The method of determining frequency characteristics of the measuring channels of information-measuring systems

 

(57) Abstract:

The method applies to information-measuring technique. The technical result of the method is in principle possible to determine the frequency characteristics in pure form without the procedure of normalization. This is achieved by the fact that in the known method, which consists in applying to the input of the measuring channel (IR) test signal (IP) and determining its spectrum (SP), one of the IR information-measuring system is used as a model and define its complex frequency response (CCH) by measuring the amplitude and phase of the JV output signal. Values CCH remember, then the exemplary inputs and controlled IR simultaneously serves IP and to determine the degree of difference CCH IR from the output signal of the controlled IR subtract the output signal of the exemplary IR. Differential amplify the signal and measure its amplitude and phase of the JV. When this IP, affecting inputs IR form of harmonic oscillations of a frequency exceeding (N+1) times the repetition rate of the IP, in the form of amplitude-modulated oscillations with the law of change of the envelope defined by the ratio of the instantaneous values of C the deposits of multiple frequencies and equal amplitudes. 2 Il.

The method applies to information-measuring technique and can be used to determine the frequency characteristics of linear two-ports in a wide range of frequencies.

A method of obtaining the amplitude-frequency characteristics (AFC) of two-and communication channels (RF Patent for invention 2012140, MKI 5 H 04 3/46, BI 8, 1994), namely, that at the entrance of a quadrupole or a communication channel signal with a linearly varying frequency, and the output perform sequential analysis of the spectrum in the frequency range of the input signal.

A significant disadvantage of this method is the impossibility of obtaining the frequency response in an undistorted, as its shape depends on the rate of change of frequency of the test signal and only when the rate of change of frequency, equal to zero, the frequency response coincides with the static shot points, when the exposure time of the test signal in the form of a sinusoidal input voltage is unlimited (Kharkevich, A. A. Spectra and analysis. ), State publishing house of physical and mathematical literature, 1962, S. 137-148).

This lack makes it impossible to resolve the contradiction between the desire policiesmost way.

Known (Patent RF 2054684, MKI G 01 R 23/16, BI 5, 1996) method of determining frequency characteristics of the measuring channels of information-measuring systems, which consists in the fact that at the input of the measuring channel serves pulse signal and determine its range, and to improve the accuracy of the complex frequency response of an exemplary measuring channel is determined on the basis of the amplitude-frequency characteristic and phase-frequency characteristic (PFC) the last measurement using sinusoidal excitation signal with the last scan frequency, the values obtained characteristics memorize, then the inputs controlled and exemplary measurement channels simultaneously serves pulse signals, from the difference of the output signals of the mentioned measuring channels define a spectrum that is divided into range of the input signal to obtain a complex frequency characteristics, added to the complex frequency response of an exemplary measuring channel to obtain the frequency response and phase characteristics of the control channel.

The disadvantages of this method, which does not allow high accuracy frequency response and phase characteristics are:

a) in the selected method for determining the frequency response and the phase response curve of the reference signal by do
b) the impossibility of determining the frequency response and phase characteristics of the control channel when exposed to the exemplary inputs and controlled channels of pulse signals so as to obtain the frequency response and the phase response curve performed the following procedures:

1. determination of the frequency response and the phase response curve of the reference channel when exposed to the deployed frequency sinusoidal input signal;

2. determining the difference between the complex frequency characteristics of exemplary and controlled measuring channels with simultaneous impact on their input pulse signal;

3. the addition (subtraction) of the complex frequency characteristics of the reference channel and the differential of the complex frequency characteristics defined in paragraph 2;

4. the distribution of frequency response and phase characteristics of the controlled measurement channel defined in paragraph (3 total complex frequency response.

As all mentioned in paragraph 1 of 4 treatments are accompanied by respective errors, the implementation of the method does not provide high accuracy.

There is a method of measuring the amplitude-frequency characteristics (Copyright certificate of the Russian Federation 1712898, MKI 5 G 01 R 27/28, BI 6, 1992), including the impact on the test object M of kolebanii the time the results of which are subjected to the operation point fast Fourier transform (FFT), while processing the response of the test unit is accomplished by the measurement modules of the amplitudes of test impact in reference to the receive channel with no frequency selectivity, the signals at the input which serves bypassing the object under test, and evaluation of the amplitudes of the signals at the timing of the reference channel is produced by the operation point FFT, and the received reference channel results are used for normalization of the estimated amplitudes of the responses of the test subject.

