Signal processing method, signal processing device, and monitoring system

A signal processing method for causing a processor to execute a process, the signal processing method comprising:

• a sensor placement step of mounting a first sensor and a second sensor on an object including a motor, the first sensor and the second sensor being configured to detect a first acceleration of a first axis and a second acceleration of a second axis generated by a vibration of the object, respectively;
• and
• executing on the processor the steps of:
• a measurement data acquisition step of acquiring first measurement data based on a signal output from the first sensor and second measurement data based on a signal output from the second sensor;
• a Lissajous figure generation step of generating a Lissajous figure based on the first measurement data and the second measurement data;
• a polar coordinate transformation step of transforming coordinates of each point in the Lissajous figure into polar coordinates and generating time series data of a first angle which is an angle formed between the first axis and a straight line, the straight line being obtained by projecting a straight line passing through an origin and each point in the Lissajous figure onto a plane including the first axis and the second axis;
• a first angle maximum peak intensity calculation step of executing frequency analysis on the time series data of the first angle and calculating a first maximum peak intensity which is a maximum peak intensity in a first frequency spectrum obtained by the frequency analysis;
• and
• a state determination step of determining whether the object is operating abnormally by comparing the first maximum peak intensity with a first threshold value.