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Show Calibration Instructions for the Analog Wind System These instructions assume that the Electric Speed Indicator Company sensors, properly modified, have been installed on a stout mast in a suitable location and that the appropriate cables and junction boxes have been installed to professional standards. The Esterline- Angus dual- channel 0- 1 ma. recorder has been installed at the lower end of the cable, at a point where 110 volt AC commercial power is available. A combination power supply and calibration circuit is required. This is housed in a tamper- proof steel box adjacent to the recorder and connected to a nearby 110 volt AC outlet. The circuit diagram for this unit is shown in Figure 18. As of the date of publication of this Snow Safety Guide, National Forests installing this wind system on Class A ski areas will be able to obtain a completed unit, ready for installation, by notifying the Alpine Snow and Avalanche Project, Rocky Mountain Forest and Range Experiment Station, 240 West Prospect Street, Fort Collins, Colorado 80521. An anemometer calibrator is also required which will provide an accurate source of exactly 4.0 volts D. C. If such a source is not available locally from electronic specialists, it can be constructed according to the diagram of Figure 17. When the lid of the power supply- calibration unit is opened, a panel will be exposed containing two toggle switches and four screwdriver- adjustable potentiometers with locking nuts. The switches turn on and off respectively the anemometer ( wind speed) and wind vane ( direction) circuits. Function of the four potentiometers, labelled R| through R/(, will be described below. The power supply-calibration unit will have been securely fastened to a wall adjacent to the recorder. The wind speed circuit is calibrated first. Purpose of this calibration is to adjust total circuit resistance so that a 4- volt signal from the anemometer will just cause the recorder pen to move to the 100 mph mark on the chart, and at the same time insure that this resistance offers a reasonable impedance match to the anemometer. Two men are required, equipped with means of communi-cation-- usua 1 ly handi- talky radios - between the anemometer mast and the recorder site. The man at the tower requires the anemometer calibrator ( Figure 17) and an accurate test meter ( B7c). First, make sure the two anemometer leads are disconnected from the cable at the terminals in the junction box at the tower base, and that the velocity switch is turned OFF at the calibration unit. Mechanically adjust the wind speed ( left- hand) pen of the recorder, using the zero- adjust level at the base of the 73 |
