Monitoring apparatus and monitoring method

A monitoring apparatus for a doctoring, wherein the monitoring apparatus comprises:

• at least one vibration sensor each of which is attached at a location of a doctor blade arrangement, the at least one vibration sensor being configured to convert a mechanical vibration of the doctor blade arrangement to an electrical signal, the mechanical vibration being caused by the doctor blade in response to a scraping operation of a rotating roll which is in contact with a moving web;
• and
• a data processing unit configured to:
• receive the electrical signal carrying information on the vibration;
• continuously and without stoppage of the rotating roll, compare said vibration with a reference of at least one previous measurement of a same grade of the web;
• and
• start one or more preventive actions in order to avoid a drop-through in the case said vibration exceeds at least one boundary of the reference.