Insights from industry

Advanced Thermocouple Technology: Expert Insights into High-Temperature Measurement

insights from industryJoep van den BrinkHead of Business Development - Heating & AutomotiveKamet Trading BV

In this interview, industry expert Joep van den Brink provides insights into high-temperature thermocouple technology. He explains the key differences, innovative designs, and personalized solutions used to optimize efficiency in extreme environments.

What varieties of high-temperature thermocouples are on the market?

When temperatures exceed 1200 °C, we commonly refer to them as high-temperature thermocouples. Beyond this limit, we often recommend noble metal thermocouples such as type S, type R, or type B. At even higher temperatures, type C and type D thermocouples are usually used.

What are the fundamental differences between Type C/D thermocouples and other popular types on the market?

Type C and D thermocouples are specialized thermocouples that are primarily used in high-temperature applications. They differ greatly in construction, materials, and performance characteristics from more common types such as Type K, J, T, and E.

Type C/D thermocouples, made from tungsten-rhenium alloys, can measure temperatures up to 2300 °C. These thermocouples are suitable for use in vacuum, inert, and reducing environments. However, they are not recommended for oxidizing environments, as this can cause damage to the thermocouples.

Other types of thermocouples have different material compositions, rendering them less suitable for use at such high temperatures. Type C/D thermocouples are often employed as a less expensive alternative to thermocouples containing noble metal alloys, like type S/R/B thermocouples. 

If type S/R/B thermocouples are required in the design, an alternative for lowering the cost of high-temperature thermocouples is to use a transition-style thermocouple.

How can the transition-style thermocouple design provide an advantage over conventional designs in extreme temperature environments?

The main advantage of a transition-style thermocouple is affordability. Customers frequently request type S/R/B thermocouples with Pt10%Rh sheaths, which are typically very expensive.

Furthermore, such a specification is often excessive, as severe temperatures are generally encountered just at the sensor’s tip. In these cases, a transition-style thermocouple is an appropriate option.

Thermocouples can then be outfitted with a suitable high-temperature “hot section” sheath and insulating materials long enough to reach a cooler zone within the furnace or reactor. At this stage, a brazed transition can be made to a less costly thermocouple or compensating material with Inconel 600 or stainless-steel sheath. This ultimately results in cost savings for the end customer.

What separates Kamet’s thermocouples from other comparable items on the market?

We generally focus on severe temperatures, which we characterize as those that exceed 1200 °C and are under challenging conditions. Below these temperatures, we offer our mineral-insulated thermocouple cables to temperature sensor manufacturers throughout Europe.

However, when temperatures exceed 1200 °C, exotic protective sheaths and specialized thermocouple alloys are required. These thermocouples often need additional calibration, X-Ray, and leak testing.

Kamet has a comprehensive knowledge of these temperatures and conditions, whether they are oxidizing, inert, reducing, or vacuum. We guarantee the best possible thermocouples regardless of the respective application, thanks to our expertise in materials science and exotic material properties, which we work on with our manufacturer, ARi Industries.

We also have our own production method for mineral-insulated cables, which allows us to control the entire process—from manufacturing the MI cable to generating the custom thermocouples—all under one roof.

Can you talk about any recent developments in thermocouple technology that Kamet has pioneered or incorporated into its product line?

ARi, our manufacturer, has been in the temperature sensor and heating market since the early 1950s. ARi was one the first companies to produce mineral-insulated cables (MI cables) to increase product performance and reliability. AerOpak and AerOrod are their trademarks for thermocouple and heater cables, respectively. 

AerOpaks and AerOrods are still the core products here at Kamet, and we are constantly refining and improving this technology. ARi also has a patent portfolio that includes wire wound hot junctions for Type C and D thermocouples, a more robust mounting for an RTD element, and a technique for producing non-circular cross-sectional shape MI Cables.

Could you discuss how you customize your thermocouples to fulfill the specific requirements of sectors like aerospace and nuclear power, where extreme temperatures are common?

