Online color analyzers provide real-time, accurate color measurements, enhancing quality control and efficiency in industrial applications
Do you have any of these concerns?:
DRIFT
“We often have to adjust our online color analyzers because they drift all the time.”
A drifting reading in an online optical colorimeter is almost always due to two factors:
- Coating/fouling forming on the optical window surfaces. Fouling cuts down the amount of excitation light entering the fluid and reduces the amount of scattered light being received by the instruments’ photodetector. Using a referenced based measurement (i.e. dual beam vs. single beam) can resolve this issue. A reference wavelength in the NIR is used to monitor the build up on the windows and the amount of absorbance it causes. Subtracting ABS(NIR) from ABS(COLOR) will correct the color absorbance signal to a give true color reading. Note that it’s important to establish any absorbance ratio between ABS(COLOR) and ABS(NIR) and weight the subtraction accordingly. For instance, if the window fouling causes half the absorbance on the NIR channel as it does on the Visible (color) channel, to get true color correction, it’s important to weight the subtraction so that ABS(true color) = ABS(COLOR)-2xABS(NIR).
- In older optical colorimeters, an incandescent bulb is often used to generate light as excitation for the measurement. However, incandescent bulbs are constructed with metal elements and over time, these elements evaporate due to their temperature and coat the inside of the bulb, making their output dimmer and yellower. Modern systems use LED’s as their light source and these resolve the aging lamp issue because the output can be held constant and doesn’t “yellow” over time.
SENSITIVITY
“We measure color in our water system but even when we visibly see a yellowing of the stream, the colorimeter we have fitted doesn’t react.”
Optical colorimeters pretty much all work using absorbance as the physical measurement. In order to measure yellow, you need to use a blue light source (yellow’s complementary color) and have a sufficiently long measurement path for the amount of yellowing you get. For detecting a yellow “tinge”, you need a longer pathlength than if you need to measure a deep yellow color. Assuming there are no issues with the equipment itself, it’s possible you need to adjust either the wavelength of light you are using for excitation and/or increase the optical path across which you are measuring. Changing wavelength is easily done in a Kemtrak unit as it takes only a few minutes to install a new LED. Optical path adjustment may mean changing your measurement cell.
MEASUREMENT CELL CLEANING
“We measure color in a “dirty” stream that causes windows to get coated with a sticky substance and we need to manually clean them often in order to keep the instrument online. What are the options for an application like this?”
Difficult flow stream conditions have often meant that optical measurement is not a practical solution for many applications. However, there are a few ways to tackle this problem:
- Install a measurement cell with a water jet system that will blast the coating off of the cell windows when actuated. The Kemtrak DCP007 has a built-in automatic routine to do this and cells can be supplied with water jets.
- Install a probe in a retractable probe housing (such as an Exner EXtract device) instead of a flowthrough cell. This will allow the probe to be withdrawn from the line, removed, cleaned and returned without having to shut the line down. Retraction and cleaning could also be automated, with the probe being withdrawn from the line every hour or so and automatically cleaned
- Install the measurement sensor (cell or probe) in a bypass loop on the main line with bypass and isolation valves. Use a quick connector type (i.e. a clamp fitting) on the measurement cell or probe to enable it to be quickly removed from line and cleaned. Reinstall and start flowing again.
Keeping an optical measurement online and reliable is achievable if pipe arrangements like a bypass are installed or automatic cleaning routines using equipment such as cleaning jets or retractors are implemented. Even where conditions are extreme, automated solutions can greatly improve the quality and consistency of the measurement while reducing the amount of manual cleaning required.
MULTIPLE COLOR MEASUREMENT
“We have a process that changes color and when it does, we need to divert the stream to a holding tank. The normal color is blue but if our inline chemical addition fails, it changes to a red color.”
This is possible using a dual channel colorimeter. One channel can be configured to measure the blue color and the other set up to measure red. The instrument will give two outputs – blue and red. During normal operation, the blue output will be trending and the red output will be at or almost zero. Should the chemical addition fail, then the trends will reverse and it will be possible to see the color change in real time. Alarm limits can be set around these trends to alert operators to the problem. Furthermore, the analyzer can be used to automatically switch the stream to your holding tank when red reaches a pre-set level, just in case the operators are handling something else at the time.
LINEARITY
“We have a Hazen scale colorimeter measuring the color of incoming raw water to our plant. The water is taken from a river and can vary dramatically in color. We are seeing non-linearity in the measurement between the online unit and our lab unit. Low color is comparable, but at high levels of color, the online instrument reads low.”
One of the challenges of colorimeter designs is excluding stray light. As color increases, absorbance of the wavelength of interest increases and the ratio of this to stray (unabsorbed light) changes, making the measurement non-linear. Many colorimeters use a white light source (often an incandescent bulb) as an excitation source and install blocking filters to exclude all wavelengths except for the wavelength of interest. Filters are not perfect and their blocking capability varies dramatically depending upon the type used. In addition, the “better” the filter, the lower its light transmission capabilities, and this impacts instrument range and performance. LED light sources are a better solution as the light they generate is only associated with the wavelength of interest, removing the need for wide out of band blocking as unwanted light is no longer there and greatly improving linearity across wide color ranges.
