Patent ID: 7634387
Filing Date: 2009-12-15
Classification: H04B

Abstract:
1. A method of monitoring a signal which varies over time to determine an alarm condition, the method comprising: providing the signal as a stream of digital values; dividing the sample stream in to equal length pieces each containing a series of the values; using a microprocessor to apply a Fourier Transform (FT) algorithm to transform each piece of the stream into a three dimensional dataset including frequency domain amplitude, frequency and time; calculating a Frequency Envelope by taking the maxima over the time dimension for a period of time, leaving a two dimensional frequency domain amplitude vs frequency dataset; applying a constant delta additively or multiplicatively to each frequency amplitude element of the Frequency Envelope to adjust sensitivity thereof to provide a threshold; comparing a plurality of the frequency amplitude elements of the stream with the threshold and triggering the alarm condition in the event that the threshold is exceeded in any frequency amplitude element of the stream.