Probes
Different probe types are available for use with TK04 which can be connected to the same instrument. All probes have a rugged design, are protected against moisture and are maintenance-free. Heating device and temperature sensor are embedded in a stainless steel tube. The probes come pre-calibrated, the users are not required to perform calibration tests themselves.
For laboratory measurements, with few exceptions all probe types can be used for all sample materials. In most cases you can choose a probe by temperature range (see the technical specification of the probes) and by shape and size of the available sample pieces, or by sample preparation possibilities. For in-situ tests always the Field VLQ should be used, the smaller laboratory probes are not adequate for this purpose.
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Classical needle probes
Classical needle probes 
The classical needle probe (Standard VLQ) has a measuring range of 0.1 to 10 W/mK, an accuracy of ± 2 % and a temperature range of -25° to 125°C. The needle requires a drill hole of 2 mm in diameter and approx. 75 mm in length. If the sample material is soft enough, the probe can be inserted into the sample without pre-drilling. Optional guiding tubes are available which are embedded into the probe at the desired measuring position. The Mini VLQ (measuring range 0.3 to 6 W/mK and ± 5% accuracy) is designed for small samples from 60 mm length.
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Probes for plane surfaces
Probes for plane surfaces are supplied in two sizes: the Standard HLQ and the smaller Mini HLQ. Both sizes can be used in the temperature range of -25° to 70°C. The Standard HLQ requires a plain and smooth surface at least 90 mm in diameter, it has a measuring range of 0.3 to 10 W/mK and an accuracy of ± 2%. For the Standard HLQ we offer a matching sample container for powder, fragments pastes and viscous liquids. The Mini HLQ is intended for small samples from 50 mm in diameter, it has a measuring range of 0.3 to 3 W/mK and an accuracy of ± 5%.
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Field Probes
For field tests a large and robust needle probe (Field VLQ) with a length of 300 mm is available. The measuring range is 0.6 to 4 W/mK, the accuracy is ± 5 % and the temperature range is -25° to 50°C. The Field VLQ is used with guiding tubes which are driven into the ground at the measuring position before inserting the probe.
Please see the technical specification for a summary of all available probes including their measuring range, temperature range and accuracy
Samples
TK04 is designed for testing solids (like soil samples, rock, plastics, glass, ceramics, construction materials, wood or foodstuffs), powder, fragments, pastes, gels and viscous liquids, and for in-situ tests in the measuring range of 0.1 to 10 W/mK. The instrument covers a temperature range of -25° to 125°C. All probes can be used for wet materials.
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Sample shape and size
Samples can be of any size and shape as long they meet the minimum size requirements. The minimum diameter according to ASTM D5334-22a is 40 mm, the minimum length is the probe length plus 20%. The higher the thermal conductivity, the larger is the necessary sample size. For soil samples, the ASTM requires larger sample dimensions. Details can be found in the technical specification of the probes and in the application notes (PDF) Choosing a suitable probe, Sample preparation and Testing thermal conductivity of soil samples.
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Fragments and powder
To describe the thermal properties of loose materials, the matrix thermal conductivity is used - which is the value that a non-porous solid block formed from the grain material would have.
Detailed instructions for determining the matrix thermal conductivity can be downloaded in PDF format: Testing fragments and powder. In our customer download section we offer a free spreadsheet file for OpenOffice, LibreOffice or Microsoft Excel which guides you step by step through sample preparation, measuring and evaluation and automatically calculates the results.