Significant disadvantages of this method are the following:

1. Use for measuring the frequency response M oscillations of predetermined frequency, amplitude and frequency are related arbitrarily, is a consequence of the need for normalization, because the change of the amplitudes and frequencies called M oscillations due to the impact of destabilizing factors on the sources of these fluctuations result in changes of the summing them - test exposure. The need for normalization requires reference channel reception and increase required to implement the FFT hardware 2 times (responses processing the dough-impact ispycameltoe reference channel for normalization, not with the frequency selectivity has led to the emergence of additional frequency-dependent errors. Indeed, in the reference channel instability amplitude and frequency of each of the M summable oscillations is accompanied by a change in the shape of the test signal, which leads to corresponding changes will be computed using the FFT values of the amplitudes of each of the M summable variations (used for normalization when determining the frequency response), but in the measuring channel in addition to the changes of the amplitudes of each of the M summable oscillations in accordance with the nature of the response of the device to change the phase of each of the M output fluctuations in accordance with the law

= arctan(B()/A()),

where a and b are respectively the real and imaginary components of the complex frequency response of the test object for a specific frequency of each of M acting on its input fluctuations. This leads to additional changes in the output waveform, so as to maintain the shape of the signal when passing through the quadrupole phase response must be linear = k.

This leads to additional changes in the output waveform, and hence to changes Osetia.

The technical result of the proposed method is in principle possible to determine the frequency response in pure form without the procedure of normalization.

The challenge which seeks a technical solution is achieved in that in the known method lies in the fact that at the input of the measuring channel serves the test signal and determine its range, one of the channels of information-measuring system is used as a model and define its complex frequency response by measuring the amplitude and phase spectra of the output signal of this channel, the values obtained characteristics memorize, then the exemplary inputs and controlled measurement channels simultaneously serves the test signal, the output signal is controlled measuring channel by measuring its amplitude and phase spectra are used to determine the complex frequency response of this channel, and to determine the degree of difference of the complex frequency characteristics of exemplary and controlled measuring channels of information-measuring system of the output signal of a controllable measurement channel subtract wygodny spectra, this test signal acting on the inputs of the measuring channels and represent the sum of N harmonic vibrations of multiple frequencies and equal amplitudes, form of harmonic oscillations of the carrier frequency

fn=n/2 = (N+1)0/4

in the form of amplitude-modulated oscillations with law changes envelope

< / BR>
In Fig. 1 shows a block diagram of an apparatus for forming a recurrent test signal, Fig.2 shows time diagrams.

In Fig.1 mark: 1 - the oscillator carrier frequency

< / BR>
2 - driver, which converts the oscillations of the carrier frequency in the sequence of rectangular pulses of the same frequency; 3 - scale Converter on the basis of the operational amplifier, the switching resistors in the feedback circuit is provided for changing a transfer ratio; 4 - electronic switch controlled by the output pulses of the imaging unit 2 and provides the switching resistors scale Converter 3.

The output voltage of the generator 1, generator 2 and the scale of the Converter 3 in the form of time diagrams for the control points of the ith follows: the need for standardization is no longer only in one case, - when the amplitudes of all frequency components of the input are equal, and therefore, when carrying out the normalization of the amplitude of the frequency components of the output signal must be divided by the same value, what not to do at all.

Indeed, if there is the possibility to synthesize a test signal representing the sum of N harmonic vibrations of equal amplitude with frequencies that are multiples of the fundamental frequency

f0=0/2 = 1/T0< / BR>
< / BR>
it corresponds to the range of

< / BR>
When the effect of this signal on the input of the investigated chetyrehkolesnika output signal of the latter on the basis of the Duhamel integral

< / BR>
where the complex frequency response of the quadrupole at = K0, a g () is its impulse response. This signal corresponds to the range of

< / BR>
Dynamic coefficient of transmission of the quadrupole (that is, when exposed to the input test signal)

< / BR>
that is, in controlled points of the frequency axis (0;20;...N0dynamic transfer coefficient coincides with the complex frequency response defined in the static mode (by setting fixed values of the frequency generator entirehouston by acting on the input test signal

< / BR>
not a problem, as in the case of impact with linearly changing frequency deviation of the shape of frequency response from some in the static mode, i.e. the proposed method can provide high accuracy.

The procedure of normalization when using the test tone

< / BR>
is not required, since the definition of AFC division of the amplitudes of the output signal of the quadrupole produce the same value, equal to the amplitude of each of frequency components of the input, i.e. the spectrum of the output voltage is subjected to only large-scale transformation.

