CN104698296A - Space charge measuring signal attenuation and dispersion factor compensation method - Google Patents

Abstract

The invention discloses a space charge measuring signal attenuation and dispersion factor compensation method which includes the steps: applying direct-current low voltage to two ends of a large-sized test sample and acquiring acoustic signal attenuation coefficient and dispersion coefficient; respectively selecting signal peaks v (t, a) and v (t, b) of a high-voltage electrode and a ground electrode and performing Fourier transformation to obtain frequency domain signals V (omega, a) and V (omega, b); calculating the attenuation coefficient alpha (omega) and the dispersion coefficient beta (omega); acquiring a system transfer function G (omega, r); performing fast Fourier transformation for measuring signals after recovery and geometric factor compensation to obtain frequency domain pulse electro-acoustic method space charge measuring signals Vs (omega, r); setting signals Vs (omega, r)*G (omega, r) after attenuation and dispersion compensation, and performing Fourier inverse transformation for the signals to obtain time domain signals. The method is applicable to the processing course of the pulse electro-acoustic method space charge measuring signals of the large-sized test sample, and the influence of attenuation and dispersion in the acoustic signal propagation process caused by viscoelasticity of insulating materials can be eliminated, so that high resolution and precision measuring signals are acquired.

Description

A kind of space charge measurement signal attenuation and the compensation method of dispersion factor

Technical field

The present invention relates to a kind of space charge measurement signal attenuation and the compensation method of dispersion factor, particularly relate to a kind of when carrying out large dimension specimen space charge measurement based on pulse radio-acoustic method (PEA), to the compensation method of acoustic wave signal decays and dispersion.

Background technology

Pulse radio-acoustic method measurement space electric charge is a kind of measuring technique widely applied at present, and the method shows gratifying sensitivity and spatial resolution in the space charge measurement of Mass lose.And the space charge measurement being applied in the large dimension specimens such as thick tabular sample (as more than 2 millimeters) and full-scale sample of cable also receives publicity day by day.But due to the viscoelasticity of insulating material, the propagation of sound wave in measured insulating medium experienced by decay and dispersion process, make material deep layer and satisfied sensitivity and spatial resolution cannot be obtained away from the space charge measurement measuring ground electrode.In the measurement of Mass lose in the past or only to material Space-charge phenomenon carry out qualitative evaluation analyze time, this phenomenon is little on the impact of measurement result, therefore need not carry out special process to its measuring-signal.And in the space charge measurement of large dimension specimen, decay and dispersion process cannot be ignored the influence of measurement result, in the measurement of especially full-scale sample of cable, sometimes cannot measure the electric charge of deep layer or interior ate electrode at all.For ensureing the accuracy of determining charge density result and satisfied spatial resolution, in measuring-signal processing procedure, process tool being compensated to decay and dispersion factor and being of great significance.

Summary of the invention

Technical matters to be solved by this invention, is to provide a kind of compensation method carrying out to acoustic wave signal decays and dispersion when large dimension specimen Space-charge is measured based on pulse radio-acoustic method.

Method of the present invention is used in the processing procedure of the pulse radio-acoustic method space charge measurement signal of large dimension specimen, the impact that the decay of acoustic signals in sample communication process and dispersion factor are brought space charge measurement signal can be eliminated, to obtain accurately and the distribution of space charge of high spatial resolution is measured.

For solving the problems of the technologies described above, the present invention adopts following technical method:

1. obtain the attenuation coefficient of acoustic signals in communication process and abbe number: calibration DC voltage is applied to large dimension specimen two ends, only produce induced charge (i.e. capacitance charge) at sample two electrode interface place, measure the space charge signal of induced charge, after system responses correction (i.e. deconvolution technique computing) and geometrical factor (as coaxial cable structure) compensation are carried out to signal, choose high-field electrode respectively and measure ground electrode place (i.e. position a and b) time domain peak-to-peak signal v (t, and v (t a), b), carry out Fourier transform, obtain its frequency-region signal and be respectively V (ω, and V (ω a), b):

In formula | V (ω, a) | with | V (ω, b) | be the frequency domain amplitude function of measuring-signal, with for frequency domain phase function, attenuation coefficient α (ω) and abbe number β (ω) is the function of ω, can be expressed as:

$\mathrm{\α}\left(\mathrm{\ω}\right)=-\frac{1}{b-a}\ln \left|\frac{V(\mathrm{\ω},b)}{V(\mathrm{\ω},a)\sqrt{a/b}}\right|$

2. measuring-signal decay and dispersion factor compensate: according to the communication process of acoustic signals in insulating medium, the transport function G (ω, r) of any r place signal attenuation and dispersion compensation is:

$G(\mathrm{\ω},r)=\frac{P(\mathrm{\ω},r)}{P(\mathrm{\ω},a)}=e^{-[\mathrm{\α}\left(\mathrm{\ω}\right)+\mathrm{j\β}\left(\mathrm{\ω}\right)](r-a)}$

This transport function can be used for the compensation of decay and dispersion process in acoustic signals communication process under frequency domain, to pulse radio-acoustic method space charge measurement signal V under frequency domain _s(ω, r), according to convolution theorem, carries out decaying and signal after dispersion compensation is V _s(ω, r) G (ω, r), carries out inverse Fourier transform to it, obtains the signal under time domain.

