These can manifest as follows:
a) Drop in flow rate, as observed on panel rotameter or digital flow indicator [RM Series, LD Series, and multipoint systems].
b) Loss in instrument sensitivity
c) Drop in flow rate and loss in instrument sensitivity, as these are related
Sensor clogs or partial occlusions generally derive from two sources.
In the first case, too much distilled or deionized water is being added to refillable sensors. Alternatively, the water is not being added properly. This can cause small amounts of electrolyte to pass through the semi-permeable membrane of the sensing electrode, which dries and leaves a residue behind. The residue can accumulate over time and decrease or prevent flow of gas through the sensor.
The second source is particulate contamination. All continuous monitoring systems [RM Series, LD Series, and multipoint systems] are provided with sample inlet filters. Portable analyzers (4000 Series) can also be provided with a filter-equipped sampling probe, and this should be done in any application that will require monitoring in dusty areas. Contact the service department for further details.