JP6206863B2 - Heat-resistant magnetic sensor - Google Patents

Description

  The present invention relates to a heat-resistant magnetic sensor for performing magnetic measurement in a high temperature environment.

  The fluxgate type magnetic sensor measures an external magnetic field (measurement magnetic field) according to the following measurement principle. First, an alternating excitation current (for example, a triangular wave current) is passed through an excitation coil wound around a magnetic core to generate an excitation (alternating) magnetic field (for example, a triangular wave magnetic field) in parallel with the external magnetic field. A magnetic flux is generated in the magnetic core due to the superimposed magnetic field of the excitation magnetic field and the external magnetic field, and even if the alternating excitation current changes in the magnetic field region where the magnetic core material is sufficiently saturated by the superimposed magnetic field of the excitation magnetic field and the external magnetic field. The magnitude of the magnetic flux does not change. The time during which the magnitude of the magnetic flux does not change is the same regardless of the polarity of the exciting magnetic field when the external magnetic field is not acting, but when the exciting magnetic field is positive or negative in proportion to the external magnetic field strength when the external magnetic field is acting. Since a difference occurs, the external magnetic field strength can be obtained using this time difference.

  A magnetic material such as permalloy having soft magnetic properties is used for the magnetic core of such a conventional fluxgate type magnetic sensor. These magnetic materials have a large differential permeability (dB / dH) in the non-magnetic saturation region, and suddenly magnetic saturation occurs with a small excitation magnetic field strength, so that the differential permeability becomes substantially zero. It is possible to easily determine magnetic saturation by using a detection coil that outputs a voltage that is proportional to the differential permeability of the detection coil and paying attention to the rising position of the output voltage of the detection coil.

  On the other hand, as a measure for improving the heat resistance of the fluxgate type magnetic sensor, a magnetic material having a high Curie temperature (for example, a Co—Fe-based material) is used to realize a magnetic sensor having a heat resistance of 200 ° C. to 600 ° C. In these cases, it is difficult for these magnetic materials to determine the magnetic saturation using the rising position of the output voltage of the detection coil because the change in the differential permeability is generally slow in the region leading to the magnetic saturation. It is. Furthermore, there is a problem that the excitation magnetic field strength necessary for coercive force and magnetic saturation increases, and the excitation current increases significantly.

  As for a measure for reducing the excitation current, a constriction is formed in a part of the magnetic core, as disclosed in Japanese Patent Application Laid-Open Nos. 2010-12789 and 2004-184098, and a magnetic flux is generated in the constriction. Methods have been proposed to deal with by causing concentration (magnetic saturation).

  However, since the Co-Fe-based material has a large excitation magnetic field strength necessary for magnetic saturation, it is necessary to increase the area ratio between the constricted portion and the non-constricted portion when magnetic saturation is caused by magnetic concentration by the constricted portion. However, there is a problem that still requires a large excitation current.

  In addition, the magnetic sensor described in the above two publications having a constriction portion provided in a magnetic core to reduce the excitation current has a configuration in which a detection coil is wound around the constriction portion. There is a problem with strength. In the configuration in which the detection coil is wound around the magnetic core itself, it is difficult to reduce the size of the magnetic sensor because the magnetic core cannot be made small in order to obtain the required mechanical strength. In the configuration in which the detection coil is wound, there is a problem that it is necessary to cope with the stress generated by the difference in thermal expansion between the magnetic core and the reinforcing material when the environmental temperature during use changes from room temperature to high temperature.

JP 2006-80338 A JP 2010-1227889 A JP 2004-184098 A

  Problems to be solved by the present invention are as follows.

  A heat resistant magnetic sensor capable of performing stable magnetic measurement in a high temperature environment (200 ° C. to 600 ° C.) is realized.

  A heat-resistant magnetic sensor capable of performing stable magnetic measurement in a high-temperature environment and a radiation environment such as a nuclear power plant is realized.

