Inline- Process- Photometer
A photometer detects the light absorbance at a specific wavelenght in the visible spectrum of the light, to measure the colour of a liquid. The detection (measurement) wavelength, depends by the measured product color. The color impression of the human eye results, if a specific bandwith of visible spectrum (approximately 400nm - 700nm) becomes absorbed. The complete visible spectrum 400nm - 700nm causes the impression of white light (no color). In case a liquid shows an absorption at 430nm - 480nm, so appears these liquid yellow. So you have to measure the absorbtion at 430nm - 480nm for the photometric detection of yellow color.
Process photometer will often measure the sample at a second wavelenght (tyically NIR 850nm [reference]). The reason for this second wavelength is, that yellow color and particles will cause an absorption at 430-480nm. The yellow color will not show any absorbtion at 850nm (NIR) but the particles will. Therefore the measurement channel (430-480nm) will detect yellow color and particles, and the reference channel (850nm) will detect the particles only. The difference of both channels results the color value. Typical color standards are APHA, ASTM D 1500, EBC, Gardener, Saybolt, etc..
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