Environmental Engineering Reference
In-Depth Information
Thermistors
Some tools contain thermistor sensors which are metal oxide semiconductor
devices. Thermistors provide a large change in resistance per degree change in tem-
perature, but they are highly nonlinear devices. There are a number of linearizing
schemes used, but in logging tools, where a dynamic range of 300 °F or more may
be needed, thermistors are problematic.
Diodes
Diodes have been used as temperature sensors in a few tools. Diodes produce a rela-
tively high change in voltage per degree, but they are limited with respect to high
wellbore temperatures.
Figure
8.1
illustrates a temperature logging tool and Fig.
8.2
a typical tempera-
ture log.
Fig. 8.1
High-resolution
thermometer. Courtesy
Schlumberger
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