Calibrating the needle probe

Thermistor bead temperature change in response to heater wire current beginning at time = 0 seconds. Two measurements each are plotted for ice (dotted lines) and THF hydrate (solid lines). Divergent responses after 0.2 seconds (inset) signal the moment when the sample begins influencing the thermistor temperature change. This point is taken as t = 0 seconds in our thermal property measurements (Click for larger image).

To determine the time delay between applying current to the probe and the measured temperature change being influenced by the sample, we compare data from the first few seconds of measurements in ice and in THF hydrate. Two measurements are plotted for each material to demonstrate the measurement reproducibility. Thermal transfer is more efficient in ice than in THF hydrate, because the thermal conductivity and diffusivity of ice are five times that of THF hydrate. The slower temperature increase in ice illustrates its effectiveness relative to THF hydrate in transferring heat away from the probe.

The measured temperature rise in the two materials diverges 0.2 seconds after current is first applied to the heater wire. Our probe calibration consists of setting time t = 0 to be 0.2 seconds after current is supplied to the heater, and referencing the temperature change,ΔT, to the thermistor temperature at that time.