Method of the present invention is applicable to the processing procedure of the pulse radio-acoustic method space charge measurement signal of large dimension specimen, the impact of decay in the acoustic signals communication process brought due to insulating material viscoelasticity and dispersion process can be eliminated, thus obtain the measuring-signal of high resolving power and measuring accuracy.

Accompanying drawing explanation

Fig. 1 is phase reversal front space charge signal schematic diagram;

Fig. 2 is phase reversal rear space charge signal schematic diagram;

Fig. 3 is that the signal attenuation of large dimension specimen space charge measurement and dispersion factor compensate process flow diagram.

Embodiment

Fig. 1 is phase reversal front space charge signal schematic diagram;

Fig. 2 is phase reversal rear space charge signal schematic diagram;

Fig. 3 is that the signal attenuation of large dimension specimen space charge measurement and dispersion factor compensate process flow diagram, comprises the steps:

Step 301: apply low-voltage dc voltage, obtains space charge measurement signal

Step 302: choose internal and external electrode place signal peak respectively as with reference to signal, to its carry out Fast Fourier Transform (FFT) obtain V (ω, a) and V (ω, b);

Step 303: calculate and obtain attenuation coefficient α (ω) and abbe number β (ω);

Step 304: obtaining ssystem transfer function is G (ω);

Step 305: Fast Fourier Transform (FFT) is carried out to the measuring-signal compensated through over recovery and geometrical factor and obtains V _s(ω, r);

Step 306: carry out decaying and dispersion compensation signal is V _s(ω, r) G (ω, r), carries out inverse fast Fourier transform to it, obtains its time-domain signal.

Make a concrete analysis of as follows:

First stage, the decay of acoustic signals in insulating material and dispersion process

In the past to the space charge measurement of Mass lose, be all carry out under insulating material is the hypothesis of the perfect medium of Acoustic Wave Propagation, both in propagation process of sound wave, there is not decay and dispersion process.To perfect medium, sound wave propagation can be expressed as:

p(t，x)＝p ₀e ^j(ωt-kx)

Wherein ω is the angular frequency of sound wave, and k is wave number, k=ω/u _sa, u _safor the phase velocity of Acoustic Wave Propagation, in perfect medium, its velocity of propagation of the sound wave of different frequency component is identical.

In fact, insulating material of polymer is not the perfect medium of Acoustic Wave Propagation, due to its viscoelasticity, acoustic signals in its communication process along with decay and dispersion process.In the space charge measurement of sheet metal specimens, because Acoustic Wave Propagation distance is very little, decay and dispersion interaction can be ignored; But when carrying out space charge measurement to the large dimension specimen such as sheet and full-scale cable, the impact of decay and dispersion interaction then be can not ignore.

For viscoelastic medium, its wave number is plural form, is expressed as

k(jω)＝β(ω)-jα(ω)

The communication process of sound wave can be expressed as:

p(t，x)＝p ₀e ^{j[ωt-k(jω)x]}＝p ₀e ^-αxe ^j(ωt-βx)

u _sa(ω)＝ω/β(ω)

Sound phase velocity of wave u _sa(ω) be the function of angular frequency, its velocity of propagation of the sound wave of different frequency is different, both the dispersion phenomenon of communication process, and the relaxation phenomenon of the reduction of intensity of acoustic wave both communication process in communication process, α (ω) and β (ω) is designated as attenuation coefficient and abbe number respectively.

Subordinate phase, obtains attenuation coefficient and the abbe number of acoustic signals

Here, for coaxial cable test specimens, under frequency domain, can be expressed as under the decay that acoustic signals is propagated in full-scale cable insulation and dispersion interaction:

P(ω，r)＝P(ω，a)e ^-α(ω)(r-a)e ^{-jβ(ω)(r-a)}

α (ω) and β (ω) is respectively attenuation coefficient and abbe number, because acoustic signals all transfers voltage signal to through identical transport function everywhere, according to convolution theorem, can estimate α (ω) and β (ω) with the voltage signal recorded.

