JPH06148300A - Alternating field measuring device and method - Google Patents

Abstract

PURPOSE:To measure a low magnetic field with high accuracy under environment receiving the effect of large electromagnetic noise and to also measure the alternating field of a high frequency area. CONSTITUTION:A magnetic field sensor 14 using a Hall element is arranged in an alternating field and a Hall current is allowed to flow to the Hall element to output a voltage waveform which is, in turn, stored in a waveform memory device 10. Next, the voltage waveform outputted from the Hall element in such a state that no Ball current flows is stored. A time base is set so that the phases of cyclical noises contained in two voltage waveforms coincide and the difference between the voltage values of two waveforms is operated in a time series by a CPU 4. The voltage waveform obtained by operation contains no noise component and becomes the effective component corresponding to a magnetic field to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for measuring an alternating magnetic field using an electromagnetic conversion element (Hall element), and more particularly to a measuring apparatus and method for a low magnetic field under a large electromagnetic noise environment. .

[0002]

2. Description of the Related Art Conventionally, a method using an electromagnetic conversion element and a method using a magnetic sensor based on the law of electromagnetic induction are well known for measuring an alternating magnetic field. A hall element is generally used as an electromagnetic conversion element, and a search coil is used as a magnetic sensor based on electromagnetic induction. The method using the search coil has an advantage that a good measurement result can be obtained for measurement of a magnetic field having a high frequency (several tens of KHz or more) and an apparatus can be obtained at low cost, but In the measurement of the alternating magnetic field, the detection capability is lowered and the practical value is low.
Further, since noise due to electromagnetic waves is easily picked up near the resonance frequency and the frequency characteristic is not uniform, it has an unsuitable surface for measurement of wide band low magnetic field. The method using the Hall element is also suitable for detecting a relatively weak magnetic field, but the output from the Hall element is small and the output must be amplified by an amplifier. At this time, depending on the characteristics of the amplifier and the method of processing the noise of the Hall element, conventionally known methods are classified into a method of performing synchronous detection and a method of using a DC amplifier.

As a method for performing synchronous detection, a device as shown in FIG. 4 is used, the direction of the Hall current is periodically switched at the time of measuring a magnetic field, noise is modulated at a switching frequency, and a signal and noise are separated by a filter. Only the signal component is extracted. This makes it possible to reduce noise components and perform highly accurate measurement. Further, since noise can be removed, there is an advantage that the GAIN of the amplifier can be increased.

On the other hand, the method using the DC amplifier is
The output voltage from the Hall element is amplified by the differential amplifier and directly output by the device as shown in FIG. In this method, the frequency characteristics of the amplifier are guaranteed up to the required frequency, it is necessary to increase the magnification of the amplifier, and the wiring is made a perfectly balanced electromagnetic shielded cable to eliminate electromagnetic noise. There are many restrictions such as the need to use a good CMRR (Common Mode Rejection Ratio) as the differential amplifier, but it is possible to measure the alternating magnetic field in a wide frequency range.

[0005]

However, in the method of performing the synchronous detection, the reproducibility of the waveform is regulated by the switching frequency, and it becomes impossible to measure the high frequency magnetic field. That is, if an alternating magnetic field is measured by this method, a switching frequency that is many times the frequency of the measured magnetic field is required. For example, when measuring the magnetic field of the deflection yoke of about 16 KHz, switching of 160 to 200 KHz is required. Circuit design becomes extremely difficult. In addition 20
A digital circuit is required to perform switching near 0 KHz, and new noise must be taken into consideration.

In the conventional method using the DC amplifier, even if the common mode noise in the wiring and the noise due to the amplifier can be reduced to some extent, the induced noise due to the unbalanced voltage of the Hall element itself cannot be reduced. In an environment where electromagnetic waves are generated, there is a problem that the output voltage of the Hall element causes large noise, and measurement of a low magnetic field becomes almost impossible.

The present invention has been made in view of the above problems, and an object thereof is to enable a highly accurate measurement of a low magnetic field even under an environment affected by a large electromagnetic noise and to achieve a high frequency. An object of the present invention is to provide an alternating magnetic field measuring device and an alternating magnetic field measuring method capable of measuring an alternating magnetic field in a region.