  Realization of a heat-resistant magnetic sensor that can stably perform periodic or continuous in-situ measurement of electromagnetic characteristics of equipment components for the purpose of diagnosing deterioration of static equipment used in high-temperature environments and high-temperature radiation environments To do.

  A heat-resistant magnetic sensor for constructing a non-contact type switch or counter that can be used in a high temperature environment and that responds to magnetic field fluctuations is realized.

The present invention is formed by winding an excitation coil and a detection coil around a magnetic core formed of a soft magnetic material into a rectangular shape or a rounded rectangular loop shape, and having a constricted portion at a part thereof. A heat-resistant magnetic sensor that passes an alternating excitation current having a frequency of 10 Hz to 1 kHz and measures the intensity of an external magnetic field acting on the magnetic core based on the output voltage of the detection coil in a high temperature environment of 200 ° C. to 600 ° C. There,
The magnetic core is integrally formed of a Co—Fe-based soft magnetic material having a Curie temperature of 600 ° C. or higher, and a constriction is formed on one of the long sides of the rectangular or rounded rectangular shape, The excitation coil is wound around the other long side where the constricted portion is not provided, and the detection coil is wound around a portion excluding the long side where the constricted portion is provided,
By evaluating the time interval difference between the positive / negative peaks and the negative / positive peak of the output voltage output from the detection coil, or the ratio of the time interval difference and the excitation period, it acts in the long side direction of the magnetic core. The external magnetic field strength is measured.

  The detection coil may be configured to also serve as the excitation coil.

  The heat-resistant magnetic sensor of the present invention uses a Co—Fe-based material (for example, permendur) having a Curie temperature of 600 ° C. or more for the magnetic core, and devise the magnetic core shape, coil arrangement position, and detection principle. This suppresses the increase in current consumption, enables miniaturization, enables measurement of magnetic field strength in a high-temperature environment, and further, does not use a semiconductor for the magnetosensitive element, so the magnetic field strength in a radiation environment It was also possible to measure.

Specifically, with respect to the shape of the magnetic core, it is possible to prevent a decrease in excitation magnetic field strength due to a demagnetizing field by adopting a configuration in which a magnetic pole is not generated in the magnetic core due to the excitation magnetic field. Further, by making the magnetic circuit into a rectangular closed loop, it is possible to provide a detection coil in a non-necked portion having a relatively high mechanical strength, and the magnetic sensor can be miniaturized. Further, by adopting a rectangular or rounded rectangular shape that is long in the direction of the external magnetic field (measurement magnetic field), the influence of the demagnetizing field due to the magnetic poles generated in the magnetic core by the external magnetic field can be reduced. Further, by providing a constricted portion on the long side of the rectangle, it becomes possible to reach a substantially magnetic saturation state with a smaller exciting current, and to further clarify the peak position of the differential permeability. Regarding the shape of the constricted portion, it was found that the cross-sectional area shape and the length do not affect if the cross-sectional area is small compared to the non-constricted portion.

  Moreover, about the structure of a magnetic core, it was able to avoid the bad influence by the leakage of the magnetic flux in the junction part which arises when it is set as a division member joining structure by making it an integral structure.

  As for the arrangement of the coils, the magnetic sensor can be miniaturized by providing the excitation coil and the detection coil in the non-constricted portion of the magnetic core having high mechanical strength.

  And as for the detection principle, the change in the peak position of the differential permeability depending on the external magnetic field (measurement magnetic field) strength is detected by utilizing the gradual change of the differential permeability of the high Curie temperature material with respect to the excitation magnetic field. With this configuration, it is possible to measure the external magnetic field strength even with the same material for which it is difficult to determine magnetic saturation, and it is not necessary to reach magnetic saturation completely as in the conventional method (differential permeability Since it is only necessary to be able to determine the peak position), it has become possible to suppress an increase in power consumption accompanying the change of the magnetic core material.

