Sensor design for water hardness detection

A new sensor design for detecting water hardness using complexometric and colorimetric concepts has been presented in this paper. Calmagite, a metal ion indicator, changes color of a solution to wine red in presence of calcium (Ca^2002B;) and magnesium (Mg^2002B;) ions at pH 10. When Ethylenediaminetetraacetic acid (EDTA) is added to the solution, it displaces the indicator from the metal-indicator complex and turns the solution blue. A red solution is transparent to a red light whereas nontransparent to a blue light and vice versa. If a photodiode is placed across the solution, the voltage (V) across the diode will vary based on how much of red or blue light passes through the solution and strikes the photodiode. Finally, based on visual inspection of color change of a water sample and voltage change, around 30% and 13% in average for blue light and 6% and 74% in average for red light, hardness of the sample is detected.