14 



3. Check to make sure the length is correct. The string should 

 be stretched when it is placed between the elbows of the 

 sensor housing. 



Conditioning the Sensing Element 



The wetness sensing element should be 'conditioned' before it is 

 attached to the LWI assembly so that it will respond properly to 

 wetting and drying. Always handle the sensing element by holding 

 the lugs. Touching the cotton line will leave grease on it which may 

 lessen the response of the element to wetting. It is suggested that two 

 or three spare elements be 'conditioned' for immediate replacement 

 in the event of vandalism or some other catastrophe that makes the 

 sensing element inoperable. The 'conditioning' may be accom- 

 plished by the following procedure: 



1. Hammer two small nails into a board and slip the lugs of the 

 sensing element over the nails. The nails should be spaced so 

 that the sensing element is stretched. 



2. Spray the element uniformly with water until it is tho- 

 roughly wetted. Use a spray atomizer, aerosal spray can, or 

 other device that provides a mist-type spray. 



3. Allow the element to dry. 



4. Repeat 4 to 6 times. 



The sensing element is now 'conditioned', and can be attached to the 

 LWI assembly. 



Attaching the Wetness Sensing Element 

 to the Sensor PVC Housing 



1. Attach one lug to the hook extending from the sensor relay 

 housing. 



2. Attach the other lug to the polyester string extending from 

 the tension-adjustor housing. 



3. If the sensing element is sagging, turn the tension-adjustor 

 knob clockwise slowly until the sensing element does not sag. 



NOTE: The construction of the LWI sensing unit is now complete. 

 It may be supported on a length of PVC tubing (see cover). 

 The length of tubing will vary depending on placement of 

 the sensing unit in the environment. Several wires should 

 be extending through the PVC 'T'. The connection of these 

 wires is explained below in the section, 'Wiring the LWI 

 sensor, unijunction assembly, and LWI relay'. 



Preparing the Unijunction Assembly 



Materials 



n') circuit board 



