SOUTH FORK INSTRUMENTS CAN ADDRESS A VARIETY OF COMMON TURBIDITY MEASUREMENT CHALLENGES.
Do you have any of these concerns:
“We are constantly having to adjust our turbidity monitors because they drift all the time.”
When simple 90° scatter technique turbidimeters are used in applications with fluids that less than almost clear (i.e. drinking water), coating/fouling quickly forms 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. This causes both drift and a reduction in sensitivity. Using a ratio based 90° scatter instrument provides compensation for window fouling and keeps the measurement stable and online.
“We want to measure very low turbidity in our process after final filtration, but our plant runs at high pressure.”
Making turbidity measurements at high pressure can be challenging. Optical windows in any turbidity measurement circuit must be rated to the design pressure of the plant. This is a problem for instruments that utilize windows with a large surface area. Kemtrak inline turbidity measurement cells, because they are fiber optic based, need only small windows into the process line and are therefore able to meet extremely high pressures.
“We have a turbidity probe but it gives very poor and non-repeatable results, particularly at lower turbidity levels.”
Turbidity probes, particularly small ones, use a backscatter or transmission technique to measure turbidity. Backscatter measurement techniques do not work well at low turbidity levels. Transmission measurement can work well at low turbidity levels, but requires a long optical path length to do so – something not generally found on optical probes.
“We measure turbidity in a steam condensate but we see a lot of failures of components in the sensor housings. It’s very expensive to keep the measurement online.”
Many turbidity sensors have “high temperature” options, but these are really just standard sensor parts mounted with some sort of plastic insulator. It’s not an effective way to measure turbidity at high temperature, and sensor failures are common. The only way to resolve this problem is to use a fiber optic-based system that has no electrical or electronic parts in the sensor housings. Kemtrak systems use fiber optics to connect the measurement cell to sensitive optical components in the electronic unit.
“We calibrate our turbidity systems using formazin standards regularly, but our results seem to vary depending upon which technician carries out the calibration.”
Calibrating turbidity systems is not a simple task. The main problem is that calibration solutions constantly settle, so readings are always on the move. Agitating to re-suspend particulate and pouring into and out of measurement cells can introduce air bubbles that create errors. Kemtrak has a simple calibration system using sealed formazin (or polymer bead) standards that are inserted into window optical paths using a unique positioning fixture, ensuring repeatable and consistent results.
“I read on my Formazin standards that they should be refrigerated. Is this really necessary?”
The chemical stability of formazin suspensions is dependent on storage conditions. Exposure to heat or direct sunlight will denature the polymer structure, while prolonged contact with ambient air will allow the fluid supernatant to evaporate while air-borne contaminants enter. Formazin standards should be stored in a cool, dark place and refrigeration will provide extended life. When using your standards, do not leave containers open longer than necessary and always seal them tightly for storage. Never pour standards back into their storage containers as this will introduce contamination and could lead to erroneous future calibrations. As a rule, a 4000 NTU formazin suspension, when stored correctly, will be stable for about one year.
SOUTH FORK PROVIDES SUPERIOR-CLASS TURBIDIMETER PLATFORMS WHICH SUCCEED WHERE LESSER MEASUREMENT SOLUTIONS STRUGGLE OR FAIL.
Many traditional turbidity measurement solutions use probes that emit light through a flat window into the process stream. Then, light is reflected/scattered back through the same window and onto a photometric detector in the sensor. While this "one-probe-does-all" approach is simple, it is insensitive to very low turbidity levels and, when installed in pipes (particularly smaller ones), wall reflections can greatly interfere with the measurement, giving false readings and erratic results. Kemtrak flow-through cells are highly sensitive to very low levels of turbidity whilst still having wide measurement range capability.
For higher range measurements, probes are used. Kemtrak probes have a 45° angled head to allow stray light to travel down pipes rather than reflect back through the optical window and create disturbance and instability.
Our systems instill a high level of confidence in the measurement by consistently producing values in agreement with those determined through offline sampling. Turbidimeters are configured to utilize the optical measurement technique—attenuated, backscatter, ratio—that best accommodates your process conditions and needs, ultimately ensuring that you know, in real time, the true state of your process stream.
What is a turbidimeter?
Turbidimeters are optical instruments used to measure the clarity of a fluid. For low level turbidity (i.e. drinking water), a light scattering technique is most often used. In this, a collimated beam of light is passed through a liquid sample. A photocell at 90° to this incident light detects light scattered by any particulate matter in the fluid. The greater the amount of scattered light, the more particulate is present in the liquid. Once the turbidity of the liquid reaches a certain point, the side scatter technique is no longer viable because the detector becomes blinded by the amount of particulate present. Once that limit is reached, attenuation and back scatter techniques can be used instead.
Each technique has a relative sensitivity, and while there is a great deal of overlap between the techniques, it is important to select the right one for the application to get the best and most satisfactory results.
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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.