CN104880608A - Cable dielectric loss sweep frequency test method based on correlational analysis method - Google Patents

Abstract

A cable dielectric loss sweep frequency test method based on a correlational analysis method of the present invention belongs to the dielectric loss measurement correlation technique field. The method adopts a dielectric loss measurement algorithm based on the correlational analysis method and a sweep frequency signal generating technology based on a DDS technology to manufacture a sweep frequency module firstly, and the sweep frequency module is composed of a keyboard input module, a liquid crystal display module, a single-chip microcomputer main control module, a sweep frequency signal generating chip, an crystal oscillator and a low pass filter circuit. The keyboard input module and the liquid crystal display module are connected with the single-chip microcomputer main control module, and the single-chip microcomputer main control module receives an artificial input value and displays the operation state of a system, thereby realizing a man-machine interaction function. According to the present invention, by using the dielectric loss measurement algorithm based on the correlational analysis method, the accurate digital measurement is realized, the defects, such as the tedious and time-consuming fixed-frequency measurement, the frequency interference, etc., are overcome, and the cable dielectric loss sweep frequency test method based on the correlational analysis method of the present invention is high in cost performance and strong in practicality.

Description

Based on the cable dielectric loss sweep check method of relevant function method

Technical field

The invention belongs to dielectric loss measurement correlative technology field, relate to a kind of cable dielectric loss Frequency Sweeping Method based on relevant function method.

Background technology

Along with the fast development of electronic technology and state inspection, the detection method of dielectric loss on-line checkingi becomes varied.On the basis of traditional dielectric loss detection method, combined digital signal treatment technology, new dielectric loss detection method is more intelligent and accurate.Mostly domestic dielectric dissipation factor detecting instrument is to measure under fixed frequency, and fixed frequency is measured loaded down with trivial details, time-consuming, and directly perceived, and the resonance phenomena between measurement point and the catastrophe point of network characteristic can be left in the basket often.Thus, detection is accurate not.Such as Zero-cross comparator method is due to some other error components such as humorous wave interference, sometimes very large on the impact of measurement result, thus the application of this kind of method in high-precision phase position difference detects is restricted.When adopting DFT algorithm, if sampling number is less, the truncation error of window and fence effect affect very large.

Summary of the invention

The defect that the present invention exists to overcome prior art, has invented a kind of cable dielectric loss Frequency Sweeping Method based on relevant function method.The method adopts the dielectric loss measurement algorithm based on relevant function method and the swept-frequency signal generation technique based on DDS technology, by scan module, current amplifier, AD conversion module, and adopt the dielectric loss measurement algorithm based on relevant function method, achieve more exact figureization to measure, and overcome the defects such as loaded down with trivial details, time-consuming, the frequency interferences that fixed frequency measures.

The technical solution used in the present invention is the cable dielectric loss sweep check method based on relevant function method, it is characterized in that, the method adopts the dielectric loss measurement algorithm based on relevant function method and the swept-frequency signal generation technique based on DDS technology; Concrete steps of the present invention are as follows:

(1) scan module is made

Scan module is made up of input through keyboard module, LCD MODULE, single-chip microcomputer main control module, swept-frequency signal generation chip, crystal oscillator and low-pass filter circuit; Input through keyboard module, LCD MODULE are connected with single-chip microcomputer main control module, single-chip microcomputer main control module receives artificial input value and display system running status, thus realizes the function of man-machine interaction; Again single-chip microcomputer main control module is connected with swept-frequency signal generation chip, controls frequency and the phase place of swept-frequency signal; The external crystal oscillator of swept-frequency signal generation chip, provides clock signal by crystal oscillator; Swept-frequency signal generation chip connects low-pass filter circuit simultaneously, thus obtains clean swept-frequency signal;

(2) frequency sweep control word is exported to the frequency of swept-frequency signal generation chip controls output signal by single-chip microcomputer main control module, and wherein frequency control word computation process is as follows:

System output frequency is:

f _out＝(f _r×W)/2 ³²(1)

