SU968858A1 - Ferromagnetic shield - Google Patents

Description

(5) FERROMAGNETIC SCREEN

one

The invention relates to a measurement technique and can be used to protect magnetic induction measures from the effects of interference from external MSI fields when checking magnetometers.

A ferromagnetic screen with alternating-current biasing is known, containing shells coaxially mounted with a gap, and provided with windings. These windings are connected to an adjustable AC source.

The magnetic field of the magnetizing windings increases the magnetic permeability of the shell material, but creates additional variable interference fields up to kOOO nT, which reduce the accuracy of measurements of magnetic fields in the screen.

A ferromagnetic screen with alternating-current biasing is known, containing ferromagnetic shells insulated from each other, and an adjustable source of alternating current, coaxially installed with a gap. The outputs of the variable source TOKaf 2j are connected to two opposite points of each shell.

The alternating current flowing through the shells is unevenly distributed across the surfaces, and they are non-uniformly magnetized. This creates an additional residual field inside the screen of the order of 10 nTl, which reduces the shielding factor, and the generated alternating field of the bias current creates alternating magnetic interference up to 1000 nTl, reducing the accuracy of field measurements inside the screen.

15

The purpose of the invention is to improve accuracy.

The goal is achieved by the fact that in a ferromagnetic screen containing two coaxial isolated

Claims (1)

20 ferromagnetic shells and an alternating current source, a second alternating current source, a phase shifter and four annular tires made of 3968 conductive material, reinforced in pairs at opposite ends of each of the envelopes, with the first alternating current source connected to the tires of the first envelope, and the second alternating current source connected to the tires of the second shell through the phase shifter anti-phase to the first source. The drawing shows a ferromagnetic screen with alternating current bias. The ferromagnetic screen contains ferromagnetic shells 1 and 2, mounted coaxially with a gap and isolated from each other. On opposite sides of shells 1 and 2, tires 3 and 5 6 are made of electrically conductive material. An adjustable AC source 7 is connected to busbars 3 and 4 of shell 1, and a second adjustable AC source 8 with phase shifter 9 is connected to busbars 5 and 6 of shell 2 with reverse polarity, in antiphase. Ferromagnetic screen works as follows. With the help of tires 3 t and 5 6, the currents under magnetisation are evenly distributed over shells 1 and 2, which ensures their uniform magnetization and a decrease in the residual field inside the screen to a level below 1. NT. However, due to the difference in the sizes of shells 1 and 2, the single-solid magnetic fields generated by the currents C and I are low tide inside the screen (amplitude and phase). The amplitudes of the variable magnetic fields from the neighboring shells 1 and 2 are measured by a magnetometer, and their equality B at the center of the screen is set by adjusting the current sources 7 and 8. The phase shift between the alternating magnetic fields from the adjacent shells 1 and 2 is determined by an oscilloscope connected to the output of the Mai-Nitometer (not shown), and is zeroed by adjusting the phase shifter 9 the polarities of the currents C and I l in the adjacent shells 1 and 2 the homogeneous alternating magnetic fields they create are subtracted, i.e. they are compensated in the center of the screen to a level of about 1 nT. Consequently, the alternating magnetic fields of interference that reach the known device 1000 nT in the proposed device are reduced to 1 nT. Testing the layout of the proposed device shows that the constant magnetic field of the Earth with induction 5 is attenuated inside the screen to 1 nT, i.e. 510 times. The alternating magnetic field with a frequency of 50 Hz from the current of magnetising each shell reaches 500 nT and is attenuated by the proposed device up to 1 nT, i.e., 500 times. In this case, the instability of the current amplitude of 0.25 causes a change in the residual field in the center of the screen by 1 nT. Thus, in comparison with the known ferromagnetic screen with alternating current biasing, the proposed screen allows for an order of magnitude increase in the shielding factor and accuracy of measurements of magnetic fields in the screens. Claim of the invention A ferromagnetic shield containing two coaxial insulated ferromagnetic shells and an alternating current source, characterized in that, in order to improve accuracy, a second alternating current source, a phase shifter and four-ring tires made of an electrically conductive material, reinforced in pairs on opposite ends of each from the shells, while the first AC source is connected to the tires of the first shell, and the second AC source is connected to the tires of the second shell through a phase switch schatel antiphase to the first source. Sources of information taken into account in the examination. 1. Albach V. W., Voss.G. A. Ein durchvorregter Dynamobleche magnetische abgeschirmter Mebraum. Z. f.Angew. Physik einschl. Nukleonik, IX Band, Heft. 3/1957, 111-1152. Cohem D.; A schielded facility for low-level magnetic measurements, Journal of Applied Physics. V. 38, No. 3, 1867, p. 1295-1296.