Instrumentation

Types of thermocouples

In this lesson, we will study types of thermocouples.

Types of thermocouples are listed below.

K

Type K (chromel {90% nickel and 10% chromium}—alumel {95% nickel, 2% manganese, 2% aluminium and 1% silicon}) is the most common general purpose thermocouple are available in its −200 °C to +1350 °C / -330 °F to +2460 °F range.

J

Type J (iron–constantan) has a more restricted range than type K (−40 to +750 °C).

N

Type N (Nicrosil–Nisil) (nickel-chromium-silicon/nickel-silicon) thermocouples are suitable for use between −270 °C and 1300 °C.

B

Type B thermocouples use a platinum-rhodium alloy for each conductor. These thermocouples are suited for use at up to 1800 °C. Type B thermocouples produce the same output at 0 °C and 42 °C, limiting their use below about 50 °C.

R

Type R thermocouples use a platinum-rhodium alloy containing 13% rhodium for one conductor and pure platinum for the other conductor. Type R thermocouples are used up to 1600 °C.

S

Type S thermocouples are constructed using one wire of 90% Platinum and 10% Rhodium (the positive or “+” wire) and the second wire of 100% platinum (the negative or “-” wire). type S thermocouples are used up to 1600 °C. use in the biotech and pharmaceuticals industry.

C

Type C (tungsten 5% rhenium – tungsten 26% rhenium) thermocouples are suited for measurements in the 0 °C to 2320 °C range. This thermocouple is well-suited for vacuum furnaces at extremely high temperatures. It must never be used in the presence of oxygen at temperatures above 260 °C.

M

Type M thermocouples use a nickel alloy for each wire. The positive wire (20 Alloy) contains 18% molybdenum while the negative wire (19 Alloy) contains 0.8% cobalt. These thermocouples are used in vacuum furnaces for the same reasons as with type C. Upper temperature is limited to 1400 °C. It is less commonly used than other types.

In the above table, one can see wire color and overall jacket color for every thermocouple.

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