Dust monitoring

The Sigrist Photometer VisGuard, available from Siemens Automation and Drives allows operators to monitor levels of dust, aerosol and particulates, whether to comply with health and safety regulations or to control ventilation systems. Based around an optical sensor, the device can be used both in situ and remotely.

Air to be sampled is extracted by a blower and carried through a flow cell, where the air is subjected to a dual-beam measurement, calculating the relation between intensity of light scattered at a 30° angle and directly transmitted light. This indicates the concentrations of particulates and aerosol in the sample, while eliminating the effects of light source fluctuations, ageing and temperature.

Extraction lengths of up to 500m are possible, though for the in situ version of the instrument, the blower is integrated with the sensor. The remote version uses separate fans, as more power is needed. The sample inlet can be fitted with a heater to eliminate mist effects, and to keep the sensor optics clean, the blower feeds filtered purge air to the flow cell, enveloping the sample in a protective shroud of clean air.

The unit is factory-calibrated using a polystyrene-latex aerosol, but an application-specific calibration can be if necessary.