关于random和broadband (multi-sine)应用的一点比较

xiejue1981

　　Multisine, sine or random generators can be used in conjunction with frequency analysers. Typically Fast
　　Fourier Transform (FFT) analysers are used for random and multisine signals and Single-Sine Correlation or Frequency
　　Response Analysers (FRA) are used for single-sine signals. The distortion is then normally of no importance. Therefore analysers are normally preferred instead of broadband r.m.s. voltmeters which, although fundamentally more accurate, are sensitive to distortion and other signals at frequencies differing from the measurement frequency. Measurement of coherence can be used to estimate whether or not the signal-to-noise ratio and the linearity of the transducers are within well-defined limits when spectral averaging is used. With random excitation and 64 averages a minimum coherence limit of 0,98 will ensure that the errors due to signal-to-noise ratio and linearity are less than 0,9 % for a dual channel  measurement. In rare cases, broadband excitation can, however, create unwanted (transverse) vibration or output signals at a measuring frequency due to non-linear behaviour of shaker or transducer at other frequencies.""