thermocouples - walla walla universitycurt.nelson/engr325/student...thermocouples naomi allsman,...
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ThermocouplesNaomi Allsman, Briana Palacios, Bryan Wolf
1.What are they?
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Definition
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A thermocouple is a thermoelectric device
used to measure temperature.
Most common thermocouple: K type
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● TTC - Hot junction ○ The junction that is placed on
the surface or in the environment that is being measured
● TCJ - Cold Junction ○ The junction that remains at a
known constant temperature
● Differential Voltage○ Voltage created by different
temperatures fed by dissimilar metals
Texas Instrument diagram of thermocouple voltage.
Set Up
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Laws of Thermocouple Usage
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● 1st Law: Homogeneous Material
● 2nd Law: Intermediate Material
● 3rd Law: Law of Successive or Intermediate Temperatures
2.How do they work?
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Operation● Unknown temperature
applied to Hot Junction● Known temperature
applied to Cold Junction● Hot and Cold Junction
voltages added together● Voltage compared to
characteristic function
Courtesy of Omega
0 5001000 1500
Temperature (deg C)
E(T)
(mV
)0
1020
3040
5060
7080
Characteristic Functions
Courtesy Wikipedia
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Seebeck Functions
Courtesy analog.com
Courtesy researchgate.com
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Example Thermocouple Conditioning Circuit
3.Applications
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4 Basic Types
Type Temperature range (C) Accuracy Materials
J -210 - 760 2.2 iron/constantan
K -270 - 1260 2.2 nickel-chromium/nickel-alumel
T -270 -370 1.0 copper/constantan
N -270 - 392 2.2 nicrosil/nisil
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Applications
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● Type K - Plants, refineries
● Type J - Vacuum applications
● Type T - Food industry
● Type N - Furnaces, kilns
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● Hooked to controllers
● Two probes○ Hot - test
○ Cold - reference
● Shuts off valve
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How They Are Used
Why use thermocouplesAdvantages
● Small
● Accurate
● Multi use
● React quickly
Disadvantages
● Expensive
● Non-linear
● Low volts
● Hard to recalibrate
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Referenceshttps://www.thermocoupleinfo.com/
https://www.analog.com/en/analog-dialogue/articles/measuring-temp-using-thermocouples.html#
http://www.ti.com/lit/an/sbaa274/sbaa274.pdf
https://en.wikipedia.org/wiki/Thermocouple
https://www.omega.com/en-us/resources/thermocouples
https://www.researchgate.net/figure/Unfiltered-and-Filtered-Thermocouple-Output_fig10_268469128
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Thanks!
Questions