| 摘要 |
A method for a fill level measurement in accordance with the running time principle, which functions dependably over a long period of time, is provided, having a fill level measuring device with an ultrasonic sensor for transmitting and receiving ultrasound, wherein a repeated check of a resonance frequency of the ultrasonic sensor is performed, 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 in that 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, a frequency at which the maximum occurs is stored as the actual resonance frequency, and during measuring operations the ultrasonic sensor is excited by the digital signal processor by means of the last determined actual resonance frequency.
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