It is a schematic diagram of the heat-resistant magnetic sensor of this invention. It is a block diagram of the magnetic measurement system which uses the heat-resistant magnetic sensor of this invention. It is a magnetic characteristic curve figure of the magnetic core in a magnetic sensor. It is a magnetic characteristic curve figure of the magnetic core provided with the constriction part in a magnetic sensor. It is a structure figure of the magnetic core in the Example of this invention. It is an output voltage characteristic curve figure of a detection coil in a magnetic sensor of an example of the present invention. It is a characteristic view which shows the relationship between the shift | offset | difference of the peak space | interval and the external magnetic field intensity in the magnetic sensor of the Example of this invention.

  The heat-resistant magnetic sensor of the present invention uses a soft magnetic material (magnetic material) having a Curie temperature of 600 ° C. or higher, such as a Co—Fe-based material (permendur), as shown in FIG. A rectangular or rounded rectangular integrated magnetic core 1 having a constricted part 4 formed in the part is produced, and an exciting coil 3 for exciting the magnetic core 1 in a long side part where the constricted part 4 is not provided. A heat-resistant fluxgate magnetic sensor having a configuration in which a detection coil 2 for detecting magnetic field strength is wound around a portion other than the constricted portion (non-constricted portion) of the magnetic core 1. Used to measure the strength of an external magnetic field (measurement magnetic field) acting in the long side direction.

  As shown in FIG. 2, the heat-resistant magnetic sensor generates a triangular wave-like excitation magnetic field by connecting an excitation coil 3 to an excitation current source 5 and flowing an alternating excitation current that changes in a triangular wave shape, thereby causing the magnetic core 1 to By exciting the output voltage of the voltage induced in the detection coil 2 by the change of the magnetic field strength of the magnetic core 1 by the amplifier 6 and processing the amplified output voltage by the signal processing circuit 7, the length of the magnetic core 1 is increased. The present invention is applied to a magnetic measurement system that measures the strength of an external magnetic field (measurement magnetic field) acting in the side direction. When the amplifier for amplifying the input signal is built in the signal processing circuit 7, the amplifier 6 can be omitted.

  The upper limit of the environmental temperature at which this heat-resistant magnetic sensor can be used depends on the Curie temperature of the magnetic material used, and the higher the Curie temperature, the higher the upper limit of the usable temperature. With a heat-resistant magnetic sensor using a magnetic material having a Curie temperature of 600 ° C., sufficient measurement results can be obtained even in an environment of about 500 ° C.

  In addition, since the magnetic core has a loop shape, no magnetic pole is generated in the magnetic core due to the excitation current, and the effective excitation magnetic field strength does not decrease due to the demagnetizing field of the magnetic pole. Furthermore, the influence of the demagnetizing field generated by the magnetic pole in the magnetic core magnetized by the external magnetic field can be reduced by making the shape of the magnetic core a rectangular shape that is long in the direction of the measurement magnetic field.

  In addition, by providing the constricted portion on one side of the long side portion extending in the measurement direction, the measurement sensitivity can be improved in the same manner as the magnetic sensor disclosed in Patent Document 3. However, since the magnetic sensor disclosed in Patent Documents 2 and 3 has an exciting coil or a detection coil wound around the constricted portion of the magnetic core, the constricted portion becomes thin when attempting to reduce the size of the magnetic sensor. The mechanical strength of the core is reduced, making it difficult to wind the coil. If a reinforcing material is applied to the constricted part to compensate for the strength reduction, thermal stress due to the difference in thermal expansion between the magnetic core and the reinforcing material occurs when the environmental temperature changes from room temperature to high temperature. There is a problem that changes occur in the magnetic properties.

  On the other hand, in the present invention, it is confirmed that the behavior of the magnetic flux change in the magnetic core is not so different as to affect the measurement between the constricted part and the non-constricted part. The detection coil is provided.

  Furthermore, the magnetic core has a low magnetic permeability when a magnetic material having a laminated structure or a magnetic material having a divided structure is used, and in the case of a magnetic material having a high Curie temperature, the leakage magnetic flux in the gap of the joint becomes large. In the present invention, in order to reduce the occurrence of leakage magnetic flux, an integrated configuration without a joint (gap) is adopted.

