A portable sensitive anemometer with proportional d.c. output and a matching wind velocity-component resolver

A new design of portable cup anemometer which employs photoelectric switching and a built-in ratemeter is described. The dimensions and slow running properties of the instrument are similar to those of the Sheppard anemometer but output readings are in voltage form linearly related to wind speed. A special light-weight rotor is used to replace the `standard' three-cup aluminium rotor when a fast response is required. The anemometer is supplied with power (12 v, 40 mA) from an external source and under normal load conditions gives an output of up to 10 v with a sensitivity of approximately 1 v per m sec -1 . Output voltage sensitivity may be decreased and range increased by shunting the load, the short circuit sensitivity being approximately 0.6 mA per m sec -1 . An a.c. signal with frequency proportional to wind speed (40 cycles per metre, 6 v peak to peak) is also provided by the anemometer as a separate output. A wind velocity-compoent resolver which derives its input voltage directly from the anemometer is also described. This instrument provides two output voltages, linearly proportional to the wind velocity components in two mutually perpendicular directions.