Patent ID: 7010974

Claim:
A method for measuring a fill level in accordance with the running time principle, having a fill level measuring device with an ultrasonic sensor consisting of a piezoelectric element in a housing for transmitting and receiving ultrasound, the method comprising the steps of: performing a repeated check of a resonance frequency of the ultrasonic sensor in the course of which the ultrasonic sensor is briefly excited to oscillate, following the excitation a signal received by the ultrasonic sensor is picked up, and the actual resonance frequency of the ultrasonic sensor is determined by means of the received signal, the received signal is digitized and supplied to a digital signal processor, a Fourier transformation of the digitized received signal is performed in the signal processor, a maximum of the Fourier-transformed received signal is determined as a function of the frequency, and a frequency at which the maximum occurs is stored as the actual resonance frequency; and exciting the ultrasonic sensor during measuring operations by the digital signal processor by means of the last determined actual resonance frequency for an as high as possible transmission output of the signal, and the transmitted ultrasonic signals are reflected after a running time which is a function of the fill level and the echo signals from the fill level are received by the ultrasonic sensor.