Pt100 calculator and resistance table

What the calculator is for

A platinum resistance thermometer changes resistance with temperature in a way IEC 60751 defines with the Callendar–Van Dusen equation. Use the calculator to check a sensor with a decade box or multimeter, set up a simulator, verify a transmitter, or find the temperature behind a resistance reading.

• 0 °C to 850 °C: R = R₀ (1 + A·t + B·t²)
• −200 °C to 0 °C: R = R₀ [1 + A·t + B·t² + C·(t − 100)·t³]
• A = 3.9083 × 10⁻³, B = −5.775 × 10⁻⁷, C = −4.183 × 10⁻¹²; R₀ = 100 Ω for a Pt100, 1,000 Ω for a Pt1000.

Worked example

At 100 °C a Pt100 reads 138.51 Ω and a Pt1000 1,385.06 Ω. Around room temperature a Pt100 changes by about 0.388 Ω per °C.

That small sensitivity is why wiring matters. In a 2-wire connection both leads add to the reading. Ten metres of 0.5 mm² copper is about 0.36 Ω per lead, so the reading is 0.72 Ω high and the temperature about 1.9 °C high. A 3-wire or 4-wire connection removes most or all of that error; with a Pt1000 the same leads cause a tenth of it.

Pt100 and Pt1000 resistance table

Common mistakes

• Using the linear 0.385 Ω/°C rule. It is exact only near 0 °C; at 300 °C the linear estimate is off by more than 5 °C.
• Mixing α = 0.00385 and α = 0.00392 sensors. Older US sensors use a different curve. Check the sensor’s α before using this table.
• Ignoring lead resistance. See the example above; select 2-wire under Advanced to see the error for your leads.
• Reading the tolerance class as a system accuracy. Class A (± 0.15 + 0.002·|t| °C) covers the element only, not the transmitter, wiring or drift.

Basis

Coefficients and tolerance classes AA, A, B and C follow IEC 60751 for industrial platinum resistance thermometers (α = 0.00385 /°C). The inverse below 0 °C is solved numerically to better than 10⁻⁹ °C.