  Further, in the conventional magnetic sensor, the external magnetic field strength is evaluated by using the change in the rising position of the differential magnetic permeability (dB / dH). However, in the high Curie temperature magnetic material, the magnetic saturation characteristic is shown in FIG. Thus, since the rise of the differential permeability is unclear as shown in FIG. 3B, it is difficult to evaluate the external magnetic field strength. However, in the high Curie temperature material, since the change in the differential permeability is gradual, the peak of the change in the differential permeability clearly appears and the position can be determined. The change in the peak position of the differential permeability due to the external magnetic field corresponds to the change in the rising position. Since the differential permeability peak appears before reaching full magnetic saturation, the peak position of this differential permeability is used to evaluate external magnetic field strength with a smaller excitation current without the need for full magnetic saturation. It is possible. Moreover, by introducing the constriction, as shown in FIG. 4A, it appears to be magnetic saturation at a low magnetic field, and the peak position of the differential permeability is more as shown in FIG. Become clear.

  Normally, the output voltage is increased by increasing the excitation frequency. However, in the case of a Co-Fe-based magnetic material having a high Curie temperature, the permeability tends to decrease as the frequency increases. The excitation frequency is desirably 1 kHz or less. Further, the maximum value of the excitation current needs to be equal to or greater than the coercive force of the magnetic core and the apparent BH curve to draw a major loop in order to prevent a zero shift due to an external magnetic field.

  Furthermore, since there is a possibility that the magnetic core has an internal strain due to the processing into the core shape, it is desirable to perform stress relief annealing after the processing.

As shown in FIG. 5, the magnetic sensor of this example has a permendur (49% Fe-49
% Co-2% V) magnetic material was subjected to electric discharge machining to produce a rectangular loop-shaped magnetic core 1 having a constricted portion 4 on the long side portion, and subjected to stress relief annealing. As for the coil, as shown in FIG. 1, with respect to the exciting coil 3, a ceramic-coated heat-resistant copper wire of φ0.3 mm was wound around the long side portion of the magnetic core 1 without the constricted portion for 70 turns. Since it is difficult to wind the detection coil 2 around the constricted portion in terms of mechanical strength, a copper wire equivalent to the exciting coil 3 is wound around the short side portion without the constricted portion for 14 turns.

  The magnetic sensor of this embodiment and the magnetic sensor for comparison are individually installed in an Helmholtz coil (HC) for applying an external magnetic field, and a triangular wave of 100 Hz and a peak value of 6 A is applied to the excitation coil 3 as an excitation current, and a detection coil The relationship between the change in the output voltage waveform of No. 2 and the applied magnetic field strength of HC was evaluated. Here, as for the frequency of the excitation current, the output voltage becomes higher at a higher frequency, but the permeability becomes smaller and the change in the output voltage waveform becomes slower, so a lower frequency of 1 KHz or less is desirable. . However, since the output voltage itself decreases as the frequency decreases as described above, it is desirable that the frequency be 10 Hz or more. As for the peak value of the excitation current, a larger value is preferable for the detection of the rise of the output voltage because the time fluctuation amount dH / dt of the excitation magnetic field is large. From the viewpoint of increasing the thickness, it is desirable to make it smaller. However, the lower limit of the peak value of the excitation current has a problem of residual magnetization (coercive force) that did not become a problem with conventional permalloy or the like. At least, the detection coil 2 has the excitation current of the excitation coil 3 on the horizontal axis. It is necessary to pass an exciting current until the bending point due to magnetic saturation shown in FIG. Under conditions where the excitation current is small and there is no inflection point due to magnetic saturation, the effect of remanent magnetization becomes obvious, and when measuring a low magnetic field after measuring a high magnetic field, the origin deviation from the previous measurement is The remaining measurement results fluctuate.

