Campbell Scientific 109-L Temperature Probe - Manual (Page 13)

Model 109 Temperature Probe
Steinhart-Hart
Linearization Error: ≤ 0.03 °C (–50 to 70 °C)
Probe Weight and Dimensions
Weight with 10 ft cable: 136 g (5 oz)
Length: 10.4 cm (4.1 in)
Diameter: 0.762 cm (0.3 in)
1 See FIGURE 6-1, Worst-case probe and measurement errors, and FIGURE 6-2, Steinhart-Hart
linearization error. Overall probe accuracy is a combination of thermistor interchangeability,
bridge-resistor accuracy, and error of the Steinhart-Hart equation. Interchangeability is the
principle component error and is predominantly offset. Offset can be determined with a single-
point calibration. Offset can be entered in the Therm109() instruction Offset parameter. The
bridge resistor has a 0.1% tolerance with a 10 ppm temperature coefficient. At temperature
extremes, the possible error in the CR200(X) series datalogger measurement may be greater than
the error that exists in the probe.
FIGURE 6-1. Worst case probe and measurement errors
-0.1
6E-16
0.1
0.2
0.3
0.4
0.5
0.6
0.7
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70
Po
ss
ib
le
Erro
r D
eg
rees
C
Temperature Degrees C
Worst Case Errors in 109 Temperature Measurement
Thermistor
Tolerance
CR200 Bridge
Measurement
Error (0.06% of
reading + 2.4 mV)
CR200 Resolution
(0.6 mV)
24.9 kΩ Resistor
Tolerance (0.1%
+ 10 ppm/°C
away from 25 °C)
5