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FAQ About Thermocouples

When you need to detect a temperature in your system, not only must you weigh various tradeoffs between temperature sensors, you must also be sure you have the right cable for data handling and to ensure accurate measurements. SAB North America has expertise in thermocouples, resistance thermometers and the cabling you need to build an optimal assembly. We’re well-positioned to answer cabling questions that pertain to your temperature measurement needs. Here is a sample of some of the questions we often answer:

Both devices have advantages. To find the ideal solution, you should match your system’s requirements with the benefits of each type of sensor. This table can help you compare each sensor:

CharacteristicsResistance ThermometerThermocouples
Dimensions larger sensor surface small sensor surface possible
Response Time relatively long short
Connection Cables copper cables thermocompensating cable
Accuracy very good good
Consistency very good satisfactory
Surface Temperature Measurement not possible possible
Hot Junction over the whole length of the RTD punctual
Robustness good very good
Spontaneous Heating has to be considered does not occur
Temperature Range up to +600°C higher temperature possible
Cold Junction not necessary necessary
Circuit Supply yes no
Vibration Resistance relatively sensitive very rugged
Jacket construction has the largest effect on response time. For example, you can speed up your response time by choosing the right metal jacket, heat transfer compounds and measurement point position. You can also talk to SAB North America’s experts to determine an ideal solution for your assembly.
Away from the hottest spot of measurement, the temperature will decrease rapidly. At this point, a temperature-resistant metal sheath is no longer necessary and it is possible to switch to an extension cable to transfer the measured value. Depending on the remaining distance, SAB North America can offer suitable cable with the right cross-section.

Thermocouple cables consist of the same element material as the thermocouple and are tested for the same temperatures.

Extension cables are made of conductors with a nominal structure that’s identical to the corresponding thermocouple and are normally tested within a temperature range of 0º up to +200ºC.

Compensating cables are made of substitute insulating material and have thermoelectric characteristics in the allowed temperature range (usually 0º up to +200ºC) as the corresponding thermocouple.

The metal jacket is an important part of a temperature sensor assembly, and it should be chosen carefully. There are several metallic alloys to resist acids, combustible gases and rust, as well as maximum temperature. SAB North America can provide an overview of various steel types to address your application's harsh environment.

Unalloyed High Temperature Steel
Max. Application TemperatureMaterial No.Material CharacteristicsApplication Range
400°C 1.305 (ASTM 105) Unalloyed steel weld-in and screw-in protecting tubes in steam lines
500°C 1.5415 (AISI A204 Gr. A) Low Alloy and high temperature steel with molybdenum addition weld-in and screw-in protecting tubes
540°C 1.7335 (AIAI A182 F11) Low-alloy and high temperature steel with chromium and molybdenum addition weld-in and screw-in protecting tubes
570°C 1.7380 (AISI A182 F11) Low-alloy and high temperature steel with chromium and molybdenum addition weld-in and screw-in protecting tubes
650°C 1.4961 High temperature austenitic chromium nickel steel (Niobium stablized) weld-in and screw-in protecting tubes
Rust and Acid Resistant Steel
550°C 1.4301 (AISI 304) Good resistance against organic acids with medium temperatures, saline solutions p.e. sulphates, sulphides, alkaline solvents with medium temperature food, luxury market, medical, apparatus engineering
550°C 1.4404 (AISI 316 L) With the addition of molybdenum it is more corrosion-proof in oxidizing acids, p.e. acid of vinegar, acidity of wine, phosphoric acid, sulphuric acid and others. There is an elevated resistance against intercrystalline corrosion by a reduced carbon content chemical, pulp, nuclear, textile, pharmaceutical, dairies and breweries
550°C 1.4435 (AISI 316 L) Elevated resistance against corrosion compared with 1.4404, smaller delta ferrite portion pharmaceutical
550°C 1.4541 (AISI 321) Good resistance against heavy products, vapor, and combustion gases. Good resistance against oxidation chemical industry, nuclear power plants, textile
550°C 1.4571 (AISI 316 TI) Elevated corrosion resistance compared to certain acids due to the addition of molybdenum. Resistant against crevice corrosion, salt water and aggressive industrial influences pharmaceutical, dairies, and breweries
The main differences among the various types are the temperature range in combination with the accuracy of the classes. The experts at SAB North America can walk you through the different types of thermocouples or customize a thermocouple to fit your needs.

 Class 1Class 2Class 3
TypeStandardMaterialTemp RangeLimit deviation (2)Temp RangeLimit deviation (2)Temp RangeLimit deviation (2)
T DIN EN 60584 Cu-CuNi -40°C to +350°C 0.5°C or 0.40% -40°C to +350°C 1.0°C or 0.75% -200°C to +40°C 1.0°C or 1.5%
U (1) DIN 43710 Cu-CuNi -- -- 0°C to +600°C ±3°C / ±0.75% -- --
J DIN EN 60584 Fe-CuNi -40°C to +750°C 1.5°C or 0.40% -40°C to +750°C 2.5°C or 0.75% -- --
L (1) DIN 43710 Fe-CuNi -- -- 0°C to +900°C ±3°C / ±0.75% -- --
K DIN EN 60584 NiCr-Ni -40°C to +1000°C 1.5°C or 0.40% -40°C to +1200°C 2.5°C or 0.75% -200°C to +40°C 2.5°C or 1.5%
E DIN EN 60584 NiCr-CuNi -40C° to +800°C 1.5°C or 0.40% -40°C to +900°C 2.5°C or 0.75% -200°C to +40°C 2.5°C or 1.5%
N DIN EN 60584 NiCrSi-NiSi -40°C to +1000°C 1.5°C or 0.40% -40°C to +1200°C 2.5°C or 0.75% -200°C to +40°C 2.5°C or 1.5%
S DIN EN 60584 PtRh 10-Pt 0°C to +1600°C 1.0°C or (3) 0°C to +1600°C 1.5°C or 0.25% -- --
R DIN EN 60584 PtRh-13-Pt 0°C to +1600°C 1.0°C or (3) 0°C to +1600°C 1.5°C or 0.25% -- --
B DIN EN 60584 PtRh30-PtRh6 -- -- 600°C to +1700°C 1.5°C or 0.50% +600°C to +1700°C 4.0°C or 1.0%

Classes 1, 2, and 3 are valid for thermocouples.
(1) Since April 1994 the standard DIN 43710 is no longer valid.
(2) For the limit deviation, the higher value is valid.
(3) 1°C or [1+(t-1100) x 0.003]°C

Get Temperature Sensors Tailor-Made To Your Requirements
As a leading manufacturer of electric thermometers for many different applications, SAB North America can help you select the right thermocouple or create a custom solution for your application. And, we can provide the right thermocouple cable with the quality and reliability your system demands. Be sure to talk to SAB North America to get all your temperature measurement questions answered.

For more information about SAB North America thermocouples and resistance thermometers, click here

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