Conventional measuring methods require up to eight hours for determining the thermal conductivity, thermal diffusivity and volumetric specific heat of a given material, and it takes three different, expensive instruments to do so. Now, though, the THB-10 (Transient Hot Bridge), a new device engineered by Pausch Messtechnik GmbH in Haan near Düsseldorf in cooperation with Germany’s national metrology institute PTB (Physikalisch-Technische Bundesanstalt), does the job much more quickly and cost-effectively. Now in serial production, the unit does all three measurements at once, and the results are usually available within a minute. Hence, the THB-10 makes it possible to perform serial measurements on slightly altered materials very quickly and at comparatively little expense and to reliably compare the findings – no matter whether the material in question is a solid, a powder, a gel, a paste or a liquid.
Advanced sensor ensures high measuring accuracy
The THB-10 comprises a printed-circuit foil sensor, a constant-current power pack and evaluation/user software. The prime component is its advanced, patented sensor consisting of a Wheatstone bridge on a special conductor path embedded in a temperature-stable foil. The bridge circuit ensures high measuring accuracy. For solid specimens of stone, glass or the like, the foil sensor is inserted and clamped in place between two specimens. For loose material of any kind, including sediment, the sensor is first mounted on a frame and then inserted into the material. For fluids, the foil can be shaped to form a cylinder and then filled with a sample of the fluid. The foil sensor has a measuring range of –40° C to 180° C.
Once the sample has been fitted with a foil sensor for mensuration, a defined electric current (selected to match the material in question) is applied. Then, special algorithms are used to calculate the material’s thermal conductivity and thermal diffusivity, as well as its volumetric specific heat (by derivation) on the basis of the resistors’ heat evolution, the amount of heat emitted to the specimen and the elapse length of time.
Easy preparation and operation for in-process measurements
The THB-10 requires minimal preparation and is quick and easy to use. User guidance is menu-driven in individual steps. As soon as the instrument is not being used correctly, a warning signal is emitted, and a message shows what went wrong. Laborious, time-consuming, error-prone reference and calibration measurements are now a thing of the past. The software control function automatically optimizes the measuring process, reduces the time expenditure and minimizes the level of uncertainty. Any remaining degree of uncertainty is unconfusingly documented. The readings are displayed with the optimal, required measuring current intensity and duration.
With all these advantages, the THB-10 is very well suited to the typical production environment and for use in small and medium-size companies. The price, too, is geared to the target group. The THB-10 has an introductory price of € 28 000. Comparable plate-base instruments that take several hours for a single measurement cost nearly twice as much.
For thermal conductivity, the instrument‘s measuring range extends from 0.02 to 100 W/mK. Depending on the particular sensor and material, its uncertainty level peaks at 3%*, and its reproducibility beats 0.5%. The thermal-diffusivity measuring range is 0.05 to 10 mm²/s,
with 6%* uncertainty and reproducibility to within 1.5%. The volumetric specific heat is calculated from the results of the thermal conductivity and diffusivity measurements.
The THB-10 is fitted with USB interfaces, an Ethernet connection and an RS232 serial interface and can connect to an IEEE-488 general purpose interface bus.
* calculation according to ISO-GUM, with k = 2