JP2000180523A - Magnetic measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic measuring device for easily removing the non-load unbalanced voltage of a magnetic sensor at the time of measuring a fine magnetic field. SOLUTION: A magnetic field is detected by a magnetic sensor 2, and the output of this magnetic sensor 2 is amplified by an amplifier circuit 3, and the magnetic field is displayed on a display circuit 4, and the unbalanced voltage of the magnetic sensor 2 is detected by a correcting circuit 5, and feedbacked to the amplifier circuit 3 so that the unbalanced voltage can be offset in this magnetic measuring device 10. This magnetic measuring device 10 is provided with a data setting means 11 for setting data equivalent to a non-load unbalanced voltage outputted from the magnetic sensor 2 at the time of shielding an earth magnetism and a data adding means 12 for adding the set data to the output of the correcting circuit 5, and feedbacking it to the amplifier circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic measuring device for measuring the intensity of a magnetic field, and more particularly to a magnetic measuring device for removing the influence of geomagnetism when measuring a small magnetic field.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a circuit configuration of a magnetic measuring device for measuring a magnetic field. A magnetic measuring device 1 includes a Hall element 2 as a magnetic sensor for detecting a magnetic field and outputting a corresponding electric signal. And an amplifier circuit 3 for amplifying the electric signal output from the Hall element 2, and a display circuit 4 for displaying the magnitude (value) of the magnetic field detected by the amplified signal.
And a correction circuit 5 for performing zero adjustment before measurement.

The correction circuit 5 detects the unbalanced voltage of the Hall element 2 and performs zero adjustment before measurement. When a magnetic field is not applied and no load is applied, the correction circuit 5 outputs a Hall signal. The unbalanced voltage of the element 2, that is, the sum (V1 + V2) of the residual voltage (V1) of the Hall element 2 and the output voltage (V2) of the Hall element 2 due to terrestrial magnetism is converted into a corresponding digital signal by the AD converter circuit 6. The A / D-converted digital signal is latched by a latch circuit 7, and the latched digital signal is again converted to a corresponding analog signal by an A / D conversion circuit 8 and fed back negatively to the amplifier circuit 3. Cancels (cancels) the unbalanced voltage of the magnetic sensor 2
I am trying to do it.

[0004] Zero adjustment of the magnetometer 1 is performed by accommodating the Hall element 2 in a cylindrical body formed of a magnetic shield member such as a permalloy having a high magnetic permeability, usually called a 0 Gauss chamber, and magnetically shielding it. Is shielded, that is, the output voltage (V2) due to the terrestrial magnetism is reduced to zero, and the residual voltage (V1) of the Hall element 2 is removed. The 0 gauss chamber is usually provided on a cap that is mounted and protected when the Hall element 2 is not used, and shields geomagnetism when the cap is mounted.

[0005]

By the way, the 0 Gauss chamber is of a simple type and cannot completely shield the terrestrial magnetism.
There is no particular problem if it is larger than 3 Gauss). However, when measuring a small magnetic field (several milli-G) below the level of the geomagnetism (about 0.3 G), it is necessary to shield the geomagnetism very well (for example, to about 0.1 mmG) in zero adjustment before measurement. It is. Therefore, in such a case, the unloaded unbalanced voltage of the Hall element 2 is removed while the geomagnetism is completely shielded in a special room (magnetic shield box or the like) provided with a magnetic shield, that is, zero adjustment is performed. There is a need.

However, a special room provided with a magnetic shield, such as the magnetic shield box, is very expensive and requires an installation space, so that it is difficult for ordinary users to secure it. There's a problem. The present invention has been made in view of the above points, and has as its object to provide a magnetic measurement device capable of easily removing a no-load unbalance voltage of a magnetic sensor when measuring a small magnetic field. I do.

[0007]

According to the present invention, there is provided a magnetic sensor for detecting a magnetic field, an amplifier circuit for amplifying an output of the magnetic sensor, and a value of the magnetic field based on an output of the amplifier circuit. And a correction circuit for detecting an unbalanced voltage of the magnetic sensor and negatively feedback to the amplifier circuit to cancel the unbalanced voltage, wherein when the terrestrial magnetism is shielded, Data setting means for setting data corresponding to the no-load unbalanced voltage output from the magnetic sensor, and addition means for adding the set data to the output of the correction circuit and negatively feeding back to the amplification circuit. It is characterized by the following.