  Next, FIG. 6 shows a change over time in the value of the output voltage of the detection coil 2 when excitation is performed under the excitation conditions. In the conventional method, the evaluation is performed based on the shift amount at the position where the output voltage becomes almost zero due to saturation of the magnetic core 1, but in this embodiment, as shown in FIG. Since the rising position of the output voltage is unclear, the evaluation is performed by the shift amount of the time intervals t1 and t2 between the positive peak and the negative peak (both corresponding to the coercive force in the pseudo BH curve). did. When the external magnetic field (measurement magnetic field) is zero, t1 = t2, but when the external magnetic field is applied, the t1 and t2 are shifted by ± Δt in proportion to the external magnetic field strength. Therefore, when the difference between t1 and t2 is obtained, 2Δt is obtained. However, since 2Δt depends on excitation conditions and the like, it is necessary to obtain a proportional constant between 2Δt and the external magnetic intensity in a state where the external magnetic field is already known.

FIG. 7 shows the relationship between the time interval difference (2Δt) between the positive / negative peaks of the output voltage and the negative / positive peak at an environmental temperature of 200 ° C., the excitation cycle ratio (percentage), and the external magnetic field intensity. This result shows that there is a correlation between 2Δt and the external magnetic field strength, and it is possible to evaluate the external magnetic field strength using 2Δt. The same correlation is recognized even when the measurement environment temperature is high. Therefore, by evaluating the time interval difference between the positive / negative peaks and the negative / positive peak of the output voltage output from the detection coil 2 or the ratio of the time interval difference and the excitation cycle, It is possible to measure the intensity of the external magnetic field acting in the long side direction of the magnetic core 1 from the correlation equation with the interval difference or the time interval ratio. However, since the magnetization becomes relatively smaller as the temperature becomes higher, measurement just below the Curie temperature is difficult.

  Regarding the influence of the presence or absence of the constricted portion 4 of the magnetic core 1, although the peak position is shifted even without the constricted portion 4, the peak shape is broad as shown in FIG. 4B. It is difficult to determine the peak position, and it is necessary to introduce the constricted portion 4.

Usually, the output voltage is increased by increasing the excitation frequency. However, in Co-Fe high Curie temperature magnetic materials, the permeability tends to decrease as the frequency increases. The excitation frequency is desirably 1 kHz or less. Further, the maximum value of the exciting current needs to be equal to or greater than the coercive force of the magnetic core material and to the extent that the apparent BH curve draws a major loop in order to prevent a zero point shift due to an external magnetic field. Furthermore, since there is a possibility that the magnetic core 1 has an internal strain due to processing into the core shape, it is desirable to perform stress relief annealing.

  The detection coil 2 can also be configured as the excitation coil 3.

  DESCRIPTION OF SYMBOLS 1 ... Magnetic core 2 ... Detection coil 3 ... Excitation coil 4 ... Constriction part 5 ... Excitation current source 6 ... Amplifier 7 ... Signal processing circuit.

Claims (2)

Formed into a rectangular or rounded rectangular loop shape by a soft magnetic material, and is configured by winding an excitation coil and a detection coil around a magnetic core having a constricted portion at a part thereof, and the excitation coil has a frequency of 10 Hz or more A heat-resistant magnetic sensor that passes an alternating excitation current of 1 kHz or less and measures the intensity of an external magnetic field acting on the magnetic core based on the output voltage of the detection coil in a high-temperature environment of 200 ° C. to 600 ° C. ,
The magnetic core is integrally formed of a Co—Fe-based soft magnetic material having a Curie temperature of 600 ° C. or higher, and a constriction is formed on one of the long sides of the rectangular or rounded rectangular shape, The excitation coil is wound around the other long side where the constricted portion is not provided, and the detection coil is wound around a portion excluding the long side where the constricted portion is provided,
By evaluating the time interval difference between the positive / negative peaks and the negative / positive peak of the output voltage output from the detection coil, or the ratio of the time interval difference and the excitation period, it acts in the long side direction of the magnetic core. A heat-resistant magnetic sensor characterized by measuring an external magnetic field strength.   2. The heat resistant magnetic sensor according to claim 1, wherein the detection coil is also used as the excitation coil.

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