Patent ID: 7412337

Claim:
A method for determining the fill level (l) in a container on the basis of the travel time (t) of a high frequency measuring signal (S HF ), which, by means of a transformation method with a certain transformation factor (K T ), is transformed into a lower frequency, intermediate-frequency signal (S ZF ), comprising the steps of: producing the transformation factor (K T ) and obtained from a difference frequency (f Sweep ), or a difference time (t Sweep ), of a difference signal (S Sweep ) between a pulse repetition signal (S PRF ) having a pulse repetition frequency (f PRF ), and a sampling signal (S Sample ) having a sampling frequency (f Sample ); altering the pulse repetition frequency (f PRF ), and/or the sampling frequency (f Sample ), on the basis of a control with control variable (c_var), through a corresponding control algorithm, such that the difference frequency (f Sweep ) is controlled to a desired value (f Sweep — setpoint ) of the difference frequency, or the difference time (t Sweep ) is controlled to a desired value (t Sweep — setpoint ) of the difference time; determining a gradient (grad) between at least two values of the difference frequency (f Sweep ), or between at least two values of the difference time (t Sweep ), as a function of the control variable (c_var); and determining, on the basis of the gradient (grad) and the difference frequency (f Sweep ), or difference time (t Sweep ), at a set control variable (c_var), an operating point (OP) of the control, and the control algorithm is adjusted accordingly thereto.