Light Emission Diode Water Thermometer: A Low-Cost and Noninvasive Strategy for Monitoring Temperature in Aqueous Solutions

Abstract

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 (∼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 °C. A prediction error of 0.1 °C and a precision of 0.07 °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.