A Photometric Technique for Determining Fluid Concentration Using Consumer-Grade Hardware

In support of a separate study to produce an exponential concentration gradient in a magnetic fluid, a noninvasive technique for determining species concentration from off-the-shelf hardware has been developed. The approach uses a backlighted fluid test cell photographed with a commercial digital camcorder. Because the light extinction coefficient is wavelength dependent, tests were conducted to determine the best filter color to use, although some guidance was also provided using an absorption spectrophotometer. With the appropriate filter in place, the attenuation of the light passing through the test cell was captured by the camcorder. The digital image was analyzed for intensity using software from Scion Image Corp. downloaded from the Internet. The analysis provides a two-dimensional array of concentration with an average error of 0.0095 ml/ml. This technique is superior to invasive techniques, which require extraction of a sample that disturbs the concentration distribution in the test cell. Refinements of this technique using a true monochromatic laser light source are also discussed.