The TLS-100 is a portable meter used to measure thermal conductivity and thermal resistivity of a variety of samples, including soil, rocks, concrete, and polymers. Tests can be performed with the push of a button and results are displayed instantly.

The Transient Line Source (TLS) meter follows ASTM D5334-14. The sensor needle consists of a thin heating wire and temperature sensor sealed in a 100 or 50 mm steel tube. The sensor is completely inserted into the sample to be tested. Heat is delivered to the sample using a constant current source (q) and the temperature rise is recorded over a defined period of time. The slope (a) from plot of temperature rise versus logarithm of time is used in the calculation of thermal conductivity (k). The higher the thermal conductivity of a sample, the lower the slope. For samples of low thermal conductivity, the slope will be higher.



  • Soil thermal conductivity testing concrete, polymers, soil and soft rock.
  • Follows international standards: ASTM D5334-14, & IEEE 442-1981
  • Portable, Economical, and Accurate
  • Easy to use
  • Standard 100 mm sensor for soft materials
  • Optional 50 mm sensor for hard materials



Materials Soil, Rock, Concrete, & Polymers
Measurement Capabilities Bulk Properties
Thermal Conductivity 0.1 to 5 W/m•K
Thermal Resistivity 0.2 to 10 m•K/W
Measurement Time 3 min. (100mm) / 5 min. (50mm)
Reproducibility Typically better than 2%
Accuracy Typically better than 5%
Temperature Range -40 to 100°C
Smallest Sample (100 mm) 50 mm (diameter or square) x 100 mm
Smallest Sample (50 mm) 50 mm (diameter or square) x 50 mm
Largest Sample Size Unlimited
Standards ASTM D5334-14, & IEEE 442-1981



Thermal Conductivity of soil with Portable Thermal Conductivity Meter TLS-100 50mm


Each TLS-100 comes equipped with the standard 100 mm sensor for testing of soil, soft materials, polymers and easy to drill materials. The needle sensor is fully inserted into an isothermal sample and a measurement is made with the push of a button. After 180 seconds, results are displayed for thermal conductivity and thermal resistivity. Saved results can also be exported to a computer, via Micro-SD card or USB connection.

Soil thermal Dryout Curves can be prepared by measuring the thermal conductivity of a sample at different moisture contents, as the sample dries from saturation. The typical drying approach involves heating the soil at an elevated temperature. The sample is removed, weighed, and measured for thermal conductivity at different time intervals, until it is fully dried


The 50 mm sensor was designed for testing hard samples, like rock and concrete. Drilling the required 4 mm diameter x 50 mm hole in rigid samples is easy with the provided masonry drill bit. When testing hard samples, a thermal contact grease is used to enhance contact between the sensor and sample.

Thermal Conductivity of concrete with Portable Thermal Conductivity Meter TLS-100 50mm



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