Best for: General purpose industrial applications: kilns, boilers, process heating, HVAC, food processing, engine testing. Works in oxidising or inert atmospheres. Type K is the default choice when no specific reason exists to choose another type.

Limitations: Susceptible to green rot (preferential oxidation of chromium in low-oxygen environments at high temperatures). Experiences calibration drift due to short-range ordering between 300°C and 600°C on repeated cycling. Not recommended in sulphurous, reducing or vacuum atmospheres above 500°C.

Best for: General industrial process measurement, particularly where reducing atmospheres are present (plastic moulding, heat treating). Type J is one of the few base metal types that can operate safely in reducing atmospheres where oxygen is deficient. Very common in older process plants in North America.

Limitations: The iron positive leg oxidises rapidly above 540°C. Not recommended above 760°C even in larger gauge sizes. Susceptible to rust in moist environments. Maximum temperature range is narrower than Type K. Type K will generally outlast Type J in the same application.

Best for: Cryogenic research, ultra-low temperature freezers, pharmaceutical cold storage, food freezing tunnels, HVAC, and any application below 0°C. Excellent repeatability between -200°C and +200°C. Type T is moisture-resistant and stable in moist, mildly oxidising or reducing atmospheres. It is the preferred type for food industry applications.

Limitations: Limited upper temperature (370°C maximum in air). The copper positive leg has high thermal conductivity, which can cause measurement errors if there is significant heat conduction along the wire. Not suitable for high-temperature industrial applications.

Best for: Applications where a strong output signal is needed to overcome electrical noise, including industrial heating, drying ovens, plastics processing. Suitable in vacuum, inert or mildly oxidising atmospheres. Non-magnetic, making it useful near strong magnetic fields such as MRI equipment, particle accelerators and scientific instruments.

Limitations: Less common than K or J, which can make replacement sensors and extension cable harder to source. Not recommended for use in sulphurous or reducing atmospheres.

Best for: Applications above 800°C where Type K shows instability or drift. Type N was specifically developed to address Type K's short-range ordering and green rot problems. The addition of silicon to both legs suppresses preferential oxidation and gives significantly better long-term stability in cyclic high-temperature applications. Good choice for gas turbines, industrial furnaces and long-term high-temperature monitoring.

Limitations: Slightly more expensive than Type K. Lower millivolt output than Type K at the same temperature. Less commonly stocked, which can complicate replacement planning. Uses the same broad temperature range as K but instruments must be configured correctly for the N curve, which is different from K.

Best for: Pharmaceutical sterilisation (autoclave monitoring), glass manufacturing, ceramic kilns, metallurgical furnaces, laboratory reference measurements. Type S was historically used as the international temperature scale reference point (ITS-90) between 660°C and 1,064°C. It is common in biotech and pharmaceutical applications because of its high accuracy and excellent long-term stability.

Limitations: Relatively low millivolt output requires high-quality instrumentation. Very sensitive to contamination. Even touching the platinum wire with bare hands deposits oils that cause drift. Must always be used inside a clean ceramic protection tube. Very expensive compared to base metal types.

Best for: Very high temperature furnace and kiln applications where Type S performance is adequate but slightly higher millivolt output is preferred. Type R has the same temperature range as Type S but with a higher percentage of rhodium which provides marginally better stability and slightly higher output at elevated temperatures. Used in glass manufacturing, metallurgy, ceramic production and high-temperature laboratory work.

Limitations: More expensive than Type S due to higher rhodium content. Same sensitivity to contamination as all noble metal types. ANSI wire colours for R are identical to Type S (both Black positive, Red negative, Green jacket), which creates identification confusion in the field. Always verify by checking the transmitter configuration or the instrument tag.

Best for: The highest temperature applications in industry: glass melting furnaces, steel and iron foundries, sintering furnaces, high-temperature metallurgy. Type B can continuously measure up to 1,820°C, which is higher than any other standard thermocouple type. Both legs are platinum-rhodium, which makes Type B unusually contamination-resistant compared to Types S and R (which have a pure platinum leg).

Limitations: Type B produces nearly zero output below approximately 50°C, which means it cannot be used in ambient temperature conditions. The very low output below 600°C makes it impractical at moderate temperatures. It is the most expensive of the standard thermocouple types. Requires a ceramic primary tube and a refractory outer protection tube.