Patent ID: 6438500
Filing Date: 2002-08-20
Classification: B41J,G01F

Abstract:
A method of detecting absence of a product in a reservoir comprising:a transmission step of transmitting a signal affected by the presence of the product in the reservoir; and detecting the presence of the signal amongst a set of signals, the signal having an occurrence duration TON, said detecting step comprising: a discrimination step, during which the signal is discriminated from the set of signals, and an output signal is delivered, the level of which represents the result of the discrimination of the signal from the set of signals; a sampling step, during which the level thus obtained is sampled in In signal samples spread over a sampling duration greater than a repetition period T; a correlation step, during which, to each sample of rank i varying from 1 to In, a state value B(i) representing the level of the sample is mapped and, during at least part of the sampling duration, a true correlation value SR is calculated, by summing, for each pair of samples of ranks i and i+Z, the instantaneous value of correlation between the state value B(i) and the state value B(i+1) the samples of ranks i and i+Z being located at instants displaced by a period T, Z being the number of samples taken during a period T of the signal to be detected; a rate calculation step, during which the rate &rgr; of samples, whose level represents the presence of the signal, is measured over at least part of the sampling duration, the rate &rgr; being the ratio of the number of samples whose level represents the presence of the signal to be detected, over the total number of samples in the part of the sampling duration; a theoretical evaluation step, during which the determination of at least one theoretical mean value is carried out; and a decision step, during which the true correlation value SR is compared with each theoretical mean value, and the presence or absence of the signal to be detected is deduced from the result of this comparison.