Thermistors: high sensitivity over a narrow range
NTC thermistors offer very high resolution and stability near ambient, which is why many precision loggers use them. Their non-linearity means calibration at several points and a fitted equation.
A thermistor's resistance falls roughly exponentially with temperature. Around room temperature a 10 kΩ device changes by about 4 %/K — ten times the relative sensitivity of a Pt100 — so small temperature changes produce easily measured resistance changes. This makes thermistors attractive for cold-chain loggers, stability chambers and medical thermometry.
Limitations
- Non-linearity: the resistance–temperature relation must be characterised per device or per batch.
- Self-heating: high resistance limits current, but small beads still heat in still air.
- Range: exposure above the rated temperature causes permanent shift.
- Interchangeability: precision types are matched to ±0.1 °C; others vary widely.
Well-aged precision thermistors can be more stable than industrial PRTs in the 0–70 °C range; their calibration history tells you whether yours are.
Frequently asked questions
- Can a thermistor logger be calibrated to 0.01 °C?
- Stable precision thermistors can, given a suitable reference and bath. The logger's electronics and resolution then set the practical limit.
References
- [1]ISO/IEC 17025:2017 — General requirements for the competence of testing and calibration laboratories
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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