Campbell Scientific 108-L Temperature Probe - Manual (Page 13)

Model 108 Temperature Probe
outlined in Section 8.3, Electrically Noisy Environments, and Section 8.4, Long
Cable Lengths.
Details of 108 probe measurement and linearization of the thermistor output
are provided in Section 8.2, Measurement and Output Linearization.
7.2.1 CRBasic
The Therm108() measurement instruction programs CRBasic dataloggers
(CR800-series, CR1000, CR3000, CR5000) to measure the 108 probe. It
supplies a 2500 mV excitation, makes a half-bridge measurement, and converts
the result to temperature using the Steinhart-Hart equation (see Section 8.2,
Measurement and Output Linearization, for more information):
Therm108 (Dest,Reps,SEChan,VxChan,SettlingTime,Integ,Mult,Offset)
Variations:
• Temperature reported as °C — set Mult to 1 and Offset to 0
• Temperature reported as °F — set Mult to 1.8 and Offset to 32
• Ac mains noise filtering — set Integ to _60Hz or _50Hz (see Section
8.3, Electrically Noisy Environments)
• Compensate for long cable lengths — Set SettlingTime to 20000 (see
Section 8.4, Long Cable Lengths)
7.2.2 Edlog
The AC Half Bridge (P5) measurement instruction programs Edlog
dataloggers (CR10(X), CR510, CR500, CR23X, 21X, and CR7(X)) to measure
the 108 probe. It makes a half-bridge measurement, and the Polynomial (P55)
instruction converts the result to temperature using a fifth-order polynomial
(see Section 8.2, Measurement and Output Linearization, for more
information):
1: AC Half Bridge (P5)
1: 1 Reps
2: 23 25 mV 60 Hz Rejection Range
3: 1 SE Channel
4: 1 Excite all reps w/Exchan 1
5: 1000 mV Excitation
6: 1 Loc [ T108_C ]
7: 200 Multiplier
8: 0 Offset
2: Polynomial (P55)
1: 1 Reps
2: 1 X Loc [ T108_C ]
3: 1 F(X) Loc [ T108_C ]
4: -26.97 C0
5: 69.635 C1
6: -40.66 C2
7: 16.573 C3
8: -3.455 C4
9: 0.301 C5
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