The DIN 43760 standardised temperature coefficient of platinum wire is: α = 0.00385. For a resistance of 100 ohms at 0 °C, this corresponds to + 0.385 ohm per °C (European α). α is therefore the average slope from 0°C to 100°C $$ \alpha = \frac{{{R_{100}} – {R_0}}}{{ {R_0} \times 100^\circ C.}} $$. There is a wide range of RTDs which have different α coefficients and ohm values at 0°C detailed in their technical properties. The most commonly used RTD is that with an α coefficient of 0.00385 and ohm value at 0°C of 100 Ω. It is known as Pt100.
| Values of some RTDs | ||
| R at 0°C (Ω) | α (Ω/Ω/°C) | Average sensitivity (Ω/°C) |
| 25.5 | 0.00392 | 0.1 |
| 100 | 0.00392 | 0.392 |
| 100 | 0.00391 | 0.391 |
| 100 | 0.00385 | 0.385 |
| 200 | 0.00385 | 0.770 |
| 470 | 0.00392 | 1.845 |
| 500 | 0.00392 | 1.963 |
| 500 | 0.00391 | 1.955 |
| 500 | 0.00385 | 1.925 |
| 1000 | 0.00385 | 3.850 |
| 1000 | 0.00375 | 3.750 |
| 10000 | 0.00385 | 38.50 |
| International standards DIN 43760 (IEC 751, BS-1904, JIS C1604) | ||
| Parameter | Class A | Class B |
| R0 | 100Ω ±0,06% | 100Ω ±0,12% |
| Alpha, α | 0,00385 ±0,000063 | 0,00385 ±0,000063 |
| Range | -200°C to 650°C | -200°c to 850°C |
| Res, RT | ±(.06+.0008|T|-2e-7T2) | ±(.12+.0019|T|-6e-7T2) |
| Temp, T | ±(0.3+0.002|T|)°C | ±(0.3+0.005|T|)°C |
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