SU879487A1 - Device for measuring infralow voltages - Google Patents

Description

The invention relates to a technique for measuring infra-low electrical voltages below 10 V using the phenomenon of superconductivity and the Josephson effect in weakly coupled superconductors. Autocompensation volts of infra-low voltages are known, in which superconducting quantum interferential interference sensors are used as a null organ — squid, containing a squid, an electronic amplification circuit, detection and filtering of a squid, an output meter, a compensation circuit and SQUID-inductance coil, to the terminals of which the measured voltage f 1 is connected. The information on the measured voltage in such volts meters is presented in an analog form, which is a disadvantage. An infra-low voltage voltmeter is also known, which contains a partially resistive squid (rescued), which is inductively coupled to an oscillating circuit connected to a high-frequency amplifier, on. the output of which includes: an amplitude detector and a frequency meter 2; The rescued is fed with a high-frequency (HF) pump magnetic flux from a separate generator connected to a coil inductively coupled to the rescued. The measured voltage is applied to the resistive section of the equestrian. The generator, amplifier, and detector form an RF pump unit, which can be implemented by other means, for example, without a generator, when the autogeneration of the amplifier is used for RF pumping. This voltmeter is digital, and the measured voltage is converted to a frequency in a rescue according to the Josephson ratio fj Ux /%,

where f is the Josephson oscillation frequency; d voltage at junction

Josephson (b / 2e 2.07-. - quantum

magnetic flux. The Josephson generation modulates with the frequency f – j the resqued impedance, which leads to amplitude modulation of the voltage on the circuit. After amplifying and detecting this voltage, a variable voltage with a frequency fj appears at the output of the detector of the RF-pump unit. The frequency f-i is measured by a frequency meter. In view of the fact that the frequency f is proportional to U, and the proportionality coefficient is the inverse of the magnetic flux quantum, i.e. is the world constant, then the calibration of the voltmeter is not required. Information on the measured voltage is represented in this voltmeter in digital form.

The amplitude of the voltage modulation envelope on the circuit depends on the hysteresis parameter of the resquad

1 21P

where is l. - inductance reskvida,

1 is the critical current of the Josephson junction, which enters the reskyd.

For normal operation of the instrument, it is necessary that the parameter t be in a certain predetermined interval, since, as and depends on the amplitude of the signal fed to the frequency meter. When the parameter K decreases below I, the rack switches to the so-called hysteresis-free mode of operation, and the signal at the detector output decreases -. In this case, the frequency meter, whose input threshold device is tuned to the signal level with a permissible value of the parameter E, is not able to measure the frequency f-j.

In the hysteresis mode of operation, the rescive at K 1) an increase in the parameter above the permissible value is also accompanied by a decrease in the signal amplitude, which leads first to a loss of the frequency meter, and with a further increase of 6 to the full insensitivity of the frequency meter to the signal.

The parameter can be changed both in the process of continuous operation of the rescue, for example, under the effect of temperature changes in the cryostat, and as a result of thermal cycling.

from room temperature to helium with multiple immersions of a resistor in a cryostat. No parameter control in a known voltmeter

It does not allow to judge the quality of the resqued and the reliability of the measurements, which is a disadvantage of the known device.

The purpose of the invention is to increase the reliability of the measurement.

This goal is achieved by the fact that in a device for measuring infra-low voltages, containing a partially resistive SQUID, is inductively coupled to an oscillatory circuit connected to a high-frequency pumping unit, which includes a series-connected high-frequency amplifier and detector, at the output

of which the frequency meter and input terminals connected to the rescvid resistive part are included, two amplitude detectors, a capacitor, an analog divider and indicating

the device, the input of one amplitude detector is connected to the output of the high-frequency pumping unit, the input of the other amplitude detector is connected to the input of the first amplitude detector through a capacitor, the outputs of the amplitude detector are connected to the inputs of the analog divider, the detector of which is connected to the indicating device, and the output of the first amplitude detector is connected to input divisible analog divider.

