Turbidity 

Turbidity is the reduction in light transmission caused by suspended and colloidal particles. It responds fast, correlates well with suspended solids, and appears in drinking water treatment requirements as well as construction stormwater and dredging permits.

RAECO Rents supplies turbidity instruments and sensors with NIST-traceable calibration included. Free ground shipping and free return shipping are included on every rental.

YSI ProDSS Multiparameter Digital Water Quality Meter
Frequently Asked Questions
Common questions about turbidity
Which turbidity standards are approved?
Only standards prepared according to Standard Methods for the Examination of Water and Wastewater, Section 2130 B. That covers AMCO-AEPA standards made specifically for the sensor, formazin prepared per Standard Methods, dilutions of 4000 FNU formazin concentrate, and StablCal standards. Standards from other sources will likely produce a bad calibration and wrong field readings.
Why am I getting negative turbidity readings?
The zero standard was contaminated. Even a brand new instrument can contaminate a zero standard to around 0.1 FNU in a lab, and cleaned but used sensors, cups and guards can push it close to 1.0 FNU. If your actual reading in the zero standard is 0.6 FNU but you entered 0, a sample at 0.3 FNU will display as -0.3 FNU.
How do I stop negative readings happening?
Keep a calibration cup and sensor guard used only for calibration and never taken into dirty water. Where equipment is properly cleaned, typical contamination runs 0.2 to 0.8 NTU, so entering a first calibration point between 0 and 1 FNU is acceptable practice. Calibrate in a lab rather than in the field where you can.
Do I need the sensor guard installed?
Yes, for both calibration and every measurement. The guard has a black-painted metal bottom that eliminates stray light reflection, which the optical measurement depends on. Check that inner surface is not badly scratched, and keep both guard and cup free of anything reflective.
How do I avoid air bubbles during turbidity calibration?
Pour the standard slowly down the side of the container rather than straight in, so you do not aerate it. Then lower the sensor in slowly with the cup tilted at roughly 45 degrees. Bubbles clinging to the sensor face read as particles and will skew the calibration.
FNU or NTU — does the unit matter?
Both describe the same 90 degree scatter measurement, but they come from different reference methods using different light sources, so values are not always interchangeable — particularly in coloured water. Check which unit your permit or method requires and report in that unit rather than converting.
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YSI ProDSS Multiparameter Digital Water Quality Meter
Water Quality Meter

YSI ProDSS Multiparameter Digital Water Quality Meter

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