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Transient Line Source (TLS-100) soil thermal conductivity meter

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.

Best For Soil, Rock, Concrete, and Polymers

ASTM D5334-22a | IEEE 442-2017

Standard Test

-40°C to 100°C


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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 are performed with the push of a button and results are displayed instantly. The TLS-100 features sensors that are auto-recognized with corresponding testing parameters automatically loaded.

The TLS-100 follows ASTM D5334-22a and IEEE 442-2017. The sensor needle consists of a thin heating wire and temperature sensor sealed in a 150, 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.

transient hot wire equation

  • Follows international standards: ASTM D5334-22a, & IEEE 442-2017
  • Economical, smart and accurate
  • Easy to use
  • Standard 100 mm / 150 mm sensor for soft materials
  • Standard 50 mm sensor for hard materials
Method TLS-100 (Included) TLS-50 TLS-150
Materials Soils, pastes, powders and solids Concrete, rocks and polymers Soils, pastes, powders and solids
Measurement capabilities Bulk properties Bulk properties Bulk properties
Thermal conductivity (W/m·K) 0.1 to 5 0.3 to 5 0.1 to 3
Thermal resistivity (mK/W) 0.2 to 10 0.2 to 3.3 0.3 to 10
Measurement time 3 minutes 3 minutes 3 minutes
Smallest sample size 100 mm in length, 50 mm in diameter 50 mm in length, 50 mm in diameter 150 mm in length, 50 mm in diameter
Largest sample size Unlimited Unlimited Unlimited
Accuracy 5% 5% 5%
Reproducibility 2% 2% 2%
Temperature (°C) -40 to 100 -40 to 100 -40 to 100
Standard ASTM D5334-22a, IEEE 442-1981 Modified ASTM D5334-14 ASTM D5334-14, IEEE 442-2017
Testing Sensors
TLS 100 mm Needle Probe
Standard 100 mm Sensor

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 convenient utility software and 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.

TLS 50 mm Sensor
Standard 50 mm Sensor

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.

TLS 150 mm Sensor
Standard 150 mm Sensor

The optional 150 mm sensor is used for in-lab and in-field testing of soil and soft materials according to IEEE 442-2017. The needle is fully inserted into an isothermal sample and measurement is made with the push of a button. After 180 seconds, results are displayed for thermal conductivity and thermal resistivity.

Related Research Papers
Find related research papers:

Conference Report The 3rd International Conference on Energy Efficiency in Historic Buildings

Energy efficiency in old building is very dependent upon how much heat is escaping through the walls. To determine this it is imperative to know the thermal conductivity of certain solid stone walls. This paper focuses on investigating the properties of some types of common stones used in traditional masonry of Scotland. The TLS-100 device is used to calculate the thermal conductivity of these stones via the transient line source method.

Freeze/Thaw Resistance of Mortar with Recycled Tyre Waste at Varying Particle Sizes

There is a growing concern for finding alternative solutions to construction materials in order to minimize their environmental impact as well as enhancing their service life. This study investigated the durability of cementitious mortars prepared by replacing fine aggregate (sand) with recycled tyre shreds and crumbs, aiming at providing an alternative outlet to tyre waste disposal.

Durability of Ternary Blended Concrete Incorporating Rice Husk Ash and Calcined Clay

Research on the combined substitution of supplementary cementitious materials (SCMs) has already demonstrated that it might be one of the few viable options to produce low-carbon concrete at scale. This paper presents an experimental investigation on the performance and durability of rice husk ash (RHA) and calcined clay (CC) in ternary blended concrete exposed to chloride attacks under wet/dry cycles.

Thermal Conductivity of Ceramics
Thermal Conductivity of Ceramics

Discovering the heat resistant and insulative nature of ceramics, through thermal conductivity testing.

Thermal Conductivity of Soil
Thermal Conductivity of Soil

Evaluating the thermal conductivity of varying soil moisture in construction and agriculture fields.

Thermal Conductivity of Snow
Thermal Conductivity of Snow

A look into the effect of compaction on the thermal conductivity of snow.

TLS-100 Accessories

rock testing kit

Rock Needle Kit

Recommended for use when testing solids such as rocks, concrete, or polymers.

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