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III. FACILITIES AND EQUIPMENT q "'~ ]II "'". ~ Figure 20.-Shielded Snow-board Installation at Laboratory. put drives a transistorized offset recorder. Record- ing is on a strip chart driven at 1 in. jhr. Full scale on the recorder can be set at 1 percent, 5 percent or IO percent of transducer full scale, yielding a most sensitive full scale recording of -,.5 inch H20. The recorder is driven back to zero after each storm by a calibrated lO-turn potentiometer-the differ- ence in the past and present pot readings is there- fore a measure of the total storm precipitation. Our particular pillow installation-which may not be ideal-has suffered from bridging; however, the dosed system readout shows none of the diurnal fluctuations that the open system, mechanical re- corder installations reportedly have. A float type, mechanical recorder, installed in parallel with our pressure transducer, exhibits these diurnal varia- tions. Insofar as snow-rate is concerned, we have been able to obtain no better results with the pil- low-and a full scale range of 0.5 inch H20-than with the compressed-scale weighing gage. Figure 24 shows a data sample. The heated tipping-bucket gage, figure 25, op. 17 ~:..t : '-,. I'~ " 1 ' " : i, \. i ,. L'''~ \" . '.. " "'~ ". ,J " ". ;; ':',,;.;". ~1."iJI'" ';:, ~"1K - .. . ..~.~ ~ ,:.::. .~ ." '.- 6~ .~ _......,._...__.~ :.." ' ~,:,'~::, :~.' Figure 21.-Compressed-scale Weighing Gage. erates just like a conventional tipping-bucket rain gage except that it has an expanded aperture, 5 ft.2, and a I-kilowatt, thermostatically controlled heater. The tips of the bucket are sensed by a mercury switch that signals an electronic circuit. The circuit drives a strip recorder-6 in. jhr.-in such a manner that the amplitude of the trace is proportional to Figure 22.-Example of Compressed-scale Weighing Gage Data.