SU1190319A1 - Apparatus for measuring magnetic susceptibility - Google Patents

Abstract

1, A DEVICE FOR MEASURING A MAGNETIC SUSTAINABILITY, containing a series-connected power generator, a thermostated LC generator, the oscillating circuit inductance of which is a sensor, a broadband amplifier, and also a recording device, with the aim of increasing sensitivity, and measurement accuracy; a serially connected reference oscillator-frequency synthesizer, a frequency mixer, a filter of a concentrated selection, a broadband intermediate amplifier, often s. W-n frequency detector, low-pass filter and variable-frequency DC amplifier with variable gain, the second input of the frequency mixer is connected to the output of a wideband amplifier, the second input of the frequency detector is connected to the second output of the reference frequency synthesizer, the output of the large-scale constant-frequency amplifier variable current gain is connected to the input of the registering device, the thermostatically controlled LC generator is made with low-power i and high-frequency, and the wide-band amplifier is high frequency. (L 2, The device according to claim 1, 1, 2), so that the power generator is made in the form of a series-connected high-frequency amplitude detector and operational DC amplifier with an initial offset, and the input from the high-frequency amplitude deo of the detector connected to the output of a broadband high-frequency amplifier, and the output of the operational amplifier with a direct current with an initial offset to the input of the LC generator,

Description

I

The invention relates to magnitude measurements and can be used; vtH measurements of the magnetic susceptibility of low-magnetic materials, such as semiconductor silt of biological objects in a wide range of external magnetic fields and temperatures.

The purpose of the invention is to increase the sensitivity and accuracy of magnetic susceptibility measurements.

The drawing shows the block diagram of the proposed device.

The device contains a series-connected thermostatic high-frequency LC generator I, a high-frequency wideband amplifier 2, a high-frequency amplitude detector 3 and a direct-current amplifier 4 with an initial bias, the output of the latter being connected to the power supply circuit of the first, a mixer. 5 frequencies, the first input of which is connected to the output of a high-frequency wideband amplifier 2, the reference oscillator-synthesizer 6 frequencies, the first output of which is connected to the second input of the mixer 5 frequencies, serially connected broadband filter 7 of concentrated selection and wideband amplifier 8 of intermediate frequency, and the input of the first connected with the output of the mixer 5 frequencies, the frequency detector 9, the first input of which is connected to the output of the wideband amplifier 8 intermediate frequency, and the second - with the second output of the reference oscillator-synthesizer 6 frequencies, serially connected low-pass filter 0, large-scale direct current amplifier 11 with variable gain, and a recording device 12, the input of the first connected to the output of the frequency detector 9.

The device works as follows.

The signal from the output of the thermostatted low-power high-frequency LC generator 1, the sensor in which is the inductance of its oscillating circuit, is fed to the input of the high-frequency wideband amplifier 2. The signal amplified by the high-frequency wideband amplifier 2 is fed to the first input of the 5 frequency mixer,

3192

and the second input of the latter receives a signal from the first output of the reference oscillator-frequency synthesizer 6, the frequency difference between the signals of the low-power high-frequency LC generator I and the reference frequency synthesizer 6 is 10 MHz and during the initial adjustment it is held with an accuracy of

units hertz. The 10 MHz signal selected by the broadband filter 7 of the concentrated selection from the 5 frequency mixer is amplified by the intermediate frequency wideband amplifier 8, fed to the first input of the frequency detector 9, and the second input receives the 10 MHz reference signal from the second output of the reference synthesizer 6 frequencies. With equal frequencies of the signals at both inputs of the frequency detector 9, there is no signal at its output. In the case of frequency inequalities of the input signals of the frequency detector 9, at its output a certain DC voltage of the corresponding polarity depends only on the difference of the frequencies of the input signals. The DC voltage passed through the 0 filter, frequencies and is amplified by a large-scale constant current damper 11 with a measurable coefficient

gain From the output of the scale amplifier 11 of direct current, the amplified voltage is fed to the input of a recording device 1-2.

When placed in the sensor, which

The inductance of the oscillating circuit of the thermostatted low-power LC-generator serves; the substance under study changes its generated frequency and amplitude

output voltage Change

the generator frequency causes the output of the frequency detector to a signal of the corresponding polarity, and this output signal is proportional to the magnetic susceptibility of the test substance, which allows the scoring of the recording device to calibrate directly in units of magnetic susceptibility. To ensure the time-frequency stability of the operation of a thermostatically controlled low-power high frequency (

3

The LC generator 1 and the elimination of the influence of the amplitude of its output signal on the measurement results of the latter is equipped with a controllable power source.

The use of negative feedback in the controlled power supply of the said generator made it possible to increase its temporal frequency stability by an order of magnitude.

The power supply of the thermostatically controlled high frequency LC generator of torus 1 consists of a series-connected high-frequency amplitude detector 3, the input of which is connected to the output of wide-band high-frequency amplifier 2, and an operational amplifier 4 of direct current, having an initial offset, the output of which is connected to the power supply circuit of the said generator .

