Thermal flow sensor and method for operating same

A method for operating a thermal flow sensor, wherein the thermal flow sensor comprises at least one sensor element and an electronics unit, the method comprising:

• putting a measuring medium in thermal contact with the at least one sensor element and periodically heating the measuring medium via an AC voltage introduced into the at least one sensor element;
• simultaneously, detecting a maximum amplitude of a curve of a temperature and/or a phase shift between a curve of the AC voltage and a curve of the temperature;
• adjusting the detected maximum amplitude and/or the detected phase shift using calibration data;
• determining an isoline using the adjusted maximum amplitude and/or the adjusted phase shift based on a mathematical or physical model of the thermal flow sensor, wherein the isoline includes a plurality of value pairs of thermal parameters of the measuring medium, the value pairs being associated with the same maximum amplitude or the same phase shift;
• deriving at least one piece of measuring medium information from the isoline;
• and
• performing a flow measurement using the thermal flow sensor, wherein the at least one sensor element generates signal values, wherein the signal values are converted using the at least one piece of measuring medium information into measurement values of an effective flow velocity of the measuring medium.