SU1553915A1 - Method of parallel spectral analysys of electric signals - Google Patents

Abstract

The invention relates to spectroscopy. The aim of the invention is to improve the accuracy of the analysis by stabilizing the parameters of bandpass filters. The method of parallel spectral analysis of electrical signals is based on the fact that, prior to obtaining the results of spectral analysis, the paired frequency reference signals are additionally shifted in phase relative to the corresponding test signals by the phase shift values introduced by the tuned bandpass filter. Summarize the detected paired frequency signals. The received signal is attenuated by a number of times equal to twice the amplitude of the corresponding test signal. Subtract the received signal from the signal proportional to the normalized transfer coefficient of the adjustable bandpass filter. The received differential signal changes its transfer coefficient to zero this signal. 1 il.

Description

315539

For parallel spectral analysis of the electrical signal described by the expression

U8xU) itVmi. sin (w, t + f.), (1) 5

where i 1,2,3, ..., n, use N parallel-connected input bandpass filters with a bandwidth of 10 2nd $ 1., which meets the condition 2D $ 1 / and; const. In this case, the center frequencies of the bandpass filters are set equal to the selected frequencies of the spectral components, i.e. about ,, uij ,. . . 15 . .., ui, ..., WN. As a result of the influence of external destabilizing factors, the center frequencies of the bandpass filters and their transmission coefficients change, and for i-ro band-pass filters, they took the values w | and k, instead of and) {k {.

According to the proposed method of parallel spectral analysis, test signals are generated.

in ,, ,, 2) eVme.sin (toe, t- (fe.) f (3)

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grids of paired frequencies tus (removable relative to the center frequency o), bandpass filters, i.e. satisfying the condition

South (wHi + U) ei) / 2. (four)

At the same time, the pair frequencies WH | - and we) of the test signals have a frequency difference defined for each i-th bandpass filter

(five)

.301

35

40

dW, CJe (-WHJ.

The frequencies and tj ei of the test paired signals are selected outside the passband 45

2 & SL- (. + ЛЛ;) - (.- дЯ;), (6).

set at 0.707 with respect to the center frequency, comparing the attenuation of the amplitudes of these signals 50 by 30–40 dB, i.e.

, - + for; ; (7)

 - a AND g. (8)

/ At the same time the difference of 1 pair frequencies, 55 (7) and Х8) exceeds the passband of the 1st filter.

   . (9;

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At frequencies (/) and (.8), the amplitude of the input signal of the i-rro band-pass filter should be attenuated by 30-40 dB compared to the amplitude of the signal at the center frequency tof of the band-pass filter. This condition ensures the correct choice of test signals of the grid of paired frequencies.

The test signals (2) and (3) are attenuated to the level of the analyzed signal (1). In particular, for example, the test signals (2) and (3) are attenuated until they exceed the effective value of the input signal, i.e.

(ten)

VH, - - VmH4.k0 Ј V8X;

Vft;

V.

(eleven)

 ei v CHV; L0. vex

where kc is the attenuation coefficient i-x of the test signals (k0 U, the same for the side frequencies WB; И Ы "; J

VBX - amplitude value of the input signal;

VK; and

v

Bi are the amplitude values of the i-th pair of attenuated test signals.

Summarize the test and weakened test signals.

U (t) U6x (t) (t) + UBi (t); k0.

(12)

Total signals (12) are passed through bandpass filters. As a result, at the outputs of bandpass filters receive electrical signals.

u, {,, - i) Vmi sin (cJ; t + if, ± dtf.) + + ViM sindJmt + c / i1 + u4Hi) + + Vie sin (- tf & t), (13)

where ± d «Јj t t / and; 5 ALfei Phase shifts introduced by the tuned i-th band-pass filter at frequencies o /,, w and u) 8j, respectively;

V (m; k i Vmj is the amplitude value of the spectral component passed through the i-th bandpass filter;

VJH k, -ke VMH), k f-k0x Vmu-, are the amplitude values of the test signals passed through the i-th bandpass filter.

The output signals (13) of the bandpass filters are detected synchronously using each WH frequency pair; H tJei as the reference test signals. When using relay synchronous detectors as reference signals, they can be used515539

used, for example, signals of type square wave with a single amplitude, the main frequencies WH, and YV; i-th pair and initial phase shifts about c / Hi and AUY. . The latter is due to the fact that, according to the proposed method, the reference signals of the pair frequencies WB; additionally shift in phase with respect to the corresponding frequency of the test-.Q output signals by values ± uitH-, and t d s; phase shift introduced by the tuned i-th bandpass filter.

