Method for determining fill level on the basis of travel time of a high-frequency measuring signal

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 (SHF), which, by means of a transformation method with a certain transformation factor (KT), is transformed into a lower frequency, intermediate-frequency signal (SZF), comprising the steps of:

• producing the transformation factor (KT) and obtained from a difference frequency (fSweep), or a difference time (tSweep), of a difference signal (SSweep) between a pulse repetition signal (SPRF) having a pulse repetition frequency (fPRF), and a sampling signal (SSample) having a sampling frequency (fSample);
• altering the pulse repetition frequency (fPRF), and/or the sampling frequency (fSample), on the basis of a control with control variable (c_var), through a corresponding control algorithm, such that the difference frequency (fSweep) is controlled to a desired value (fSweep—setpoint) of the difference frequency, or the difference time (tSweep) is controlled to a desired value (tSweep—setpoint) of the difference time;
• determining a gradient (grad) between at least two values of the difference frequency (fSweep), or between at least two values of the difference time (tSweep), as a function of the control variable (c_var);
• and
• determining, on the basis of the gradient (grad) and the difference frequency (fSweep), or difference time (tSweep), at a set control variable (c_var), an operating point (OP) of the control, and the control algorithm is adjusted accordingly thereto.