Campbell Scientific CDM-VW300 Series Dynamic Vibrating-Wire Analyzer System - Manual (Page 90)

Appendix F. Thermistor Information
3. Steinhart-Hart equation error
4. Precision of the bridge resistors
5. Accuracy of the datalogger voltage measurement
6. Temperature coefficient of the bridge resistors
Errors three through six are usually sufficiently small that they can be ignored.
The wire resistance is primarily an offset error and its effect can be removed by
the initial calibration. Errors caused by the change in wire resistance due to
temperature and thermistor interchangeability are not removed by the initial
calibration. FIGURE F-1 through FIGURE F-4 show how wire resistance
affects the temperature measurement for a Geokon 4500 vibrating-wire
piezometer.
ERROR = (ACTUAL
– COMPUTED) DEG C
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
ERROR AT –5 C ERROR AT 25 C ERROR AT 60 C
LEAD LENGTH IN FEET
(THOUSANDS)
0.0 2.0 4.0 1.0 3.0 5.0
FIGURE F-1. Temperature measurement error at three temperatures
as a function of lead length. Wire is 22 AWG with 16 ohms per
1000 feet.
F-2