How to choose Gauss meter

The Tesla meter (Gauss meter) made according to the Hall effect principle has a wide range of applications in measuring magnetic fields. This instrument is composed of two parts, the Hall probe and the instrument. The size, performance and package structure of the Hall element in the probe play a key role in the accuracy of the magnetic field measurement.

The Hall Effect Teslameter's accuracy for uniform, constant magnetic field measurements is typically 5%-0.5%, and high-accuracy measurement accuracy can reach 0.05%. However, the measurement of the non-uniform magnetic field on the magnet surface is not accurate. It is often different instruments, or the same type of instrument, different probes, or different sides of the same probe. To measure the magnetic field of the same magnet surface, at the same position (it seems to be the same position), the displayed results are quite different and the error can exceed 20% or even 50%.

There are two reasons for the above differences: First, the position of the Hall element package in different probes is different, or the components are not in the middle of the two sides of the probe. In the uniform magnetic field, these probes will not feel the change of the magnetic field due to the change of position, and the measurement data will not cause errors due to the difference in position. When different probes are used to measure a divergent, non-uniform magnetic field on the surface of the magnet, although the surface appears to be placed in the same position, the internal Hall element does not sense the magnetic field in the same position. With different field values, the measurement results are certainly not the same. In general, for a radial probe, the smaller the thickness is, the closer the internal Hall element is to the surface, and the larger the reading of the magnetic field at the measurement surface, the reading when using a thin probe to measure the surface magnetic field can be higher than 20% of the conventional probe (tested The smaller the size of the magnet, the greater the curvature of the magnet surface, the more uneven the surface magnetic field distribution, the greater the difference in measurement data), but no matter how thin the probe, its internal magnetic-sensitive part always has a gap with the magnet surface, it is impossible for Zero distance. Therefore, it is impossible to measure the true surface magnetic field. It can only be said that the thinner the probe used, the more the readings reflect the surface magnetic field of the magnet.

The second reason is that in different Hall probe types, the size of the sensitive area of ​​the Hall element packaged is different. Earlier body Hall elements, such as silicon and silicon Hall elements, typically have dimensions of 4 x 2 mm2, 6 x 3 mm2, 8 x 4 mm2, and a minimum of 1.5 x 1.5 mm2. The effective sensitive area is basically It is the size of the component itself and its area is large. If such a Hall element is used to measure magnetic flux divergent small magnets, magnet corner portions or multi-pole magnetized surface magnets. Only the average value of the magnetic induction through the surface of the element can be reflected. This value must be less than the maximum value of this area. If a small Hall element such as a gallium arsenide Hall element is used in a sensitive area, the effective area of ​​the sensitive area is approximately 0.1×0.1 to 0.2×0.2 mm2, which is much smaller than the area of ​​the body element. This element can better reflect the field distribution of the surface magnetic field, and the measured maximum value is also closer to the actual value of the maximum magnetic induction in the area.

From the previous analysis, it can be seen that the actual value of the surface magnetic field (ie, the true value) is impossible to measure with the Hall effect method. In other words, it is impossible to find and establish a unified, common surface magnetic field standard. Only ways to measure the actual value of the surface magnetic field can only be sought.

How to measure the magnetic field on the surface of the magnet by Hall effect method - Gauss meter how to select the probe A permanent magnet measurement instrument The permanent magnet measurement instrument is a special instrument for measuring the magnetic properties of various permanent magnet magnetic materials. We usually use the instrument: Gauss meter (Tesla meter), BH hysteresis loop instrument and so on. Fluxmeter 1, Gaussmeter (Teslameter): used to measure the magnetic field strength and air gap magnetic field strength of various permanent magnets.

2. Fluxmeter: Used to measure the permanent magnetic flux induced magnetic flux.

3, BH hysteresis loop instrument: used to measure permanent magnetic materials Br, Hcb, Hcj, BHmax and other magnetic performance parameters, can automatically draw hysteresis loop and demagnetization curve.

Second, Gauss meter (Tesla meter)

1. Classification of Gaussmeters (Teslameters): Analog, Digital, Portable.

2. Application of Gaussmeter (Teslameter) (a) Surface magnetic field measurement of permanent magnets: Gauss meter (Tesla meter) is used to measure the surface magnetic field strength of permanent magnet products, mainly for the quality and magnetization of permanent magnet products. After the evaluation of the consistency of the magnetic properties; usually measured magnetic field intensity in the center of the surface of the magnet to measure, by comparing the standard sample data to determine whether the product is qualified, but also can ensure the consistency of the material.

(b) Measurement of air gap magnetic field: The use of a Gauss meter (Tesla meter) to measure the magnetic field of a gas is widely used, and it is useful in the fields of scientific research, electronics manufacturing, and machinery. At present, the industries where applications are more typical are the two industries of motor and electro-acoustic.

(c) Measurement of residual magnetism: if the demagnetization effect of the workpiece is demagnetized, it is tested.

(d) Magnetic flux leakage measurements: such as horn magnetic leakage measurements.

(e) Measurement of the environmental magnetic field 3. Gaussmeter (Teslameter) Selection: The selection of a Gauss meter (Teslameter) should start with the measurement object and consider the following aspects:

a, magnetic field type: magnetic field is divided into two kinds of DC magnetic field and AC magnetic field, permanent magnetic material magnetic field intensity should be measured using DC Gauss meter;

b. Range of the instrument: Define the approximate magnetic field range of the measured object, and select the range of the instrument should be greater than the measured magnetic field;

c, measurement accuracy: refers to the resolution of the instrument, such as the resolution is 1Gs or 0.1Gs;

d. Probe Selection: Usually, the test probes of the instrument manufacturers have a variety of different specifications to meet various test requirements. The measurement of surface magnetic field strength usually does not need to consider the probe specifications.

