Iec 60404 4 2008

The changes of the magnetic flux density shall be calculated from the following relationship: A N α B 2 b bK = where ΔB is the measured change of the magnetic flux density, in teslas; K

Object

This clause describes the ring method used to obtain the normal magnetization curve and the hysteresis loop.

General

This method is effective for measuring magnetic field strengths up to 10 kA/m, but with careful management to prevent heating the test specimen, it can also be applied at higher magnetic field strengths.

Effect of temperature on the measurements

To ensure accurate measurements, it is essential to prevent excessive heating of the test specimen Testing should occur at an ambient temperature of (23 ± 5) °C, and the specimen's temperature must not exceed 50 °C, which will be monitored using a temperature sensor.

For materials which are particularly temperature sensitive, product standards may define lower or higher test specimen temperatures.

Test specimen

The test specimen is a homogeneous unwelded ring of rectangular or circular cross-section

The cross-sectional area of the ring is determined by the product dimensions, uniformity of magnetic properties, instrumentation sensitivity and space required for the test windings

Usually the cross-sectional area is in the range of 10 mm 2 to 200 mm 2

When preparing the test specimen, it is crucial to avoid work hardening or heating the material, as these factors can impact its magnetic properties The specimen should be shaped through turning and finished with light grinding, ensuring adequate coolant is used to prevent overheating Additionally, the edges of the rings must be deburred for optimal results.

To minimize the impact of radial variation in magnetic field strength, the ring's dimensions should maintain an outer to inner diameter ratio of no more than 1.4, ideally below 1.25 A ratio nearing 1.4 will result in increased radial variation of the magnetic field strength.

To determine the cross-sectional area of a test specimen for a stack of laminations or a toroidal wound core, it is essential to calculate it using the mass, density, and the inner and outer diameters of the ring The density should be the conventional value provided by the manufacturer for the specific material The calculation can be performed using the appropriate equation.

A is the cross-sectional area of the test specimen, in square metres;

The outer diameter of the test specimen is denoted as \$D\$ in metres, while the inner diameter is represented by \$d\$ in metres The mass of the test specimen is indicated by \$m\$ in kilograms, and the density of the material is expressed as \$\rho\$ in kilograms per cubic metre.

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The dimensions of the test specimen must be measured using a micrometer or vernier gauge to obtain the outside and inside diameters of the ring, along with its height or diameter The mean cross-sectional area should be calculated with an uncertainty of ±0.5% or better.

The mean magnetic path length of the test specimen shall also be calculated with an uncertainty of ±0,5 % or better from the relationship:

D+ π l (2) where l is the mean magnetic path length of test specimen, in metres.

Windings

Before winding, it is essential to connect to the core to verify the insulation of the windings A temperature sensor should be attached to the test specimen, and a thin layer of insulating material must then be applied over the ring.

Firstly, a secondary winding of insulated copper wire shall be wound evenly round the core

The dimensions of the secondary winding shall be determined and the mean cross-sectional area, A c, of the secondary winding shall be calculated

The magnetizing winding must be constructed with wire capable of handling the maximum magnetizing current and should have enough turns to achieve the required magnetic field strength, wound evenly in one or more layers around the core This winding can be made in several ways: a) using a large number of turns of a single conductor wound closely and uniformly around the entire ring, b) utilizing a smaller number of turns from a multicore cable, where the individual cores are interconnected to function as a single multilayer winding, or c) employing a combination of rigid and flexible conductors that can be opened to insert the ring (which contains the secondary winding and insulation) and then closed to create a uniformly wound toroid around the ring.

If necessary, the wound ring is immersed in an oil bath or subjected to an air blast in order to cool it

Using a uniformly distributed secondary winding in the above arrangements can lead to significant errors during ring tests These errors occur because winding a ring specimen in a toroidal shape creates an effective circular turn with a diameter equal to the mean diameter of the ring, potentially magnifying the inaccuracies.

The interaction between the effective mutually inductive circular turns of the magnetizing and secondary windings, along with the flux parallel to the ring's axis, influences the circumferential flux When utilizing a multiconductor cable for the magnetizing winding, the primary turns of the supplementary mutual inductance increase with the number of cores, potentially introducing errors of several percent, especially at high field strengths where the test specimen's permeability decreases To mitigate this error, it is recommended to wind a turn back on the secondary winding along the ring's mean circumference or, ideally, to arrange the magnetizing cable in pairs of layers, alternating between clockwise and anti-clockwise winding.

