AWWA C671-21 pdf download.Online Turbidimeter Operation and Maintenance
4.2.1 Sidestream turbidimeters. Sidestream turbidimeters (also referred to as process turbidimeters) are designed to continuously measure turbidity as a sample passes the turbidimeter’s optical elements (i.e., light source and detector). For filtration effluent, online turbidimeters can continually show that a filtration system is or is not operating within all regulatory compliance limits; if a filter is out of compliance, these instruments are typically the first line of defense in notifying the plant personnel that a breach in the filtration process has occurred. With the sidestream configuration, the sample flows into a cell external to the process and the analysis takes place in an analysis chamber (e.g., flow cell) where the view volume is free of external or process interferences. These are complete flow- through instruments and the sample continuously passes through the instrument as described in ASTM D7726.
4.2.1.1 Flow range. The instrument shall be operated within the manufacturer’s recommended flow range, which is designed to optimize the removal of bubble interferences and prevent particle fallout. The instrument shall be operated at the low end of the recommended range if the samples possess a high presence of dissolved gases, and it shall be operated at the high end of the recommended range if particle fallout is a concern.
Most low-range turbidimeters are the sidestream design since these are typically better for low-turbidity measurements. The passage of samples into the instrument helps to condition the sample by removing bubble interference as well as reducing stray light from outside sources. Although these instruments possess the advantages noted previously, they are also sensitive to flow, pressure, settling of particles, and fouling of optical surfaces. To prevent measurement error because of these variables, it is recommended that sample pressure and flow be kept consistent during measurement.
4.2.1.3 Potential fouling. The potential fouling of internal surfaces should always be considered. The instrument’s optical surfaces—namely the detectors and any windows through which light passes—should be inspected to ensure they are free of any deposits, such as oxides of manganese or iron, that could form over time. These surfaces should be cleaned as instructed by the instrument manufacturer. Deviation from the manufacturer’s recommendations could cause damage to these surfaces.AWWA C671-21 pdf download.