Cleaning method for NMR check weighing system

A method of cleaning a surface of a transport mechanism from ferrous particles, in a magnetic resonance technique check weighing apparatus in which a first magnetic field is applied in a first direction in an interrogation zone for creating a net magnetisation within a sample located within the interrogation zone and an alternating magnetic field is applied in a second direction in the interrogation zone for temporarily changing the net magnetisation of the sample located within the interrogation zone, with monitoring of energy emitted by the sample as the net magnetisation of the sample returns to its original state and generating an output signal having a characteristic which is proportional to the energy emitted;

• the method comprising disposing in effective proximity to the surface of the transport mechanism to be cleaned, a permanent magnet cleaning device, the magnet cleaning device being located outside the interrogation zone so as not to interfere with the interrogation zone.