The obtained reference signals are described by the expressions:

 one

i. , „.

u "- (t) if

 + if “j ± 14

20

(t I I, Sin (2m-1)

Oe; t - - fret

(15)

As a result of the synchronous detection of the signal (13) using the reference signals (14) and (15), signals are received

V .; T- S u,) - u, Hi (t) dt

-k0-k, - k i VmHi

i. "(16)

 t; S u, 1 (t -uoei (t) dt

Lb to

 WO vrofto k; -vmBi,

(17)

„; and Cg-, - constant time

low-pass filters; 40 kf is the transmission coefficient of a synchronous detector;

-k, k, is the proportionality coefficient proportional to the amplitude values of the test signals and transmission coefficients k0, k1

50

and k,.

The difference and half sum of the detected paired frequency signals are determined.

beats; V V Ktv-n - vm.,);

V7, - 0,5CVb + V ,,) K (V fVm & i) / 2.

O9)

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The difference voltage (18) adjusts the center frequency of the corresponding band pass filter until the difference voltage is zero, i.e. to the value of v. ABOUT

or

V v ttiHivwBi

(20J

0

five

0

five

0

0

five

WITH WHICH (A). Sh

Equality (20) is established by symmetrically arranging the values of the paired frequencies wHl- and u.) Bi on the frequency axis with respect to the center frequency w-, equal to half the sum of the paired frequencies.

separating the difference signal (18), containing information about the magnitude and sign of the amplitude difference of the test signals depending on the magnitude and sign of the detuning of the bandpass filter, provides an adjustment of the center frequency and), the corresponding bandpass filter to the nominal value Uj. Excluding the effect of the phase shift introduced by the detuning of the bandpass filter on the test signal improves the accuracy of the center frequency adjustment. This allows the selection of test signal frequencies away from the passband, which increases the noise immunity of the main signal being analyzed.

According to the proposed method, the received signal (19) is attenuated by a number of times equal to twice the amplitude value of the corresponding test signal, i.e. in 2N ei 2S-VmH; pa3, where is the steepness of the transformation, is, for example, one. Since in case of equality (20), the transfer coefficients k Hi and k ft; on the frequencies WMJH and fli are equal, i.e. k Hl- k 6; k (then receive the signal

VVi V2i / 2Nci K-VmHi / 2Noi v - - SV,

(21)

where k k 0 k, / SLB is the proportionality coefficient.

Subtract the received signal (21) from the signal

Vo; k, k, (22)

where ka k0k, / S is the proportionality coefficient equal to the above value, which is proportional to the normalized transfer coefficient k of the 1st adjustable band-pass filter:

jLLJLJ- k k h kgK;

v

/

 V0i - VKi k2 (ks - k). ()

15

The received difference signal (23) changes the transfer coefficient of the i-ro bandpass filter (by changing, for example, the gain of the active filter or by changing the Resistance of the passive filter resistors) until this signal is zero, i.e. up to V d 5 0 or

kt (kt - kp - 0. (24)

Equality (24) is achieved at C, e k (-, i.e., when setting the transmission coefficient of the 1st band filter changed by external destabilizing factors equal to the nominal value of k ;.

If, during synchronous detection, the reference signals were not shifted in phase, then the detected signals would have been obtained

 v,} To VmM ,. cosdifHi;

V-ji K V mei cos / J (fe,

d) de DCC and & 4ui Additional phase shifts introduced by a bandpass filter.

Half sum

v - o, s (v; - v ;;)

0 ,, created & 1 + Ґt; created and difference

Mi

 V - Vl; cos (- V

mm i

SOЈSH „, J

The detected signals in this beam contain an error due to the values of phase shifts and tfji and DCs introduced by tuned field filters in the total signals of the form (12). As a result, when adjusting with differential voltage V. The center frequency of the corresponding bandpass filter results in an error of adjustment depending on the values of t / ei and i / Hj. Similarly, an error occurs in adjusting the transmission coefficient of the 1st band filter when using voltage V. . Introduction to reference signals WH; and additional phase shifts .and a if e ensures the elimination of errors in the adjustment of the center frequencies and transmission coefficients of the band-pass filters. Indeed, in synchronous detection: signals of the form (13) using reference signals (14) and (15)

cos "f Lf6 cosdji / gj- gj) About

eight

0

five

P

five

0

5 40 45 50 5

 - itfH. ) 0.

