Thermocouple Reference Calculator

Thomas Johann Seebeck, an Estonian-German physicist, discovered in 1821 that a closed circuit of two dissimilar metals generates a continuous current when one junction is at a different temperature than the other. Seebeck originally attributed the effect to magnetism (he called it "thermomagnetism"), but Hans Christian Ørsted correctly identified it as a thermoelectric phenomenon — now the Seebeck effect. Its inverse, the Peltier effect (current produces cooling or heating), was discovered by Jean Charles Peltier in 1834.

Standardization of thermocouple types came in waves. Platinum-based Types R and S were calibrated to the International Temperature Scale in 1927 — still the reference standards for high-temperature calibration. Base-metal types K (chromel-alumel), J (iron-constantan), and T (copper-constantan) were standardized by ANSI and ASTM in the 1960s and remain the workhorse types for industrial and commercial use. Type N (nicrosil-nisil) was developed in the 1980s to solve drift problems with Type K at high temperatures.

NIST publishes polynomial approximations (ITS-90 standard) that characterize each type\'s V-T curve to better than ±0.1 °C over its rated range. Modern thermocouple signal-conditioning ICs (Maxim MAX31855, Analog Devices AD594) embed these polynomials plus a cold-junction sensor and amplifier into a single chip, producing a linear digital or analog output ready for an ADC. The 1821 discovery remains one of the oldest still-commercialized electrical phenomena.

Pick a thermocouple type (K for general use, T for cryogenics, R/S/B for high-temp precision). Choose whether to convert temperature → voltage or voltage → temperature. Enter the value plus the cold-junction reference temperature (0 °C for an ice bath, 25 °C for room-temp electronic CJC). The tool applies the NIST polynomial for that type and returns the conversion plus local sensitivity in µV/°C.

Important: the raw thermocouple voltage measures the temperature difference between the hot junction and your measurement device\'s terminals. If your terminals aren\'t at 0 °C, you must add the voltage equivalent of the terminal temperature to the measurement — this is cold-junction compensation. Electronic CJC chips do this automatically; for bench measurements with a multimeter, use an ice-bath reference or record the ambient and correct afterward. Everything runs client-side.