A compensated thermal anemometer and flowmeter

Abstract

A THERMAL anemometer with unusual sensitivity, accuracy, and ruggedness has been developed for laboratory and industrial use. It operates from a heated noble metal thermopile which is placed in the airstream whose velocity is to be measured. The anemometer is practically independent of temperature over a considerable range since both the hot and cold junctions are exposed to the airstream and are equally affected by ambient temperature. Radiation effects tend to cancel in the same manner. Thermopile probes of suitably chosen materials have been used satisfactorily at temperatures as low as — 65 degrees Fahrenheit and to above 300 degrees Fahrenheit. The outstanding feature of this anemometer is that the transient thermal voltage produced in the heated thermopile by sudden changes in ambient temperature is counterbalanced by the equal and opposite transient thermal voltage of an unheated thermopile located in the probe and exposed to the airstream whose velocity is being measured. This arrangement compensates completely for rate of change of temperature.