Do you know the meaning of Reference Option on a UVAS sensor?

Document ID

Document ID TE10926

Published Date

Published Date 04/24/2019
Do you know the meaning of Reference Option on a UVAS sensor?
"Reference" option for UVAS
The UVAS probes, regardless of path length, have the ability to measure light absorbance or transmittance at 254 and 550 nm.  Generally speaking, dissolved organics and particulate matter absorb/scatter light at 254 nm while only particulate matter affect readings at 550 nm.  The reading at 550 nm is known as the “reference” whereas the reading at 254 is the “measured” reading. When Reference is set to ON, the net absorbance (A254-A550) is determined. This attempts to remove the contribution of particulate matter. When Reference is set to OFF, only the absorbance at 254 is considered, which includes dissolved organics and particulate matter. Turning Reference to ON is generally appropriate when estimating the dissolved organic content of wastewater (ie. BOD or COD). However, in UV Disinfection applications, one is interested in the transmittance of the water to be treated.  Dissolved organics and particulate matter both reduce the effectiveness of UV disinfection and should be included in a transmittance measurement for control of the process.  The Reference setting should be set to OFF for UV disinfection applications.

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