50 
straight line in volts per °C. This deviation in °C for each series 
resistor is plotted over the temperature range 9 to 19°C in figure 
BBG 
It can be seen from figure B5 that, for the conditions stated, 
2670 ohms in series with the thermistor yielded the best linearity. 
This is shown more pointedly in figure B6 where the maximum de- 
parture from linearity is plotted as a function of the series re- 
sistor. As an example of how the data shown in figure B6 were 
obtained, refer to the curve labeled 2500 ohms in figure B5. An 
examination of this curve shows that the maximum departure from 
linearity over the full range is approximately +0.012°C. This thenis 
the magnitude of linearity associated with 2500 ohms. Figure B6 
shows pointedly the importance of finding the optimum value of the 
series resistor if extreme linearity is required. Note on this 
curve that the value given by the method of Beakley (eq. B3a) 
yielded poorer results than the value given by eq. (15); this may 
be due to the fact that for the particular thermistors considered 
(table B1), the empirical equation on which Beakley based his 
work did not hold well. There is some difficulty in obtaining the 
correct value of the constant, 0, in the original empirical equation 
and eq. (B3a). However, there is also some uncertainty in apply- 
ing the method of eq. (B15) because 72g, , and “, are only 
defined as the resistance at low, medium, and high temperatures. 
These points might be defined more precisely as the end points 
and the midpoint of the desired temperature range. This was done 
in the preceding example with good results. 
In discussing linearity, care must be taken to define ter- 
minology. As was stated earlier, linearity in this paper refers 
to the departure of the function e (7) from a straight line through 
UPS 8) gio) = WC, AMaS) WEIS not necessarily the best straight 
line fit for all cases considered, but merely a convenient standard 
for comparison. 
Although, for our work, a 10°C range (9 to 19°C) was re- 
quired, figure B7 may be useful in determining the degree of 
linearity that can be expected over different temperature ranges. 
Figure B7 is based on the following equation given by Beakley.* 
The maximum error (departure from linearity) is given, by: 
*Reference B38, page 55 