[0008]

In order to solve the above problems, an alternating magnetic field measuring apparatus according to the invention of claim 1 is a magnetic field sensor using a Hall element, and a Hall current is passed through the Hall element. Hall current control device capable of controlling ON / OFF of the hall current, voltage waveform output from the magnetic field sensor when the hall current is in the ON state, and the hall current in the OFF state A waveform storage means for storing the voltage waveform output from the magnetic field sensor, and a calculation means for aligning the time axes of the two voltage waveforms stored in the waveform storage means to calculate the difference between the voltage values in time series. , And.

In the alternating magnetic field measuring method according to the second aspect of the invention, a magnetic field sensor using a Hall element is installed in an alternating magnetic field, and a Hall current is passed through the Hall element to output from the Hall element. A first step of storing a voltage waveform in a waveform storage means;
A second step of maintaining the position where the step is performed and storing the voltage waveform output from the hall element in the state in which the hall current does not flow in the hall element by the waveform storage means; and the voltage waveform stored in the first step. And a third step of aligning the time axes of the voltage waveforms stored in the second step and calculating the difference in voltage value in time series.

According to a third aspect of the present invention, in the alternating magnetic field measuring method according to the second aspect, the voltage waveform is stored in the first step in a state where no Hall current flows through the Hall element, and the second step is performed. It is assumed that a hall current of the hall element is passed and a voltage waveform is stored.

The magnetic field sensor is one in which a Hall element is formed on a substrate, and is provided with a terminal for flowing a Hall current and a terminal for detecting a voltage generated on both sides of the Hall element. It is desirable that it is not easily affected by noise. The hall current control device has a switch so that the hall current can be manually turned on and off.
It may be F or O by CPU
It may be controlled to N or OFF.

The waveform storage means may store the voltage waveform output from the Hall element as it is as an analog amount, but it is desirable that it be digitized and stored at an appropriate sampling period. The calculation means is, for example, CP
U or the like can be used. In this calculation, the time axes of the two voltage waveforms are aligned so that the phases of the noises coincide with each other, and a method of synchronizing with the noise source having periodicity can be adopted.

[0013]

In the alternating magnetic field measuring apparatus according to the first aspect of the present invention, the Hall current control apparatus for controlling ON / OFF of the current flowing through the Hall element and the case where the Hall current is in the ON state and the OFF state are both In the above, since it has a waveform storage means for storing the voltage waveform output from the magnetic field sensor, a voltage waveform in which an output component proportional to the strength of the magnetic field to be measured and noise are combined, and a voltage waveform containing only noise And can be detected and stored separately. That is, when the Hall current is in the ON state, the output from the Hall element is a voltage proportional to the magnetic strength, and noise due to electromagnetic waves generated due to imbalance in the Hall element and the like are superimposed on this. There is. On the other hand, when the hall current is in the OFF state, the output is not affected by the strength of the magnetic field, and only noise due to the electromagnetic wave is output. Furthermore, the time axes of the two stored voltage waveforms are matched by the calculating means,
Differences in voltage values are calculated in time series, and when the potential difference is obtained by matching the phase of noise with periodicity, the noise component due to electromagnetic waves is erased and the hall component is proportional to the strength of the magnetic field. The active ingredient output from the device is obtained.

In the alternating magnetic field measuring method according to claim 2,
In the first step, a hall current is passed through the hall element to detect the voltage waveform output from the hall element. The voltage waveform stored in the waveform storage means is an effective component corresponding to the strength of the measured magnetic field and noise due to electromagnetic waves. Are overlapped. Second
In the process, the voltage waveform output from the Hall element is detected without flowing the Hall current through the Hall element, and the stored voltage waveform is a waveform of only noise due to electromagnetic waves. In the third step, the time axes are aligned so that the alternating magnetic fields of the two voltage waveforms and the noise phase match, and when the difference in voltage value is calculated, the noise component synchronized with the alternating magnetic field is removed, and the measurement will be performed. A voltage waveform corresponding to the strength of the magnetic field is obtained.

According to a third aspect of the present invention, in the alternating magnetic field measuring method according to the second aspect, the output waveform obtained in the second step is detected in the first step, and in the second aspect, the output waveform obtained in the first step. Is detected in the second step, and since the difference between the two is calculated in the third step, the obtained result is the same as the alternating magnetic field measuring method according to claim 2.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an alternating magnetic field measuring apparatus according to an embodiment of the invention described in claim 1. In FIG. In this alternating magnetic field measuring apparatus, an AC magnetic field measuring probe 1 having a magnetic field sensor 14 at its tip and this AC magnetic field measuring probe 1 are connected,
A sensor box 2 for controlling the hall current and amplifying the output voltage, a digital oscilloscope 3 for A / D converting the waveform of the output voltage, and storing the digital oscilloscope while controlling the operation of the digital oscilloscope. The CPU 4 and the CPU 4 capable of calculating the generated waveform data form a main part.

