a device used to measure the mass flow of a particulate transported with the aid of a gas . the device includes an arrangement which is used to create an electromagnetic field , with a measuring area being defined therein . an evaluation device for electromagnetic radiation which is reflected at least off of the solid is connected to a detector . the evaluation device is provided with a differentiator which is connected to the detector for detecting reflected electromagnetic radiation . a rectifier is connected to the differentiator in order to determine an amount , whereby mass flow is obtained from the reflection amount . the reflection is measured , at least from the solid within the measuring area of the magnetic field , whereupon the differential quotient is determined as a function of time from the chronological progression of the measuring signal and the absolute value is obtained therefrom . a measuring signal is obtained from the non - homogeneity of the electromagnetic field , forming the integral over time of the amount of the reflected power per time . the measuring signal is proportional to the mass flow .