The sheathed thermocouple consists of two conductors made of thermocouple material.

These are enclosed in magnesium oxide and a stainless steel sheath (e.g. Inconel 600). In the measurement technology sector, this is referred to as a sheathed measuring cable. This is shortened to the required length and the two wires are joined together (in almost all industrial applications, these are welded together in order to withstand vibrations and shocks).

The open part is then refilled with magnesium oxide and sealed with a pastille.

The magnesium oxide ensures that the sheathed thermocouples are optimally fixed and can withstand high pressures and temperatures (depending on the thermocouple type, see table) without any problems due to their structure. The robust, vibration-resistant design ensures a long service life. Just like the sheath resistance thermometers, the sheath thermocouples can also be bent and thus adapted to their operating environment.

A sheathed thermocouple can be constructed in three different ways. An exposed or perforated measuring point is suitable for very fast response times. If a pressure-resistant, corrosion-resistant structure is required that can also withstand mechanical influences, an uninsulated structure is advantageous. Another variant is to insert magnesium oxide as an insulating material between the measuring point and the sleeve wall. This is referred to as an insulated sheathed thermocouple. This protects the MTE from electrical influences and is therefore more resistant to insulation. However, the insulation also increases the response time accordingly. To counteract this, insulated sheathed thermocouples with a small diameter are often used in industrial applications.