Technical Overview

In order to solve the problem of low real-time calculation accuracy of dynamic signal frequency and amplitude,The East proposedYLS high-precision frequency amplitude calculationsquarelawThis technology is a technique for precise frequency and amplitude measurement of dynamic signals, which breaks through the limitations of general dynamic signal analyzersFFT accuracy limitationThe difficult problemThe software algorithm accuracy can reach decimal 15~16 bit accuracy, the frequency accuracy of the actual measurement system combining software and hardware can reach decimal 8-bit accuracy，this methodCompared to traditional algorithmsImproved accuracy了6~7 orders of magnitude.

The factors that affect the accuracy of frequency testing mainly lie in two aspects: hardware clock source and software algorithm. This article only discusses the impact of software algorithms on frequency accuracy.

1、 Industry pain points: problems with traditional frequency calculation

The time-domain waveform of a general virtual instrument after ADC is usually usedFFTConduct frequency spectrum analysis to obtain results such as frequency and amplitude. If the signal sampling frequency is SF and the number of FFT calculation points is N, the frequency resolution is df=SF/N, and the frequency error range is ± 0.5df. When the actual signal frequency is not an integer multiple of the frequency resolution, spectrum leakage will occur, and the amplitude error range is0~36.3%.

To improve amplitude accuracy, windowing or smoothing methods are often used, but these methods can only improve amplitude accuracy to a certain extent, while sacrificing frequency accuracy.

To improve frequency accuracy, it is often necessary to increase the number of analysis points N or useZoom FFTThese refinement methods require more analysis points and are difficult to achieve real-time computation, and cannot guarantee improved amplitude accuracy. Therefore, it is an international challenge to enable virtual instruments to obtain high-precision frequency and amplitude in real time.

From the specific accuracy indicators, the frequency and amplitude accuracy of virtual instruments generally reach 3 to 5 decimal digits,It can only achieve a precision of 6 bits, and the calculation and analysis are very complex and time-consuming.

2、 Solution: ProposedYLS high-precision frequency amplitude calculation algorithm

YLS high-precision frequency amplitude calculation algorithmIt was proposed by the EastThe high-precision frequency meter and amplitude meter method is a special method that combines time-domain and frequency-domain calculations. Based on the FFT calculation results, it is further optimized and iteratively calculated to accurately calculate the frequency, amplitude, and initial phase of several spectral peaks in the spectrumThe algorithm process is shown in the figure1shown.

Figure 1 Basic Parameters of Dynamic SignalYLSexact algorithmflowchart

Without considering hardware acquisition errors, using only 1024 points of data for fast real-time calculations can achieve decimal 12-14 bit precision，And foreign instruments are usedofConventional methods can only achieve 6~7-digit decimal precision，It can be seen that this method improves accuracy by 6~7 orders of magnitude.image2To use the sine signal generated by the virtual signal generator of Dongfang Institute and verify the accuracy of the YLS algorithm, the signal frequency is set to 123.456789012345 Hz,Set the amplitude to 123.456789012345 mV， Figure 3 shows the use of DongfangYLS high-precision frequency amplitudeComparing Figure 2 and Figure 3, it can be seen that the algorithm can recognize the frequency and amplitude in real-time,YLS high-precision frequency amplitudeThe frequency and amplitude accuracy of the algorithm can reach 12Position.

Figure 2 Simulate the frequency and amplitude of the signal generated by the signal source

Figure 3 YLSThe frequency and amplitude displayed by high-precision frequency amplitude calculation software

Due to the fact that the accuracy of YLS algorithm is much higher than the measurement accuracy of hardware system, the natural frequency error and amplitude error of hardware system can be accurately measured in advance through standard signal source and YLS algorithm, and then the frequency and amplitude results can be corrected online during real-time measurement process. The implementation process is shown in the figure4As shown, this method can increase the frequency measurement accuracy of the instrument from 10 to 10 without using an external clock reference-5Or 10-6The scale has been increased to 10-8Increase by 2-3An order of magnitude.

image4 Hardware frequency amplitude calibration process based on YLS algorithm

3、 Actual test effect

3.1Expert review results

On November 25, 2012, by AVIC304The test report conducted by a testing team consisting of six experts from the research institute, the Chinese Academy of Metrology, and the Beijing Institute of Metrology and Testing Science shows that (the following is an excerpt from the test report):

1.YLSHigh precision frequency measurement technology:

The error range of the software algorithm is1×10-12~1×10-14The typical value is4×10-14The measurement error range of the hardware system is1×10-8,The typical value is6×10-10And conventionalFFTThe measurement error range of the method is1×10-4 ~ 4×10-3.

