Measuring the phase response of a seismometer using superimposed sine signals.

The sine calibration can be used for measuring the phase response of a seismometer. However, it has two shortcomings: (1) Transient responses that cannot be used for data processing appear multiple times. This increases the time consumption of the calibration test. (2) Testers have to manually select the steady-state response waveform from the sine response waveform of each frequency. This makes it difficult to realize automatic data processing. In this article, we introduce a new method of measuring the phase responses using superimposed sine signals and use this method to measure the phase responses of two seismometers in the frequency range of 0.002 to 1 Hz. In the test, the transient response appears only once. Therefore, the time span of the response waveform that cannot be used for data processing is greatly reduced. Moreover, when we select the steady-state response waveform, it is only necessary to avoid the transient response at the beginning of the response waveform. Therefore, it is easier to realize automatic data processing. We measure the phase responses of the seismometers 20 times with this new method and find that the largest standard deviation is only 0.0143°. We compare the mean value of the results of the multiple tests with the result of the traditional sine calibration and find that the largest error is only 0.019°. This work demonstrates that this new method is not only very accurate but also overcomes the two shortcomings of the traditional sine calibration. [ABSTRACT FROM AUTHOR]