Model 109SS Temperature Probe
2. Accuracy
The overall probe accuracy is a combination of the thermistor's interchangeability
specification and the accuracy of the bridge resistor. The Steinhart and Hart
equation used to calculate temperature has a negligible error (Figure 2-1). In a
"worst case" the errors add to an accuracy of
±
0.6
°
C over the range of -40
°
to 70
°
C
and
±
0.49
°
C over the range of -20
°
C to 70
°
C. The major error component is the
interchangeability specification (tolerance) of the thermistor. The bridge resistor
has a 0.1% tolerance with a 10 ppm temperature coefficient. Figure 2-2 shows the
possible worst case probe and measurement errors.
Steinhart & Hart - Tabulated values
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
Temperature Degrees C
Error Degrees C
FIGURE 2-1. Steinhart and Hart
FIGURE 2-2. Possible Errors
3
