L-type thermocouple

Thermocouple type L – the most important information before purchase

Wondering what makes the L-type thermocouple stand out from other temperature sensors? In our latest blog post, we delve into the world of thermocouples, focusing on the unique properties and applications of the L-type thermocouple. You'll learn how these sensors work, where they are used, and what advantages and disadvantages they have over other types of thermocouples. In addition, we'll take an in-depth look at their construction, characteristics, and key differences between the L-type thermocouple and other common types, such as K, J, T, and E. If you're interested in temperature measurement technology and want to learn more about how L-type thermocouples can be used in various industries, this post is for you. Read on!

What is an L-type thermocouple?

An L-type thermocouple is a temperature sensor that works on the principle of the Seebeck effect, where an electrical voltage is generated by the temperature difference at the junction of two different metals. This thermoelectric sensor, also known as Fe-CuNi (iron-constantane), consists of two thermocouples: one made of iron (Fe) and the other of constantan (CuNi), a copper-nickel alloy.

Plug-in thermocouple with head type B with measuring insert type J, K, L, S, B

Plug-in thermocouple with head type B with measuring insert type J, K, L, S, B

Characteristics of L-type thermocouples

L-type (Fe-CuNi) thermocouples perform well in a wide range of applications at temperatures from -200°C to 600°C. They offer precise temperature measurement, although they may not be as accurate as other types of thermocouples. Constructed of iron and constantan, they offer good thermal conductivity and measurement stability. However, be aware of their limited corrosion resistance in acidic or humid environments.

L-type thermocouples are generally less expensive than other types, making them a good choice for users with limited budgets. They provide stable measurements over their temperature range, which is important in applications requiring consistency and repeatability. These devices are an excellent choice for reliable temperature measurements in a variety of applications, especially where budget and environmental constraints play a key role.

Applications for L-type thermoelectric sensors

L-type thermoelectric sensors, known for their moderate sensitivity and resistance to quite high temperatures up to 600°C, are widely used in various industries. Here are five major areas of their application:

  • Machinery and heavy industry: Often used for temperature monitoring in industrial machinery and equipment. Their resistance to high temperatures makes them ideal for tracking the condition of components in heavy equipment, such as industrial furnaces and motors.
  • Heating and cooling systems: They are used to monitor and regulate temperature in HVAC (heating, ventilation and air conditioning) systems, where precise temperature measurements are crucial for energy efficiency and user comfort.
  • Chemical industry: In the chemical industry, they are used to monitor processes that require precise temperature control, especially in chemical reactors and processing facilities.
  • Food industry: In the food industry, where temperature control is critical to maintaining product quality and safety, these thermocouples are used for temperature monitoring in cooking, baking, freezing and storage processes.

    Scientific research and laboratories: Used in laboratories to monitor and record temperatures in scientific experiments, where reliability and accuracy of measurements over a wide temperature range are needed.
machinery industry

L-type thermocouples are used in the engineering industry

Advantages and Disadvantages of Type L Thermocouples


  • High-temperature stability: Type L thermocouples are known for their ability to operate stably at high temperatures, making them suitable for industrial applications where such conditions are prevalent.
  • Good accuracy and repeatability of measurements: They provide relatively accurate and repeatable temperature measurements, which is crucial in applications demanding precision.
  • Durability and environmental resistance: They are characterized by good mechanical strength and resistance to corrosion and other harsh environmental conditions.
  • Wide measurement range: They can measure temperatures within a broad range, making them versatile in various applications.
  • Simplicity of use and maintenance: They are relatively easy to install and do not require complex maintenance.


  • Limitations at very low temperatures: Despite their effectiveness at high temperatures, they may have limitations in very low-temperature ranges.
  • Potential accuracy issues with long-term use: Long-term exposure to high temperatures can affect the accuracy of measurements.
  • Calibration requirement: They may require regular calibration to maintain high measurement accuracy.

It's important to note that the specific advantages and disadvantages of Type L thermocouples may vary depending on the application and specific requirements.

Sheathed thermocouple (901210) type K, J, L or N in stainless steel sheath

Comparison of Type L Thermocouples with Other Types

Comparing Type L temperature sensors with other thermocouple types provides a clearer understanding of their unique properties and applications. Here are the key differences:

Material Composition:

  • Type L Thermocouples: Composed of nickel-chromium and nickel-iron wires, offering moderate resistance to high temperatures and corrosion.
  • Other Thermocouple Types (e.g., K, J, T, E): Each type has a specific material combination (e.g., chromel-alumel for type K), affecting their temperature range, corrosion resistance, and accuracy.

Temperature Range:

  • Type L: Suitable for medium-temperature applications.
  • Types J and K Thermocouples: Better suited for very high temperatures, making them more useful in heavy industries and high-temperature processes.

Accuracy and Stability:

  • Type L: Offer moderate accuracy and stability.
  • Types T and E Thermocouples: Typically offer higher accuracy and are more stable in lower temperature ranges.

Corrosion Resistance:

  • Type L: Have moderate corrosion resistance.
  • Types K and E Thermocouples: Known for better corrosion resistance, making them more suitable in aggressive chemical environments.


  • Type L: Comparably priced to other popular thermocouple types.
  • Specialized Types (e.g., B and S): Significantly more expensive (e.g., platinum-rhodium), but offer higher accuracy and stability in extreme conditions.

Suitability for Applications:

  • Depending on the specific application requirements, different thermocouple types may be more or less suitable.
  • Selecting the appropriate type depends on the required temperature range, corrosion resistance, accuracy, stability, and budget. Type L thermocouples are a good choice for applications requiring moderate accuracy and temperature resistance at a reasonable cost.

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About the author

My name is Ewelina Szmit and I have been working in the field of content marketing for several years, combining my professional skills with my passion for writing. I believe that even the most technical topics can be presented in an interesting and accessible way for everyone. Outside of work, I develop my creativity by creating newspaper collages. I like to spend my free time most actively, walking my dog or running.

Ewelina Szmit


Ewelina Szmit - Content specialist +48 71 339 32 94 Ewelina.Szmit@jumo.net +48 71 339 32 94

Jakub Dąbrowski

Technical specialist

Jakub Dąbrowski - Inside Sales Engineer +48882351471 Jakub.Dabrowski@JUMO.net +48882351471


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