Method for determining the inner diameter of a surge pipe using a fill level measuring device

A method for determining a pipe inner diameter of a surge pipe, which, for measuring fill level of a fill substance located in a process space of a container, extends into the process space or is mounted alongside the container and connected with the process space, the method comprising:

• transmitting a first radar signal according to an FMCW principle with a first center frequency into the surge pipe and receiving a corresponding first received signal after reflection on a locationally fixed reference;
• generating a first intermediate frequency signal according to the FMCW principle based on the first transmitted signal and the first received signal and ascertaining a frequency of the first intermediate frequency signal;
• transmitting a second radar signal according to the FMCW principle into the surge pipe with a second center frequency, which differs from the first center frequency, and receiving a corresponding second received signal after reflection on the locationally fixed reference;
• generating a second intermediate frequency signal according to the FMCW principle based on the second transmitted signal and the second received signal and ascertaining a frequency of the second intermediate frequency signal;
• ascertaining the pipe inner diameter based on:
• the first center frequency, the second center frequency, the frequency of the intermediate frequency signal, and the frequency of the second intermediate frequency signal.