Operating temperature of the wire

As shown, the operation of the anemometer is based on the heat ex­change between the hot wire and the fluid stream which is more effective the higher the operating temperature of the sensor. There must, however, be a limit to temperature due to the acceleration of the oxi­dation of the wire and the decrease in its tensile strength at high temperatures.

The usual operating temperature for sensors operating in the air at room temperature is in the range 150 + 250°C. This implies that the electrical resistance of the sensor is 1.5 + 2 times the resistance at room temperature.

In practice, the operating temperature is established by inserting an appropriate resistance in the arm of the bridge opposite to the sensor: this is a fixed resistor suitable to the sensor, or a winding compensated for ambient temperature, or a variable resistance in order to allow changes at will of the sensor temperature.

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