Then the center frequency of the bandpass filter is adjusted by a differential voltage.

  KtVmeicos "fipe- VmH cos (AfH

 K (vme, - vmHi) -v; f,

those. equal to the voltage (1b).

With a tuned bandpass filter

mn

V№B, V,, voltage V. with

h hch ... i, i R-

i ieTOM cos and O is written as:

Vs; 0.5K (VhHi + Vmfl,) K-VmH; K-Vmel K-V,.

This voltage adjusts the gain of the corresponding bandpass filter. Moreover, the control voltage does not contain errors depending on andWe; and ACh that provides high-precision adjustment of the transfer coefficient.

The analyzer of the spectrum of parallel action contains a wideband amplifier 1, adders 2-4, summing amplifiers 5-7 with an adjustable gain, a generator of 8 paired frequency grids, band-pass filters 9-11 of the first, 1st and N-ro parallel channels, drivers 12- 14 control signals, amplitude detectors 15-17, an electronic switch 18, a pulse counter 19, and a digital oscilloscope or recorder 20.

Band-pass filters 9-11 have two control loops — at the center frequency and at the gain.

The analyzer of the spectrum of parallel action works as follows. The analyzed signal (1) is fed to the input of the wideband amplifier 1, where it is amplified to the required level. From the output of the broadband amplifier, the analyzed signal is fed to the combined first inputs of the adders 2-4. The second inputs of the adders 2-4 receive test signals with frequencies of life; and Wei- The latter are formed using a pair-frequency grid generator 8. The generator 8 generates a signal of both sinusoidal and rectangular shape with the main frequencies WH, and w fl; for every i-th pair.

To form the 1st pair test signal, the output sinusoidal signals (2) and (3) of the generator 8 are summed in pairs using summing 1st amplifier 6. The selection of the transfer coefficients k0 of the amplifiers 5-7 sets the required values of the test signals fed to the second inputs adders 2.3 and 4, respectively. From the outputs of adders 2-4, signals of the form (12) are fed to the inputs of a flat filter 9-11, respectively. In this case, the center frequencies of the band-pass filters 9-11 correspond to the selected frequencies of the spectral components. The bandwidth of the bandpass filters at the level of 0.707 is determined by the expression (6).

As a result of filtering, the outputs of the bandpass filters 9-11 appear in the form of signals (13), which are fed to the inputs of the amplitude detectors 5-17, as well as to the first signal inputs of the drivers 12-14 of the control signals of the bandpass filters.

The adjustment of the center frequency and the transmission coefficient of the 1st bandpass filter is performed until the difference signals (18) and (23) are equal to zero.

The output signals of the tuned bandpass filters are detected with amplitude detectors 15-17. As a result, the inputs of the electronic switch 18 receive signals equal to the amplitude values of the spectral components of the analyzed signal (1). These signals through an electronic commutator arrive at the input of a digital oscilloscope 20 (or recorder).

The electronic switch 18 is switched by means of a pulse counter 19, controlled by the output low-frequency pulses of the generator 8. The sweep of the digital oscilloscope 20 is synchronized by the leading edge of the low-order output pulse of the counter 19

The proposed method of parallel spectral analysis of electrical signals is characterized by an increased accuracy of the analysis. This is achieved

five

0

five

0

five

0

five

0

due to additional stabilization, the filter transmission coefficient along with stabilization of its center frequency. This eliminates the effect of phase shifts introduced by the tuned bandpass filter at the frequencies of the test signals. In addition, the instability of the amplitudes of the test signals is inevitable.

Excluding the effect of phase shift improves the accuracy of the center frequency adjustment. This allows selection of test signal frequencies outside the bandwidth, which increases the noise immunity of the main signal being analyzed.

The stabilization of the transmission coefficients of the bandpass filters, along with the stabilization of the center frequencies, increases the accuracy of the spectral analysis.

The proposed method ensures the elimination of errors due to temporal and temperature instability characteristics of bandpass filters.

Claims (1)

Invention Formula A method of parallel spectral analysis of electrical signals by the author. No. 1471147, characterized in that, in order to improve the accuracy, prior to obtaining the results of spectral analysis, the reference frequency signals are additionally shifted in phase relative to the corresponding test signals by the phase shift values introduced by the tuned band pass filter, the received signal is attenuated times equal to twice the amplitude value of the corresponding test signal, subtracts the received signal from the signal proportional to the normal a given transfer coefficient of the tuned bandpass filter, and the received differential signal, its transfer coefficient is changed until the signal is zero.