The present invention relates to a method for monitoring a signal having a multi-band frequency, and more particularly, to a method for monitoring a signal having a multi-band frequency capable of effectively and precisely monitoring signals having various frequency bands from a low frequency band generated in a facility such as building up to a high frequency band.
Generally, a state monitoring system of a machine system or a health monitoring system of a building has used several signal interpreting methods in order to diagnose the machine system and the building.
For example, a fast-Fourier transform (FFT) interpreting method or an application interpreting method based on the FFT analyzing method has been universally used in the state monitoring system of the machine system or the health monitoring system of the building.
In order to use the FFT interpreting method, it is an important factor to determine an entire frequency band of interest and a frequency resolution.
Since a maximum ratio between revolutions per minute (RPMs) of input and output terminals of a gear transmission and an accelerator/decelerator included in the machine system may be 100 or more, it is inevitable to select a wide frequency band.
Meanwhile, since behavior of a low speed region is very important, a high resolution of a low speed frequency band is simultaneously required. For example, in the case of the building, a natural frequency is mainly within 1 Hz and disturbance of wind and earthquake becomes about up to 100 Hz, and thus, interpretation in a wide frequency band is required in the building.
In order to perform a wide band high resolution frequency analysis, data sampled at a high speed over a long period of time should be acquired, and integrated FFT should be performed on the acquired data.
That is, since an entire interpretation frequency band corresponds a half of a sampling rate, when the entire frequency band is large, the sampling rate cannot but be large. In addition, since the high resolution corresponds to an inverse number of an entire measurement time, measurement for a long period of time is required in order to obtain the high resolution, and a capacity of a storage for storing related data therein cannot but become large.
Therefore, an amount of data sampled for a long period of time is vast, such that a huge amount of calculation is required in the case in which the FFT is performed on the vast amount of data at the same time, which is very disadvantageous in terms of real-time monitoring.
For example, in an actual structural health monitoring system (SHM), the FFT may be performed on numerous data (about 260,000 data) measured at a sampling rate of about 200 Hz for about 20 minutes.
Therefore, in the case in which an amount of data frequency-sampled for a long period of time is vast, an amount of calculation is very large and a size of one set of data is vast, such that it is difficult to manage a database, and a time interval between records for managing the data is very large, such that it is difficult to analyze a tendency.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.