A wind speed measuring device comprising a constant temperature heat generating device that generates heat at a predetermined set temperature or around the predetermined set temperature;
- wherein
- the constant temperature heat generating device comprises an electricity input portion, a heat generating element, a switching element, a voltage comparing portion, a first negative characteristic thermistor element, and a plurality of resistance elements;
- the heat generating element and the first negative characteristic thermistor element define a wind speed sensor;
- the heat generating element is configured to generate heat with electricity supplied from the electricity input portion;
- the switching element is between the electricity input portion and the heat generating element;
- the voltage comparing portion is configured to control turning on and off of the switching element;
- the first negative characteristic thermistor element is thermally coupled to the heat generating element to be close to the heat generating element in temperature, the first negative characteristic thermistor element having a resistance value at the predetermined set temperature as a threshold resistance value;
- the first negative characteristic thermistor element and at least one resistance element are connected in series to define a temperature detection voltage dividing circuit;
- a temperature detection voltage is output from a connection point between first negative characteristic thermistor element and the resistance element of the temperature detection voltage dividing circuit;
- at least two resistance elements are connected in series to define a comparison voltage dividing circuit;
- a comparison voltage is output from a connection point between one resistance element and another resistance element of the comparison voltage dividing circuit;
- each of:
- (a) resistance values of the resistance element of the temperature detection dividing circuit and the resistance elements of the comparison voltage dividing element, and (b) the voltages applied to the temperature detection voltage dividing circuit and the comparison voltage dividing circuit are set such that the temperature detection voltage is equal to the comparison voltage when a temperature of the first negative characteristic thermistor element is equal to the predetermined set temperature and a resistance value of the first negative characteristic thermistor element is equal to the threshold resistance value;
- the voltage comparing portion is configured to compare the temperature detection voltage and the comparison voltage, and when the temperature of the first negative characteristic thermistor element is less than the predetermined set temperature and the resistance value of the first negative characteristic thermistor element is larger than the threshold resistance value, the voltage comparing portion turns on the switching element, and when the temperature of the first negative characteristic thermistor element is more than the predetermined set temperature and the resistance value of the first negative characteristic thermistor element is smaller than the threshold resistance value, the voltage comparing portion turns off the switching element;
- the switching element repeats the on and off to apply a pulse voltage from electricity input portion to the heat generating element;
- and
- a wind speed of a wind contacted with the wind speed sensor is calculated based on a wave form of the applied pulse voltage.