1 Air gap magnetic field measurement: The dimensions of the probe should be taken into consideration when it is visited. If the probe size is larger than the air gap to be measured, it cannot be entered into the air gap under test and it cannot be used.

2 probe direction selection: The probe direction is divided into two kinds of horizontal and axial, the user should choose to adapt the probe according to the measured object when the probe is selected;

3 Probe connection line: The length of the probe cable of the instrument manufacturer is usually fixed. If there are special measurement requirements, when the probe line needs to be extended or shortened, it should be proposed to the manufacturer. Gaussmeter e, power supply: Desktop gaussmeter usually uses AC 220V power supply, portable gaussmeter uses battery power.

f, function selection 1 conventional functions: polarity judgment, maximum value locking, etc.;

2 Portability: For outdoor operation or on-site measurement, a portable gauss meter (portable) with good portability can be selected. Such instruments are small in size and light in weight and are powered by batteries.

3 rapid measurement of the production line: the instrument has upper and lower limit settings and alarm functions;

4 AC magnetic field measurement: used to measure the intensity of alternating magnetic field at low frequency (1-400Hz);

Third, the fluxmeter fluxmeter is generally directly measuring the magnetic induction flux of the probe coil, use more is coupled with Holm Hertz coil, this method is mostly compared with the standard sample, and then determine the product's eligibility.

Before using the fluxmeter, it must be warmed up as required, and the integral drift should be adjusted during use so that the drift amount is within the specified range. Clear the zero before each measurement to release the residual charge or drift integral charge of the integrating capacitor.

When the magnetic circuit of the magnet is closed, the fluxmeter can be used to measure and calculate the remanence. The specific calculation method is: Br = Φ/N/S Where: Φ - magnetic flux; N - number of turns of the coil; S - magnet Cross-sectional area.

When the fluxmeter is used to test the conformity of the product, the relative position of the sample and the coil to be measured must be the same as the “relative position of the standard sample and the coil”. If the product's performance range has stringent requirements, the product with the upper limit performance and the product with the lower limit performance should be preserved for calibration and inspection.

Fourth, permanent magnet BH hysteresis loop measuring instrument permanent magnet BH hysteresis loop measuring instrument can measure magnetic hysteresis loop and demagnetization curve of permanent magnetic material, accurate measurement of remanence Br, coercive force HcB, intrinsic coercive force Magnetic properties such as HcJ and maximum energy product (BH)max.

With the rapid development and application of computer system integration technology, magnetic measurement systems based on computer operation platforms have also emerged.

5. Magnetization When the magnet length is near the magnetization coil, the vertical center of the magnet should coincide with the vertical center of the magnetization coil. This ensures that the magnetic field strength at both ends of the magnet is equal and the symmetry of the magnetization is ensured. Reduce the magnetic field strength on both surfaces of the magnet due to the magnetization method.

Theory has proved that the magnetic field strength at both ends of the magnetizing coil is 1/2 of the magnetic field strength at the center point of the coil. When the magnet approaches the length of the magnetizing coil, it may not be able to saturate and magnetize the products above H and SH series. When the magnetic field intensity is not large enough, even the M and N series products cannot be saturated and magnetized. In general, the length of the magnetizing magnet is preferably less than 2/3 of the magnetizing coil.

VI. Judgment of easy magnetization direction of magnets There are problems with the orientation (easy magnetization direction) for square squares and cylinders oriented perpendicularly to each other. It is possible to use magnetized products or borrow instruments for identification. The specific methods are as follows:

(1) Identification with magnetized products: For square squares, due to the anisotropy of the material, the magnetic chips are arranged in the orientation direction, so the orientation direction is easy to magnetize, and after the magnetization, the opposite-phase suction and suction force is greater. The suction force in the non-orientation direction is small, and the orientation direction of the judgment is identified in order; the magnet for detection should be slightly larger, and the difference in the size of the suction force when passing the magnet is not easy to distinguish; for the cylinder with vertical axial orientation, only the magnetization can be generally used. The magnets are tested: the surface of the cylinder is sucked by a magnet, and the cylinder is sucked up. The direction perpendicular to the ground is the orientation magnetization direction;

(2) Using magnetic flux meter to identify: A magnet can be sucked on a square material. The direction of the magnet is perpendicular to the flux coil. The surface with a relatively large magnetic flux value is an orientation surface. The direction perpendicular to this surface is the orientation direction. .

Gaussian (G), non-international magnetic induction unit. Named after Gauss, a German physicist and mathematician.

Single pull conversion: 1T (Tesla) = 1000MT (millensilla) = 10000GS (Gaussian)

1MT=10GS

What is a Hall effect semiconductor chip placed in a magnetic field of magnetic induction B, the direction of the magnetic field perpendicular to the sheet, as shown in the figure. When a current I flows through the sheet, an electromotive force EH is generated in a direction perpendicular to the current and the magnetic field. This phenomenon is called a Hall effect. This electromotive force is called a Hall potential, and the above-described semiconductor sheet is called a Hall element.

The principle is briefly described as follows: The excitation current I flows in from the a and b ends. The magnetic field B acts on the sheet from directly above. In this case, the direction of movement of the electron e is opposite to that of the current and will be affected by the Lorentz force FL and shifted inward. This side forms a stack of electrons and generates an electric field E in the c and d directions of the sheet. The more electrons are accumulated, the larger the FE, and the electromotive force EH established between the end faces of the semiconductor sheets c and d is the Hall potential.

From experiments, it can be seen that the greater the current I flowing into the exciting current end, the stronger the magnetic field strength B acting on the sheet, and the higher the Hall potential. The direction of the magnetic field is reversed, and the direction of the Hall potential is also changed. Therefore, the Hall sensor can be used to measure a static magnetic field or an alternating magnetic field.