Self-heating in resistance thermometers
The measuring current warms the sensing element. The effect depends on the medium — so calibrate at a current and condition representative of use.
A resistance thermometer is read by passing a current through it; that current dissipates power in the element and raises its temperature slightly above its surroundings. In a stirred bath the effect is small; in still air or a poor-fitting dry-block well it can be many millikelvin or more.
Managing it
- Use the lowest practical measuring current and keep it the same in calibration and use.
- Measure at two currents and extrapolate to zero if the lowest uncertainty is required.
- State the current and medium on the certificate so the user can judge transferability.
For most industrial and logger applications the effect is below other uncertainties, but it should be estimated rather than ignored.
Frequently asked questions
- How big is self-heating in a Pt100?
- With 1 mA in a stirred bath, typically 1–3 mK; in still air it can be tens of millikelvin or more. Many industrial readouts use lower currents to reduce it.
- How is self-heating measured?
- Read the thermometer at the normal current and at √2 times the current; the difference in indicated temperature equals the self-heating at the normal current, which can then be corrected or budgeted.
References
- [1]IEC 60751 — Industrial platinum resistance thermometers and platinum temperature sensors
- [2]JCGM 100:2008 — Guide to the expression of uncertainty in measurement (GUM)
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.
Have a question on this topic?
Ask ValiTrac AI and see the evidence and calculation behind the answer.
Ask ValiTrac AIFree calculator: Guard band / decision rule
Turn a tolerance and an expanded uncertainty into acceptance limits under ILAC-G8 rules, and see the false-accept and false-reject risks.
Open the calculatorCalibration on ValiTrac
Support calibration workflows, uncertainty budgets and certificate generation.
See the calibration workflowRelated articles
How to calibrate a Pt100
Calibration by comparison against a reference thermometer, and the factors that decide the uncertainty.
The reference thermometer's contribution to uncertainty
The reference contributes its certificate uncertainty, its drift since calibration, and any interpolation or self-heating effects. Together they set the floor of what can be claimed.