Methods of measurement by the ring method

Magnetic field strength

The magnetizing current shall be measured with an uncertainty of ±0,5 % or better The magnetic field strength shall be calculated from the following relationship: l

H is the magnetic field strength, in amperes per metre;

N 1 is the number of turns of magnetizing winding of the ring; l is the mean magnetic path length, in metres;

I is the magnetizing current, in amperes.

Magnetic flux density

The secondary winding N2 (B coil) must be linked to a flux integrator, such as an electronic integrator, ballistic galvanometer, or fluxmeter The calibration of this integrator should follow one of the procedures outlined in annex B, ensuring an uncertainty of ±1% or better.

The changes of the magnetic flux density shall be calculated from the following relationship:

Kb Δ (4) where ΔB is the measured change of the magnetic flux density, in teslas;

K B is the flux integrator calibration constant, in volts seconds; αB is the reading of the flux integrator;

N 2 is the number of turns on the secondary winding of the ring;

A is the cross-sectional area of the ring, in square metres

For direct reading of the ΔB, the flux integrator may be adjusted so that K B/(N 2 A) becomes a power of 10

When the secondary winding is tightly wound around the test specimen, the air flux within the secondary winding remains negligible for magnetic field strengths ranging from 0 to 4 kA/m, eliminating the need for any corrections However, at higher magnetic field strengths, it is necessary to apply an air flux correction as specified by equation (8).

Connection of apparatus

The apparatus is connected as shown in figure 1

A stabilized direct current source E, with a ripple content of less than 0.1% or a battery, is connected to the magnetizing winding N1 on the ring specimen through a current-measuring device A and a reversing switch S1, which is unnecessary if a bipolar current source is used The current in the magnetizing circuit is controlled by resistor R1 when switch S2 is closed; however, if a stabilized supply with a continuously controllable output is utilized, resistor R1 is not needed This setup is essential for determining the normal magnetization curve and measuring the tip points of hysteresis loops Additionally, switch S2 and resistor R2 are required in certain configurations to ascertain the complete hysteresis loop, while the secondary circuit includes the secondary winding N2 (B coil) connected to the flux integrator.

Determination of normal magnetization curve

The test specimen must be thoroughly demagnetized from a magnetic field strength of at least 5 kA/m through repeated reversals of a gradually decreasing demagnetizing field Additionally, specimens exposed to higher magnetic field strengths, such as those machined with a magnetic chuck, should be demagnetized from an appropriately high field prior to testing.

To ensure complete penetration of the magnetic field in the test specimen, it is essential that the dwell time after each reversal exceeds 2 seconds for a cross-section of 10 mm × 10 mm, and 10 seconds for a cross-section of 20 mm × 20 mm.

The flux integrator must be calibrated using one of the methods outlined in annex B Once S 2 is closed, the normal magnetization curve should be established through one of the specified methods.

To implement this method, connect the output from the flux integrator to the Y axis of an X-Y recorder, plotter, or computer interface A low-value calibrated resistor (e.g., 0.1 Ω or 1 Ω) should be placed in series with the magnetizing winding, with its potential terminals linked to the X axis of the recording device This setup allows for overall calibration, enabling direct readings of magnetic flux density and magnetic field strength on the chosen interface.

The magnetizing current shall be steadily increased from zero to the value to produce the required maximum magnetic field strength The magnetization curve is then produced on the

X-Y recorder, plotter or computer interface

Method B: point-by-point method

A low current, which corresponds to a low magnetic field strength, will be passed through the magnetizing winding N1 The current will be reversed approximately 10 times using the reversing switch S1 to achieve a steady cyclic state in the material During this process, switch S3 will remain closed to keep the flux integrator at zero Once switch S3 is open, the flux integrator reading will be recorded, allowing for the calculation of the corresponding magnetic flux density related to the reversal of the magnetizing field.

By gradually increasing the magnetizing current and repeating the process, we can obtain values for magnetic field strength and magnetic flux density, allowing us to plot the normal magnetization curve.

The magnetizing current shall never be decreased during the measurements, otherwise the test specimen shall be demagnetized before resuming measurements.

Determination of a complete hysteresis loop

The test specimen shall be demagnetized in accordance with 3.6.4 and the hysteresis loop shall be determined by one of the following methods

Method A of section 3.6.4 mandates the use of additional equipment Initially, the flux integrator must be zeroed, followed by passing a current through the magnetizing winding N1 to achieve the maximum required magnetic field strength This current should be gradually decreased to zero, reversed, increased to its maximum negative value, reduced to zero again, reversed once more, and finally increased to its maximum positive value.