The magnetic field sensor 14 uses a hall element, and the hall element is adhered to a ceramic base and is not easily affected by electromagnetic noise. The cable connecting the magnetic field sensor 14 and the sensor box 2 is perfectly balanced and has an electromagnetic shield.

The sensor box 2 is supplied with electric power from the sensor power supply device 5 and is output from the hall element and a hall current controller 7 having a switch for controlling ON / OFF of the hall current flowing in the hall element. It has a built-in differential amplifier 8 for amplifying the voltage waveform. The hall current controller 7 arbitrarily turns on and off the hall current.
It can be a state. Further, the differential amplifier 8 can amplify the voltage waveform output from the Hall element and output the voltage waveform to the digital oscilloscope 3 regardless of whether the Hall current is ON or OFF. It has become. A common amplifier is used as the differential amplifier 8 with a good in-phase component removal ratio to reduce common noise, and the sensor box itself is also electromagnetically shielded to prevent electromagnetic waves from entering. The sensor power supply device 5 includes a power supply for flowing a hall current and a power supply for a differential amplifier, and is electromagnetically shielded to prevent it from becoming a source of generation of electromagnetic noise.

The digital oscilloscope 3 is an A / D
It includes a converter 9, a storage device 10 for storing a digitized waveform, and a display device 11 for displaying the waveform. The A / D converter 9 corresponds to a frequency component of the input waveform, It can be digitized at an appropriate sampling cycle. The storage device 10 is capable of separately storing two or more waveforms, and a voltage waveform output from the Hall element when the Hall current is in the ON state and a voltage waveform when the Hall current is in the OFF state. Entered back and forth,
Each of these can be stored. The display device 11 can display a waveform by a cathode ray tube.

The CPU 4 uses the sensor box 2
The operation of digitizing and storing the waveform input to the digital oscilloscope 3 from the CPU and the stored data
4 has a function of controlling the operation to be transferred to 4 and a function of calculating the difference between the time axes of the two waveform data transferred from the digital oscilloscope 3. The method of aligning the time axes of these two waveform data may be such that the phases of the periodic noise components contained in both waveform data can be aligned so that, for example, the halls are synchronized with the noise source. If the output waveform from the element is stored, the difference may be calculated by sequentially tracking the digitized data in time series. Note that GPIB or RS232C is used to transfer data between the digital oscilloscope and the CPU.

Next, the operation of the alternating magnetic field measuring apparatus of the above-mentioned embodiment, which is an embodiment of the invention described in claim 2, will be described. The magnetic field sensor 14 provided at the tip of the AC magnetic field measurement probe 1 is installed in the magnetic field to be measured (20). The hall current control device in the sensor box is turned on and a hall current is passed through the hall element (21). At this time, the voltage output from the Hall element is amplified by the differential amplifier 8 in the sensor box (22) and output to the digital oscilloscope 3.

Although the voltage waveform input to the digital oscilloscope 3 is an analog quantity, it is sampled at an appropriate period and converted into a digital quantity (23). The digitized waveform data is stored by the waveform storage device 10 built in the digital oscilloscope 3 (24).
At this time, a trigger is applied from the noise source, and the waveform data is stored in synchronization with the periodic noise.
[First waveform data] Along with this, the waveform is displayed on the display device 3 (25), and the operator can confirm the waveform. FIG. 3A shows an example of the waveform stored as described above.

Next, the hall current controller is turned off so that the hall current does not flow through the hall element (2).
6). At this time, the voltage output from the Hall element is amplified by the differential amplifier 8 in the sensor box (27),
Output to the digital oscilloscope 3. The voltage waveform input to the digital oscilloscope 3 is digitized (28) and stored by the waveform storage device 10 (2).
9). At this time as well, as in the case of the first waveform data, a trigger is applied from the noise source and the waveform data is stored in synchronization with the noise. [Second Waveform Data] FIG. 3B shows an example of the waveform stored as described above.

