JP2003294447A - Azimuth angle measurement device - Google Patents

Abstract

(57) [PROBLEMS] To reduce the input range of an A / D converter while securing required measurement accuracy of an azimuth angle measuring device. SOLUTION: An input range adjustment offset value 7b is output to a subtractor 3, and the subtracter 3 calculates a difference between the output of the Hall element 1 output from the amplifier 2 and the input range adjustment offset value 7b. Then, the output of the Hall element 1 from which the input range adjustment offset value 7b has been subtracted is output to the A / D converter 4 for A / D conversion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an azimuth angle measuring device, and is particularly suitable for application when detecting the azimuth by detecting geomagnetism.

[0002]

2. Description of the Related Art In recent years, with the spread of mobile phones and PDAs, the needs for navigation systems for pedestrians have increased, and the demand for direction sensor systems for measuring the pedestrian's current position as well as the direction of travel has increased. . Here, in order to measure the pedestrian's traveling direction,
There is a method of detecting the geomagnetism and obtaining the azimuth by using an inexpensive Hall element.

[0003]

However, since the geomagnetic signal is very small, comparing with this signal amplitude,
Since the Hall element has a large offset amount, and there is a leakage magnetic field such as a speaker inside the mobile device, as a direction sensor for measuring the geomagnetism, the magnetic sensor output due to this leakage magnetic field is added to the offset. There are major challenges.

Therefore, an A / D converter with a large input range is required to perform signal processing by digitally converting the output from the Hall element under an offset amount larger than that of the geomagnetic signal. As a result, geomagnetic measurement is performed. In order to maintain the accuracy of, it is necessary to use an A / D converter with a large number of input bits. Therefore, it is necessary to use an expensive A / D converter, which leads to an increase in the cost of the azimuth measuring device, and the voltage accuracy per bit in the analog circuit portion of the azimuth measuring device that amplifies the geomagnetic signal becomes strict. There is a problem that the load on the circuit design increases.

Further, there is a problem that the offset amount of the Hall element and the leakage magnetic field strength of the magnet used for the speaker are easily changed depending on the temperature, and the measurement accuracy is deteriorated depending on the use environment of the azimuth measuring device. Therefore, the first object of the present invention is to ensure the necessary measurement accuracy while maintaining the A / D
An azimuth measuring device capable of reducing the input range of a converter.

A second object of the present invention is to provide an azimuth angle measuring device capable of suppressing deterioration of measurement accuracy due to temperature changes.

[0007]

In order to solve the above-mentioned problems, according to the azimuth measuring device according to claim 1, a magnetic sensor for detecting geomagnetism and an A / D for converting an analog signal into a digital signal. A converter, an offset value calculating means for calculating a first offset value necessary for fitting the output of the magnetic sensor into the input range of the A / D converter, and an output of the magnetic sensor subtracting the first offset value. An analog subtractor input to the A / D converter, a digital addition means for adding the first offset value calculated by the offset value calculation means to an output value from the A / D converter, and an addition by the addition means Digital subtraction means for subtracting the second offset value superimposed on the magnetic sensor from the result, and the subtraction result by the digital subtraction means Based characterized in that it comprises a bearing calculation means for calculating the azimuth.

As a result, even when the input range of the A / D converter is narrow, the output of the magnetic sensor is reduced to the A / D value by subtracting the first offset value from the output of the magnetic sensor.
It is possible to use the A / D converter by allowing it to fall within the input range of the D converter and digitally adding the first offset value to the output of the magnetic sensor that has been digitally converted by the A / D converter. Instead, the original output of the magnetic sensor can be obtained.

Therefore, even when the input range of the A / D converter is narrower than the amplitude of the amplified geomagnetic signal, the output of the magnetic sensor can be digitized while ensuring the required measurement accuracy. Since the number of input bits of the A / D converter can be reduced, it is possible to easily calculate the azimuth based on the output from the magnetic sensor while suppressing an increase in cost.

According to another aspect of the azimuth angle measuring device, the offset value calculating means sets the output of the magnetic sensor from which the first offset value is subtracted within the input range of the A / D converter. Thus, the first offset value is increased or decreased. This makes it possible to obtain the first offset value by using the A / D converter for A / D converting the output of the magnetic sensor, simplifying the circuit configuration for obtaining the first offset value, and reducing the cost. It is possible to suppress the increase.

