JPS631253Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a magnetic property measuring device for measuring the magnetic properties of a magnetic material in response to an alternating current signal.

As is well known, various devices have been developed for measuring the magnetic properties of magnetic materials in response to alternating current signals, that is, the B-H characteristics or the M-H characteristics. Figure 1 shows the configuration of a conventional B-H characteristic measuring device.
is a sine wave oscillator, 12 is an amplifier, 13 is a current-voltage conversion resistor, 14 is a coil containing a magnetic core of the sample to be measured,
15, 16 are voltage amplifiers, 17 is an integrator, 18,
Reference numerals 19 and 20 are output terminals, which are connected, for example, to the X- and Y-axes and ground input terminals of a display such as an oscilloscope, respectively.

Now, the primary (excitation) winding of the sample coil 14
L ₁ , the number of turns of the secondary (detection) winding L ₂ is N ₁ ,
N ₂ , the average magnetic path length of the magnetic core is l (cm), and an excitation current i ₁ i ₁ = im sin2πft ……( ₁ ) with frequency f (Hz) and peak value im (A) is supplied to excitation coil 1. Then, the magnetizing force H (Oe) is H=4π/10·N ₁ /l·im sin(2πft) ...(2).

On the other hand, the magnetic flux density inside the magnetic core due to this magnetizing force is B
(gauss), and the cross-sectional area of the magnetic core is S (cm ² ). The magnetic flux φ (maxwell) interlinking with the detection coil N ₂ is as follows. If the peak value of the magnetic flux density B is Bm, φ = S・B = S・Bm sin(2πft) ……(3) Therefore, the voltage induced in the detection coil N ₂
e ₂ (V) is e ₂ = −N ₂ (dφ/dt) × 10 ^-8 = −2πfN ₂ SBmCOS (2πft) × 10 ^-8 ... (4) Integrating this with the time constant τ = CR, the The integration result e ₀ (V) is: e ₀ = 1/CR∫ ^t _O e ₂ (t) dt = −N ₂ S/CRBm sin (2πft) × 10 ^-8 = e _n sin (2πft) ……(5 ). Therefore, Bm=-CR/N ₂ Oe _n ×10 ⁸ (gauss) ...(6). That is, in the device shown in FIG. 1, an exciting current i ₁ is supplied to an exciting coil L ₁ to generate a magnetizing force H, and a detection coil L ₂ is used to record the time change ( By inducing an electromotive force e ₂ proportional to dB/dt) and applying it to the integrating circuit 17, a voltage e ₀ proportional to the magnetic flux density B is obtained. Therefore, for example, the resistor 13 provides a voltage e ₁ proportional to the excitation current i ₁ . When this is supplied to the X terminal of the oscilloscope and e ₀ is supplied to the Y terminal, a B-H curve is drawn on the screen.

However, in the device with the above configuration, the excitation coil is attached to the sample.
Both coils L ₁ and detection coil L ₂ must be provided. Therefore, it is impossible to measure, for example, a magnetic head that has been completed with only an excitation coil. Further, in such a magnetic head, the characteristics measured with a circular sample and the completed one are such that the magnetic characteristics deteriorate due to processing. Therefore, it is necessary to be able to perform measurements using magnetic cores of arbitrary shapes.

Therefore, an apparatus is being considered that can measure a magnetic core of any shape using only an excitation coil. This device is based on the principle explained below.

Now, the voltage e(t) across the excitation coil wound around a magnetic core of arbitrary shape is expressed as e(t)=i(t), where the applied current is i(t), the resistance of the coil is r, and the number of turns is N. )・r+N・dφ/dt×10 ^-8 ...(7) Here, if the cross-sectional area of the magnetic core is S (cm ² ), φ=B・S, and the magnetic flux density B is the magnetizing force of the coil is H, the magnetization of the magnetic core is M, and the relative permeability of the vacuum is μ. ₀ , B=μ ₀ H + 4πM ...(8) Therefore, the above equation (7) is e(t)=i(t)r+NSdB/dt×10 ^-8 ...(9) = i(t) r+μ ₀ NSdH/dt×10 ⁻⁸ +4πNSdM/dt×10 ⁻⁸ ……(10). Therefore, from equation (9), e _r = i(t)r
or, from equation (10), if a voltage corresponding to e _r + e _h = i (t) r + μ ₀ NS dH/dt×10 ^-8 is applied to e(t) with opposite polarity, in the former case, the magnetic flux In the latter case, a voltage proportional to the time change (dB/dt) of the density B and, in the latter case, to the time change (dM/dt) of the magnetization M is obtained.
By integrating this, a BH curve or an MH curve can be obtained.

