抄録
If the detecting element of a radiation pyrometer is exposed in the air, its output varies merkedly with the wind velocity. Some behavior of an anemometer designed on the base of this fact is reported. When a couple of pieces of metal foil having different total thermal emissivity is placed parallel to the air stream and is heated by radiation of constant radiant flux, the relation of the inverse of temperature difference between the pieces at steady state (θ-1) to the square root of velocity of the stream (u1/2) is expected to be linear.
The result, which supports this assumption is obtained on the measurement for the wind velocity between 20cm/s and 5m/s. Experiment is performed on the pair of the pieces of platinum foil (3mm×4mm×0.005mm) as the detecting element, which was suspended with tellurium-bismuth thermocouples in a small wind tunnel made of glass tube of 25mm in diameter and is heated by constant radiation.
The result of the experiment for the slower stream shows that the relation of the logarithm of temperature difference between the metal foils (logθ) to the velocity of the air stream (u) is linear. Representing the temperature difference when the velocity is zero by θs, the value of logθs is in good agreement with the extrapolated value of the straight line indicating this linear relation, which is expressed as logθs-logθ=u/τu. τu is a constant concerning the sensitivity having the value of 28cm/s in this work, but θs varies with radiant flux density on the detector foils. The value of θs can be used conveniently as the measure of adjustment of flux density.
