Patent ID: 8446287

Claim:
A method for monitoring a loose part in a fluid flow path using a plurality of sensors which are placed in predetermined positions on a wall defining the fluid flow path for detecting information on sound or vibration, said plurality of sensors being configured to output a group of detection signals upon detection of the information, said method comprising: a first false signal determination step comprising comparing a pattern of the order and difference in time of output of the group of detection signals from the plurality of sensors with reference patterns to determine whether or not the group of signals are false signals; a second false signal determination step comprising comparing a rising gradient of one detection signal which is selected from the group of detection signals and which has been output early with that of another detection signal which is selected from the group of detection signals and which has been output late to determine whether or not the group of signals are false signals; a third false signal determination step comprising obtaining a damping time of the waveform of one detection signal which is selected from the group of detection signals and determining whether or not the selected detection signal is derived from an impact and thereby determining whether or not the group of signals are false signals; a fourth false signal determination step comprising comparing the frequency spectra of the group of detection signals to determine whether or not the group of signals are false signals; and a fifth false signal determination step comprising comparing the rising gradients, damping times, and frequency spectra of the group of detection signals obtained in the second to fourth false signal determination steps with those of known detection signals determined as false signals in the past, and determining whether or not there are any detection signals in the group of detection signals that have the same properties as the known detection signals, thereby to determine whether or not the group of signals are false signals.