Abstract
A new method to automatically measure thermal diffusivity incorporating analogue computer technique in the previously used pulse method is explained.
In the pulse method, a high-intensity heat pulse such as a laser pulse is absorbed in the front surface of a thermally insulated specimen, and the resulting temperature rise at the rear surface is measured by a thermocouple and recorded with an oscilloscope and a camera. The thermal diffusivity is calculated from the specimen thickness and the time lapse required for the rear surface temperature to reach one-half of the maximum value. This time lapse is determined by the graph of time V.S. temperature of the rear surface.
We propose the new system to decide the thermal diffusivity without a graph or calculation. The fundamental principle of it is the same as the above mentioned measuring method except that an analogue computer is led into the system and the temperature of the rear surface is sampled twice after the heat pulse absorption. The time interval between the two samplings, is fixed and the sampled values are held in an analogue memory device. The ratio of the temperature of the 1st sample to that of the 2nd sample must be different when the thermal diffusivity varies. The variation of the ratio of the two samples is simulated in the analogue computer with the variable of the thermal diffusivity. By this simulation the value of the thermal diffusivity of the tested specimen is decided when the simulated ratio of two sample temperatures is equal to the measured ratio on the specimen.
The simulator is composed of integrators, comparators, multipliers, sample-holders and a thermal diffusivity indicator. With this new system the thermal diffusivity is determined with the accuracy of ±10%.
