Turbidimeters
A turbidity meter (turbidimeter) is used to measure suspended particles in a sample. A beam of light is directed through a sample vial and the amount of light reaching a sensor on one side of the beam (at 90°) corresponds to particulates in the sample measured in Nepholometric Turbidity Units (NTU). Known turbidity standards are used to calibrate the system and the units are re-calibrated every 3 months.
Inline turbidimeters in the lab are HF Scientific MicroTOL Turbidimeters. The maximum turbidity that can be read by most of them is 1000 NTU, but you will occasionally come across one with maximum turbidity of 100 NTU. If the turbidity exceeds the maximum, the turbidimeter will report values up to 1100 NTU (for the 1000 NTU max) and 110 (for the 100 NTU max). The serial cable from the turbidimeters communicate through RS-485. When connecting a turbidimeter to the computer (which uses RS 232), a converter must be used. These can be found in the filing cabinet in B60.
Air bubbles in the sample flow will cause the turbidity reading to be higher than expected. If you are working with a setup that has coagulant passing through the sample vial, it might be necessary to periodically clean the sample vial. To do so, remove the sample vial, clean with detergent and rinse thoroughly with distilled or deionized water. TAKE CARE not to scratch the sample vial as this would alter the sample reading. Screw the vial back into the unit and wipe with a Chemwipe to remove water and any oil or dirt from fingers and reinsert into the turbidimeter body.