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Show The DC generator anemometer ( A25b) is less responsive to rapid speed changes, but offers the distinct advantage of a linear relationship between output voltage and wind velocity. Circuitry and calibration procedure for this- unit are given in Appendix C. This type of anemometer is recommended for most installations, but special problems may require an alternate selection ( see discussion under Maintenance). The analog wind vane ( B2) uses a 360° stepping potentiometer attached to the vane shaft. This gives a varying resistance whose value is determined by orientation of the vane. At one point on the circle there is a jump from zero to maximum resistance. The vane body should be oriented so that this jump occurs at the most infrequent wind direction. Appendix C gives circuit and calibration procedure for the resistance- type wind vane. Accuracy of this type of wind direction record depends on accurate voltage regulation of the power supply. See Figure 18 for circuit details. The analog style of wind record requires two conductors between anemometer and recorder, and three conductors between the wind vane and recorder. The saving of six conductors over those required for the contact vane can offer such a substantial saving in the cost of a long cable that this system often will be the most economical in spite of the higher cost of the components. Especially for long lines, where resistance of a single conductor becomes an appreciable part ( say l/ 10th) of the input circuit resistance to the recorder ( not the meter movement resistance) then separate circuits ( five conductors in all) should be used for anemometer and vane to avoid interaction between the two. The analog system for wind recording described here is specified as standard for new installations in Class A ski area, unless special problems dictate otherwise. The detailed record of gusti-ness, peak velocities, and the character and changes in wind patterns provide much useful information for avalanche hazard forecasting that is not available from a digital ( contact anemometer) record. Continuous Wind Speed and Direction ( Digital System) Because a number of Class A ski areas already have digital systems using contact anemometers and vanes, this latter system will also be described in detail. The ultimate goal of the snow and avalanche data reporting network, however, will be to install analog wind systems at all Class A areas. The contact anemometer described above may be connected to a strip- chart operations ( event) recorder. An operations recorder drives a clock- driven chart on which are inked lines, up to 20 on the heavy duty models ( A28a). The pen drawing each line can be |