection signal 14Khd of the frequency selective attenuator H and the target value Hr of the change from the deflection magnetic field of the sensor cores a and b. A proportional integrator circuit I that outputs icr is provided, and the control current command signal icr of the proportional integrator circuit I is used as one differential input voltage of the amplifier J, and the output side of the amplifier J is controlled by the control winding B _3. Connected to the other winding terminal 18 of the control winding B ₃ and outputs the control current ic, which is the output of the amplifier J, to the control winding B ₃ →
Allowed to flow into A _3, the voltage flowing the output of the other winding terminals 15 of the control windings A ₃ to the resistor Rd and the other differential input voltage of the amplifier J.

With the above circuit, a current that cancels or reduces the detected magnetic field H _x in the sensor cores a and b is generated in the control windings B ₃ and A.
_It is controlled so that it flows to ₃ .

The shape of the sensor cores a and b in the transformers A and B is a rod shape, a strip shape, or a linear shape that forms an open magnetic circuit, respectively. As a material of the cores a and b of the transformers A and B, the magnetism of a ferromagnetic material is used. A material such as an amorphous alloy or permalloy is used.

Thus, at the input ends 1 and 6 of the primary windings A ₁ and B ₁ of the sensor cores a and b, an alternating current 9 (iex) and a direct current 10 (id
c) is superimposed and added, and sensor cores a and b are applied with alternating current 9
And apply an AC magnetic field while simultaneously applying a DC current 10
Apply a DC excursion magnetic field.

Thus, the detected magnetic field H applied to the sensor cores a and b
_The signal 12 amplitude-modulated by _{x is applied} to the sensor cores a and b.
Of the secondary windings A ₂ and B ₂ of the output terminals 3 and 8 of
After passing through the low-noise amplifier F, the synchronous rectifier G rectifies the signal 12 in synchronism with the primary side alternating current 9, extracts a signal 13 having a polarity corresponding to the direction of the magnetic field H _{X to} be detected, and further selects the frequency. The signal 14 obtained by removing the component of the primary side alternating current from the signal 13 is extracted by the sex attenuator H.

As described above, the change in the induced electromotive force on the secondary windings A ₂ , B ₂ side according to the detected magnetic field H _X sensed by the sensor cores a, b can be extracted as the signal 14. At this time, as shown in FIGS. 2 and 3, the sensor cores a, b
The magnitude of the deflection magnetic field Hdc, −Hdc by the direct current 10 that magnetizes the magnetic material used for is set so as to fall within the nonlinear region larger than the discontinuous magnetization range M ₁ of the magnetic material. Preferably, the deflection magnetic field Hdc, -Hdc is set to a rotating magnetization range M ₃ which is larger than the discontinuous magnetization range M _{1 and} smaller than the saturation magnetization range M ₂ , and a direct current 1
The magnitude of the alternating current 9 to be superimposed on 0 is set so as not to fall within the discontinuous magnetization range M ₁ and the saturation magnetization range M ₂ .

As a result, the excitation regions of the sensor cores a and b are deviated to a nonlinear region larger than the discontinuous magnetization range M ₁ , and the detected magnetic field H _X is sensed in the deviated excitation region, optimally the rotating magnetization range M ₃ . Perform magnetic field measurement.

FIG. 2A shows the magnetization characteristics of the magnetic materials of the cores a and b of the transformers A and B when the magnetic field to be detected is zero (H _X = 0), and FIG. 3A shows the same H _X. It shows the same magnetization characteristics when> 0.

FIG. 2B shows the induced voltage of the secondary winding due to the AC current 9 in the vicinity of the DC excursion magnetic fields Hdc, -Hdc applied to the sensor cores a, b when there is no magnetic field to be detected (H _X = 0). (Es
chp) and (eschn) and the addition signal 12 (esch) thereof. Each induced voltage (eschp) and (eschn)
Since and are added differentially, the AC current 9
The component due to is hardly shown in the detected waveform.

FIG. 3B shows the induced voltage (eschp) in the secondary winding due to the AC current 9 in the vicinity of the DC excursion magnetic field applied to the sensor cores a and b when there is a magnetic field to be detected (H _X > 0) and ( eschn) and a signal 12 (esch) which is the added voltage thereof. Similarly, induced voltages (eschp) and (eschp
Since n) is differentially added, only the addition signal (esch) based on the change in the operating magnetization level of each core caused by the magnetic field to be detected is represented.

As described above, the control current command signal icr is output from the proportional integrator circuit I based on the difference Hr-Khd = ε between the signal 14Khd obtained from the frequency selective attenuator H and the target value Hr, and the control current ic is output via the amplifier J. Flow through the control windings B ₃ and A ₃ .

The control currents ic reversely excite the sensor cores a and b to reduce or cancel the detected magnetic field Hx, that is, the variation of the induced electromotive force. To reduce or cancel this change, control winding B
_3, for detecting the measured magnetic field Hx from current ic flowing to A _3.
Rd is a resistor for taking out the detection of the measured magnetic field Hx as a voltage Rdic.