The two waveform data stored as described above are transferred to the CPU 4 (31), and the two waveform data are recorded in chronological order.
The difference between the voltage values of the two voltage waveforms is calculated (32). At this time, both waveform data are collected in synchronization with the noise generation source, and if the digitized data are sequentially associated, the time axes will be aligned so that the phases of noise having periodicity will match. . The waveform data [third waveform data] obtained as a result of the calculation is stored in the storage device of the CPU 4, transferred to the digital oscilloscope 3 (33), and input to the waveform storage device 10 (34).

The third waveform data transferred to the digital oscilloscope 3 is displayed by the display device 11 (3
5). The third waveform data output to the external recording device 6 is visualized by means such as printout (36). FIG. 3C shows an example of the waveform obtained by the above calculation.

Since the third waveform data obtained as described above is the difference between the first waveform data and the second waveform data, the noise component commonly contained in both waveform data is removed, The waveform data corresponds to the strength of the magnetic field to be measured. Examples of magnetic fields that can be measured in this manner include high-frequency magnetic fields such as TV deflection yokes, high-frequency transformers, and arc welding.

[0027]

As described above, according to the first aspect of the present invention.
In the alternating magnetic field measuring apparatus according to the invention described in 1, in both the state where the Hall current is flowing in the Hall element and the state where it is not flowing, it is possible to detect the voltage waveform output from the Hall element, 2 by calculation means
Since it is possible to calculate the difference in voltage value by aligning the time axes of two waveform data, the noise component that is commonly included in both waveform data is removed, and it is easy to be affected by the electromagnetic wave noise. It is possible to obtain an alternating magnetic field measuring device capable of accurately measuring a low magnetic field.

Further, in the alternating magnetic field measuring method according to claim 2 or 3, the voltage waveform output from the hall element is measured in both the state where the hall current is flowing in the hall element and the state where it is not flowing. Since the time axis of the two waveform data is detected and the difference between the voltage values is calculated by the calculation means, the noise component commonly included in both waveform data is removed, and the situation is easily affected by noise due to electromagnetic waves. It is possible to accurately measure the low magnetic field even below.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an alternating magnetic field measuring apparatus which is an embodiment of the invention described in claim 1.

FIG. 2 is a flowchart showing an alternating magnetic field measuring method which is an embodiment of the invention described in claim 2.

3 is a diagram showing an example of a voltage waveform detected by the alternating magnetic field measuring apparatus shown in FIG. 1 or by the alternating magnetic field measuring method shown in FIG.

FIG. 4 is a schematic diagram showing a configuration of a conventional magnetic field measuring device.

FIG. 5 is a schematic diagram showing a configuration of a conventional magnetic field measuring apparatus.

[Explanation of symbols]

1 AC magnetic field measurement probe 2 Sensor box 3 Digital oscilloscope 4 CPU 5 Power supply device for sensor 6 Recording device 7 Hall current control device 8 Differential amplifier 9 A / D converter 10 Waveform storage device 11 Display device

Claims (3)

[Claims] 1. A magnetic field sensor using a hall element, a hall current control device capable of flowing a hall current through the hall element and controlling ON / OFF of the hall current, and the hall current A waveform storage unit that stores a voltage waveform output from the magnetic field sensor in the ON state and a voltage waveform output from the magnetic field sensor in the OFF state of the Hall current; and a waveform storage unit stored in the waveform storage unit. An alternating magnetic field measuring apparatus, comprising: a calculating unit that calculates a difference between voltage values in time series by aligning time axes of two voltage waveforms. 2. A first step in which a magnetic field sensor using a hall element is installed in an alternating magnetic field, and a hall current is passed through the hall element to store a voltage waveform output from the hall element in a waveform storage means. A second step of maintaining the magnetic field sensor at the position where the first step is performed, and storing a voltage waveform output from the hall element by the waveform storage means in the state where no hall current flows through the hall element; and the first step. The alternating magnetic field measuring method, further comprising: a third step of aligning the time axes of the voltage waveform stored in step 2 and the voltage waveform stored in the second step and calculating a difference in voltage value in time series. . 3. The alternating magnetic field measuring method according to claim 2, wherein the voltage waveform is stored in a state where no Hall current flows in the Hall element in the first step, and the Hall current of the Hall element in the second step. A method of measuring an alternating magnetic field, characterized in that a voltage waveform is stored by flowing a current.