According to another aspect of the azimuth measuring device, the offset value calculating means sets the output of the magnetic sensor so that the output of the magnetic sensor falls within the input range of the A / D converter. The first offset value is calculated so that the difference between the output of the output-controlled magnetic sensor and the center value of the input range of the A / D converter is minimized.

As a result, the first offset value can be calculated without repeating the increase and decrease of the first offset value, and the calculation time of the first offset value can be shortened. Further, according to the azimuth measuring device of claim 4, the magnetic sensor for detecting the geomagnetism, the temperature data acquisition means for acquiring the temperature data of the magnetic sensor, and the magnetic sensor based on the temperature data of the magnetic sensor. It is characterized by comprising offset value correction means for correcting the offset value of the sensor, and azimuth calculation means for calculating the azimuth based on the output of the magnetic sensor from which the corrected offset value is subtracted.

As a result, it becomes possible to correct the offset value of the magnetic sensor based on the temperature of the magnetic sensor, and even when the offset amount of the magnetic sensor fluctuates with temperature, the measurement accuracy of the azimuth measuring device deteriorates. Can be suppressed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An azimuth measuring device according to embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an azimuth angle measuring device according to a first embodiment of the present invention.

In FIG. 1, the azimuth measuring device includes a Hall element 1, an amplifier 2, a subtractor 3, an A / D converter 4,
A CPU 5, a D / A converter 6 and a memory 7 are provided. Here, the Hall element 1 is for detecting geomagnetism, and is preferably, for example, a compound semiconductor system such as InSb, InAs or GaAs, or a Si monolithic Hall element.

The memory 7 also stores the true offset value 7a of the Hall element 1 and the input range adjusting offset value 7b. Here, the true offset value 7a of the Hall element 1 includes the offset value for the geomagnetic signal. Specifically, not only the offset unique to the Hall element 1 but also the inside of the portable device in which the Hall element 1 is mounted is included. Leakage magnetic field such as a speaker that generates a magnetic field at
The output detected by is also included.

The true offset value of the Hall element 1 is 7
In addition to the electrical offset of the Hall element itself, the offset due to the leakage magnetic field of the speaker inside the mobile device is added to a. Therefore, after the azimuth measuring device is installed in the mobile device, the calibration operation is performed. The offset value 7a is preferably set individually for each mobile device.

Further, the input range adjusting offset value 7b
Is set so that the output of the Hall element 1 falls within the input range of the A / D converter 4. And Hall element 1
The output from is amplified by the amplifier 2 and input to the subtractor 3. On the other hand, the CPU 5 reads the input range adjustment offset value 7b from the memory 7 and outputs the input range adjustment offset value 7b to the D / A converter 6.

Then, the D / A converter 6 converts the input range adjustment offset value 7b into an analog value, and outputs the analog-converted input range adjustment offset value 7b to the subtractor 3. Then, the subtracter 3 calculates the difference between the output of the Hall element 1 output from the amplifier 2 and the input range adjustment offset value 7b, and the output of the Hall element 1 from which the input range adjustment offset value 7b is subtracted. A
Output to the / D converter 4.

Here, the output of the Hall element 1 itself is A / D.
Even when the input range of the converter 4 is exceeded, the input range adjustment offset value 7b is set so that the output of the Hall element 1 falls within the input range of the A / D converter 4, so the input range adjustment offset value is set. 7b
The output of the Hall element 1 from which is subtracted can be normally A / D converted using the A / D converter 4.

Then, the Hall element 1 from which the input range adjusting offset value 7b is subtracted by the A / D converter 4
When the output of is converted into a digital value, the CPU 5 reads the input range adjustment offset value 7b from the memory 7. Then, the Hall element 1 before the input range adjustment offset value 7b is subtracted by digitally adding the input range adjustment offset value 7b to the digital output of the Hall element 1 from which the input range adjustment offset value 7b has been subtracted Calculate the digital output of.

As a result, the output of the Hall element 1 itself becomes A
The digital value of the original output of the Hall element 1 can be calculated without passing through the A / D converter 4, and even when the input range of the A / D converter 4 is narrower than the output range of the Hall element 1, the Hall element 1 One analog output can be digitized. When the digital output of the hall element 1 is obtained, the CPU 5 reads the true offset value 7a of the hall element 1 from the memory 7, and subtracts the true offset value 7a of the hall element 1 from the digital output of the hall element 1. .

