M&M SELF STUDY

SUBMITTED BYK.KOUSHIKRV COLLEGE OF ENINEERING

THERMOCOUPLE- TYPES AND APPLICATION

Thermocouple Temperature Limit

Type K Thermocouple (Nickel-Chromium / Nickel-Alumel)

• The type K is the most common type of thermocouple. It’s inexpensive, accurate, reliable, and has a wide temperature range.

• Type K thermocouples usually work in most applications as they are nickel based and exhibit good corrosion resistance

• Temperature Range:Thermocouple grade wire(–270 to1260C) Extension wire(0 to 200C)• AccuracyStandard: +/- 2.2C or +/- .75%Special Limits of Error: +/- 1.1C or 0.4%

Type J Thermocouple (Iron/Constantan):

• Composed of a positive leg which is iron and a negative leg which is approximately 45 % nickel-55% copper

• The type J is also very common. It has a smaller temperature range and a shorter lifespan at higher temperatures than the Type K.

• Temperature Range:Thermocouple grade wire: -210 to 760CExtension wire: 0 to 200C• AccuracyStandard: +/- 2.2C or +/- .75%Special Limits of Error: +/- 1.1C or 0.4%

Type T Thermocouple (Copper/Constantan)

• The Type T is a very stable thermocouple and is often used in extremely low temperature applications such as cryogenics or ultra low freezers.

• Temperature Range:Thermocouple grade wire(-270 to 370C)Extension wire(0 to 200C)• Accuracy :Standard: +/- 1.0C or +/- .75%Special Limits of Error: +/- 0.5C or 0.4%

Type E Thermocouple (Nickel-Chromium/Constantan)

• Composed of a positive leg, which is approximately 90% nickel, 10 chromium and a negative leg, which is approximately 95% nickel, 2% aluminum, 2% manganese and 1% silicon.

• The Type E has a stronger signal & higher accuracy than the Type K or Type

• Temperature Range:Thermocouple grade wire (-270 to 870C)Extension wire(0 to 200C)• Accuracy :Standard: +/- 1.7C or +/- 0.5%Special Limits of Error: +/- 1.0C or 0.4%

Type N Thermocouple (Nicrosil / Nisil)

• The Type N shares the same accuracy and temperature limits as the Type K. The type N is slightly more expensive.

• Type N has also been found to be more stable than Type K in nuclear environments.

• Temperature Range:Thermocouple grade wire(-270 to 392C)Extension wire, 32 to 392F (0 to 200C)• Accuracy :Standard: +/- 2.2C or +/- .75%Special Limits of Error: +/- 1.1C or 0.4%

Thermocouple Material Vs EMF[5]Types T, J, and K are most commonly used thermocouples (see Table 16.8 of the “Handbook”).

Type S Thermocouple (Platinum Rhodium - 10% /

Platinum)• Composed of a positive leg which is approximately

90% Platinum, 10% Rhodium and a negative leg which is approximately 94% Platinum, 6% Rhodium.

• Used in very high temperature applications in the BioTech and Pharmaceutical industries. High accuracy and stability.

• Temperature Range:Thermocouple grade wire(-50 to 1480C)Extension wire(0 to 200C)• Accuracy :Standard: +/- 1.5C or +/- .25%Special Limits of Error: +/- 0.6C or 0.1%

Type R Thermocouple (Platinum Rhodium -13% /

Platinum)• Composed of a positive leg which is approximately 70%

Platinum, 30% Rhodium and a negative leg which is approximately 94% Platinum, 6% Rhodium.

• The Type R is used in very high temperature applications. It has a higher percentage of Rhodium than the Type S, which makes it more expensive.

• High accuracy and stability.• Temperature Range:Thermocouple grade wire (-50 to 1480C)Extension wire(0 to 200C)• Accuracy :Standard: +/- 1.5C or +/- .25%Special Limits of Error: +/- 0.6C or 0.1%

Type B Thermocouple (Platinum Rhodium – 30% /

Platinum Rhodium – 6%)• Composed of a positive leg which is approximately 14%

chromium, 1.4% Silicon and 84.6% Nickel, a negative leg which is approximately 4.4% Silicon, 95.6% Nickel.

• The Type B thermocouple has the highest temperature limit of all of the thermocouples listed above. It maintains a high level of accuracy and stability at very high temperatures.