[0008] By simply setting data corresponding to the unloaded unbalanced voltage output from the magnetic sensor when the terrestrial magnetism is shielded by the data setting means and adding the set data to the output of the correction circuit by the adding means, Thus, the unloaded unbalanced voltage of the magnetic sensor can be canceled. This eliminates the need for a magnetic shield box or the like provided with a magnetic shield when performing zero adjustment of the magnetic measurement device before measurement, and improves the usability of the magnetic measurement device.

According to a second aspect of the present invention, the adding means adds the data to the output of the correction circuit when measuring a minute magnetic field. When measuring a small magnetic field at a level lower than the earth's magnetism, the output of the correction circuit that removes the influence of the normal earth's magnetism outputs data equivalent to the unloaded unbalanced voltage of the magnetic sensor in a state where the earth's magnetism is almost completely shielded. In addition, the unbalanced voltage of the magnetic sensor can be canceled very well. Thereby, a minute magnetic field can be measured accurately.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a circuit configuration of a magnetometer according to the present invention. In FIG.
The magnetism measuring device 10 includes a Hall sensor 2 as a magnetic sensor for detecting a magnetic field, an amplifying circuit 3 for amplifying an electric signal output from the Hall element 2, and a magnitude (strong) of the magnetic field detected based on the amplified signal. Display circuit 4 for displaying
A correction circuit 5 for removing (cancelling) the unloaded unbalanced voltage of the Hall element 2 before the measurement of the magnetic field, and a data setting means 11 for almost completely removing the influence of geomagnetism when measuring the minute magnetic field. , Data adding means 12 and the like. The magnetic measurement device 10 can measure a wide range of magnetic field (for example, several milligrams G to several tens KG) from a small magnetic field at a level lower than the earth's magnetism to a strong magnetic field. The same components as those of the conventional magnetometer shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

As described above, the correction circuit 5 has a geomagnetic (about
0.3G) is a correction circuit for adjusting zero before measurement of the magnetic measurement device 10 when measuring a magnetic field larger than 0.3 G).
Using a simple 0 Gaussian chamber or the like, the geomagnetism applied to the Hall element 2 is shielded to cancel (cancel) the no-load unbalanced voltage (hereinafter, referred to as “data A”). Therefore, the cancellation of the no-load unbalanced voltage of the Hall element 2 by the correction circuit 5, that is, the zero adjustment is rougher than the case where the geomagnetism is completely shielded.

The data setting means 11 comprises a data setting circuit 15 for setting digital data, and a DA converter 16 for converting a digital signal output from the data setting circuit 15 into a corresponding analog signal. . The data setting circuit 15 is used to almost completely eliminate the influence of the Hall element 2 due to the geomagnetism when measuring a minute magnetic field (several millimeters G to several tens of millimeters G) smaller than the geomagnetism (about 0.3 G). It is. The data setting circuit 15 cancels (cancels) the no-load unbalanced voltage of the Hall element 2 in a state where the geomagnetism is completely shielded (less than 1/100 of the geomagnetism).
To set the voltage (data) for
A voltage (data) for canceling the no-load unbalanced voltage is set by input means such as a three-digit BCD code switch.

The data for canceling (cancelling) the unloaded unbalanced voltage is obtained by bringing the magnetometer 10 into a room provided with a magnetic shield, such as a magnetic shield box, and almost completely reducing the terrestrial magnetism acting on the Hall element 2. Shielded and magnetically unloaded. In this state, the voltage (hereinafter referred to as “data B”) is set by the data setting circuit 15 so that the display on the display circuit 4 becomes 0, that is, the unloaded unbalanced voltage of the Hall element 2 is offset to 0. Set. Therefore, the data B corresponds to a no-load unbalanced voltage in a state where the geomagnetism acting on the Hall element 2 is almost completely shielded. As described above, the data B is a value for setting the display value of the display circuit 4 to 0 when the magnetic field acting on the Hall element 2 is 1/100 or less of the geomagnetism. Then, this data B is hereinafter referred to as the Hall element 2 in this magnetometer 10.
Is a unique value of. This set data B is DA
The conversion circuit 16 converts the signal into a corresponding analog signal (voltage).

The data adding means 12 comprises a switch 17 and an adding circuit 18. The switch 17
It is linked with a measurement range changeover switch (not shown) of the magnetic measurement device 10 and is turned on when the measurement range is switched to a low range, for example, a 20 mmG range in order to measure a minute magnetic field, and is output from the data setting circuit 15. The supplied data B is supplied to the adding circuit 18. Adder circuit 18
Add the data B from the data setting means 15 to the data A output from the correction circuit 5 and feed back negatively to the amplifier 3.

