The present document describes a flow measuring apparatus for measuring a flowof particles through a section of afluid dispensing apparatus, comprising at least one photo-detection devicecomprising a light source and a detector, wherein the lightsource is configured to emit electromagnetic radiation onto the detector alonga light path, wherein the detector is configured tomeasure disturbance of the electromagnetic radiation by the flow of particlesto provide measurements of the presence, mass andvelocity of particles within said section of a fluid dispensing apparatus.Also described is an inhalation apparatus for drug delivery byinhalation comprising a flow measuring apparatus of the present invention.