17 



220 ohm and 470k phm resistors (see Fig. 17). 



d. Solder the negative (silver) strand to the negative lead of 

 the electrolytic capacitor (see Fig. 17). 



e. Sever the speaker wire about 10 to 20 cm from its entrance 

 into the hygrothermograph, an.d solder 'quick disconnect' 

 plugs to each of the cut strands. This will allow the hygro- 

 thermograph to be detached from the sensor unit without 

 disturbing the apparatus. 



6. Wire the sensor relay to the 12 V lantern battery. 



a. Connect the second long length of speaker wire to the 

 plugs on the other speaker wire lead extending from the 

 PVC T'. 



b. The other end of this wire is attached to the battery. 

 NOTE: This completes the construction and wiring of the LWI 



apparatus. 



Operational Check of the Leaf Wetness Indicator Circuitry 

 and Trouble- shooting 



The electrical circuitry connecting the sensor relay, sensor- 

 indicator assembly, unijunction assembly, and the LWI pen arm 

 relay can be checked by the procedure outlined below: 



1. Depress the sensor-indicator button. 



a. If the LED glows, proceed to step 2. 



b. If the LED does not glow, loosen the wing nut and turn the 

 tension-adjustor knob clockwise slowly until the LED 

 glows. Proceed to step 2. 



(1) If there is continued failure of the LED to glow, this 

 may be due to: 



(a) improper wiring: check all wiring and connections 



(b) low battery charge 



(c) malfunctioning LED 



(2) Correct the problem and proceed to step 2. 



2. Push and hold the unijunction accelerator switch. In a few 

 seconds, the LWI pen arm should click up and down to 

 indicate that the LWI sensor relay is in the 'wet' mode. 



a. If the pen arm does respond, release the switch and care- 

 fully reset the tension-adjustor knob to its original posi- 

 tion. 



b. If the pen arm does not respond, trouble-shoot as follows: 



(1) Check the wiring and all electrical connections between 

 the sensor relay, unijunction assembly, and the LWI 

 pen arm relay. 



(2) Check the charge on the battery. It must be higher 

 than 9 V. 