A case where a magnetic field is measured by a magnetic measuring device will be described below. When the magnetic measurement device 10 measures a magnetic field at a level higher than the terrestrial magnetism, for example, the switch 17 is turned off when the measurement range is equal to or larger than the 20 G range. The Hall element 2 is shielded from terrestrial magnetism by the 0 gauss chamber provided in the protective cap, and the output voltage at this time is set to a no-load unbalanced voltage. The unloaded unbalanced voltage is detected by the correction circuit 5 and negatively fed back to the amplifier circuit 3 as described above, and is canceled (canceled). As a result, the display circuit 4 becomes zero apparently.

In the case of measuring a small magnetic field of a low level equal to or lower than the terrestrial magnetism, for example, a magnetic field of several milli-G, the data B is set by operating the input switch of the data setting circuit 15. Then, when the measurement range of the magnetism measuring device 10 is selected to be a low range, for example, a 20 mmG range, the switch 17 is turned on, and the data B output from the data setting circuit 15 is supplied to the addition circuit 18 and the correction circuit 5 , And is negatively fed back to the amplifier circuit 3.

The data B output from the data setting circuit 15 is a voltage that cancels (cancels) the no-load unbalanced voltage of the Hall element 2 in a state where the Hall element 2 is almost completely shielded from geomagnetism. By adding to the data A as a correction signal by the 0 Gaussian chamber from 5, the Hall element 2 can be brought into the same state as zero-adjustment (calibration) in a room provided with a magnetic shield. Thereby, zero adjustment of the magnetometer 10 can be performed in a state of 1/100 or less of the earth magnetism, and a minute magnetic field of about several mG can be accurately measured.

When measuring a very small magnetic field, data B for canceling (uncancelling) the unloaded unbalanced voltage of the Hall element 2 in a state where the terrestrial magnetism is shielded is input in a hardware manner, that is, a data setting circuit. Although the input is performed by operating the 15 input switches, the input is not limited to this. When inputting by software, that is, when a memory for storing the data B is provided and the measurement range is switched to a low range, The data B may be read from the memory. Such a configuration is preferable because cost reduction, simplification of the circuit configuration, improvement in handling of the measurement device, and the like can be achieved.

[0019]

As described above, according to the present invention,
Data corresponding to the unbalanced voltage output from the magnetic sensor when the geomagnetism is shielded is set by the data setting means, and the set data is added to the output of the correction circuit by the adding means, so that the magnetic sensor can be easily turned off. The load imbalance voltage can be canceled, the zero adjustment of the magnetometer can be performed under the same condition as the state where the terrestrial magnetism is almost completely shielded, and the minute magnetic field can be measured accurately. Moreover,
A room or the like provided with a magnetic shield, such as a magnetic shield box, is unnecessary, and zero adjustment can be performed easily and accurately at the time of use.

According to the second aspect of the invention, by adding the data to the output of the correction circuit when measuring the minute magnetic field, the unbalanced voltage of the magnetic sensor can be canceled very well. Thereby, it is possible to accurately measure a minute magnetic field at a level lower than that of the earth magnetism.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a circuit configuration of a magnetometer according to the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a conventional magnetometer.

[Explanation of symbols]

 1, 10 Magnetic measuring device 2 Hall element (magnetic sensor) 3 Amplifier circuit 4 Display circuit 5 Correction circuit 6 A / D conversion circuit 7 Latch circuit 8, 16 D / A conversion circuit 11 Data setting means 12 Data addition means 15 Data setting Circuit 17 Switch 18 Addition circuit

Claims (2)

[Claims] A magnetic sensor for detecting a magnetic field; an amplifier circuit for amplifying an output of the magnetic sensor; a display circuit for displaying a value of the magnetic field by an output of the amplifier circuit; A correction circuit for detecting and negatively feeding back to the amplifier circuit to cancel the unbalanced voltage, wherein the data corresponding to the unloaded unbalanced voltage output from the magnetic sensor when geomagnetism is shielded A magnetic measurement device comprising: data setting means for setting the data; and addition means for adding the set data to the output of the correction circuit and performing negative feedback to the amplification circuit. 2. The magnetic measuring apparatus according to claim 1, wherein the adding means adds the data to an output of the correction circuit when measuring a minute magnetic field.