Non-Steady-State Probes for Thermal Conductivity Measurement

The Non-Steady-State Probe (NSSP) measurement method (also known as transient line source, thermal needle, hot needle, heat pulse- and hot wire technique) has the fundamental advantages that it is fast and absolute while the sample size is not critical. Hukseflux is specialised in NSSP design. Special models have been developed for in-situ field experiments. For permanent installation in soils, a dedicated model, TP01, is available. TP08 has been designed and tested in collaboration with the Applied Physics Group of Wageningen University.

TP02 Thermal Sensor

The TP02 Non-steady-state probe for thermal conductivity measurement offers the possibility to perform a practical and fast measurement of the thermal conductivity (or thermal resistivity) of the medium in which it is inserted at the highest accuracy level. It works in compliance with the ASTM D5334-14, D5930-97 and IEEE 442-1981 standards. The standard TP02 probe has proven suitability in soils, thermal backfill materials, sediments, foodstuff, powders, sludges, paints, glues and various other materials.

TP08 Small Size

The TP08 thermal properties sensor is a small size non-steady-state probe for thermal conductivity measurement. The TP08 is a probe that offers the possibility to perform a practical and fast measurement of the thermal conductivity (or thermal resistivity) of the medium in which it is inserted at a high accuracy level. It works in compliance with the ASTM D5334-14, D5930-97 and IEEE 442-1981 standards. The TP08 is a small version of type TP02, made for situations where the length of the TP02 poses a problem. The standard TP08 probe has proven its suitability for soils, thermal backfill materials, sediments, foodstuff, powders, sludges, paints, glues and various other materials.

Accessories for the TP02 and TP08:

• Guiding Tubes for TP Thermal Needles
  • GT01 guiding tubes for TP08
  • GT02 guiding tubes for TP02
• Calibration Reference Cylinders
  • CRC01 for TP02 and TP08

Hukseflux specialises in Non-Steady-State probe design. The primary model of the Hukseflux product range is the TP02. This model offers optimal measurement accuracy by a combination of its design features. For some applications however the requirements regarding the sample size are such that the needle length and diameter of the TP02 are too large. For this category of samples, TP08 has been designed. Having a needle length of 70 mm, with the junction at around 17 mm from the tip, and a diameter of 1.2 mm, samples of around 80 ml can be analysed. (35 mm depth). In some cases samples can even be smaller (consult Hukseflux). In TP08 the reference junction of the thermocouple is located in the base. A high quality measurement with TP08 requires that not only the sample but also the base are at a stable (preferably the same) temperature. Usually this is achieved by clamping the base into the same material (metal) that holds the sample.

Suggested use

• studies of ocean sediments
• studies of small samples
• studies of high cost samples (uranium sludge)

Optimal Accuracy:

TP02 incorporates 2 thermocouple junctions in the needle producing a voltage output, U, that is proportional to ΔT. The one in the tip is not heated. The main signal is the differential signal between this hot joint at 1/3 of the length and the cold joint at the tip. In this configuration the voltage before starting the measurement is always small, independent of the medium temperature. In designs with only one sensor in the needle, the signal U will appear on top off a larger signal. The two junction design has a superior accuracy when measuring at high and low temperatures. In addition, by having both the cold- and the hot junction in the needle, the sensitivity to temperature changes of the medium is minimised.

• Temperature sensor in the base: The reference temperature sensor in the base (Pt1000) serves as a “cold junction” measurement for establishing the absolute medium temperature T. This is required by ASTM.
• Temperature and moisture resistance: All the materials in TP02 are highly temperature resistant. It has a full stainless steel needle and base. TP02 is completely sealed. It has a welded tip. This no-compromise sealing guarantees the long term stability of the sensor. Designs with glued sealing or epoxy housings are less reliable in this respect, particularly when working in moist environments.
• Standard cables and connectors: Putting the Pt1000 temperature sensor in the base allows the use of normal copper core cables and connectors for cable extension of TP02.
• Data processing: The data obtained with TP02 can be processed in any normal spreadsheet program.

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