JPH10160810A - Magnetism measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetism measuring apparatus by which an offset adjusting speed and an offset adjusting accuracy are improved and which eliminates a need of an offset adjusting process in its manufacture. SOLUTION: A background magnetic field which is measured by a magnetism detecting element 1 and by a magnetism measuring circuit 2 is fetched by a CPU 6 through a differential amplifier 4 and an A/D converter 5. When a measured value V2 is at +10V or higher, one bit each is turned on and off from an MBS in a D/A converter 7, and a comparison is executed sequentially. When the measured value is within ±10V, signal corresponding to the measured value is returned to the differential amplifier 4 from the D/A converter 7, the signal of the D/A converter 7 of the differential output 4 becomes zero, and the above processing operation is repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetometer in which a change in a magnetic field is smaller than an absolute value of an indicator during an indication.

[0002]

2. Description of the Related Art Conventionally, as a method of canceling an offset magnetic field in a magnetic field measuring device, a method of performing a manual adjustment by using both a coarse adjustment and a fine adjustment knob, an MSB of a D / A converter
From 1 bit at a time and driven by successive approximation,
A method of driving by an integration method of sequentially accumulating from the LSB of the D / A converter and approaching the target value is adopted.

[0003]

The above-described conventional offset adjustment method has a problem that it takes time and effort to adjust the offset in the case of manual adjustment.
In the case of the successive approximation method using the A-converter, there is a problem that the offset adjustment accuracy is difficult and an adjustment step is required at the time of manufacturing. There was a problem that a process was required. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a magnetometer capable of eliminating the offset adjustment step at the time of manufacturing while improving the offset adjustment speed and the offset adjustment accuracy. Aim.

[0004]

According to the present invention, a measurement output of a magnetic measuring means is taken into an arithmetic means via an A / D converter, and a predetermined voltage is applied to a D / A according to a measurement output of only a background magnetic field.
Return to the measurement signal acquisition means via the converter, in the magnetometer for performing the offset adjustment, means for instructing the offset adjustment, and if the measured value exceeds a predetermined range under the instruction of the offset adjustment, by successive comparison Means for performing offset adjustment, and A when the measured value falls within a predetermined range.
The value corresponding to the measured value taken through the / D converter is D
Means for setting a value to the / A converter and returning to the measurement system a plurality of times.

In this magnetometer, when the offset is adjusted by the instruction means, the input is made only of the background magnetic field, and the measurement signal is taken in. A / A converter performs successive approximation, and when the acquired value becomes equal to or less than a predetermined value, a signal corresponding to the measured value is returned to the measured value via the D / A converter. The process is repeated multiple times.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is a block diagram showing a hardware configuration of a magnetometer according to one embodiment of the present invention. This magnetometer comprises a magnetism detecting element 1 and a magnetism measuring circuit 2
When a differential amplifier 4 that receives the input signal V ₁ of the from the magnetic measuring circuit 2, an A / D converter 5 for converting an analog output signal V ₂ of the differential amplifier 4 into a digital signal, A / D converter A CPU 6 for receiving and storing output signals from the CPU 5;
It comprises a D / A converter 7 for converting a digital signal output from the CPU 6 into an analog signal as an offset signal and applying it to a minus input terminal of the differential amplifier 4, and an output circuit 8. The magnetism detecting means 1 and the magnetism measuring circuit 2 constitute the magnetism measuring means 3. The output circuit 8 is an output circuit that outputs a display element, an analog output signal, a digital output signal, and the like. In general, for example, when a magnetic field change of several nT is measured with a background magnetic field of 50,000 nT, the offset magnetic field refers to the background magnetic field. Further, offset adjustment refers to canceling out the offset magnetic field. An example of a measurement range when measuring a magnetic field change of about several nT is, for example, ± 100 nT. In this case, when the measured magnetic field is 100 nT and the magnetic measurement circuit and its supply power are ± 15 V, V ₂ is generally set to 10 V. The offset adjustment operation of the magnetometer according to the above embodiment will be described using the specific values.

