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Figure 3.—Overall view of height sensor showing slidewire contact at one end of the slidewire as one of the stops strikes the 
shelf. The phonopickup wire connections to each end of the slidewire are also shown. 
The slidewire disk extends above and below the shelf 
through a 1- by 6 1/2-inch slot cut in the shelf (fig. 4). 
The contact arm, mounted at one end of the slot, is 
made from a double thickness of 0.005-inch shim brass 1 
inch wide. Actual contact with the slidewire is made 
through a piece of 24-gage platinum wire soldered to the 
brass contact arm. 
Fine adjustment of the contact pressure is made using 
a screw threaded through the end of the box and attached 
to the contact arm by a light bronze spring and a fishing 
tackle swivel (fig. 5). The contact pressure on the 
slidewire should be kept as light as possible to allow the 
disk to turn with as little counterweight as possible 
without having the contact stick cause a ‘‘stairstepped”’ 
record. About 30 grams is the minimum amount of 
weight that can be used. 
To allow the sensor to operate properly with a 
minimum contact pressure, the slidewire and contact 
must be kept clean. The slidewire should be rubbed with 
a pencil eraser, then with a clean handkerchief, and the 
platinum contact should be burnished with a piece of 
paper. The slidewire and contact should be cleaned every 
2 or 3 days. 
The sensor and the plant are connected by a length of 
30-gage copper wire, one end of which is connected to 
the slidewire disk and the other end is fastened to a 
clamp which in turn is attached to the plant leaf. The 
clamp is an ordinary spring-type clothespin with the jaws 
modified by cementing pieces of plastic to them to 
produce a gripping surface of 3/4 by 1 inch. The clamp 
jaws are faced with a sponge rubber-moleskin cloth 
material or with sponge rubber.® 
Stops made of 3/4-inch lengths of 5/8-inch OD 
polystyrene tubing? cemented to the slidewire disk with 
® Dr. Scholl's Molefoam, which has its own adhesive (softens 
somewhat in wet weather), or pieces of sponge rubber innersole 
fastened with contact cement. 
2 Obtained from Burstein-Applebee Co., Kansas City, Mo. 
