Light emission diode water thermometer: a low-cost and noninvasive strategy for monitoring temperature in aqueous solutions

A spectroscopic device for monitoring the temperature of aqueous solutions is presented. It uses a 950 nm light emission diode as light source and two photodiodes as detectors. Temperature is monitored following the thermally induced absorbance changes of the water-OH second overtone (approximately 960 nm). A linear response between the light absorbed by an aqueous solution and its temperature is found in the range from 15 to 95 degrees C. A prediction error of 0.1 degrees C and a precision of 0.07 degrees C in temperature measurement can be achieved. Up to 0.1 M of electrolyte concentration can be present in the solution without significantly affecting the temperature measurement. Different strategies, such as remote (noninvasive) or in situ (using a fiber-optic probe) temperature measurement, are shown, and their relative advantages are discussed.