Then, the CPU 5 makes the true offset value 7
The azimuth is calculated based on the digital output of the hall element 1 from which a is subtracted. FIG. 2 is a diagram illustrating an input range adjusting method according to an embodiment of the present invention. In FIG. 2, in a state where the offset OF1 of the Hall element 1 is mounted,
The signal OUT from the hall element 1 is output.

Here, the signal O carrying the offset OF1
When the input range DR of the A / D converter 4 is set so that the UT can take charge, the A / D converter 4
It is necessary to widen the input range DR of, and the cost of the A / D converter 4 is increased. Therefore, the offset OF
The offsets OF2 and OF2 ′ are subtracted from the signal OUT having the offset OF1 according to the amplitude of the signal OUT having the offset OF1 so that the signal OUT having 1 added thereto falls within the input range DR of the A / D converter 4. Input to the A / D converter 4.

As a result, even when the input range DR of the A / D converter 4 is narrow, the offsets OF2, O
The signal OUT from which F2 'has been subtracted can be A / D converted. Then, the offsets OF2 and OF2 ′ subtracted from the signal OUT on which the offset OF1 is added are stored, the signal OUT from which the offsets OF2 and OF2 ′ are subtracted is A / D converted, and then the A / D conversion result is obtained. The offsets OF2 and OF2 'are digitally added.

As a result, even when the input range DR of the A / D converter 4 is narrow, the digital value of the signal OUT with the offset OF1 can be obtained. FIG. 3 is a block diagram showing a schematic configuration of an azimuth angle measuring device according to the second embodiment of the present invention. In FIG.
The azimuth measuring device includes a hall element 21, an amplifier 22, a subtractor 23, an A / D converter 24, a CPU 25, a D / A.
In addition to the converter 26 and the memory 27, the temperature sensor 2
8 are provided.

In addition to the true offset value 27a of the Hall element 21 and the input range adjusting offset value 27b, the memory 27 also stores a temperature correction coefficient 27c for temperature-correcting the offset of the Hall element 21. . Here, the true offset value 27a of the Hall element 21
Includes an offset value for the geomagnetic signal. Specifically, not only the offset unique to the Hall element 21 but also a leakage magnetic field such as a speaker that generates a magnetic field inside the mobile device in which the Hall element 21 is mounted is The output detected by the hall element 21 is also included.

The input range adjustment offset value 27
b is set so that the output of the Hall element 21 falls within the input range of the A / D converter 24. The output from the Hall element 21 is amplified by the amplifier 22 and input to the subtractor 23. On the other hand, the CPU 25 reads the input range adjustment offset value 27b from the memory 27 and outputs the input range adjustment offset value 27b to the D / A converter 26.

Then, the D / A converter 26 converts the input range adjusting offset value 27b into an analog value,
Input range adjustment offset value 2 after analog conversion
7b is output to the subtractor 23. Then, the subtractor 23
The difference between the output of the Hall element 21 output from the amplifier 22 and the input range adjustment offset value 27b is calculated,
The output of the Hall element 21 from which the input range adjusting offset value 27b is subtracted is output to the A / D converter 24.

When the A / D converter 24 converts the output of the Hall element 21 from which the input range adjustment offset value 27b is subtracted into a digital value, the CPU 25
Stores the input range adjustment offset value 27b in the memory 27
Read from. Then, the digital output of the Hall element 21 from which the input range adjustment offset value 27b is subtracted,
The input range adjustment offset value 27b is digitally added, and the digital output of the hall element 21 before the input range adjustment offset value 27b is subtracted is calculated.

When the digital output of the hall element 21 is obtained, the CPU 25 takes in the temperature of the hall element 21 measured by the temperature sensor 28 via the A / D converter 24. Then, the CPU 25 calculates the temperature correction coefficient 27c based on the temperature measured by the temperature sensor 28, and based on the temperature correction coefficient 27c, the hall element 21.
The true offset value 27a of is corrected for temperature.

Then, the CPU 25 subtracts the true offset value 27a of the temperature-corrected hall element 21 from the digital output of the hall element 21 and subtracts the true offset value 27a of the temperature-corrected hall element 21 from the hall element 21. Compute the bearing based on the digital output. As a result, the offset value 27a of the Hall element 21 can be individually corrected according to the environmental temperature, the magnetic flux density of the speaker magnet or the like changes due to the change of the environmental temperature, and the offset amount due to the leakage magnetic flux of the speaker or the like. It is possible to calculate the azimuth with high accuracy even when is changed.

