Jeung T. Kim
Acoust. and Vib. Lab., Korea Res. Inst. of Standards and Sci., P.O. Box 3, Daedok Science Town, Daejon, Korea 305-606
An instantaneous frequency analysis is a technique to examine a signature for the rotating machinery if the signal has several transitions within a cycle. This paper discusses the conditions of existing negative frequency components in the instantaneous frequency. By using a simple signal that consists of two frequency components, the instantaneous frequency analysis is conducted while the amplitude ratio between two frequency components has been changed. The calculation shows that, depending on the amplitude ratio, the instantaneous frequencies have averaged, zero-valued, or negative components. It turns out that the negative-valued instantaneous frequencies, which have been regarded as the noise effect, are the consequence of the calculation process for the multisignal components. The criteria to show the condition of the negative values in instantaneous frequencies is given in terms of the relative amplitude ratio and the frequency difference. In this paper, a vibration signal monitored from a rotating machinery is also examined as an application example in order to show the existence of negative instantaneous frequencies components.