The cycle duration should be between 30 to 60 seconds; however, certain materials like pure iron may need a longer time to ensure proper magnetization of the test specimen in response to the applied magnetic field, while also preventing significant drift of the flux integrator zero over time.

The test specimen must be demagnetized before applying a current through the magnetizing winding N1 to achieve the maximum required magnetic field strength The tip points of the hysteresis loop will be identified by measuring the corresponding values of magnetic field strength and magnetic flux density, following method B of section 3.6.4.

To determine portion PQ of the hysteresis loop, switch S1 is closed in position 1 while switch S2 is opened, allowing for the measurement of the corresponding magnetic field strength and the change in magnetic flux density By adjusting resistor R2, multiple points on the curve can be obtained.

PQ can be obtained The point Q is obtained with switch S 2 closed and measuring the change in magnetic flux density when opening switch S 1

The value of the magnetic field strength at each point is calculated from the corresponding measured value of current flowing (see equation (3))

The value of the magnetic flux density at each point is calculated from the following relationship:

B P ′ is the flux density at the point P′ of curve PQ, in teslas;

The magnetic flux density at the tip of the hysteresis loop, denoted as B P, is measured in teslas Additionally, ΔB represents the change in magnetic flux density observed when switch S2 is opened while switch S1 remains closed in position 1, also measured in teslas.

Portion QS of the hysteresis loop is determined, with switch S 2 open, by closing switch S 1

Changes in magnetic field strength and magnetic flux density are measured starting with switch S 1 in the open position and closing it to position 2

The value of the magnetic field strength at each point is calculated from the measured value of the current flowing when S 1 is closed in position 2 (see equation (3))

The value of the magnetic flux density at each point is calculated from the following relationship:

B Q ′ is the magnetic flux density at the point Q′ on curve QS, in teslas;

The magnetic flux density at point Q is denoted as B Q, measured in teslas The change in magnetic flux density, represented as ΔB, occurs when switch S1 is closed in position 2 while switch S2 remains open, also measured in teslas.

To obtain the complete hysteresis loop, the switching sequence shall be in accordance with the arrangement given in table 1 to maintain the test specimen in a steady cyclic state

Table 1 – Switching sequence to maintain the test specimen in a steady cyclic state

Closed (1) Closed (1) Open Closed (2) Closed (2) Closed (2) Open Closed (1) Closed (1)

Closed Open Open Open Closed Open Open Open Closed

Resistors R 1 and R 2 respectively are adjusted to obtain:

– resistor R 1 : values of magnetic field strength +H or –H, that is point P or point S on the loop (figure 2);

– resistor R 2 : values of magnetic field strength +H′ or –H′, that is points P′ and T′ or points

Q′ and S′ on the loop (figure 2)

To ensure accurate measurements and eliminate drift errors in the flux integrator, it is essential to analyze the entire hysteresis loop Notably, the STUP section of the loop exhibits symmetry with another portion, which can be leveraged for more precise results.

PQRS, measurements may be made for only one-half of the hysteresis loop.

Determination of remanent flux density

The remanent flux density of a material, measured in teslas, is defined as the magnetic flux density when the magnetic field strength is zero, as indicated by point Q on the hysteresis loop or its symmetrical counterpart, point T.

Determination of coercive field strength

The coercive field strength of a material, measured in amperes per meter, is defined as the magnetic field strength at which the magnetic flux density equals zero within a given hysteresis loop This value can be identified at point R on the hysteresis loop or at the symmetrical point U.

Uncertainty by the ring method

The total uncertainty in the measurement of the magnetic flux density or the magnetic field strength normally expected is less than or equal to, ±2 % when using measuring instruments

The A2:2008 standard specifies that the estimated uncertainty for measurements using the point-by-point method should be less than or equal to ±1% However, when a complete magnetization curve or hysteresis loop is obtained through the continuous recording method, the overall uncertainty may increase due to the uncertainty and resolution of the recording system or computer interface.

As the result of the measurements is affected by changes in temperature, precautions must be taken to avoid heating the test specimen (see 3.3)

4 Determination of the magnetic characteristics by the permeameter method

Object

Clause 4 describes the permeameter method for determining the normal magnetization curve and the hysteresis loop.