Next, according to the flowchart shown in FIG.
The offset adjustment operation of the magnetometer according to the embodiment will be described. The offset adjustment is started by operating an offset mode designator attached to the CPU 6. The instruction of the offset mode may be changed to the instruction automatically performed at the end of the production, or the offset adjustment can be started by operating the offset adjustment mode key as needed. When the offset adjustment operation starts, first, the output of the A / D converter 7 is fetched and the CPU
In 6 determines whether the V ₂ exceeds the ± 10v (ST2). If V ₂ exceeds ± 10 V, V
_The D / A converter 8 performs successive approximation so that ₂ is within ± 10 V (ST3). ST4 In V _2, it is determined whether it is within ± 10v, ST until within 10v
3 and the successive approximation processing is continued. The successive approximation method is D /
The A / D converter 7 is turned on / off one bit at a time from the MSB side, and set while monitoring the change in V ₂ through the A / D converter 5. In the case of a 16-bit A / D converter, measurement is completed at a maximum of 16 times. If when setting gradually this adjustment method from LSB is required up to 2 ¹⁶ times setting (integration method).

[0008] V_TwoIs within ± 10v, ST4 judgment
Is YES, and then V through the A / D converter 5._TwoMeasure
(ST5). And this V_TwoIs 0v
In the CPU 6, the measured value V is supplied to the D / A converter 7._TwoEquivalent to
A signal is set (ST6). Actually V_TwoIs 0v
Even if the D / A converter 7 is set by the CPU 6,
Error of the dynamic amplifier 4, the A / D converter 5, and the D / A converter 7
The amount corresponding to remains as output. In other words, it becomes 0v
No. Therefore, it is further determined in ST7 whether variable = 2, and n
= 1 from the state of variable 0 until variable = 2
(ST8) and returns to ST5._TwoA
/ D converter 5 and V _TwoIs 0v
D / A converter 7 is set (ST6) so that
Until n = 2, that is, ST5 and ST6 are performed twice
repeat. Offset adjustment is completed by two repetitions
Complete. This will be done at least twice.

The error of the first adjustment in ST6 is assumed to be 10%
If this is done twice, the error will be about 1%. This is the case when the resolution of the D / A converter 7 and the A / D converter 5 is 1% of 10v, that is, sufficiently smaller than 100mV. FIG. 2 is a circuit block diagram showing a hardware configuration of a magnetometer according to another embodiment of the present invention. The magnetic measuring device of this embodiment returns the output of the D / A converter 7 to the differential amplifier 4 in the circuit of FIG. Are different. The adjustment is performed in the same manner as in the magnetometer shown in FIG.
The output of the magnetic measuring circuit 2 corresponds to V ₂ again.

[0010]

According to the present invention, means for instructing offset adjustment, means for performing offset adjustment by successive approximation when the measured value exceeds a predetermined range under the instruction of offset adjustment, Is within a predetermined range.
The value corresponding to the measured value taken through the / D converter is D
Since the offset adjustment is provided with means for repeating the setting by the A / A converter and returning to the measuring device a plurality of times, the offset can be quickly and accurately adjusted, and the offset can be automatically performed. There is an effect that it is not necessary to adjust each time.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating a hardware configuration of a magnetometer according to another embodiment of the present invention.

FIG. 3 is a flowchart for explaining offset adjustment of the magnetometer according to the embodiment shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic detection element 2 Magnetic measurement circuit 4 Differential amplifier 5 A / D converter 6 CPU 7 D / A converter

Claims (1)

[Claims] 1. A measuring output of a magnetic measuring means is taken into an arithmetic means via an A / D converter, and a predetermined voltage is supplied to a measuring signal taking system via a D / A converter in accordance with a measuring output of only a background magnetic field. Means for instructing an offset adjustment in a magnetic measuring device for performing return and offset adjustment; means for performing an offset adjustment by successive approximation when a measured value exceeds a predetermined range under the instruction of the offset adjustment; Means for setting a value corresponding to the measurement value taken in through the A / D converter to the D / A converter and returning the value to the measurement system a plurality of times when is within a predetermined range. Magnetometer.