Wherein, f _outfor output frequency, f _rfor reference clock frequency, W is corresponding frequency decade control word;

The computing formula of frequency control word is:

W＝2 ³²×f _out/f _r(2)

Owing to adopting 32 phase accumulators, then outputing signal resolution is:

Δf _out＝f _r/2 ³²(3)

(3) swept-frequency signal that scan module exports is carried out voltage amplification; Voltage amplifier in the present invention is a complex type amplifier, and by DC power supply, the voltage-drop loading that voltage amplifier exports is in tested cable; Again the current signal of tested cable is amplified, afterwards by the voltage of AD conversion module sampling cable and the current signal after amplifying;

(4) flow to algorithm process unit to the voltage and current signal of previous step sampling to carry out calculating based on the dielectric loss of relevant function method; Concrete computation process is as follows:

Voltage and current expression:

$\left\{\begin{array}{c}u\left(t\right)=U_m\sin \left(\mathrm{\ωt}\right)\\ i\left(t\right)=I_m\sin (\mathrm{\ωt}+\mathrm{\θ})\end{array}\right.---\left(4\right)$

Wherein, u (t) and i (t) is respectively voltage and electric current, U _mand I _mbe respectively voltage and current amplitude, ω is the frequency of electric current and voltage, and θ is the phase differential of electric current and voltage;

Waveform is without time delay, and its voltage autocorrelation function is:

$\begin{array}{c}{R}_u\left(0\right)={\∫}_{-\∞}^{+\∞}u\left(t\right)u(t-\mathrm{\τ})\mathrm{d\τ}=\frac{1}{T}{\∫}_0^T{u}^2\left(t\right)\mathrm{dt}\\ ={\∫}_0^T{\left(U_m\sin \left(\mathrm{\ωt}\right)\right)}^2\mathrm{dt}=\frac{{U_m}^2}{2}=U_r^2\end{array}---\left(5\right)$

In formula, T is the primitive period, R _u(0) be voltage auto-correlation, τ is sampled time skew, U _rfor voltage effective value;

In like manner, electric current autocorrelation function is:

$R_i\left(0\right)=\frac{{I_m}^2}{2}=I_r^2---\left(6\right)$

In formula, R _i(0) be electric current auto-correlation, I _rfor current effective value;

Electric current and voltage cross correlation function are:

$\begin{array}{c}{R}_{\mathrm{iu}}\left(0\right)={\∫}_0^{T}i\left(t\right)u\left(t\right)\mathrm{dt}={\∫}_0^T{I}_m\sin (\mathrm{\ωt}+\mathrm{\θ})\·U_m\sin \left(\mathrm{\ωt}\right)\mathrm{dt}\\ =\frac{U_m{I}_m}{2}\cos \mathrm{\θ}=I_r{U}_r\cos \mathrm{\θ}\end{array}---\left(7\right)$

Wherein, R _iu(0) be the cross-correlation of voltage and electric current; Then the angle of electric current and voltage is:

$\mathrm{\θ}=\arccos \frac{R_{\mathrm{iu}}\left(0\right)}{\sqrt{R_i\left(0\right)R_u\left(0\right)}}---\left(8\right)$

Dielectric loss angle is:

$\mathrm{\δ}=\frac{\mathrm{\π}}{2}-\mathrm{\θ}=\frac{\mathrm{\π}}{2}-\arccos \frac{R_{\mathrm{iu}}\left(0\right)}{\sqrt{R_i\left(0\right)R_u\left(0\right)}}---\left(9\right)$

(5) except fundamental signal, also there is direct current and high-order odd harmonic harmonic component in voltage to be measured, current signal, form interference to dielectric loss measurement, overcome these interference just needs to extract first-harmonic; The mode of wavelet multiresolution analysis is adopted to extract the fundametal compoment of signal; By judging the quality of wavelet basis function by the result of wavelet analysis method processing signals and the error of notional result, determine wavelet basis function thus; The present invention selects Daubechies 5 rank small echo (being called for short db5 small echo);

(6) sweep check of cable dielectric loss is carried out; Open system power supply, by input through keyboard swept frequency, start test, scan module produces swept-frequency signal, voltage amplifier carries out voltage amplification to swept-frequency signal, voltage-drop loading after amplification is in tested cable, the electric current of tested cable is sampled by AD conversion module after current amplifier amplifies, AD conversion module is sampled the voltage signal of tested cable simultaneously, the voltage and current signal of sampling is given algorithm process unit and is undertaken calculating based on the dielectric loss of relevant function method by algorithm process unit, and draw out dielectric loss spectrogram, complete shutdown system power supply to be tested.

