Patent ID: 7826309

Claim:
A method for measuring a fill level of a fill substance in a container and for monitoring at least one predetermined fill level (L MIN , L MAX ), using a fill level measuring device working according to a travel-time principle, comprising the steps of: sending, in each measuring cycle, transmission signals (S) toward the fill substance and receiving their echo signals (E); deriving an echo function from the echo signals (E) which represents an amplitude of the echo signals (E) as a function of travel-time (t) for determining the exceeding or falling beneath of the predetermined fill levels (L MIN , L MAX ); and determining a measure for the area under the echo function in a region (I, II) of particular travel-time (t MIN , t MAX ) to be expected for the predetermined fill level (L MIN , L MAX ) determining the fill level, based on the echo signals (E), according to a first evaluation, and based on the echo signals (E), according to a second evaluation independent of the first evaluation; and observing whether the fill level exceeds or falls beneath the predetermined fill level (L MIN , L MAX ) wherein: it is detected that the fill level exceeds the particular predetermined fill level (L MIN , L MAX ) when the measure exceeds a predetermined reference measure; it is detected that the fill level falls beneath the particular predetermined fill level (L MIN , L MAX ) when the measure falls beneath a predetermined reference measure, and said measure corresponds to an integral over the echo function in the region (I, II) of the particular travel-time (t MIN , t MAX ) to be expected for the predetermined fill level (L MIN , L MAX ).