Technical information

Inserts for temperature dry-well calibrators
WIKA data sheet IN 00.42

Temperature dry-well calibrators are a popular type ofinstrument for checking temperature measuring instruments.
The construction and operation of a temperature dry-wellcalibrator is as follows:■ In a solid body (the insert), there is a customer-specificnumber of bores.
■ In these bores are located the temperature probes/
measuring instruments to be tested (test items).

■ The solid body is tempered to the test temperature using adry-well calibrator and its temperature controller, in orderto calibrate the test items.
■ The temperature in the bores of this block (insert)
depends upon the correct selection of the framework
conditions.

Framework conditions for the use of the correct inserts
The two decisive framework conditions in the selection of theinsert are two properties:
Material
The dimensions and the material of the inserts are matchedto the block construction. The exterior design with chamfers,
offset edges or a vent hole ensures that the best stability canbe ensured within the insert. Over the complete temperature
range of a dry-well calibrator, only one material is used:■ Aluminium (up to 450 °C [842 °F])
■ Brass (up to 650 °C [1,202 °F])
■ Ceramic (up to 1,200 °C [2,192 °F])
The material, in turn, ensures that the temperatureis transferred sufficiently quickly to the immersed
thermometers. The better this material is matched to theblock construction, the quicker is the transfer time of thetemperature to the test items.

Correct insert, bore size and material Temperature probe Insert■ Dimensions■ Material■ Bore size Bore for insert
 Temperature calibrator

Dimensions
The bores in the insert are matched to the probes whichshould be immersed and tempered. The bores in diametersof 0.3 ... 0.5 mm [0.01 ... 0.02 in] should be bigger than thediameter of the thermometers which should be immersedin the bore. This is the optimal dimension which preventsa mechanical jamming of the sensor through thermal
expansion and, in addition, ensures the lowest air gap.

WIKA data sheet IN 00.42 ∙ 07/2018

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Data sheets showing similar products and accessories:
To improve the total uncertainty of the calibration with a temperature dry-well calibrator; seedata sheet IN 00.32

Some scenarios that can lead to measuring errors
Insert from another calibrator
An exchange of inserts from one calibrator to another is notreadily possible. Material and dimensions do not match. In
addition, it is possible that the diameter of the insert does
fit, but not the length and this protrudes at the top of thecalibrator. This dramatically affects the heat transfer. Thus
the specifications from the data sheet can no longer bemaintained.

Insert from another calibrator Temperature probe Insert■ Dimensions■ Material■ Bore size Bore for insert
 Temperature calibrator

Dimensions of the insert too small
If the external dimensions of the insert are not matched to theblock, then there can be air gaps which act as an insulator.
These prevent that the specifications from the data sheet canno longer be met, a stable temperature cannot be controlled
and also the set point cannot be achieved.

Dimensions of the insert too small Temperature probe Insert■ Dimensions too■ Bore sizesmall■ Material

 Bore for insert
 Temperature calibrator
 Air gap too large

Wrong material of the insert
Should the material not match the block, the heat transfer
can no longer be guaranteed to be optimal. This possibly
prevents the specifications from the data sheet being able to
be maintained. In the worst case, the insert material would
not endure the maximum service temperature and wouldmelt. Thus, the calibrator could no longer be used.

Wrong material of the insert Temperature probe Insert■ Outer diameter■ Wrong material■ Bore size Bore for insert
 Temperature calibrator



WIKA data sheet IN 00.42 ∙ 07/2018

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Bore too short
If the bore in the insert is drilled too short, the temperature in
the block will not match that on the display. This has an axial
gradient, meaning that there is a temperature difference frombottom to top. Calibrators are always measured at the bottomof an insert. Should such a short bore be required due tothe probe, then one uses an additional, external reference
which is immersed to the same depth. Thus, the traceably
calibrated display of the calibrator is no longer trusted, rather
only the external reference.

Bore too shortWorking with an external reference is currently very
widespread and has significant benefits.

 Temperature probe Insert■ Dimensions■ Material■ Bore too short Bore for insert
 Temperature calibratorAdvantages with measurements with an external reference
Flexible application of the equipment■ A dry-well calibrator and an external reference can also be
used independently of one another.
■ By acquiring multiple external references, different levelsof accuracy can be achieved with a calibrator.
■ Almost all probe lengths can be calibrated with goodresults; so long as the thermometers are inserted to thesame depth in the calibrator (“success guarantee”).

Measurements with external reference

Simple return and accurate calibration possible for theexternal reference
If one no longer trusts the display of the calibrator - to be able
to do this, then the display must definitely be calibrated - onemust read the reference value on an external instrument.
The external reference must be traceably calibrated. This iseasier to send than a calibrator, due to the dimensions andweight. In addition, for an external reference it is not just acomparative calibration which is feasible, but possibly also acalibration at fixed points.
A comparative calibration and a fixed-point calibration of thereference promise higher accuracies.

 Temperature probe Insert■ Dimensions■ Material■ Bore too short Bore for insert
 Temperature calibrator
 Reference

temperature probe

07/2018 EN© 07/2018 WIKA Alexander Wiegand SE & Co. KG, all rights reserved.
The specifications given in this document represent the state of engineering at the time of publishing.
We reserve the right to make modifications to the specifications and materials.

WIKA data sheet IN 00.42 ∙ 07/2018

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WIKA Alexander Wiegand SE & Co. KG
Alexander-Wiegand-Straße 30
63911 Klingenberg/GermanyTel.
+49 9372 132-0
info@wika.de
www.wika.de