EXO Extended Range Turbidity Sensor

EXO Turbidity SensorFor those measuring turbidity for storm water, construction run-off, flood events, TMDLs or other water quality concerns, YSI offers the EXO submersible field sensor to make accurate and extended range (0-4000 FNU) turbidity measurements in marine and fresh waters for water quality sampling and monitoring.

What Is Turbidity?
Turbidity is the indirect measurement of the suspended solid concentration in water and is typically determined by shining a light beam into the sample solution and then measuring the light that is scattered off the particles which are present. The suspended solid concentration is an important water quality factor and is a fundamental measure of environmental change. The source of the suspended solids varies in nature (examples include silt, clay, sand, algae, organic matter) but all particles will impact the light transmittance and result in a turbidity signal.


Benefits of the EXO Turbidity Sensor, as part of the EXO multiparameter water quality sonde:

Extended range: Measure turbidity across a wide range, from 0 to 4000 FNU, with minimal change in accuracy (see spec below)

Automatic sensor cleaning: The EXO2 water quality sonde’s wiper cleans the turbidity sensor to avoid fouling and maintain accuracy for up to 90 days of continuous water quality monitoring

Quick and reliable calibration: Sensor diagnostics and graphical software with calibration QA/QC speeds up the calibration process and provides assurance of calibration success

Reduced costs: Reduce reagent consumption with concurrent calibration of up to 6 turbidity sensors at one time. Configure sensors at one location and distribute to various field sites.

Sensor Type: Optical, 90° scatterRange: 0 to 4000 FNU
Accuracy: 0-999 FNU: 0.3 FNU or ±2% of reading, whichever is greater; 1000-4000 FNU: ±5% of reading*
Response: T63<2 sec
Resolution: 0-999 FNU: 0.01 FNU; 1000-4000 FNU: 0.1 FNU
Measurement Units: FNU. With appropriate correlation data, units can also be changed to NTU, RAW or TSS.


About FNU
FNU, or Formazin Nephelometric Unit, refers to the unit of measurement in a turbidimeter that uses infrared light to detect scattering at 90 degrees of the incident light beam. The wavelength of infrared light for the EXO turbidity sensor is 860±15 nm. FNU is similar to NTU, or Nephelometric Turbidity Unit, in that both measure scattered light at 90 degrees from the incident light beam, but NTU measures with a white light.

FNU is the default calibration unit for the EXO sensor, but users are able to change calibration units to NTU, raw sensor signal (RAW) or total suspended solids (TSS) if the user enters the appropriate correlation data.

Because the optics of the EXO turbidity sensor is slightly different from the optics in the 6-Series turbidity sensors, it is likely that there will be a slight discontinuity in field readings taken with the two systems after calibration in the same laboratory standard. For users who are concerned about this difference, YSI will be able to provide support in rationalizing historical 6-Series data to EXO data with minimal effort.

In addition, the slightly different optics of the EXO sensor will result in a different calibration value for the commonly used YSI midrange AEPA-AMCO standard—124 FNU for EXO vs. 126 NTU for the YSI 6136 sensor.

*Performance based on 3-point calibration done with YSI AMCO-AEPA standards of  0, 124, and 1010 FNU. The same type of standard must be used for all calibration points.

To obtain published accuracy spec, calibration must be completed with standards in the following ranges:
1st point: 0.0-1.0
2nd point: 12.4 or 124
3rd point: 1010 (or 4000 NTU Formazin once December 2013 software update is available)


Ask a Question to our technical applications team about the EXO Turbidity Sensor

Request Pricing for the EXO Turbidity Sensor as part of an EXO multiparameter sonde

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