• Temperature Range:Thermocouple grade wire (0 to 1700C)Extension wire (0 to 100C)• Accuracy :Standard: +/- 0.5%Special Limits of Error: +/- 0.25%

Thermocouple Accuracies

Thermocouple Conductor Type Limits of Error

Standard Special

Type K ±2.20C or ±0.75% ±1.10C or ±0.4%

Type T ±1.00C or ±0.75% ±0.50C or ±0.4%

Type J ±2.20C or ±0.75% ±1.10C or ±0.4%

Type N ±2.20C or ±0.75% ±1.10C or± 0.4%

Type E ±1.70C or ±0.5% ±1.00C or ±0.4%

Type S ±1.50C or ±0.25% ±0.60C or ±0.1%

Type R ±1.50C or ±0.25% ±0.60C or ±0.1%

Type B ±0.5% ±0.25%

[2]The accuracy of a thermocouple depends on many factors including but not limited to electrical interference and the purity of the metals used.

Sheath Materials[6]• AluminumMax temperature: 600 °C or (315°C). Commercially pure aluminum. Used in special applications requiring good thermal conductivity. • 304 Stainless Steel Maximum temperature:900°C.Lowest cost corrosion resistant sheath material available.Subject to damaging carbide precipitation• 446 Stainless SteelMaximum temperature:1150°C.Good resistance to sulfurous atmospheres at high temperatures.Good corrosion resistance,this alloy the highest heat resistance• Inconel 601 Maximum temperature: 2300°F (1260°C) Outstanding oxidation resistance. Designed for high temperature corrosion resistance.Good in carburizing environments, and has good creep rupture strength. Other materials include Copper, Molybdenum, Monel 400, Tantalum,etc.

SheathMineral insulation

• [4]The operating principle of antenna-coupled nanowire thermocouples(TCs) combines the wave nature of IR radiation,Joule heating, and the Seebeck effect.

• Single metal is used,Junction is formed by attaching a dipole antenna

• Antenna receives the electromagnetic waves,and the radiation-induced currents heat the hot junction of the thermocouple (TC).

• This creates a temperature difference between the hot and cold junctions

• The influence of surface electron scattering on the mean free path of the electrons yields a thickness dependence of the Seebeck effect and makes single-metal thermocouples possible

Antenna Coupled Thermo-Couple

Self-validating Thermocouples With IntegratedFixed-point Units• Self-validated measurements

of temperatures above 1000 *C

• The use of miniature fixed-point cells and modules with defined and stable melting temperatures of pure metals which are combined directly with commonly used type B thermocouples to detect their drift effects

• Heat the milk quickly from a holding temperature to the required temperature for destroying microbes and harmful enzymes (for example 72 degrees C).

• Holding the milk at this temperature, pass it through a length of tubing at a closely controlled flow rate.

• The milk exits the process at the far end of the tubing, after the required time interval (for example 22 seconds).

• If the milk is still at the required temperature at the exit point, it is allowed to continue on for further processing.

Use Of Thermocouples In commercial HTST pasteurization

processing for milk.

• The basic application requirements for the temperature measurement are:

• Operating range of 55 degrees to 85 degrees C.

• No physical damage from out-of-range temperatures.

• Total measurement accuracy +- 0.5 degrees C.

• Long term drift +- 0.2 degrees C.• Maximum settling time 4 seconds.

• In nuclear applications thermocouples are strongly affected by intense neutron fluxes.

• Selection of appropriate alloys for the sheath can allow to use Nickel based thermocouples up to 1300°C for nuclear applications. • At temperatures higher than 1000°C conventional Inconel600 sheathed type N thermocouples can experience a drift of several degrees, while in the new sheath the drift of type N thermocouples is limited to about ±1.5°C.

• The composition of conventional alloys used for thermocouple sheath is designed to withstand highly oxidizing or carburizing atmospheres.

Low Drift Type N Thermocouples

Temperature Measurement Errors[4]

ConductionConvectionRadiationResponse TimeNoise• Grounding issues and shorts, especially on metal

surfaces

Pros And Conso Simple, ruggedo High temp. operationo No resistance lead wire

problemso Point temp. sensingo Fastest response to

temperature changeso A wide useful

temperature range,o Are inherently differential, o Reliable and inexpensive

Least stable, least repeatableLow sensitivity to small temperature

changesExtension wire must be of the same

thermocouple typeWire may pick up radiated electrical noise

of not shieldedLowest accuracyvery low output, on the order of 40

μV/ °C.Slight nonlinearityneed for calibration.

References• [1]Mechanical Measurements by Thomas G.

Beckwith and N. Lewis Buck• [2]Johannes A. Russert etal Institute for

Nanoelectronics University of Notre Dame, U.S.A.• [3]http://www.utrm.rub.de/doc/fachlabor/

skript_en_temperature-laboratory.pdf• [4]978-1-4799-8275-2/15/$31.00 ©2015 IEEE• [5]Investigation of self-validating thermocouples

with integrated fixed-point units• [6]http://www.thermometricscorp.com/sheath-

material.html