28 



FIG. 13. Steps required in seating the sensor relay into the test cap 

 and in fashioning and installing a hook onto the wire 

 extending from the sensor relay: hook for sensor attach- 

 ment and wire to bind hook to relay (a); hook bound in 

 position (b); slits cut in PVC test cap (c). 



FIG. 14. Wiring diagram for the sensor relay and the sensor- 

 indicator assembly. 



FIG. 15. Construction of the sensor PVC housing and the cotton 

 wetness-sensing element. 



FIG. 16. Rear-view of 4-pen arm hygrothermograph showing 

 attachment of the unijunction accelerator switch (a) and 

 the unijunction circuit board (b). 



FIG. 17. Close-up of unijunction components on the circuit board: 

 positive end of capacitor (a); 470knresistor (b); junction of 

 the 220 a and 470 ka resistors (c); 220 Q resistor (d); Tj 

 transistor (e). 



FIG. 18. Wiring diagram of the digital rain gauge and rain- 

 intensity pen arm relay. 



FIG. 19. Attachment of the plexiglass mount and unijunction 

 accelerator switch for the 3-pen arm hygrothermograph. 



FIG. 20. Rear-view of the 3-pen arm hygrothermograph showing 

 attachment of the pull-type solenoid, spacer, and spring. 



FIG. 21. Schematic representation of the electrical circuitry for the 

 3-pen arm solenoid unijunction assembly and unijunction 

 accelerator switch. 



