AI audit of the RTD Tolerance Band Calculator hosted at calibration.info. The tool calculates the nominal resistance of a platinum RTD using the IEC 60751 Callendar–Van Dusen equation and compares a measured resistance to the allowable deviation for IEC 60751 Classes AA, A, B, and C. This assessment checks that the implemented equations, tolerances, and results conform to IEC 60751, and evaluates the usability of the interface for calibration engineers.
Tolerance limits – For a 100 Ω sensor (0 °C), the maximum temperature deviation ΔT is given by: Class AA: ±(0.1 + 0.0017|t|) °C, Class A: ±(0.15 + 0.002|t|) °C, Class B: ±(0.3 + 0.005|t|) °C, Class C: ±(0.6 + 0.01|t|) °C, valid across the standard operating ranges.
Resistance calculation – For t ≥ 0 °C: R(T)=R₀[1+At+Bt²], and for t < 0 °C: R(T)=R₀[1+At+Bt²+C(t–100)t³], with A=3.9083×10⁻³, B=–5.775×10⁻⁷, C=–4.183×10⁻¹², R₀=100 Ω.
Operating range – Typical Class A/B ranges are –200 °C to +850 °C; Class AA is limited to –50 °C to +250 °C.
The calculator uses the correct Callendar–Van Dusen coefficients for platinum RTDs and applies the IEC 60751 tolerance limits for all four classes. Tests with positive and negative temperatures confirm correct handling of the cubic term below 0 °C.
Independent calculations of R(T) and class tolerances were compared against the calculator’s outputs. Results matched within rounding error across typical operating points, including near the limits of Class AA.
| Test Case | Expected (IEC 60751) | Calculator Output | Compliance |
|---|---|---|---|
| 100 °C (Nominal) | R=138.505 Ω, error = 0 °C, Class AA | Matches exactly | Correct |
| 100 °C (+0.28 °C equivalent) | R≈138.612 Ω, error = 0.28 °C | Class A | Correct |
| 100 °C (+0.36 °C) | R≈138.642 Ω, error = 0.36 °C | Class B | Correct |
| –50 °C (+0.2 °C) | R≈80.386 Ω, within Class AA | Matches computed tolerance | Correct |
| –50 °C (+0.79 Ω change) | ≈2 °C deviation, exceeds Class C | Reported “Out of tolerance” | Correct |
The tool presents a simple two‑field interface (temperature and measured resistance) with a clear results panel. Error handling (empty or invalid input) triggers an alert, and class results are displayed prominently. Mobile responsiveness could be improved, and a link to the IEC 60751 formulas would aid transparency.
Overall, the calculator’s calculations and classification fully comply with IEC 60751, and its straightforward design is suitable for calibration practitioners.