CS547 Conductivity and Temperature Probe and A547 Interface
14
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
