SU1325381A1 - Method of measuring current noises and device for effecting same - Google Patents

Abstract

The decision can be used to build sound level meters. The purpose of the 5 1 invention is to increase the sensitivity of the measurement. The device that implements the method contains ballast and measurable resistors 3 and 4, amplifiers 9 and 10, multiplier II, low pass filter 12 and recording unit 13. Introduction of two circuits consisting of Zi 6 bandpass filters and detectors 7 and 8, and carrying out a test signal generator in the form of high voltage generator 1 and 2: the voltage eliminates the influence of thermal noise on the measurement result by applying signals II to the multiplier II with the same tocopes and different thermal noises. This allows them to distinguish and measure current noise of lesser intensity, rather than thermal noise. 2 sec. f - ly, 2 ill. (L tann OO Yu O with 00 Fig, 1. "L.

Description

The invention relates to a measurement technique and can be used to build highly sensitive sound level meters.

The purpose of the invention is to increase sensitivity by eliminating the influence of thermal noise on the measurement result.

FIG. 2 is a functional diagram of the device implementing the proposed method for measuring current noise; FIG. 2 is a spectrogram illustrating the operation of the device.

On c1) 6, 2, the notation is: S, (f) is the spectral density of the current noise; S () is the spectral density cyMMafiHoro of thermal and excess noise of resistors and input devices; A is the coefficient characterizing the intensity of the current duster; B - coefficient characterizing the intensity of the excess component

20

in S. (f); Sn - the amount of white mist

B-S ,,

 about

f and

u (); f is the current frequency; voltage across the resistor; fj is the frequency of the first high-frequency generator; fj is the frequency of the second high frequency .Sjlflfil- 2

foot generator;

spect

The equal density of the high-frequency oscillation f modulated by current noise.

The device consists of two generators 1 and 2 of high-frequency voltage, connected to ballast 3 and measured by A resistors. Two bandpass filters 5 and 6 connected to detectors 7 and 8 are connected to a common point of resistors, from whose outputs a signal is fed to amplifiers 9 and 10 connected to multiplier J and a series chain from low pass filter 12 and recording unit 13.

The method is carried out as follows.

The resistor circuit with the measured resistor serves the sum of two oscillations of the frequencies f and f. As a result, in the spectral sections with central frequencies f and f, the sum of the amplitude-modulated-Hbtx vibration noise f and f, respectively, is obtained (Fig. 2). These areas are filtered, and then detected and amplified in low frequency amplifiers. As a result. Pick up two signals from the gum of identical current noise.

Sh

5 253812

and uncorrelated terms of thermal noise, since they are formed by differences in the spectral regions. These signals are multiplied. As a result, a constant component is obtained, which is caused by the product of identical current noise and the spectral density of the fluctuating interference, which is caused by the product of uncorrelated thermal noise. The constant component carrying information about the intensity of current noise is filtered and indicated.

The device works as follows.

The high-frequency voltage of each of the generators 1 and 2 in the circuit of resistors 3 and 4 is subjected to amplitude modulation by current noise with a spectrum S (f), as a result, around frequencies f

20

35

and f, (FIG. 2), the constituents are described by the ratio 8y () / 2 and S (f-fj) / 2, respectively. To obtain amplitude modulation, a nonlinear element is needed. In the device, this role fulfills the measured resistor 4. When current flows through the negro, current noise caused by the fluctuation of its resistance.

30 The voltage across the resistor will have a component of the product of the current per phpuk.trutiruyuschy part of the resistor, which will allow to obtain amplitude modulation. Show this mathematically.

Let the current be sinusoidal voltage.

I (t) I,

sih u) p t.

40

The measured resistor is represented as a constant resistance R and a fluctuating part 4R (t). The voltage across the resistor is

U (t)

loP-o

I (t) Rt (1 +

.

R "

) sinuJpt,

50

where R (t) is RO + dR (t).

This is a record of the amplitude-modulated signal. Here, the ratio R (t) / RQ is the modulation index, and the spectrum lR (t) determines the spectrum of the modulating signal.