Effects of the Invention As described above, the present invention is a detection device that detects a detected magnetic field in a state where an alternating magnetic field based on an alternating current is superposed on the sensor core by applying a direct current deviation magnetic field to the sensor core. It is possible to reduce the magnetic noise of the sensor core. Further, since each secondary winding voltage generated based on the AC excitation current, which is an auxiliary signal for detection, is differentially canceled, the output is modulated by the AC excitation current, but In particular, by devising such that only the detected magnetic field appears, it becomes possible to detect an extremely small detected magnetic field.

Further, in the prior art, as described above, the method for detecting the AC excitation current due to the magnetic field to be measured, the phase deviation of the secondary winding voltage, or the change of the pulse position, the detection of the high frequency magnetic field is also limited in principle. Therefore, the responsiveness was extremely poor.

The present invention adopts the method of detecting the magnetic field to be measured from this current value by the method of reducing or canceling the variation of the induced electromotive force due to the secondary winding by the current flowing in the control winding as much as possible. The detection range of the magnetic field to be measured is remarkably expanded, and the linearity between the magnetic field to be detected and the measured value can be detected extremely. In addition, the thickness of the winding, the size of the core, the circuit capacity, etc. can be selected arbitrarily. As a result, it was possible to provide a magnetic field detection device having the ability to correspond to all measurement targets having a magnetic field in the detection range. Further, there is an advantage that a stable magnetic field can be detected without being affected by a disturbance factor such as an external temperature. In addition, high-frequency response is enabled by using high frequency for auxiliary excitation AC current, and detection operation with reduced core noise can be performed by applying DC excursion magnetic field to the sensor core, resulting in high sensitivity and high range. The magnetic field detector can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a magnetic field detection device showing an embodiment of the present invention,
2A is a diagram showing the magnetization characteristic curve of the sensor core in the case where the magnetic field to be detected H _X = 0 in FIG. 1 and the applicable range in magnetic field detection, and FIG. 2B is the primary side of the sensor core in FIG. 2A. Waveform diagram of AC current and secondary winding voltage, Fig. 3A
Is a diagram showing the magnetization characteristic curve of the sensor core and the applicable range in the magnetic field detection when the magnetic field to be detected H _X > 0 in FIG. 1, and FIG. 3B is the primary side alternating current of the sensor core in FIG. 3A. It is a waveform diagram of the secondary side winding voltage. A, B ... Transformer, A ₁ , B ₁ ... Primary winding, A ₂ ,
B ₂ ... secondary winding, a, b ... sensor core, A ₃ ,
B 3 _...... control winding, D ...... DC power supply, 10 ...... DC current, E ...... AC power source, 9 ...... alternating current, G ...... synchronous rectifier, H ...... frequency selective attenuator, H _X ... … Magnetic field to be detected,
M ₁ ... Discontinuous magnetization range, M ₂ ... Saturation magnetization range, M ₃
...... Rotary magnetization range, F …… Low noise amplifier, I …… Proportional integrator circuit, J …… Amplifier, Rd …… Control current detection resistor, C
₁ , C ₂ , C ₃ ... Resistance.

Claims (1)

[Claims] 1. Using two sensor cores forming an open magnetic circuit, and connecting an AC power supply and a DC power supply in series or in parallel to the primary winding of each sensor core to superimpose an AC current and a DC current. Then, the alternating current excites the sensor cores to apply an alternating magnetic field, and the direct current causes a direct current deviation magnetic field in the same direction to the detected magnetic field to the one sensor core and the other sensor. A DC bias magnetic field in the opposite direction to the magnetic field to be detected is applied to the core, and the magnitude of each bias magnetic field due to the DC current that magnetizes each sensor core is larger than the non-continuous magnetization range of the sensor core. , The detected magnetic field is sensed in the non-linear region, and a change in the induced electromotive force corresponding to the detected magnetic field is extracted as a signal in the secondary windings of the sensor coils. Up A synchronous rectifier that rectifies in synchronization with the primary side alternating current and extracts a signal having a polarity corresponding to the direction of the magnetic field to be detected, and a frequency selectivity that extracts a signal obtained by removing the primary side alternating current component from the signal of the synchronous rectifier. An attenuator is further provided, and a control winding is provided on each of the sensor coils. As a control system of the control winding, a detection signal of the frequency selective attenuator and a change amount from the deflection magnetic fields of the both sensor cores are provided. Is provided with a proportional-integral circuit that outputs a control current command signal based on a difference from the target value, and a control current output through the proportional-integral circuit is passed through the control windings. A magnetic field detection device that reversely excites a core to reduce or cancel a change in the induced electromotive force, and detects a measured magnetic field from the control current that reduces or cancels the change.