Temperature Measurement · Glossary

What is Alpha Coefficient?

Symbol: αΩ/Ω/°CTemperature Measurement

Alpha coefficient is the average change in RTD resistance per degree between 0 and 100 °C, divided by the resistance at 0 °C.

Alpha Coefficient Explained

Alpha identifies the RTD curve. The industrial standard IEC 60751 platinum has α = 0.00385. Other curves exist, such as 0.003916 and 0.00392 used by some older standards.

The transmitter must be set to the same curve as the sensor, otherwise the reading is wrong at every point except 0 °C.

Alpha Coefficient Formula

α = (R₁₀₀ − R₀) ÷ (100 × R₀)

R₁₀₀	resistance at 100 °C
R₀	resistance at 0 °C

Example: Pt100: (138.51 − 100) ÷ 10,000 = 0.00385 per °C.

Calculators for Alpha Coefficient

CalculatorRTD CalculatorFree online calculator with formula and worked example.CalculatorPt100 TableFree online calculator with formula and worked example.

Free Downloads

Free downloadTemperature Measurement Cheat SheetFree printable PDF cheat sheet.

Frequently Asked Questions

What is Alpha Coefficient?

Alpha coefficient is the average change in RTD resistance per degree between 0 and 100 °C, divided by the resistance at 0 °C.

What happens if the alpha is wrong?

The reading is correct at 0 °C and drifts further off as temperature rises, about 2 °C off at 100 °C for the 0.00385 versus 0.00392 curves.

Is alpha the same as temperature coefficient?

Yes, it is the mean temperature coefficient of resistance over 0 to 100 °C.

Learn more on the blog

What is an RTD and how it works

A practical guide on instrumentationblog.in with more detail on alpha coefficient and how it is applied on real plants.

Read Full Article

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