The temperature sensor 28 does not necessarily have to be provided in the azimuth angle measuring device, and the temperature data may be obtained from another temperature sensor provided in the portable device in which the azimuth angle measuring device is mounted. . FIG. 4 shows the third aspect of the present invention.
It is a block diagram showing a schematic structure of an azimuth angle measuring device concerning an embodiment.

In FIG. 4, the azimuth measuring device has X,
Hall elements 31a to 31c for Y and Z axes, multiplexer 32, driving device 33, chopper switch 34, amplifier 35, subtractor 36, integrator 37, sample hold circuit 38, A / D converter 39, interface circuit 4
0, timing generation circuit 41, EEPROM 42, D /
An A converter 43, a temperature sensor 44, a CPU 45, and a tilt sensor 46 are provided.

In the EEPROM 42, the true offset values of the Hall elements 31a to 31c, the input range adjustment offset value of the A / D converter 39, the gains and offsets of the Hall elements 31a to 31c are temperature-corrected. The temperature correction coefficient and the like are stored. here,
The true offset value of each Hall element 31a to 31c includes
The offset value for the geomagnetic signal is also included. Specifically, not only the offset unique to each Hall element 31a to 31c, but also the leakage of a speaker or the like that generates a magnetic field inside the mobile device in which each Hall element 31a to 31c is mounted. The output of the magnetic field detected by each of the Hall elements 31a to 31c is also included.

The input range adjustment offset value of the A / D converter 39 is set so that the signals output from the Hall elements 31a to 31c fall within the input range of the A / D converter 39. And the hall element 31a
To 31c are connected to the chopper switch 34 via the multiplexer 32, and the driving device 33 drives the Hall elements 31a to 31c via the chopper switch 34.

Here, when the chopper switch 34 outputs a driving voltage or a driving current to the hall elements 31a to 31c, the chopper switches drive the hall elements 31a to 31c to perform 90 ° chopper driving or 360 ° chopper driving. It can be carried out. In this chopper driving method, the chopper switch 34 is driven while exchanging the drive terminals and the signal output terminals of the Hall elements 31a to 31c.

As a result, the Hall elements 31a to 31c
You can cancel most of your own offset terms. The signals output from the Hall elements 31a to 31c are input to the amplifier 35, amplified by the amplifier 35, and then input to the subtractor 36. Here, the CPU 45
Indicates that the signals output from the Hall elements 31a to 31c are A
The gain of the amplifier 35 can be adjusted so that it falls within the input range of the / D converter 39.

On the other hand, the CPU 45 reads the input range adjustment offset value from the EEPROM 42 and outputs the input range adjustment offset value to the D / A converter 43 as required. Then, the D / A converter 43
Convert the input range adjustment offset value to an analog value,
The offset value for input range adjustment after the analog conversion is output to the subtractor 36.

The subtractor 36 calculates the difference between the signals of the Hall elements 31a to 31c output from the amplifier 35 and the input range adjustment offset value, and the input range adjustment offset value is subtracted. Hall element 31a-
The signal of 31c is output to the integrator 37. Then, the integrator 37 integrates the signals of the Hall elements 31 a to 31 c from which the input range adjustment offset value has been subtracted for a specified time, and then outputs the integrated signals to the A / D converter 39 via the sample hold circuit 38.

Here, the integration time in the integrator 37 can be adjusted so that the signals output from the Hall elements 31a to 31c fall within the input range of the A / D converter 39. Then, in the A / D converter 39, each Hall element 31a from which the input range adjustment offset value is subtracted
When the output of ~ 31c is converted into a digital value, the CPU
45 is an EEPROM for input range adjustment offset value
Read from 42.

The input range adjustment offset value is digitally added to the digital output of each Hall element 31a to 31c from which the input range adjustment offset value has been subtracted, and the input range adjustment offset value before subtraction is performed. The digital output of each Hall element 31a-31c is calculated. Then, when the digital outputs of the hall elements 31a to 31c are obtained, the CPU 45 causes the hall elements 31a to 31c measured by the temperature sensor 44 via the A / D converter 39.
Take in the temperature of 31c.

