247 CONDUCTIVITY AND TEMPERATURE PROBES
8
8.2 TEMPERATURE MEASUREMENT ERROR
The overall probe accuracy is a combination of the
thermistor's interchangeability specification, the
precision of the bridge resistors, and the polynomial
error. In a "worst case" all errors add to an
accuracy of ±0.4°C over the range of -24° to 48°C
and ±0.9°C over the range of -38°C to 53°C. The
major error component is the interchangeability
specification of the thermistor, tabulated in
Table 8.2-1. For the range of 0° to 50°C the
interchangeability error is predominantly offset and
can be determined with a single point calibration.
Compensation can then be done with an offset
entered in the measurement instruction. The bridge
resistors are 0.1% tolerance with a 10 ppm
temperature coefficient. Polynomial errors are
tabulated in Table 8.2-2 and plotted in Figure 8.2-1.
TABLE 8.2-1. Thermistor Interchangeability
Specification
Temperature
Temperature (°C) Tolerance (
±°C)
−40 0.40
−30 0.40
−20 0.32
−10 0.25
0 to +50 0.20
TABLE 8.2-2. Polynomial Error
-40 to +56 <±1.0°C
-38 to +53 <±0.5°C
-24 to +48 <±0.1°C
FIGURE 8.2-1. Error Produced by Polynomial Fit to Published Values
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