Sample applies the low amplitude value DC voltage of short time, make it only in electrode and sample contacts interface induced charge (i.e. capacitance charge), space charge measurement is carried out to it, choose its internal and external electrode a, measuring-signal peak, b place is as reference signal, measuring-signal as shown in Figure 1, for the ease of understanding and calculating, reversal of poles is carried out to external electrode place signal, as shown in Figure 2, assuming that measuring-signal peak, interior electrode b place is the result of measuring-signal peak, external electrode a place after propagating generation decay and dispersion, respectively Fast Fourier Transform (FFT) is carried out to it, obtain signal V (ω under its frequency domain, and V (ω a), b)

In formula | V (ω, a) | with | V (ω, b) | be the frequency domain amplitude function of signal, with for frequency domain phase function, attenuation coefficient α (ω) and abbe number β (ω) is:

$\mathrm{\α}\left(\mathrm{\ω}\right)=-\frac{1}{b-a}\ln \left|\frac{V(\mathrm{\ω},b)}{V(\mathrm{\ω},a)\sqrt{a/b}}\right|$

Attenuation coefficient α (ω) in thick plate-like sample and abbe number β (ω) computing method similar with it.

Phase III, measuring-signal decay and dispersion factor compensate

According to the communication process of acoustic signals in insulating medium, the transport function G (ω, r) of the signal attenuation of r place and dispersion compensation is:

$G(\mathrm{\ω},r)=\frac{P(\mathrm{\ω},r)}{P(\mathrm{\ω},a)}=e^{-[\mathrm{\α}\left(\mathrm{\ω}\right)+\mathrm{j\β}\left(\mathrm{\ω}\right)](r-a)}$

This transport function can be used for the compensation of decay and dispersion process in acoustic signals communication process under frequency domain, to pulse radio-acoustic method space charge measurement signal V under frequency domain _s(ω, r), according to convolution theorem, carries out decaying and signal after dispersion compensation is V _s(ω, r) G (ω, r), carries out inverse Fourier transform to it, obtains the time-domain signal through overdamping and dispersion compensation.The compensation process of whole decay and dispersion factor as shown in Figure 3.

The above is the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the premise without departing from the principles of the invention; can also make some improvements and modifications, these improvements and modifications are also considered as protection scope of the present invention.

Claims (5)

1. space charge measurement signal attenuation and the compensation method of dispersion factor, for when pulse radio-acoustic method carries out the space charge measurement of large dimension specimen to the compensation of acoustic wave signal decays and dispersion;

It is characterized in that, described method comprises the steps:

DC low-voltage is applied to large dimension specimen two ends, obtains attenuation coefficient and the abbe number of acoustic signals;

Choose respectively high-pressure stage and ground electrode place signal peak v (t, a) and v (t, b), carries out Fourier transform, obtain its frequency-region signal V (ω, a) and V (ω, b);

Attenuation coefficient α (ω) and abbe number β (ω) is obtained by calculating;

Obtain ssystem transfer function G (ω);

Fast Fourier Transform (FFT) is carried out to the measuring-signal compensated through over recovery and geometrical factor, obtains pulse radio-acoustic method space charge measurement signal V under frequency domain _s(ω, r);

The signal set after decay and dispersion compensation is V _s(ω, r) G (ω, r), carries out inverse Fourier transform to it, obtains the signal under time domain.

2. space charge measurement signal attenuation as claimed in claim 1 and the compensation method of dispersion factor, is characterized in that, described frequency-region signal V (ω, a) and V (ω, b) be respectively:

In formula | V (ω, a) | with | V (ω, b) | be the frequency domain amplitude function of measuring-signal, with for frequency domain phase function.

3. space charge measurement signal attenuation as claimed in claim 2 and the compensation method of dispersion factor, it is characterized in that, described attenuation coefficient α (ω) and abbe number β (ω) are respectively:

。

4. space charge measurement signal attenuation as claimed in claim 3 and the compensation method of dispersion factor, it is characterized in that, according to the communication process of acoustic signals in insulating medium, the transport function G (ω) of any r place signal attenuation and dispersion compensation is:

。

5. space charge measurement signal attenuation as claimed in claim 4 and the compensation method of dispersion factor, it is characterized in that, described transport function can be used for the compensation of decay and dispersion process in acoustic signals communication process under frequency domain, to pulse radio-acoustic method space charge measurement signal V under frequency domain _s(ω, r), according to convolution theorem, carries out decaying and signal after dispersion compensation is V _s(ω, r) G (ω, r), carries out inverse Fourier transform to it, obtains the signal under time domain.