Campbell-scientific 247-L Conductivity and Temperature Manual de usuario descargar pdf (Pagina 12)

247 CONDUCTIVITY AND TEMPERATURE PROBES

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

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 18

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Campbell-scientific 247-L Conductivity and Temperature Manual de usuario Pagina 12