Principle of the permeameter

The instrument's principle is demonstrated in Figures 3 and 4, where the test specimen is securely clamped between two robust steel yokes that create a flux closure path These yokes can be constructed from one of three materials: a) two strip-wound C-cores made of grain-oriented steel according to IEC 60404-8-7, b) two strip-wound C-cores of nickel iron as outlined in IEC 60404-8-6, or c) two stacks of laminations derived from electrical steel in compliance with IEC 60404-8-2.

IEC 60404-8-3, IEC 60404-8-4, IEC 60404-8-7 or IEC 60404-8-8, or d) two yokes machined from solid low carbon steel or soft iron

For testing round or square bars, pole pieces must be made from two pairs of low carbon steel or soft iron blocks, precisely machined to fit the test specimen closely (refer to figures 3c and 3d) It is essential that the pole pieces possess high permeability to ensure a low reluctance path for the magnetic flux between the test specimen and yokes.

Two types of permeameter are shown in figures 3 and 4 having the following properties:

Type A: range of magnetic field strength: 1 kA/m to 200 kA/m; magnetizing coil: on former around test specimen; minimum length of test specimen: 250 mm;

H measuring systems: search coil or Hall probe

Type B: range of magnetic field strength: 1 kA/m to 50 kA/m; magnetizing coil: wound around yoke; minimum length of test specimen: 100 mm;

H measuring system: Rogowski-Chattock potentiometer

The requirements of 3.3 shall also apply to the permeameter methods

Test specimen

For testing with type A permeameters, specimens must be at least 250 mm long, while type B permeameters require a minimum length of 100 mm The specimens should have a cross-sectional area ranging from 10 mm² to 500 mm² and can be in the form of a round, square, rectangular, or hexagonal bar with a uniform cross-section.

To minimize the air gap between the test specimen and the pole pieces, it is essential to machine the specimen's surface in contact with the pole pieces through turning or grinding, using adequate coolant to avoid overheating Additionally, for materials sourced from sheet or coil, one strip measuring 30 mm in width should be cut parallel to the rolling direction, while another strip should be cut perpendicular to it, with each strip measured separately.

The cross-sectional area of the test specimen is determined by measuring necessary dimensions at equal intervals along the test length, specifically using a micrometer to assess transverse dimensions approximately every 10 mm The mean cross-sectional area is calculated from these measurements, with an uncertainty of ±0.5% Additionally, the variation between the largest and smallest cross-sectional areas must not exceed 0.5% of the mean area.

Methods of measurement by the permeameter method

Measurement of magnetic field strength

The magnetic field strength shall be measured with an uncertainty of ±1 % or better by one of the following methods:

Type A permeameters consist of a search-coil with a length ranging from 10 mm to 50 mm, as illustrated in figure 5c This search-coil is connected to a magnetic flux integrator, which must be calibrated following one of the methods outlined in annex B.

The search-coil consists of two coils arranged in series, positioned on opposite sides of the test specimen or coaxially wound in series opposition These coils must be constructed on non-magnetic, non-conducting formers The effective area-turns product of the search-coil should be measured with an uncertainty of ±0.5% using one of the methods outlined in annex A.

The sensitivity of the flux integrator and the range of magnetic field strength to be measured determine the number of turns on the search-coils Additionally, a Hall effect device or other passive sensing methods can directly measure a magnetic field with an uncertainty of ±0.5% or better Calibration of these devices can be achieved in a known field solenoid or a uniform magnetic field using a suitable nuclear magnetic resonance probe.

Type B permeameters can be utilized by either demonstrating that the variation of magnetic field strength in the radial direction is negligible using methods applicable to type A permeameters, or by employing a Rogowski-Chattock potentiometer, which is a C-shaped H-potentiometer coil connected to a magnetic flux integrator.

The H-potentiometer coil must consist of a continuously wound coil with an axis positioned along a semicircle of a maximum diameter of 40 mm, or it may utilize a series of discrete coils connected in series, ensuring their axes are aligned to avoid significant discontinuities in the magnetic potential integration Additionally, the end faces of the coil system should be within 0.5 mm of the test specimen's surface.

The effective area-turns product of the H-coils shall be determined with an uncertainty of ±0,5 % by one of the methods given in annex A

Using one of the coil arrangements described in a) or d) above, the changes of the magnetic field strength shall be calculated from the relationship:

= μ Δ (7) where ΔH is the change of magnetic field strength, in amperes per metre;

K H is the calibration constant of the flux integrator (H), in volts seconds; αH is the reading of the flux integrator (H); μ0 is the magnetic constant (4 π 10 –7 henrys per metre);

(NA) is the effective area turns product of the H-coil, in square metres

For direct reading of the values, the flux integrator may be adjusted so that K H /[μ0(NA)] becomes a power of 10.

