Method and device for distinguishing material by thermal conduct

Details Method and device for distinguishing material by thermal conduct Method and device for distinguishing material by thermal conduct

1980-12-05

1982-08-17

Goldstein, Herbert

Thermal measuring and testing

Determination of inherent thermal property

Thermal conductivity

G01N 2518, G01N 2718

Patent

active

043443150

ABSTRACT:
Natural diamonds can be distinguished from simulated diamonds in seconds by merely touching a hand held probe to the gems. The tip of the probe includes a rounded gem contacting head of high thermal conductivity and low thermal mass. The head is preferably of gold-coated copper. It is supported on a high thermal resistivity neck extending from a large spring biased thermal mass. The head supports a thermistor heater element and a thermistor temperature sensing element within an annular space. Pulses of power are cyclically applied to the heater element to produce a predetermined amount of heat flow from the probe through the sample gem. The resulting change in temperature of the contacting head is determined by sensing the change in resistance of the sensing thermistor and weighting that change by the sensed thermistor resistance. The weighting function is carried out by a gain-controlled amplifier. The change-in-temperature signal controls a meter and LEDs which indicate whether the gem is natural or simulated.

REFERENCES:
patent: 2951360 (1960-09-01), Sampson
patent: 3611786 (1971-10-01), Schorr
patent: 3668927 (1972-06-01), Howell et al.
Sweat, "A Miniature Thermal Conductivity Probe for Foods".
Sandberg et al., "Heat Capacity and Thermal Conductivity from Pulsed Wire Probe", J. of Physics E., vol. 10, 1977, pp. 474-477.
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Dittmar et al., "A Cyclically Controlled Device for a Thermoconductivity Probe Used in Measurements of Blood Flow", International Conf. on Biomed. Transducers, 353-359, 1975.
Ostinskaya et al., "A Experimental Device for Measurement of Thermal Conductivity of Diamond Monocrystals" in Inzhenerno-Fizicheskii Zhurnal, vol. 32 #4, pp. 620-624, 4/77.
Schulte, "A Pulsed Comparator for the Measurement of Thermal Conductivity" in Conf. Ther. Cond. 1970, pp. 589-598.
"Operation and Maintenence Manual for T-C100 Thermal Comparator", by Lafayette Instrument Co.

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