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

Error Degrees C

0.03

0.025

0.02

0.015

0.01

0.005

0

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

-0.005

Temperature Degrees C

FIGURE 2-1. Steinhart and Hart

FIGURE 2-2. Possible Errors

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