The OPC AeroMon series utilises the stray light principle, i.e. the individual aerosol-carried particles cross a focused laser beam. The flashes of stray light this creates are recorded by a highly sensitive photo detector and ranged according to size and number with the aid of a multi-channel analyser. Depending on the design of the device, the measured data is transferred via one ore more analogue interfaces (4..20mA), or via a digital interface (e.g. RS485 or Modbus RTU) to various measured value acquisition systems (e.g. monitoring system, building automation etc.) for visualisation, whereby different communications protocols are available.