temperature characteristics (typical variations are +20 percent in 
nominal resistance at 25°C), and hence are not directly interchange- 
able. Since the feature of interchangeability in sensor units is very 
desirable, a method was worked out (see Appendix A) for determi- 
nation of the optimum values of two resistors (fig. 1, Appendix A), 
one in series and one in parallel with the thermistor, in order to 
obtain the same resistance vs. temperature calibration curve for 
all sensor units. This process is called normalization. The therm- 
istors used were Veco 32A1,* which is the bead type with a glass 
probe covering. They are 2 inches in length, have adjacent leads, 
and have a nominal resistance at 25°C of 2000 ohms. 
Small watertight housings were constructed to contain the 
thermistor and normalizing resistors (fig. 3). The normalizing 
resistors were wire wound on ceramic bobbins and have radial 
leads, allowing the thermistor to be passed through the bobbin 
holes. These components together with fiber spacers and a wire 
*Victory Engineering Corp., Springfield Road, Union, New Jersey 
LAS IC. 
CYEINDER 
STUFFING 
TUBE 
- 7 EPOXY 
: <_< 
~ ee FILLING 
COLLAR I 
e GUARD 
RESISTORS 
FIBER 
SPACERS THERMAL 
LAG 
COAT ING 
Figure 3. Thermistor assembly 
