Method for checking the proper functioning of a level indicator

A method for checking the proper functioning of a fill-level measuring device which determines the fill level of a fill substance in a container, the fill substance defining a substance, comprising the steps of:

• transmitting measuring signals toward the surface of the substance at which the measuring signals are reflected;
• performing a distance determination, at predetermined or selectable time intervals based on the travel time of the measuring signals;
• ascertaining a current wanted echo signal at a current fill level based on the current measured value curve;
• ascertaining an expected value for quality of a wanted echo signal at least one predetermined fill level;
• ascertaining a signal/noise ratio of a wanted echo signal to disturbance echo signals as the expected value for quality;
• predetermining a critical value of a minimum signal/noise ratio for the proper functioning of the fill-level measuring device;
• comparing the ascertained expected value for quality of the wanted echo signal at the predetermined fill level with a predetermined critical value for quality;
• and
• diagnosing an error condition, when the ascertained expected value falls below the predetermined critical value.