21 



the field during dry weather, or when checking the performance of 

 the sensing element during dry weather. 



Calibrating for condensation. 



It is possible to 'fine tune' the seni^ing element so that it will 

 respond to condensation in addition to precipitation. If this degree 

 of sensitivity to moisture is desired, the procedure to follow is similar 

 to the calibration procedure for precipitation described above except 

 that observations for condensation on the foliage, rather than pre- 

 cipitation, must be made. 



Wiring the Digital Rain Gauge and 

 Rain-intensity Pen Arm Relay 



Materials 



(1) Digital rain gauge (Edmund Scientific Co., Barrington, New 

 Jersey 08007; catalog # 72,319). The rain gauge includes one 

 tipping bucket and rain collector for 0.25 mm measurements, 

 one digital counter, and two battery clips. 



(2) 9V batteries 



(4) wire connectors 



(1) roll of electrical tape 



(1) roll of 18 gauge wire 



Instructions (refer to Fig. 18) 



1. The tipping bucket comes wired with a length of two- 

 conductor speaker wire. Loosen the screw on the side of the 

 digital counter housing and insert the end of the wire 

 through the hole below the screw. 



2. Slit the end of the speaker wire to separate the copper and 

 silver strands for about 10 cm. 



3. Strip about 1 cm of insulation from each battery clip wire 

 and snap the clips onto the 9V batteries. 



4. Connect the two positive leads from the batteries to the 

 copper wire coming from the tipping bucket (a), and solder 

 and cover with a wire connector. 



5. Solder the two lengths of 18 gauge wire to the prongs on the 

 12V rain-intensity relay attached to the plexiglass stage in 

 the hygrothermograph. Cut the wires about 60 cm (long 

 enough to extend from the hygrothermograph to the digital 

 counter). 



a. Insert the wires through the drilled holes in the upper 

 stage plate and the hygrothermograph base plate. 



b. Connect one wire to the negative lead of one of the batter- 

 ies (b), then solder and cover with a wire connector. 



