In terms of parameters of thermocouples, the first is the division mark, which refers to the type, such as K type, J type, T type, E type, N type, S type, R type, B type, etc. Each type has a different material composition, for example, K-type is nickel chromium nickel silicon, while S-type is platinum rhodium 10 platinum. The temperature range corresponding to these graduation marks is also important, for example, the K-type can usually measure -200 ° C to+1300 ° C, while the S-type can measure around 0 ° C to 1600 ° C.

Then there is the temperature range, each thermocouple has a different working temperature range, and users need to choose the appropriate type according to their actual application. For example, S-type or B-type may be used in high-temperature environments, while T-type or E-type may be used in low-temperature environments.

Accuracy or error range is also a key parameter. Thermocouples with different division marks have different errors in different temperature ranges. For example, a K-type thermocouple has an error of ± 1.5 ° C within the range of -40 ° C to+375 ° C, and the error may increase to ± 0.4% of the reading at higher temperatures.

In terms of output signal, the output of the thermocouple is a millivolt level voltage, but the specific value needs to be referred to the corresponding calibration table because the relationship between thermoelectric potential and temperature is nonlinear. It may be necessary to explain why cold end compensation is needed, because thermocouples measure the temperature difference between the two ends, and usually require a known temperature at the reference end (cold end) in order to accurately calculate the temperature at the measuring end.

The material composition is equally important, and thermocouples with different division marks use different metal combinations, which affect their corrosion resistance, oxidation resistance, and applicable environment. For example, J-type thermocouples are made of iron constantan and are suitable for reducing atmospheres, while S-type thermocouples are used for oxidizing high-temperature environments.

Response time is also a parameter that may be related to the diameter of the thermocouple and the material of the protective sleeve. Finer thermocouples respond faster, but may be more susceptible to damage. In addition, the installation method (such as insertion depth, fixing method) can also affect measurement accuracy and response speed.

There is also linearity, although the output of thermocouples is nonlinear, certain types may be closer to linearity within a specific temperature range, which may simplify signal processing in certain applications.

In addition, users may also be concerned about the durability, long-term stability, anti-interference ability (such as electromagnetic interference), and applicable environmental conditions (such as oxidizing and reducing atmospheres, vacuum, etc.) of thermocouples. For example, some thermocouples are prone to deterioration in specific atmospheres and require protective sleeves.

It may also be necessary to mention international standards such as IEC 60584 or ASTM E230, which specify the performance and tolerances of different types of thermocouples, helping users choose products that meet the standards.

Now, I need to check if there are any missing parameters. For example, polarity, positive and negative electrode materials of thermocouples, correct connection methods during wiring, and avoiding measurement errors caused by reverse direction. The insulation resistance of thermocouples, especially at high temperatures, may decrease, affecting signal accuracy.

In addition, economy is also a factor, for example, precious metal thermocouples (such as S-type, R-type, B-type) have higher costs, while low-cost metal thermocouples (such as K-type, J-type, T-type) have lower costs, and users may need to choose according to their budget.

When organizing these parameters, it is necessary to present them in a clear structure, which may be organized according to division marks, temperature ranges, materials, accuracy, output characteristics, application considerations, and other aspects. At the same time, it may be necessary to remind users to consider factors such as measurement temperature, environmental conditions, accuracy requirements, response time, and cost when making choices.

Finally, it is important to ensure the accuracy of information, such as temperature range and precision data, by referring to the latest standard materials to avoid outdated information. If there are any uncertainties, it may be necessary to consult relevant standards or materials for confirmation.

Thermocouples are temperature sensors based on the Seebeck effect, and their parameter selection directly affects measurement accuracy and applicable scenarios. The following is a detailed explanation of the key parameters:

1. Dividing number (type)

Different material combinations correspond to different types, common division marks and characteristics:

K-type (nickel chromium nickel silicon): -200 ° C~+1300 ° C, universal type, high cost-effectiveness.

J-type (iron constantan): 0 ° C~+750 ° C, suitable for reducing atmospheres.

T-shaped (copper constantan): -200 ° C~+350 ° C, with good low-temperature stability.

E-type (nickel chromium constantan): -200 ° C~+900 ° C, high sensitivity.

S/R/B type (platinum rhodium alloy): High temperature type (S: 0~1600 ° C, B: 0~1800 ° C), high precision but high cost.

2. Temperature range

Working temperature: maximum/minimum measurement temperature for different division marks (taking into account the temperature resistance of the protective sleeve).

Short term overload: Some models may briefly exceed the nominal range (such as the K-type which can reach 1370 ° C).

3. Accuracy (error range)

According to the IEC 60584 standard, errors are divided into three levels:

Standard level: For example, the K-type has an error of ± 1.5 ° C between -40 ° C and 375 ° C, and a reading of ± 0.4% above 375 ° C.

Special level: higher accuracy, such as S-type with an error of ± 1 ° C or ± 0.25% reading between 0 and 1600 ° C.

4. Output characteristics

Thermoelectric potential: millivolt level output (non-linear), requiring reference to a calibration table or formula conversion (such as polynomial fitting).

Sensitivity: For example, K-type is about 41 μ V/° C, and E-type is about 68 μ V/° C (higher sensitivity is suitable for measuring small temperature differences).

Cold end compensation: It is necessary to eliminate the influence of reference end temperature through freezing point method or electronic compensation (such as using temperature chips).

5. Materials and Structure

Electrode material: precious metals (such as platinum rhodium) are heat-resistant but expensive; Low cost metals (such as nickel based) are economical but prone to oxidation.

Protective sleeve: Material (stainless steel, ceramic, etc.) affects corrosion resistance, response time, and applicable environment.

Insulation material: Magnesium oxide or ceramic insulation should be used at high temperatures to avoid electrical leakage.

6. Response time

Time constant: related to diameter (e.g. bare wire with a diameter of 0.5mm takes about 0.1 seconds, while with a casing of 6mm, it can take several seconds).

Installation impact: The insertion depth should be ≥ 4 times the diameter of the sleeve to ensure sufficient heat conduction.

7. Environmental adaptability

Oxidative/reducing atmosphere: J-type resistant to reduction, S-type resistant to oxidation, B-type suitable for vacuum high temperature.

Electromagnetic interference: Cables need to be shielded to avoid signal noise (especially in industrial environments).

8. Economy and lifespan

Cost: Low cost metal type (K/J/T), high price of precious metal type (S/R/B).

Lifespan: Material degradation at high temperatures (such as K-type drifting above 1000 ° C) requires regular calibration.

9. International standards

IEC 60584: Definition of division marks, tolerances, and testing conditions.

ASTM E230/E2758: American standard specification, similar to IEC.

Selection suggestions

Prioritize the temperature range before considering the environment (oxidation/corrosion).

Accuracy requirement: Select S/B type for high temperature scenarios and K/E type for conventional scenarios.

Response speed: thin diameter thermocouple or exposed contact.

Budget: Precious metal types are suitable for laboratories or high-precision industries, while low-cost metals are suitable for general use.

By integrating the above parameters, the performance of thermocouples can be optimized in industrial control, laboratory, or environmental settings. In practical applications, signal conditioning circuits (such as amplification and cold junction compensation) need to be combined to improve measurement reliability.