YSI EXO Turbidity Sensor
- 0 to 4000 FNU measurement range
- T63<2 sec response time
- 0.3 FNU or ±2% of reading accuracy from 0 to 999 FNU
|599101-01||EXO turbidity sensor|| |
|608000||6080 turbidity standard, 0 FNU (ProDSS & EXO); 0 NTU (6136), 1 gallon|
|607200||6072 turbidity standard, 12.4 FNU (ProDSS & EXO); 12.7 NTU (6136), 1 gallon|
|607300||6073G turbidity standard, 124 FNU (ProDSS & EXO); 126 NTU (6136), 1 gallon|
|607400||6074 turbidity standard, 1010 FNU (ProDSS & EXO); 1000 NTU (6136), 1 gallon|
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 of 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.
The EXO Turbidity sensor employs a near-infrared light source and detects scattering at 90 degrees of the incident light beam. According to ASTM D7315 method, this type of turbidity sensor has been characterized as a nephelometric near-IR turbidimeter, non-ratiometric. This method calls for this sensor type to report values in formazin nephelometric units (FNU). FNU is the default calibration unit for the EXO sensor but users are able to change calibration units to nephelometric turbidity units (NTU), raw sensor signal (RAW), or total suspended solids (TSS) assuming the user enters the appropriate correlation data.
The RAW value is a value unaffected by user calibrations and provides a range from 0-100, representing the per cent of full scale that the sensor detects in a sample. While all turbidity sensors will read consistently in formazin, other calibration solutions and field readings will vary between different models of turbidity sensors. These differences are thought to be a result of differing optical components and geometries and the resulting detection of varying suspended sediment characteristics. This effect is inherent in the nature of every turbidity sensor, and as a result readings between different model turbidity sensors are likely to show different field values even after calibration in the same standards.
For long-term, in situ continuous monitoring of turbidity, the EXO2 sonde has a wiper to clean the turbidity sensor to avoid sensor fouling and maintain accuracy.
The sensor units can be changed using the KorEXO Software and entering the desired parameter code while in the edit template menu.
The calibration frequency is ultimately up to the end user. Common calibration intervals are bi-weekly, monthly, quarterly, etc.
Yes, the EXO sonde platform is designed for us in freshwater and marine environments. The only exception is that the ISE sensors for ammonium, nitrate, and chloride are for freshwater use only. When using the EXO sonde and sensors in saltwater applications it is recommended that you use anti-fouling options outlined in this guide: https://www.ysi.com/File%20Library/Documents/Tips/E108-Antifouling-Tips-Book.pdf
This simply means that the sensors themselves have on-board memory and maintain calibration settings on the probe versus the sonde. This allows sensors to be switched between sondes without the need to recalibrate.
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