The TPS sensor is comprised of a flat, double-spiral of Nickel, encapsulated between layers of dielectric insulation. The sensor is electrically connected to a separated power supply and electrical resistance sensing circuit. An auto-balancing Wheatstone bridge is used to maximize electrical resistance sensitivity at the sensor spiral, which is critical for measuring a wide range of thermal conductivity. During a measurement, a current passes through the spiral and creates an increase in temperature, which is recorded over time. Heat generated, dissipates into the sample at a rate dependent on the thermal transport characteristics of the material.
A unique feature of the Hot Disk TPS, is the ability to remove the effects of contact resistance from a measurement without the use of a contact agent. Contact resistance presents itself as a non-linear region at the start of the calculated results for the transient measurement. This is easily identified and removed, manually or automatically, leaving a linear slope free of contact resistance.
From this slope, high accuracy thermal conductivity (W/mK) and thermal diffusivity (mm2/s) is calculated, without the need of complex calibration. Additional properties including volumetric heat capacity (MJ/m3K) and thermal effusivity (Ws½/m2K) are automatically calculated and displayed.