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波形的非线性失真度是评定振动台运动精度的一项重要技术指标,而目前国内外还没有直接测量波形频率低于2Hz的失真度仪,这就限制了低频标准振动台的使用范围,而这正是地震系统及其它一些低频测振系统共同关心的部分。本文提出的超低频波形失真度测量法,是应用FFT方法在频域上展示并量取各次谐波幅值,通过简单计算得出超低频失真度量值。我们已用该方法对中国计量科学院生产的垂直向低频标准振动台和水平向振动台作了频率低于2Hz的失真度量值测试,并获得结果。在国内首次扩大了该套振动装置的使用频率下限,为地震仪及低频测振仪的标定工作作出了贡献。该方法也适用于其它如机电转换装置及电信号发生、记录、转换装置的失真度量值测试。
The nonlinear distortion of the waveform is an important technical index for evaluating the motion accuracy of the vibration table. At present, there is no direct measurement of the distortion instrument whose waveform frequency is lower than 2Hz at home and abroad, which limits the use range of the low-frequency standard vibration table. This is exactly the common concern of seismic systems and other low frequency vibration measurement systems. In this paper, the ultra-low frequency waveform distortion measurement method is to use FFT method to display and measure the amplitude of each harmonic in the frequency domain, and obtain the ultra-low frequency distortion measure value through simple calculation. We have used this method to measure the distortion of frequencies below 2Hz for the vertical low-frequency standard vibrating table and horizontal vibrating table produced by China Academy of Metrology, and obtained the results. For the first time in China, the lower limit of the frequency of use of the vibrating device was increased, contributing to the calibration of seismometers and low-frequency vibrometers. This method is also applicable to other distortion measurement tests such as electromechanical transducers and electrical signal generating, recording and converting devices.