Measurement of magnetic flux density

Magnetic flux density must be measured with an uncertainty of ±1% or better using specific methods One effective approach involves utilizing a flux-sensing coil (B-coil) with a length ranging from 10 mm to 50 mm, which should be connected to a flux integrator The calibration of this flux integrator must follow the procedures outlined in annex B.

The magnetic flux density may require correction based on the strength of the magnetic field and the relative cross-sectional areas of the test specimen and the flux-sensing coil.

The corrected value of the magnetic flux density is given by the following relationship:

B is the measured value of magnetic flux density, in teslas; μ0 is the magnetic constant (4 π 10 –7 henrys per metre);

A c is the cross-sectional area of the flux-sensing coil, in square metres;

A is the cross-sectional area of test specimen, in square metres

A compensating coil with an effective area matching that of the air section between the winding and the test specimen can be connected in series opposition to the flux-sensing coil.

+A2:2008 The changes in magnetic flux density shall be calculated from the relationship:

B N α Δ (9) where ΔB is the change of the magnetic flux density, in teslas;

K B is the calibration constant of the flux integrator (B), in volts seconds; αB is the reading of the flux integrator (B);

N 2 is the number of turns of the flux-sensing coil;

The cross-sectional area of the test specimen, denoted as A in square meters, is measured alongside the magnetic polarization, which has an uncertainty of ±1% or better The magnetic flux density is then calculated using this value, along with the magnetic field strength, based on the established relationship.

B is the magnetic flux density, in teslas; μ0 is the magnetic constant (4 π 10 –7 henrys per metre);

J is the measured magnetic polarization, in teslas

Magnetic polarization, denoted as J, will be measured using compensated polarization coils (J-coils) linked to a calibrated flux integrator, as outlined in annex C There is no need for a correction for air flux.

The changes of the magnetic polarization shall be calculated from the relationship:

J N α Δ (11) where ΔJ is the change of the magnetic polarization, in teslas;

K J is the calibration constant of the flux integrator (J), in volt seconds; αJ is the reading of flux integrator (J);

N 2 is the number of turns on the polarization sensing coil;

A is the cross-sectional area of the test specimen, in square metres

For direct reading of the values, the flux integrator can be adjusted so that KJ/(N 2 A) becomes a power of 10.

Connection of apparatus

The apparatus is connected as shown in figure 6

A stabilized direct current source, E, with a ripple content of less than 0.1% or a battery, is connected to the magnetizing winding N1 via reversing switch S1 If a bipolar current source is utilized, the reversing switch S1 is unnecessary When switch S2 is closed, the current in the magnetizing circuit is regulated by resistor R1.

A stabilized power supply with proper output current control eliminates the need for resistor R1 in measuring the normal magnetization curve and hysteresis loops using the continuous recording method However, for the point-by-point method, switch S2 and resistor R2 are necessary to determine the hysteresis loop The secondary circuit includes a search-coil wrapped around the test specimen, which is connected to a flux integrator.

Determination of the normal magnetization curve

The test specimen shall be demagnetized in accordance with 3.6.4

The calibration of the magnetic flux integrator for measuring magnetic field strength and magnetic flux density or polarization must follow the guidelines outlined in annex B Subsequently, the normal magnetization curve can be established using one of the specified methods.

To implement this method, connect the output from the magnetic flux integrator linked to the magnetic field strength measuring coils to the X input of an X-Y recorder, plotter, or computer interface Simultaneously, connect the output from the magnetic flux integrator measuring magnetic flux density or polarization to the Y input of the same device The entire system must be calibrated to provide direct readings of magnetic field strength and magnetic flux density.

The magnetizing current shall then be increased from zero to the value required to produce the maximum magnetic field strength The magnetization curve will then be produced on the

X-Y recorder, plotter or computer interface

To achieve a steady cyclic state in the material, a small current will be passed through the magnetizing winding N1 and reversed approximately 10 times using the reversing switch S1 During this process, switches S3 and S4 will remain closed to keep the flux integrator at zero Once switches S3 and S4 are opened, the readings from the flux integrator will be recorded, corresponding to the values of magnetic field strength and magnetic flux density or polarization.

