Thermocouples and laws of thermocouples and materials used for it and advantages and limitations

1. M&M SELF STUDY
SUBMITTED BY
K.KOUSHIK
RV COLLEGE OF
ENINEERING

2. Thermocouple
Temperature Limit

3. 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)
• Accuracy
Standard: +/- 2.2C or +/- .75%
Special Limits of Error: +/- 1.1C or 0.4%

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 760C
Extension wire: 0 to 200C
• Accuracy
Standard: +/- 2.2C or +/- .75%
Special Limits of Error: +/- 1.1C or 0.4%

5. 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%

6. 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%

7. 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%

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

9. 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%

10. 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%

11. 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%

12. 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.

13. Sheath Materials[6]
• Aluminum
Max 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 Steel
Maximum 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.

14. • [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

15. Self-validating Thermocouples With Integrated
Fixed-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

16. • 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.

17. • 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

18. Temperature
Measurement Errors[4]
• Conduction
• Convection
• Radiation
• Response Time
• Noise
• Grounding issues and shorts, especially on metal
surfaces

19. Pros And Cons
o Simple, rugged
o High temp. operation
o No resistance lead wire
problems
o Point temp. sensing
o Fastest response to temperature
changes
o A wide useful temperature
range,
o Are inherently differential,
o Reliable and inexpensive
Least stable, least repeatable
Low sensitivity to small temperature
changes
Extension wire must be of the same
thermocouple type
Wire may pick up radiated electrical noise
of not shielded
Lowest accuracy
very low output, on the order of 40 μV/
°C.
Slight nonlinearity
need for calibration.

20. 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_tempe
rature-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