Then, the CPU 45, based on the temperature measured by the temperature sensor 44, each of the Hall elements 31a to 31.
Calculate the temperature correction coefficient of gain and offset of c,
Based on this temperature correction coefficient, each Hall element 31a-3
The 1c gain and true offset value are temperature corrected.
Then, the CPU 45 uses the digital outputs of the Hall elements 31a to 31c to perform temperature-corrected Hall elements 31a.
The true offset value of ~ 31c is subtracted, the gain is corrected, and the azimuth is calculated based on the temperature-corrected digital output of the Hall element 21.

Further, the CPU 45 takes in the inclination angle data from the inclination sensor 46 as necessary, and further considers the inclination angle data to calculate the azimuth. 5 and 6
9 is a flowchart showing an azimuth angle measuring method according to a fourth embodiment of the present invention. As shown in FIG.
After sending the keup signal (step S1), a specified voltage is supplied to each of the Hall elements 31a to 31c (step S).
2).

Next, the gain of the amplifier 35 defined for each hall element 31a to 31c is set (step S3), and the hall element 31a to 31c is regulated via the D / A converter 43. The offset correction value is supplied to the subtractor 36 (step S4). Next, the integrator 37 integrates the signals of the Hall elements 31a to 31c from which the offset correction value has been subtracted for a prescribed integration time (step S5), and the integration result is A / D.
By inputting to the converter 39, it is checked whether the integration result is within the input range of the A / D converter 39 (step S6).

When the integration result output from the integrator 37 overflows to the + side (step S
7), the offset correction value supplied to the subtractor 36 is increased (step S8), and the integration result output from the integrator 37 overflows to the − side (step S8).
7) Decrease the offset correction value supplied to the subtractor 36 (step S9).

When the offset correction value supplied to the subtractor 36 is increased or decreased and the integration result output from the integrator 37 falls within the input range of the A / D converter 39, the offset correction value at that time is obtained. EEPROM 42
And the offset correction value stored in the EEPROM 42 is added to the output value from the A / D converter 39 (step S10).

Then, the processes of steps S4 to S10 are performed for all the hall elements 31a to 31c (step S11). Thereby, the Hall elements 31a to 31
A / D converter 39 having a narrower input range than the signal of c
Even in the case of using, the Hall elements 31a to 31c
The digital value of the signal can be calculated.

Next, in FIG. 6, when the digital values of the signals of the hall elements 31a to 31c are obtained, the CPU 45 reads the true offset values of the hall elements 31a to 31c from the EEPROM 42, and the hall elements 31a to 31a.
The external magnetic field strength is calculated by subtracting the true offset value from the signal of 31c (step S12) (step S13).

Next, when there is no output from the tilt sensor 46 (step S14), the CPU 45 determines each hall element 31.
The azimuth is calculated from the ratio of the external magnetic field strengths a to 31c (step S15). On the other hand, the CPU 45 uses the tilt sensor 46.
If there is an output from the tilt sensor 46 (step S14), the output from the tilt sensor 46 is fetched (step S16), and from the ratio of the external magnetic field strengths of the Hall elements 31a to 31c and the tilt angle data, from the horizontal plane of the azimuth measuring device. The azimuth is calculated by correcting the inclination (step S17).

FIG. 7 is a flowchart showing an azimuth angle measuring method according to the fifth embodiment of the present invention. In FIG. 7, after transmitting a Wakeup signal to the measurement circuit (step S21), a specified voltage is supplied to each of the Hall elements 31a to 31c (step S22). Next, each Hall element 31a
To 31c, the specified gain of the amplifier 35 is set (step S23), the integration time of the integrator 37 is set to 1 / N of the specified value, and the hall elements 31a to 31c are set in the integrator 37. Is integrated for the integration time of 1 / N of the specified value (step S24).

Then, when the processes of steps S23 and S24 are performed for all the Hall elements 31a to 31c (step S25), the integration result of the integrator 37 is input to the A / D converter 39 so that the integrator 37 operates. An offset correction value that minimizes the difference between the integration result of (1) and the input range center value of the A / D converter 39 is obtained (step S2).
6).

When the offset correction value is obtained, the offset correction value at that time is stored in the EEPROM 42, and the offset correction value at that time is supplied to the subtractor 36 via the D / A converter 43 (step S2).
7). Next, in the integrator 37, the signals of the respective Hall elements 31a to 31c from which the offset correction value at that time is subtracted,
Integration is performed for a prescribed integration time (step S28), and the integration result is input to the A / D converter 39 to calculate the digital value of the integration result.

