How is the appropriate path length determined for Nitratax and UVAS sensors based on process application?

Document ID

Document ID TE9284

Published Date

Published Date 02/19/2018
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Question
How is the appropriate path length determined for Nitratax and UVAS sensors based on process application?
Summary
Determination of the appropriate path length for Nitratax and UVAS probes
Answer
Both the Nitratax and the UVAS use light absorbance methodologies to measure nitrate and dissolved organics, respectively.  Choosing the correct path length for a given application requires an understanding that dissolved nitrate, dissolved organics and particles (among others) block light-thus all contribute to the final measurement's absorbance value.  Both the NITRATAX sc and UVAS sc compensate for this "interference" from the dissolved nitrate, dissolved organics, and particles through reference light sources; however there may be applications where the combination of these compounds absorb too much light, and cause insufficient light to be transmitted to the analyzer's measurement detectors.  This will lead to inaccurate measurements, frustration, and lots of wasted time.  To avoid this situation, the chart below was created as a general guide to choosing the appropriate path length based on application.  If followed correctly, the instrument will be appropriate for the application 95% of the time.
An automatic diagnostic test determines if the combined absorbance is too much for the measurement detectors.  If the message, "EM Too High" appears on the sc controller, and the lenses of the sensor are clean (with window cleaning solution or dilute HCl), then a smaller path length is necessary for the application. "EM" means "measurement extinction", or the absorbance at the main measurement detector, and this message says the absorbance exceeds the capabilities of the detector.  Another quick check is to enter the SENSOR SETUP menu, choose DIAG/TEST, TEST/MAINT, SIGNALS, and view the EM value while the sensor is installed in the application.  If the value is between 2500 and 3000, then a smaller path length sensor should be installed.
Nitratax
5 mm Clean, clear water applications, such as: drinking water effluent, tertiary (filtered) wastewater, and clear industrial waters.
2 mm Dirty, cloudy water applications, such as: wastewater mixed liquor, wastewater BNR systems, secondary wastewater effluent, and raw drinking water.
1 mm High solids, sludge applications, such as: wastewater above 4000 mg/L, industrial waters with high solids content, and high nitrate content.
 
UVAS
50 mm Clean, clear water applications, such as: drinking water effluent, membrane filtered wastewater, and clear industrial waters.
5 mm Low solids content water such as secondary wastewater effluent.
2 mm Dirty, cloudy water applications such as wastewater mixed liquor, wastewater BNR systems, secondary wastewater effluent, and raw drinking water.
1 mm High solids, sludge applications such as wastewater above 4000 mg/L, industrial waters with high solids content and high dissolved organic content.
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