Process color measurements of liquids are critical in maintaining precise process control and meeting product quality specifications. Color changes indicate other process variables such as overheating, dilution ratios and finished product appearances. Photometrically monitoring color measurements inline enables real-time, precise control of color addition, color removal, or color avoidance process automations.
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Typically process color measurements are made by extracting samples from the process piping and analyzing them in a lab either visually or using a spectrophotometer. optek colorimeters can immediately detect color changes in process liquids directly in your pipeline. A focused beam of light passes from the lamp through the process medium and is partially absorbed, changing its intensity. This absorbance is color / wavelength dependent, and an indication of the fluid color. The change is then detected by the colorimeter’s detector module, and converted to a signal reading.
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Inline Process Color Measurement Benefits |
- Continuous representation of the degree of color directly inline
- Eliminate human interpretation errors
- Reduce the opportunities for product contamination
- Increase operating efficiency
- Minimize or eliminate out of spec product
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Process Color Measurements:
Color Removal, Color Addition, and Color Avoidance |
Processes requiring color removal, often times use filters and filtering media to strip out unwanted color. Installing an optek colorimeter after these filters, immediately detects unwanted coloring, assuring proper product specifications. Similar installations near color dosing systems monitor the process ensuring proper color parameters. In general, we monitor a substance as it is added to the process stream until the desired concentration is reached. The most common process color measurement is color avoidance. Heat exchanger leak detection, yellowing caused by overheating or charring and trace color detection in water or organic solvents due to contaminations are examples of color avoidance.
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| Dual channel Colorimeter Measurements |
Optek dual channel colorimeters are superior to all single channel colorimeters in sensitivity, repeatability, and precision. Effects like varying background turbidity or window fouling will not affect the process color measurements. After the light beam has been partially absorbed by the process medium, the remaining light is split into two beams. Each of these beams then passes through a narrow band-pass interference filter blocking out all but the analytical and reference wavelength.
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The analytical wavelength is chosen to match the absorption characteristic of the component being analyzed, while the reference wavelength is a selected wavelength or bandwidth known not to be absorbed in the specific process medium. When the reference reading is subtracted from the analytical reading, the result is the pure analytical color measurement regardless of background turbidity fluctuations or fouling.
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| Color Scales |
There are many color scales in use today. Optek colorimeters can be configured to correlate to many color scales. A few of the more popular scales are described below.
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The APHA (American Public Health Association) scale is based on yellowness. Originally created to measure waste water, the APHA scale is based off water dilutions of platinum-cobalt (PtCo).
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Saybolt and ASTM color scale are common to the petroleum industry, for water white finished products such as jet fuel, lubricating waxes, and heating oils. The Saybolt scale is the most difficult scale for the human eye to monitor, for it is nearly colorless.
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In the brewing industry color scales such as ASBC-SRM and EBC are used.
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Other color scales such as ICUMSA, AOCS, and HAZEN are used in sweetener and edible oil refining industries.
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