24 



B) Heat the plexiglass carefully with a flame or heat strip until 

 the plexiglass becomes flexible. 



C) Bend the plexiglass to form a 90 degree angle; cool to harden 

 in position. 



D) Drill 3 holes in a triangle-pattern in the 5 cm end. 



E) Position the plexiglass on the metal upright plate of the 

 hygrothermograph, 1.5 cm from the top and 2 cm from the 

 front edge. 



F) Drill and tap three holes in the upright plate to correspond 

 with the 3 holes in the plexiglass. 



NOTE: If the model pictured is used, a 1 .5 x 3.0 cm hole must be 

 cut in the plexiglass mount to clear the temperature- 

 sensing apparatus before attaching the mount to the 

 upright. 



G) Drill a 6 mm hole 4 cm from the 5 cm mark and 2 cm from the 

 back edge of the plexiglass mount; then attach the Unijunc- 

 tion Accelerator Switch. (See Fig. 20) 



H) Drill a 4 mm hole 7 cm from the 5 cm mark and 5 cm from the 

 front edge of the plexiglass mount; then attach the rain- 

 intensity 12V relay and pen arm. (See pp. 8-12 for construct- 

 ing the relay and pen arm.) 



I) Drill two 4 mm holes in the back edge of the plexiglass mount 

 and two corresponding 4 mm holes in the circuit board. The 

 holes will be used later to attach the circuit board to the 

 plexiglass mount. 



J) Drill a 6 mm hole in the hygrothermograph base similar to 

 the hole drilled for the 4-pen arm design (see p. 9). This hole 

 allows wires to be passed through the hygrothermograph 

 base. 

 K) Mount the plexiglass onto the hygrothermograph upright. 



Mounting the 12 V Solenoid to the 

 Hygrothermograph Upright 



Materials 



(1) T6X12-C-12VDC pull-type solenoid, duty cycle continuous 

 (Guardian Electric Mfg. Co., Chicago, Illinois) 



(2) spacers, 2.54 cm long 



(2) 30 cm long bolts, and 4 nuts 



Instructions (refer to Fig. 20) 



A) File flat the end of the humidity adjustment rod to a width of 

 2 mm to allow the rod to fit into the groove of the solenoid 

 shaft. Insert a pin through the shaft and rod to fasten the 

 assembly. 