FIGS. 2 and 3 show a BH curve measuring device using this principle.

In the configuration shown in FIG. 2, first, switch 2
1 to the DC power supply 22 side, and the DC current to the amplifier 2
3. Sample to be measured 2 via current-voltage conversion resistor 24
Supply to 5. Further, the voltage across the resistor 24 is supplied to a differential amplifier 28 together with the output voltage at one end of the resistor 24 via a voltage amplifier 26 and a variable resistor 27. Then, the variable resistor 27 is adjusted to make the output voltage of the differential amplifier 28 zero. In this state, the switch 21 is switched and the sine wave oscillator 29
supply more alternating current. Then, differential amplifier 2
The output voltage of 8 is the inductance component, that is, the above (9)
It is obtained as a voltage proportional to dB/dt of the second term on the right side of the equation. This is converted into a voltage proportional to the magnetic flux density B of the magnetic core by an integrator 30, and inputted from an output terminal 31 to the Y axis of an oscilloscope, for example, and
When a voltage proportional to the applied current is obtained from the output of the voltage amplifier 26 and supplied to the X-axis of the oscilloscope via the output terminal 32, a B-H curve is drawn on the screen. Note that 33 is a ground output terminal.

However, although this device allows the shape of the sample to be measured to be arbitrary and does not require a detection coil, B-
Only the H curve can be measured.

Therefore, an apparatus shown in FIG. 3 is a further improvement of this apparatus and is capable of measuring the B-H curve and the MH curve. Note that the same parts as in FIG. 2 are given the same reference numerals.

The apparatus shown in FIG. 3 includes a circuit to be measured consisting of an amplifier 35 for supplying an excitation current to a sample to be measured 34, a current-voltage conversion resistor 36, and the first and second terms on the right side of equation (10). From a cancellation voltage generation circuit consisting of a variable resistor 37, a phase shifter 38, a current-voltage conversion resistor 39 for generating a voltage component, the circuit under test, and an output amplifier 40 for supplying the same current value. It is characterized by its composition. In order to measure the B-H curve with this device, as described above, first, switch 21 is set to the DC power supply 22 side, switch 41 is set to the sample 34 side, and DC current is supplied to each circuit. Then, a voltage equal to the voltage due to the internal resistance of the sample 34 is generated by the variable resistor 37, and this and the voltage of the circuit under test are respectively supplied to the differential amplifier 28, so that the output voltage of the differential amplifier 28 becomes zero. Adjust the variable resistor 37 accordingly. In this state, when the switch 21 is switched and alternating current is supplied from the sine wave oscillator 29, a voltage proportional to the time change of the magnetic flux density B in the magnetic core of the sample 34 is obtained as the output of the differential amplifier 28. When this is supplied to the Y-axis and X-axis of the oscilloscope via the integrator 30 together with the output voltage of the voltage amplifier 26, a B-H curve is drawn on the screen.

On the other hand, when measuring the MH curve, an air-core coil 42 having the same shape and the same number of turns as the sample to be measured 34 is provided, and a switch 41 is used to switch between these coils. First, the switch 41 is set to the air-core coil 42 side, and an AC excitation current is supplied from the sine wave oscillator 29, and a voltage having the same amplitude and phase angle as the terminal voltage of the air-core coil 42 is applied to the variable resistor 37 and the phase shifter 3.
8 to make the output voltage of the differential amplifier 28 zero. In this state, switch 41 is set to sample 3.
4 side, a voltage proportional to the time change (dM/dt) of only the magnetization M of the magnetic core of the sample 34 is obtained as the output of the variable amplifier 28. When this is supplied to the Y-axis and X-axis of the oscilloscope together with the output voltage of the voltage amplifier 26 via the integrator 30, an MH curve is drawn on the screen.