By successively increasing the magnetizing current and repeating this procedure the normal magnetization curve can be plotted

The magnetizing current shall never be decreased during the measurements, otherwise the test specimen shall be demagnetized before resuming measurements.

Determination of a complete hysteresis loop

The test specimen shall be demagnetized in accordance with 3.6.4 and the hysteresis loop shall be determined by one of the following methods

Method A of section 4.4.4 requires specific additional equipment The flux integrator must be zeroed before applying a current sufficient to achieve the maximum magnetic field strength through the magnetizing winding N1 This current should be gradually decreased to zero, reversed, and then increased to its maximum negative value, followed by a return to zero, a reversal, and an increase to the maximum positive value The entire cycle should take between 30 to 60 seconds, although some materials, such as pure iron, may need a longer duration to ensure proper magnetization of the test specimen while preventing significant drift in the zero reading of the sensing device.

To achieve the maximum magnetic field strength, a current must flow through the magnetizing winding N1 The peak points of the hysteresis loops will be identified by measuring the related values of magnetic field strength and magnetic flux density, following the guidelines outlined in method B of section 4.4.4.

To determine portion PQ of the hysteresis loop, switch S1 is closed in position 1 while switch S2 is opened, allowing for the measurement of the magnetic field strength and the change in magnetic flux density or polarization By adjusting resistor R2, multiple points on curve PQ can be obtained through successive measurements, with point Q being specifically identified during this process.

S 2 closed, and by measuring the change in magnetic flux density or polarization when opening switch S 1

To obtain the complete hysteresis loop, the switching sequence shall be in accordance with table 1 in 3.6.5

Resistors R 1 and R 2 respectively are adjusted to obtain:

– resistor R 1 : values of magnetic field strength +H or –H, that is point P or point S on the loop (figure 2)

– resistor R 2 : values of magnetic field strength +H′ or –H′, that is points P′ and T′ or Q′ and S′ on the loop (figure 2)

To eliminate drift errors in the flux integrator, it is essential to measure the entire hysteresis loop Notably, the STUP section of the loop exhibits symmetry with another portion, which aids in achieving accurate results.

PQRS, measurements may be made for only one-half of the hysteresis loop.

Determination of remanent flux density

The remanent flux density of a material, measured in teslas, is defined as the magnetic flux density when the magnetic field strength is zero, as indicated by point Q on the hysteresis loop or its symmetrical counterpart, point T.

Determination of coercive field strength

The coercive field strength of a material, measured in amperes per meter, is defined as the magnetic field strength at which the magnetic flux density equals zero within a given hysteresis loop This value can be identified from the location of point R on the hysteresis loop or its symmetrical counterpart, point U.

Uncertainty by the permeameter method

The total uncertainty in measuring magnetic flux density or magnetic field strength is typically ±3% when using instruments with an estimated uncertainty of ±1% for individual point measurements However, when determining a complete magnetization curve or hysteresis loop through continuous recording, the overall uncertainty may increase due to the uncertainty and resolution of the recording system.

As the result of the measurements is affected by changes in temperature, precautions shall be taken to avoid heating the test specimen (see 3.3)

The ultimate uncertainty of test equipment is influenced by various factors, including the measuring instruments and the conditions under which measurements are taken As a result, it is often challenging to define the absolute accuracy achievable Factors such as shape parameters, end effects, corner effects, variations in path length and cross-section, and the hysteresis characteristics of yokes can lead to significantly different test results, even when specimens are sourced from the same material batch and tested in different permeameters To optimize the use of any apparatus, it is essential to minimize these error factors to acceptable levels.

Usually that occurs where coercivity is reasonably large (> 1 kA/m) or at inductions above those corresponding to maximum permeability in the test specimen

The test report shall include as applicable:

– type and identification mark of material;

– shape and dimensions of the test specimen;

– method and/or type of permeameter;

– type of H and B or J sensor;

In the analysis of magnetic properties, the average values of magnetic flux density or polarization are compared for measurements taken both parallel and perpendicular to the rolling direction, under the same specified magnetic field strength.