The invention has the beneficial effects as follows that can realize high-precision swept-frequency signal exports, have certain load capacity, cost performance is high, practical.

Accompanying drawing explanation

Fig. 1 is the formation sketch of scan module.

Fig. 2 is wireline test wiring diagram, and wherein, 1 leads core for cable, and 2 is conductive fabric.

Fig. 3 is dielectric loss spectrogram, and abscissa axis represents frequency, and axis of ordinates represents dielectric loss value, and curve represents the variation tendency of dielectric loss with frequency of tested cable.

Embodiment

Describe specific embodiment of the invention in detail below in conjunction with technical scheme and accompanying drawing, Fig. 1 is the formation sketch of scan module.The present invention selects AD9850 and C8051F340 single-chip microcomputer to devise a scan module.This scan module is made up of input through keyboard module, LCD MODULE, single-chip microcomputer main control module, swept-frequency signal generation chip, crystal oscillator and low-pass filter circuit; Scan module can produce the frequency sweep of frequency range arbitrarily in 0.1Hz to 1kHz frequency range, under can realizing low frequency, high precision frequency sweep exports, its frequency resolution is 0.01Hz, and output LOW voltage is 2V, can realize exporting higher than the voltage of 100V by low-pass filtering and voltage amplification module.

Amplifying signal is loaded on cable, because the electric current by cable is very little, need to amplify electric current before AD sampling, signal after sampling gives algorithm process unit, carry out the digitized measurement based on relevant function method, thus obtain dielectric loss value, then measured value is depicted as dielectric loss spectrogram.

The concrete steps of cable dielectric loss sweep check method are as follows:

(1) scan module is manufactured

Select AD9850 as swept-frequency signal generation chip in scan module, external active crystal oscillator provides reference clock signal for AD9850.As shown in Figure 1, frequency sweep control word is exported to the frequency that AD9850 controls output signal by single-chip microcomputer C8051F340, power pins adds shunt capacitance elimination high-frequency harmonic, the signal that chip produces exports the swept-frequency signal meeting frequency requirement after low-pass filtering, low-pass filter circuit adopts the oval filtering circuit in 5 rank, single-chip microcomputer C8051F340 connects keyboard load module and LCD MODULE simultaneously, receives artificial input value and display system running status, thus realizes the function of man-machine interaction;

According to design objective, frequency resolution is 0.01Hz, calculates reference clock frequency f by formula (1) (2) (3) _r<42.94MHz, gets f _rfor 40MHz.

This scan module can produce the frequency sweep of frequency range arbitrarily in 0.1Hz to 1kHz frequency range, and under can realizing low frequency, high precision frequency sweep exports, and its frequency resolution is 0.01Hz

(2) swept-frequency signal that scan module exports is carried out voltage amplification; Voltage amplifier in the present invention is by DC power supply, and adopt OP07 and PA340 to form complex type amplifier, such input offset voltage is just determined by prime amplifier OP07.By setting the closed-loop gain of PA340 in this power supply, OP07 and PA340 connects, and reaches satisfactory interchange and exports.In initial designs, AD9850 output voltage amplitude is 2V, and the interchange that can realize positive and negative more than 100V after voltage amplification module exports.

The voltage-drop loading that voltage amplifier exports is in tested cable; Again the current signal of tested cable is amplified, afterwards by the voltage of AD conversion module sampling cable and the current signal after amplifying; AD sampling module selects 24 high-precision A/D conversion chip ADS1241, and crystal oscillator is 2.4576MHz, and adopt 4 line modes to be connected with single-chip microcomputer, supply voltage is 3.3V, and reference voltage is 2.5V.

