Temperature. Use a thermometer accurate to 1.0 C. Wipe the 

 temperature-sensing element with a clean, soft cloth. Support the 

 thermometer tip near the temperature sensing element and note the 

 temperature after the thermometer has come to rest. Then adjust the 

 temperature pen arm apparatus according to directions supplied 

 with the hygrothermograph. 



Relative humidity. Use a sling psychrometer or other instru- 

 ment capable of measuring relative humidity with 2.0% or better 

 accuracy. Make sure the humidity is measured within the shelter or 

 away from direct exposure to sunlight. Adjust the humidity pen arm 

 apparatus according to directions supplied with the hygrothermo- 

 graph. 



Digital Rain Gauge Assembly 



The digital rain gauge assembly consists of the following main 

 components: rain collector (aj, Fig. 2), tipping bucket (Fig 3), digital 

 counter (a2, Fig. 2), and the rain-intensity relay and pen arm (Fig. 1). 

 The rain gauge is wired to record each 0.25 mm of rainfall on the 

 digital counter and on the hygrothermograph chart. The rain gauge 

 was selected because of its accuracy (0.25 mm + 5%) and low cost. 

 Rain gauges with greater accuracy are available, but they are also 

 considerably more expensive. 



Operation. A tipping-bucket is located in the base of the rain 

 collector (Fig. 3). The bucket is actually two buckets joined together. 

 One bucket is always aligned with the orifice in the rain collector. 

 When 10 cc of water (equivalent to 0.25 mm of rainfall) are passed 

 from the rain collector to the tipping-bucket, the bucket tips causing 

 the water to drain while at the same time aligning the second bucket 

 with the orifice. 



A magnetic bead is attached to the center of the tipping-bucket, 

 and is located adjacent to a magneswitch (b, Fig. 3). When the 

 bucket tips, the magnetic bead swings along the magneswitch, caus- 

 ing two metallic strips in the switch to be momentarily drawn 

 together. At this time the circuitry that connects the switch to the 

 digital counter and the rainfall-intensity pen arm is completed. The 

 digital counter is advanced one unit and the pen arm is pulled 

 downward and then quickly returned to its resting position as the 

 magnetic bead continues its swing and the metallic strips are again 

 separated. The power required to trip the digital counter and the pen 

 arm relay is provided by two 9 V transistor batteries housed in the 

 digital counter. 



The digital counter provides a direct reading of the amount of 

 rainfall that has occurred within a given period, while the rainfall- 

 intensity pen arm traces the distribution and intensity of rain on the 

 hygrothermograph chart over the same period. With most rain peri- 



