Convert between temperature and resistance for Pt100, Pt500 and Pt1000 sensors on the IEC 60751 curve, or Ni1000 on DIN 43760, with the tolerance of each accuracy class.
Pt100
138.510.3793 Ω per °C hereClass B: ±0.8 °CTolerance by class, wire-wound element
On two wires, every ohm of lead loop resistance reads as 2.637 °C too hot at this temperature.
Work out the lead error at 100 °CPt100 resistance
138.51Ω
Check the values to see a result.
Lead resistance, self-heating and the transmitter add their own error.
R(T) = R0 × (1 + A × T + B × T² + C × (T − 100) × T³), with C = 0 at and above 0 °C
A Pt100 sensor at 100 °C (212 °F) reads 138.51 Ω.
Tip: A two-wire Pt100 reads about 2.6 °C high for every ohm of lead loop resistance. Use three or four wires on any real run.
A Pt100 is a platinum resistance thermometer that reads 100 Ω at 0 °C and rises by about 0.39 Ω for each degree. A Pt1000 follows the same curve at ten times the resistance, 1000 Ω at 0 °C. The calculator converts either way on the IEC 60751 curve and gives the tolerance of the sensor’s accuracy class at that temperature.
R = R0 × (1 + A × T + B × T2)
R0 is 100 Ω for a Pt100, 500 Ω for a Pt500 and 1000 Ω for a Pt1000. The IEC 60751 coefficients are A = 3.9083 × 10−3 and B = −5.775 × 10−7. At 100 °C a Pt100 reads 100 × (1 + 0.39083 − 0.005775) = 138.51 Ω.
R = R0 × (1 + A × T + B × T2 + C × (T − 100) × T3)
The Callendar-Van Dusen equation adds a third term with C = −4.183 × 10−12, which matters at cryogenic temperatures and hardly at all near 0 °C.
T: solve R(T) = Rmeasured
Above 0 °C the quadratic can be solved directly; below it the calculator solves the curve numerically. A quick estimate is (R − 100) ÷ 0.385 for a Pt100, which is within about 1 °C from 0 to 100 °C.
class B: ±(0.3 + 0.005 × |T|) °C
Class A is ±(0.15 + 0.002 × |T|), AA ±(0.1 + 0.0017 × |T|) and C ±(0.6 + 0.01 × |T|). Each class applies only over the range IEC 60751 gives for the element type, wire-wound or thin-film.
A multimeter across a Pt100 reads 109.73 Ω. On the IEC 60751 curve that is 24.99 °C. The quick estimate, 9.73 ÷ 0.385, gives 25.3 °C, close enough to spot a faulty sensor but not to calibrate one.
Temperature 24.99 °C Open in the calculator
Below 0 °C the resistance falls below R0. At −40 °C a Pt1000 reads 842.71 Ω, and a class B element is within ±0.5 °C.
Pt1000 resistance 842.71 Ω Open in the calculator
At 100 °C a Pt100 reads 138.51 Ω. Class B allows ±(0.3 + 0.005 × 100) = ±0.8 °C, so a class B sensor may read anywhere from 99.2 to 100.8 °C before any lead or transmitter error.
Pt100 resistance 138.51 Ω Open in the calculator
Resistance on the IEC 60751 curve, with the class B tolerance of a wire-wound element. A Pt500 reads five times the Pt100 figure.
| Temperature (°C) | Pt100 (Ω) | Pt1000 (Ω) | Class B (±°C) |
|---|---|---|---|
| −150 | 39.72 | 397.23 | 1.05 |
| −100 | 60.26 | 602.56 | 0.8 |
| −50 | 80.31 | 803.06 | 0.55 |
| −40 | 84.27 | 842.71 | 0.5 |
| −30 | 88.22 | 882.22 | 0.45 |
| −20 | 92.16 | 921.60 | 0.4 |
| −10 | 96.09 | 960.86 | 0.35 |
| 0 | 100.00 | 1,000.00 | 0.3 |
| 10 | 103.90 | 1,039.03 | 0.35 |
| 20 | 107.79 | 1,077.94 | 0.4 |
| 30 | 111.67 | 1,116.73 | 0.45 |
| 40 | 115.54 | 1,155.41 | 0.5 |
| 50 | 119.40 | 1,193.97 | 0.55 |
| 60 | 123.24 | 1,232.42 | 0.6 |
| 70 | 127.08 | 1,270.75 | 0.65 |
| 80 | 130.90 | 1,308.97 | 0.7 |
| 90 | 134.71 | 1,347.07 | 0.75 |
| 100 | 138.51 | 1,385.05 | 0.8 |
| 120 | 146.07 | 1,460.68 | 0.9 |
| 150 | 157.33 | 1,573.25 | 1.05 |
| 200 | 175.86 | 1,758.56 | 1.3 |
| 250 | 194.10 | 1,940.98 | 1.55 |
| 300 | 212.05 | 2,120.52 | 1.8 |
| 400 | 247.09 | 2,470.92 | 2.3 |
| 500 | 280.98 | 2,809.78 | 2.8 |
| 600 | 313.71 | 3,137.08 | 3.3 |
100 Ω at 0 °C and 138.51 Ω at 100 °C. The average change over that range is 0.385 Ω per °C, which is why the IEC curve is called Pt385.
A Pt1000 changes by about 3.9 Ω per °C against 0.39 Ω for a Pt100, so the same lead resistance causes a tenth of the error. That makes Pt1000 the better choice for two-wire connections and battery-powered electronics. Pt100 remains common with three- and four-wire transmitters.
In a two-wire Pt100 circuit, every ohm of lead loop resistance reads as about 2.6 °C too high. Three- and four-wire connections cancel most or all of it. The RTD lead resistance error calculator works out the error for a cable run.
Both read 1000 Ω at 0 °C, but nickel is far more sensitive: a DIN 43760 Ni1000 reads 1617.79 Ω at 100 °C against about 1385 Ω for a Pt1000, and its curve bends more. It covers only −60 °C to 250 °C and its class B tolerance is wider, ±(0.4 + 0.007 × T) °C above 0 °C. Ni1000 is common in heating and ventilation controls. Some controllers use the Ni1000 TK5000 curve instead, which reads about 1500 Ω at 100 °C, so check which one the input expects.
Most are. IEC 60751 sensors use α = 0.00385. Some older North American sensors use α = 0.00392, a different curve, so check the datasheet before using these figures.
A Pt100 with a 4-20 mA head transmitter connects to a ZIO. For pipes, tanks and cold stores, a TES probe sensor measures temperature directly and reports over the wireless mesh.
