Date: July 2025
Scope: Verification of compliance of the Calibration.info Pt100 Sensitivity Calculator with IEC 60751:2008 requirements for platinum resistance thermometers (PRTs).
Temperature–Resistance Relationship
The calculator correctly implements the IEC 60751 Callendar–Van Dusen equations:
Rt=R0(1+At+Bt2)R_t = R_0(1 + At + Bt^2)Rt=R0(1+At+Bt2) for 0 °C≤t≤850 °C0 °C ≤ t ≤ 850 °C0 °C≤t≤850 °C.
Rt=R0[1+At+Bt2+C(t–100)t3]R_t = R_0[1 + At + Bt^2 + C(t – 100)t^3]Rt=R0[1+At+Bt2+C(t–100)t3] for −200 °C≤t<0 °C-200 °C ≤ t < 0 °C−200 °C≤t<0 °C.
Coefficients A=3.9083×10−3A=3.9083×10^{-3}A=3.9083×10−3, B=−5.775×10−7B=−5.775×10^{-7}B=−5.775×10−7, C=−4.183×10−12C=−4.183×10^{-12}C=−4.183×10−12 match IEC 60751 values.
Sensitivity Calculation (dR/dT)
The derivative formula has been corrected to fully align with IEC 60751:
dRdT=R0[A+2BT+C(4T3−300T2)]for T<0 °C.\frac{dR}{dT} = R_0\bigl[A + 2BT + C(4T^3 − 300T^2)\bigr] \quad \text{for } T<0 °C.dTdR=R0[A+2BT+C(4T3−300T2)]for T<0 °C.The previous non‑standard constant offset has been removed. Testing at –100 °C now yields dR/dT≈0.405308 Ω/°CdR/dT ≈ 0.405308 Ω/°CdR/dT≈0.405308 Ω/°C, matching the analytical IEC value.
Validation Against IEC Data
Resistance values (e.g., R(−100 °C)≈60.26 ΩR(−100 °C) ≈ 60.26 ΩR(−100 °C)≈60.26 Ω) match IEC 60751 Table 1 within 0.01 Ω.
Forward and reverse ΔR/ΔT functions now produce results consistent with the standard across the full –200 °C to 850 °C range.
Following correction of the negative‑temperature derivative, the Pt100 Sensitivity Calculator is now fully compliant with IEC 60751:2008 for both resistance and sensitivity calculations. No further discrepancies were identified.