(3) carry out calculating based on the dielectric loss of relevant function method to the voltage and current signal of above-mentioned sampling, concrete computation process is undertaken by formula (4) ~ (9);

(4) owing to also there is direct current and high-order odd harmonic harmonic component in voltage to be measured, current signal except fundamental signal, form interference to dielectric loss measurement, overcome these interference just needs to extract first-harmonic; The mode of wavelet multiresolution analysis is adopted to extract the fundametal compoment of signal.We are mainly by judging the quality of wavelet basis function by the result of wavelet analysis method processing signals and the error of notional result at present, determine wavelet basis function thus.The present invention selects Daubechies 5 rank small echo.

(5) carry out the sweep check of cable dielectric loss by above-mentioned steps, and draw out dielectric loss spectrogram.Wireline test wiring diagram as shown in Figure 2, adopts conductive fabric to be wound around to tested cable, is formed and artificially arrange screen layer.Open system power supply during test, by input through keyboard swept frequency, start test, scan module produces swept-frequency signal, voltage amplifier carries out voltage amplification to swept-frequency signal, voltage-drop loading after amplification is in tested cable, the electric current of tested cable is sampled by AD conversion module after current amplifier amplifies, AD conversion module is sampled the voltage signal of tested cable simultaneously, the voltage and current signal of sampling is given algorithm process unit and is undertaken calculating based on the dielectric loss of relevant function method by algorithm process unit, and draw out dielectric loss spectrogram, complete shutdown system power supply to be tested.

As shown in Figure 3, in figure, horizontal ordinate is test frequency to the dielectric loss spectrogram that the present invention draws, and ordinate is for recording dielectric loss, and curve reflects the variation tendency of dielectric loss with frequency, can find out, along with the increase of frequency, dielectric loss totally presents the trend diminished.

Claims (1)

1. based on a cable dielectric loss sweep check method for relevant function method, it is characterized in that, the method adopts the dielectric loss measurement algorithm based on relevant function method and the swept-frequency signal generation technique based on DDS technology; The concrete steps of sweep check method are as follows:

(1) scan module is made

Scan module is made up of input through keyboard module, LCD MODULE, single-chip microcomputer main control module, swept-frequency signal generation chip, crystal oscillator and low-pass filter circuit; Input through keyboard module, LCD MODULE are connected with single-chip microcomputer main control module, single-chip microcomputer main control module receives artificial input value and display system running status, thus realizes the function of man-machine interaction; Again single-chip microcomputer main control module is connected with swept-frequency signal generation chip, controls frequency and the phase place of swept-frequency signal; The external crystal oscillator of swept-frequency signal generation chip, provides clock signal by crystal oscillator; Swept-frequency signal generation chip connects low-pass filter circuit simultaneously, thus obtains clean swept-frequency signal;

(2) frequency sweep control word is exported to the frequency of swept-frequency signal generation chip controls output signal by single-chip microcomputer main control module, and wherein frequency control word computation process is as follows:

System output frequency is:

f _out＝(f _r×W)/2 ³²(1)

Wherein, f _outfor output frequency, f _rfor reference clock frequency, W is corresponding frequency decade control word;

The computing formula of frequency control word is:

W＝2 ³²×f _out/f _r(2)

Owing to adopting 32 phase accumulators, then outputing signal resolution is:

Δf _out＝f _r/2 ³²(3)

When frequency resolution is 0.01Hz, calculate reference clock frequency f _r<42.94MHz, chooses f _rfor 40MHz;

(3) swept-frequency signal that scan module exports is carried out voltage amplification; Voltage amplifier in the present invention is a complex type amplifier, and by DC power supply, the voltage-drop loading that voltage amplifier exports is in tested cable; Again the current signal of tested cable is amplified, afterwards by the voltage of AD conversion module sampling cable and the current signal after amplifying;