HAZARDOUS AREA USE
“We need to measure the color of different grades of oil in real time but our piping is small and the explosionproof color analyzers and sensors we have seen are huge. We don’t have space to install a big cabinet or build a support structure!”
An inline colorimeter doesn’t need to be large. Local units need large explosion-proof housings and wired sensors must include heavy enclosure to house their electrical and electronic components. Using fiber optics, sensors do not have electrical/electronic components, so a small cell can be fitted in your existing line (just like a pipe fitting) and connected to a dedicated colorimeter electronic unit mounted remotely in a convenient place. Fiber optic runs can be very long (up to 100m), so even the analyzer doesn’t need to be explosion-proof if it can be fitted inside a switch room or control panel where ordinary area equipment is permitted.
Learn more about the impact of photometer design on photometer validation methods and the pros and cons of various verification methods.
SOUTH FORK DELIVERS ACCURATE, RELIABLE AND LOW COST OF OWNERSHIP INLINE COLOR MEASUREMENT SOLUTIONS SPECIFICALLY CONFIGURED TO SUIT YOUR APPLICATION NEEDS.
All of our color measurement solutions are built upon the tried and tested Kemtrak DCP007 industrial photometer platform. The Kemtrak DCP007 platform offers a stable optical absorbance bench, highly configurable for a wide range of wavelengths from UV through the near infrared. Once connected through rugged fiber optic cables to one of Kemtrak's wide array of inline measurement cells, the DCP007 provides real-time color/concentration measurement of liquids or gases for process control, monitoring and quality control purposes.
We recognize the need to deliver a measurement solution which is not only accurate and reliable, but also cost effective. The high reliability and performance of Kemtrak color measurement systems translates to a low cost of ownership through minimal maintenance requirements and a positive contribution to the process quality and efficiency.
COLOR MEASUREMENT METHODS FOR STANDARD SCALES LIKE ASTM, HAZEN, PT-CO, APHA, SAYBOLT, ETC. OR SCALE-LESS BY DEPTH/INTENSITY
APHA, Platinum-Cobalt (Pt-Co) and Hazen are different names for the same color scale specified by ASTM D 1209, BS5339:76 (1993), DIN 53409 and ISO 6271-1:2004(E). The APHA color scale measures the yellowness of a liquid, and is well suited for both quality control and contamination detection. It is regularly used to evaluate the purity of clear liquids in a wide range of applications as diverse as drinking water quality control, NGL color control and iron concentration in groundwater.
For APHA color measurement, photometers are configured to use a measurement wavelength of 380 and 500nm depending upon range. Deeply colored processes (> 500 APHA) use measurement cells with a fairly short optical path-length (OPL) while slightly colored process streams (<100 APHA) require a longer OPL. An NIR reference wavelength is used to compensate for both turbidity in the process stream and window fouling over time, ensuring the measurement remains accurate.
A wide variety of color scales are used throughout industry. Different measurement wavelengths and optical pathlengths for DCP007 absorbance photometers are available to provide measurements to these different color scales.
Color scales are not always used. Process streams can also be monitored for color depth/intensity using absorbance or user specified units.
SOUTH FORK HAS INLINE COLOR MEASUREMENT SOLUTIONS FOR EVEN THE MOST NICHE APPLICATIONS.
While Kemtrak color photometers are commonly found in industries such as pharmaceutical, food and beverage, chemical, and oil and gas, measuring color to standard scales such as APHA/Hazen and Saybolt color scales, we also have solutions for many industry-specific color applications, such as the ICUMSA color scale for sugar.
Off-the-shelf solutions are often not up to the challenge posed by the specificity of these applications—it is critical that the analyzer be configured to reproduce whatever offline standard (visual or otherwise) is being used, online.
We have supplied color measurement systems for many applications with specific requirements. Applications include:
- Product color control for QA/QC
- Filtration bed monitoring
- Ion exchange column monitoring
- Leak detection
- Contaminant detection
- Interface detection
The Kemtrak DCP007 absorbance photometer is designed to reliably measure concentration and color, even in turbid or hazy flow streams. The unique referencing system used by Kemtrak analyzers removes the effects of solids suspended in the flowing stream to give a “true color” measurement. To achieve this, the DCP007 measures at two wavelengths simultaneously: a primary wavelength to measure color and a reference wavelength to measure and compensate for any offset to the color measurement caused by haze and fouling. An additional benefit of measuring two wavelengths is that multiparameter measurement can often be provided from the same instrument: color/concentration of the stream and solids/turbidity content.
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SOUTH FORK INSTRUMENTS IS COMMITTED TO SOLVING YOUR FACTORY AND PROCESS AUTOMATION CHALLENGES
Using effective communication and an in-depth understanding of your industry to develop practical solutions for your measurement needs.
SOUTH FORK INSTRUMENTS
3845 Buffalo Road
Auburn, CA 95602
Tel: (+1) 925-461-5059
