Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
Measurement method of direct magnetic properties of soft magnetic alloys
This standard is applicable to measuring the magnetic parameters on the basic magnetization curve and hysteresis loop of ring specimen made from soft magnetic alloys (Fe-Ni, Fe-Co-V, Fe-Al alloys, etc.) at room temperature. These magnetic parameters are: magnetic flux density B, magnetic field intensity H, permeability μ, residual magnetic flux density Br, coercivity Hc, squareness ratio Br/Bm.
Other measurement methods are allowed to use if these magnetic parameters are not greater than the measurement error.
1 Measuring principle and lines
1.1 According to the principle of electromagnetic induction, the magnetic flux in the test specimen changes if the magnetization current in the magnetizing circuit changes, and the induced electromotive force is generated at both ends of the measured winding.
The DC magnetic parameters of the test specimen are determined according to the deflection and magnetization current of the ballistic galvanometer.
1.2 The principle circuit diagram of impact measuring device is shown in the figure below.
Circuit diagram of measuring principle
K1, K2, K3——double-pole two-way switch; K4, K5, K6——single-pole one-way switch; R1——slip-line rheostat; R2, R3, R4——resistance box; R5——equivalent resistance of secondary coil of the transformer; A, A1——DC ammeter; A2——AC ammeter; G——ballistic galvanometer; E——DC magnetizing power supply; M——standard transformer; T1——autotransformer; T——demagnetizing transformer; N1——magnetizing winding; N2——measured winding
1.3 The standard transformer M in this measuring device is used to calibrate the ballistic galvanometer. Autotransformer T1 and demagnetizing transformer T are used to demagnetize the test specimen.
2 Test specimen
2.1 For the strip material with a thickness of not less than 0.15mm, a ring specimen is used, with an inner diameter of 32mm, an outer diameter of 40mm and an overlapping thickness of 5–7mm. For the strip material with a thickness of less than 0.15mm, a strip with a width of 10mm is taken along the rolling direction and wound into a ring specimen with an inner diameter of 25mm and an outer diameter of 32mm.
2.2 The test specimen shall be smooth, without burrs, cracks or other defects.
2.3 Before heat treatment, measure the inner diameter and outer diameter of the test specimen with caliper with accuracy of 0.02mm, then calculate the average diameter with Formula (2). Weigh the test specimen with a balance with sensitivity of one thousandth of a gram, and then calculate the cross-sectional area of the test specimen with Equation (3).
2.4 Heat treatment shall be carried out first for the prepared test specimen. The heat-treated test specimen shall not be subjected to stress (impact, compression, tension, bending, vibration, etc.).
2.5 Put the heat-treated test specimen into a test specimen box made from nonmagnetic insulating material, and evenly wind the measured winding N2 outside the test specimen box, and then wind the magnetizing winding N1.
3 Instruments and components in the measuring device
3.1 Ballistic galvanometer
Free vibration period is not less than 18s;
The constant of electric quantity is not greater than 10-8C/(mm·m);
The current constant is not greater than 10-9A/(mm·m).
3.2 DC ammeter A and A1
A and A1 are multi-range ammeters with accuracy of not lower than 0.5 grade, and their measuring ranges are 1mA to 6A and 1mA to 1A respectively.
3.3 DC magnetizing power supply E
Output voltage: 0–20V, continuously adjustable;
Output voltage stability: not greater than ±0.05% per minute;
Ripple voltage: not greater than 2mV at full range
Output current: 0–6A.
3.4 Standard transformer M
The accuracy of standard transformer shall not be lower than 0.2 grade, and the mutual inductance value may be 0.1 or 0.05H.
3.5 Sliding rheostat R1
The maximum allowable current of the rheostat is 6A.
3.6 Resistance box (R2, R3, R4)
The resistance range is 0–100,000Ω, the minimum step value is 0.1Ω, and the power is not less than 0.25W.
3.7 Resistance R5
The resistance value is equal to that of the secondary coil of the transformer.
3.8 Verification of instruments
Instruments and meters shall be sent to the metrological department regularly for verification.
4 Measurement procedure
4.1 Firstly, the ballistic galvanometer is calibrated by the standard transformer. As shown in Figure 1, connect the two ends of the measured winding N2 with the equivalent resistance of the test specimen measured winding, switch K2 and K3 to position 1, turn off K4, connect K6 to M, and adjust the rheostat R1 to make the primary coil of the standard transformer have an appropriate current I. The light spot of the ballistic galvanometer is deflected after the current is reversed by switch K1, and the ballistic constant K of the ballistic galvanometer is calculated by Equation (1):
K＝2MI/a_1 (1)
where,
K——the ballistic constant of the ballistic galvanometer, Wb/scale division;
M——the standard mutual inductance coefficient, H;
I——the current, A;
a1——the light spot deflection of the ballistic galvanometer, scale division.
The deflection of galvanometer is averaged at 1/3, 1/2 and 2/3 of the scale during constant K measurement. The ballistic constant K of ballistic galvanometer is related to its series resistance R3 and parallel resistance R4. R3 and R4 shall be adjusted according to the measurement requirements, and then the constant may be measured.
4.2 If the measurement is conducted below the inflection point of the basic magnetization curve, the test specimen shall be demagnetized by induction method before measurement, as shown in Figure 1. Switch K2 and K3 to position 2, connect the test specimen to the demagnetization circuit, adjust the autotransformer T1 to magnetize the test specimen to be basically saturated (exceeding the inflection point of magnetization curve), slowly pull out the secondary winding of demagnetizing transformer T for about 1m, then turn the secondary winding at an angle of 90 degrees and turn off the power supply. The demagnetization time is about 20s and the demagnetization frequency is 50Hz.
4.3 Measurement of the magnetic flux density and permeability under a given magnetic field intensity. During measurement, connect the test specimen to the measuring device according to Figure 1, switch K1 and K2 to position 1, and K3 to position 2, turn off K4, connect K6 to rheostat R5, adjust rheostat R1 to meet the given magnetization current, reverse the current by switch K1, and record the light spot deflection a of the ballistic galvanometer, and calculate the magnetic field intensity and magnetic flux density and permeability of the test specimen under the magnetic field intensity by Equations (4), (5) and (7).
4.4 During measurement under each magnetic field, carry out magnetic exercise under this magnetic field first with frequency of about once per second for about 7–10 times.
4.5 After measuring the magnetic flux density, measure the residual magnetic flux density Br under the same magnetic field, turn off the power with K1, record the deflection scale a0 of the ballistic galvanometer, and calculate the residual magnetic flux density Br by Equation (6) with a0.
4.6 Measure according to the steps in 4.3 under a given magnetic field, then turn on K4, and record the deflection scale ac of the ballistic galvanometer after quickly switching K1 from position 1 to position 2, adjust R2 repeatedly until ac=a/2, and calculate coercivity Hc by Equation (4) with the indicated value Ic of A1.
4.7 To protect the ballistic galvanometer, switch K5 may be turned on only when reading the light spot deflection of the ballistic galvanometer.
1 Measuring principle and lines
2 Test specimen
3 Instruments and components in the measuring device
4 Measurement procedure
5 Calculation
6 Measuring error
Annex A (Informative)
