Jewel Bearing Splits Anemometer Start Speeds

January 18, 1999

Newton MA – a low-friction jewel bearing from Waltham. MA-based Bird Precision helped Nielsen-Kellerman Co. (Chester, PA) cut anemometer starting speeds in half when compared to existing designs. While most portable anemometers require wind speeds of between 0.6 and 0.8 m/sec to set the impeller in motion, the Kestrel series’ impeller rotates in 0.3- to 0.4-m/sec winds, says Nielsen-Kellerman’s Michael Naughton.
Bird Precision designed the super-polished, sapphire, conical-vee bearing that supports the patented, anodized-aluminum impeller used in both the Kestrel 1000 and 2000 anemometers. The ultra-low coefficient of friction allows the anemometer to register nearly imperceptible breezes (0.7 mph), explains Naughton, yet also measures gale-force winds (up to 89 mph), with an accuracy of + or – 3% or better.

Less than five inches long and weighing only 1.5 oz, the anemometers let anyone that works or plays outdoors measure even low windspeeds with high accuracy. A study fiberglass housing projects the 25mm impeller from damage. But if need be, the impeller is easily replaced without tools, at a cost of about $15.

"Most portable anemometers weigh over one pound and are less accurate" says Naughton. The Kestrel 1000 pocket wind meter and the Kestrel 2000 wind speed / temperature/wind chill indicators are less cumbersome than the analog devices currently available, he adds. A magnet rotates with the impeller and sensors count the number of rotations to calculate the wind speed. A digital display offers settings for knots, meters per sec, kilometers per hour, miles per hour, feet per minute, and Beaufort. And users can choose between Fahrenheit and Celsius for temperature and wind chill readings.
Kestrel anemometers are waterproof and float, and come with a protective carrying case and a convenient neck lanyard. The battery is easy to replace, says Naughton, and provides 400 hours of use.

Bird Precision creates synthetic ruby and sapphire bearings in a wide variety of shapes and sizes. The company also manufactures precision orifices ranging in size from 0.0008 to 0.0350-inch that can be produced in high volumes. To cut anemometer starting speeds in half, the Kestrel 1000 and 2000 rely on a patented impeller design and a low-friction jewel bearing.

Hardened proprietary alloy double conical shaft 1-mm diameter x -10mm long Non magnetic, Non corrosive.

Anodized aluminum impeller on axis accuracy +or – 3% 25mm diameter.