Patent attributes
A method for determining a process variable of a product in a tank based on a time delay of electromagnetic waves. The method further comprises forming a measurement signal comprising a sequence of values, each value representing a time correlation between a pulse of a reference signal and a reflected signal, sampling and digitizing this measurement signal to form a digital signal, identifying a time window of the digital signal including the surface echo peak, determining a relative time period between a reference time corresponding to the predefined reference and a beginning of the time window, time-to-frequency transforming the digital signal in the time window to obtain a phase spectrum, determining a relative phase shift of the spectrum and using the relative phase shift to calculate a corresponding time shift, and determining the time delay by adding the relative time period and the time shift.