However, in this device, the excitation circuit requires two circuits: the circuit under test and the cancellation voltage generating circuit, and each of them has separate amplifiers 35 and 40. Adjustment in which the voltage drop caused by the resistance and the voltage drop caused by the inductance of the air-core coil 42 alone are canceled out by the voltage generation circuit and the output voltage of the differential amplifier 28 is made zero is extremely complicated. Moreover,
There are many errors because the output amplifier is not a constant current, is affected by the impedance of the sample, and does not flow the same current waveform.

As mentioned above, none of the conventional magnetic property measuring devices were satisfactory.

This idea was made based on the above circumstances, and it has a simpler configuration than the conventional one, and the B-H curve and M
It is an object of the present invention to provide a magnetic property measuring device that can measure -H curves with high precision and high stability.

An embodiment of this invention will be described below.

In FIG. 4, 51 is a sine wave oscillator. One end of this oscillator 51 is connected to the input end of a constant current amplifier 52. The output end of this constant current amplifier 52 is connected to terminals 54 and 55 to which the sample to be measured 53 is connected.
Of these, the terminal 54 is connected. Said terminal 5
5 is connected to the terminal 58 of the terminals 58 and 59 to which a reference resistor 56 equal to the DC resistance of the sample measured in advance or a reference air-core coil 57 having the same shape and number of turns as the sample is connected. The terminal 59 is connected to the grounded other end of the sine wave oscillator 51 and the constant current amplifier 5 via a resistor 60.
Connected to 2. This resistor 60 is a current detection resistor and a current-voltage conversion resistor of the constant current amplifier 52. Further, a differential amplifier 6 is connected to the terminals 54 and 55 to take out the voltage between the terminals of the sample to be measured 53.
The terminals 58 and 59 are connected to the input terminal of a differential amplifier 62 which takes out the voltage between the terminals of the reference resistor 56 or the air-core coil 57. The output terminals of these differential amplifiers 61 and 62 are connected to the input terminal of a differential amplifier 63 which extracts the voltage difference between them. This differential amplifier 63 obtains the differential (dB/dt) or (dM/dt) of the magnetic flux density B or magnetization M of the magnetic core in the sample to be measured 53 with respect to time t, and its output end is connected to the output terminal 64. and is connected to an integrator 65. This integrator 65 integrates the differential output and outputs a voltage proportional to the magnetic flux density B or magnetization M, and its output end is connected to an output terminal 66. In addition, a voltage amplifier 6 is connected to the terminal 59.
7 input terminals are connected. This voltage amplifier 6
Reference numeral 7 detects the current flowing through the resistor 60 and outputs a voltage proportional to the magnetizing force H, and this output end is connected to an output terminal 68. Further, the other end of the sine wave oscillator 51, a differential amplifier 61,
62, 63, the integrator 65, and the ground terminals of the voltage amplifier 67 are all connected to an output terminal 69.
The sample 53 to be measured may be a magnetic core of any shape as long as only an excitation winding is provided, and for example, magnetic cores of magnetic heads, transformers, motors, etc. can be measured.

The operation in the above configuration will be explained. Note that the operating principle is the same as the formula described above. First, when measuring the B-H curve, the sample 53 to be measured is connected to the terminals 54 and 55, and the resistor 56 equal to the winding resistance of the sample 53 is connected to the terminals 58 and 59. Further, a display device such as a Y-axis terminal of an oscilloscope is connected to the output terminal 64 or 66, an X-axis terminal of the oscilloscope is connected to the output terminal 68, and an output terminal 69 is connected to a ground terminal. In this state, while visually observing the output waveform of the output terminal 68, the sine wave oscillator 51 is adjusted to generate an excitation current having a desired current amplitude and frequency. Then, a voltage proportional to (dB/dt) is obtained at the output terminal 64 from the differential amplifier 63 set to a predetermined amplification degree, and a magnetic flux density B is obtained from the integrator 65. Further, the voltage amplifier 67 outputs a voltage proportional to the magnetizing force H to the output terminal 68. Therefore, a BH curve is drawn on the screen of the oscilloscope.

