DE19636757C1 - Magnetic remanence measuring device for permanent magnet - Google Patents

Abstract

The measuring device uses a Helmholtz coil coupled to a fluxmeter, with a measuring amplifier inserted between them. At least the Helmholtz coil is magnetically screened, with the screening positioned symmetrically relative to the coil winding surfaces. The screening may be provided by a monitor screening or the entire measuring device may be contained within a screened chamber.

Description

The invention relates to a measuring arrangement for determining the Retentivity of permanent magnets consisting of a Helmholtz coil and a fluxme connected to the Helmholtz coil ter.

From IEEE Transactions on Magnetics, Vol. 24, No. July 4 1988, pages 2108-2111, Helmholtz coils are known Use the remanence of permanent magnets. From the This publication is the basic physical laws that ei underlying such measurement, known.

Furthermore, from IEEE Transactions on Magnetics, Vol. MAG-14, No. 5, Sept. 1978, pages 572-573, Helmholtz coils used to measure satiety induction.

Furthermore, Rev. Sci. Instrument. 50 (9), Sept. 1979, Pages 1115-1119 a flux meter known, which with a Measuring amplifier is coupled.

It is generally known to carry out precision measurements on magnets with the help of Helmholtz coils and flux meters. By turning a magnet in the homogeneous area of a Helmholtz coil, a voltage U _{i is} induced in the turns of the coil. According to the generally accepted method, this voltage is applied directly to the input of a flux meter. A fluxmeter mainly consists of an integrator. The flux meter then forms the integral of the change in time of the applied voltage U _i , which leads to the fact that the magnetic flux Φ is determined, which is proportional to the polarization J _{r of} the magnet.

For the investigation of permanent magnets of different dimensions solutions are Helmholtz coils of different dimensions  used. This procedure results from the fact that small duration Magnetize only a small signal in large Helmholtz coils deliver and large permanent magnets in small Helmholtz coils cannot be imported.

Furthermore, for carrying out precision measurements Knowledge of the so-called coil constants K of the Helmholtz coils necessary. The from the manufacturers of the Helmholtz Spu len specified values of the coil constant K and also the ex perimentally determined values, which can be determined using calibration magnets are determined, but usually have one Error of about 1-2%.  

The coil constant K of a Helmholtz coil is defined:

where Φ is the magnetic flux, µ _{0 is} the magnetic field constant and m is the magnetic moment.

This error of the coil constant K results from the ma genetic influences from the vicinity of the Helmholtz coils, which, as can be seen immediately, is the magnetic flux Φ be influence. Such magnetic stray fields arise, for. B. from iron fittings of the furniture of the laboratory equipment or also from electromagnetic fields used in the Flux meters as well as in installed computers at the location of the Helmholtz coils.

The displacement of a Helmholtz coil that is close to one Tin wall is built up to a distance of about 20 cm under certain circumstances already to a change of the coil constant lead K by about 1 to 2%.

The object of the present invention is therefore a measurement arrangement of the type mentioned at the beginning develop that the measurement accuracy and sensitivity of the Helmholtz coils is noticeably improved and that only a Helmholtz coil must be used.

According to the invention, this object is achieved by a measuring arrangement at the beginning mentioned type, consisting of a Helmholtz coil and one with the Helmholtz coil connected fluxmeter, where between the flux meter and the Helmholtz coil a measuring ver is switched stronger and at least with the Helmholtz coil is surrounded by a shield.

By interposing an amplifier, which should be as low-noise and drift-free as possible, between the Helmholtz coil and the flux meter, the induced voltage U _i is amplified by a factor f <1, so that the voltage f × U _i is present at the input of the flux meter . Thus, a higher value for the measured magnetic flux is available, which indicates an increase in the sensitivity.

By providing the Helmholtz coils with a magneti shielding, for example the shape of a han can have the usual monitor shielding, the measurement accuracy and sensitivity of the Helmholtz coil or the entire measuring arrangement by two effects increased.

On the one hand, the Helmholtz coil protects against external interference fields shielded, resulting in a significant reduction in down frequent noise. On the other hand, the shield leads to increase the effective coil constant K by approximately 10 to 15% compared to an unshielded Helmholtz coil. This leads to an increase in the measurement signal in the same order of magnitude and thus to a further increase the measuring accuracy.

The Helmholtz coil is preferably used in relation to its the winding surfaces are shielded symmetrically, which means a be particularly good shielding is achieved.

Overall, one obtains through the measuring arrangement according to the invention a significant increase in sensitivity and accuracy the Helmholtz coils.

Claims (4)

1. Measuring arrangement for determining the remanence of permanent magnets consisting of:

• - A Helmholtz coil and
• - A flux meter connected to the Helmholtz coil, a measuring amplifier being connected between the flux meter and the Helmholtz coil and at least the Helmholtz coil being surrounded by a shield.

2. Measuring arrangement according to claim 1, characterized in that the helmet holtz coil symmetrically with respect to their winding surfaces is shielded. 3. Measuring arrangement according to one of claims 1 or 2, characterized in that as Ab shielding a monitor shield is provided. 4. Measuring arrangement according to claim 1 or 2, characterized in that the ge Entire measuring arrangement is introduced into a shielding chamber.