Thermistors are special solid temperature sensors that behave like temperature-sensitive resistors; hence their name is a contraction of “thermal” and “resistor”. They are mostly very small bits of special material that exhibit more than just temperature sensitivity.
During the last 60 years or so, only ceramic materials (a mix of different metal oxides) was employed for production of NTC thermistors. In 2003, AdSem, Inc. (Palo Alto, CA) developed and started manufacturing of NTC thermistors made of semiconductors materials, Silicon and Germanium, having both higher and lower temperature measurement capabilities and better overall performance than any ceramic NTC thermistors.
Thermistors are highly-sensitive and have very reproducible resistance Vs. temperature properties. They are used inside many other devices as temperature sensing and correction devices as well as in specialty temperature sensing probes for commerce, science and industry.
Thermistors typically work over a relatively small temperature range, compared to other temperature sensors, and can be very accurate and precise within that range, although not all are. Some, like the semiconductor types have expanded the reach of these little devices.
Below are some links to website sources of thermistors, both Positive Temperature Coefficient (PTC) and Negative Temperature Coefficient (NTC) — see comments for which vendors offer which types.
The general rule of thumb is that most vendors default offerings are NTC, unless they say otherwise.
Like many things on the Web, it is a bit of underedited data, but edited enough to make it useful to some, hopefully you.
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