(4) flow to algorithm process unit to the voltage and current signal of previous step sampling to carry out calculating based on the dielectric loss of relevant function method; Concrete computation process is as follows:

Voltage and current expression:

$\left\{\begin{array}{c}u\left(t\right)=U_m\sin \left(\mathrm{\&omega;t}\right)\\ i\left(t\right)=I_m\sin (\mathrm{\&omega;t}+\mathrm{\&theta;})\end{array}\right.---\left(4\right)$

Wherein, u (t) and i (t) is respectively voltage and electric current, U _mand I _mbe respectively voltage and current amplitude, ω is the frequency of electric current and voltage, and θ is the phase differential of electric current and voltage;

Waveform is without time delay, and its voltage autocorrelation function is:

$\begin{array}{c}{R}_u\left(0\right)={\&Integral;}_{-\&infin;}^{+\&infin;}u\left(t\right)u(t-\mathrm{\&tau;})\mathrm{d\&tau;}=\frac{1}{T}{\&Integral;}_0^T{u}^2\left(t\right)\mathrm{dt}\\ ={\&Integral;}_0^T{\left(U_m\sin \left(\mathrm{\&omega;t}\right)\right)}^2\mathrm{dt}=\frac{{U_m}^2}{2}=U_r^2\end{array}---\left(5\right)$

In formula, T is the primitive period, R _u(0) be voltage auto-correlation, τ is sampled time skew, U _rfor voltage effective value;

In like manner, electric current autocorrelation function is:

$R_i\left(0\right)=\frac{{I_m}^2}{2}=I_r^2---\left(6\right)$

In formula, R _i(0) be electric current auto-correlation, I _rfor current effective value;

Electric current and voltage cross correlation function are:

$\begin{array}{c}{R}_{\mathrm{iu}}\left(0\right)={\&Integral;}_0^{T}i\left(t\right)u\left(t\right)\mathrm{dt}={\&Integral;}_0^T{I}_m\sin (\mathrm{\&omega;t}+\mathrm{\&theta;})\&CenterDot;U_m\sin \left(\mathrm{\&omega;t}\right)\mathrm{dt}\\ =\frac{U_m{I}_m}{2}\cos \mathrm{\&theta;}=I_r{U}_r\cos \mathrm{\&theta;}\end{array}---\left(7\right)$

Wherein, R _iu(0) be the cross-correlation of voltage and electric current; Then the angle of electric current and voltage is:

$\mathrm{\&theta;}=\arccos \frac{R_{\mathrm{iu}}\left(0\right)}{\sqrt{R_i\left(0\right)R_u\left(0\right)}}---\left(8\right)$

Dielectric loss angle is:

$\mathrm{\&delta;}=\frac{\mathrm{\&pi;}}{2}-\mathrm{\&theta;}=\frac{\mathrm{\&pi;}}{2}-\arccos \frac{R_{\mathrm{iu}}\left(0\right)}{\sqrt{R_i\left(0\right)R_u\left(0\right)}}---\left(9\right)$

(5) except fundamental signal, also there is direct current and high-order odd harmonic harmonic component in voltage to be measured, current signal, form interference to dielectric loss measurement, overcome these interference just needs to extract first-harmonic; The mode of wavelet multiresolution analysis is adopted to extract the fundametal compoment of signal; By judging the quality of wavelet basis function by the result of wavelet analysis method processing signals and the error of notional result, determine wavelet basis function thus; The present invention selects Daubechies 5 rank small echo;

(6) sweep check of cable dielectric loss is carried out; Open system power supply, by input through keyboard swept frequency, start test, scan module produces swept-frequency signal, voltage amplifier carries out voltage amplification to swept-frequency signal, voltage-drop loading after amplification is in tested cable, the electric current of tested cable is sampled by AD conversion module after current amplifier amplifies, AD conversion module is sampled the voltage signal of tested cable simultaneously, the voltage and current signal of sampling is given algorithm process unit and is undertaken calculating based on the dielectric loss of relevant function method by algorithm process unit, and draw out dielectric loss spectrogram, complete shutdown system power supply to be tested.