The drawing shows a structural diagram of the proposed device.

The device for measuring infra-low voltages consists of a resquad 1 with a 2 Josephson junction and clamps 3 for supplying the measured voltage. Reskquid I is inductively coupled to coil 4 of an inductance of an oscillating circuit 5 connected to

5 input amplifier 6 high frequency operating in auto-generation mode. At the output of amplifier 6, detector 7 is turned on. Amplifier 6 and detector 7 comprise a high-frequency block 8

Claims (2)

0 pumping. The output of block 8 is connected to a frequency meter 9, an amplitude detector 10 directly and an amplitude detector 11 through a capacitor 12. The outputs of the detectors 10 and 11 are connected to the inputs of the analog divider 13, and the detector 10 is connected to the input 14 (Divisible). At the output of divider 13, the indicating device 15 is turned on. The volt-ampere characteristic of the cock 5, associated with rescued 1, is stepwise with the parameter g 7 1. For operation of the resumed system, the first plateau of the characteristics, i.e. the first part of the characteristic where the amplitude of the voltage on the circuit 5 remains almost constant when changing in some limits the amplitudes of the high-frequency pumping coming from the high-frequency amplifier 6 entered into the autogeneration mode. The height of the first plateau varies with the frequency of the Josephson generation within the parallelogram, which illustrates the mechanism of amplitude voltage modulation on circuit 5. The mode of operation on the first plateau is determined by the coefficient ck of the positive feedback of the amplifier 6, the characteristic of the feedback line slope on the current-voltage character of tick, () of circuit 5. The maximum of the amplitude b of the voltage on the circuit 5 is determined by the ratio b - (Fo / 2) (I / v) SX H /), and the interval a in which the amplitude of the voltage fluctuates contour 5 under the influence of Josephson Coy ratio generating and OSF-ob / iM, where u) - angular frequency vysokochast hydrochloric pump; L, is the inductance of coil 4 of the oscillatory circuit 5; M is the mutual inductance of coil 4 and resquad 1. Hence, the ratio b / a is equal to b / a-Gagseoe K and depends almost linearly on parameter 6, which gives grounds to use the ratio b / a to determine the parameter e. At the output of detector 7, an amplitude modulation envelope of the voltage on circuit 5 is selected. This signal is fed to detector 10, which allocates its amplitude proportional to b, and through condensate 12 to detector 11, which extracts the amplitude of the signal without a constant component proportional to a / 2. The divider 13 produces a voltage proportional to b, a voltage proportional to a / 2. The result of dividing 2b / a is induced by the device 15, the scale of which is calibrated in units of the parameter t. The dependence of parameter 6 on the ratio b / a is linear except for a small initial segment. This leads to an almost linear scale of the device 15 for the values of the parameter C 1, 5. The introduction of two amplitude-detectors, a capacitor, an analog divider and an indicating instrument made it possible to solve the problem of monitoring the parameter C during operation of the device for measuring infra-low voltages. The proposed device can also be used to control the parameter 6 of the rescue in the process of setting it up. Apparatus of the Invention A device for measuring infra-low voltages, comprising a partially resistive squid inductively coupled to an oscillating circuit connected to a high-frequency pumping unit comprising a series-connected high-power amplifier. Frequency and the detector, the output of which includes a frequency meter and input terminals connected to the resistive part of the SQUID, is characterized in that, in order to increase the measurement accuracy, two amplitude detectors, a capacitor, an analog divider and a display device are inserted, the input of one amplitude detector is connected to the output of the high-frequency pumping unit, the input of another amplitude detector is connected through a capacitor to the input of the first amplitude detector, and their outputs are connected to the inputs of an analog divider, the output of which is connected n to pokazshayuschemu device, wherein the output of the first amplitude detector connected to the inputs of similar splitter dividend. Sources of information taken into account in the examination 1.Lsolimer L. Tunnel effect in superconductors and its application. M., Mir, 1974, p. 388. 2. US patent number 3622881, cl. 324-120, published. 11.11.71.