– ambient temperature during the measurement;

– temperature of the test specimen during the measurement;

– estimated uncertainty of the measurements

Figure 1 – Circuit for the determination of the magnetic characteristics by the ring method

Figure 3b – Section A-A of the permeameter

Figure 3 – Typical arrangement of a type A permeameter

Figure 4 – Typical arrangement of a type B permeameter

Figure 5a – Flux-sensing coil (B-coil), wound around the test specimen

Figure 5b – Principle of the compensated J-sensing coil

Figure 5c – Field-sensing coils (H-coils), Figure 5d – Field-sensing coils (H-coils), concentric type – outer and inner coils flat type – two coils connected in connected in series opposition series addition

Figure 5e – Rogowski-Chattock potentiometer discrete coil system for H measurement

Figure 5 – Arrangement of search coils

Figure 6 – Circuit for the determination of the normal magnetization curve and hysteresis loop of bar specimens using a double yoke permeameter

Calibration of search-coils can be achieved through two primary methods: first, by sending the search-coil to a mutually approved standards laboratory for calibration; second, by determining the effective area-turns product of the search-coil through comparison with a standard search-coil, utilizing the circuit illustrated in figure A.1.

A 20 Hz frequency supply, characterized by low capacitive currents in circuit elements, is generated using an oscillator and power amplifier The search coil and secondary winding of the mutual inductor are arranged in series opposition, adjusting the mutual inductance until balance is achieved For detection, a high-gain frequency selective amplifier paired with a cathode ray oscilloscope is utilized.

A standard search-coil, with an effective area-turns product measured to an accuracy of ±0.2%, is positioned at the center of a coil system that ensures a uniform magnetic field throughout the volume of the tested search-coil The variable mutual inductor, M, is calibrated to achieve balance.

By replacing the standard search-coil with one of unknown value and re-balancing the circuit, the effective area-turns product of the second coil can be calculated using the mutual inductor readings based on a specific relationship.

(NA) is the effective area-turns product of the unknown coil, in square metres;

(NA) s is the effective area-turns product of the standard coil, in square metres;

M t is the mutual inductor reading for the bridge balance, using the unknown coil, in henrys;

M s is the mutual inductor reading for the bridge balance using the standard coil, in henrys

Figure A.1 – Circuit for the calibration of search-coils

Methods of calibrating the flux integrator

One of the following four methods of calibrating the flux integrator is normally used:

– changing a current in a calibrated mutual inductor;

– using a reference magnet in conjunction with a calibrated search-coil;

– a volts seconds source traceable to the fundamental units of voltage and time

The primary winding of a mutual inductor, with a specified value, replaces the primary winding of the ring core or the magnetizing winding of the permeameter Meanwhile, the secondary winding of the mutual inductor is connected in series with other components.

– the secondary winding of the ring or the B coil when measuring the magnetic flux density;

– the H coil when measuring the magnetic field strength

To calibrate, a suitable change, ΔI, is made in the value of the current passing through the primary winding of the inductor, and the flux integrator reading αc is recorded

The calibration constant of the flux integrator shall be calculated from the relationship: c

K is the calibration constant of the flux integrator, in volts seconds;

M is the mutual inductance, in henrys; ΔI is the change in primary current, in amperes; α c is the reading of the flux integrator

For the subsequent measurements of the magnetic flux density and the magnetic field strength, the secondary winding of the mutual inductor shall be short-circuited

When using a resistor in series with the integrator, it is essential to adjust this resistor If a series resistor is not utilized, a correction must be made to the calibration constant of the flux integrator based on the specified relationship.

R F is the input resistance of the flux integrator, in ohms;

R is the internal resistance of the sensing coil, in ohms;

R M is the resistance of the secondary winding of the mutual inductor, in ohms

The flux integrator shall be connected in accordance with the circuit of figure B.1 comprising:

– a two-position change-over switch (a = charge, b = discharge);

– a flux integrator of internal resistance R F

The calibration of the flux integrator is carried out as follows

1) Measure the voltage U to which the calibrated capacitor C is charged by means of a calibrated voltmeter, the change-over switch being in position a

2) The switch is changed to position b, causing the capacitor to discharge A quantity of electricity Q = CU flows through the entire circuit Only the quantity

Q S q = + + + (B3) flows through the flux integrator, producing a deflection a

3) The charge sensitivity is given by: q R r S R F

4) A variation of the magnetic flux Δϕ in one turn of the search-coil causes the circulation of a charge Δq: circuit F of résistance R r S R q + + +

From this statement the relationship between the flux integrator calibration constant, K, and the charge sensitivity may be deduced as:

5) The flux integrator calibration constant, K, is given by:

C is the capacitance, in farads;

U is the potential difference across capacitor, in volts;

S is the shunt resistance, in ohms; α is the flux integrator reading

A reference magnet, preferably of AlNiCo permanent magnet material, is first calibrated using a magnetic resonance probe

A calibrated search-coil is linked to the input of the flux integrator, and it is placed within the area of uniform magnetic flux density in the reference magnet, allowing for the recording of the flux integrator's reading.

