The test equipment of magnetic declination
Geomagnetic
declination refers to the angle between the magnetic north direction and true
north direction anywhere on the earth. When the local magnetic north is eastward,
the geomagnetic declination is positive, otherwise it is negative. In most areas
of mainland China, the geomagnetic declination is between -10° and +2°. In
Taiwan, it is about -4°~-3°.
![](https://icdn.tradew.com/file/201606/1569468/png/7538335.png?x-oss-process=image/quality,Q_90)
In fact, in
permanent magnets, there will be some deviations between the magnetization
direction of the magnet and the actual physical direction.
At present, in
most magnetic material production processes, the accuracy and consistency of
the magnetizing direction of the material are not critical. However, as the
application fields of magnetic materials become wider and wider, the accuracy
of permanent magnets is getting higher and higher. Compared with the
requirements of traditional magnetic materials, the new application technology
has more special requirements for the magnetic performance of permanent
magnets. Because the final magnetization vector direction (magnetic
declination) of permanent magnets has an extremely important impact on the
performance of precision magnetic components, permanent magnets the magnetic
declination angle of a magnet is an important index to measure the performance
of permanent magnets.
The earliest
products for magnetic declination measurement of rare-earth permanent magnet
devices can be traced back to the 1990s. The "vector magnetic moment test
system" produced by the American LDJ company (merged by Laboratorio Elettrofisico)
and the product of the German Brockhaus company have been reported, 2010 Years
later, the new magnetic declination test system designed by the German matesy
company using magnetoresistance matrix, and domestic enterprises still use the
traditional coil method for measurement.
1. Helmholtz
coil method measurement: single-axis or three-axis Helmholtz coils are used to
test the three magnetic moment components Mx, My and Mz respectively, and the
total magnetic moment M and magnetic deviation can be obtained through simple
mathematical calculations Angle θz.
![](https://icdn.tradew.com/file/201606/1569468/jpg/7538337.jpg?x-oss-process=image/quality,Q_90)
![](https://icdn.tradew.com/file/201606/1569468/jpg/7538339.jpg?x-oss-process=image/quality,Q_90)
2. M-axis
magnetoresistance matrix method: Use matrix-distributed magnetic field sensors
to test the spatial magnetic field distribution B1, B2..., Bn of permanent
magnetic devices, and then obtain the total magnetic moment M and magnetic
declination θz through more complex mathematical calculations.
![](https://icdn.tradew.com/file/201606/1569468/jpg/7538338.jpg?x-oss-process=image/quality,Q_90)
Test accuracy:
A
measurement system should not only measure the value, but also ensure its
accuracy. Even if any measurement system cannot avoid errors, there are still
ways to reduce its range. Under normal circumstances, there are two main types
of errors that need to be considered, namely mean deviation and uncertainty.
The following will compare two different measurement methods from these two aspects.
1. The main
sources of deviation in the Helmholtz coil method are the accuracy of the
calibration of the Helmholtz constant and the accuracy of the fluxmeter. Things
to note are:
1-1. Design of
the coil structure: If the test sample has a strong magnetic moment signal in
the main axis direction, it can be used as the outermost coil of the three-axis
to reduce the difficulty of processing. This structure has been imitated by
other companies after we used it.
1-2. Accurate
calibration of coil constant: It can be calibrated by high-precision constant
current power supply and Gauss meter.
1-3. Inspection
of the uniform area of the coil: Gauss meter can be used for
multi-point inspection to meet the size requirements of the tested sample.
1-4. Inspection
of the orthogonality of the coil: use a three-dimensional Gauss meter for
inspection, and use a square magnetic steel rotation measurement to fine-tune
the platform surface.
1-5. The flux
meter can be calibrated with a volt-second generator or a high-level flux
meter.
1-6. The angle
accuracy can be inspected by using standard angle wedge addition or other
means.
2. The main
source of deviation of the M-axis magnetic moment scalar method is the
linearity of the sensor and the positioning accuracy of the installation. The
linearity can be calibrated in a standard magnetic field, and the positioning
accuracy can be corrected by standard samples. Matsy GmbH is kept by the German
PTB. For standard samples, the relevant software can be corrected well to achieve
accurate measurement. The angle accuracy inspection method can also be carried
out by adding a wedge with a standard angle.