Further, in the case of the MH curve, an air-core coil 57 having the same shape and the same number of turns as the sample to be measured 53 is connected to the terminals 58 and 59 instead of the reference resistor 56. In this state, when an excitation current having a desired current amplitude and frequency is supplied from the sine wave oscillator 51, dM/dt is obtained at the output terminal 64 and magnetization M is obtained at the output terminal 66. Further, a voltage proportional to the magnetizing force H is output to the output terminal 68. Therefore, an MH curve is drawn on the screen of the oscilloscope.

According to the above configuration, B
It is possible to measure -H curves or M-H curves. Furthermore, the sample to be measured 53, a reference resistor 56 or an air-core coil 57, and a resistor 60 are connected in series, and a constant current amplifier 52 supplies a desired excitation current that is not affected by the impedance of the sample to this series circuit. Therefore, since an excitation current having the same waveform flows through the sample 53, the reference resistor 56, etc., it is possible to significantly improve measurement accuracy and stability compared to the conventional method.

In addition to the methods shown in the above embodiments, various measurement methods can be considered for this invention. For example, the terminal 54,
Connect air-core coils of the same shape and winding to 55, 58, and 59, respectively, and adjust the impedance of both to be completely equal so that the output voltage of the differential amplifier 61 becomes zero, and then connect one of the air-core coils to By inserting a magnetic core of any shape, such as a magnetic thin film, into a coil, it is possible to measure the M-H curve of the magnetic core. In addition, a magnetic head-like structure in which the same coil is applied to a magnetic core provided with an air gap having exactly the same characteristics is connected to the terminals 54, 55, 58, and 59, respectively.
After adjusting the output voltage of the differential amplifier 61 to zero, when a magnetic thin piece or a magnetic material having a relatively high coercive force is brought into close contact with one side, its magnetic properties are measured according to the change in impedance at that time. can. By utilizing this, it is possible to provide magnetic flaw detectors, thickness gauges, etc.

As described in detail above, this invention has a simpler configuration than the conventional one, and can measure the B-H curve and M-H curve of a sample of arbitrary shape with a single winding with high accuracy. A magnetic property measuring device capable of highly stable measurement can be provided.

[Brief explanation of the drawing]

FIGS. 1 to 3 are block diagrams showing different conventional magnetic property measuring apparatuses, and FIG. 4 is a block diagram showing an embodiment of the magnetic property measuring apparatus according to the present invention. 51... Sine wave oscillator, 52... Constant current amplifier, 53... Sample to be measured, 56, 57... Reference resistor, reference coil, 60... Current detection resistor, 61,
62, 63...Differential amplifier, 65...Integrator, 6
7...Voltage amplifier.

Claims (1)

[Scope of utility model registration request] A sine wave oscillator capable of generating any frequency, a constant current amplifier connected to one end of this sine wave oscillator to amplify the oscillation output and make it a constant current, and a connection to the sample to be measured to which the output current of this constant current amplifier is supplied. A terminal, a reference connection terminal that is connected in series to this sample-to-be-measured connection terminal, and is connected to a resistor or coil that corresponds to the sample to be measured, which is made up of a magnetic material and a coil wound around the magnetic material; a current detection resistor connected in series between the connection terminal for the sine wave oscillator and the other end of the sine wave oscillator, and first and second voltage detection means for detecting voltages across the sample connection terminal to be measured and the reference connection terminal, respectively. And these first and second
a differential voltage detecting means for detecting a difference component of the voltage detected by the voltage detecting means; an integrating means to which the output voltage of the differential voltage detecting means is supplied; and a first integrating means for detecting the voltage across the current detecting resistor. 3. A magnetic property measuring device characterized by comprising: voltage detecting means according to item 3.