
69
Figure 8.1. Percentage change in infrared flux due to case thermistor errors.
Using these values, the difference between the measured temperature at a given resistance
and the calculation at that resistance is no more than 0.02 °C through the temperature range
-60 °C to 50 °C. Figure 8.1 illustrates the effect of a positive deviation in the determination
of the case temperature on the calculated ‘case flux’ from the correct value. This difference
may be due to sam pling errors, an incorrect therm istor reading (e.g. the case therm istor is
not representing the actual cold junction temperature) or an incorrect thermistor inversion
equation. As can be seen, unless the error is greater than approximately 5%, the overall accuracy
of the measurement is not greatly affected.
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