4. Configuration of Sheathed Thermocouple Assemblies
Sheathed thermocouple assemblies
differ from thermocouple assemblies in their smaller design and their bending
properties, which means that they can also be used in measurement locations that
are difficult to access. In addition, they are vibration-proof and
pressure-resistant. A sheathed cable consisting of a heat-resistant and
corrosion-resistant metal tube (sheath tube), in which the thermocouples are surrounded on all
sides by a highly compacted mineral insulation
powder, is used in the manufacture of
sheathed thermocouple assemblies. The insulation powder insulates the thermocouple
wires both from one another and from the
sheath tube. The outer sheath tube
diameter ranges from 0.25 to 15mm. Sheathed cables of this type
are manufactured according to special procedures, which involve drawing the
entire material compound (protection tube, insulation and thermocouple
wires), through appropriate deformation steps (e.g. rolling and
drawing using intermediate annealing), from an outer diameter
of approx. 15 to 25mm to the desired end diameter (0.25 to
15mm) and winding it up in the form of
cable coils.
The sheathed thermocouple manufacturing process cuts the
required sheathed cable to length and straightens it. The thermocouple wires are then welded together
at one cable end (measuring point), with the sheath
tube being sealed at this end and an end
cap made of the same material. At the other cable end, the
so-called junction, the free ends of the thermocouples are
connected to a suitable plug or a ceramic base, for example, as
requested by the customer.
Figure 3 shows a sheathed thermocouple assembly with
connected standard plug:
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