We tailor our thermocouples to match the unique requirements of each application. In the aerospace sector, AMS2750 calibration is often required, which mandates very strict tolerances for permitted deviation (Type R & S: ±1.8 °C or ±0.1 %, Type B: ±1.8 °C or ±0.25 %). In these conditions, we ensure that our thermocouples meet these standards.

For nuclear applications, hafnium oxide insulation is frequently required because of its radiation properties. This form of insulation helps to reduce signal distortion caused by radiation from the application.

Another crucial factor is the choice of sheath material for the thermocouple. Some thermocouples are subjected to extremely high temperatures together with specific atmospheric conditions.

Before making an offer, we gather as much information as possible from the customer regarding temperatures, applications, industrial requirements, operating environment, presence of graphite, and so on.

What are the current challenges in the thermocouple industry, and how does Kamet solve them through its products or services?

One of the industry’s most difficult ongoing challenges is determining which thermocouple to use and in what specific environment. It is very difficult to decide which sheath material extends the lifetime of a thermocouple, particularly at temperatures exceeding 1200 °C.

Things can also get complicated when part of the operation is in an oxidizing atmosphere up to 300 °C while another part is in a reducing environment with elevated temperatures. These applications require both material science and application understanding.

As in many industries, supply chain interruptions also continue to be a challenge. To mitigate the potential damage, we increased our contact with ARi and collaborated more closely with our current vendors.

We find and test raw materials from various suppliers, use different designs, and even create new ones using raw materials on hand to manufacture comparable products. As a result, Kamet and ARi maintain frequent internal contact, as do ARi’s Supply Chain Planner/Buyer and Product Managers. 

Finally, thermocouples’ application environments and requirements are becoming increasingly demanding. Therefore, ARi has to constantly find new solutions through the acquisition of new materials, research and development, and the expansion of their product catalogs.

How does the collaboration between Kamet and ARi Industries improve the process from R&D to production for custom thermocouple solutions?

High-precision temperature readings start with the quality of raw materials used to manufacture AerOpaks and thermocouples. ARi takes pride in using only the finest materials for our products. Our raw material providers and products undergo rigorous testing to ensure exceptional quality.

What role does client feedback play in the ongoing development of your thermocouple products?

Customer feedback is essential for continuous improvement, particularly because each application requires a specific solution. If the application’s atmospheric conditions differ from the standard scenario, it can impact the thermocouple’s performance. Therefore, customer input is crucial for enhancing our high-temperature thermocouples.

How does Kamet support its clients with after-sales service and technical support?

We employ a strong customer-focused approach to ensure our clients are involved at every stage, minimizing potential complications. Our process typically begins with an initial discussion with the customer to understand the issues they are facing. We provide a quote only after developing a customized solution.

Once the quotation phase is complete and we receive an order, we generate a drawing for client approval. Production begins only after the client approves the drawing.

All our thermocouples come with 3.1 and calibration reports. Additionally, we can provide further documentation, such as X-ray results, helium leak test results, heat treatment details, and special calibration traceable to NIST, if required.

For after-sales support, we ensure full traceability of all our thermocouples. For special projects, we organize meetings between our ARi engineers and the customer to evaluate test findings and suggest further improvements to our thermocouples. We also offer warranties on our thermocouples.

About Joep van den Brink

Joep is a passionate business development manager with about 9 years of relevant work experience within the industry (e.g. research institutes, aerospace, furnace manufacturing). In those nine years, he has been focused on high temperature applications (>1200°C) in demanding environments. Joep's expertise lies in steering project collaborations between Kamet's technical engineers and clients to develop a customized solution for special applications.

About ARi Industries

ARi Industries has been a pioneer in manufacturing mineral insulated cable to enhance product performance and reliability since its foundation in 1952. Now a leader in the industry, ARi offers a range of metal-sheathed, mineral insulated thermocouple cables, including custom solutions tailored for specific temperature, environmental, and process requirements. All standard AerOpak® cables feature high-purity MgO insulation and meet ASTM E-230 accuracy standards, with extensive inventories maintained for prompt availability. 

 

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