CABLES AND 



THERMISTOR 



ELEMENTS 



Figure Al. Sixteen-channel temperature measurinf; unit. 



contact, as they are extremely fragile. They were therefore cast in a cylinder 

 formed by pouring a plastic, Furnane 502, Epocast, with General Mills 125 Ver- 

 samid, into a 1-inch outside diameter Lucite tube. The thermistor beads in par- 

 allel, their compensating resistor, and the three-conductor electrical cable were 

 mounted in the cylinder. Figure A2 shows the assembled unit and its construc- 

 tion. The sensing beads project 1/8 inch from the end of the cylinder and are 

 protected by two hoops of l/l6-inch stainless steel wire embedded in the plastic. 

 The plastic bonds with the glass covering of the bead and the outer insulation of 

 the electrical cable to form a watertight unit (fig. A2 shows details of mounting). 

 The outer end of the cable has a three-contact plug for insertion in a jack on the 

 recorder panel. The plastic bonds well with almost all materials, is simple to pour 

 having only two ingredients, and does not deteriorate appreciably. It can be 

 poured into a Lucite tube directly, eliminating the necessity for special molds. 

 A simple Wheatstone bridge circuit was employed (fig. A3) in which the re- 

 sistances i?, and R2 are fixed; K,; consists of ten resistors arranged so that any one 

 of them may be switched into the circuit. The values of these resistors are selected 



29 



