Thermocouple Types

A thermocouple measures the difference between the measuring junction and the reference (cold) junction, so every reading needs cold-junction compensation. Sensitivity is small — tens of microvolts per °C — so wiring and amplification matter more than the sensor.

Type	Conductors	Range (°C)	Sensitivity (µV/°C)	Notes
K	Chromel / Alumel	−200 … 1260	41	General purpose, cheap, most common
J	Iron / Constantan	−40 … 750	55	Older equipment; iron leg rusts
T	Copper / Constantan	−200 … 350	43	Cryogenic and low temperature, very stable
E	Chromel / Constantan	−200 … 900	68	Highest output of the base-metal types
N	Nicrosil / Nisil	−200 … 1300	39	Like K but far less drift at high temperature
S	Pt-10%Rh / Pt	0 … 1600	10	Noble metal, high temp, low output
R	Pt-13%Rh / Pt	0 … 1600	12	Noble metal, high temp
B	Pt-30%Rh / Pt-6%Rh	600 … 1700	8	Very high temperature only

Use matching thermocouple extension wire — ordinary copper wire creates a second junction and a new error. For −200…600 °C an RTD is usually more accurate; see the thermistor & RTD tool.

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