Setting the initial supply voltage (around the selected value of the thermostatted high-frequency LC-generator is carried out by setting the initial bias on the direct input of the operating-; direct current amplifier 4,

The output high-frequency voltage of a thermostatted high-frequency LC generator 1, amplified by a wideband high-frequency amplifier 2, is fed to the input of a high-frequency amplitude detector 3 and from its output as a constant component is fed to the inverse input of an operational amplifier 4 of direct current. At the output of the operational amplifier 4 DC, the voltage is equal to the difference between the initial set voltage and the amplified voltage of the DC component rectified by the high-frequency amplitude detector 3. The supply voltage varies depending on the change in the magnitude of the generation of the thermostatically controlled high-frequency LC generator 1 him. Further control of the operation of the power source of the aforementioned generator occurs automatically.

The cutoff frequency stabilization lx), 1 Hz. Power dissipated by power supply, 410 mW. Time3194

but the frequency instability of a thermostatically controlled low-power, high-frequency LC generator when powered from such a source is no more than 10 Hz / h.

The inductance coil of the thermostatted low-power high-frequency LC generator inductance, which is a probe, is cylindrical and connected to an electronic circuit using a coaxial line 80 mm long consisting of a 12 mm diameter nickel silver tube and a central copper wire 1 mm in diameter centered three Teflon washers, placed together with the electronic circuit in the thermostat.

The frequency mixer is assembled on a two-gate field-effect transistor

KP 350 B, the source of which includes a broadband filter of concentrated selection with a bandwidth of 3 MHz, made three-link on

LC elements with external capacitive coupling and an average operating frequency of 10 MHz. . ,

Broadband intermediate frequency amplifier is made of three-stage

and assembled on transistors, in the collector circuits of which two-circuit bandpass filters are included. Total broadband intermediate frequency amplifier gain for band

bandwidth of 3 MHz and an average operating frequency of 10 MHz is -. Matching the input and output impedances of the cascades of the broadband intermediate frequency amplifier

achieved through the use of autotransformer communication with collector circuits and weak communication with basic circuits. Connection collector and base loops — selected below

critical. In order to avoid the dependence of the output voltage on the frequency, the last stage of the broadband intermediate frequency amplifier is made by an amplifier operating in the limiting mode. The load of the last stage of the wideband amplifier of the intermediate frequency is the oscillatory circuit of the frequency detector, tuned to the average operating frequency of the wideband amplifier of the intermediate frequency 10 MHz.

The frequency detector is made according to the fractional detector scheme assembled on. diodes, with a separate source of the reference signal, for which the second output of the reference oscillator-frequency synthesizer is used. To suppress the parasitic amplitude modulation and to compensate for the asymmetry of the frequency detector, caused by the nonidentity of the parameters of the diodes, trimmer peristors are included before the load resistors. The width of the linear portion of the statistical frequency-amplitude characteristic of the private detector is i1.2 MHz with a slope of 0.5 V / MHz. The deviation from linearity at the edges of the tO, 5Mrn range does not exceed 1%.

A U-shaped low-pass LC filter with a cut-off frequency of 3 kHz was used to suppress the high-frequency component contained at the output of the frequency detector.

A KAAO UD-2 operational amplifier, covered by a local negative feedback, the depth of which was chosen from the condition of providing an appropriate gain, was used as a scaled DC amplifier with a variable gain. Setting the voltage zero at the output of the scale amplifier

The direct current is applied by a bias voltage applied to its inverse input.

To ensure stable operation of the device as a whole, the mixer

Five frequencies, a broadband intermediate frequency amplifier, a frequency detector, a direct current amplifier, are placed in a common passive thermostat made of a syringe.

Experiments have shown that the proposed device has a sensitivity of 2-10 with a measurement error of 1.5%. The time is nest5. The output voltage is 5 µV / h.

Claims (2)

1 . A MAGNETIC SUSCEPTIBILITY MEASUREMENT DEVICE, comprising a power generator in series, a thermostatic LC generator, the oscillator circuit inductance of which is a sensor, a broadband amplifier, and a recording device, which is related to the fact that, in order to increase the sensitivity and measurement accuracy , it introduced a series-connected reference oscillator-frequency synthesizer, a frequency mixer, a concentrated selection filter, a broadband amplifier of an intermediate frequency, frequencies a second detector, a low-pass filter and a scaled DC amplifier with a variable gain, the second input of the frequency mixer connected to the output of a broadband amplifier, the second input of the frequency detector connected to the second output of the reference oscillator-frequency synthesizer, the output of a scaled DC amplifier with a variable gain connected to the input of the recording device, the thermostatically controlled LC-generator is low-power and high-frequency, and the broadband amplifier is high-frequency. 2. The device according to π. 1, characterized in that the generator! power supply made in. in the form of a series-connected high-frequency amplitude detector and an operational DC amplifier with an initial bias, the input of a high-frequency amplitude detector connected to the output of a broadband high-frequency amplifier, and the output of an operational DC amplifier with an initial bias to the input of an LC generator.