Low-Maintenance Turbidimeter for Potable Water Applications

Higher demand for safe drinking water and tighter monitoring of contaminants in potable water are in contrast to the current trend towards reducing maintenance / operating costs and remote controlled plants. Main maintenance tasks on a regular base for turbidimeters are cleaning the optical windows and replacement of the light source as well as readjustment / recalibration with a primary standard. A new approach with a non-contact, LED turbidimeter reduces maintenance efforts significantly and thereby contributes to lowering the cost of ownership.

State of the art turbidimeters for potable water analysis are based on the nephelometric measurement principle as described in the Standard Methods [1] and adapted by ISO (ISO 7027 [2]) or EPA (EPA 180.1 [3]). A ratio turbidimeter measures the ratio between scattered and transmitted light. If just the transmitted light is detected, it is a single beam turbidimeter.

The set up is quite simple but there are some disadvantages, especially in terms of maintenance effort.

Several tasks have to be conducted on a regular base for these types of turbidimeters to ensure its reliability and functionality.

The main maintenance tasks
Cleaning of optical windows The turbidimeters consist of a flow cell design, where the optical windows are in direct contact with the sample. It is obvious, that cleaning is sometimes necessary, which means maintenance hours, causing operating costs. Cleaning the optical windows often requires a readjustment of the turbidimeter’s sensitivity.

Replacement of the light source
A light bulb with a tungsten filament has to be replaced at least once a year which needs a readjustment or recalibration of the turbidimeter. Additionally, a decrease of the lamp intensity leads to wrong measurement values if not monitored correctly

Chamber drain
Settled particles in the measurement chamber have to be removed from time to time to avoid interference based on a carry-over effect.