Research On Phase Characteristics Test Technology Of Data Collector Based On Sine Wave

The data collector is the key equipment in the digitization of seismic observation.The technical performance of the data collector has an important impact on the acquisition of high-quality observation data.Amplitude-frequency characteristics have been common in practical testing,while phase-frequency characteristics are difficult to test,but it is very important to understand the impact of data quality.The difficulty of phase-frequency characteristic testing is that the digital signal is output after storage,processing and formatting.The additional delay caused by these processes is uncertain,which makes the traditional input-output method can not be used.Therefore,starting from the frequency spectrum of the signal,the FFT analysis method can accurately obtain the initial phase of the output signal sequence,and the phase-frequency characteristics can be analyzed by the relative phase relationship before and after input.First of all,we understand the internal structure of the data collector and the signal processing flow of the data collector.The system characteristics of the data collector are mainly related to the internal digital FIR filter,including the minimum phase FIR filter and the linear phase FIR filter.After understanding the phase-frequency characteristics of the two kinds of filters and the influence of timing on the phase characteristics of the digital filter,it provides a basis for the subsequent method of deducting the group delay,and also deepens the cognition of the relative phase relationship obtained during data processing.For example,the existence of integer 2?jumps between the two frequency points has the function of identification and correction.According to the monotonicity of the theoretical phase characteristics,the jump points of the relative phase characteristics are corrected.Secondly,there is a widespread truncation effect in the process of digital signal processing,which leads to spectrum leakage and errors caused by data changes.Therefore,the all-phase FFT method and the periodic FFT method are used,and the all-phase FFT method solves the influence of the truncation effect,while the periodic FFT method truncates the signal sequence with integer period length when the data is truncated,which avoids the truncation effect.The relative phase relationship is successfully obtained by using the all-phase FFT method and the periodic FFT method.The slope of the relative phase relation is related to the group delay,and the maximum impulse response of the filter reflects the theoretical delay of the filter.We compare that only when the group delay is 0,can we obtain the phase characteristics of the filter under the action of timing.However,the deviation of timing will also lead to different group delay,so we will use data timing to avoid the deviation of test phase characteristics caused by different group delay.Finally,we verify the feasibility of all-phase FFT method and periodic FFT method through practical tests.Within the allowable error,the phase-frequency characteristics of the data collector restored by the measured data are the same as the theoretical characteristics.Combined with the test method,the source of error is analyzed,and the improvement scheme is put forward.