Then, the offset correction value stored in the EEPROM 42 is added to the output value from the A / D converter 39 (step S29). And step S4
To S10, all Hall elements 31a to 31c
(Step S30). Next, the CPU 45
When the digital values of the signals of the Hall elements 31a to 31c are obtained, the azimuth is calculated by performing the processing of steps S12 to S17 of FIG.

In the embodiment shown in FIG. 7, the method of setting the integration time of the integrator 37 to 1 / N in order to compress the signals of the Hall elements 31a to 31c has been described. The integral gain of the integrator 37 may be set to 1 / N. However, amplifier 3
When the amplifier gain of 5 is set to 1 / N, step S26
When the offset correction value obtained in step S27 is used, it is necessary to multiply the offset correction value obtained in step S26 by N times.

When compressing the signals of the Hall elements 31a to 31c, a predetermined offset correction value may be subtracted and then the signals of the Hall elements 31a to 31c may be compressed. FIG. 8 is a flowchart showing a calibration method during azimuth measurement according to the sixth embodiment of the present invention.

In FIG. 8, after the Wakeup signal is sent to the measuring circuit (step S41), each Hall element 31a is
The specified voltage is supplied to 31c (step S42). Next, the CPU 45 acquires the outputs of the Hall elements 31a to 31c (steps S43 and S44), and takes in the output of the temperature sensor 39 (step S45).

Here, the outputs of the Hall elements 31a to 31c may be calculated by the method of FIG. 5, the method of FIG. 7, or another method. . The temperature may be obtained from a bandgap reference in the IC or an external temperature sensor. Next, the hall elements 31a to 31
The mobile device equipped with c is rotated twice by 90 degrees around the Z axis (vertical axis), and step S43 to
The process of S44 is performed (steps S46 and S47).

Here, each Hall element 31a to 31a is rotated by rotating it twice every 90 degrees and measuring each time.
Both the gain and offset of c can be determined. If you just want to find the offset,
All you have to do is rotate it 80 degrees. Next, each Hall element 31
By substituting the measured values into the functions of the temperature T of a to 31c and the gain correction value P, the proportional constant α of each function is obtained (step S48).

Here, as a function of the temperature T and the gain correction value P, for example, a cubic function P = α · F (T) = α · (a
^{T 3 + bT 2 + cT +} d) to set the. Then, the temperature characteristics of the plurality of Hall elements are measured in advance, the constants a, b, c, d are obtained by curve fitting, and the EEPROM 4
2 can be stored. Next, each Hall element 31
By substituting the measured values into the functions of the temperature T of a to 31c and the offset correction value Q, the proportional constant β of each function is obtained (step S49).

Here, as a function of the temperature T and the offset correction value Q, for example, a cubic function Q = β · G (T) = β ·
Set (eT ³ + fT ² + gT + h). Then, regarding the composite offset of the offset magnetic field by the hall element and the speaker, the temperature characteristics of the temperature T and the offset correction value Q are measured in advance, or simulation calculation is performed, and the constants e, f, g, and h are obtained by curve fitting. And can be stored in the EEPROM 42.

Then, all the Hall elements 31a to 31c
For the above, the proportional constants α and β obtained in steps S48 and S49 are stored in the EEPROM 42 (step S5).
0, S51). The functions P and Q do not necessarily have to be cubic functions, and the proportional constants α and β do not have to be applied to the entire function, for example, Q = β · (fT ² + gT) + h
You may make it use the function form, such as.

FIG. 9 is a flow chart showing an azimuth angle measuring method according to the seventh embodiment of the present invention. In FIG. 9, after transmitting a Wakeup signal to the measurement circuit (step S61), a specified voltage is supplied to each of the Hall elements 31a to 31c (step S62). Next, the CPU 45 acquires the outputs of the Hall elements 31a to 31c (steps S63 and S64) and takes in the output of the temperature sensor 39 (step S65).

Next, the current offset value of each Hall element 31a-31c is obtained by substituting the measured temperature into the predetermined function of the temperature T of each Hall element 31a-31c and the offset correction value Q (step S66). Next, by subtracting the current offset value of each Hall element 31a-31c from the signal of each Hall element 31a-31c,
The geomagnetic output is calculated (step S67).

