Optically based method and apparatus for accurately and automatically measuring the melting temperature of a material of interest

Abstract

The melting point of a test substance is determined by placing it in a glass capillary tube within a metal block equipped with an electrical heater and temperature monitoring device. The temperature of the metal block and sample are gradually increased, often to temperatures that would damage electronic components. The output of a light emitting diode located a short distance from the metal block and away from the high temperature is coupled into a hollow tubing having highly reflective internal walls that carries the radiation to the glass capillary tube containing the test substance. A second hollow tube, also having highly reflective internal walls, is connected to a light detector that collects reflected radiation from the capillary tube. At the melting point of a solid, the light reflecting properties of the test substance decrease causing the light signal collected by the second reflective tube to decrease. The melt point is recorded as a change in the output voltage from the detector. The melting point detector is equipped with a number of ports for capillary tubes, internally reflective tubes, light emitters and detectors so that many phase transition points of different samples can be determined in one heating cycle. The outputs from the detectors are input to a computer and the detector signals are correlated with the temperature of the block. Melt point measurement accuracy is enhanced and analysis speed is improved by making the rate of heating of the block inversely responsive to the phase transition of the sample. This is done by correlating the first derivative of the light intensity with respect to temperature to the amount of heat input to the block.

Dependencies are inferred from the claim text.