The calibration constant K of the flux integrator can be calculated from:

B is the magnetic flux density in the gap of the reference magnet in teslas; α is the flux integrator reading;

(NA) is the effective area of search-coil, in square metres

The effective area of a search-coil can be determined by comparing it with a standard search-coil as outlined in annex A, or, if it is manufactured with high precision, by calculating its dimensions and the number of turns.

The flux integrator shall be connected to a volts seconds source which shall be traceable to the fundamental units of voltage and time

Figure B.1 – Circuit for calibration the flux integrator by the capacitor discharge method

Requirements for the J-compensated coil system

The J-compensated coil system can be made from a combination of three concentric coils

A flux-sensing coil with $N_{2a}$ turns is connected in series opposition to a pair of coils, each with $N_{2b}$ turns, which are also connected in series opposition This configuration of coils is designed to compensate for the air flux in the flux-sensing coil The area $A_2$ between the two air flux compensating coils is selected based on a specific relationship.

A 1 is the cross-sectional area of the flux-sensing coil, in square metres

In practical applications, achieving an exact match for the equation with values N 2b and A 2 may be unfeasible Therefore, it is advisable to select the product N 2b A 2 to be marginally greater than N 2a A 1.

Adding a resistance in parallel to the air flux compensation coils can reduce their sensitivity to match that of the flux-sensing coil When no test specimen is present, the entire coil system should produce no output when removed from a uniform magnetic field or when there is a change in the surrounding magnetic field strength.

3 Détermination des caractéristiques magnétiques par la méthode du tore 37

3.3 Influence de la température sur les mesures 37

3.6 Méthodes de mesure par la méthode du tore 39

3.6.1 Intensité du champ magnétique d'excitation 39

3.6.4 Détermination de la courbe d'aimantation normale 40

3.6.5 Détermination d'un cycle d'hystérésis complet 40

3.7 Incertitude par la méthode du tore 42

4 Détermination des caractéristiques magnétiques par la méthode du perméamètre 43

4.4 Méthodes de mesure par la méthode du perméamètre 44

4.4.1 Mesure de l'intensité du champ magnétique d'excitation 44

4.4.4 Détermination de la courbe d'aimantation normale 46

4.4.5 Détermination d'un cycle d'hystérésis complet 47

4.5 Incertitude par la méthode du perméamètre 48

Annex A (normative) Etalonnage des bobines de mesures 55

Annex B (informative) Méthodes d'étalonnage de l'intégrateur de flux 57

Annex C (informative) Conditions à remplir par un système de bobines compensées pour la mesure de J 60

Figure 1 – Circuit pour la détermination des caractéristiques magnétiques par la méthode du tore 50

Figure 3 – Configuration typique d'un perméamètre de type A 51

Figure 4 – Configuration typique d'un perméamètre de type B 52

Figure 5 – Configuration des bobines de mesure 54

Figure 6 – Circuit pour la détermination de la courbe d'aimantation normale et du cycle d'hystérésis à l'aide d'un perméamètre à double culasse (échantillon en barreau) 54

Figure A.1 – Circuit pour l'étalonnage des bobines de mesure 56

Figure B.1 – Circuit d'étalonnage de l'intégrateur de flux par la méthode de la décharge d'un condensateur étalon 59

Tableau 1 – Séquence des commutations nécessaires au maintien de l'éprouvette dans un état cyclique stable 42

Partie 4: Méthodes de mesure en courant continu des propriétés magnétiques des matériaux magnétiquement doux

The International Electrotechnical Commission (IEC) is a global standards organization comprising national electrotechnical committees Its primary goal is to promote international cooperation in standardization within the fields of electricity and electronics To achieve this, the IEC publishes international standards, technical specifications, technical reports, publicly accessible specifications (PAS), and guides, collectively referred to as "IEC Publications." The development of these publications is entrusted to study committees, which allow participation from any interested national committee Additionally, international, governmental, and non-governmental organizations collaborate with the IEC in its work The IEC also works closely with the International Organization for Standardization (ISO) under an agreement established between the two organizations.

Tiêu đề	Iec 60404 4 2008
Thể loại	International Standard
Năm xuất bản	2008
Thành phố	Geneva

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