SU851296A1 - Device for measuring magnetic susceptibility - Google Patents

Description

(54) DEVICE FOR MEASURING MAGNETIC SUSTAINABILITY

one

The invention relates to magnetic measurements by resonant methods and can be used to measure the magnetic susceptibility of weakly-j magnetic substances and materials.

Devices are known that contain an oscillator with an oscillating circuit, the inductance of which is fo sensor1m. A frequency meter is connected to the output of the oscillator. When a magnetic medium is introduced into the sensor field, the inductance of the latter increases, which leads to a decrease in the frequency of oscillations of the oscillator. Measured frequency judged by the magnetic susceptibility of the medium 1

The disadvantage of such devices is owner. The sensitivity is low, 20 due to the fact that the change in frequency is determined only by the change in the inductance of the oscillating circuit.

It is also known a device consisting of an auto-oscillator with external feedback, an oscillating circuit containing an inductive sensor and a frequency meter-periodometer. When entering the medium in the sensor field, the period

oscillations of the oscillator are changed, which makes it possible to judge x of the medium {2.

The disadvantages of this device are low sensitivity, due to the fact that the change in the oscillation period is determined only by the change in the inductive branch of the oscillating circuit, and also the nonlinear dependence of the oscillation period m on the magnetic susceptibility X of the medium.

The purpose of the invention is to increase the sensitivity and to obtain a linear dependence of the 1 st of the oscillation period on the magnetic susceptibility.

This goal is achieved by introducing a second inductive sensor, an oscillator with controlled conductivity of gyration, made on three transistors and two voltage-controlled resistors, as well as a linear device into a device containing an oscillator with an inductive sensor in an oscillatory circuit and a digital meter for the oscillation period. frequency-voltage converter, the gyrator being turned on between two inductive sensors, and the oscillator circuit of the self-oscillator

The inputs are connected to a digital meter of the oscillation period and a frequency-voltage converter, the output of which is connected to the control electrodes of the voltage-controlled resistors.

The drawing shows a block diagram of the proposed device.

The device contains an auto-oscillator 1 on a tunnel diode, an inductive sensor 2, which is an element of an oscillatory circuit, a gyrator 3 on three bipolar transistors 4, 5 and 6 and two controlled resistors 7 and 8 on field-effect transistors with feedback resistors 9-12 , a second inductive sensor 13, a linear frequency-voltage converter 14 and a digital meter 15 of the oscillation period.

A gyrator 3 is connected between two inductive sensors 2 and 13. Such a system forms an active oscillating circuit, the inductive branch of which is inductance of sensor 2, and the capacitive branch is capacitance C, simulated by gyrator 3 at points 16 and 17, equal to:

C (1)

where, is the inductance of the sensor 13;

G is the conductivity of gyration. The oscillation period T of the oscillator with an active circuit is determined by the known formula

.With 21ED

(2)

where lol is the sensor inductance in. In case of equality L,; B, 1, we get

T 2 ".LG (3)

The value of the conductivity of gyration G in this case is determined by the magnitude of the resistors 7 and 8, and

P1

  R

where R R7 R8 (here R7H R8 is the resistance of controlled resistors 7 and 8, respectively) .. Since R f (U), where U is the output voltage of the frequency converter 14, the total oscillation frequency of the oscillator causes a change in conductivity gyration G, and also, as follows from expression (3), a change in the oscillation period.

The device works as follows.

When introducing a controlled weakly magnetic medium, the inductances of the sensors 2 and 13 increase in direct proportion to the x value of the medium. So

like 145. B L (x), then from expression (3) it follows that the oscillation period of the oscillator 1 increases linearly depending on the magnitude of the magnetic susceptibility of the medium. In this case, the linearity of the dependence T f (x) is preserved in an unlimited range of changes x. Increase inductance. Tei U, j and L., reduces the oscillation frequency, which causes a decrease in voltage U at the output of the frequency-voltage converter 14. This also leads to a decrease in the resistances R7 and R8 of the controlled resistors 7 and 8, which, as follows from expression (4), increases the resistance of gyration G and, as a result, further increases the oscillation period T of the oscillator 1. Changes T are recorded by a digital oscillation meter 15, the scale of which

0 can be directly graduated,; v real. units of magnetic perception.

The proposed device allows to increase its sensitivity and

5 to obtain a linear dependence of the oscillation period on the magnetic susceptibility, of the studied medium.

Claims (1)

1. Instruments for scientific research, 1970, W 5, p. 3-8. 2, Geophysical instrumentation, 1973, 51, p. 23-26. -jMzzbEO