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1594A/1595A Super-Thermometer
Specications
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257 Ω. Divide the result by the sensitivity of the PRT (dR/dT) at 420 °C. This can be found in the PRT calibra-
tion report. For this example, 0.4 Ω/°C is used. The resulting uncertainty is 0.0013°C.
2.2.5.5.2 Measurement Noise at 420 °C
The noise of the measurement at 420 °C is observed using the Standard Error of the Mean statistic eld of the
1595A. In this example it is 0.00003 °C.
2.2.5.5.3 Combining the Uncertainties
To calculate the entire uncertainty of the measurement, the standard uncertainties from the 1595A should be
combined with the (k = 1) PRT calibration uncertainty at 420 °C. The standard uncertainties are combined by
RSS and then multiplied by the required coverage factor.
2.2.5.6 Example 5: Measuring a 10 kΩ Thermistor
In this example, a 1595A is used to measure a 10 kΩ thermistor probe at 0 °C. The 1595A accuracy, when
measuring the thermistor probe is based on the following:
●
Resistance accuracy of the 1595A
●
Measurement noise
2.2.5.6.1 Resistance Accuracy
First, calculate the 1595A absolute resistance accuracy at 26839.94 (the resistance of the 10-k Ω thermistor
probe at 0 °C) when using the 10 k Ω internal reference resistor. The one-year absolute resistance accuracy
is 4 ppm of reading (k = 1). This is converted to temperature by dividing 4 ppm by 1.0 × 10
6
and multiplying
by 26839.94 Ω. The result is then divided by dR/dt of the thermistor probe at 0 °C which, in this example, is
1244.9 Ω/°C. The nal result is 0.000085 °C.
2.2.5.6.2 Measurement Noise
Measurement noise is best observed by using the Standard Error of the Mean statistics eld of the Super-Ther-
mometer. In this example, the standard error of the mean is 0.000004 °C.
2.2.5.6.3 Combining the Uncertainties
If the thermistor probe is being measured in temperature mode with calibration coefcients, the standard
uncertainty of the calibration (listed on the calibration report) would be combined by RSS with the resistance
accuracy and measurement noise uncertainties.