Thermocouple Seebeck Voltage

Formula

Description

A thermocouple generates a voltage proportional to the temperature difference between its measurement junction and its reference (cold) junction, with the proportionality constant being the Seebeck coefficient S. This is a linearized approximation; real thermocouple voltage is a polynomial function of temperature. Common types and their approximate Seebeck coefficients: Type K (chromel-alumel) ≈ 41 µV/°C, Type J (iron-constantan) ≈ 52 µV/°C, Type T (copper-constantan) ≈ 43 µV/°C, Type E (chromel-constantan) ≈ 61 µV/°C.

Variables

• V — Output voltage (µV level, entered in base unit V)
• S — Seebeck coefficient (µV/°C, entered as V/°C in base units)
• ΔT — Temperature difference between hot and cold junctions (°C)

Practical Notes

The Seebeck coefficient varies with temperature, so this linear model is accurate only for small temperature ranges. For precision measurements, use NIST polynomial tables for the specific thermocouple type. Cold junction compensation (CJC) is required because the reference junction is not at 0°C — either use a physical ice bath or an electronic CJC sensor. Thermocouple signals are very small (typically mV) and require high-gain, low-noise amplification.