WIKA TR10-J - Manual (Page 10)

11208287.06 10/2013 GB/D/F/E
10 WIKA operating instructions resistance thermometers, thermocouples
GB
If these thermocouples cool too quickly (quicker than approx. 100 °C per hour), the undesirable
disordered crystal lattice occurs again during cooling in the range from approx. 600 °C to
approx. 400 °C. In the characteristic curve of type K, however, a consistently ordered alignment
state is assumed and provided with values. This results in a fault of thermoelectric voltage of up
to approx. 0.8 mV (approx. 5 °C) in this range. The K effect is reversible and is largely eliminated
again by annealing above 700 °C, followed by correspondingly slow cooling.
Thin sheathed thermocouples are particularly sensitive in this respect. Cooling in resting air can
already lead to deviations of 1 K.
In type N thermocouple, it has been possible to reduce this short-range-order effect by alloying
both legs with silicium.
The application range of these thermometers is limited both by the permissible maximum
temperature of the thermocouple and by the max. temperature of the thermowell material.
Listed models are available both as single or dual thermocouples. The thermocouple will be
delivered with an insulated measuring point, unless explicitly specified otherwise.
Tolerance value
For the tolerance value of thermocouples, a cold junction temperature of 0 °C has been taken as
the basis. When using a compensating cable or thermocouple cable, an additional measuring
error must be considered.
For limiting deviations and further specifications, see the corresponding WIKA data sheet and
technical information sheet IN 00.23, “Application of thermocouples”.
4. Design and function
4.1 Description
These thermometers (resistance thermometers and thermocouples) detect temperatures in
processes. These thermometers are suitable, depending on the version, for low, medium and high
process requirements.
They can be assembled as cable probes or as thermometers with a connection head. Optionally,
a temperature transmitter can be built into the connection head. For this temperature transmitter,
separate operating instructions will be enclosed.
Certain thermometer versions can be combined with a large number of thermowell designs.
Operation of these thermometers without a thermowell is only appropriate in special cases.
4.2 Scope of delivery
Cross-check scope of delivery with delivery note.
3. Specifications / 4. Design and function