Thin Heater Apparatus for thermal conductivity measurement

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THASYS offers measurement of the thermal conductivity or total thermal resistance of plastics, composites and electrical insulation / interface materials. THASYS works according to the ASTM 1114-98 standard; providing an accurate, fast, uncomplicated and absolute measurement. It consists of a Thin Heater Apparatus (THA01) and a Measurement and Control Unit (MCU). Employing a specially designed high accuracy thermopile sensor, THA01 can handle thin sample materials (typically 0.1 to 6 mm, but sometimes down to 0.01mm). The method is considered superior to procedures according to ASTM D5470. Using a climate chamber a large temperature range can be covered, performing measurements at regular intervals. THASYS is fully PC controlled. For use with high thermal conductivity thin foil materials a different model, type THISYS, is available.


ASTM C 1114-98 "Standard Test Method" for "Thin Heater Apparatus" (THA) is a relatively new standard (1998) that offers the possibility to perform fast measurements with high accuracy, across a fairly large temperature range.
The THA principle relies on the fact that a thin heater has negligible lateral heat flow. With a combination of a very thin heater, two relatively thin samples of similar thickness and two heat sinks it is possible to generate a homogeneous thermal field with known heat flux through the samples.

By measuring the flux φ (derived from heater power), the differential temperature across the samples, ΔT,amp, and the effective sample thickness, H,eff, it is straightforward to calculate the thermal conductivity λ:

λ = φ H,eff / ΔT,amp

The measurements of φ, H,eff and ΔT,amp are all direct measurements of power, dimensions and temperature. This is contrary to methods like the "guarded hot plate", that require reference materials or calibrated heat flux sensors. The THA provides an absolute instrument.

THA01 Design

The technological novelties are a thin thermocouple thermopile (proprietary Hukseflux design) performing an accurate and ultra-sensitive differential ΔT measurement, and the fact that the measurement is performed in a bath of glycerol. The latter reduces contact resistance and facilitates the THA operation. Commonly used methods like ASTM D 5470 - 01 have shown to be highly sensitive to contact resistance. THASYS offers a solution to this problem. The THA01 can handle samples of 0.01 to 6 mm thickness. Samples typically are sheet materials with a size of 70 by 100 mm. The measurement accuracy depends on the total thermal resistance of the samples. In case of very thin samples (0.01mm), measurement accuracy can be improved by "stacking", i.e. using four or more samples instead of the usual two. The measurement essentially is done at the temperature of the THA01. If necessary the temperature can be changed by putting the whole THA01 in a climate chamber, performing measurements while the instrument temperature changes across the required range. The thermopile is attached with its cold joints to one of the heat sinks. Its hot joints are incorporated in the thin heater. The samples are put in between the heat sinks and the heater. Errors due to contact resistance are minimized by using glycerol fluid. In a simplified description, the measurement consists of a heating cycle and a measurement to establish ΔT.

MCU01 Design

The MCU performs the functions of measurement and control as well as data storage. It is PC operated. Software in a Windows environment is part of the delivery. The parameters cycle time, sample thickness and heater area are entered and the experiment is started from the screen.


Verification of the stability can be done by repeated (yearly) testing of Pyrex 7740 samples that are included in the delivery. The calibration is traceable to NPL. THASYS is suitable for use by ISO certified laboratories.

Suggested use

  • Plastics and composites thermal analysis
  • Electrical interface materials

More information

Please consult the manual for a full list of THA01 specifications. This manual is available free of charge as a PDF file via e-mail. The ASTM standard C1114-98 can be obtained from ASTM as a PDF file. A pressure cell is optional on THASYS. For use with high thermal conductivity materials the model THISYS is available.

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