Sensor element with membrane and combined heating and temperature-measuring conductor paths

A method for determining at least one thermal property of a fluid medium, the method comprising:

• heating a membrane with a first electrical heating element that forms a conductor path arranged on the membrane,
• the membrane is connected to a frame by strips and is held by the frame,
• the membrane is surrounded by a defined volume of the fluid medium within a cover, and
• the cover ends flush with the frame, so that the cover and the frame form a flush surface;
• transferring heat from the membrane and the first electrical heating element to the fluid medium surrounding the membrane;
• transferring heat from the fluid medium to the frame, wherein the frame has a lower temperature than the membrane;
• determining temperatures of the membrane and the frame;
• regulating the temperature of the membrane by regulating an electrical power for heating the membrane;
• determining the thermal property of the fluid medium using by the electrical power that is used to regulate the temperature of the membrane and using a known temperature difference between the membrane and the frame;
• and
• regulating the temperature of the frame.