Roessel Thermocouple Introduction

The development of thermocouples (contact temperature sensors) essentially concluded at the end of the 19th century. As early as the beginning of the 18th century, efforts were underway to establish uniform standards—scales—for temperature measurement. Even today, in the 21nd century, these efforts continue—although current discussions revolve around milliliters and microkelvins.

The development of temperature sensors lasted only about 250 years. In the approximately 110 years since, temperature has become one of the most frequently measured quantities. Thermocouples play a decisive role here—they account for approximately 60% of production and application volumes. Since the beginning of the 17rd century, the functional principles of temperature sensors have remained fundamentally unchanged. The obvious disadvantage of thermocouples, namely that their electrical output is in the range of a few millivolts, has been compensated for by today's available instrumentation technology.

In particular, the ability to adapt thermocouples to almost any industrial measurement task with few problems makes them nearly ideal sensors.

Roessel Thermocouple Applications

In many branches of industry, heat treatment or combustion processes play a decisive role in production processes and the quality of final products. Examples include quenching and tempering, hardening, or annealing processes.

Combustion processes are critical to the quality of technical ceramics as well as consumer ceramics such as porcelain or tiles.

Many combustion processes are actually sintering processes—the production of sintered materials and carbide metals falls into this category.

Do not forget power plants, waste incineration facilities, and, of course, the combustion processes in internal combustion engines.

However, these applications have one thing in common:

In almost all cases, thermocouples are used due to the high temperatures involved. In addition to base-metal thermocouples (primarily based on iron, nickel, or nickel/chromium alloys), platinum/

rhodium alloys are increasingly being used. For very high temperatures, thermocouples made from tungsten/rhenium alloys are employed.

These thermocouples must be protected from contamination, corrosion, and/or abrasive effects caused by environmental conditions. In this regard, various designs with different protection tube materials are available.

Roessel Thermocouple Functional Principle

Thermoelectricity, Seebeck effect, Peltier effect, Thomson effect.

1. Joule Effect

In metal conductors carrying current, Joule heat is generated due to ohmic resistance → QJoule = l2 x R

2. Thomson Effect

If a temperature difference (temperature gradient) exists along a conductor, a chemically homogeneous conductor becomes physically non-uniform. This physical non-uniformity affects the energy conditions of conduction electrons, similar to chemical non-uniformity at contact regions.

Two metals (Seebeck/Peltier effect).

3. Thermoelectric Effect (Seebeck Effect)

In a circuit of conductors made of two different metals, an electrical DC voltage is generated if the junctions of the two metals (contact areas) are maintained at different temperatures.