Next, the current gain correction value of each Hall element 31a to 31c is obtained by substituting the measured temperature into a predetermined function of the temperature T of each Hall element 31a to 31c and the gain correction value P (step S68). . Next, the current gain correction value of each Hall element 31a to 31c is calculated in step S
The sensitivity variations of the Hall elements 31a to 31c are corrected by multiplying the geomagnetic output obtained in 67 (step S69). The processes of steps S68 and S69 may be omitted.

Then, all the Hall elements 31a to 31c
When the output by the geomagnetism is obtained (step S7)
0) The azimuth is calculated based on these outputs (step S71).

[0067]

As described above, according to the present invention,
By adding the first offset value subtracted from the output of the magnetic sensor in the analog area in the digital area, A
Even if the input range of the D / D converter is narrow, it is possible to digitize the original output of the magnetic sensor while ensuring the required measurement accuracy, and suppress the increase in cost, while reducing the output from the magnetic sensor. Based on this, it becomes possible to easily calculate the azimuth.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an azimuth angle measuring device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an input range adjusting method according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a schematic configuration of an azimuth angle measuring device according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a schematic configuration of an azimuth angle measuring device according to a third embodiment of the present invention.

FIG. 5 is a flowchart showing an azimuth angle measuring method according to a fourth embodiment of the present invention.

FIG. 6 is a flowchart showing an azimuth angle measuring method according to a fourth embodiment of the present invention.

FIG. 7 is a flowchart showing an azimuth angle measuring method according to a fifth embodiment of the present invention.

FIG. 8 is a flowchart showing a calibration method during azimuth measurement according to a sixth embodiment of the present invention.

FIG. 9 is a flowchart showing an azimuth angle measuring method according to a seventh embodiment of the present invention.

[Explanation of symbols]

Hall elements 1, 21, 31a to 31c 2, 22, 35 amplifier 3,23,36 Subtractor 4, 24, 39 A / D converter 5, 25, 45 CPU 6, 26, 43 D / A converter 7,27 memory 7a, 27a True offset value of Hall element 7b, 27b Input range adjustment offset value 27c Temperature correction coefficient 28,44 Temperature sensor 32 multiplexer 33 Drive 34 Chopper switch 37 integrator 38 Sample and hold circuit 40 interface circuit 41 Timing generation circuit 42 EEPROM 46 Tilt sensor

Continued front page    (72) Inventor Masaya Yamashita             3050 Okada, Atsugi City, Kanagawa Prefecture Asahi Kasei Corporation             In the company F term (reference) 2F029 AA07 AB01 AC02 AD02                 5H180 AA21 CC17 CC30 FF04 FF27                       FF37

Claims (4)

[Claims] 1. A magnetic sensor for detecting geomagnetism, an A / D converter for converting an analog signal into a digital signal, and a first offset necessary for keeping an output of the magnetic sensor within an input range of the A / D converter. An offset value calculating means for calculating a value; an analog subtractor for inputting the output of the magnetic sensor subtracting the first offset value to the A / D converter; and a first offset calculated by the offset value calculating means. A digital addition means for adding a value to the output value from the A / D converter; a digital subtraction means for subtracting the second offset value superimposed on the magnetic sensor from the addition result by the addition means; and the digital subtraction means. And an azimuth calculation means for calculating an azimuth based on the subtraction result by the azimuth angle measuring device. 2. The offset value calculating means is the first
The first offset value is increased or decreased so that the output of the magnetic sensor from which the offset value is subtracted falls within the input range of the A / D converter.
The azimuth measuring device described. 3. The offset value calculation means controls the output of the magnetic sensor so that the output of the magnetic sensor falls within the input range of the A / D converter, and outputs the output of the output-controlled magnetic sensor. The azimuth measuring device according to claim 1, wherein the first offset value is calculated so that a difference from the input range center value of the A / D converter is minimized. 4. A magnetic sensor for detecting geomagnetism, temperature data acquisition means for acquiring temperature data of the magnetic sensor, and offset value correction for correcting an offset value of the magnetic sensor based on the temperature data of the magnetic sensor. An azimuth angle measuring device comprising: means and an azimuth calculation means for calculating an azimuth based on the output of the magnetic sensor from which the corrected offset value is subtracted.