To achieve high accuracy of determination of identity exemplary and controlled measuring channels with simultaneous impact on their entrance test signal

< / BR>
assessment is used as the ratio of the spectrum of the difference of the output signals from these channels to the spectrum of the input test signal

< / BR>
As the amplitude of the harmonics of the test signal are equal Um1= Um2... = UmNand their growing phase is proportional to the harmonic number "K" to determine the KISM(jk0) it is enough to know Umwah(jk0) (define |Code and the same number |Uincluding infrastructure(jk0)|, and for determining the difference between the phase characteristics of the phase of each harmonic of the difference of the output voltages is necessary and sufficient to subtract the already known phase of the corresponding harmonic of the input test signal).

Thus, using the test signal

< / BR>
by measuring the amplitude and phase of the input test signal, and the amplitudes and phases of the output signals exemplary and measuring channels and the difference between their output voltages allows you to define the frequency characteristics of these channels, as well as the degree of their differences.

The reduction of the volume of the measuring procedures for determining exemplary frequency response and the measured channel, as well as in determining the extent of the identical response of these channels provides a basis to improve the accuracy of determining the frequency response of the measuring channels of information-measuring systems. However, the implementation of the required measurement procedures requires the impact on the input test signal

< / BR>
i.e. the sum of sines of equal amplitudes generated by N generators, with a certain initial angle of the phase shift. Stabilization of the amplitudes and initial phases of N generators Harmon>However, the known ratio (Dwight Century, Tables of integrals and other mathematical formulas. - M.: Nauka, 1966, S. 82)

< / BR>
in relation to the analyzed test signal f1(t) allows to change the nature of the transformations in the formation of the latter.

Indeed, the representation of the test signal

< / BR>
as

< / BR>
allows you to treat it as an amplitude-modulated (AM) oscillation, because AM formally oscillation represents the work envelope Um(t) and the harmonic filling.

In the test signal f1(t) is a harmonic function fill (i.e., the oscillation of the carrier frequency) performs oscillation sin where the repetition frequency of the test signal f1(t). The envelope function Um(t) performs periodic oscillation representing the ratio of the instantaneous values of sinusoidal oscillations with a multiplicity of frequencies N equal to the number of summed to obtain the test signal harmonic vibrations of multiple frequencies and equal amplitudes. This representation of the test signal allows for its formation to use N generators vibrations of multiple frequencies, but only one oscillation frequencyn= (N+1)
< / BR>
fluctuations of the carrier frequency fn=n/2 = (N+1)f0/2 = (N+1)0/4 and constant amplitude Umserved on a log scale Converter operational amplifier (op-amp), the transmission coefficient which is determined by the ratio of resistances ku=ROS/R1(where ROSa resistor connected between the inverting input and output OS and R1a resistor connected between the inverting input and output of the signal source), change the switch resistors ROSin the moments passing by fluctuations of the carrier frequency through the zero instantaneous value that provides a constant kuwithin an interval equal to half the period of oscillation of the carrier frequency.

Set forth in connection with the task, as well as in connection with the proposed functions of the specific measuring and converting device structural scheme allows to conclude that the reduction in measurement and conversion procedures to achieve the goal is the basis for approval of improving precision.

The method of determining frequency characteristics of the measuring channels of information-measuring systems, which is characteristic by measuring the amplitude and phase spectra of the input and output signals of this channel, characterized in that a test signal serves simultaneously to the input of an exemplary measuring channel and determine its frequency response, and to determine the degree of difference of the complex frequency characteristics of exemplary and controlled measuring channels of the output signal of a controllable measurement channel subtract the output signal of an exemplary measuring channel, the differential signal amplify and measure its amplitude and phase spectra.

 

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FIELD: measurement technology.

SUBSTANCE: analyzer can be used for measuring level of frequency distortions introduced by audio channel. Analyzer has two spectrum analyzers which are used to determine signal spectra at output and input of tested four-terminal network. Input and output signal spectra are subject to normalization and are introduced into subtraction unit and later to unit for determining normalized signals difference module. Signal from unit for determining module is sent to integrator to find end value, which characterizes area of frequency distortions introduced by four-terminal network. According to another version of analyzer the module is substituted by squarer. Analysis of frequency characteristics can be performed without turning four-terminal network into special measuring mode.

EFFECT: improved truth of information; increased precision of measurement.

2 cl, 3 dwg

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