2.YLSHigh precision amplitude measurement technology:

The error range of the software algorithm is1×10-12~1×10-14The typical value is5×10-14The measurement error range of the hardware system is1×10-3,The typical value is7×10-4. And conventionalFFTThe measurement error range of the method is 8×10-2 ~ 3×10-1.

3. Frequency amplitude calibration technology is used for a certain acquisition instrument abroad:

Frequency error is caused by6×10-7 ~2×10-5Raise to9×10-8Within, maximum improvement1105Double; The amplitude error is caused by3×10-3Raise to2×10-4Within, maximum improvement73Twice.

4. Frequency amplitude calibration technology for domestic useINVCollector:

Frequency error is caused by3×10-7~4×10-6Raise to4×10-8Within, maximum improvement99Double; The amplitude error is caused by5×10-3 Raise to7×10-4Within, maximum improvement368Twice.

3.2 Comparison of Accuracy between Frequency and Amplitude Software Algorithms

Using a foreign countryThe instrument was compared with the precision algorithm of Dongfang Institute, and the results are shown in the figure5And the picture6As shown in the figure, the horizontal axis in the two graphs represents the sampling frequency of the signal, and the vertical axis represents the measurement accuracy. The meaning expressed in the two graphs is to compare the accuracy of analyzing a signal with a fixed amplitude and frequency using different sampling frequencies. The number of analysis points is 1 for both graphs024Point. From Figure 5 and Figure 6, it can be seen that the accuracy of the high-precision frequency and amplitude algorithm proposed by Dongfang changes very little with the sampling frequency, while the frequency and amplitude accuracy of the comparison manufacturer rapidly decreases with the increase of the sampling frequency. Because the number of sampling points remains unchanged, the signal period collected after the sampling frequency increases decreases, resulting in a decrease in the accuracy of traditional FFT based algorithms, while Dongfang's high-precision algorithm is greatly affected.

image5 Comparison of Accuracy between Dongfang Institute Algorithm and Foreign Manufacturer Frequency Algorithm

image6 Comparison of Accuracy between Dongfang's Algorithm and Foreign Manufacturers' Amplitude Algorithm

3.3 Comparison of Measurement Accuracy between Software and Hardware Systems

Dongfang Institute System and International for the Application of High Precision Frequency Amplitude TechnologyThree instruments were compared and tested, and the results are shown in the figure7As shown in Figure 7, the horizontal axis represents signal frequency and the vertical axis represents measurement accuracy. The meaning expressed in Figure 7 is to perform frequency and amplitude analysis on signals with different frequencies using a fixed sampling frequency and number of analysis points. As the signal frequency changes, the analysis accuracy of the high-precision algorithm of Dongfang Institute remains basically unchanged, while the accuracy of the other three systems abroad is greatly affected by the signal frequency. The fundamental reason is that the sampling frequency and number of analysis points remain unchanged, and the lower the signal frequency, the fewer signal cycles are collected. The accuracy based on FFT algorithm is lower, while the high-precision algorithm of Dongfang Institute is basically not affected.

image7Oriental Institute System and InternationalComparison chart of manufacturer frequency measurement accuracy

4、 Application Cases

The Hong Kong Zhuhai Macao Bridge is a long cross sea bridge and has been rated as one of the "Seven Wonders of the Modern World" by foreign media. It represents that China's bridge construction capacity has reached an advanced levellevelThe total length of the Hong Kong Zhuhai Macao Bridge55 kilometers, yesA cross sea passage that integrates a bridge, a double decker island, and a tunnel.

Construction environment of Hong Kong Zhuhai Macao Bridgeveryadverse.manyKey engineering technologiesLack of experienceFor example, the immersed tube tunnel technology, the Hong Kong Zhuhai Macao Bridge with a total length of about 55 kilometers, has nearly 30 kilometers located underwater, with a project volume ofhugeBig,And there are many issues that need to be addressedTechnical difficulties. Europe has a century old immersed tube tunnel technology, but the core technology is controlled by a few countries such as the Netherlands and GermanycountryIt's technologyofOffering sky high technical consulting feesIn the endweYou can only walk independently on your ownThe path of innovation.

InThe most important aspect of engineering——mostThe next section of immersed tubeInstallation ofDuring the process, high-precision sensors were used to communicate with Dongfang InstituteYLS high-precision frequency amplitudeAlgorithm to achieve precise underwater testing of immersed tubes, and the foreign party has previously offered a price of 1 for the underwater precision measurement and control system0~15Billion RMB. The design deviation target for immersed tube installation is10cmAnd ultimately achieved one end deviation0.8mmDeviation on the other end2.6mmAccurate installation and successful completion of the immersed tube installation task, Dongfang SoftwareHong Kong Zhuhai Bridge immersed tubeThe image in docking posture monitoring is shown in Figure 8.

image8 Hong Kong Zhuhai Bridge immersed tubeInterface attitude monitoring software screen of Dongfang Institute