Low-cost weather sensor based on thermal impedance measurements

Two examples of self-controlled wind and weather sensors for everyday usage based on temperature-dependent resistors are described and the potential for further enhancing sensor properties like long-term stability, self-calibration and selectivity is discussed. To measure the velocity and direction of wind, three PTC elements are placed under a known angle to each other around a cylindrical flow body. Based on sensor models obtained by pre-operation measurements, the interesting properties are calculated from output voltages by an optimization procedure. Besides the measurement result itself, also its quality follows directly from the optimization output giving a tool to monitor on-line the sensor´s state. By periodically changing the power supply of the sensing element and measuring parameters of the resulting thermal impedance, various sources of influence like ambient temperature, rain drops or snow on the device´s surface can be separated. Prototype sensors have been developed and evaluated with satisfactory results.