Deposit build-up on the prism surface disturbs the measurement. Look out for an abnormally high concentration reading or an upward concentration (CONC) drift.
In most applications the prism keeps clean due to the self-cleaning effect. If coating occurs, check the following:
- Sufficient flow velocity, see Pipe mounting checklist.
- A temperature difference between process fluid and sensor probe can cause coating. This can happen with small flows if the thermal insulation is inadequate. In some cases it also helps to insulate the clamp connector.
In case of a coating problem, the preferred solution is to try to increase the flow velocity, for example, by installing a pipe portion with smaller diameter.
Consider installing a wash nozzle, if increasing the velocity or using a flow booster does not provide a solution. See Prism wash.