Band-pass filters 5 and 6 allocate portions of the spectrum near the frequencies f and f. In this case, the value of 5y () can be characterized only by the member R, since, and f, are chosen within

313

10 kHz. This leads to the fact that, after detecting in detectors 7 and 8 and passing through low-frequency devices 9 10, two signals are received at the inputs of multiplier 11, containing current components S (f), grouped after detection near zero, and the magnitude of noise fluctuations with uniform spectral

density

V2 s

about

what explains

by the fact that the uncorrelated noise is summed to the left and to the right of the frequencies f, and.

five,

20

25

f J. It is important to note here that the yyum S (f) supplied to alternator A and I is the same in both channels, and the noise with a spectrum of 12 is uncorrelated, as it is formed by different parts of the initial density 5 u (), namely around the frequencies f, and f, respectively.

Indeed, thermal noise is in no way dependent on the leakage current and, therefore, it does not create amplitude modulation of the generator signals. The magnitude of the spectral density of thermal noise is determined by the Nyquist formula. This does not include the value of the flowing current,

In the band-pass filters 5 and 6, the spectral regions near the central frequencies are cut., And fn. These two segments are uncorrelated between themselves — and after

the detections are converted into two uncorrelated low-frequency processes. .35

At the output of the multiplier 11 in b-. is the constant Sotavavl, due to the spectral density

1. A method of measuring current noise, containing the operation of supplying a test signal to resistors, amplifying the jpy MOB in two identical channels, which are then multiplied, and the result is filtered and recorded, J characterized in that, with the purpose of increasing the frequency signal, the sum of two high-frequency voltages, for example, rectangular, high-frequency amplitude-modulated noise oscillations are filtered at frequencies of the test signal and detected in each canape before amplified it.

2. A device for measuring current noise, containing a series-connected test signal generator, ballast and measuring resistors, as well as two amplifiers, the outputs of which are connected to the input of a multiplier, the output of which is connected through a low-pass filter to the recording unit. . Partly with the fact that two circuits are introduced from a series-connected band-pass filter and detector, and the test signal generator consists

S (t). Due to uncorrelated thermal noise from series-connected generations, the YZS spectrum does not form a constant component. Nohtor high-frequency voltage,: while both inputs bandpass filters. Connected to the common output of resistors, and the outputs of the detectors to the inputs of the corresponding amplifiers.

Gaining useful information the constant component is filtered in a filter .12

and registers in block 13.

Thus, the physical situation is physically as follows. With this method, signals with the same current and different thermal noise are fed to the multiplier. This makes it possible to distinguish them, moreover, to measure current noises of lesser intensity than thermal ones.

five,

0

five

0

five

Claims (2)

1. A method of measuring current noise, containing the operation of supplying a test signal to resistors, amplifying the jpy MOB in two identical channels, which are then multiplied, and the result is filtered and recorded, J characterized in that, with the purpose of increasing the frequency signal, the sum of two high-frequency voltages, for example, rectangular, high-frequency amplitude-modulated noise oscillations are filtered at frequencies of the test signal and detected in each canape before amplified it. 2. A device for measuring current noise, containing a series-connected test signal generator, ballast and measuring resistors, as well as two amplifiers, the outputs of which are connected to the input of a multiplier, the output of which is connected through a low-pass filter to the recording unit. . Partly with the fact that two circuits are introduced from a series-connected band-pass filter and detector, and the test signal generator consists of the series included of the series included high-frequency voltage tori,: herewith, both inputs of bandpass filters are connected to the common output of resistors, and the outputs of the detectors are connected to the inputs of the corresponding amplifiers. "V4 Editor E. Papp Compiled by N.Mikhalev Tehred L.OlynnykKorrektor A.Zimokosov Order 3103 / AOT circulation 730 Subscription VNIIPI USSR State Committee according to the inventions and discoveries of PZOZZ, Moscow, Zh-35, Raushsk nab., 4/5 Proivol1 T1 rnio-I (1lig aphic1e enterprise, Uzhgorod, Proektna str., 4